US3910087A

US3910087A - Hydraulic-forming machine

Info

Publication number: US3910087A
Application number: US533992A
Authority: US
Inventors: Everett E Jones
Original assignee: Boeing Co
Current assignee: Boeing Co
Priority date: 1974-12-18
Filing date: 1974-12-18
Publication date: 1975-10-07
Anticipated expiration: 1992-10-07
Also published as: GB1505669A; DE2534226A1; AU8250075A; FR2294779B1; JPS5171574A; FR2294779A1

Abstract

Hydraulic-forming apparatus for compressively conforming a workpiece to the contour of a die by applying uniform forming effort from pressurized hydraulic pressure fluid in a pressure cell chamber surrounding both the part and die. Pressure is transmitted to the part and die through a pressure deformable plastic mandrel, the pressure supporting the part and die in their natural attitudes and causing the part to conform to the shape of the die without distorting the adjacent areas of the workpiece. The fluid pressure system includes means for pressurize the pressure cell chamber to pump output pressure, a lower pressure amplifier for intermediate pressurization of the system and a high pressure amplifier to apply maximum forming pressures to the workpiece. Each amplifier includes a pressure multiplying apparatus such as a reciprocative piston assembly in which a larger diameter master piston drives a smaller diameter slave piston to develop higher hydraulic pressures for use in the forming apparatus. The fluid pressure amplifiers communicate with the pressure cell chamber so that reciprocation of each piston assembly incrementally increases the fluid pressure therein. The lower pressure amplifier output has a designed maximum pressure at which the lower pressure amplifier is isolated from the pressure cell chamber and the higher pressure amplifier operates to further increase the fluid pressure applied to the pressure cell chamber. Upon completion of pressurization of the pressure cell chamber to the desired pressure for forming the workpiece, the hydraulic fluid activating the higher pressure amplifier is released and is caused to flow back into a reservoir through a velocity control means in the conduit. The velocity control means provides a tortuous path for the hydraulic fluid to prevent damage to the equipment from sonic or near sonic flow rates.

Description

United States Patent [191 ,1 ones Oct. 7, 1975 HYDRAULIC-FORMING MACHINE [75] Inventor: Everett E. Jones, Wichita, Kans.

[73] Assignee: The Boeing Company, Seattle,

Wash.

[22] Filed: Dec. 18, 1974 [21] Appl. No.: 533,992

Primary Examiner-Victor A. DiPalma Attorney, Agent, or Firm-Christensen, OConnor, Garrison & Havelka [57] ABSTRACT Hydraulic-forming apparatus for compressively con forming a workpiece to the contour of a die by applying uniform forming effort from pressurized hydraulic pressure fluid in a pressure cell chamber surrounding both the part and die. Pressure is transmitted to the part and die through a pressure deformable plastic mandrel, the pressure supporting the part and die in their natural attitudes and causing the part to conform to the shape of the die without distorting the adjacent areas of the workpiece. The fluid pressure system includes means for pressurize the pressure cell chamber to pump output pressure, a lower pressure amplifier for intermediate pressurization of the system and a high pressure amplifier to apply maximum forming pressures to the workpiece. Each amplifier includes a pressure multiplying apparatus such as a reciprocative piston assembly in which a larger diameter master piston drives a smaller diameter slave piston to develop higher hydraulic pressures for use in the forming apparatus. The fluid pressure amplifiers communicate with the pressure cell chamber so that reciprocation of each piston assembly incrementally increases the fluid pressure therein. The lower pressure amplifier output has a designed maximum pressure at which the lower pressure amplifier is isolated from the pressure cell chamber and the higher pressure amplifier operates to further increase the fluid pressure applied to the pressure cell chamber. Upon completion of pressurization of the pressure cell chamber to the desired pressure for forming the workpiece, the hydraulic fluid activating the higher pressure amplifier is released and is caused to flow back into a reservoir through a velocity control means in the conduit. The velocity control means provides a tortuous path for the hydraulic fluid to prevent damage to the equipment from sonic or near sonic flow rates.

26 Claims, 11 Drawing Figures kkckkkakk M21, m; V 7 y M 26 A402,

U.S. Patent Oct. 7,1975 Sheet 1 of5 3,910,087

US. Patent 0a. 7,1975 Sheet2 of5 3,910,087

U.S. Patent 0a. 7,1975 Sheet4 of5 3,910,087

W mi (PEHOAD (Wm/r) U.S. Patent Oct. 7,1975 Sheet 5 of5 3,910,087

w ia

- i a my (may P6653005 Pam/0) HYDRAULIC-FORMING MACHINE BACKGROUND OF THE INVENTION This invention relates to hydraulic-forming apparatus of the type in which forming effort for conforming a metal blank to the contour of a die is exerted compressively through a pressure deformable mandrel surrounding the workpiece and die, and more particularly to multiple stage pressurization systems for controlling the forming effort exerted and to depressurize the unit after forming is completed.

Presently-known hydraulic-forming systems typically achieve maximum forming pressures of from 5,000 pounds per square inch (psi) up to 25,000 psi. For the purpose of forming parts using powder metallurgy techniques and for workpieces difficult to form, it is desirable to increase the pressure capability of such systems. This is especially true in processing workpieces composed of stainless steel, titanium, hafnium and other exotic metals which require extremely high forming pressures. Moreover, it is desirable to increase the versatility of the apparatus to accommodate a wider variety of shapes and sizes of parts and to achieve a wider range of formed shapes. One way to achieve these increases in the apparatus forming pressure capability and ac commodations of a press would be to merely enlarge or increase the scale of presently known pressure chamber components and the hydraulic pumping and control systems associated therewith. Such a solution is undesirable from the standpoint of overall system complexity, compactness, safety, speed, operating costs and other economic factors. Additional pumps would be required in the enlarged system to compensate for the increased compressibility of the pressure exerting system due to the added amounts of hydraulic pressure fluid and compressible mandrel material surrounding the blank and die which would be necessary to fill the added pressure chamber volume. Further, the extremely high discharge velocities produced by decompression of the hydraulic pressure fluid, forming core, and associated relaxation in tension of the pressure chamber during depressurization of the apparatus at the end of a forming cycle would endanger operating personnel and equipment unless very large and costly protective enclosures and safety systems including surge suppression devices were added to presentlyknown hydraulic systems and designs.

It is therefor an object of the present invention to provide hydraulic-forming apparatus operable at form ing pressures substantially greater than those presently available while overcoming the aforementioned difficulties of prior art hydraulic-forming apparatus. A related object is to provide such apparatus capable of achieving the pressures achieved by forming pressures substantially higher than the prior art devices.

An additional object is to provide hydraulic-forming apparatus which is compact, structurally simple, and economical to operate. A further related object is to provide such apparatus useful to locally form one sec tion of elongated workpieces. A still further related object is to provide hydraulic-forming apparatus with multiple access ports to the pressure chamber which enable rapid and easy removal or advancement of workpieces and dies through the apparatus.

Another object is to provide hydraulic-forming apparatus including surge suppression or control equipment for suppressing or eliminating catastrophic failures and shock waves in the hydraulic system and for preventing damage and injury to operating personnel as a result of rapid depressurization of the apparatus at the termination of a forming cycle.

Another object is to provide hydraulic-forming apparatus of increased pressure chamber volume with the capability of accommodating larger parts wherein the equipment for controlling and operating the hydraulic system includes a multiple stage hydraulic fluid supply to first accommodate, by means of a lower pressure, higher volume hydraulic source, the compressibility of the hydraulic-forming system; and secondly, apply a substantially higher hydraulic pressure from a lowervolume, higher-pressure hydraulic source, thereby achieving a substantially higher hydraulic-forming pressure in a hydraulic-forming system of reasonable size and of convenient operability.

SUMMARY OF THE lNVENTlON In accordance with the present invention, hydraulicforming apparatus particularly useful for compressively conforming a section of a workpiece to the contour of a die includes a pressure vessel means defining a pressure chamber surrounding a pressure deformable mandrel, within which the workpiece and die are positioned. Compressive forming effort is exerted circumferentially upon the workpiece and die through the mandrel by increasing the pressure of hydraulic pressure fluid within the surrounding pressure chamber.

.The fluid pressure in the pressure chamber is first brought up to the maximum output pressure of a hydraulic fluid source, then incrementally increased by a low pressure amplifier up to an intermediate fluid pressure, and then is increased by a high pressure amplifier. The amount of forming pressure exerted by the pressure amplifiers is controlled by a pressure selector switch, which is selectively responsive to the fluid pressure applied to the pressure amplifiers for deactuating the pressure amplifiers when the fluid pressure reaches the maximum desired forming pressure. A transition pressure switch, responsive to fluid pressure applied to the lower pressure amplifier actuates the high pressure amplifier, as needed, for selected forming pressures greater than the intermediate fluid pressure developed by the lower pressure amplifier.

A preferred embodiment of the invention includes three electromagnetically actuated control valves, two of which are selectively responsive to the pressure selector and alternatively responsive to the transition pressure switch elements for actuating and deactuating the low and high pressure amplifiers. The third control valve actuates an unload valve for depressurizing the pressure chamber after the forming cycle is completed. The pressure amplifiers may include a double-acting master piston, at least one face of which has a large surface area relative to the surface area of a slave piston which is movable conjointly with the master piston. An input pressure chamber and a second pressure chamber, respectively associated with the large face and an opposite face of each master piston, are alternately pressurized with hydraulic pressure fluid in order to produce reciprocative motion of each piston assembly which thus incrementally increase the pressure in output chambers respectively associated with each slave piston. Both output chambers communicate with the pressure chamber surrounding the mandrel. A check valve means in the hydraulic conduit from the low pressure amplifier permits repeated cycling of the low pressure amplifier and isolates the low pressure amplifier from the pressure vessel pressure chamber during operation of the high pressure amplifier. A surge control valve positioned in the exhaust line from the high pressure amplifier controls fluid velocity and flow regime to eliminate or minimize shock waves during depressurization. The cylindrical pressure vessel is provided with two end breach screws for clamping the tubular mandrel therebetween.

Other objects, advantages and applications of the present invention will become apparent from the detailed description to follow taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a combined partial side elevation and schematic outline of hydraulic-forming apparatus and control systems according to the present invention.

FIG. 2 is a cross-sectional view taken along lines 22 of FIG. 1 showing the interior of the hydraulic-forming machine pressure cell.

FIG. 3 is a cross-sectional view taken along lines 33 of FIG. 1.

FIG. 4 is a cross-sectional view of the velocity control means utilized in this invention.

FIG. 5 is a schematic circuit diagram of one portion of the l volt segment of the control means used in the preferred embodiment of this invention.

FIG. 6 is a schematic representation of the lower voltage portion of the control system of this invention.

FIG. 7 is a schematic representation of another part of the l 10 volt portion of the control system utilized in the preferred embodiment of this invention.

FIG. 8 is a schematic representation of one portion of the hydraulic circuitry of this invention showing the preloading of the apparatus with pump pressure.

FIG. 9 is a schematic similar to FIG. 8 showing the mid-range pressure operation.

FIG. 10 is a schematic similar to FIGS. 8 and 9 showing high pressure operation of the system.

FIG. 11 is a schematic similar to FIGS. 8, 9 and 10 showing completion of the forming cycle and release of the pressure from the forming chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly to the drawings wherein like numerals indicate like parts, there is seen in FIG. 1 an overall schematic and partial side elevational view of the apparatus of this invention in the nonpressurized mode such at completion of a forming cycle or prior to initiation of a forming cycle. Hydraulic pump 10 is situated to withdraw hydraulic fluid from reservoir 11 and force the fluid into conduit 62 thus providing the primary source of hydraulic pressure fluid for the system. Valve 140 permits depressurization of conduit 62 by flow of hydraulic fluid into return conduit 63. The pressure in conduit 62 may be noted at pressure gauge 85.

A circumferential pressure cell shown generally at 40 includes a pressure container 27 surrounding a chamber block 123 which in turn encloses a hydraulicforming chamber 12. A pair of

breach screws

107 and 107a are shown threaded into the chamber block 123 to hold the elements of the hydraulic forming cell in place. The hydraulic duct 28 communicates with fluic chamber 12 which comprises a substantially cylindrica chamber means bounded on its exterior by the inner surface of chamber block 123 and on its interior b1 bladder 14. Bladder 14 in turn engages the forming core mandrel 105 which comprises a pressure deform able material such as polyurethane or the like. Posi tioned inside the mandrel are workpiece 25 and die 2t which are supported by end plates 106 and 106a. The deformable mandrel 105 surrounds the workpiece 25 and the die 26 so that pressure imposed upon the mandrel 105 through bladder 14 is equally distributed circumferentially about the workpiece and die.

In FIGS. 2 and 3, cross-sectional views of the pressure cell 40 are shown at two locations along the axis of the cell. In FIG. 2, workpiece 25 is shown in engagement with the contoured surface of die 26. In FIG. 3, a job 26a in die 26 is shown. Imposition of pressure from the surrounding deformable mandrel 105 will force workpiece 25 into engagement with the surface of die 26.

Pressure is supplied to hydraulic duct 28 and thereby to fluid chamber 12 serially from three sources according to the ultimate pressure desired. The first source of pressure is via conduit with the hydraulic control system in the preload circuit mode as is shown in FIG. 8. Valve 101 has been repositioned so that pressure from pump 10 may flow through valve 101 into conduit 70 and thence through check valve 15 into the bottom of lower range pressure intensifier 37, through check valves l8, l9 and 60 and then into flow chamber 12. In this manner hydraulic fluid at pump output pressure acts upon the bladder 14 and the mandrel I05 and thereby upon the workpiece 25 to urge the workpiece 25 into conformance with the die 26.

To achieve a medium range of pressures, the lower range pressure intensifier 37 is utilized. Double-acting piston 32 is adapted to travel up and down in cylinder 29 due to hydraulic pressure imposed either in upper chamber 30 or in lower chamber 31. A slave piston 33 having a substantially smaller diameter than master pis ton 32 is solidly connected to master piston 32 by piston rod 36. Downward travel of master piston 32 causes fluid within chamber 39 to become pressurized and forced into fluid chamber 12. The travel of master piston 32 and slave piston 33 is controlled by the flow of hydraulic fluid through valve 102. To cause downward travel of the piston assembly, valve 102 is switched to the position shown in FIG. 9 for mid-range pressure. In this position hydraulic fluid from pump 10 is forced into upper chamber 30 forcing the piston assembly downward. If it is necessary to cycle the piston assembly in order to achieve the pressures desired in fluid chamber 12, valve 102 is returned to the position shown in FIG. 1, thereby pressurizing the fluid contained in lower chamber 31 and permitting the hydraulic fluid in upper chamber 30 to exhaust to reservoir 1 1. Valve 102 may then be returned to the position shown in FIG. 9 so as to cause downward travel of the piston assembly and consequential pressurization of the fluid contained in chamber 39.

For high range pressure, the higher range pressure intensifier 57 is utilized. Similar in structure to the lower range pressure intensifier 37, the higher range pressure intensifier 57 includes a piston assembly comprising master piston 52, piston rod 56, and slave piston 53. Substantial pressure intensification is achieved by the ratio of the areas of piston 52 and piston 53. Pressure imposed within upper chamber 50 when the hydraulic circuit is in the position shown in FIG. causes downward motion of the piston assembly with consequential pressurization of the fluid contained in chamber 59, the pressure being transmitted into fluid chamber 12 through hydraulic duct 28.

Once the desired pressure for forming has been achieved, the pressure in fluid chamber 12 may be relieved by activating the chamber pressure release system. That system includes the valve actuator piston 17, unload check valve 16, and conduit 78. By imposing pump hydraulic fluid under pressure from pump 10 through

valves

101 and 138 into valve actuator 17, the ball valve 16 is unseated and pressurized fluid permit ted to flow through conduits 78 back into reservoir 11.

Both pressure intensifiers have an emergency depres surization system which permits pressurized fluid to be dumped from both sides of the

upper pistons

52 and 32. This safety system includes valve 130 and conduit 75 connected into higher pressure intensifier 57 through

check valves

131 and 132, and into lower pressure intensifier 37 through

check valves

133 and 134. The presence of these check valves permits pressurization desired on either side of the piston; however, upon opening valve 130, the pressure on each side of the piston will be equalized.

HYDRAULIC CIRCUIT SEQUENCE The hydraulic system at rest, that is, at the termination of a forming cycle or at the beginning of the cycle is shown in FIG. 1. Valve 101 is positioned so that check valve 16 is unseated and any pressure in fluid chamber 12 is dumped into conduit 63 via conduit 78. The workpiece and die 26 are placed within the pressure fluid chamber 12 surrounded by deformable mandrel 105. Pump 10 is then actuated forcing hydraulic fluid into conduit 62 which acts as a manifold to distribute the hydraulic fluid to the various fluid pressure users in the system. As shown in FIG. 1, the hydraulic fluid under pressure enters chamber 31 of lower pressure intensifier 37 via conduit '74, the lower chamber 51 of pressure intensifier 57 via conduit 77, and maintains unload check valve 16 in the open position. The hydraulic circuitry is then switched to the preload circuit as is found in the partial hydraulic circuitry diagram in FIG. 8. In this condition valve 101 has been switched so that the pressure on valve actuator piston 17 is relieved and the unload check valve 16 closed. Conduit 70 is pressurized with hydraulic fluid which flows into compression chamber 39 through check valve 15, thence into compression chamber 59 through

check valves

18 and 19, and into fluid chamber 12 through check valve 60 and hydraulic duct 28. In this fashion all of the compression chambers in the accumulators and the fluid chamber 12 are pressurized to the output pressure of pump 10. Under some circumstances, pressure developed by pump 10 may be sufficient to cause the desired forming effort to be imposed on workpiece 25. In such an event, the valve 101 would then be switched so that valve actuator 17 would open unload check valve 16 thereby depressurizing the system.

In the event that a higher pressure is required for forming the workpiece 25, the hydraulic circuitry would be switched to that shown in the partial hydraulic diagram (FIG. 9) in which valve 102 is reversed so that pressure from pump 10 enters conduit 73 and pressure previously imposed upon conduit 74 is exhausted and returned to reservoir 11 (not shown). In this mode of operation, the piston assembly, comprising piston 32, piston rod 36 and slave piston 33, is caused to move downwardly against the pressure already imposed upon chamber 39 due to the relief of pressure in chamber 31 and the imposition of pump pressure in chamber 30 above the piston 32. Since the upper face of piston 32 is of substantially greater area than the lower surface of slave piston 33, a substantial intensification of fluid pressure is achieved in chamber 39. Chamber 39 is in fluid communication with fluid chamber 12 and therefore the pressure in fluid chamber 12 is raised to the same level as that in compression chamber 39. Piston assembly 32 and slave piston 33 travel downwardly under the influence of pressure in chamber 30 until either the desired pressure is achieved, as indicated by pressure responsive means 22, or the piston assembly makes the full travel along its length to the position shown in dotted lines. Upon achieving either of these events, valve 102 is switched so that pressure in chamber 30 is exhausted to reservoir 11 and pressure from pump 10 is imposed upon the lower side of piston 32,

- that is, into chamber 31. This causes piston 32 to rise,

drawing slave piston 33 upward with it. Pressure of pump 10 remains in conduit causing flow of fluid at pump pressure into chamber 39. Check

valves

18 and 19 prevent blackflow of the medium pressure hydraulic fluid from fluid chamber 12 into chamber 39. If desired, the functions of lower range pressure intensifier 37 may be repeated in order to bring the fluid pressure in fluid chamber 12 up to the maximum pressure attain able in intensifier 37 by repeated cycling thereof. This would be the case, for example, when workpiece 25 must be deformed a large distance to conform to the die 26, thus requiring a substantial volume of hydraulic fluid.

Upon attaining the maximum pressure obtainable from lower range pressure intensifier 37 or upon attaining the pressure necessary to carry out the forming of workpiece 25, which is achievable at a level below the maximum pressure provided by intensifier 37, unload check valve 16 may be activated by valve actuator piston 17 and the system depressurized. Should a higher pressure be necessary than that achievable through use of lower range pressure intensifier 37, the higher range pressure intensifier 57 may be activated by switching valve 103 to the position shown in FIG. 10. The hydraulic circuitry shown therein causes fluid at pump pressure to enter conduit 76 and pass into the upper chamber 50 of higher range pressure intensifier 57. The hydraulic fluid in chamber 59 would already be at the maximum output pressure of intensifier 37. Pressure inside chamber 50 causes piston 52 to travel downwardly forcing fluid out of the chamber 51 and back into reservoir 11 and causing slave piston 53 to travel downwardly within chamber 59. Due to the very substantial greater area of piston 52 as opposed to slave piston 53, a high pressure intensification is achieved, whereby the fluid in chamber 59 is raised to a very high pressure and forced into fluid chamber 12 via hydraulic duct 28. Piston 52 travels downwardly until it either reaches the maximum travel. possible as shown in dotted lines or the desired pressure in chamber 12 is achieved. At that time valve 103 is again switched to the position shown in FIG. 1, and pressure fluid in chamber 50 exhausts into reservoir 11 while pump pressure is applied to the lower surface of piston 51. This causes slave piston 53 to rise in chamber 59 relieving the pressure therein. At that time valve 101 is returned to the position shown in FIG. I, causing unload check valve 16 to be opened permitting the highly pressurized hydraulic fluid in chamber 12 to exhaust into reservoir 11.

When exhausting hydraulic fluid from cylinder 50, extremely high flow rates are occasionally encountered. To prevent damage to the equipment and danger to operating personnel, the flow control device shown in FIG. 4 is utilized to suppress excessive flow rates. A plug 42 is placed within the body 43 of the surge control valve 41. The structure provides a circuitous path for the hydraulic fluid through ducts 44 to induce turbulence and prevent unduly high oil velocity. The chamber 45 being of a larger diameter than fluid conduit 76 further acts to prevent damage to the apparatus from high oil velocity, frequently approaching sonic speeds.

Since the ratio of areas of the upper piston and slave piston are known values, the pressure achieved in fluid chamber I2 may be readily ascertained by reading the pressure of the fluid in chamber 30 or chamber 50 depending upon which intensifier is being utilized. For example. pressure switches 22 and 20 may be utilized to determine the pressure level and then to activate other functions of the hydraulic system as discussed above.

CONTROL AND OPERATION OF HYDROFORMER Power to the machines control circuits is turned off and on through switches S1 and Sl-A, FIG. 5.

The momentary closing of normally open switch S1, FIG. 5, provides a circuit to relay coil R9. The energized relay coil closes contacts R9-1 and R9-3 and opens contacts R9-2. The closed contacts R9-l provide a holding circuit to the R9 relay coil through normally closed switch SI-A. The closed contacts R9-3 provide a closed circuit for the machine operating circuit. The open R9-2 contacts turn the L2 indicator light off, and closed contacts R9-I turn the L1 indicator light on.

The machine power circuit may be turned OFF" by momentarily opening switch Sl-A, breaking the holding circuit to power relay coil R-9 thereby returning the circuit to its normal position, as shown in FIG. 5.

The machine control circuit is energized by momentarily closing switch S2, FIG. 5, which energizes relay coil R closing contacts RS-l and R5-2 and opening contacts R5-3.

The closed contacts RS-I, FIG. 5, provide a holding circuit through normally closed switch S3 to relay coil R5. The open R5-3 contacts turn the L5 light off, and the closed contacts RS-l turn the L3 light on.

The closed contacts R5-2 provide a circuit to the transformer T1 and rectifier RF-l to provide a 28V DC current to terminals TBS-l and TB3-l in the machine sequencing circuit. This DC circuit energizes relay coil R4, FIG. 6, and closes contacts R4-l, FIG. 5, setting up a potential circuit for the hydraulic directional control valves.

The hydraulic pump motor 10, FIG. 5, is started by momentarily closing switch S5, FIG. 5, which provides an energizing circuit to relay coil R7, FIG. 5, which closes relay contacts R7-l and R7-2 and opens R7-3 contacts. The closed R7-l and R7-2 contacts and normally closed switch S4, FIG. 5, provide a holding circuit to relay coil R7 and a sustained circuit to the pump motor and indicator L6. The opened contacts R7-3 turn the L4 indicator light off. The pump motor is turned off by momentarily opening the normally closed switch S4, returning the circuit to its normal position as shown in FIG. 5.

The machine has two integrated automatic circuits; one for forming pressures up to 50 KSI known as the low pressure circuit, and a second circuit for forming pressures above 50 KSI known as the high pressure circuit. Forming pressures are selected using rotating switch S36, FIG. 6.

The low pressure forming circuit is as follows: When switch S8, FIG. 6 is momentarily closed, it starts an automatic pressurization of chamber 23, FIG. 3, and then a depressurization of chamber 23, FIG. 2. Its sequence is as follows: 7

When switch S8 is momentarily closed, FIG. 6, a circuit is provided to relay coil R3 to close contacts R3-l and provide a holding circuit to relay coil R3 through the normally closed contacts R6-l. This circuit also energizes time delay relay coils R8 and R6 and normally closed contacts R6-2 to energize the coil of latching relay Rl-A. The time delay relay R6 is set for a longer time delay than R8, and R8 is delayed until the preload pressure cycle is completed, FIG. 8.

The energized latching relay coil Rl-A closes contacts RlA-2 to provide a circuit to light indicator light L8, FIG. 6, and RlA-l, FIG. 5, provides a circuit through previously closed contacts R4-l to one of the solenoids of hydraulic directional control valve I01. Fluid under pressure is now directed through preload check valve 15, and

transition check valves

18 and 19 and into chamber 23. Naturally this also pressurizes

cylinders

39 and 59, with pump pressure.

When these areas are pressurized, time delay relay contacts R8-1 are closed providing a circuit to energize solenoid 112 of hydraulic directional control valve 102 and shift valve 102 to direct fluid under pressure to the top side of piston 32. When this has occurred, the time delay relay R6 opens contacts R6-I and R6-2, FIG. 6, breaking the holding circuit to the coils of relays R3, Rl-A, R6 and R8. Relays R3, R6 and R8 return to their normal position as shown in FIG. 6. Relay Rl-A, being a latching relay, will retain the contacts RlA-l in a closed position even though the coil is de-energized.

When the energized solenoid 112 in directional control valve 102 shifts the hydraulic valve to direct fluid under pressure to the top side of piston 32, it forces piston 33 down into cylinder 39 intensifying the pressure in

cylinders

39, 59 and chamber 12.

When the fluid pressure against piston 32 is sufficient to actuate pressure switch 21, a circuit is provided through pressure selector switch S36 and switch S31. this closed circuit energizes the latching relay coils Rl-B and R2-A.

The energized R2-A relay coil closes contacts R2A-1 and R2A-2. The closed R2A-I contacts provide a circuit to light unload indicator light L7. The closed R2A-2 contacts provide a circuit through previously closed contacts R4-l to energize relay coil R11, which closes contacts R1 l-l, R1 1-2 and Rll-3. These closed circuits energize

solenoids

113 and 115 in hydraulic

directional control valves

102 and 103, respectively, and solenoid in hydraulic directional control valve 101,

which shifts valves 101' and 102 into the unload position as shown in FIG. 1. Valve 103 was not moved because it was in its normal position for low pressure forming and is only used in high pressure forming which is described later.

The shifted valve 102 now directs fluid under pressure to the bottom of piston 32, returning it to its normal position. Valve now directs fluid under pressure to piston 17 to force check valves 16 from its seat, FIG. 1, and release the fluid pressure in chamber 12 and cylinder 59.

The manual cycle completion switch S9 is now momentarily closed, energizing latching relay coil R2-B, opening contacts R2A-2 and R2A-1 and lighting cycle completion light L9. The opened R2A-1 turns off the unload indicator light L7, FIG. 6. The opened R2A-2 contacts break the circuit to relay coil R11, causing relay contacts R11-1, R11-2 and R11-3 to open, deenergizing one solenoid in

directional control valves

102 and 103 and one solenoid in directional control valve 101. The low pressure forming cycle is now complete.

The high pressure forming cycle is as follows:

The pressure selector switch S36 is set to a pressure in the higher operating range and in contact with switch S20. When form switch S8, FIG. 6, is momentarily closed, the coils of relays R3 and R6 are energized, closing contacts R3-1, providing a holding circuit through normally closed timed delayed relay contacts R6-1 and R6-2 to relay coils Rl-A, R3, and R8. R6 and R8 are time delay relays, and their function is the same as described in the low pressure circuit. R6 is timed to open and break the holding circuit after R8 has been delayed long enough to preload pressure chamber 12, chamber 39 and chamber 59 with pump pressure.

The energized latching relay coil Rl-A closes contacts RlA-l, FIG. 5. and R1A-2, FIG. 6. RlA-l closed contacts provide a circuit to solenoid 111 of valve 101, which directs pump pressure fluid through preload check valve 15, and

transition check valves

18 and 19 into chamber 12. Naturally this also provides pump pressure fluid in

cylinders

39 and 59, FIG. 1.

After these areas have been pressurized with pump pressure, time delay relay contacts R8-l, FIG. 5, are closed providing a circuit to one solenoid of directional control valve 102. After this circuit has been made, time delay relay R6 opens the holding circuit contacts R6-1 and R6-2, FIG. 6, breaking the holding circuit to relay coil R3, RlA, R6 and R8, FIG. 6.

Solenoid 112 in directional control valve 102 directs fluid under pressure to the top side of piston 32 forcing it and piston 33 down, intensifying the pressure in cylinder 39, which in turn intensifies the pressure in cylinder 59 and chamber 12. When the fluid pressure against the top of piston 32 is sufficient to actuate transition pressure switch 22, a 6), through closed RlA-2 contacts and closed pressure switch S22 energizes the coil in relay R12, closing contacts R12-l (FIG. 6). R12-2 and R12-3 (FIG. 5). Closed contacts R12-l provide a holding circuit to R12 coil. Closed R12-2 contacts, FIG. 5, provide a circuit to solenoid 114 of directional control hydraulic valve 103. Closed R12-3 contacts provide a circuit to solenoid 1 13 of directional control hydraulic valve 102. The valve directs fluid to the bottom of piston 32 bringing it back to its normal position.

Valve 103 directs fluid to the top of piston 52 forcing piston 52 and piston 53 down, intensifying the pressure in cylinder 59 and chamber 12. When pump pressure on the top side of piston 52 is sufficient to actuate pressure switch 20, a circuit is provided to latching relay coils R2-A and Rl-B, which opens R1A-2 contacts breaking the holding circuit to R12 relay coil, FIG. 6, which opens contacts R12-1 (FIG. 6), R12-2 and R12-3 (FIG. 5) to de-energize

solenoids

113 and 114 of

valves

102 and 103, respectively.

The energized coil of relay R2-A, FIG. 6, also closes contacts R2A-2, FIG. 5, to provide a circuit to relay coil R11 which closes contacts R1 1-1, R11-2 and R11- 3, which in turn provide circuits to solenoid 113 of valve 102, solenoid 115 of valve 103 and solenoid of valve 101 (FIG. 5). These valves unload the forming pressure in the chamber 12, FIG. 1. Valve 103 reverses the pressure on piston 52 returning it to its normal position. Valve 101 applies pressure to piston 17 to force check valve 16 from its seat and release the remaining pressure in chamber 12. Solenoid 113 in valve 102 had previously been energized to return the piston 32 to its normal position.

Emergency unload switch S7, FIG. 6, can be actuated anytime during a forming cycle to duplicate this pressure unloading operation because it duplicates the circuit provided by

pressure switches

20 or 21.

The machine can be operated manually as well as automatically. To manually preload the system. switch S33 is momentarily closed energizing relay coil R-10, closing contacts RIO-1 and R10-2 establishing a holding circuit through normally closed switch S34, to solenoid 111 of valve 101 to preload

cylinders

39, 59 and chamber 12, FIG. 3, with pump pressure. L14 and L15 are lighted. This pressure can be unloaded through unlead check valve 16 when switch S34 is momentarily opened and combined switch S37 is momentarily closed. The opening of switch S34 breaks the holding circuit to solenoid 111 of valve 101 and momentarily closed switch S37 energizes solenoid 110 of valve 101 to shift the directional control valve 101 and pressurize piston 17 to force check valve 16 from its seat and release the pressurized fluid in

cylinders

39 and 59 and chamber 12.

To manually operate the machine, the manual piston control switch S40 is actuated, setting up a start circuit as previously described. The preload valve switch S33 is actuated setting up the preload circuit and preloading the hydraulic working area as previously described.

Forming pressures in the medium pressure range are developed by momentarily closing piston forward switch S42, FIG. 7. The momentary closing of switch S42 energizes relay coil R14 closing contacts R14-1 and opening contacts Rl4-2. The closed R14-1 contacts provide a holding circuit to relay coil R14, and a circuit through previously closed contacts R16-1 to energize solenoid 112 of valve 102, so that fluid pres sure is now directed to the top side of piston 32 forcing it down, intensifying the pressure in

cylinders

39 and 59, and chamber 12. The pressure intensification is measured by the pump pressure gauge 85. If pressures above the medium pressure range are desired, the piston forward switch S44, FIG. 7, is momentarily closed after piston 32 reaches its maximum pressure.

The momentary closing of switch S44, FIG. 7, energizes relay coil R15, closing contacts R15-1 and opening contacts R15-2. The closed R15-1 contacts and normally closed switch S45, FIG. 7, provide a holding circuit to relay coil R15, and they also provide a circuit through previously closed contacts R17-2, to solenoid 114 of valve 103, to direct fluid pressure to the top of piston 52 to push piston 52 forward and intensify the pressure in cylinder 59 and chamber 12. The intensified pressure is read on the pump pressure gauge 85.

To unload the pressure circuit, switch S43 is momentarily opened breaking the holding circuit to relay coil R14 and opening contacts R14-l and closing contacts R14-2. The closed contacts R14-2 provide a circuit through normally closed switch S43 and previously closed contacts Rl6-2 to solenoid 113 of valve 102, which shifts the directional control valve and direct fluid pressure to the bottom of piston 32, returning it to its retracted position.

Switch S45, FIG. 7, is now momentarily opened breaking the holding circuit to relay coil R15, opening contacts RlS-l and closing contacts R15-2. A circuit is now provided through normally closed switch S45 through closed contacts R15-2 and previously closed contacts R17-1 to solenoid 115 of directional control valve 103 to shift the valve and direct fluid pressure to the bottom of piston 52, returning it to its retracted position, reducing the pressure in chamber 12 and cylinder 59.

The combined switches S34 and S37 are now actuatcd. The normally closed switch S34 is opened breaking the holding circuit to relay coil R10, opening contact RIO-1, de-energizing solenoid 111 of valve 101. The closing of switch 537 provides a circuit to so lenoid 1 10 of valve 101 shifting the directional control valve 101 to direct fluid pressure to the piston 17 which pushes the ball check 16 from its seat and releases the pressurized fluid in cylinder 59 and chamber 12.

While the inventor has set forth the preferred embodiments of his invention herein, it will be apparent to one skilled in the art that this invention may be practiced in variant forms all within the scope of the appended claims.

What is claimed is:

1. An apparatus for compressively conforming a metal part to the contour of a die, a pressure vessel defining a pressure chamber, a pressure-deformable mandrel enclosed within the chamber, the part and the die being positionable inside the mandrel, supply means for supplying pressure fluid, means for selectively connecting the supply means with the pressure vessel pressure chamber to prepressurize the pressure vessel pressure chamber;

low pressure amplifier means having an input chamber selectively connectable with the supply means and an output chamber in communication with the pressure vessel pressure chamber, the low pressure amplifier means being operable when the input chamber is pressurized with pressure fluid from the supply means to increase the pressure in the pressure vessel pressure chamber for exerting compressive forming effort through the mandrel upon the part, the low pressure amplifier means being operable to increase the fluid pressure in the pressure vessel pressure chamber up to a first maximum fluid pressure;

high pressure amplifier means having a second input chamber selectively connectable with the supply means and a second output chamber in communication with the pressure vessel pressure chamber, the high pressure amplifier means being operable when the second input chamber is pressurized with pressure fluid from the supply means to increase the fluid pressure in the pressure vessel pressure chamber for exerting compressive effort through the mandrel upon the part;

control valve actuator means responsive to the transition pressure means for connecting the supply means with the first-mentioned input chamber to operate the low pressure amplifier to increase the fluid pressure in the pressure vessel pressure chamber for selected forming pressures up to the first maximum pressure, and alternatively for connecting the supply means with the first-mentioned input chamber to operate the low pressure amplifier to increase the fluid pressure in the pressure vessel pressure chamber up to the first maximum pressure, and then for connecting the supply means with the second input chamber to operate the high pressure amplifier to further increase the fluid pressure in the pressure vessel pressure chamber for selected forming pressures greater than the first maximum pressure;

the control valve means also being responsive to the pressure selector means for depressurizing the firstmentioned input chamber, and alternatively the first-mentioned and second input chambers when the fluid pressure in the pressure vessel pressure chamber reaches the selected forming pressure; and,

depressurization means responsive to the pressure selector means for depressurizing the pressure vessel pressure chamber upon depressurization of the first-mentioned input chamber and alternatively with depressurization of the first-mentioned and second input chambers.

2. The apparatus according to claim 1, wherein the low pressure amplifier means comprises a reciprocative piston assembly including a double end face master piston, a single end face slave piston movable conjointly with the master piston, one end face of the master piston being exposed to the first-mentioned input chamber, the other face of the master piston being exposed to a second chamber, the end face of the slave piston being exposed to the first-mentioned output chamber, the surface area of the one end face of the master piston being substantially greater than the surface area of the end face of the slave piston, and wherein the control valve means includes means for connecting the supply means to the first-mentioned input chamber for pressurizing the first-mentioned input chamber to move the piston assembly in one direction to increase incrementally the pressure in the first-mentioned output chamber, and alternately for connecting the supply means to the second chamber for pressurizing the second chamber to move the piston assembly in the reverse direction, and including intermediate valve means intermediate the first-mentioned output chamber and the pressure vessel pressure chamber for preventing reduction in fluid pressure in the pressure vessel pressure chamber during movement of the piston assembly in the reverse direction, whereby the fluid pressure in the pressure vessel pressure chamber is increased in increments by moving the piston assembly in the one and the reverse directions in alternate sequence.

3. The apparatus according to claim 1, wherein the high pressure amplifier means comprises a reciprocative piston assembly including a double end face master piston. a single end face slave piston movable conjointly with the master piston, one end face of the master piston being exposed to the second input chamber, the other face of the master piston being exposed to a second chamber, the end face of the slave piston being exposed to the second output chamber, the surface area of the one end face of the master piston being substantially greater than the surface area of the end face of the slave piston. and wherein the control valve means includes means for connecting the supply means to the second input chamber for pressurizing the second input chamber to move the piston assembly in one direction to increase incrementally the pressure in the pressure vessel pressure chamber and alternately for connecting the supply means to the second chamber for pressurizing the second chamber to move the piston assembly in the reverse direction.

4. The apparatus according to claim 1, wherein the low and high pressure amplifiers each comprise reciprocative piston assemblies including master pistons having faces respectively exposed to the firstmentioned and second input chambers, and wherein the surface area of the master piston face associated with the high pressure amplifier is greater than the surface area of the master piston face associated with the low pressure amplifier.

5. The apparatus according to claim 1, includin means defining a primary flow passage between the second output chamber and the pressure vessel pressure chamber, and means defining a secondary flow passage between the first-mentioned output chamber and the pressure vessel pressure chamber, and wherein the check valve means includes a one-way valve in the secondary flow passage, the one-way valve adapted for allowing passage of hydraulic pressure fluid through the secondary flow conduit only in a direction of flow from the first-mentioned output chamber to the pressure vessel pressure chamber.

6. The apparatus according to claim 5, wherein the secondary flow passage is between the first-mentioned output chamber and the primary flow passage.

7. The apparatus according to claim 6, wherein the secondary flow passage is between the first-mentioned output chamber and the second output chamber.

8. The apparatus according to claim 1, including discharge means for receiving pressurized pressure fluid flowing from the second input chamber, valve means intermediate the discharge means and the second input chamber, the valve means including means for confusing the flow of pressurized pressure fluid leaving the second input chamber during depressurization thereof.

9. The apparatus according to claim 8, wherein the confusing means includes a disc member extending perpendicularly to the flow of pressurized pressure fluid through the valve means, the disc member having a plurality of holes therethrough, the holes being of various diameters and being positioned at various angles relative to the flow so as to create confusion in the flow through the holes.

10. The apparatus according to claim 9, including means defining a bypass flow channel terminating at ports on either side of the disc member.

11. The apparatus according to claim 1, wherein the pressure vessel comprises an open ended tubular housing, the housing having a first inner diameter, first and second end sealing means for respectively sealing either end of the housing, the mandrel being tubular with a diameter less than the first. inner diameter. the pres-' sure vessel pressure chamber surrounding the mandrel between the end sealing means, an elongated part and an elongated die being positionable inside the mandrel with their lengths extending axially of the mandrel, first and second clamping means respectively threadedly coupled with either end of the housing for axially clamping the end sealing means and the mandrel therebetween, the first and second clamping means and the end sealing means each having relatively axially alignable apertures through which the portions of the elongated part and die on either side of the part section to be conformed are extendable.

12. The apparatus according to claim 1, wherein the control valve means comprises a valve selectively operable for connecting the first-mentioned input chamber with the supply means, and valve actuator means responsive to the pressure selector means for operating the valve means.

13. The apparatus according to claim 12, wherein the pressure selector means includes a time delay relay, the actuator means being energizable by the time delay relay, the time delay relay adapted for energizing the actuator means once the pressure chamber has been prepressured with pressure fluid from the supply means.

14. The apparatus according to claim 13, wherein the pressure selector means includes a second time delay .relay, the actuator means also being de-energizable by the second time delay relay, the second time delay relay adapted for de-energizing the actuator means once the fluid pressure in the pressure vessel pressure chamber has been increased by the low pressure amplifier.

15. The apparatus according to claim 12 including discharge means for receiving pressurized pressure fluid from the first-mentioned input chamber, and wherein the valve is further selectively operable for connecting the first-mentioned input chamber to the discharge means, the actuator means alternatively being responsive to the transition pressure means for further operating the valve.

16. The apparatus according to claim 1, wherein the control valve means comprises a valve selectively operable for connecting the second input chamber with the supply means, and valve actuator means responsive to the transition pressure means for operating the valve means.

17. The apparatus according to claim 16, including discharge means for receiving pressurized fluid from the second input chamber, and wherein the valve is fur ther selectively operable for connecting the second input chamber with the discharge means.

18. The apparatus according to claim 1 including discharge means for receiving pressurized pressure fluid from the pressure vessel pressure chamber, and wherein the depressurization means comprises unload valve means intermediate the discharge means and the pressure vessel pressure chamber operable for selectively allowing passage of pressurized pressure fluid from the pressure vessel pressure chamber, the unload valve means being responsive to the pressure selector means for allowing flow of pressurized pressure fluid therethrough simultaneously with depressurization of the first-mentioned and second input chambers.

19. The apparatus according to claim 18, wherein the discharge means communicates with the second output chamber.

20. The apparatus according to claim 19, wherein the unload valve is intermediate the discharge means and the second output chamber.

21. The apparatus according to claim 18, including pressure responsive actuator means for Operating the unload valve means, a control valve for selectively connecting the supply means with the pressure responsive actuator means for operating the unload valve means, the control valve being responsive to the pressure selector means.

22. The apparatus according to claim 21, wherein the control valve alternatively connects the supply means with the pressure vessel pressure chamber.

23. The apparatus according to claim 1, wherein the pressure selector means comprises a plurality of pressure responsive switching elements, one group of the switching elements being responsive to fluid pressure in the first-mentioned input chamber and another group of the switching elements being responsive to the fluid pressure in the second input chamber, and means for selecting one of the switching elements, the control valve means being responsive to the selected one of the switching elements.

24. The apparatus of claim 1, wherein the transition pressure means comprises a pressure responsive switch element responsive to pressure in the first-mentioned input chamber.

25. A method for compressively conforming a portion of a metal blank to the contour of a die using pressurized pressure fluid surrounding a pressure deformable mandrel for transmitting compressive forming effort to the metal blank, first and second reciprocative pistons each movable in one direction to incrementally increase the pressure of the pressure fluid and alternately movable in a reverse direction without increasing the pressure of the pressure fluid, comprising the steps of:

moving the first piston in one direction to incrementally increase the pressure of the pressure fluid and alternately moving the first piston in a reverse direction, and wherein the first piston is moved in the one direction and then in the reverse direction in alternate sequence until the pressure of the pressure fluid is incrementally increased to a desired forming pressure less than a transition pressure;

alternatively moving the first piston in the one direction and then in the reverse direction in alternate sequence until the pressure of the pressure fluid reaches the transition pressure; and

moving the second piston in the one direction so as to further incrementally increase the pressure of the pressure fluid to a second desired forming pressure greater than the transition pressure while simultaneously therewith holding the first piston stationary.

26. The method of claim 25 including the additional step of moving the second piston in the reverse direction.

Claims

1. An apparatus for compressively conforming a metal part to the contour of a die, a pressure vessel defining a pressure chamber, a pressure-deformable mandrel enclosed within the chamber, the part and the die being positionable inside the mandrel, supply means for supplying pressure fluid, means for selectively connecting the supply means with the pressure vessel pressure chamber to prepressurize the pressure vessel pressure chamber; low pressure amplifier means having an input chamber selectively connectable with the supply means and an output chamber in communication with the pressure vessel pressure chamber, the low pressure amplifier means being operable when the input chamber is pressurized with pressure fluid from the supply means to increase the pressure in the pressure vessel pressure chamber for exerting compressive forming effort through the mandrel upon the part, the low pressure amplifier means being operable to increase the fluid pressure in the pressure vessel pressure chamber up to a first maximum fluid pressure; high pressure amplifier means having a second input chamber selectively connectable with the supply means and a second output chamber in communication with the pressure vessel pressure chamber, the high pressure amplifier means being operable when the second input chamber is pressurized with pressure fluid from the supply means to increase the fluid pressure in the pressure vessel pressure chamber for exerting compressive effort through the mandrel upon the part; control valve actuator means responsive to the transition pressure means for connecting the supply means with the firstmentioned input chamber to operate the low pressure amplifier to increase the fluid pressure in the pressure vessel pressure chamber for selected forming pressures up to the first maximum pressure, and alternatively for connecting the supply means with the first-mentioned input chamber to operate the low pressure amplifier to increase the fluid pressure in the pressure vessel pressure chamber up to the first maximum pressure, and then for connecting the supply means with the second input chamber to operate the high pressure amplifier to further increase the fluid pressure in the pressure vessel pressure chamber for selected forming pressures greater than the first maximum pressure; the control valve means also being responsive to the pressure selector means for depressurizing the first-mentioned input chamber, and alternatively the first-mentioned and second input chambers when the fluid pressure in the pressure vessel pressure chamber reaches the selected forming pressure; and, depressurization means responsive to the pressure selector means for depressurizing the pressure vessel pressure chamber upon depressurization of the first-mentioned input chamber and alternatively with depressurization of the first-mentioned and second input chambers.

3. The apparatus according to claim 1, wherein the high pressure amplifier means comprises a reciprocative piston assembly including a double end face master piston, a single end face slave piston movable conjointly with the master piston, one end face of the master piston being exposed to the second input chamber, the other face of the master piston being exposed to a second chamber, the end face of the slave piston being exposed to the second output chamber, the surface area of the one end face of the master piston being substantially greater than the surface area of the end face of the slave piston, and wherein the control valve means includes means for connecting the supply means to the second input chamber for pressurizing the second input chamber to move the piston assembly in one direction to increase incrementally the pressure in the pressure vessel pressure chamber and alternately for connecting the supply means to the second chamber for pressurizing the second chamber to move the piston assembly in the reverse direction.

4. The apparatus according to claim 1, wherein the low and high pressure amplifiers each comprise reciprocative piston assemblies including master pistons having faces respectively exposed to the first-mentioned and second input chambers, and wherein the surface area of the master piston face associated with the high pressure amplifier is greater than the surface area of the master piston face associated with the low pressure amplifier.

5. The apparatus according to claim 1, including means defining a primary flow passage between the second output chamber and the pressure vessel pressure chamber, and means defining a secondary flow passage between the first-mentioned output chamber and the pressure vessel pressure chamber, and wherein the check valve means includes a one-way valve in the secondary flow passage, the one-way valve adapted for allowing passage of hydraulic pressure fluid through the secondary flow conduit only in a direction of flow from the first-mentioned output chamber to the pressure vessel pressure chamber.

11. The apparatus according to claim 1, wherein the pressure vessel comprises an open ended tubular housing, the housing having a first inner diameter, first and second end sealing means for respectively sealing either end of the housing, the mandrel being tubular with a diameter less than the first inner diameter, the pressure vessel pressure chamber surrounding the mandrel between the end sealing means, an elongated part and an elongated die being positionable inside the mandrel with their lengths extending axially of the mandrel, first and second clamping means respectively threadedly coupled with either end of the housing for axially clamping the end sealing means and the mandrel therebetween, the first and second clamping means and the end sealing means each having relatively axially alignable apertures through which the portions of the elongated part and die on either side of the part section to be conformed are extendable.

14. The apparatus according to claim 13, wherein the pressure selector means includes a second time delay relay, the actuator means also being de-energizable by the second time delay relay, the second time delay relay adapted for de-energizing the actuator means once the fluid pressure in the pressure vessel pressure chamber has been increased by the low pressure amplifier.

17. The apparatus according to claim 16, including discharge means for receiving pressurized fluid from the second input chamber, and wherein the valve is further selectively operable for connecting the second input chamber with the discharge means.

25. A method for compressively conforming a portion of a metal blank to the contour of a die using pressurized pressure fluid surrounding a pressure deformable mandrel for transmitting compressive forming effort to the metal blank, first and second reciprocative pistons each movable in one direction to incrementally increase the pressure of the pressure fluid and alternately movable in a reverse direction without increasing the pressure of the pressure fluid, comprising the steps of: moving the first piston in one direction to incrementally Increase the pressure of the pressure fluid and alternately moving the first piston in a reverse direction, and wherein the first piston is moved in the one direction and then in the reverse direction in alternate sequence until the pressure of the pressure fluid is incrementally increased to a desired forming pressure less than a transition pressure; alternatively moving the first piston in the one direction and then in the reverse direction in alternate sequence until the pressure of the pressure fluid reaches the transition pressure; and moving the second piston in the one direction so as to further incrementally increase the pressure of the pressure fluid to a second desired forming pressure greater than the transition pressure while simultaneously therewith holding the first piston stationary.