CA2056416A1 - Integrated stereolithography - Google Patents

Abstract

An improved stereolithographic apparatus and method is described.
In one embodiment, the improvement comprises immersing at least a portion of a part (109) in a volume of a liquid solvent in a vapor degreaser while subjecting the portion to ultrasonic agitation to substantially remove excess resin (111). Several examples of solvents are provided, including ethanol, and Freon TMS. In a second embodiment, the improvement comprises building the part (109) on a layer of liquid resin (103) supported by a volume of a dense, immiscible, and UV transparent intermediate liquid, and integratably immersing at least a portion of the built part (109) in the intermediate liquid, and then either subjecting the immersed portion to ultrasonic agitation to substantially remove excess resin (111), or subjecting the immersed portion to UV light. Several examples of intermediate liquids are provided, including perfluorinated fluids, such as Fluorinert FC-40, and water-based salt solutions, such as solutions of magnesium sulfate or sodium chloride in water.

Description

WO90/l5674 PCT/US90/03002 2 0 ~ 6 ~ ~ 6 `: t~

DESC~IPTION

Intearated Stereo~ithoara~hy Bac~round Of The Invention 1. Cross-Reference to Related ADplications This application is related to U.S. Patent Application Serial Nos. 182,823; 182,830; 183,015;
182,801; 183,016; 183,014; and 183,012; all filed April 18, 1988, and all of which are hereby fully incorporated by reference herein as though set forth in full. Continuations-in-part of U.S. Patent Application Serial Nos. 182,830; 183,016; 183,014; and 183,012, were filed on November 8, 1988, all of.which are.hereby fully incorporated by reference hereinias though set forth in ' full. The Serial Nos. for the above mentioned : 15 continuations-in-part are, respectively, 269,801; 268,816;
268,337; 268,907 (all for Serial No. 182,830);'268,429 (for Serial No. 183,016); :268,'408 (for.: Serial No.
. . . . . . . . .. .. . .
183,014);..and 268,428-~for.Serial No. I83,072).~~Another related ,application ~is Serial No. ..265jO39,--filed October 31,.1988, which is .hereby.fully incorporated by reference..herein. as though -set. forth..in : full. A
continuation~ application of-S.N.-269,801 was filed on March~31, ...1989jj,which.-is hereby..fully ~incorporated ~by . rleference herein as though set forth in..full'.~ The Serial No.~,for.~the.above-mentioned.continuation application is S.N. 331,644. A continuation-in-part application of'S.N.
182,j823.was.filed on April 17,~l1989,'.which is hereby fully incorporated by~ reference herein-as-though set::forth'qn full. ,~ The./...Serial;r~No..-~.-for- the - above-'mentioned continuation-in-part application-is S.N.-339,2i-6~:C~';

2. Field of the Invention e.~
. This invention relates- generally to- an improved stereolithographic.method and apparatus of the type for ... . .. ~, ., 6` f,-?,~56 , 2 building a part at the surface of a volume of liquid resin, the imprdvement comprising building the part on the surface of a layer of the resin, which layer is supported by a volume of a dense, immiscible liquid, and then performing additional stereolithographic processing on at least a portion of the built part while it is immersed in the liquid.-.

3. Background of tke Invention Stereolithography refers generally to the process of10 reproducing a part by curing successive two-dimensional cross sections of the part at the surface of a volume of a liquid,resin and then stacking the cross-sections together to form a high resolution reproduction of the part. The first step in the process is the part building step, whereby successive two-dimensional cross-sections of the part are formed using an apparatus known as a stereolithography apparatus (hereinafter "SLA"). The SLA
builds the part by tracing successive cross-sections of the part at the,surface of the liquid resin~ with'syner-gistic -stimulation, such as`a W -laser beam or the like, at a sufficient exposure so ~that-'thé ;exposed resin , -~hardens,~and 'successively lowering the cured cross-sections below the surface so that fresh liquid resin will , flow over ,the'`cured cross- sections which will form the 25 ;next-cross-section.~The éxtent~~to which the resin hardens ,, ,beyond the.,~suxface:is known'as'th'é cure-'depth. Th'e SLA
, ' ,.lowers the cured~cross-sections~!to within a~cure depth'of ,",,,,~the :surface~of the liquid ''resin`~so that 'the next-cured ,,?cr,oss-section,:will '~adhere to-,the~ a'lréady 'cured' cross-30 ~,s,ections.-:--In:*his manner, a'~lamin'ar build-up of the~part ,"~is formed,at the surface.;-This-'process is describéd in more"detail~in~U.S.'Patent~No.'.4,575`,330~'~('hëréinafter the '330 patent), which is hereby fully incorporated by reference herein as though~set forth`--in-fuil.
; In one embodiment of''an SLA,'illustrated in Figure la, a volume of W curable liquid resin 22 or the'like is - , ' , 2 0 S ~ ~ 1 6 placed in vat 21 to form a designated working surface 23.
W light source 26 or the like is placed above the surface to produce synergistic stimulation which strikes the surface at point 27. The light source is controllably directed by computer control system 28 to draw successive patterns representing successive two-dimensional cross-sections of a part on the surface 23.
Cured cross-sections are formed on platform 29 which is also under the control of computer control system 28.
After a cross-section is formed, the computer directs platform 29 to lower itself a particular distance further into the liquid resin 22, so that the cured cross-sections will be lowered below the surface, allowing fresh liquid resin to flow over the cured cross-sections. Optionally, the platform is lowered by more than one layer thickness, and then raised to within one layer thickness after the fresh liquid resin has flowed over the surface. Then, the computer directs the light source to draw out the next cross-section on the surface at a particular exposure so that the cross-sëction being formed has a sufficient cure depth to penetrate beyond the surface of the resin and .. ... .. , ~ . . . ;, .
adhere to the cured cross-sections.
- In Figure la, the laminar build-up of the part is indicated by reference numerai 30, ànd successive cross-.. .. , . .., , .~. . , ~ ... .
sections of the build-up are indicated by reference numerals 30a, 30b, and 30c, respect;ively.
~ A Another embodiment is illustrated in Fig. lb. As ..illustrated, a layer 22 of W curable liquid resin or the , like~is supported3by a heavier, W; transparent, non-miscible liquid 320 In addition, the non-miscible liquid supporting the layer~ of liquid resin is placed in a vat 21! which has a W transparent window 33, constructed of quartz or theilike,~at the bottom of the vat. W light ;;source 26 or the like is placed below the bottom of the 35 ~vat and synergistic stimulation from the source is directed by the control computer to pass through the window and the intermediate liquid to strike and cure the ' , ~ 4 liquid resin from below, which curing takes place at the interface 23 between the resin and the non-miscible liquid, which interface is the lower surface of the resin layer. The W light strikes the resin/liquid interface at point 27, and is directed by the computer to draw patterns representing cross-sections at the interface.
The first cured cross-section adheres to platform 29.
In certain instances, other cross-sections may also adhere to the platform. After a cross-section is formed, platform 29 is controllably directed by the control computer to raise itself a particular distance so that a corresponding volume of fresh liquid resin will flow under the cured cross-sections at the interface 23. Optionally, the elevator may be raised more than one layer, and then dropped down to within one layer thickness after the fresh ~liquid resin has flowed under the cured cross-sections.
Next, the control computer directs the W light source or the like to trace a pattern of a next cross-section at the interface at a suff'icient exposure so that the cure depth of the cross-section will be sufficient to adhere to the cured cross-sectlons.
Traditlonàliy; an SLA, aftér bù~iding à part,~does not perform any of' the other steps in the~overall stéreolitho-graphlc process iliustrated in Figure 2a.
This overall process will'now be described. In step l, a solid or surface model of a part is~designèd~on a CAD
system. In'stép''2',`'thë'~CAD model~is`oriented in'-'CAD space' to minimize' problems ~downstrèam~'~with-iithe -remaining stereolithographic''stéps, and also~à base~or-support is added to attach to and support the'part while it3i`s-being built. In 'step '3, the'CAD model `is formatted to~'provide a generic'surface~representation ~of the part-'called an .STL file'~~which'~ is'' compatiblë with~' an- "interface ` specificati'on rëquirèd t'o~communicatè the file to~the SLA, an3 which `interfac~e ënàblës'thé'SIA to'remain independent of the specific CAD system. In stép`4,' the .STL file for the part is "siiced" by a SLICE'computer (with certain WO90/156~4 PCT/US90/03002 20S~416 ` ~ ...
SLICE parameters such as layer thickness) to provide two dimensional cross-sectional data descriptive of successive cross sections of the part. Collectively, the cross-sectional data is referred to as an .SLI file. In addition, portions of the .STL file, representing the base or support for exa~ple, are optionally "sliced" separately to form their own .SLI files with different SLICE
parameters from that used to slice other portions of the file. In step 5, the .SLI files are transmitted from the SLICE computer to another computer known as the PROCESS
computer via Ethernet or floppy disk. In step 6, all the .SLI files for a part are merged into a single file. In step 7, the user specifies certain part building parameters such as cure depth, exposure times, and laser delay and stepping values, as required by the part's geometry and end use. The laser beam ~does not move over the resin surface continually, but instead, moves in steps over the surface with a delay at each step. The laser step size and delay largely determines the exposure and hence cure depth.achieved.. In step 8,' which is the part building-step, -the W laser beam is directed' by the PROCESS computer to trace out patterns represented by the two-dimensional cross-sectional .data with- theibuilding . ..parameters specified .in step 7, with the 'result'-that the liquid resin is.cured where the laser strikes -.to^-`form . successive..~layers of.the part:at the surface.;'-The'first ...,,layer adheres.to a horizontal platform'locatedrjust''below ,.. the~Jsurface Lof.the...:liquid resin."~';The platform is .. ..connected-to;ian .elevator~which.lowers--the ~'platform;also under control.of the PROCESS.~computer.` ~After a layer ~s cured, the platform is caused:to dip-into'~the-liquid so that~.fresh liquid~;will. flow.i-over *he':~cured layer to providev.a~.thin film from iwhich the ne`xt~lâyer`'will be .cured. The next layer is drawn after a'pa'us'e'!to allow the ...; , ... ..
35 iliquid surface to level.. The~exposure of the'W-iaser and the thickness of the fresh-liquid are:controlled so that ...the cure depth of the next layer is such that it will . _ .. ... . .

W090/l5674 PCT/US90/03002 f ~: ~

~ ` ~ '"'"'' 6 adhere to the cured layer. The process is repeated until all layers have been cured to form a reproduction of the three-dimensional part. In step 9, the part is drained to remove excess resin (hereinafter referred to as part cleaning), the part is then ultraviolet cured to complete the photopolymerzation process (hereinafter referred to as post-curing), and the supports are next-removed. Optional finishing steps such as sanding, or assembly into working models and painting, may also be performed.
Figure 2b illustrates the major components of an apparatus known as SLA-1 used to perform 'the stsps described above. A more recent commercial embodiment is the S~A-250, which is functionally similar to the SLA-1, except for the addition of a leveling blade for'leveling the surface of~the higher viscosity-resins typically used with the SLA-250. An even more recent embodiment is the SLA-500 which has a larger vat for building larger parts.
As illustrated, the major components comprise SLA 34 and post-curing apparatus'35 (hereinafter referred to as a ~''PCA"). The major subcomponents of-~'the -SLA are illustrated in Figure~-2c. '~As- illustrated,-- the SLA
comprises SLICE computer assembly 36,' which is ,~Aelectrically coupled via Ethernet ~o-electronic'cabinet ~ assembly 37, which is also mechanic'ally'and'electrically ?5 ` coupled to chamber assembly 38, and to optics''assembly 39.
. As~"illustrated, ,the SLICE computer'~assemb~y'~'comprises ~",rl(monitor,40,-SLICE~computer-41j and keyboard'42',--integrated ~,ltogether as-shown,~ The SLICE'computer also~lnterfacës to a._CAD/CAM.system ~(not~hown)~ either: through'"Ethe'rnet, 30 ~floppy disks, or,any:other data transfer~method, for the 7 ~ transfer_of~,the .STL~files.~
~ , The-electronic,sicabinet assembly is illu'strated both ,. Linj~Figures^l2c and 2e,~ in~which~llike''~component's and , subcomponentsjare identified withjlike'r'eference numérals.
35j As illustrated, the electronic cabinet assembly is coupled to the SLICE computer assembly by-means of Ethernet cable 43. Moreover, the electronic cabinet assembly,' in turn, .

2~11 6 comprises RROCESS computer 44, keyboard 45, and monitor 46, integrated together as shown in Figure 2c. In addition, as illustrated in Figure 2e, the assembly further comprises laser power supply 47, and other power supplies (not shown) for the high-speed dynamic mirrors 49, and for the elevator motor 50. The assembly further comprises AC power distribution panel 4a ~ a control panel .,..(shown but not identified with a reference numeral), plug-. in circuit boards for control of the monitor, keyboard, and optional printer (not shown), plug-in driver (not shown) for control of the high-speed dynamic mirrors, and plug-in driver (not shown) for control of the vertical (Z-stage) elevator. The control panel includes a power on switch/indicator, a chamber light switch/indicator, a laser on indicator, and a shutter open indicator.
operation and màintenance parameters, including fault diagnostics and laser performance information, are displayed on the monitor. The.operation of the PROCESS
computer is controlled by keyboard entries. Also, work 20, surfaces around the,.keyboard and disc drive are-covered ,,,,with formica~for efficient.,.long cleaning and long wear.
,~. The optics"assembly is illustrated in Figure 2c, and .. . .. .
comprises laser 51, laser cover 52, shutters 53, beam . , turn,ing mirrors s54a~and .54b,. beam expander-55, dynamic 25~,mirrors .56, and~optics ,cover 57. -As,,illustrated, the ;",laser and related optical components.are mounted on':top of the.,electronic,cabinet~and~,chamber--assembly..-~Also, the ,.. laser,and~optics; are~cov,ered with.laser..and~:optics covers ~521and~57,,-!"r~especti,v,ely,;which.:may be.,removed.to ! 'service 30 ,the~laser and-optics. For,safety reasons,-the-covers are a,tta,ched,,to the chamber,and:,electronic cabinet-assembly iwit,h,.fasteners,,..and;,a speciaL-tool is.;.required~to;unlock 3j th~ cov,er,fasteners.J"In addition,-:interlodk switche's are activated when the covers are removed. ~ The`~-interlock switches activate dual solenoid-controlled shutters to block the;laser beam when either cover is removed.

WO90/~5674 PCT/US90/03002 6~ ~

The laser is preferably a helium cadmium (HeCd) laser. In addition, the shutters, beam turning mirrors, beam expander, and dynamic mirrors are all mounted on an optics plate (not shown) placed on top of the electronic cabinet and chamber assembly. ' As illustrated, the shutters are preferably rotary solenoid-activated shutters which are situated at the~laser output'to'block the laser beam when a safety interlock is opened. The beam-turning mirrors reflect the laser beam along an optical path through the beam expander, which enlarges and then focuses the laser beam so it will achieve a'`certain size on the surface of the liquid resin. ''The dynamic mirrors are under control of the PROCESS computer', and diréct the laser beam to trace out patterns on'the surface- of the liquid resin according to the cross-sectional data provided by the SLICE computer. A quartz'window (not shown) separates the optics 'assembly from the chamber assembly, in which is placed in the liquid resin. The dynamic mirrors direct the laser beam along an optical path through the quartz--' window -to :the liquid resin surface. The quartz window~allows the laser beam to énter the chamber assembly,~ but otherwise`'-isoiates the two assemblies. ~ ~-;- '- ~ ''-~'- : ~ --. . r, The chamber assembly is illustrated in~Figurés'2c and 2d. As illustrated'in Figure~2c,'the5'chamber assembiy 38 comprises~-a chamber (not~ identI'fiéd 'with''a' réference numeral), chamber -door~57:which`'opens-into~the~'chamber, ., storage compartment 58,:and--'sto'rage compartment'door 59.
~ Turning to,^.Figure~i2d, i~the ~'chamber- ~asse~ ly`~further 30; comprises platform 60,'reaction vat'~6~ 'elev^a`tor''62,`a ~YIfirst beam profiler'63~-a~second beam p'r'ofiler''(not shown) _~ diagonally~located ~across'~the vat~-from'the''first''beam ,~ profiler,-heater/fan~64,~air filter~'6'5,~chambe'r 1'ight 66, -and~shelf 67.;~ r~. ~`?n; ~
-I~ ~.The chamber~in which~the part is formed is designéd for operator safety -and -`to -ensure uniform' operating conditions. The chamber may be'heated to approximately 40 .

WO90/l5674 PCT/US90/03002 degrees C (104 degrees F) by means of the heater/fan, and the air in the chamber is circulated and filtered by means of the heater/fan and air filter. The overhead light illuminates the reaction vat and work surfaces. An interlock on the cabinet door, preferably a W blocking plexiglass access door, when opened, activates a shutter to block the laser beam.
The reaction vat is installed in the chamber on guides which align it with the elevator and platform. The liquid resin is then placed in the vat.
The platform is attached to the vertical axis (or Z-stage) elevator. A part is formed cross-section by cross-section on the platform which is successively immersed in the liquid resin and therefore lowered into the vat while the part is being formed. After a part is formed, the platform on which the part is placed is raised to a position above the vat, and then disconnected from the elevator and removed from the chamber for post processing.
Handling trays are provided to catch dripping resin.
, , The beam profilers are mounted diagonally across the reaction vat from one another at the focal length of the laser.~t The dynamic mirrors are'periodically directed to ,direct the~laser beam onto the- beam profilers, which ~ measures the beam intensity profiIe.~ The data may be displayed,- on the terminal either as a profile with ,, --;,intensity contour lines or as a single number representing , J;,jthe overall-~(integrated) beam:'intensity. This data is , ,,used-,to determine whe'ther~the'mirrors should be cleaned ,!t~ and~aligned, whether~~*he-laser should~-be serviced, and ~30 what building parameter values such às~`laser stepping and delay valves (which together largely-determine exposure) "-r_~will-yield-cured ,t resin'Sof'~'a':particular-`~cure''depth and width. '' '`
' ': t ~ The PCA,is illustrated in-Figure~2f. As illustrated, the PCA comprises a chamber :'(not' identified with a , reference numeral~, W lamps 68 -on adjustable stems, turntable 69,:-front 'and top doors ~ 70a and 70b, . ~ ': ' .

~;~64~6~ , 10 respectively, with respective front and top UV blocking windows 73a and 73b, cooling and vent fan 71, control panel 72 with power switch and timer (not shown), and stand 74.
The W lamps are preferably three 400 watt metal-halide W -enhanced lamps, with reflectors, which can be positioned in the chamber for optional post curing. The turntable is preferably a one revolution per minute turntable which rotates the part for uniform post-curing.
The doors, located at the front and top, are for loading and unloading parts. Both doors are interlocked to turn of f the W lamps and turntable when they are opened, and have W blocking windows to block the passage of W light to allow safe viewing of the parts. The cooling and vent fan is preferably a 240 cubic feet per minute fan.
Turning again to FIG. 2a, as indicated, after a part is built, it is further processed in a post-processing step. A typical post-processing step is comprised of the following substeps:
1) Raising the part out of the vat of resin.
; ~2) Allowing the part to drain into the-vat ~e.g.
from about-lO minutes to about an hour~. -.. ..
; 3) Removing the part (and platform, if--desired) from the SLA and placing it on an absorbent pad.
. .. ~
4) Optionally placing the part/platform in a low ?(~ temperature -oven~ (heated : to ~ a~ temperature between-jroom temperature and a temperature _,",,, 3~ effective for;thermally curing,~the resin,~e.g., r~ .from~about room-temperature.to about lOO degrees jC, r andLpreferably fromA-about~60 -to about r~9O
degrees C).
;5~ 7;Optionally;~removing excess resin with cotton swabs. r~
_ r 6) Optiona}ly coating the,part surface -with resin to give good surface finish. - - : ~
~ .. . . . . .
7); Optionally giving the part a guick exposure of flood W (or other radiation as appropriate for .

11 20~6~i6 ~, the photoinitiator in the resin) to set the surface.
8) Optionally immersing the part in cool water, such that the water fills all cavities in the part, if possible.
9) Applying flood W light to the part (or other radiation as appropriate for the photoinitiator -. in .the resin), optionally while the part is under water (or another appropriate liquid medium).
lO) Optionally rotating the part as necessary to provide a uniform cure.
11) Removing the part from the platform, if necessary.
12). Repeating substeps 6-10, if necessary.
As set forth in more detail in co-pending U.S. Patent Application Serial No. 183,014, and its co~pending ..continuation-in-part, Serial No. 268,408, in carrying out substeps 3.).and 4.), once the part is placed on the absorbent pad, it can be.left.to drain in the open-air at roomj*emperature for--a period-of~''time ranging~anywhere from minutes to a couple of.days,.after which time it can be..placed-into-an-oven or.otherwise heated --In addition, . . ; .. . ......... ... .
.the following, sometimes competing, considerations should 25. be balanced when carrying. out these~ substeps.'' It is .important .to avoid. part warpage -due to':~temperature, ~.... gravity,-.or other conditions~capable:.of exerting a"force .,j on~the;part;jto remove all.excess.resin from the'~surfaces ~ .of the.part before..further-.post-processing;'~andi*ocavoid 30 .over~,absorption o~ pxygen; which ~inhibits:post~'~curing substeps 8.)j 9.) and 10.):~above) since oxygen acts as an , .,inhibitor.;of rthe ~chemical~:.reaction~involved in 'l^ater .~,photopolymerization.-,.-- ~ r Optionally, the use of solvents can be combined'with the use of the absorbent pad and oven`heating to drain the . part. In this approaoh, the part is contacted, e.g. by spraying, brushinq! soaking, or the like', with a solvent , :, , ,. . : : :

. ~
;.
'.; ~

WO 90/15674 PCr/US90/03002 6 `-:

, .~ ; 12 suitable for reducing the viscosity of the resin on the surface of the part, without leaching unpolymerized resin from inside the part. The liquid surface resin and the solvent form a solution of relatively lower viscosity, causing the resin to drain more quickly from the part.
Suitable solvents depend on the resin, but are, in general, organic solvents, preferably of intermediate polarity, such as methanol, methlylethylketone, ethanol, isopropyl alcohol, trichloroethane, or th'e like.
As set forth in more detail in co-pending U.S. Patent Application Serial No. 183,012, and its co-pending continuation-in-part, Serial No. 268,428, in carrying out substeps 6.) and 7.), surface discontinuities in the part may then be filled in w~th resin to provide a smooth surface finish. Surface discontinuities may arise, for example, because of the stepwise nature of part building, which may leave the part with a stairstep appearance and corresponding.rough surface.finish. The part may then be given a rapid exposurej e.g. from a few seconds to no more than about a..minute,~preferably :about 15 'to about 30 . seconds, of flood W:light (or other radiationrappr'opriate ; to the resin being used) to set the surface.' The process .. of_coating and.,setting- with W light can b'e -repeated .several times, as necessary, to obtain a smooth surface finish over the entire-;part. In addition,~the W 'light .~ should strike-the surface of the:part as uni'formly as .possible, which can be accomplished,'for example, by using multiple lamps ~imultaneously.-from^different`'angies, by ~ using ~high?quality.-.;reflectors~to distr'ibute' thë light .around the?.part,.iby rotating.the part or the':'lamps,-'or thè
.~ like. As~ described~in-:more.detail.in the~next-séction, .c. .thelUV-.lamps A are.~.preferably mercury-~discharg'e-'or'-metal halide lamps, such as, for example,~-rPhillipsi3~!(Belgium) .~.HPA..400S ~'Mercury Vapor Burner.-~ r' r ~-. As explained in co-pending U.S.~:-Patent 'Application ..., Serial No. 182,830, its co-pendinq:continuation-in-part, ~Serial .No. 269,801, and its co-pending continuation, WO 90tl5674 PCI`/US90/03002 Serial No. 331,644, sometimes the part is built deliberately undersized so that when the surface discontinuities caused by the stairstep appearance of the part are filled in, the part will be the right size.
Alternatively, as explained in those applications, sometimes the part is built deliberately oversized so that after sanding to remove the stairstep appearance, the part will be the right size. Another alternative is to build a part as close as possible to the correct size. In these instances, substeps 6.) and 7.) are eiiminated.
As set forth in more detail in co-pending U.S. Patent Application Serial No. 183,016, and its co-pending continuation-in-part, Serial No. 268,429, in carrying out substep 8.), the part is ..then immersed in water, or another liquid medium such as a salt solution, a fluorocarbon such as trichlorotrifluoroethane, an organic solvent, such as polyethylene glycol telomers or ethanol, etc. during a flood W exposure (or exposure to other radiation depending on the resin) of sufficient duration to completely cure .the part. This substep may ..be necessary, since .after the part.building.step, the part . . . . . .
may not be completely.cured, but instead may only be partially cured,.and in a corresponding-"green" state.
.; . .. . .. , . . ~ ~ . .. . . .. . .
The liquid.medium preferably has a similar specific gravity to the partially poly~erized part, to.provide an optimum level of.buoyancy,.-such that-distortion risks due .i .' J''-- ~ ' . C ' to~ gravity are minimized;~preferably absorbs-~-infrared radiation coming from the W .light source so that the part ,is not heated.by. the,infrared energy, and also. absorbs heat away from the part. that is generated. during the poly~erization reaction;.,and:preferably.acts ;as. ajheat exchanger~ by transmitting-heat awayjj-from the.part without a pronounced.increase..in.~the.temperature~of the :liquid medium itself.- Preferably,-the liquid .and part are at ambient temperature when the part .is immersed...in thé
liquid, e.g. jthe liquid is generally between about 15 and about 35 degrees C. Ideally, the liquid temperature is . .. .. . . . . . .

' .

WO 90tl56~4 PCI`/US90/03002 ~6~S~6 ,, ~ ~
maintained at a selected level, typically within plus or minus 5 degrees C, as long as there is sufficient water to contribute a large enough thermal mass such that its temperature does not change dramatically during exposure to radiation from the W lamps during the curing process.
Optionally, the liquid can be recycled through a heat exchanger to maintain it substantially at room temperature and to reduce the quantity of water required. Another option is to filter the liquid to remove impurities, or the W light may be filtered to remove certain peak absorption wavelengths from the impinging ràdiation to promote uniform curing by adding a suitable photoinitiator to the liquid-to perform the same function.
Post-curing is performed using the PCA illustrated in Figure 2f, which is described in the earlier section. The part is first placed'in a vessel transparent to W 'light, such as a quartz or pyrex container, and should then be placed inside the PCA and situated with respect to the W
. light so--that the W light strikes the entire surface of :20 ~the part-as uniformly as possible.-- ' ~' '''' ' .
: - ~ As with substeps'6.) and 7.), this can be'carried out by using"multiple lamps' simultaneously from différent -angles, using'-high`guality reflectors to distribute the ..light around the'part or'by'rotating the part or the lamps or.the like. ' -' - ' ' The-~W ;lamps~'are preferably-high -pressure mercury discharge.~.or metal'halide'L'lamps,~-such as,- for'example, ~: Phiilips'~:(Belgium)-HPA 40bs ~"Mercury'Vapor Burnér'." The W light 'isitypicâllyi'of-mixed-wavelengths in the''about ~.30 250 to about~750'nm range'; with;the ma~ority'in the'range ... ., of about~300 *o about'400'''nm.~'Moreover, the''intensity of .:c-(:the light;striking:~the:s'urface-is about 20 mW~pe'r 'square r r~ cm to.:about-~100'mW:pér'sguare'cm'in~'the about 300~to about .; -400 ~nm..range.-~ The post-cure time wili~typically range from-about 7 to abo'ut 15 minutés. - ' .- : ..A significant disadvantage of the above approach is that...the post-processing substeps are manual, time-W090/1~674 PCT/US90/03002 , ~
.. .
2 ~ 1 6 consuming, and subject to significant errors in operatingconditions because of the absence of computer control of these substeps. In addition, these substeps are typically performed in physically separate areas, which require the part to be transported from area to area to complete the stereolithographic process, and also require a large physical area. The result is -that the overall stereo-lithographic process is extremely fragmented.
In addition, regarding post-processing substeps 2.) -5.), the part cleaning substeps, additional problems arethat it is difficult to completely remove excess resin, especially from difficult-to-reach areas of the p~rt such as corners or detailed features using thermal draining, and it is also difficult to eficiently dispose of the excess resin. If a solvent is used, disposal of the solvent intermixed with resin is also a problem. Even if the part is allowed 'to drain on an absor~ent pad, the absorbent pad must be disposed of after the part has drained excess resin'into it. 'Disposal is an important environmental''consideration, as the resin tends to be tacky~and'difficult'to clean up, and certain resins may have a level of~toxicity associated with them, so that : disposal'~may be complicated from a heàlth perspective.
~e_ Moreover,;the exposure of the part to oxygen may inhibit 25 -subsequent post-'curing becausë of the action of oxygen in --inhibi~ing'polymerization.'''Also,"the action of gravity while the part is draining ~ay distort the ,part.~ In addit~on, the optional use o~ cotton swabs in substep 5.) --~to"clean hard-to-reach portions of thë part.is very-time consuming, -and -aiso'~does not rêadlly provide for uniform application-from part to part. Finally, ln substep-4 ) ~the'low~temper~aturë''ven,'if allowed to act. on the part too-~long, can 'lead~' to ;distortion and additional undesirable curing, especially if the resin is thermally-35~tcurable.`-~' ' ' '', ,, , . ~
' --'' A disadvantage'of the part-building step described above is that thë inventory of resin required maybe - ' . ~
.' ' ' ',' ~ ~ :
, .

~6 substantial, particularly for the building of large parts.
The large inventory of resin is required since the size of the vat in which is placed the. liquid resin must be scaled to the size of the part, and the entire vat must be filled with resin even though a part may only require a quart of resin to build, and the resin which remains in the vat may have to be replaced about every six ~onths or less, since this is the shelf-life of the resin. A large inventory may be required to replenish this turnover without significant delays. In addition, large parts may require a large vat, which may further increase the inventory requirements. In fact, the inventory required to support a large vat may be a reason why many commercial em~odiments of Sl,A's are limited to building small parts.
Besides the expense, the l,rge inventory has- the additional disadvantage that the pace of technological change in the development.of resins is great,- and a large inventory might become obsolete by the time it:is used.
, It is an object of the present invention to 20''provide means with~ which;.~to ~integrate~;~the~.:various ' stereolithographic steps. or substeps ~described above .. .. ... ... .. .. . . . ..
toge'ther. Another object.is to improve part-cleaning by making it more effective, by reducing the distortion which ' part cleaning may cause, and by reducing;or eliminating 25''the disposal problem. A further object is to reduce the -~resin inventory required for ~the.building of larger parts.
t~y~ c, .J ~ 3 r~ -' t ~. ~
SummarY~Of The Invention ~ ..~ ....~ , ..-- .^-~ ' The'-!present 'invention is directedj..to an .improved -`'- stereolithographic method and~apparatus of the .type for~
30--drain1ng-excess resin off of a part,. the.~improvement .~- comprising-means'^'`fo'r~cleaning excess resin from~at~least a portlon~of the'`'part with ultrasonic .agitation.while it :-is^~imm'ersëd'in'a''liq'u^id solvent.
~ The present invention is also directed to an-improved stereolithographic method and apparatus of the type for building`:a part~'at the surface of a volume of liquid r r ....

-:~

WO90/~5674 PCT/US90/03002 2056~16 ~ ' resin, the improvement comprising means for building the part at the surface of a layer of the resin supported by a volume of a dense, i~miscible, W transparent intermediate liquid, and means for performing additional stereolithographic processing on at least a portion of the built part while it- is immersed in the -intermediate liquid. Such additional stereolithographic processing may include subjecting the immersed portion to ultrasonic agitation, or flooding it with W light.
The subject invention is also directed to an improved stereolithographic method .and apparatus of the type for building a part by directing synergistic stimulation to .impinge upon the surface of a volume of the liquid resin from above, the improvement comprising means for building a part by directing synergistic stimulation to impinge from above upon the surface of a layer of the resin supported by a volume of a dense, immiscible, W
transparent intermediate liquid.
The above and other objects and advantages of this invention will :~be apparent. from the -foll'owing more detailed description-when :taken in conjunction'with the accompanying drawings of:illustrative embodiments.
.. , - : ....... .
..,Brief_pescription Of-The Drawinas - ' FIG. la illustrates an-embodiment of an SLA; :
25.,.~ ,FIG..lb.,illustrates_a second embodiment of a SLA;
FIG. 2a illustratesj,~ steps '; in '! i the~ ovérall stereolithographic process;
FIG. 2b illustrates a--commercial embodiment of:an SLA
; .3.,, and,PCA used in-the process,of-FIG.'2a';''" ~
3~0, ,~..,,sFIGs. 2c, 2d..and.:2e.illustrate:thè major components ;~ ,and-~subcomponents of~the SLA--of FIG.'2b;'~ 5~
,FIG. 2f illustrates~the'~'majoricomponents-'of~thè PCA
, of.FIG.~-2b; :- .l~., :,~.. ~--:-:':-'' "`'~"'`~'~'' ~''''-~7 ';
,,~,. ..,,FIG. ~3a is;ca .,side view of a' bench' top ';vapor degreaser; :-.~ ' - - ~' `''''~

: :

- . :: ~- .

6 .
'1,.~ ' FIG. 3b is a perspective view of an embodiment of a vapor degreaser for larger parts;
FIG. 3c is a perspective view of an embodiment of a vapor degreaser for use with flammable solvents;
FIG. 4a illustrates a top view of a dual chamber embodiment of the subject invention;
, FIG. 4b illustrates a side view of the dual chamber embodiment of FIG. 4a during part-building;
FIG. 4c illustrates a side view of the dual chamber embodiment of FIG. 4a during part cleaning;
FIG. 4d illustrates.a side view of the dual chamber embodiment of FIG.,4a during post-curing;
FIG. 5a illustrates a side view of the travelling platform in the dual chamber vat embodiment of FIGs. 4a-: 15 .4d; .-. . . - -FIG. 5b illustrates a frontal view of the travelling platfsrm of FIG. 5a;
FIG. 5c illustrates a top view of the travelling platform of,FIG. 5a;. ~
20 . ,".,-,FIG. ,5d,!illustrates..a.side view-of the travelling ,~.., platform of FIG. 5a.during post-curing;-:-`-- -'``
.~j FIG. 5e- is a .perspective.yiew of: the travelling platform of FIG. 5a;
FIG. 6a illustrates a top Yiew of a~single chamber vat embodiment of,the subject invention; and-:-:
..,, ~ FIG.b6b,illustrates:a side view of-the'single chamber - vat embodiment ofiFIG. 6a.~
., . . i ~ ,.. .
-~ Descrip~ion-Of The Preferred Embodiment ^ ~:-An embodimeint of the subject invention~is illustrated30 ~inijFIG.r3a.j,~ This,embodiment~provides improved means for part cleaning~using:a vapor.degreaser'!such:ras a'Sonix IV
^- Model BTj612-,Bench.Top.~.Vapor-Degreaser.- -As illustrated, a vapor degreaser comprises boil sump 75, rinse tank 76, ,..vapor zone ~77,; above -the -boil :sump and rinse tank, , .. . ~ .. .. .
refrigeration coils 78a and 78b which are at;the top of the vapor zone, and freeboard area 79 above the vapor . ~ ' .:

2 ~
19 .:
zone. Ultrasonic transducers (not shown) are situated below the bottom of the rinse tank. Also, a heater (not shown) is provided for heating the boil sump, and a refrigeration unit (not shown) is provided for cooling the refrigeration coils. The freeboard area is a buffer above the vapor zone which is required to help prevent vapor from the degreaser from escaping into the atmosphere. It helps achieve this by providing an area where any vapor that extends beyond the vapor zone can condense. Option-ally, a spray wand (not shown) is also provided.
The vapor degreaser operates as follows. First, avolume of a suitable cleaning solvent such as Freon TMS
(preferably about a 94:6 (wt/wt) mixture of Freon TF and methanol), isopropanol, ethanol, propylene carbonate, water based cleaners, trichlortrifluoroethane (a/k/a Freon TF) or 1, 1, l trichloroethane (hereinafter "TCE") is placed in both the boil sump and the rinse tank. Other examples are possible, and the above is not intended to be limiting. . In FIG. 3a, the -volume of the solvent is indicated.by liguid levels 80a' and 80b respectivèly for . the boil ~sump and "the- rinsë tank. 'Isopropanol and c~.- ethanol, howeverj-are';flammable, and additional safety ''J precautions should--be~made when using these solvents.
. - (See FIG.;3ciand'!associated~text.) . ~ Second,--the boil sump':is heated until the solvent . ..,~boils, and.thereafter-~evaporat'es (Freon TMS boils'at`about - 103 degrees-F,~while~TCE:-~boils ~at' aDout '165 degrees F) .(about -39;and-..74W7degrees~C; 'r'espectively). '~Third, the refrigeration coils^are`-cooled:by the refrigeration unit, :the cooled coils act to~condensè the~evaporatéd;solvent on the coils, andAthetcondensed'^solvent thén drips'back into the3rinse-tank.~ By~this~action, the solvent is clèaned, . since:c:any;contaminants'of the solvent`'will be ieft in the -~`? boil .sump .when~the ~solvent'evaporates; ~ This''w`il~ be 35~, important~for immersion'';cleaning (see below), `whereby a part is cleaned by immer'sing it in the volume of solvent placed in the rinse tank'.:- As the part is cleaned, excess j .

`',' :~

`` : " ' '........... '. : -.

WO90/156~4 PCT/US90/03002 ~6~ ~;, 20 ,~; .:;, .,. ~
resin will dissolve in the solvent. The solvent mixed with the dissolved resin will then spill over into the boil sump as indicated by reference numeral 81 in FIG. 3a, at which point the solvent will be cleaned through the evaporation and condensation process described above.
To clean a part, the part is immersed in the solvent situated in the rinse tank for about a few minutes, optionally while the ultrasonic transducers are turned on, and then removed. Advantageously, the ultrasonic transducers are tuned to a frequency of about 25 to-about 40 KHz. The part should be immersed in the solvent for less than about ten minutes, preferably less than about five minutes, and most preferably.-less than about two minutes. If the part is i~mersed for more than about ten minutes, the part may distort. .This process may be repeated for hard-to-clean parts.
Alternatively, in the case of thin layers of excess resin, instead of immersing the part in the .liquid solvent, the part can be cleaned by placing it within the vap~or zone and immersing it .in the.solvent vapor. ~he action of the solvent vapor in condensing on the'part; and then drlpping off of it, cleans the part. As .indicated earlier,~the:vapor zone is the area;above the.boil sump and resin tank where the..solvent vapor collects.~'' The outer limits of the.vapor zone is largely.determined by ~the condenser coils;on.~which.-the solvent..vapor condenses.
2 j~ Another..alternative._to immersion .cleanin~ besides vapor.?cleaning is spray cleaning,:whereby:the spray,wand ~. Jis~used to spray.solvent~onithe part.~ 3~' , Another example of.-~.a vapor degreaser embodiment of the sub;ect invention for.,larger.:parts is shown in;FIG.
3b. As illustrated, this-example comprises-degreaser 82 ,~ and s~till, 8L3,..which~are~coupled together_as~shown'~with pipes 89b and 89c.~cThe degreaser comprises main tank 92, overflow tank 84!~weir.85" pump 86,-7filter.87, valvei88a, ' and pipe~89a. .As illustrated, a volume of ~solvent is placed in.the main tank as indicated by.liquid level 90b, ,"
. - :
. ' . .' ' .

WO9n~15674 PCT/US90/03002 2~4 ~ 6 which can spill over through the weir into the overflow tank. The liquid solvent which spills over into the overflow tank is indicated by liquid level 9Oa. In addition, the pipe is coupled to the overflow tank near the bottom, which coupling is indicated by reference numeral 91a, and is also coupled at the other end to the main tanks, which coupling is indicated by reference numeral 91b. Spaced along the pipe starting from end 91a is valve 88a, pump 86, and filter 87. Also provided is an ultrasonic transducer (not shown) placed in the main tank.
The still comprises main tank 83a into which is placed the volume of solvent, which is indicated by liquid level 90c. The still also comprises a heater (not shown) for heating the solvent in the still to its boiling point and thereafter evaporating the solvent, refrigeration coils (not shown) placed above liquid level 90c for condensing the evaporated solvent, and a vapor zone (not shown) placed between the liquid .surface and the refrigerator coils. Note that the refrigeration coils are . . .
..situated so that..condensed solvent collects-.in-separator : 83b. The separator acts to separate out water which may have condensed in the solvent. :(O~ course,~in the-case of .. ...... .. .. .
water-based solvents,-~his may. not be necessary.) Pipe .. ~ ........ . . . .. .. . .
25~..89c is located between the overflow tank:of the degreaser and;the stillc.as spown._ Between the ends of-the pipe is valve.88b. . Pipe.~89b is-coupled to:separator 83b~of the . still at one end,. which-¢oupling is-..indicated by 91d, and . is also coupled~to.the~main.tank of.the degreaser at the 30~ other~.~end,.~which~coupling ,is- indicated ~jby.'reference ..... ... . . ~ ~ .. .... ... . . . .
. numeral.9lc.~ Also..provided as part of.:the still~is-drain .,83c-;. :i l ~ J _~ V,r ~ T ; .~ r ~J ~ i ; ~ ~
The.example of FIG.--3b.;has two~modes.of opëration: a degreasing mode~and~a.di-tilling.mode~of ~r operation,-which will each be explained in turn. .~
j In the degreasing mode,- valve 88b,- situated between .the still and the degreaser, is closed. In addition, the - - : : , ' .: ' ~ ' . . . ' ., -.. . . - . ~ . . - .
' ' ' ' - , ' ~' ' ' : ' ' , ' ~ ~
' .. . ~:: . - :

WO90/156~4 PCT/US90/03002 ~6~ Y ~ 22 still is turned off. First, the pump is turned on, and solvent will thereafter be pumped out of the overflow tank at 9la and through the filter back into the main tank at 9lb. Second, solvent will thereafter flow over the weir and into the overflow tank ready to be pumped through the filter again.
The part is immersed in the main tank for about a few minutes until it is clean. The agitation of the solvent as it is pumped through the filter acts to clean the part.
Also, the solvent in the main and overflow tanks is kept at ambient temperature, which is about 23-24 degrees C.
Optionally, the ultrasonic transducer can be turned on to agitate and further clean the part through ultrasonic vibrations.
lS ; The function of the distilling mode of operation is to clean the dirty solvent. The solvent should be cleaned periodically such that the resin content remains below about 20% by weight, and preferably below about 5~ by weight. In this mode of operation, the pump is turned 20 ,off, and valve~ 88b -between the overflow' tank of the - degreaser-~and'~^the still ;-is`:'opened.' ~ The -still then , operates-to clean the solvent in a similar manner to that : ,,,discussed earlier with respect to the bench top degreaser.
; Dirty-solvent (which is intermixed'with~dissolved resin) 25 ,,,flows into the main tank of-the still through-pipé 89c.
-,i ,Th,en, ~the~heater-in the J still heats the'dirty solvent to ,~ the,boiling point whereupon it~evaporates and condenses on thQ, ,refrigeration- coils~ ~wh'ich'`1 are-i cooled-- by' the ~Ir~ ,refrigerator unit.~ The condensed solvent'then drips~into 3~0 ~thejseparator,---whereupon it flows to'-the main'tank'of the .,degreaser,through~end ;9lc 'of''pipe 89b by means'of the force of gravity. The contaminants remain in the iiquid ~,s,olvent-jwhich~stays,at-the'bottom of the';'main`tank of the _ .r still,~~and ~this?~solvent~ can ~eventually ! be~removed by opening drain 83c. , ' ' -'' ---'' '' ' ''' '' A,suitable commercial degreaser'for this example is the Calsonics Co. Model CT-2424-RS Refrigerated Solvent ` .:: , , .
. " '~' ' . ' . :' ' ' , .

WO90/l~674 PCT/US90/03002 20~6~6 -i ~`

Cleaning Tank. A suitable commercial still for this example is a Branson Series ~RS-40 Solvent Recovery Still.
The bench top degreaser of FIG. 3a comes with a refrigeration unit included. The larger Calsonics degreaser of FIG. 3b should have a refrigeration unit added when using Freon TMS as the solvent because of its lower boiling point. Alternatively, if TCE is used, a less expensive approach is to use chilled water for cooli~g.
Optionally, the Calsonics degreaser of FIG. 3b could be fitted with two HPA 400 W lamps, the same lamps as used for the PCA described earlier. This will allow parts, after they have been.cleaned, to be post-cured either while immersed in the liquid solvent or the solvent vapor. However, post-curing while the part is immersed in a solvent liquid may be preferable to post-curing the part while immersed.in vapor since the UV light may break down the vapor into a corrosive ~aterial which can rust the stainless steel of the degreaser main tank... In this instance, about.2% nitromethane can be added to the .. ~ solventjto inhibit this breakdown. , ..... . -....... .
..; . In the~case of a flammable solvent.such as ethanol, . it may.be important to add certain hardware features for .... . . ..
! safety~ purposes such .as explosion-proof .electronics, cooling means to prevent overheating of the solvent, and an exhaust duct to carry away .flammable .vapors.. An ;, embodiment of a vapor d~egreaseri.incorporating.the above hardware~.features, is r illustrated.:.in:~ FIG.--.3c. --- The . particular.embodiment.illustrated was~.designed by Bronson, 30 ~but.other~jexamples~are possible. ,~
As illustrated, the embodiment achieves-explosion-proof.electronics by,~re~otely.:locating rpower .supply 93 .. from .the. main body-~iof.-the degreaser, identified -with reference numeral 95, and-keeping,the other .electronics (not shown? under positive pressure of nitrogen. --:
...Cooling~is provided.by water~jacket 94,.-which is wrapped. around the ~body of the .~.degreaser as shown.
. _ . . .
-:

.. - . . , :: .
: - . ': :' : ' . : ~

WOgO/15674 PCT/US90/03002 ~6~3C r `; ~ . ?
~ 24 Optionally, cooling could be provided with a timer to prevent the extent to which the solvent is allowed to heat up .
An exhaust ~fan (not shown) could be provided, interlocked to the power supply so that fumes would be sucked away during operation. In addition, means should be provided for guiding the exhaust fumes to the'outside.
Otherwise, the FIG. 3c embodiment operates in a similar manner to the embodiments described above.
Specifically, for use with flammable solvents, the modifications shown in FIG. 3c could be added to the bench top degreaser of FIG. 3a,'or alternativelyj could be added to the degreaser of FIG. 3b for use on larger parts.
- - The examples illustrated in FIGs. 3aj 3b and 3c provide a means for part cleaning using`-either immersion, vapor, or spray cleaning with a suitable-solvent such as Freon T~S, Freon TF, TCE, ethanol', isopropanol, propylene carbonate, or water-based cleaners. Other examples are possible,~ and the above is not intended to be limiting.
- In the case of-immersion cleaning, optional physical agitation by means~of:a pump 'or'~ultrasonic;agitation by means-~of~ultrasonic transducers can'be providad to enhance the -effectiveness-of the cleaning. - In addition, post-curing'can be optionally integrated into the examples of FIGs. 3a, 3b or 3c through the''installation of W flood lamps:into the~degreaser~~ '''~^~'' '; - - ' ^i J :i _Any -of- the.~above:^~approa'ches are~ supérior- when compared to~ draining,-since the s'olv'ent/resin !disposal ~ ;~problem-isisubstantially~reduced,':-if'not-eiiminated. In fact, all the above approaches providë't'a'''mea'ns to-clean -~-O~and,reclean dirty-solvent. In` the'-'case'-of draining, on ~-~ the~;otherlhand,~any~excess-resin'or dirty'solvènt'must be n-J ;~disposed of. ~Even ~f-an absorbent''i~pad is used to'capture ~r:drainage~:~the pad~must'be~Ldis'posed of. r ~ 9l The above ~approaches~ also' may 'signific'antly reduce ; the.Jtime required~-to' clean-~-the': part compa'red with draining, which is advantageous since it reduces''thé time . .- .
.
- ' ' ' " '~

W~90/1~674 PCT/US90/03002 2056~1~
the part is exposed to oxygen before post-curing. As discussed earlier, oxygen exposure inhibits post-curing.
In addition, draining, particularly thermal draining, can result in significant distortions of the part, through the force of gravity on the part after thermal weakening of the part at higher temperatures, which distortions are reduced or eliminated with the above approaches. Another benefit is that- immersion cleaning in a liquid solvent coupled with physical or ultrasonic agitation will clean hard-to-reach areas of a part. In addition, the use of ultrasonic transducers or physical agitation means can reduce the time a part is immersed in a solvent. This is advantageous, since prolonged immersion or thermal draining can distort the part.
The above approaches are also beneficial because they result in a cleaned part which is nearly dry to the touch, and tack free, and which retains a good surface definition. Xegarding.spray cleaning, spray cleaning with a mixture of solvent/compressed air--is -effective for cleaning large parts, and water-based solvents are ,particularly~effective for'spray clea`ning`.~' ' `~ '' -~ A consideration with':thè^u'se of a bench''top'degreaser - - in conjunction with:Freon TMS is that solvent in the rinse - tank may become saturated''with--resin in -about séveral hours, so that excess;resin may float to the surface'of . the.liquid solvent.~ ~:''--'~' -~''- ~;~ ' '~
:; . ?:In;this instance, the'~degreaser can-bë fitted with an ;automatic ski~mer, and-'thé'-`resin'la^yer'can bë skimmëd off ~ and discarded.s~Option`ally,~'th`e generation of the floating 303-.1ayer;~canrJbe inhibited -'by'-'enriching-the ~solvçnt`'with methanol,iwhich.:increases~"the''solubility~of the soivent for dissolved resin. Preferably''3any'additional'methanol should be~added to _the1-boil sump ~since;the'94:6 weight .,t~mixture-~of ~Freon .and methanol~'~(which-const'itute's Freon 35-~ TMS)-should.:be .kept-approximateiy 'constant iin the rinsè
..... tank~for purposes-of cléaning efficiéncy;--The additional methanol can be added to the boil'sump without compromis-. . . - , ~ , - ~:

- ~ , WO90/15674 PCT/US9OtO3002 i 6 ing this ratio in the rinse tank because the 94:6 by weight mixture is the only azeotrope of Freon and methanol. As a result, it will have a lower boiling point than any other mixture, and will vaporize at a lower temperature than the other mixtures. Therefore, if the temperature is kept low enough, only the 94:6 weight mixture will vaporize regardless if additional methanol is added to the boil sump,- and only this mixture will condense in the rinse tank.
An important aspect of other embodiments of the subject invention is supporting a layer of liquid resin on the surface of a volume of a dense, immiscible, W
transparent, intermediate liquid. The intermediate liquid should be dense enough to support the resin, and in addition,.should be appropriate for immersion cleaning and immersion.post-curing. As will be described in the body of this application, the use of the intermediate liquid to support a resin layer provides a means for part cleaning and post-curing to be integrated with part building so that a single apparatus can perform all these ~unctions.
Another advantage.is.that;the use.:of a floating-layer will reduce the.resin inventory required,--making it less costly to build.large.parts. The thickness of:the resin layer ~ can, ln principle, be only one building layer,-i.e., about 10~20 mils, but ..an implementation which may be easier would provide for about several inches of resin'floating at the surface, so,that.control,of...the thickness may be unnecessary~during part building. ~If only-one building layerfthickness were provided,-then during:~part building, the thic~kness ofj~the.resin layer may:have to be monitored, and the resin..layerlmay have-to be replenished after'each ., j , , . , ", ., ~, . .................................. .
cross-sect~ion~were~jcured~ J~ . m' '~ 5 '~ """ '~
~ ~ Many~rintermedia~te. liquids-_can- be-~used.~ " The''main reguirements.o~ the ~iquids are that they be approximately denser~than..the.resln,..substantially insoluble'~in it,' and substantially.transparent to W light. The liquids''should be approximately denser than the resin so that they will ., .

. ' ' . ` .

.
27 ~ 6 ` ~J,~ ' support the resin layer, and so that any excess resin shaken off during part cleaning will float to the surface and rejoin the resin layer. This will make it unnecessary to distill and reclaim the intermediate liguid in order to reuse it. They should be substantially insoluble in the resin so that they will remain separated from the resin layer which could otherwise mix with it, and inhibit passage of the synergistic stimulation, such as W light or the like, through the liquid. Also, they should be substantially insoluble in the resin so that distillation and.reolamation of the liquids will not be required to clean them. Finally, they should be substantially transparent to synergistic stimulation such as W light or the like so that a part can:be post-cured while immersed in the liquids.
Regarding the density rsguirement, the intermediate liquid should be at least about 5% more dense than the resin. For example, a preferred resin used in a current commercial embodiment of a stereolithography apparatus (which commercial embodiment is referred to as the SLA-.,,250)~is Cibatool.XB-,5081,,-.which has.a density of-about ,;~1.14 g/ml. It has been found that an intermediate-liquid .. having .a .density of at.-least-:about --1.2-g/ml''will be .. . . . .
.~ acceptable with this resin. ~.For.example, a mixture of magnesium sulfate in water is possible having-a density of ,...at,least about 1.2 g/ml. Another example is-a:mixture of , sodium .chloride..-in_water.,iwhich is possible rhaving a '.,~density;.of about3,.1.2 g/ml.-1* Asilarge~Ja:différence in densi$y.as.possible ~ill insure clean:and-rapid's`eparation.
of the;liquid from~,the~resin;-~
. .; ,.Regarding~ ,s,plubilityj~-.,the: '.liquid - should be ., substantially..insoluble,-in,~,the~ resin.-;,r For'rexample, .. .. . .. . . ..
,,,current,resins-are~moderately~hydrogen bonded-liquids with ..?,a solubility parameter,~of,~about lO to about~~12~(cal/cm3).
35,.For these~ resins,~ an~r~appropriate iintermediatë'-^'liguid _.should have~a solubility parameter as.different~from the solubility of the resin -as possible. ~For 'example, a ~ 6~,i~',',`~,,'`,'~,`, 28 poorly hydrogen bonding liquid having a solubility parameter of less than about 7 (cal/cm3)K will be possible.
Aliphatic fluorocarbons are examples of such liquids having solubilities in the range of about 5.5 to about 6.2 (cal/cm3).~ Alternatively, a strongly hydrogen-bonded liquid with a solubility parameter of greater than about 20 (cal/cm3)~ is also possible. Water is an example of such a liquid having a solubility parameter of about 23.4 (cal/cm3).~ Additional examples can be found in "Polymer Handbook," 2nd Edition, Wiley-Interscience, pp. IV-337 and ff., which is hereby fully incorporated by reference herein as though set forth in full.
In addition to the solubility parameter discussed above, those skilled in the art may also use a qualitative measurement of solubility, and intermediate liquids are also .possible based on. this qualitative measurement.
Also, it has been found that the dielectric constant of the liquid is a good indication of its solubility in the resin, and intermediate liquids are also possible based on a consideration of the dielectric constant. Thè
.-,dielectric constant of..the~preferred`rèsin used~in the SLA-250,. Cibatool~ X8-5081,-is about' 4', and with this resin, it has.been.found that intermediate liquids having - a dielectric..constant of about-3 or'less,- or''about`lO or more, are possible.~
:~ ,J, Regarding-.transparency to~-light, ~thé -7 intermediate .liquid should.~be substantially~transparent~to''light:in the-r~ ~ region. of wavelength.iwhere.'-the post-curing takes plàce.
~ Thisj~s,because.~iduring post-curing,~~a'finishëd part will be immersed in the intermediate liguid,-'an'dithe liquid .Jr~ must~be substantially..transparent~to the W ';iight so it w~ reach the.part for.post-curing.:-~Current résins'have their peak_curing:activity~'near~about'230''!nm,-and'mercury ~ lamps~presently -used for:-~post-cùrin'g'; have--their peak 35 output~near about 265~nm.~~-Therefor'ë',^~;for:the' present~
. commercial embodiment:-of~the.Jsystem,' the intermëdiate liquid should be substantially transparent to light in the .. .... ..
. . . -~- , 2 0 ~ 6 ~ 1 6 ~ .

wavelength range of about 230 to about 290 nm. Other - intermediate liquids are possible, however, since the wavelength of the light used for post-curing could change.
The transparency will also depend on the dimensions of the vat used. The SLA-500 is a recent commercial embodiment of a stereolithography apparatus (the SLA-250 is an earlier embodiment), and a key aspect of the SLA-500 is to build biqger parts than with the SLA-250.
Accordingly, the vat used in the SLA-500 is approximately 20 inches in length and width, whereas the vat used in the SLA-250 is approximately 12 inches in length and width.
For a liquid to be substantially transparent to W light, at least about 80% of the UV light should penetrate to the -middle of the vat. Thereforè, for the SLA-250, at least about 80% of the light should penetrate about six inches into the liquid, whereas for the SLA-500, at least a~out 80% of the W light should penetrate about 10 inches into the liquid.'- Both water-based salt solutions and fluorinated'liquids meet this requirëment. ' The transparency also depends'on how much resin ~dissolves''in~''thë^liquid during'-'part''clëaning' since the dissolved resin ''';may ~strongiy absorb light of the - '-appropriate 'wavelengths,' and -interferë 'wi~h thë post-; curing. Therefore;')the trans'parency wilI' dépend on the solubility of the resin in the liquid,'and account must be '~ ~ taken of the solubiiity 'in~choosing'a liquid.
':' Twro examples of'-denisë in'termèdiate l'iquids which have :it.. been found to'be';'àcce'ptable~'for use'w'ith 'Ci~atool XB-5081 j are perfluorinated'~igh-boiling liquids such as Fluorinert FC-40 (3M Corp.~ and water-baséd salt soluti'ons such as magnesium sulfate~or`'sodium~chloride'in wàter.~ Fluorinert -FC-40 r has a ~density 'of~~approxima'tely'' 1.5 g/ml., a ~ t~ a - ~magnesium 'sulfate in-water'solution is possible having a density of at leas`t-~abou't-i.-2 gjmi., and a sodium chloride in water"~solution-is possiblë`'hàving a dénsl;ty of about 1.2 g/ml. '~-idditional~examplés'of'posslble iiquids are . . ~ .
..

. .
.. .

.

WO90/l5674 PCT/US90/03002 ( ~,61 ~ .
6~ ` ' `

perfluorodimethylcyclohexane (PCR Inc.) and trichlorotri-fluoroethane (a/k/a Freon TF -- DuPont Corp.).
The foregoing examples are given by way of illustration only for use with Cibatool XB-5081, and are not intended as limiting the use of other intermediate liquids, ~specially with other resins. For example, any completely fluorinated liquid with a boiling point higher than the temperature that the liguid will be maintained in the vat (a/k~a the "use temperature") is acceptable.
Fluorinert FC-40 was suggested above only on the basis of cost and availability.
Other examples of aqueous solutions of salts are also possible. The addition of the salts acts to increase the density and decrease the resin solubility. , Salts of cesium are attractive because of their high density and solubility in water. Salts of iodide or bromide may also be useful. Improvements in the aqueous solutions mentioned above are possible by increasing the salt concentration, thereby decreasing the tendency for mutual solubility between the liquid and the resin.
The advantage of`using the,perfluorinated liquids is that they,have negligible solubility,in the resin and low . I ~ . . . . . . . .. . . .......... .
vapor pressure, and~are substantially inert. The,benefit of a liquid having a low vapor pressure is that the liquid will have a high ,boiling~point, and ~will not easily evaporate or generate bubbles when ,the platform is dipped into the liquid, throug~out ,part ;,building. If the intermediate liquid evaporates.and.generates bubbles, the bubbles could be,~introducedl~into ,the -iresinj-~and a distortion of the final part introduced.,~e r ~ .~
A consideration in using the prefluorinated liquids is their high cost.,,r~ypical costs~of these liquids at present compared with that ,of the resins-and~the water-based salt solutions are listed below- ,, perfluorinated liquids~ S900/gallon ''''' water-based salt solutions: $1/gallon resin: S360~gallon 2~6~6 31 ' : .
On the other hand, the intermediate liquids (unlike the resins) are not consumed, and need only to be replaced rarely. Using a liquid resin alone in the vat may be more expensive even with the perflourinated liquids since the resin may only have a shelf-life of only about six months, and may have to be replaced at this point even if it is not consumed in building a part. For the SLA-500, for example, about 80 gallons of resin are required to fill the vat, and since only about one quart of resin is used to make a.part, almost the entire contents of the vat may have to be replaced about every six months. This turnover of.the consumed resin ~eans that a larger inventory of resin may be required, with a corresponding larger up-.front investment. In addition, because of the rapid pace : 15 of technological development of resins,.the inventory may become obsolete by the time.it is used.
'These problems may be aggravated when many types of resin (which differ by certain characteristics such as color or conductivity3 are used to build different layers of the part. In this instance, in-.the traditional .approach lof~ part ~building,.. where -a; volume ~of' resin unsupported by~an intermediate liquid is placed in a'vat, a large inventory (on the order of about.80 gallons) of each type o~ resin used.may be required. . By floating a layer.of each resin on a volume of an.intermediate liquid, ~ ian inventory of only approximately.5-lO gallons (depending ; ~ on.the thickness of the resin-~layer)iof each:type~of resin .5may.be all that-is required.
, ~ A. consideration~-in.the_:use-'of.water-based~-salt solutions.,with~Cibatool GXB-5081 is~.-a--possiblé;~slight .) compromise in.performance with these-.solutions compared ., with~the. perfluorinated rl iquids.- .In~some:~instances, it ; has beenlfound that.~the surface~of:a l!green~ part`~prépared 3 i~,through the use of a.water-based salt.solution;may'have'a '35 rougher surface texture, apparently due to the's'olub'ility . o~ the solution in'the.~resin,?which manifests itself in the final part as a rougher surface texture. Density and .. ~, .... .

(~ ....

` ; ' ? " ` ' transparency seèm adequate, however, and do not appear to be diminished in any way. Also, any compromise in performance may not be present for other resin formulations, better matched for use with water-based salt solutions. In addition, the water-based salt solutions are inexpensive.
- A second consideration is that all salts'may not be possible for a particular resin since some salt-solutions may not be dense enough for that resin. To support the resin layer, the intermediate liquid should be denser than the resin, and preferably at least about 5% more dense.
For example,'Cibatool XB-5081 has a density of about 1.14 g/ml, and an intermediate liquid which has a density of at least about 1.2 g/ml is preferred for supporting this resin. Examples of such liquids are a water-based solution of sodium chloride (NaCl) in water maintained at a temperature of about 20 to about 30 degrees C, with a concentration of sodium chloride in water of about 311 g/l; or a water-based solution of magnesium sulfate (MgS04) in water maintained at a temperature in about 'the above ~-range, with-a concentration of magnesium sulfaté~in~water -~ of about 229 g/l. ~Both of these liquids have~dénsities of about 1.2 g/ml.
~ A consideration in choosing a-salt is the rapidity with which the density of-the'solution can be incrèas'ed by JI~ increasing the concentration of salt'in the sol'ution. For 7 ,' example, increasingrthe~percentage b-y weight;'of'salt~in a ' cesium chloride solution from about 26%-to abou* io%, and J j_then.to-about 64%;-;-will~increase ''the`~ensity of the 30,~;resulting ~solution from ~aboutil.24~g/ml ~to~;about'~l.i2 ;J; g!ml, and then-to about 1'.88 g/ml,'àt about'20 degréës C.
A second examplelis that by--increas'in'g the~percëntage by weight-.of,~alt-in a magnesium~sulfaté~'solut'ion from'about ; 15% to about 20%,iand then to about 26%,' will;inc'reasë'the 35~:density of the resultant-solution from about'i.16 gjml to about 1.22 g/ml,-and then to about'1.308 g/ml9~at^about 20 degrees C. -A third example is that by increasing the .
.~

:
.. ~ ~ ... .
- ~ .

WO90/~5674 ,;. ~CT/US90/03002 2os6~l 6 percentage by weight of salt in a sodium chloride solution from about 15% to about 20%, and then to about 26%, will increase the density of the resultant solution from about 1.11 g/ml to about 1.15 g/~l, and then to about 1.20 g/ml.
A second consideration in choosing a salt is how close the resultant solution is to its saturation point.
If a solution near its satura~ion point cools slightly, some salt crystals may form, which could be introduced into the resin, and cause a distortion in the final part.
In addition, a solution near the saturation point may not provide desired flexibility, because it may not be possible to. significantly increase the density 'of the solution by adding more salt if this should"ever be desired, for example, to support a denser resin.
For example, at about 20, -about 25, and about 30 degrees C, a sodium chloride solution has a saturation point of about 364, about 365, and- about' 367 g/l, - respectively. In this temperature range, a concentration of about 311 g/l of sodium chloride in water is required to achieve a density of about 1.2 -g/ml. At th~s ~,, concentration level,- the solution is~about.'85% saturated.
..If~a density .of.about 1.23 g/ml is-~desired,`'however, a concentration~of about 367 g/l sodium chloridë in' water will be required, with the -result 'that ''at' -this concentration level.:;the solution' will` be aboùt'-100%
. saturated. . As ~ a..result,.~ -further- -incréasés in .concentration:may not-be-possible,~i'and in-addition, if this solution cools.~downj-salt.'crystals may form.~
Another example is a;solution of magnesium sulfate in water. At about 20, about 25, and about-30 ~egree~ C, a magnesium sulfate solution has a saturation point-of àbout .. 356, about 380, and about 403:g/l, respectively.'-'In this temperature range, a concentration 'offaboùt-'229-`'g/i of magnesium sulfate in water.will.be required to achieve a density of about 1.2 g/l.: At this concentration 'ievel,'~
the solution is only about 64% saturated. If a density of about 1.23 g/ml is desired, a concentration of about 273 . . ~

, ~ : '-'- ' WO 90tl~67J ~6 PCT/US90/03002 g/l of magnesium sulfate in water will be required, and at this concentration level, the solution will only be about 77% saturated.
In some instances, it may be possible to increase the saturation point of a solution by increasing the temperature at which the liquid is maintained. In fact, a given rise in te~perature may have a grea~er impact on the saturation point of some salts than with others. A
sodium chloride solution, for example, has a saturation point of about 357 g/l at about O degrees C, and a . saturation point of about 391 g/l at about lOO degrees C.
A magnesium sulfide solution, on the other hand, has a saturation point of about 260 g/l at about O degrees C, and a saturation point of about 738 g/l at about lOO
degrees C. A rise in temperature from about -20 to about 30 degrees C, will only increase the saturation point of a sodium chloride solution from about 364 to about 367 g/l, while the same temperature rise will increase the saturation point of a magnesium sulfate-solution from 20..about 356 to about 403 g/l.
., .. In .other~instances;:it may be~possible ~to:-7increase the density by increasing the molecular~weight'of thé~salt used, or alternatively,.by increasing the'atomic weight of ~;.the metal in the salt..Since a.mole of each salt will add 25; roughly the same volume.to a~solution, ~the'greàter the molecular weight, the greater.:the impa'ct on densi~y; -For . several salts, the molecular~weight is~provi`de'd'below:
Salt .~ .2 Molecular weight:~Lglmole`)'' ~ ~Cesium Sulfate~ o 361;~ Jin~
30 .Magnesium Sulfate ,;~ .120- '^-' --'''~':`-: i' .~.Sodium~Chloride ~ S 58~ -J ' '~ '^~ -~ ''' ^~ ' ''-' '~'''' ' '' ' ' '' . For these"salts, the atomic weight-of the: metal used to i~o make~up,the~salt.issas follows ^ ,~
~Me~ 'L-3~ Atomic Weight (a/mole3'~
35 .Cesium s~ 133.- - - r,, ~ -t .' ' ~ ' '- ' ' -' . Magnesium ; -.; ' - 24~ -~ '`' ' .Sodium- - ; ;- . 23 .'' ~-.. .

.

' ' ' WO90~156~4 PCT/US90/03002 6 4 1 6 . ~ :

Consideration of the above tables suggests that a particular density solution can be achieved with a solution having a relatively low concentration of cesium sulfate ~compared to its saturation point), a higher concentration of magnesium sulfate (compared to its saturation point), and an even higher concentration of sodium chloride (compared to its saturation point). A
consideration of the actual. data confirms this. The saturation points of solutions of cesium sulfate, magnesium sulfate, and sodium chloride are about 1780 g/l, about 356 g/l, and about 364 g/l, respectively, at about 20 degrees C. At about this temperature, the required concentrations (compared to their saturation points) of these salts to achieve a solution density of about 1.2 g/ml is about 14% for cesium sulfate, about 64% for magnesium sulfate, and about 85% for sodium chloride.
A third consideration in choosing a salt is whether the salt is photoreactive. Iodide salt, for example, may be partially photoreactive. A photoreactive salt may absorb W light, and interfere with post-curing.:~-A .fourth consideration in chooæing a~salt is the material used to construct the vat. ~For the SLA 250, for example, the vat is made out of aluminum, and as is-known, chloride is corrosiye.toraluminum.
A fifth consideration in choosing a salt is theirisk of introducing contaminants .in the~resin, which.may.-be a serious problem in3,the application of stereolithography to investment;casting- (a/k~a. the..lost.-.~plastic--.;process).
J According to this process, a finished:part~is dipped,into a casting material,~.the"plastic is_burned..off,:.and'then metal is poured lnto the sp?ce vacated by.the plastic. If salt has contaminated the resin used toimake the part,~ the burn mg off~ of~ the ~plastic amay ~leave~ a; saltS ash afterwards, which~could lead to imperfections:in the-metal part. In general, any.contamination of the resin by more than about 1% by the salt.may leave an unacceptable ash, unless a salt with an organic cation such as salts of WO ~/1~6~4 PCT/US90/03002 - alkyl ammonium or salts of just ammonium are used, since they may completely burn out with the resin. Examples of such salts are ammonium sulfate or ammonium nitrate.
The above examples are provided for illustrative purposes, and are not intended to be limiting. Based on the considerations set forth above, other salts and other intermediate liquids are possible, and, one of ordinary skill would be able to select an appropriate salt or intermediate liquid for a particular resin and set of operating parameters based on these considerations.
A second embodiment of the subject invention is illustrated in FIGs. 4-5 in which like componénts are identified with like reference numerals. An important object of this embodiment is the integration of part cleaning and post-curing into part building, and to facilitate this integration, a dual chamber resin vat is provided, a top view of which is illustrated in FIG. 4a.
As illustrated in FIG. 4a, the dual chamber vat comprises a first chamber 100, and a second chamber 101 separated from the first chamber by partition 102. Resin :~ } layer~-103 floating ~on i1ithe intermediate'' liquid (not ; identified with a reference numeral)' only is placèd in the : ~first ~ chamber," while the ~'intermediate ' liquid (not identified with a reference-numeral~'only is placed'in the 25- second chamber. In'~addition,; the'''second ~chamber is ; -~provided with-;a-plurality of ~spaced W flood^lamps or the likej;identified with~refe'renc'e numerals'104a,' iO4b,-104c, ~ respectivelyiqsituated'on tXe'walls (side and'topj of the e~cchamber for/~looding'the intërior-of-the~'cham~ r''with W
30~i 1ight during post-curi'ng;'`'The'-second~chamber i's covered;
;_ as shown,--;rwith removàble'opaquë cover '105, whic^h cover ! also- has a 'fW~ fI~ood light,-'' ident'ifie'd''wl~th reférence -~ numeral,:lo4d,i-situated on~it--for`'fiooding'the interior of :the second chambèr''with~ W iight;dûring' post-cùring.
J~_ ~ -; ' The~dual chamber-vat-integrates part building, part cleaning, and post-curing into one apparatus. A sidê view : . . .~ . .. .., . . . . , .~

, ,. . . .. . . . . . . . . .

( :: 2~,~.6 ~1 6 ~ r, 37 ~
of the dual chamber vat during part building is illustrated in FIG. 4b.
As illustrated, partition 102 does not extend all the way to the bottom of the vat. Instead, extending to the bottom of the vat is hinged shutter 106 which, as shown, is placed in the open position during part-building.
Also,.as illustrated, the second chamber is provided with a volume of the intermediate liquid, while the first chamber is provided with a resin layer 103 floating on a volume of the intermediate liguid. The.resin supported by the liquid forms a resin/liquid interface, and with the shutter in the open position, the resin/liquid interface should be kept above the bottom 102a of the partition so that the resin will not flow over to the second chamber.
This can be accomplished by placing a sufficient amount of . intermediate liguid in the two chambers so that the resin/liquid interface will be above the bottom 102a of . the partition.
.. Also shown in FIG. 4b is travelling platform 107 situated on guide rails 108 for guiding the platform from the first to the second chambers with:the-shutter-placed ..
;in the.open positioniafter part building and part cleaning . . are completed. .FIGs. 5a-5e illustrate~:the.-travelling ..... platform and- associated.iguide ~rails -for guiding the platform.~between;the two chambers. .~
.. . ~ ..Turning ~now to FIG.-- 5aj which.~-provides an . illustration tof-,a ~side-~view.,~.of~.a :dual lchamber''vat, .-.
part lO9. is ~shown~ situated-;.on -travelling platform 107 ~ which is placedron top of carriage 115.'-; The-~platform and 30,..carriage move laterally between.the:chambers-in the vat by ,means of guidejrails;108.-. FIG. 5b shows~a frontal~view of the..arrangement of-FIG.-5a.~Platform3107 moves vertically f, .,,.,by~.means~of a.Z-stage elevator (not.shown), which'has two ~. arms, 114a ~and~ 114b,-, which.-:are placed ~underneath' the 35J platform as shown to .support .it as the Z-stage elevator .~ moves-vertically along elevator:rails~:(not shown).--When .. . ~ . . . . .. . .
it, is desired to have the platform..move into the'second ,.... - ~ - .

, WO90/l5674 PCT/US90/03002 f .
~6~` `` `` ` ` 38 '' chamber, the Z-stage elevator lowers itself sufficiently so that the platform rests on ridges 115a and llSb of carriage llS. Between the ridges and below the platform is hollow area 113 into which the arms of the Z-stage elevator fit when the elevator has lowered the platform onto the carriage. After this has been accomplished, the platform and carriage are caused to move into the next -- chamber, as illustrated in FIG. 5d, at which point post-curing begins after the hinged shutter has been closed.
When post-curing has been completed, the platform and carriage can be moved back into the first chamber, as illustrated in FIG. 5a, and if the arms of the Z-stage elevator have not been moved, they will not interfere with the movement of the carriage back into its original position, and when the carriage has been-moved'back to this position, the Z-stage elevator arms will continue to fit into the hollow area between ridges 115a and 115b of the carriage, and below the platform. Then, the Z-stage elevator can raise the platform by means of the arms so 20 ~that the post-cured part can be removed, and so that ~anotheripart can~be built.~:' ''' -'~: ':/"'' ~ ; - ;~
A top view of-the'arrangement~'of FIGs'.- 5a and 5b is shown in FIG. 5c, which shows Z-stage elevàtor arms 114a and 114b supporting platform 107;(the-portions of~the arms underneath the platform aré shown with dashed'~linès~. A
control computer (not shown) may also bé'iprovided for --- controlling ithe movement rof;`the ~platform-'b'e'twéen the chambers, and:for opening'and closing the hinged shutter.
~ Arperspective view of the arrangement ôf FIGs. 5a and 5b is shown~in~FIG.~ 5e,~!~which';shows:'élevat'or^-raiis~'l16,' which are~used~to guide' plàtform 107~in à '?vertical _direction. ;1 Also~-shown'~is ~~carriagë li5rl'fo'r- supporting platform ~ 107,~after~ the`~;platform''~has '''been ' lowered ~ sufficiently by the Z-stage elevator,: a'nd'~linear raiis 108 35 ~for* guiding the ~carriagelplatform;''~'in a horizontal -- direction. Also illustrated'is hinged shu'tter;106, which can be opened to alIowAthe carriage/platform to move into .

WO90/l5674 PCT/US90/03002 f": '`
2~6~16 `
39 ` .
the second chamber, or closed to isolate the resin layer in the first chamber from W light originating from the second chamber during post-curing.
Turning back to FIG. 4b, during part building, the platform is progressively lowered through the resin/liquid interface and into the liquid itself as the build-up of the part, identified with reference numeral 109 in FIG.
4b, continues.
Note that during part building, as the part building proceeds, there is a danger, particularly with thin resin layers, that the close proximity of the resin/liquid interface to the upper surface of the resin will affect part building. It has been found that this has little consequence on part building if the resin layer is about an inch or more in thickness. If the resin layer is less ,than this, part building may,be affected more,since the movement of the completed portions of the part as they pass through the interface may cause a temporary,disrup-tion-at the interface, which disruption can extend approximately a .quarter inch .on either side .of the , ~Jinterface both~-into the resin layer,:and.into *he,-liguid.
- A resin layer~of about an inch or more will reduceior~even eliminate the impact this disruption may,,.have on.: the ,. sur,face of the resin layer,.and hence on.part building 25,--,itself. J j.- . , : .:.. ., ,~; ..
.,.;,..,~ Aslthe completed portions of ,the part..are.lowered beneath.,the.!resin/liquid interface, part- cleaning can .begin..~.A,side view,of~the,,dual chamber,.yat.during~part .~ cleaningr~is~illustrated in FIG. ~4c. :.-",,.~-, .,-. , ~
30_ ~ Ascthe built layer,s ,of.-the,part-are lowered-beneath ~,. the~interface~ excess resin adhering to the built portions ~.is-,,stripped,~away.~,,-,It, has been found .that .ultrasonic .~rjycagitation~.greatly ~accelerates".this,~ process,, .for.~which .".., purpose,.-!ultra,sonic~transducer -.llO.:is provided:.in the first.chamber of-the vat,as illustrated~in..FIG..4c.i As ~,, illustrated, the excess resin, identified withSreference .. numeral 111 in - FIG. 4c, is shaken off into. the WO90/l5674 PCT/US90/03002 intermediate liquid, which causes the resin, being of lighter density than the liquid, to float to the surface and recombine with the resin layer. When part cleaning has been completed, the entire part will be immersed in S the intermediate liquid as illustrated in FIG. 4c. A
major benefit of part cleaning as described above is that the need to dispose of excess resin and intermixed solvent, and the need to clean the solvent through distillation, followed by reclamation, which is attendant with other approaches, is eliminated. In addition, compared with other approaches, it may'be easier to clean hard-to-reach portions of a part.
- Compared to the embodiments of FIGs. 3a and 3b, it may not be possible to use an intermediate liquid which is also a cleaning solvent. This is because the action of the solvent could interfere with part~'building and post-curing since the solvent'could cause the'part to dissolve while the part is immersed, and in addition, -dissolved - - resin in the liguid could absorb W light, and therefore interfere with post-curing. This is in spite of'-the fact Jthat the~composition-of a~-typical solventt'`i.e.,''-'a-mixture ?~of:Freon TF-and methanol, is similar to the composition of ~ an illustrative intermediate'liquid:described~ earlier, -~ -~i.e.,-Freon~TF~-alone.' As~a result,''for this embodiment, the use of Freon TF is a preferred intermediate~liquid -Ci~ compared with Freon ~MS'evén~though`'Freon TF~alone may be -~ less~efficieht'by itself`as a:solvent-compared''with'!Freon ~~f-'TMS.~However,'!any'~diminished cleaning power:can be-taken up by the action ofithé''ultrasonic transdu~c'er~ Al'so, as 30.-described~'in ~more:detail` ea'rlier with' respect to the . ;o embodiments of-FIGs.~'; 3a; and 3b, o'ther-approaches for -,r~-enhancing~part cleaning are possible,'such"as' physical . .J '-'agitation,~ heating':~up ~ the ~ va't, '-~or ''v'apor;-- ori;spray ~r~ degreasing.q In addition,~'water-bàsed'-'salt"isolùt'i'o'ns may belmore'effective than Freon-TF for'part cleaning.'-'-~ ^-~ Turning back to FIG. 4c, after the'exc'es~s''~r'esin has : heen substantially cleaned off, with-the hinged-shutter , .. .

WO90/l~74 PCT/US90/0300 i'- .~ .
2056,~1 6`~

between the chambers in the open position, the platform on which the built part is placed is moved along guide rails 108 into the second chamber. At this point, post-curing begins after the hinged shutter is closed.
A side view of the dual chamber vat during post-curing is illustrated in FIG. 4d. As illustrated, after the platform is moved along the guide rails (not shown) into the second chamber, shutter 106 is closed to substantially block W light from the W ~flood lamps, 104a, 104b, 104c, 104d, respectively, from entering the first chamber where the resin layer is situated. If this light were allowed to substantially enter the first chamber, it could partially polymerize the resin layer.
After the shutter has been closed, post-curing can begin while the part is immersed in the liquid as described in more detail in U.S. Patent Application Serial No. 183,016, and its CIP, Serial No. 268,429. As'described in those applications, post-curing has been found very advantageous in stereolithography, yielding much higher accur'acy parts, particularity when the part'is immersed in water or water-based solutions.~ Post-curing while the pa`rt~'is~`'immersed ,in~a:~liguid~:isibeneficial since'the''liquid'car'r'ies away the heat of reaction generated in~the'post-curing,'which - heat could-otherwise cause distortion'of`the'part,'~'-'and in 25L addition,:removes oxygen frsm-the surface,-i which'-could otherwise inhibit post-curing,'-and leave'~a-tacky surface.
~ ost-curing; the.fi~part e~while5-it- isi;;immersed in a -~ ~ perfluorinated liguid will al o be advan'tageous; since the ;thermal conductivity,!heat~'diffu'sion charactéristics', and oxygen solubility of these liguids'arè comparable to likè
; characteristics.for water-~ased solutio'ns'.~
The~;intermediate --liquid '~'should '-7 'bé''- s'ubstantially transparents:to~W ~light.to-provide`for/;post-curing. As - ~explained;in~morerdetail~above,~thi's-règui'rement-dëpends 35 ;onithe;dimensions'~of the~':vat used.'''-'-Thé'-~liquid should be - such that at least about~80% of-the W light penetrates to . about the middle'of the vat.'~For an SLA-250 having about .:

: - : :

:. : ~ :

WO90/1~674 PCT/US90/0300~ ' 6 ~ ),6 ~ !

a 12 in. vat, the critical penetration is about 6 inches, while for an SLA-500 having about a 20 in. vat, the critical penetration is about 10 inches.
When post-curing has been completed, the part can be 5 removed for manual finishing. Optionally, certain part finishing steps such as filling surface discontinuities with-liquid resin followed by flash setting of the surface as described in more detail in U.S. Patent Application Serial No. 183,012, and its CIP, Serial No. 268,428, can be integratably performed in the second chamber using the W lamps.
Other embodiments of the subject invention are possible. FIGs 6a and 6b illustrate a single chamber vat into which is placed resin layer lll floating on a volume of intermediate liquid. FIG. 6a shows a top view where the vat is equipped with a plurability of spaced, UV flood lamps 112a, 112b, 112c, and 112d. FIG. 6b shows a side view of.the vat, which is equipped with platform 117 situated in the same chamber as W flood lamps-112 and ultrasonic transducer 110. :Part building and part . ..cleaning take;place as...described earlier with the two . chamber vat embodiment. However,.before post-curing can ..take place,i..the.~resin layer should;:be'pumped off or scooped away by a pump-or scoop (not-shown), or alterna-25 j.tively, a hinged shutter-(not shown):can be added,'`which ~;jshutter.is -situatediso that~after the:platform/part has been~moved to a predetermined .location for-post-curing, ;. the hinged-shutter,can be closed.throughout post-curing to . substantially block W light.-emitted;by the W .flood'lamps 30,from the resin layer.rJP. ~ s -..~. -_l. -: i!~.
Additional advantages and modifications~will readily D occurj.to.those.skilled in.the art...i~.The invention in its ~ broaderj.aspects is~not, therefore,rlimited.to the specific ...... , .details, representative methods, and:illustrative éxamples : ~.. ~ . .. ... ..... . . . .
shown and~described. -Accordingly,~departures'~may be madë
frrom such-details without departing~from the~-spirit or . scope of applicant's general inventive.'concept, and the _ ~ .. . .

. . .:, .: ., W O 90/15674 P(~r/US90/03002 ~ 20S6~16 invention is not intended, nor should it be construed, as limited to the examples and embodiments illustrated and described, except as by the appended claims.

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Claims (47)

AMENDED CLAIMS
[received by the International Bureau on 24 October 1990 (24.10.90);
original claims 1,2,7,8,16,17,19,27,30,31,34,35,38.39 and 42 amended;
new claims 43-47 added; other claims unchanged (13 pages)]

1. An improved stereolithography apparatus of the type for building a part at the surface of a volume of material capable of selective physical transformation upon exposure to synergistic stimulation, the improvement comprising means for building the part at the surface of a layer of said material capable of selective physical transformation supported on a volume of a dense, immisci-ble, and substantially inert, intermediate liquid, and means for integratably performing additional stereolithog-raphic processing on at least a portion of the built part while immersed in the intermediate liquid.

2. The apparatus of Claim 1 wherein the additional stereolithographic processing means comprises one or more sources of synergistic stimulation for subjecting an immersed portion of the built part to said synergistic stimulation, and isolating means for substantially isolat-ing the material capable of selective physical transforma-tion from the synergistic stimulation.

3. The apparatus or Claim 1 wherein the additional stereolithographic processing means comprises one or more ultrasonic transducers which ultrasonically agitate the immersed portion of the built part.

4. The apparatus of Claim 2 wherein the isolating means comprises a dual chamber vat having a first chamber containing the material capable of selective physical transformation supported by the volume of the intermediate liquid and a second chamber containing a second volume of.
the intermediate liquid, a movable platform on which the part is built for moving the built part along a predeter-mined path from the first to the second chambers, and a hinged shutter placed along the predetermined path between the two chambers having an open and a closed position, wherein the built part is moved from the first chamber to the second chamber by means of the platform when the hinged shutter is open, wherein the second chamber has a periphery and an interior, and the source of synergistic stimulation is spaced around the periphery, wherein the shutter is closed after the built part is moved to the second chamber, and wherein the source of synergistic stimulation thereafter impinges upon the part.

5. The apparatus of Claim 2 wherein the isolating means is a pump for pumping off the layer of material capable of selective transformation before post-curing.

6. The apparatus of Claim 2 wherein the isolating means is a scoop for scooping off the material capable of selective transformation before post-curing.

7. The apparatus of Claim 2 wherein the isolating means comprises a single chamber vat containing the layer of material capable of selective physical transformation supported by the volume of the intermediate liquid, a movable platform on which the part is built for moving the built part to a predetermined location, a hinged shutter having an opened and closed position, wherein the built part is moved by means of the platform to the predeter-mined location when the hinged shutter is open, wherein the vat has a periphery around which the source of syner-gistic stimulation is spaced, wherein the shutter is closed after the built part is moved to the predetermined location, and wherein the source of synergistic stimula-tion thereafter impinges upon the part.

8. An improved stereolithography apparatus of the type for building parts by directing synergistic stimula-tion to impinge from above upon the surface of a volume of material capable of selective physical transformation upon exposure to synergistic stimulation, the improvement comprising means for building the part by directing the synergistic stimulation to impinge from above upon the surface of the material capable of selective physical transformation upon exposure to synergistic stimulation supported on a volume of an intermediate liquid having a density which is at least about 5% greater than the density of the material capable of physical transformation upon exposure to synergistic stimulation, a solubility which is less than about 7 (cal./cm3)1/2 or at least about 20 (cal./cm3)1/2, and wherein the intermediate liquid has a surface, and at least about 80% of light having a wavelength in the range of between about 230 to about 290 nm. penetrates to at least between about six to about ten inches into the intermediate liquid beyond the surface.

9. The apparatus of Claim 8 wherein the intermedi-ate liquid has a density of at least about 1.2 g/ml.

10. The apparatus of Claim 8 wherein the intermedi-ate liquid is maintained at a predetermined temperature during part building, and the intermediate liquid is a perflourinated liquid having a boiling point approximately greater than this temperature.

11. The apparatus of Claim 10 wherein the intermedi-ate liquid is Fluorinert FC-40.

12. The apparatus of Claim 8 wherein the intermedi-ate liquid is a water-based salt solution.

13. The apparatus of Claim 12 wherein the salt solution is a solution of magnesium sulfate in water.

14. The apparatus of Claim 12 wherein the salt solution is a solution of sodium chloride in water.

15. The apparatus of Claim 12 wherein the salt solution is less than about 85% unsaturated.

16. An improved method of the type for building a part on the surface of a volume of a material capable of selective physical transformation upon exposure to syner-gistic stimulation, the improvement comprising the steps of building the part on the surface of a layer of the material capable of selective physical transformation upon exposure to synergistic stimulation supported by a volume of a dense, immiscible, intermediate liquid transparent to synergistic stimulation, and then integratably performing additional stereolithographic processing on at least a portion of the built part while it is immersed in the intermediate liquid.

17. The method of Claim 16 wherein the additional stereolithographic processing comprises subjecting the immersed portion of the built part to a source of syner-gistic stimulation while substantially isolating the layer of material capable of physical transformation from the synergistic stimulation.

18. The method of Claim 16 wherein the additional stereolithographic processing comprises subjecting the immersed portion of the built part to ultrasonic agita-tion.

19. An improved method of the type for building a part by directing synergistic stimulation to impinge from above upon the surface of a volume of a material capable of selective physical transformation upon exposure to synergistic stimulation, the improvement comprising the step of building the part by directing synergistic stimu-lation to impinge from above upon the surface of a layer of the material capable of physical transformation upon exposure to synergistic stimulation supported by a volume of an intermediate liquid having a density which is at least about 5% greater than the density of the material capable of physical transformation and having a solubility which is less than about 7 (cal./cm3) 1/2 or greater than about 20 (cal./cm3)1/2, and wherein the intermediate liquid has a surface, and wherein at least about 80% of light having a wavelength in the range of between about 230 to about 290 nm. penetrates to at least between about six to about ten inches into the liquid beyond the surface.

20. The method of Claim 19 wherein the intermediate liquid has a density of at least about 1.2 g/ml.

21. The method of Claim 19 wherein the intermediate liquid is maintained at a predetermined temperature during part building, and the intermediate liquid is a perfluori-nated liquid having a boiling point approximately greater than this temperature.

22. The method of Claim 21 wherein the intermediate liquid is Fluorinert FC-40.

23. The method of Claim 19 wherein the intermediate liquid is a water-based salt solution.

24. The method of Claim 23 wherein the salt solution is a solution of magnesium chloride in water.

25. The method of Claim 23 wherein the salt solution is a solution of sodium chloride in water.

26. The method of Claim 23 wherein the salt solution is less than about 85% unsaturated.

27. An improved stereolithographic apparatus of the type for draining a part of excess working material capable of selective physical transformation upon exposure to synergistic stimulation, the improvement comprising means for immersing at least a portion of the part in a volume of liquid solvent in a vapor degreaser, and means for subjecting the immersed portion to ultrasonic agita-tion to substantially remove the excess untransformed material from the portion.

28. The apparatus of Claim 27 wherein the solvent is ethanol.

29. The apparatus of Claim 28 wherein the portion of the part is immersed in the liquid solvent for less than about ten minutes, preferably less than about five min-utes, and most preferably less than about two minutes.

30. An improved stereolithographic apparatus of the type for draining a part of excess working material capable of selective physical transformation upon exposure to synergistic stimulation resin, the improvement compris-ing means for immersing at least a portion of the part in solvent vapor of a vapor degreaser to substantially remove the excess working material from the portion.

31. An improved stereolithographic apparatus of the type for draining a part of excess working material capable of selective physical transformation upon exposure to synergistic stimulation, the improvement comprising means for immersing at least a portion of the part in a volume of liquid solvent in a vapor degreaser, and means for physically agitating the liquid solvent to substan-tially remove the excess working material from the por-tion.

32. The apparatus of Claim 31 wherein the physical agitation means is a pump for pumping the solvent.

33. The apparatus of Claim 32 wherein the solvent is Freon TMS.

34. An improved stereolithographic apparatus of the type for draining a part of excess working material capable of selective physical transformation upon exposure to synergistic stimulation, the improvement comprising means for immersing at least a portion of the part in a liquid solvent to substantially remove excess working material from the portion, and post-curing means for integratably subjecting the immersed portion to sufficient synergistic stimulation to provide final dimensioning of the part.

35. An improved stereolithographic method of the type for draining a part of excess working material capable of selective physical transformation upon exposure to synergistic stimulation, the improvement comprising the steps of immersing at least a portion of the part in a volume of liquid solvent of a vapor degreaser, and sub-jecting the immersed portion to ultrasonic agitation to substantially remove excess working material from the portion.

36. The method of Claim 35 wherein the solvent is ethanol.

37. The method of Claim 36 wherein the portion of the part is immersed for less than about ten minutes, preferably less than about five minutes, and most prefera-bly less than about two minutes.

38. An improved stereolithographic method of the type for draining a part of excess working material capable of selective physical transformation upon exposure to synergistic stimulation, the improvement comprising the step of immersing at least a portion of the part in solvent vapor of a vapor degreaser to substantially remove excess working material from the portion.

39. An improved stereolithographic method of the type for draining a part of excess working material capable of selective physical transformation upon exposure to synergistic stimulation, the improvement comprising the steps of immersing at least a portion of the part in a volume of liquid solvent of a vapor degreaser, and physi-cally agitating the liquid solvent to substantially remove excess working material from the portion.

40. The method of Claim 39 wherein the liquid solvent is pumped.

41. The method of Claim 40 wherein the solvent is Freon TMS.

42. An improved stereolithographic method of the type for draining a part of excess working material capable of selective physical transformation upon exposure to synergistic stimulation, the improvement comprising the steps of immersing at least a portion of the part in a volume of a liquid solvent in a vapor degreaser, and integratably subjecting the immersed portion to a source of synergistic stimulation.

43. An improved stereolithography apparatus of the type for building a part at the surface of a quantity of material capable of selective physical transformation upon exposure to a source of synergistic stimulation, the improvement comprising:
means for building the part at the surface of the layer of material capable of selective physical transfor-mation supported on a quantity of salt water based solu-tion which is substantially transparent to synergistic stimulation including means for immersing the part into said salt water based solution:
vat means for integrating part building, part clean-ing and post-curing wherein a quantity of salt water based solution has a density sufficient to support the part, acts as a solvent for cleaning excess material from said part when said part is immersed therein, and said vat means includes means for selectively subjecting said part to further synergistic stimulation for curing and final dimensioning.

44. The apparatus of Claim 43 wherein said vat means comprises a vat having a first chamber containing the layer of material capable of selective physical transfor-mation supported by the volume of the salt water based solution and a second chamber containing a second volume of the salt water based solution, a means for moving the built part along a predetermined path between said first and second chambers, and a shutter means disposed along said path between said first and second chambers having an open and a closed position, wherein the built part is moved from the first chamber to the second chamber when the shutter means is open and wherein the shutter means is closed after the built part is moved to the second chamber such that a source of synergistic stimulation impinges the built part in said second chamber to effect post-curing and final dimensioning.

45. An improved method of stereolithography for building a part at the surface of a quantity of material capable of selective physical transformation upon exposure to a source of synergistic stimulation, the improvement comprising the steps of:
providing a quantity of salt water based solution being transparent to synergistic stimulation, having sufficient density to support said material capable of selective physical transformation and having a solubility parameter sufficient to remove excess material of said part not selectively transformed upon exposure to syner-gistic stimulation;
progressively immersing portions of the built part into said quantity of salt water based solution to clean excess material from said part;
exposing said cleaned part to a source of synergistic stimulation directed through said quantity of salt water based solution to effect final curing and dimensioning.

46. A method according to Claim 45 wherein said step of providing a quantity of salt water based solution includes the step of maintaining a solution of sodium chloride (NaC1) in water at a temperature of about 20-30-C, with a concentration of sodium chloride in water of about 311 g/l.

47. The method of Claim 46 wherein said step of providing a quantity of salt water based solution includes the step of maintaining a water based solution of magne-sium sulfate (MgSo4) in water at a temperature of approxi-mately 20-30° C, with a concentration of magnesium sulfate in water of about 229 g/l.