WO2000035648A1 - A method for molding composite structural plastics and objects molded thereby - Google Patents

Abstract

A method for molding composite structural plastic components is disclosed wherein such components are cast from a polymerizable thermoset or thermoplastic composition (233) in a conventional metalcasting mold (203). In the instant invention, a low viscosity thermoset or thermoplastic composition having reinforcing fibers distributed therein is poured into conventional metalcasting molds, obviating the need for high heats and pressures associated with injection or compression molding of composite materials as taught in the prior art. Using metalcasting tooling and procedures heretofore used solely in the casting of production metal parts permits 'no pressure' molding without high added heat, with the object to be fabricated being fully cured by the action of a catalyst at relatively low exothermic resin temperatures. This method furthermore enables fabrication of high quality composite structural plastics in traditional soft tool molds and molds produced using rapid prototyping techniques. This economical molding technique permits production of quality structural molded plastics utilizing low cost molds heretofore used only in the prototyping of plastic visual aids.

Description

A METHOD FOR MOLDING COMPOSITE STRUCTURAL PLASTICS AND

OBJECTS MOLDED THEREBY

This application is a continuation-in-part (CIP) application under 37 C.F.R.

§1.53(b)(2) of U.S. Application Serial No. 08/714,813 filed September 17, 1996, and U.S.

Application Serial No. 08/877,410 filed June 16, 1997, the disclosures of which are incorporated

by reference herein as if provided in their entirety.

FIELD OF THE INVENTION

This invention relates to a method of molding composite, structural plastics and the

objects fabricated thereby. In particular, this invention relates to a method of casting plastic

commercial components in conventional metalcasting molds without the need for injection or

compression molding. This invention further relates to the rapid fabrication of prototypes in

composite, structural plastics using conventional soft tooling or rapid prototyping techniques.

BACKGROUND OF THE INVENTION

The use of molds to create parts of varying size, quality and implementation pervades the

industrial landscape. Over 4000 metal casters cast over 32 billion pounds of metal annually in

metal foundries all over the world. In the foundries, metals are processed into commercially viable shapes by melting and pouring a molten metal into a mold. In this manner, structural

items can be fabricated from steel, iron, copper, aluminum and like materials for a virtually

limitless variety of applications.

Selection of a specific metalcasting process depends upon several factors, including,

without limitation, the metal or alloy selected, casting size and complexity, surface finish,

dimensional tolerances, production quantities and cost constraints. In addition, selection of a

mold must anticipate whether the process uses expendable molds which are used only once and

then discarded (i.e. in sand casting operations) or metal molds intended for repeated use (i.e. as

used in permanent molding and diecasting). No matter what metalcasting process is used,

however, all processes share two main objectives: the pattern must be removable from the mold

without damage, and the casting must be removable from the mold or die without damage to

either of the die or the casting (see 1996 CD&A Reference handbook). Various metalcasting

processes are described hereinbelow.

1. Conventional Metalcasting Processes:

a. Sand Casting

Sand casting metal is the backbone of several predominant industries, such as the

automotive industry, because the materials and the tooling used in the process are inexpensive

and rapidly produced. More than 80% of all castings made in the United States are produced by

green sand moldings (see 1996 CD&A Reference handbook). The term "green sand" denotes a

mixture of raw sand and a binder that has been tempered with water. Sand molding is a multipurpose metal-forming process in which a pattern is made of

wood, metal or plastic based upon the design specifications of the casting. In a conventional

sand casting process illustrated in Figure 1A, a pattern 10 is usually constructed in two parts

which include a bottom part 10a and a top part 10b to allow ease of pattern removal from a mol

Parts 10a and 10b are aligned with each other using a plurality of registration pins 13.

Referring to FigJB, bottom part 10a of the pattern is placed upside down on a molding

board 16. In this way, the pattern defines a desired shape within a bottom half 18a of a mold 18

The bottom half 18a of mold 18 is then filled with green sand 19 as shown in Figure IC. Sand

19 is compacted firmly around and over the pattern by manual or mechanized compression

means, such as a ram 21. The bottom half 18a of mold 18 is then inverted and set on a board or

pallet 24, and molding board 16 is removed therefrom, as seen in Fig. ID. Top part 10b of the

pattern is aligned with bottom part 10a and set using a plurality of alignment pins 26. The

separation of the pattern parts defines a recognizable parting plane 27 therebetween such that a

shape is defined in the top half 18b of mold 18 that is substantially symmetrical to that defined i

the bottom half .

As shown further in Figure IE, the top half 18b of mold 18 is filled with sand 19 which

then compacted over and around the top part 10b of pattern 10 with ram 21. A vertical channel

or sprue 27 is cut into the top half 18b of mold 18 to provide an ingress for pouring molten met

into a mold cavity. Mold 18 is then parted along parting plane 27, and pattern 10 is removed

therefrom. As depicted in Fig. IF, a horizontal channel or runner 29 is cut in the lower half 18a of

mold 18 so as to be in communication with sprue 27 to accommodate flow of molten metal

therethrough. If it necessary to compensate for metal shrinkage during the process, one or more

risers 31 can also be cut into the mold. As further illustrated in Fig. 1G, a sand core 33 is set in

place and positioned using core prints 14 that are created in the mold by pattern 10 (shown in

Fig. 1A). Mold 18 is finally closed thereafter and ready to produce a casting.

Sand casting can be used to mold a wide range of materials having considerable

complexity. The low tool and die costs associated with this method, coupled with the ability to

produce varying lot sizes of materials (i.e. a few pieces or huge quantities can be produced) make

sand casting desirable for a wide range of applications. However, a significant disadvantage of

this type of molding process is that the mold is a single use mold which inhibits high volume

production. Furthermore, the use of binder within the sand anticipates the release of toxic

substances into the environment upon removal of the binder and disposal thereof. The low tool

and die costs are compromised by high labor and finishing costs which are incurred during the

production cycle.

b. Permanent Molding

In permanent mold casting (also known as "gravity diecasting"), a metal mold consisting

of at least two parts is repeatedly used for components that require high volume production. A

conventional permanent mold arrangement is illustrated in Figure 2. Up to 99% of such molds

currently in use are made of steel or plaster; however, these mold molds may also be constructed of cast iron, graphite, copper or aluminum.

Molten metal is poured into a mold 41 having mold halves 41a and 41b and a core 43.

Mold 41 is a permanent mold wherein the metal cools more rapidly than in a sand mold and

produces a finer grain structure with enhanced mechanical properties and tighter dimensional

tolerances. As can be seen from Fig. 2, mold 41 emulates the sand casting procedure described

hereinabove, except that a material such as metal or plaster is used in place of sand. In this

process, a mold configuration 44 is formed in the mold which corresponds to the desired

configuration of the cast product. A sprue 45 is defined for pouring of molten metal into the

mold cavity defined by mold configuration 44.

Although the permanent mold process has moderate labor costs and low finishing costs,

the problems associated with this procedure include limitations on casting size coupled with high

initial tooling costs, which make the process prohibitively expensive for low production

volumes. In addition, several alloys and shapes are not amenable to permanent mold casting due

to part line location, complex undercuts in the design or difficulty in removing the casting from

the mold. Lot size is limited to large quantities, making the process untenable for small scale

molding. Furthermore, mold coatings which are often required to protect the mold from erosion,

cracking and other forms of metal degradation can deleteriously effect surface finish.

c. Diecasting

Diecasting is a permanent molding process is primarily for high production of intricately-designed components cast from zinc, lead, tin, aluminum, copper or magnesium.

There are two types of diecasting machines: cold chamber (illustrated in Figure 3A) and hot

chamber (illustrated in Figure 3B). In either method, a molten alloy 51 is manually or

automatically poured into a shot well 53A or 53B and injected into a die 55A or 55B under

pressure. The locking force in diecasting machine operation keeps the die halves firmly closed

against the injection pressure exerted by a plunger 57A or 57B as the plunger injects the molten

metal.

As further shown in Figure 3A, during cold chamber diecasting, molten metal is held at a

constant temperature in shot well 53A prior to high-pressure injection thereof by piston 59A into

die 55 A. The cold chamber method is primarily used with metals of higher melting

temperatures, such as aluminum and magnesium. Conversely, as shown in Fig. 3B, during hot

chamber diecasting, molten metal is held in a temperature-controlled holding pot 58 and

automatically discharged through a port 56 located at the top of shot well 53B. Discharges occur

between each high-pressure injection of the molten metal to die 55B. The hot chamber method is

primarily useful with those metals having low melting temperatures, such as zinc alloys.

Either form of the diecasting process allows part designers to use complex designs and

cast-in inserts of other materials, such as steel, iron, brass and ceramics. However, the material

used for the cast components themselves is limited to a narrow choice of materials such as zinc,

aluminum, brass and magnesium. This method, those most economical where applicable,

includes high tool and die costs and is only practical for production of large quantities of components.

d. Investment Casting

In an investment casting process, shown in Figure 4, a ceramic slurry is poured around

disposable pattern typically formed of paraffin waxes or plastics. The slurry is allowed to harde

to form a disposable mold, and the pattern is destroyed upon melting during the firing of the

ceramic mold. Later, molten metal is poured into the ceramic mold. After the metal solidifies,

the mold is broken to remove the casting therefrom.

Two processes are generally used to produce investment casting molds: the solid mold

and the ceramic shell method. The ceramic shell method dominates the use of this production

technique and is therefore illustrated as a series of discrete steps in Figure 4. Wax is injected int

an aluminum die to form a pattern that replicates the desired casting configuration (1). For

smaller castings, several wax patterns are affixed to a common tree so as to accommodate larger

lot sizes (2). The wax components are then dipped into a liquid ceramic slurry (3) and coated

with dry refractory sand until a shell is developed thereon (4). The wax is then melted out in a

furnace (5) wherein the shell is hardened, producing a single-piece shell mold (6). Molten metal

is poured into the ceramic mold (7), and the shell is broken away after the metal has cooled and

solidified (8). The solidified metal component may be subjected to further finishing processes

(9) and inspected thereafter (10) to assess the quality of the component and its applicable uses.

Because the wax pattern can be made with internal passageways to create complex castings, the investment casting process enables mass production of complex shapes and

reproduction of fine details with tighter dimensional tolerances. However, initial tooling costs

for larger castings are extremely high, and the size and weight of components which can be

produced by this method are limited, imposing escalated time and financial burdens on the

manufacturer.

e. Shell Molding Process

In a shell molding process, the steps of which are shown in Fig. 5, a thermosetting resin-

bonded silica sand 62 is placed on a heated pattern 65 for a predetermined length of time (1).

Heating cures the resin, causing the sand grains to adhere to each other to form a sturdy shell that

constitutes one-half of a thin-shelled mold 66 (2). Upon ejection of the pattern 65 from the shell

66 (3), the shell is manually joined with its complementary other half to make a complete shell

mold 68 (4).

Castings made by this method typically exhibit more accurate dimensional tolerances

than conventional sand castings with a high degree of reproducibility. A wide choice of

materials can be used in this process for the production of moderately complex designs, with the

exception of low carbon steels. Tool and dies costs are low, yet the process requires larger lot

sizes to be practicable. Moderate-to-high labor and finishing costs are also associated with this

method. f . Lost Foam Casting

Lost foam casting is also known as expanded polystyrene (EPS) molding, expendable

pattern casting, evaporative foam casting, the full mold process, the cavityless casting process

and the cavityless EPS casting process. In a lost foam casting process, the steps of which are

shown in Fig. 6, a one-piece pattern 71 is made of expanded polystyrene and covered with a thin

refractory coating (1). Pattern 71 is embedded in unbonded sand 72 within a vented container 73

(2). Molten metal that is poured into a sprue 73a vaporizes the polystyrene instantaneously (3),

quickly reproducing the pattern to form a finished product 78 (4). Gases 76 which are formed

from the vaporized pattern escape through the pattern coating, sand 72 and the vents of container

73.

This process is advantageous in that is requires no cores and enables production of

complex, close-tolerance castings with near net shape. Furthermore, castings can be made by the

lost foam process with no parting lines and with a substantial reduction in capital investment and

operating costs. However, pattern handling requires considerable care, resulting in labor costs

that are very high and further limiting the types of materials that can be used.

2. Selection of Metalcasting Process Methods

Molding systems and casting processes other than those described hereinabove are used

to make metalcastings, such as vacuum molding and use of centrifugal casting machines.

However, when all of these processes are considered together, no one process emerges as a

dominant low cost production method suitable for casting a wide array of configurations. Furthermore, no one method enables easy transition among production objectives. The

employed processes must often be changed due to a change in volume production or material

selection, even if other casting specifications remain the same. The inability to employ a single

system or process to produce a broader spectrum of castings maximizes operating and

maintenance costs, especially if the required specification and volume cannot be met by the

system or process that is already in place. Generally, specialization always leads to higher costs

and lengthier production times, and the same is true with traditional metalcasting methods.

3. Modern Substitution of Plastics

In light of the problems associated with conventional metalcasting procedures, injection

and compression molders and fiber reinforced plastics have become increasingly utilized in the

production of articles once exclusively made through such procedures. Both injection molding

and compression molding processes have been used to provide fiber-reinforced equivalents of

metal objects. In both of these processes, resin and a reinforcing fiber are combined and formed

into a shape that can be molded. While the material is in the mold, high added heat melts the

resin and ensures a complete transition into a fully cross-linked and cured polymer. This high

added heat is applied in concert with sufficient pressure to force the material into a mold.

Typical temperatures reach ranges of 250-650 °F and typical pressures reach 150-5000 psi.

An increasing number of businesses are molding composite structural plastics to produce

objects in place of equivalent metal parts. Molding the plastics to achieve net shape, weight

reduction, corrosion resistance and reduced energy costs is desirable in many industries not only to reduce production costs but also to improve performance of the molded objects. As a result,

the metalcasting industry is slowly, yet definitively losing ground to more modern synthetic

materials and the use thereof in a wide variety of industrial applications.

a. Prototyping

In view of the far-reaching and advantageous application of modern plastics, many

industries, including the automotive industry, covet the ability to bring a product from

conception to full-scale product development in the shortest time span. In most cases, this

involves an early step of producing at least a non- functional, visual display prototype of the

object to be manufactured. Prior to recent computer developments in prototyping, wood forms

would be machined to provide the form of the object so that a wax, plastic or rubber pattern

could be made quickly in order to produce at least a handful of three-dimensional models prior to

manufacture. Such models have always been unfilled plastics, incapable of serving as structural

prototypes.

Today, computer-aided design (CAD) is frequently employed for at least rapid

visualization of an article to be manufactured. While enormously useful to engineers studying

the best production methods for the object, CAD has been further improved so as to actually

produce a three-dimensional object for handling, visualization and limited suitability testing.

These CAD techniques include stereo lithography (SLA), laminated object manufacturing,

selective laser sintering (SLM), fused deposition modeling (FDM) and solid ground curing

(SGC). These techniques use powder, liquid or sheets of polymers or other materials which are sequentially formed together, eventually producing a prototype of the desired object.

Hereinafter, all of these CAD techniques are collectively referred to "rapid prototyping

techniques".

For virtually all of the prototype techniques, including conventional soft tooling and

state-of-the-art CAD prototype production methods, the result is a prototype with relatively low

temperature resistance and strength. While extremely useful at the early visual stage of product

development, these prototypes cannot be used to fully evaluate the functionality of a finished

product. A typical example of current prototype fabrication is found in the automotive industry.

If a prototype for a nylon intake manifold is required, for example, an initial model would be

made using a rapid prototyping technique such as SLA. However, to test the functionality of the

prototype, automotive design engineers then have to make a steel mold and inject nylon to

produce the same design in plastic so that the prototype will withstand high temperatures and

stresses. In effect, the designer is repeating the prototyping procedure at great expenditures of

money and time.

b. Industrial Applications

The automotive industry is a primary example of the inevitable conversion from

metalcasting to plastic part production to optimize performance of molded parts while reducing

the production costs associated therewith. Thus, throughout this specification, reference will be

made to this ubiquitous industry. However, it is understood that the present invention methods

and systems, and the products rendered thereby, are amenable to a limitless number of applications in a multitude of industries around the world.

Molded nylon intake manifolds, for example, already constitute 5% of the relevant

market, and manufacturers have indicated that such manifolds will eventually replace the

conventional aluminum designs currently in use. However, the process of conversion from

aluminum to plastic production has been slow because of the high cost for prototype and

production injection molding tooling and associated process equipment. The conversion to

plastic requires production of new, custom-made steel molds which are prohibitively expensive

for most producers. Therefore, a molder must wait until the automaker allocates a budget to pay

for this very expensive tooling.

During the average development program, it takes 10-12 weeks to produce a steel mold.

Due to the high temperatures (i.e. 500-600° F) and pressures (i.e. 3000-5000 psi) required with

nylon injection molding, molds must be machined out of tool steel. Along with the development

of the manifold has been the development of a method to produce the intricate internal passages

previously created with sand cores when casting manifolds in aluminum. The method used with

injection molding nylon is known as the lost core process. It uses a soft metal such as tin-

bismuth as the soluble core material. The metal is first melted, and then injection molded in a

steel mold to produce the core. A steel mold is required due to the high melt temperature of the

metal and the stress it places on the mold material when injected. The average development

program consumes three steel injection molds for the nylon manifold and three steel molds to

mold the expendable tin-bismuth cores. Costs for the development program alone can exceed $1 million just for prototype tooling.

Since inception, injection molded manifolds have used the lost core process to provide

rather simple manifold design configurations. As engineers have embraced nylon injection

molding, the complexity of the designs and their core packages have increased significantly.

Engineers and molders have experienced extreme difficulty not only in preventing shifting of the

tin-bismuth cores, but also in melting out the cores, thereby creating a crisis for the nylon

manifold business and the automotive industry. The current manifold designs are so complex

that the core package weights are extremely dense and heavy. A popular N8 engine manifold,

for instance, has 160 lb of metal in its core package, causing the core to shift in the mold as a

result of its own mass. This anomaly is further aggravated by the high injection pressures of the

nylon molding compounds.

In addition, since nylon cannot be injection molded in thick cross-sections, the injection

molded manifolds can only have thin wall thicknesses ( i.e 3-4 mm), significantly less than the

thicknesses of a conventional sand cast aluminum manifolds (i.e 6-10 mm). The cost of the

injection molded materials also mandates thin wall designs. As a result, injection molded

manifolds are much noisier than their aluminum counterparts in that they do not dampen the

noise, vibration and harshness (ΝNH) generated by the engine as well as cast aluminum

manifolds. c. Comparison With Metalcasting

Injection molding plastics are similar in costs to diecast metals such as magnesium, yet

magnesium and most structural injection-moldable plastics cost twice as much as cast aluminum.

It is usually felt that injection molding is the lowest cost form of molding plastics and that

casting is more expensive. Sand casting, however, is the slowest method of casting metals from

a cycle-time standpoint, but the tooling is the least expensive. Diecasting is the fastest curing

method, but the tooling is significantly more expensive and has a short life. In the past, where

plastics have been cast, they always required the use of steel molds which is what prevented

them from being costs effective with injection molding. Therefore, the need has been felt for a

process which integrates the benefits of conventional metalcasting methods and the inherent

performance advantages of plastics.

Being able to cast structural plastics using non-traditional plastic tooling has advantages

over metalcasting aluminum, particularly in the rapidity of tooling production, the long life of the

tooling and the significant cost savings in both the tooling and the materials. Cycle times for

such a method of casting plastics are comparable to diecasting aluminum and injection molding

plastics. In addition, the metal caster realizes significant cost savings by reclaiming the ability

the ability to make the plastic compound in-house. For example, the ingredients which comprise

a typical glass-reinforced nylon compound (i.e. the monomer, the catalyst, the fiber, etc.) if

purchased separately, can result in a cost of $0.80-$0.90 per pound of compound. In comparison,

a typical injection moldable grade nylon currently used to mold manifolds, already mixed and

made available as a ready-to-use compound, can cost $1.25-$ 1.75 per pound of compound. Therefore, if cure of parts could be achieved as quickly as injection molding in molds that are as

inexpensive as those used in sand casting or which can be rapidly fabricated at a lower cost than

machined steel molds, then a low-cost method of producing plastic equivalents of metal casted

objects would be obtained.

Bridging the Gap

a. Prior Art Solutions

The desire to use more varieties and amounts of plastic materials arises from this need to

use lower cost methods while retaining the structural integrity of the products made thereby.

Plastics are amenable to fabrication in simple and complex forms, enabling volume production of

various industrial components. An example is disclosed in commonly assigned U.S. Patent No.

4,848,292 (the '292 Patent), which is incorporated by reference herein. The '292 Patent

discloses a cylinder head and engine block assembly for an internal combustion engine wherein

both the cylinder head and engine block are formed from a fiber-reinforced phenolic resin. The

fiber reinforcement preferably includes fiberglass or graphite fibers having a length of about V."

to 1". The head and block are either injection or compression molded to achieve close

tolerances, enhanced structural integrity and elimination of most secondary machining

operations. In either process, dry resin powder and a reinforcing fiber are pre-mixed and formed

into a shape that can be molded. Where injection molding is used, the phenolic molding

compound is injected into the mold cavity at injection molding temperatures and pressures to fill

the cavity and molding chamber. A lightweight engine block and head assembly according to invention reduces overall

engine weight by up to 60%, reduces noise, minimizes rust and corrosion and significantly

reduces the duration and cost of manufacture by reducing the number of secondary machining

operations that must be performed to give the assembly its finished shape (i.e. post-mold drilling

of bores to accommodate correspondingly sized stud bolts). Composite molding times are

significantly shorter than times required for conventional metalcasting, promoting mass

production thereof. Additionally, the components are capable of maintaining higher horsepower

for their weight than conventional metal parts. Such engines further effectively maintain their

shape, dimensional stability and structural integrity at high operating temperatures and have a

greater strength-to-weight ratio than metal.

Thus, the combination of a high mechanical strength (particularly at operating

temperatures), thermal stability, fatigue strength and excellent compressive strength exhibited by

structural composite plastic components makes the materials highly desirable for mass

production and continued incorporation into mainstream production cycles. Such materials also

exhibit excellent resistance to wear, corrosion, impact, rupture and creep, and components

fabricated from such materials reliably operate in the presence of engine fuels, additives, oils and

exhaust. Since these characteristics are amenable to various other application, manufacturers

have identified the need to develop new prototyping and production programs which incorporate

fabrication of a multitude of structural plastic designs and exploit their advantageous properties

commercially. b. Present Inventive Solutions

In co-pending and commonly assigned U.S. Application Serial No. 08/714,813, the

disclosure of which is incorporated by reference herein, a method for molding composite

structural plastics in molds traditionally used in foundries for molding metal parts is described.

The same basic method can be employed to produce not only inexpensive prototypes utilizing

soft tooling or rapid prototyping techniques, but also to form molds suitable for structural,

prototype or final product fabrication. Such an application is disclosed in co-pending and

commonly assigned U.S. Patent Application 08/877,410, which is also incorporated by reference

herein. Thus, a low-cost and rapidly developed molded prototype part, or its commercial

equivalent, can be used by design engineers not only to visualize the objects in a hands-on three-

dimensional representation, but also to test the object in the actual environment to which the

finished product is going to be exposed. Extremely important costs savings are realized both in

fabrication of the prototype and in time saved in bringing a newly-conceived product to market.

Thus, it is desirable to combine the desirable characteristics of composite materials with

conventional, readily available metalcasting procedures and molds to develop and implement a

successful method which permits the use of conventional metalcasting molds to fabricate

composite, structural plastic prototypes and products thereby. In addition, it is desirable to

develop a material and casting process to produce a structural prototype having functional

properties equivalent to those of a finished product using current soft tooling or rapid prototyping

techniques, thereby reducing design cycle time and concurrently reducing the elapsed time

between conception and market introduction SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a method for molding composite

structural plastics in conventional, readily available metalcasting equipment.

It is another object of the present invention to produce a structural plastic component t

using conventional, readily available metalcasting equipment.

It is a further object of the present invention to permit molding of composite, structural

plastics without the need for high temperature equipment for post-cure cycles.

It is yet another object of the present invention to permit molding of low cost and

lightweight composite plastic equivalents to foundry-produced metal objects.

It is still another object of the present invention to reduce the amount of required

machining of components after casting.

It is another object of the present invention to provide a method for utilizing soft tooling

and modern rapid prototyping techniques in order to fabricate structural, composite plastic

prototype parts.

It is still another object of the present invention to provide a simple, low-cost single step

method for producing a prototype part having equivalent visual and structural characteristics to the actual part to be co commercially produced.

It is yet another object to reduce the viscosity of flowable resins and combine such resins

with short-length reinforcing fibers so as to enable pouring of the combination into a

conventional metalcasting mold.

A method for molding composite structural plastic components is disclosed wherein such

components are cast from a polymerizable thermoset or thermoplastic composition in a

conventional metalcasting mold. In the instant invention, a low viscosity thermoset or

thermoplastic composition having reinforcing fibers distributed therein is poured into

conventional metalcasting molds, obviating the need for high heats and pressures associated with

injection or compression m molding of composite materials as taught in the prior art. Using

metalcasting tooling and procedures heretofore used solely in the casting of production metal

parts permits "no pressure" molding without high added heat. In the case of a thermoset resin,

the object to be fabricated is fully cured by the action of a catalyst at relatively low exothermic

resin temperatures. In the case of a thermoplastic resin, curing is generally achieved

independently of a catalytic reaction or high added heat and pressure. With respect to either a

thermoset or thermoplastic resin, the resin is brought to a viscosity sufficient to maintain

suspension of a plurality of reinforcement fibers therein.

The invention furthermore discloses a method of fabricating high quality composite

structural plastics in traditional soft tool molds and molds produced using rapid prototyping techniques. This economical molding technique permits production of quality structural molded

plastics utilizing low cost molds heretofore used only in the prototyping of plastic visual aids.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1A to 1G show a schematic representation of a sand molding metalcasting

process of the prior art.

Figure 2 shows a permanent mold used in permanent mold metalcasting process of the

prior art.

Figures 3A and 3B show a cold-chamber diecasting machine and a hot-chamber

diecasting machine, respectively, of the prior art.

Figure 4 shows a schematic representation of an investment casting process of the prior

art.

Figure 5 shows a schematic representation of a shell molding metalcasting process of the

prior art.

Figure 6 shows a schematic representation of a lost foam casting process of the prior art.

Figure 7A shows a flowchart of the present invention method of casting structural plastic components in conventional metalcasting molds using a thermoset resin.

Figure 7B shows a flowchart of the present invention method of casting structural plastic

components in conventional metalcasting methods using thermoplastic resins.

Figures 8 A to 8H shows a schematic representation of a plastic casting method of the

present invention.

Figures 9A to 9H show a schematic representation of a soft tooling prototype according

to a method of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the instant invention, low viscosity thermoset or thermoplastic resins in a liquid state

are combined with reinforcing fibers, and the mixtures are poured into traditional casting molds,

including those used in the conventional molding processes described hereinabove. The present

invention teaches an economical molding technique that enables production of composite

structural prototypes and commercial products using molding procedures that are currently

employed in foundries with standard equipment and without costly heat treating equipment or

post-mold cure cycles. As used herein, the terms "structural composite" and "structural plastic"

will be used synonymously to mean functional components derived from selected composite

materials. Referring now to the figures, the preferred embodiments of the present invention can now

be described. Figures 7A and 7B provide flowcharts illustrating the present invention method for

molding composite structural plastics utilizing thermoset and thermoplastic compositions

respectively.

Referring to Figure 7A, at Block 101, the structural thermoset composite which will

comprise the final molded component is selected. The specific thermoset selection is dependent

upon several factors, such as the desired configuration and performance characteristics of the

molded component as well as the actual application thereof.

As shown in Figure 7A, a flowable thermoset resin is combined with a catalyst and a dry

reinforcement fiber at Block 103. The sequence in which the components are mixed has no

effect on the process (i.e. fibers and resin may be mixed before adding the catalyst, or catalyst

and fibers may be mixed before adding the mixture to resin). Mixture of the components is

effected by using mixing means such as an industrial paddle mixer to obtain a thorough

integration of the components with one another. Care must be taken to ensure that the fiber is

sufficiently dry so as to obtain minimum moisture content, preferably less than 100 ppm.

The selected resin has a sufficiently low viscosity so as to allows mixture of the resin

with high percentages of fiber reinforcement, preferably achieving fiber loadings of 10-65%

volume by weight. At such viscosity, the fibers are sufficiently suspended within the resin so as

to achieve adequate dispersion therethroughout without settling of the fibers. Selected reinforcement fibers can be fiberglass, graphite, Kevlar® or ceramics. Relatively short fiber

lengths are employed as compared with conventional resin transfer methods, with the fibers

being milled or flaked at lengths of 1/16", 1/8" or 1/4" and widths between 10-40 microns

inclusive, with 10 microns being a preferred width. It is essential to the present invention to

utilize relatively short fiber lengths so as to effectively combine the fibers with the low viscosity

resin. Such a combination results in a low bulk density compound that can be poured, rather than

pushed under pressure. However, woven chopped, unidirectional, random and non-woven fibers

may be added in selected regions of a mold for additional structural integrity.

Once a thermoset composition chemically cross-links into a cured and solidified shape,

the composition cannot return to its original form. The thermoset resins that can be used include,

but are not limited to, unsaturated polyester, phenolic, epoxy resin, urethane and vinyl ester

resins. These compositions have low enough viscosity (i.e. 100-3,000 cps) to allow mixture of

the resin with high percentages of fiber reinforcement material.

A preferred low viscosity thermoset resin for use in the present invention is phenolic

resin, which exhibits high mechanical and thermal stability equal or superior to that of aluminum

at operating temperatures. More specifically, resole phenolic are preferred because they are one-

stage resins manufactured by heating phenol and formaldehyde using an alkaline catalyst. By

"one-stage" is meant that the formaldehyde-phenol mole ratio must be greater than one, enabling

resoles to cross-link in the presence of heat without the addition of more formaldehyde to

promote cure. Resole phenolics may use either water or ethylene glycol as a solvent. Since phenolics are cross-linked through a condensation reaction, the use of ethylene glycol as a

solvent is preferred to minimize the amount of water in the cure process.

Alternatively, resoles can be cured without additional heat through the addition of

catalysts. As a suitable catalyst, resole phenolic generally require strong acids such as phosphoric

acid and toluene sulfonic acid to effect a complete cure. Typical catalysts are 2-20% by weight,

and typical glycol percentages by weight are 50% for the resin and 17% for the catalyst. The

resin can be handled in virtually any manner for convenient dispensing , which handling methods

are well known in the art. It is important to emphasize that with this method, the ingredients

which are required to make the resin-fiber-catalyst compound can be separately purchased by the

metal caster and formed into the compound thereby, alleviating much of the front end cost

associated with acquiring moldable plastic materials.

Referring again to Figure 7 A, the resinous mixture of Block 103 is de- aerated at Block

105 to achieve sufficient viscosity for pouring of the mixture into a conventional mold. De-

aeration is accomplished by agitating the mixture in a conventional manner, such as by rolling

the mixture in a container, stirring the mixture, vibrating the mixture or combining these action

until a sufficient viscosity it obtained. Additionally, the container which holds the mixture can

also be subjected to a vacuum which not only promotes de-aeration, but also removes water from

the mixture that is given off during the cure cycle. If a prototype is being fabricated using soft

tooling, the mixture from Block 103 is de-aerated until the resin is at a viscosity sufficient for

pouring of the mixture into a conventional soft tool mold such as a wax, plaster, plastic, spray metal or rubber mold.

At Block 107, the mixture of Block 103 is poured into the mold after passage of an

amount of time sufficient to maintain suspension of the short reinforcement fibers therein, yet

still permit flow of the mixture. Determination of the appropriate time span depends upon the

percentages of catalyst used within the mixture. The mixture should not be poured into the mold

cavity until its viscosity reaches the point at which it is just about to thicken through the cross¬

link process. In this manner, the fibers do not settle or become congested during pouring,

thereby ensuring the desirable structural integrity if the molded component after cure is

complete. Due to the exo herm that is released during polymerization, the temperature of the

mixture is typically in the range of 100 °F- 130° F. Typical gelation cycle times may be from 15

seconds to 8 hours, although the mixture may not enter the mold until the last seconds of the

reaction, when sufficient viscosity is attained. For certain applications it may be desirable to heat

the mixture and/or mold to a maximum temperature of +120 F in order to minimize the loss of

heat created by the exothermic reaction.

At Block 109, the mixture is poured into a suitable foundry mold, such as sand,

permanent, diecast, shell molds or the like as described hereinabove. Dispensing equipment such

as automatic measuring dispensing equipment that is well known in the art may be used to fill the

mold. As stated above, the mold may be pre-heated to accelerate curing. Alternatively, the mold

may also be subjected to a vacuum to facilitate the complete filling of the mold during the pour

of the mixture thereinto. Finally, the mold is disassembled and the finished molded object is removed therefrom at

Block 111. If required, a completed object formed from a thermoset may be subjected to a post-

mold cure in an oven heated to +250 F for 1-2 hours to effect complete curing and moisture

removal. No such post-mold cure is required for thermoplastic materials.

Referring now to Figure 7B, a process similar to that illustrated in Figure 7 A is shown,

except that the structural plastic component is formed from a thermoplastic resin selected at

Block 10Γ, rather than a thermoset resin. Thermoplastics differ from thermosets in that, like

metals, thermoplastics can be re-melted and re-solidified after initial solidification. Typically,

thermoplastics are always injection molded while thermosets are almost always compression

molded. In their traditional commercial form, thermoplastics require high added heat and high

pressures to melt the material (which typically comes in a pellet form), fill the mold and solidify

it. Pellets are obtained by first melting a thermoplastic resin into a paste-like viscosity, then

mixing the resin with chopped fiber in an extrusion or extrusion-type process. The mixture is

finally cooled so the compound solidifies into a form that can be chopped into pellets sold by the

producer.

To manufacture a thermoplastic part, an injection molding machine is required. An

injection molding machine preheats the pellets and then plasticizes them for forcing them

through a screw under high pressure and using high shear rates to soften the pellet. This increase

in temperature ranges from about 150°F-700° F, depending upon the type of thermoplastic, and

thereby lowers the viscosity of the composition from a solid to a very high viscosity, paste-like compound capable of maintaining a plurality of reinforcement fibers in suspension during the

liquid phase. Then, under pressures as high as 1000-5000 psi, the compound charge is injected

into a heated metal mold. If the pellet were not melted and subjected to high pressures, its solid

or high viscosity state would not allow it to fill a mold and the cure. The mold is kept hot at a

pre-set temperature so the compound does not set as it enters the mold, thereby preventing the

mold from being completely filled as well as aiding in the cure process.

In conventional metalcasting, a solid metal is melted to a very low, almost water-like

viscosity allowed to rest and then either poured or pushed into a mold, causing the molten

metal's temperature to quickly drop and solidify into a part. Mold temperature is not as

important and typically not even addressed with metalcasting molds. The typically operate at

room temperature without any temperature controls. The molten metals' low viscosity allows

the metal to quickly enter and fill the mold before solidifying. In order for a thermoplastic to

behave in a similar way to molten metals and liquid thermosets, it must be put into a low viscid

state as well (100-3000 cps) and kept liquid while being mixed with fibers, as shown at Block

103'. The types of fibers that can be utilized are the same as those utilized with respect to

thermoset resins.

The resin mixture is allowed to rest and de-aerate as can be seen at Block 105', after

which it de-aerates (Block 105'), gels (Block 107') and is poured or pushed into a metalcasting

mold and allowed to solidify into a finished product form (Block 109'). Like metal, a

thermoplastic resin can be either pushed or poured into a mold having a temperature that is at ambient or at least lower than the temperature of the resin mixture. The rapid cooling of the

plastic article in the cooler mold cures the article instantly, just like metal. In this manner,

thermoplastic resins that previously required injection and compression molding machines, and

associated high pressures and added heat and steel molds, can be molded in traditional

metalcasting molds. Simultaneously, reinforcement fibers which previously settled within a

liquid thermoplastic composition can now be suspended for the duration of the fabrication

process. This ability to maintain multiple types of reinforcement fibers in suspension is

important in order to define and obtain desirable physical and performance characteristics in the

completed plastic component.

In the instant invention, liquid thermoplastics have sufficient viscosity for integration

with short fiber reinforcements, permitting production of the same high quality composite,

structural plastic parts which have heretofore been injection and compression molded in more

expensive and complicated steel molds. Most thermoplastic compositions can be put into a

liquid form suitable for pouring into a mold. The resins which can be used include but are not

limited to nylon, polyethylene (PE), polypropylene (PP), polyetherketone (PEK), polyamide

imide (PAI), polyether imide (PEI), polyphenylenesulfide (PPS), polybenzimidazole (PBI),

polsulfone (PS), polyarylethersulfone (PAS), poly(ethylene terephthalate) (PET), acetals and

polycarbonate. When in a liquid state, they are, or can be put into, a low enough viscosity (i.e.

100-3,000 cps) to allow mixing with high percentages of fiber reinforcements of the types

described hereinabove. Nylon resins, of which nylon 6 is currently the only castable nylon, are often preferred

over other thermoplastics because of their high cost/performance ratio. The high mechanical and

thermal stability of thermoplastics is generally comparable to that of cast aluminum in the

manufacture of complex production components, such as automotive air intake manifolds. The

casting of nylon is a well-established art and is used primarily to produce stock shapes such as

round bars and flat plates which are sold and then machined into a final design, although casting

of parts to a near net shape has also been accomplished. Such parts have, to this point, been sold

primarily as unfilled parts or, if filled, incoφorating some type of filler other than reinforcement

fibers kept in suspension as realized with the present invention.

Thermoplastics, particularly plastics such as caprolactam (nylon 6), are available in a

solid form which must be liquefied so as to be suitable for pouring into a mold. One method of

liquefying thermoplastic compositions such as caprolactam requires melting the resin into a

liquid and then using a catalyst and activator to complete chemical transition of a flowable

thermoplastic resin into a solidified part, as illustrated in Figure 7A with respect to a thermoset

resin. The caprolactam must be warmed to about 69° C before the catalyst and activator (heated

to about 100°C-150°C) are added along with any reinforcement fibers. The catalyst and

activator complete the cure into a solid nylon 6 part without the need for high added heat or high

injection pressures.

In the alternative, thermoplastic powders such as those described hereinabove can be

diluted with a solvent that completely dissolves the resin into the solvent or keeps them in suspension. Either method would yield a low viscosity liquid thermoplastic mixture.

As with thermoset resins, the ingredients which are used to make a resin-fiber compound

or resin-fiber-catalyst compound mixture using a thermoplastic resin can be purchased separately

in bulk and formed into a compound on-site. The compound, as before, is allowed to rest, de-

aerate and gel, all just prior to being poured into a mold. The fibers within such mixture are held

in suspension due to the low viscosity of the resin, which is defined to maintain such suspension

depending upon the type of fiber used therein.

The same de-aeration method described hereinabove with respect to thermoset resins can

also be employed with thermoplastic resins to ensure suspension of fibers within a resinous

composition, whether thermoset or thermoplastic. As the resin starts to cure (as with a

thermoset) or re-solidify (as with a thermoplastic), the fibers lose their tendency to settle or

congregate. Because different fibers have different corresponding weights, the viscosity of the

resin, whether thermoset or thermoplastic, can be varied accordingly to keep the fibers in

suspension for the duration of the gelation process (Block 107 or Block 107'). In this manner,

the fibers can be dispersed throughout the resin in a desired pattern and maintained in such

position until a full cure is achieved.

When selecting the polymerizable composition to be cast, thermoset resins and

thermoplastic resins stand apart due to their inherently advantageous physical and performance

characteristics. The creep resistance of thermosets, for example, is significantly superior to that of components formed from other resins. In addition, the enhanced chemical resistance of

thermosets and thermoplastics, combined with the ability to withstand extreme environmental

conditions, further enhance the attractiveness of these materials for a wide variety of

applications. Although such materials are preferred, the present invention method is not limited

by the types of materials enumerated herein and may be utilized with any polymerizable

composition conducive to the practice thereof.

Insofar as the present method can be adapted for the fabrication of structural plastic

prototypes and objects molded therefrom, the ability to take a liquid thermoset or thermoplastic

resin and simply pour it into a soft tool mold such as a wax, plaster, plastic, rubber or spray metal

mold is one of the quickest and least expensive ways for producing a desired prototype part.

This is done routinely if all that is required is a model of the part primarily for viewing purposes.

However, this technique is ineffective for visual and working models capable of physically

emulating the production part. The reason for this is that these molds traditionally accommodate

only low temperature resistant and low stress resins.

The mold itself may be made by first making a model or pattern of the object to be

molded out of plastic or using rapid prototyping techniques. The mold is then cast in a liquid or

soft formable material such as wax, plastic, rubber or spray metal or rubber soft tool molds, or

one developed using rapid prototyping techniques. Additionally, the mold may be a negative of

a predetermined pattern. Typical procedures include using liquid resin, such as a polyurethane

mixed with a curing agent or using a liquid wax or rubber formulation such as silicone rubber mixed with a curing agent, pouring the material over the model so as to encase the model in the

soft tooling material and removing the encapsulating material when it cures to a solid, the model

being held in a suitable container so as to be able to be freed of the encapsulating material.

These soft tool mold making techniques are well known in the art.

It is emphasized that the same method and mixture for producing prototype parts can also

be used with equal economy and convenience to fabricate molds. Molds made with this process

are capable of withstanding temperatures up to 400° F. This composite structural plastic mold

can then be used for prototype or production run for processing materials requiring high

temperatures during the molding procedure, including thermoplastics such as nylon and high

temperature resistant, or structurally reinforced thermoset plastics such as phenolics and epoxies.

If using a thermoset composition, curing of the liquid mixture is accomplished entirely by the

catalytic action, with an exofherm being generated by the reaction between the resin and the

catalyst. When the molded object is cured it is simply removed from the mold and the process

may then be repeated as required.

Figures 8 A through 8H illustrate the construction and use of a typical sand mold in

conjunction with the method of the present invention. Even though the present invention method

is described with reference to a sand casting procedure, it is understood that such description is

for example only and in no way limits the application of the subject matter of the instant

disclosure. The inventive method disclosed herein is applicable to a variety of conventional

metalcasting operations, including but not limited to shell molding, diecasting, permanent molding and other such methods as described hereinabove.

Figure 8 A shows a two-piece pattern 201 representing the object to be molded. Pattern

201 has a base portion 201a and a top portion 201b. In Figure 8B, base portion 201a is inverted

and shown in place in a bottom portion 203a of a mold box 203. Mold box 203 further includes a

removable base 212 which holds shows a sand and binder mixture 205 that fills the bottom

portion of the box as shown in Figure 8C. A manual or automatic compacting means such as

ram 210 compresses the sand around the base pattern 201a.

Now referring to Figure 8D, mold box 203, along with sand 205 and base portion 201a

therein, is inverted and base 212 is removed therefrom. The bottom portion of mold box 203 is

placed on a permanent mold box base 214 having supporting feet 215. Top portion 201b of

pattern 201 is aligned with bottom portion 201a, and sand 205 fills a top portion 203b of mold

box 203 wherein top portion 201b is positioned to define a separation plane 217. Ram 210 is

again used to compact the sand around the pattern piece.

As shown in Figure 8E, a funnel-shaped opening or sprue 220 is cut in sand 205 which

extends along the width of top portion 203b of mold box 203. Top portion 203b is removed

from bottom portion 203a along separation plane 217, as further shown in Figure 8, thereby

permitting removal of pattern 201 from the mold box. Two vent holes or risers 222 can be cut in

sand 205 which extend from a top half 225a of empty mold configuration 225, with bottom

portion 203 a of the sand-filled mold box having a lateral cut-out 227 in the sand so as to form a channel with the funnel-shaped opening 220 in the top half of the mold box when joined. Figure

8G shows the completely prepared mold just before pouring of the liquid resin. The two empty

mold configuration halves 225a and 225b are now joined together, forming a single complete

mold configuration.

The resinous mixture as described hereinabove with respect to Figures 7A and 7B can

now be manually or automatically poured into the mold, for example, by placing the mixture into

a beaker 231 as shown in Figure 8H. The liquid mixture 233 is poured into the mold 225 with a

funnel 232 placed in the correspondingly sized and shaped opening 220 in the top half of the

mold. In this manner, the liquid plastic mixture fills the mold and is allowed to cure therein.

Sand 205 is broken away, releasing the finished product which is a composite, structural plastic

object 225'.

Wax-based cores and molds of various types other than the sand cast mold described

hereinabove may be used with the present invention due to the removal of high pressure and high

added heat from the conventional casting process. Such a wax core obviates shifting of the core

within a molded product and enables easy and inexpensive removal thereof. The use of a hollow

or solid wax core or mold not only enables recycling of materials, but, more importantly, enables

melting of the core from the mold. More specifically, use of a hollow wax core enables easy

removal thereof through application of vibratory motion or, alternatively, freezing of the mold to

make the wax brittle and prone to fracture. Additionally, cooler temperatures within the mold

itself allow the wax to shrink, making it easier to remove the core. Various types of binders such as wax binders may also be used with the present

invention, which binders extend the life of a sand cast mold beyond a single use. In conventional

foundry sand casting procedures, the resin binder holding the sand together is burned off,

allowing the sand to be shaken out. In the present method, since no external heat is applied or

required or desired, a binder is used that breaks down/decomposes with water. Such a binder is

available from Ashland Chemical Co. and Borden Chemical Co.

A thermoplastic resin that is selected for a particular application must be in a liquid state.

As previously stated, preferred methods of producing a liquid resin include melting a

pre-manufactured resin, incoφorating reinforcement fibers into resin during a resin

manufacturing process wherein the resin is already be in a low viscid state, or by placing the

manufactured resin in an emulsion.

If using a thermoplastic such as nylon 6 in the present invention, a preferred method of

use involves the addition and combination of fiber reinforcements while the nylon 6 resin is

being manufactured. The process for manufacturing nylon 6 involves three components: a

monomer (i.e. caprolactam), an activator and a catalyst. The typical activator is HDI-

caprolactame pre-polymer and caprolactam and the typical catalyst is aliphatic cyclic amide,

sodium salt. Typical activator and catalyst ratios are .50-3%) by weight. The activator and

catalyst must be heated separately until they are in a liquid state. This is accomplished by raising

the temperature of each to 100°C-200° C. All three materials are usually manufactured in a

solid, flake form. When melted to the correct temperature, the three components are mixed thoroughly and the mixture maintained at slightly higher temperatures (typically 150°C-170° C),

until the desired chemical reaction occurs that produces nylon 6.

Reinforcement fibers in a milled or chopped strand form can be integrated with a

flowable resin by effecting vibration, soaking or mixing of the fibers within the resin to effect

suspension thereof. Any of these methods may be implemented to maintain the fiber in

suspension until the viscosity of the resin enables the resin to independently suspend the fibers

therein. For instance, milled glass fibers may be vibrated in combination with a resin into which

the fibers are positioned. Once the resin attains a viscosity to suspend the fibers on its own, the

vibrations cease. Although the resin's viscosity can be predicted to determine at what point

fibers will remain in suspension, fillers may also be used to maintain the suspension until cure is

achieved.

It is important to emphasize that at these temperatures, sufficient viscosity of the

composition is attained so as to allow suspension of the fibers within the resin. During mixture

and curing, such fibers remain in position for the duration of the casting procedure. The resin's

viscid state prevents the fibers from settling or grouping within the resin to create undesirable

fiber clumps which inhibit pouring and result in non-functional plastic components. With the

present invention, the part designer can provide the definition of the component's end use and the

desired performance characteristics associated therewith, and follow with a definition of a fiber

dispersion pattern which ensures compliance with such goals. The dispersion pattern can be

easily obtained with the resin composition and maintained therein by determining and maintaining the appropriate resin viscosity associated with the particular fiber weight (i.e.

fiberglass, ceramic, etc.). Thus, the dispersion pattern is maintained in suspension until cure is

attained, and the component is ready for its predicted commercial applications.

In the method of the present invention as employed in a sand casting procedure, since the

high heat of molten metal is neither involved nor desired, a sand binder only has to withstand the

temperature of the thermoplastics involved. Therefore, wax has proven to be a suitable binder, as

well as a built-in mold release. These waxes are either paraffin-based with fillers, or polymer

based using such polymers as polyethylene and polypropylene. The elimination of toxic foundry

sand binders has a major impact on the metal caster since the disposal of resin sand binders is a

significant environmental issue facing metal casters.

Using the aforedescribed methods, composite plastics can be cast around the same types

of molds and cores used in metalcasting. Traditional injection and compression molding

compounds cannot be used with the same type of metalcasting molds because they require

pressure to fill the mold and extreme heat to cure the resin. Using the disclosed method, mold

life is prolonged 300-500% over injection and compression molds due to lack of high pressure

and high added heat. In addition, metalcasting molds are 50-300% less expensive than the hard

steel tooling required by injection and compression molds.

With metalcasting, including injection and compression molding, mold release agents

must be capable of withstanding high temperatures. Due to the lower temperatures encountered in the method of the present invention, although these traditional mold release agents can be

employed, simple low temperature baπier coatings such as polyethylene film can be used.

The same mixture as that taught and used with respect to Figures 7A and 7B can also be

used to fabricate molds for similar use in prototype part fabrication or for more demanding

applications requiring greater mold strength and high temperature resistance which would render

typical soft tool or rapid prototyping molds unacceptable. Figures 9A to 9H illustrate an

alternative embodiment of the present invention wherein a composite, structural plastic mold is

fabricated and used to produce composite, structural plastic components therefrom. Referring to

Figure 9A, a two-piece wood or metal pattern 301 having a base portion 301a and a top portion

301b represents the object to be molded. Similar to the sand casting procedure shown and

described in Figures 8 A to 8H, base portion 301a is shown in Figure 9B positioned in a bottom

portion 303a of a mold box 303 having a removable base 312.

Further referring to Figure 9C, a liquid silicone rubber-curing agent mixture 304 fills

bottom portion 303a and cures. In Figure 9D, bottom portion 303a, having base portion 301a and

cured rubber 304' therein, is inverted and base 312 is removed to define a separation plane 317.

The curable rubber is also used to fill top portion 303b of the mold box and cures therein as

illustrated in Figure 9E. As before, two vent holes or risers 322 can be cut into cured rubber 304'

along with a lateral cut 327 so as to form a channel with the funnel-shaped opening 320.

Figure 9G shows the completely prepared mold just before pouring of the liquid resin. The two empty mold configuration pieces 325a and 325b are aligned and joined to form a single

mold configuration. A resinous, fiber-reinforced mixture such as that prepared in Block 103 of

Figure can now be poured into the mold from a beaker 331 into a funnel 333 through funnel

opening 320.

For some applications, the prototypes part can become the commercial product, thereby

obviating the need for production of a purely visual aid prior to fabrication of a functional

component. The ability to remove a costly and redundant element of the concept-to-market

process, namely, the production of a visual prototype upon which to base future commercial

embodiments, is important to the implementation of the present invention as it relates to

prototyping procedures. Elimination of the "in-between" visual aid provides options for the

designer about whether to alter the cuπent design or proceed with production with the design as

is. Further confirmation of the functionality of the design can thereby be made to assist in the

decision making process, without the time and costs associated with making purely visual

prototypes for every alteration between initial concept and working model.

The following examples are provided to demonstrate the versatility of the present

invention method for molding structural plastics and the ease with which the method can be

implemented in already-existing molding and metalcasting systems. The examples are provided

to emphasize these benefits and do not limit the applicability of the present invention in any way.

EXAMPLE 1 Formulation and Procedure for Utilizing the Inventive Method Using a Thermoset Resin

Materials:

Resin: liquid resole phenolic resin having the formula: phenol formaldehyde polymer 70-80%; ethylene glycol 10-12%; phenol 7-10% and formaldehyde 1-3%. Resin viscosity is 500 cps.

Catalyst: p-toluene sulfonic acid, 44%; phosphoric acid 3%, ethylene glycol 53%.

Fiber: milled fiberglass

Procedure:

Mix in acid catalyst at room temperature in a 10% by weight ratio. Mix resin and catalyst

together using standard paddle type mixer. Add and blend the fiberglass fiber in a volume of

30-35% by weight using the paddle. De-aerate the mixture by continuing to stir the mixture in a

container. In this example, shelf life at room temperature before the mixtures becomes too

viscous to pour is 10-12 minutes. Monitor the mixture temperature. Pour into a sand mold at a

maximum of 130 F as mixture starts to gel. After hardening remove sand from mold. Heat treat

the composite, structural plastic product at 250 F for one hour to remove residual moisture

therefrom.

EXAMPLE 2

Formulation and Procedure for Utilizing the Inventive Method Using Nylon 6 When Reinforcement Fibers are Added During the Manufacturing Process

Materials:

monomer: e-caprolactam catalyst: caprolactam sodium salt, i.e such as that produced under product name Bruggolen CIO, a trademark of L. Bruggeman Chemical Company

activator: caprolactam, i.e such as that produced under the name Bruggolen C20 (powder form) or Bruggolen C230 (liquid form), both of which are trademarks of L. Bruggeman Chemical Company

fiber: 1/8" chopped fiberglass stands

Procedure:

Monomer viscosity (melted) is 100 cps. The monomer in flake form is melted at

140° C in a dry atmosphere. When the monomer is molten, add and combine in chopped

fiberglass strands in a volume of 33% by weight using a paddle mixer. In a separate container,

melt the activator flake at 140° C. The activator percentage should be based upon 1% by weight

of caprolactam weight. In a separate container, melt the catalyst flake at 140° C. The catalyst

percentage should also be 1% by weight of caprolactam weight. Combine the

caprolactam/fiberglass mixture with the activator and catalyst using a standard mixer. De-aerate

the mixture and monitor the temperature thereof to a maximum temperature of 100°C-150° C.

Other steps are completed as outlined in Example 1 above. No post-mold heat treatment is

required. In this example, since the mold is subjected to considerably less heat than it would be

with molten metals, a binder that breaks down with water or low heat may be used (i.e. a resin or

wax).

EXAMPLE 3

Formulation and Procedure for Utilizing the Inventive Method for Nylon 6 When Reinforcement Fibers are Added After a Pre-Manufactured Resin is Melted

Materials:

Resin: nylon 6 in powder form. All other materials are as identified in Example 2.

Procedure:

Melt the resin to a desired viscosity of about 3000 cps at temperatures of 400°F-700° F.

Add chopped milled fiberglass in a volume of 33% by weight of the resin and de-aerate the

mixture. Slowly lower the temperature of the mixture until the precise moment when further

cooling will prevent the mixture from being poured into a mold. No heat treatment is required,

although the mold can be pre-heated to about 100°C-150°C to accelerate cure.

Thus, a method for utilizing standard foundry molds is provided which combines the

advantageous properties of structural plastics with already-existing metalcasting equipment,

thereby enabling molders to meet the changing demands of manufacturers. Foundries can

consider this method for replacing metal objects, as the disclosed method renders structural

composite plastic products having mechanical and thermal properties superior to those of

equivalent metal parts and parts produced by injection or compression molding procedures.

Furthermore, working prototypes can be produced with the same low cost and speed

previously attainable only for non-functional visual prototype parts. Reinforced thermoset or

thermoplastic resins are simply poured into molds made by existing techniques, producing prototype parts having equivalent visual and physical qualities to the actual part to be

commercially produced. For some applications, the prototyped part can become the commercial

product. The same reinforced resins can be employed to fabricate molds equivalent in

convenience and economy to soft tool molds, yet possessing sufficiently enhanced temperature

resistance and physical strength so as to be able to directly compete with hard tool molds for

many prototype or production applications, (i.e. producing prototypes that have the same

properties as the production parts in molds previously only used for the making of non-structural

plastic prototype visual aids and models).

The present invention combines the desirable characteristics of composite materials with

conventional, readily-available metalcasting procedures and equipment to develop and

implement a successful method which permits the use of conventional metalcasting molds to

fabricate composite, structural plastic prototypes and products thereby. The present invention

also enables manufacture of such products thereby in an infinite number of both simple, and

complex configuration, in varying lot sizes and with an optimum level of repeatability. High

quality plastic components are obtained without the high pressure or heat associated with

injection and compression molding, thereby negating the need for expensive steel tooling and

maintenance thereof.

Various changes to the foregoing described and shown method and corresponding

structures would now be evident to those skilled in the art. Accordingly, the particularly

disclosed scope of the invention is set forth in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A method of casting at least one composite structural plastic component from a

flowable polymerizable composition, comprising the steps of:

a.) providing a conventional metalcasting mold used in a conventional

metalcasting process;

b.) selecting a flowable polymerizable composition;

c.) combining said flowable composition with a plurality of short reinforcement

fibers into a flowable mixture;

d.) de-aerating said mixture for a time sufficient to lower viscosity of said

composition so as to simultaneously retain pourability of said mixture and sufficiently cure and

suspend said fibers in said composition;

e.) pouring said mixture into said mold;

f.) curing said composition so as to form a composite structural plastic

component thereby; and

g.) removing said component from said mold.

2. The casting method of claim 1 wherein said conventional metalcasting process is

selected from the group consisting of an expendable mold process using a permanent pattern, an expendable pattern process and a permanent mold process.

3. The casting method of claim 2 wherein said expendable mold process using a

permanent pattern is selected from the group consisting of green sand molding and shell

molding.

4. The casting method of claim 2 said expendable pattern process is selected from

the group consisting of lost foam casting and investment casting.

5. The casting method according to claim 2 wherein said permanent mold process is

selected from the group consisting of diecasting and permanent mold casting.

6. The casting method of claim 1 wherein said flowable composition is a thermoset

resin.

7. The casting method of claim 6 wherein said thermoset resin is selected from the

group consisting of unsaturated polyester, phenolic, epoxy, urethane and vinyl ester resins.

8. The casting method of claim 6 further comprising the step of combining said

mixture with a catalyst.

9. The casting method of claim 8 wherein said catalyst is selected from the group consisting of toluene sulfonic acid and phosphoric acid.

10. The casting method of claim 6 further comprising the step of curing said

thermoset resin after said removing step.

11. The casting method of claim 1 wherein said composition is a thermoplastic resin.

12. The casting method of claim 11 wherein said thermoplastic resin is selected from

the group consisting of nylon, polyethylene, polypropylene, polyetherketone, PAI, PEI, PPS,

PBI, polystyrene, p-Aminosalicylic acid, poly( ethylene terephthalate), acetals and polycarbonate.

13. The casting method of claim 1 wherein said reinforcement fibers are selected from

the group of milled or flaked fibers consisting of fiberglass, graphite, Kevlar or ceramics.

14. The casting method of claim 13 wherein said reinforcement fibers have a length

of length of 1/16".

15. The casting method of claim 13 wherein said reinforcement fibers have a length

of 1/8".

16. The casting method of claim 13 wherein said reinforcement fibers have a length

of 1/4".

17. The casting method of claim 13 wherein said reinforcement fibers have a width of

about 10 microns to 40 microns, inclusive.

18. The casting method of claim 17 wherein said reinforcement fibers have a width of

about 10 microns.

19. The casting method of claim 1 wherein said de-aeration step includes putting said

composition resin into a low viscosity state.

20. The casting method of claim 19 wherein said fibers are placed in suspension in

said low viscosity resin.

21. A method of fabricating composite, structural plastic molds, comprising the steps

of:

a.) placing a three-dimensional model of a part to be molded into a container;

b.) selecting a flowable polymerizable composition;

c.) combining said flowable composition with a plurality of short reinforcement

fibers into a flowable mixture;

d.) pouring said mixture into said container so as to envelop said model

therewith;

e.) allowing said mixture to cure into a solid, composite structural plastic about

said model, thereby encapsulating said model within said plastic and creating an impression of said model within said plastic; and

f.) removing said model from said solid, composite structural plastic so that said

impression of said model remains within an interior portion of said solid plastic, said interior

portion begin accessible from an area external to said solid plastic so as to enable filling said

interior portion with a flowable polymerizable composition.

22. A composite structural plastic component formed by casting a flowable

polymerizable composition in a conventional metalcasting mold, said product formed by the

steps of:

a.) providing a conventional metalcasting mold used in a conventional

metalcasting process;

b.) selecting a flowable polymerizable composition;

c.) combining said flowable composition with a plurality of short reinforcement

fibers into a flowable mixture;

d.) de-aerating said mixture for a time sufficient to lower viscosity of said

composition so as to simultaneously retain pourability of said mixture and sufficiently cure and

suspend said fibers in said composition;

e.) pouring said mixture into said mold;

f.) curing said composition so as to form a composite structural plastic

component thereby; and

g.) removing said component from said mold.

23. The casting method of claim 22 wherein said conventional metalcasting process is

selected from the group consisting of an expendable mold process using a permanent pattern, an

expendable pattern process and a permanent mold process.

24. The casting method of claim 23 wherein said expendable mold process using a

permanent pattern is selected from the group consisting of green sand molding and shell

molding.

25. The casting method of claim 23 said expendable pattern process is selected from

the group consisting of lost foam casting and investment casting.

26. The casting method according to claim 23 wherein said permanent mold process

is selected from the group consisting of diecasting and permanent mold casting.

27. The casting method of claim 22 wherein said flowable composition is a thermoset

resin.

28. The casting method of claim 27 wherein said thermoset resin is selected from the

group consisting of unsaturated polyester, phenolic, epoxy, urethane and vinyl ester resins.

29. The casting method of claim 27 further comprising the step of combining said

mixture with a catalyst.

30. The casting method of claim 29 wherein said catalyst is selected from the group

consisting of toluene sulfonic acid and phosphoric acid.

31. The casting method of claim 27 further comprising the step of curing said

thermoset resin after said removing step.

32. The casting method of claim 22 wherein said composition is a thermoplastic resin.

33. The casting method of claim 32 wherein said thermoplastic resin is selected from

the group consisting of nylon, polyethylene, polypropylene, polyetherketone, PAI, PEI, PPS,

PBI, polystyrene, p-Aminosalicylic acid, poly(ethylene terephthalate), acetals and polycarbonate.

34. The casting method of claim 22 wherein said reinforcement fibers are selected

from the group of milled or flaked fibers consisting of fiberglass, graphite, Kevlar or ceramics.

35. The casting method of claim 34 wherein said reinforcement fibers have a length

oflength of 1/16".

36. The casting method of claim 34 wherein said reinforcement fibers have a length

of 1/8".

37. The casting method of claim 34 wherein said reinforcement fibers have a length of 1/4".

38. The casting method of claim 34 wherein said reinforcement fibers have a width of

about 10 microns to 40 microns, inclusive.

39. The casting method of claim 38 wherein said reinforcement fibers have a width of

about 10 microns.

40. The casting method of claim 22 wherein said de-aeration step includes putting

said composition resin into a low viscosity state.

41. The casting method of claim 40 wherein said fibers are placed in suspension in

said low viscosity resin.

42. A composite structural plastic mold, said mold made by the steps of:

a.) placing a three-dimensional model of a part to be molded into a container;

b.) selecting a flowable polymerizable composition;

c.) combining said flowable composition with a plurality of short reinforcement

fibers into a flowable mixture;

d.) pouring said mixture into said container so as to envelop said model

therewith;

e.) allowing said mixture to cure into a solid, composite structural plastic about said model, thereby encapsulating said model within said plastic and creating an impression of

said model within said plastic; and

f.) removing said model from said solid, composite structural plastic so that said

impression of said model remains within an interior portion of said solid plastic, said interior

portion begin accessible from an area external to said solid plastic so as to enable filling said

interior portion with a flowable polymerizable composition.

43. A method of casting at least one composite structural plastic component from a

flowable polymerizable composition, comprising the steps of:

a.) providing a conventional metalcasting mold used in a conventional

metalcasting process;

b.) selecting a flowable polymerizable composition;

c.) combining said flowable composition with a plurality of short reinforcement

fibers into a flowable mixture;

d.) de-aerating said mixture for a time sufficient to place lower viscosity of said

composition so as to simultaneously retain pourability of said mixture and sufficiently cure and

suspend said fibers in said composition;

e.) pouring said mixture into said mold;

f.) curing said composition so as to form a composite structural plastic

component thereby; and

g.) removing said component from said mold.

44. A system for molding composite structural plastic components, comprising:

a conventional metalcasting mold used in a conventional metalcasting process;

a flowable polymerizable composition;

a plurality of reinforcement fibers;

means for mixing said flowable composition and said reinforcement fibers into a

resinous compound;

means for placing said flowable composition in a low viscosity state; and

means for pouring said compound into said mold so as to cast a component

thereby.