Compression molding using a self aligning and activating mold system

Abstract

A compression molding system and method, including a mold set and one or more hydraulic cylinders (42,44) that create a self-aligning and self-activating operating unit. The hydraulic cylinders can include a combination of activation and clamping cylinders. The mold set includes a first and second mold section (22,24) and a source of heat (87) is provided to heat the mold set. The mold sections are constructed of individual plates or bar (16), and machined to define a mold cavity (25). Reinforcement plates (38,41) can be attached to the mold sections and add structure and integrity to the system. A computer control system (56) interprets data from the activation hydraulic cylinders and monitors and controls hydraulic fluid flow into and out of each cylinder and a power unit pumps hydraulic fluid into and out of the chambers within the activation and clamping cylinders (42,44).

Description

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to compression molding, and specifically to compression molding using a self-aligning and activating mold system and method.

[0004] 2. Discussion of the Prior Art

[0005] Various molding processes exist to produce both simple and complex shapes having a wide range of geometry and thickness. Two existing processes are compression molding and resin transfer molding.

[0006] Compression molding converts uncured (un-exposed to heat) thermoset sheet molding compounds (SMC) known in the art into various products by applying pressure in a closed mold that is heated to cure (set) the SMC. SMC molding typically includes a compression mold mounted into a hydraulic press of sufficient tonnage to generate adequate internal force to cause the heated SMC material to flow and fill the mold. In use, a charge (material to be formed) of SMC is placed on a lower section of a mold set. The press is closed under controlled conditions to bring the two mold sections together resulting in compression molding of the SMC. These systems typically require a molding pressure of between 750 psi (53 bar) to 1500 psi (103 bar) to adequately flow the compound and fill the mold cavity. The molds are typically heated to around 290° F. to 310° F. to complete the cure (set) of the thermoset resin used in the SMC material. The mold/press remains closed and under pressure during the cure cycle. The duration of the cure cycle is determined by part thickness. A typical cure time for a 0.125 inch thick part would be between 60 and 90 seconds.

[0007] Currently, a high tonnage compression press is required to generate the molding pressures necessary to form a standard SMC part. These presses require special installation and deep foundations of reinforced concrete and can weigh many tons and can be over twenty (20) feet in height. Because of their large size and weight, the presses are usually assembled in one facility, disassembled, and then shipped in sections and re-assembled on-site. This increases overall costs and start-up times.

[0008] Thus, conventional SMC presses are expensive and therefore require a long-term investment. Molds (tools) used in a conventional SMC compression process are similarly expensive due to the required structural integrity necessary to handle the high molding pressures. The molds are typically machined from at least two rectangular solid steel billets. These billets are engineered to withstand the high pressures of compression molding. Billet machining can remove as much as fifty percent of the original material, thus adding to the overall cost of the mold design. Because of the size and expense of SMC compression molding operations, SMC part production is usually restricted to high volume parts (e.g., more than 50,000 units annually). Mid and low volume product runs are often prohibitively expensive to produce using this technology.

[0009] A second conventional molding process is resin transfer molding (RTM). RTM injects a liquid thermoset resin into a heated or unheated mold cavity containing a dry glass preform (such as sheets of woven glass material or fiberglass) and allowed to solidify (or cure) into a desired part shape. RTM is common and widely used in industry.

[0010] In use, RTM systems typically have upper and lower mold halves. These halves are usually separated using a chain hoist. Once open, the dry glass preform is placed into the mold cavity. The mold halves are then placed back together and the preform is sealed within the mold halves. The resin is injected into the mold cavity, impregnating the preform. The pressure needed to complete the injection is typically 50 psi (3.5 bar). The resin can then cure at either room temperature or a predetermined elevated temperature depending on the desired rate of cure. Once the mixture has solidified, the mold is opened and the part is removed.

[0011] Resin transfer molds typically have a thin nickel tool surface backed by epoxy. The structural elements that support the tool surface can include a combination of plywood, fiberglass and steel. RTM tools are constructed at relatively low cost when compared to SMC compression molds since little structural integrity is needed to handle its relatively low molding pressures (50 psi compared to 1000 psi in SMC systems). In addition, the RTM process uses no press and has limited infrastructure costs.

[0012] Though relatively inexpensive, RTM has many limitations that make the process undesirable. These include a frequent inability to make a final shape part; a relatively long cycle time; multi-phase operations are often required; very operator skill dependent; part geometry limitations; limited ability to achieve class A surface finish (i.e. visible or show surface); and part-to-part inconsistency. Given the above limitations, RTM is mainly used for very low production volumes, non-class A surface parts, and simple shapes.

[0013] It would be advantageous to overcome the limitations of the RTM systems without the expense and structural requirements of the conventional SMC systems. New SMC compounds have recently been developed that mold at much lower pressures (e.g., between 75 psi to 350 psi). These are now products known in industry as low pressure molding compounds (LPMC) and low pressure sheet molding compounds (LPSMC) which are sold respectively under the trademarks CRYSTIC IMPREG made by Scott Bader Company Ltd of Northamptonshire, England and SMC-LITE made by Ashland Specialty Chemical Company (Composite Polymers Division) of Columbus, Ohio. Such compounds include glass fiber composite impregnated with polyester resins or low viscosity resins including isophthalic and orthosphthalic resins and the like. A new system and method, combining the simplicity and cost effectiveness of an RTM system with the part consistency and class A finish capability of the SMC compression mold process is now possible for molding the new LPMC and LPSMC materials.

SUMMARY OF THE INVENTION

[0014] Accordingly, the present invention provides a compression molding apparatus and method using a self-aligning and activating mold (SAAM) system. The present invention uses fabricated steel molds to mold the new low pressure molding compounds (LPMC) and low pressure sheet molding compounds (LPSMC). Using a fabricated mold set integrated to a series of hydraulic cylinders to create a self-contained operating unit, the system eliminates the need for a solid steel tool/mold set operated by a conventional high tonnage hydraulic press.

[0015] In one embodiment of the present invention an apparatus for compression molding includes a mold set having first and second mold sections and a source of heat for the mold set. At least one activation cylinder is mounted to either the first mold section or the second mold section and has a retraction chamber and an extension chamber. The activation cylinder further includes a cylinder rod having an end mounted to the other of the first and second mold sections.

[0016] In another embodiment of the present invention a method of compression molding is provided using an apparatus that includes a mold set having first and second mold sections and a source of heat for the mold set. At least one activation cylinder is mounted to one of the first and second mold sections. The activation cylinder includes a retraction chamber and an extension chamber, and further includes a first cylinder rod having an end mounted to the other of the first and second mold sections. At least one clamping cylinder is mounted to one of the first and second mold sections. The clamping cylinder includes a second retraction chamber, a second extension chamber, and a second cylinder rod having a second end releasably mounted to the other of the first and second mold sections. The method includes heating the mold set; placing a charge of material to be formed on one of the first and second mold sections; moving one of the mold sections towards the other mold section; actuating the second cylinder rod to meet the one mold section and actuating a lock member to releasably hold the second cylinder rod end to the one mold section; and pressing the mold sections together at a predetermined pressure for a predetermined time to mold the charge of material.

[0017] In another embodiment of the present invention a method of compression molding is provided using an apparatus including a mold set having a first and second mold section, and a source of heat for the mold set. At least one activation cylinder is connected to one of the mold sections. The activation cylinder includes a retraction chamber, an extension chamber, and further includes a cylinder rod having a cylinder rod end mounted to the other of the mold sections. The method comprises the steps of heating the mold set; placing a charge of material to be formed on one of the mold sections; moving one mold section towards the other mold section; and pressing the mold sections together at a predetermined pressure for a predetermined time to mold the charge of material.

[0018] While most mold sets of this invention are oriented so as to use upper and lower sections to benefit from the force of gravity in insertion of moldable material in the lower mold section, it will be understood that the invention is equally applicable to configurations wherein the sections are positioned in a side-by-side orientation (See FIG. 13). Thus, it should be understood that the invention contemplates the use of first and second mold sections irrespective of their orientation, and that the use of the terms “upper” and “lower” herein is for illustrative purposes and for ease of understanding, only, and should not be deemed to limit the scope of the invention to any particular orientation of the mold sections.

[0019] Other advantages and features of the present invention will become more apparent to persons having ordinary skill in the art to which the present invention pertains from the following description taken in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

[0020] The foregoing advantages and features, as well as other advantages and features will become apparent with reference to the description and figures below, in which like numerals represent like elements and in which:

[0021] FIG. 1 is a perspective view of a compression molding system of the present invention;

[0022] FIG. 2 is a side view of a fabricated mold set of the present invention before the mold cavity is machined;

[0023] FIG. 3 is a side view of a fabricated mold set of the present invention machined to a desired work piece shape;

[0024] FIG. 4 is a side view of a fabricated mold set of the present invention including reinforcement plates;

[0025] FIG. 5 is a side view of the compression molding system of the present invention including a clamping hydraulic cylinder and an activation hydraulic cylinder;

[0026] FIG. 6 is a compression mold system of the present invention in an open position;

[0027] FIG. 7 is an alternate embodiment of the present invention using four activation cylinders;

[0028] FIG. 8A is a plan view of the alternate embodiment in FIG. 7;

[0029] FIG. 8B is a sectional view cut through line 8B-8B in FIG. 8A;

[0030] FIG. 9 illustrates steps of a compression mold system of the present invention in an open position loading a charge, a closed position molding the charge, and in an open position removing the molded charge;

[0031] FIG. 10 illustrates an alternate embodiment of the present invention having one activation cylinder;

[0032] FIGS. 11A & 11B illustrate a top view of FIG. 10 and a sectional view cut through line 11B-11B in FIG. 11A respectively;

[0033] FIG. 12 illustrates an alternate embodiment of the present invention including four activation cylinders and two clamping cylinders.

[0034] FIG. 13 illustrates of the present invention mounted on a truck having activation and clamping cylinders.

DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention relates to a compression molding system that combines the advantages of the conventional sheet molding compound (SMC) systems with the resin transfer molding systems (RTM) while eliminating known disadvantages of each of these systems. The present invention replaces both the large solid steel mold set mounted to a conventional high tonnage hydraulic SMC press and instead uses a fabricated or bar-stock mold set integrated to a series of strategically placed hydraulic cylinders and optional reinforcement plates.

[0036] Generally, the present invention is a self-contained, self-aligning and self-activating molding (SAAM) system 20 capable of developing the pressure required for compression molding of new low pressure molding compounds (LPMC) and other similar materials that have low pressure molding and curing capabilities. The new LPMC material changes state (such as to a liquid) when heated thereby requiring less pressure to mold a shaped part. The present invention achieves the desired molding capabilities in a smaller, lighter and less expensive package compared to conventional SMC molding systems. It is also an improvement over the RTM system in that the limitations of the RTM system as outlined previously, are eliminated.

[0037] The present invention can be operated on a typical six-inch reinforced concrete factory floor, eliminating the need for a larger concrete pad as required by conventional SMC molding systems. The working height of the new SAAM molding system 20 can be designed to suit the operators by altering the location of the activation cylinders and defining the desired height of the support pillars. The system 20 can be assembled, tested, demonstrated and approved in one facility and shipped assembled to the manufacturing plant as a “turn-key” operation. Thus, the system provides a cost advantage through reduced capital cost, and a faster time for set up and production.

[0038] The major components of the molding system 20 of the present invention are the mold set, hydraulic cylinders, hydraulic power unit, and system controller. FIG. 1 illustrates an embodiment of the present invention utilizing a plurality of mold sets and cylinders connected together. Alternate embodiments of the present invention demonstrate variations in the types of application available by varying the number and configuration of the types of hydraulic cylinders, the mold set shape and the orientation of the molding apparatus. The apparatus of the present invention can be oriented horizontally or vertically depending on the particular application.

[0039] FIG. 2 illustrates the mold sections of a mold set before the mold sections have been machined. The mold sections can include a plurality of individual plates or a plurality of solid steel bar-stock 16, connected together in various shapes and sizes to form a mold set the shape and size of a desired part. The plates (or bar-stock) 16 can be made of steel or any other material capable of supporting the forces generated during the molding process for a given application. The plates (or bar-stock) 16 may be pre-formed to the approximate part shape by methods such as bending, rolling, flame/gas cutting, and forging. The plates (or bar-stock) 16 may be connected together along their perimeter using conventional means such as welding, as shown by weld points 26, or bolting (not shown). Once connected, the plates 16 form a lower mold section 22 and an upper mold section 24. The mold sections 22 and 24 are then machined to create a desired mold cavity 25 corresponding to the part to be molded (FIG. 5). Conventional methods such as milling or computer numerically controlled (CNC) machining can be used to machine the mold sections. This mold set replaces the need to machine the mold from a single steel billet.

[0040] Most mold sets of this invention are oriented to use a lower mold section and an upper mold section to benefit from the force of gravity in insertion of moldable material in the lower mold section. It will be understood that the invention is equally applicable to configurations wherein the mold sections are positioned in a side-by-side orientation (See FIG. 13). Thus, it should be understood that the invention contemplates the use of first and second mold sections irrespective of their orientation, and that the use of the terms “upper” and “lower” herein is for illustrative purposes and for ease of understanding, only, and should not be deemed to limit the scope of the invention to any particular orientation of the mold sections.

[0041] The mold sections 22 and 24 can also include a heat cavity 43 configured to receive a heating element, which may be, for example, a resistance heater, or, preferably a heated fluid medium such as hot oil or steam (FIG. 2). A conventional pumping system 86 can be used to heat and pump steam or oil into and out of the heat cavities 43 (FIG. 1). The particular heat cavity 43 shown in the figures is representative of the type of cavity required for use of steam as a heating medium. If hot oil is being used, a smaller cavity design will suffice. The heating medium is pumped into the heat cavities 43 through heat ports 45 and heats the mold sections 22 and 24 to the required temperature needed to mold a particular work piece (FIGS. 11A & B).

[0042] The molding system 20 can be supported by a plurality of support pillars 14 to place the molding system 20 at a height convenient for a typical worker. The support pillars 14 can be affixed on one end to the lower mold section 22 using conventional methods such as bolting or welding. The opposite end of the support pillars 14 can be mounted to the floor using conventional methods such as lag bolts. The support pillars 14 support the weight of the system 20 and securely fasten the system 20 to the floor to prevent it from moving and reduce excessive vibration during operation. FIGS. 1 and 7 show two different types of support pillars 14, but any number of other possible support pillar configurations could also be used.

[0043] FIG. 3 illustrates the machined mold surfaces 32 and 33 of mold sections 22 and 24. The machined mold surfaces 32 and 33 represent the shape of the part to be molded and define the mold cavity 25. Surfaces 32 and 33 can also be surface finished by conventional means known in the art (e.g., repairing, detailing, grinding, sanding, and polishing) to create an acceptable production surface finish. Mating perimeter surfaces 34 and 35 of the upper and lower mold sections serve to define the periphery of mold cavity 25 and are oriented parallel to each other.

[0044] FIG. 4 illustrates the mold sections 22 and 24 including reinforcement plates 36, activation hydraulic cylinder mounting plate 38, clamping hydraulic cylinder mounting plate 39, activation hydraulic cylinder rod end mounting plate 40, and clamping hydraulic cylinder rod end mounting plate 41, all of which are mounted to the mold sections 22 and 24 using conventional means such as welding or bolting. The illustrated embodiment shown in FIG. 1 is shown with six sets of reinforcement plates 36 (a first set on each upper mold section 24 and a second set on each lower mold section 22). The reinforcement plates 36 provide strength and stability to the molding system 20 and can vary in quantity, shape, size and location depending on the size and particular embodiment of the molding apparatus. Stopping blocks 37 can be mounted to either the perimeter surface 34 of lower mold section 22 or perimeter surface 35 of upper mold section 24 and are used to set the gap between the upper and lower mold sections 22 and 24 by stopping the mold surfaces 32 and 33 from contacting each other. The thickness of the part to be molded may be dictated by the size of the stopping blocks 37. The stopping blocks 37 can be various shapes and sizes depending on the particular mold system design and for the particular part to be molded.

[0045] FIG. 5 illustrates an embodiment of the present invention where the mold sections 22 and 24 are connected to an activation hydraulic cylinder 42 and a clamping hydraulic cylinder 44. The activation cylinder 42 can raise and lower the upper mold section 24 to allow convenient removal of a work piece. The clamping cylinder 44 allows for additional reinforcement to maintain the mold set in a closed position during operation.

[0046] The activation hydraulic cylinder 42 is mounted to the activation hydraulic cylinder mounting plate 38 on the lower mold section 22 and the clamping hydraulic cylinder 44 is mounted to the clamping hydraulic cylinder mounting plate 39 on the lower mold section 22. The activation hydraulic cylinder 42 has a first cylinder rod 46 attached to a first piston 60. First cylinder rod 46 has a first cylinder rod end 48 that is fixedly mounted to the activation hydraulic cylinder rod end mounting plate 40 on the upper mold section 24 and extends slidably through a closely fitting aperture in plate 38. The activation hydraulic cylinder 42 includes two chambers defined as a first retraction chamber 62 and a first extension chamber 64. Chambers 62 and 64 can have one or more fluid entry and exit points 80. Fluid is pumped to and from the first retraction and extension chambers 62 and 64 to provide the clamping and extension force needed to move upper mold section 24 to and from lower mold section 22 using a conventional pumping system 86 and computer control system 56 (such as a Position Linear Control (PLC) illustrated in FIG. 1).

[0047] The clamping hydraulic cylinder 44 has a second cylinder rod 50 attached to a second piston 66. The second cylinder rod 50 has a second cylinder rod end 52 that extends into and through the clamping hydraulic cylinder rod end mounting plate 41 and is configured to releasably lock into position into a rod end slide coupler unit 54. In the preferred embodiment, the clamping hydraulic cylinder rod end mounting plate 41 includes the rod end slide coupler unit 54, which is configured to receive the second cylinder rod end 52. FIG. 5 illustrates the rod end slide coupler unit 54 in its closed position locking the second cylinder rod end 52 securely in position. The rod end slide coupler unit 54 engages when the upper mold section 24 reaches a predetermined pause position. Preferably, the predetermined pause position is when the upper mold section 24 is within approximately 25-50 mm of the lower mold section 22.

[0048] The clamping hydraulic cylinder 44 has two chambers defined as a second retraction chamber 68 and a second extension chamber 70. Each chamber 68 and 70 can have one or more second fluid entry and exit points 82. Fluid can be pumped to and from the second retraction and second extension chambers 68 and 70 using the pumping system 86 and PLC control system 56. The clamping hydraulic cylinder 44 assists in providing the clamping and extension forces needed to hold the upper and lower mold sections 22 and 24 together during the molding process.

[0049] FIG. 6 illustrates the embodiment shown in FIG. 5 in an open position with the rod end slide coupler unit 54 shown in its open position. When the mold sections 22 and 24 are in an open position, a part loading and removal zone 58 is created. With the rod end slide coupler unit 54 in its open position, the second cylinder rod end 52 can be removed from the clamping hydraulic cylinder rod end mounting plate 41, and the first cylinder rod 46 can be extended to raise the upper mold section 24. When upper mold section 24 is closing towards lower mold section 22, the first cylinder rod 46 and second cylinder rod 50 provide sufficient forming/closing pressure to mold the part within the mold cavity 25. Pressure typically remains constant during the complete curing stage.

[0050] In the illustrated embodiment shown in FIGS. 5 & 6, the clamping hydraulic cylinder 44 assists the activation hydraulic cylinder 42 in holding the mold sections 22 and 24 in a closed position during operation. The activation hydraulic cylinder 42 in combination with the clamping hydraulic cylinder 44 generate the clamping force required to keep mold sections 22 and 24 together and under pressure during the molding and curing stages. Only the activation hydraulic cylinder 42 controls the movement of mold section 24 away from mold section 22 to allow for part removal.

[0051] In summary, the clamping hydraulic cylinders 44 differ from activation hydraulic cylinders 42 in four ways. First, as stated above, the clamping hydraulic cylinders 44 provide clamping force only to hold the mold sections 22 and 24 together during the molding stage. The clamping hydraulic cylinders 44 do not aid in raising and lowering the upper mold section 24. Second, the clamping hydraulic cylinders 44 have a unique latching mechanism (the rod end slide coupler unit 54). By comparison, the activation hydraulic cylinders 42 have a fixed attachment on the first cylinder rod ends 48. Third, the clamping hydraulic cylinders 44 allow unfettered ingress and egress of the charge/part because the second cylinder rod 50 does not reach into the charge/part loading/unloading zone 58 and can be retracted out of the way. Finally, the clamping hydraulic cylinders 44 are more economical, since second cylinder rod 50 has a shorter stroke.

[0052] In an alternate embodiment (FIGS. 7 & 8), a system 20′ using the present invention includes only four activation hydraulic cylinders 42 and no clamping hydraulic cylinders 44. The activation hydraulic cylinders 42 can open the mold sections 22′ and 24′ to allow insertion and removal of the molded parts and provide the required pressure for molding of a part. In this embodiment, the system 20′ is inverted in that the activation hydraulic cylinders 42 are attached to a top side of the upper mold section 24′. The activation cylinder rod end 48 is fixedly attached to the lower mold section 22′ instead of the upper mold section 24′. As the upper mold section 24 moves away from the lower mold section 22′ during operation, the activation cylinders 42 move with the upper mold section 24′. Reinforcement plates 36′ are included in this embodiment and are positioned on the sides and exterior of the mold sections 22′ and 24′. These optional reinforcement plates 36′ add strength and stability of the system in configurations where higher pressures are indicated.

[0053] In another embodiment, the system 20″ includes only one activation hydraulic cylinder 42 and no clamping hydraulic cylinders 44 (FIGS. 10-11). In this embodiment, the cylinder 42 is positioned centrally to distribute the load equally and insure that the perimeter surfaces 34″ and 35″ of upper and lower mold sections 22″ and 24″ remain parallel during operation. This embodiment is similarly inverted with the activation cylinder 42 being attached to the topside of the upper mold section 24″. This type of single activation system would be used for compression molding of smaller components that require less pressure. The smaller size of the system would also eliminate the need for reinforcement plates 36 used in the previous embodiments.

[0054] FIG. 12 illustrates another embodiment of the molding system 20′″ of the present invention. This configuration illustrates four activation cylinders 42 and two clamping cylinders 44. FIG. 13 illustrates a mobile embodiment 20″″ of the present invention where the molding system is mounted to a truck to provide for the ability to locate the molding process at a desired remote location. In this embodiment the molding system is oriented horizontally and is mounted to the truck on tracks to allow the mold sections to slide along the tracks as they move together and apart during operation. This embodiment illustrates a compression molding system of the present invention having one activation cylinder 42 and one clamping cylinder 44.

[0055] The activation hydraulic cylinders 42 and clamping hydraulic cylinders 44 of the present invention are typically arranged on the periphery of the mold tool set except as illustrated in FIGS. 10 and 11. In the illustrated embodiments of FIGS. 1, 7 & 12, the activation hydraulic cylinders 42 and the clamping hydraulic cylinders 44 are placed symmetrically around the mold set. The activation hydraulic cylinders 42 and clamping hydraulic cylinders 44 can be placed in a wide range of alternative layouts to suit the specific molding conditions and parameters as well as sound engineering requirements. The activation hydraulic cylinders 42 and clamping hydraulic cylinders 44 can be placed in an alternating layout or the cylinders 42 and 44 can be in an opposing layout where all the activation cylinders 42 are one side and the clamping cylinders 44 are on the opposite side of the particular system. The key to configuring cylinder 42 and 44 placement is to maintain an equal distribution to limit vertical and side mold deflection caused by pressure during production, and keep the upper mold section 24 parallel to the lower mold section 22.

[0056] The movement of each activation hydraulic cylinder 42 can be monitored by linear transducers (not shown), which are encased in the body of each activation hydraulic cylinder 42. The transducers transmit continuous linear position data to the computer control system (PLC) 56 in FIG. 1. The PLC 56 interprets incoming data from all the activation hydraulic cylinders 42 in a given system. The PLC 56 also monitors and controls hydraulic fluid flow into and out of each activation hydraulic cylinder 42 and clamping hydraulic cylinder 44 via valves at each cylinder's fluid entry and exit points 80 and 82. The PLC 56 can also control the operation of the clamping hydraulic cylinders 44 when they are included in the system. The PLC 56 insures uniform speed, position, and self-alignment of the first cylinder rods 46 so that the upper and lower mold sections 22 and 24 always remain parallel and aligned with each other.

[0057] The molding system 20 of the present invention is designed to meet the individual needs of a specific part to be molded. Therefore, the forces acting on the mold sections 22 and 24 must be calculated for a specific configuration. First, the surface area of the part is calculated. Next, the maximum pressure required to mold the part is determined. The product of surface area and maximum required molding pressure determines the tonnage required for the particular molding system (surface area×required molding pressure=tonnage). Required molding pressure can vary from part to part depending on the complexity and geometry of the part, the depth of draw and desired finish. Steeper and deeper draw parts with thin wall thickness will require higher molding pressures. The typical pressures for the present invention range between 70 psi (5 bar) and 50 psi (11 bar) when using LPMC, but may increase to 350 psi (27 bar) for LPSMC products.

[0058] Hydraulic cylinders must also be evaluated to determine their output force. Output force is a function of the effective area of the cylinders. The cylinder's effective area is calculated using the formula for piston area (cylinder bore) minus the rod diameter area (effective area=piston area−rod diameter). The total output force of the activation hydraulic cylinders 42 and clamping hydraulic cylinders 44 is specified to exceed the molding force.

[0059] The method of using the molding system 20 of the present invention utilizing an activation hydraulic cylinder 42 in combination with a clamping hydraulic cylinder 44 as shown in FIGS. 1, 5 & 6, will now be described. Alternative methods can be employed depending on the particular embodiment (described above) to be used. The compression molding process begins with the mold sections 22 and 24 in the open position and heated to approximately 300 degrees Fahrenheit. The heating process is achieved by injecting hot oil or steam through ports 45 and into heat cavities 43 positioned just below the mold surfaces 32 and 33 (FIGS. 8B & 11B). A pre-weighed charge (usually a sheet of material) of a low-pressure molding compound (LPMC) is placed in position on the lower mold section 22. The PLC 56 commands the molding sequence to initiate. Fluid is pumped out of the first extension chamber 64 and into the first retraction chamber 62 causing the mold sections 22 and 24 to close.

[0060] When the upper mold section 24 reaches the predetermined pause position, (approximately 25 to 50 mm depending on the charge and molding parameters) from the lower mold section 22, the clamping hydraulic cylinder 44, second cylinder rod end 52 and slide coupler unit 54 are engaged to assist the activation hydraulic cylinder 42 in holding the upper and lower mold sections 22 and 24 together.

[0061] At the same time, the closing speed of the cylinders 42 and 44 is slowed to the required forming speed. Forming speed is determined by trial and error and differs based on part geometry and LPMC formulation.

[0062] The upper mold section 24 continues to move towards the lower mold section 22 until the mold cavity 25 is closed. This means that either the upper mold section 24 has closed onto the lower mold section 22 with stopping blocks 37 (if used), or the upper mold section 24 has closed against the LPMC material trapped in the mold cavity between the upper and lower mold sections. Once the mold is closed, the “cure time” duration is started.

[0063] The cure time is dependent on the thickness of the part being molded—usually between 60 to 90 seconds per 0.125″ (3 mm) of thickness. Following the cure cycle completion, a command to open the mold set will be issued by the PLC 56.

[0064] Fluid is evacuated from retraction chambers 62 and 68 of the activation hydraulic cylinders 42 and clamping hydraulic cylinders 44 while simultaneously being pumped into the extension chambers 64 and 70. The transfer of fluid causes the upper mold section 24 to separate from the lower mold section 22 to a pause position (the same pause position as for the closing phase). At this position, the rod end slide coupler unit 54 is disengaged, the activation hydraulic cylinder 42 extends, lifting the upper mold section 24 to a position that allows removal of the molded part. Simultaneous with the activation hydraulic cylinder 42 being extended to open the mold sections 22 and 24, the clamping cylinder rod 50 can be retracted to increase accessibility if required. FIG. 9 illustrates the process showing the mold set in an open/ready position, a closed molding position and a part removal position respectively. In an embodiment that does not include a clamping hydraulic cylinder 44, the steps in the above method would apply excluding the steps related to the clamping hydraulic cylinder 44.

[0065] The above-described embodiments of the present invention are provided purely for purposes of illustration. Many other variations, modifications, and applications of the invention may be made.

Claims

1. An apparatus for compression molding a charge of material into a work piece comprising: a mold set including a first mold section and a second mold section; at least one activation cylinder mounted to one of said first and second mold sections, said at least one activation cylinder being adapted for extending and retracting a first cylinder rod, said cylinder rod slidably extending through an aperture in said one mold section and having an end attached to the other of said first and second mold sections; and a source of heat for the mold set.

2. The apparatus of claim 1 wherein said at least one activation cylinder comprises a hydraulic cylinder having extension and retraction chambers each connected to a controllable source of pressurized hydraulic fluid.

3. The apparatus of claim 1, wherein said source of heat for said mold set comprises steam.

4. The apparatus of claim 1, wherein said source of heat for the mold set comprises hot oil.

5. The apparatus of claim 1, wherein said source of heat for the mold set comprises resistance heat.

6. The apparatus of claim 1, further comprising at least one clamping cylinder mounted to one of said first and second mold sections, said at least one clamping cylinder being adapted for extending and retracting a second cylinder rod having a second end releasably mounted to the other of said first and second mold sections.

7. The apparatus of claim 6 wherein said at least one clamping cylinder comprises a hydraulic cylinder having extension and retraction chambers each connected to a controllable source of pressurized hydraulic fluid.

8. The apparatus of claim 1, further including a computer control system connected to the compression molding apparatus to control the mold process and insure that said first and second mold sections remain substantially parallel to each other during operation.

9. The apparatus of claim 8 further comprising linear transducers encased in said activation cylinders, wherein said transducers transmit continuous linear position data to said computer control system, and wherein said computer control system interprets incoming data from said at least one activation cylinder and monitors and controls hydraulic fluid flow into and out of said retraction and extension chambers.

10. The apparatus of claim 7 further comprising linear transducers encased in the activation cylinders, wherein said transducers transmit continuous linear position data to a computer control system, and wherein said computer control system interprets incoming data from said at least one activation cylinder and said at least one clamping cylinder and monitors and controls hydraulic fluid flow into and out of said retraction and extension chambers.

11. The apparatus of claim 1, wherein said first and second mold sections are comprised of a plurality of individual plates connected together.

12. The apparatus of claim 1, wherein said first and second mold sections are comprised of a plurality of solid steel bar-stock pieces connected together.

13. The apparatus of claim 6, wherein said first and second mold sections are comprised of a plurality of individual plates connected together.

14. The apparatus of claim 6, wherein said first and second mold sections are comprised of a plurality of bar-stock pieces connected with together.

15. The apparatus of claim 1, wherein said first mold section and second mold section in a closed position have an interior surface that defines a mold cavity.

16. The apparatus of claim 1 further comprising support pillars affixed to one of said first and second mold sections.

17. The apparatus of claim 1, wherein said at least one activation cylinder is arranged on a periphery of said mold set.

18. The apparatus of claim 1, wherein said at least one activation cylinder is positioned substantially in the center of said mold set.

19. The apparatus of claim 6, wherein said at least one activation cylinder and said at least one clamping cylinder are arranged on a periphery of said mold set.

20. The apparatus of claim 19, wherein said at least one activation cylinder and said at least one clamping cylinder are arranged in opposing orientation to each other.

21. The apparatus of claim 19, wherein said at least one activation cylinder and said at least one clamping cylinder are arranged in an alternating layout.

22. The apparatus of claim 1, wherein one of said first and second mold sections includes a plurality of stopping blocks.

23. The apparatus of claim 1, wherein the charge of material is molded at a force of 75 to 350 psi.

24. The apparatus of claim 1, wherein said mold set includes reinforcement plates attached along an exterior surface of said mold set.

25. The apparatus of claim 6, wherein said mold set includes reinforcement plates attached along an exterior surface of said mold set.

26. A method of compression molding using an apparatus including a mold set having first and second mold sections, means to heat the mold set, at least one activation cylinder connected to one of the first and second mold sections, the at least one activation cylinder including a retraction chamber, an extension chamber and a first cylinder rod having a first cylinder rod end attached to the other of the first and second mold sections, and at least one clamping cylinder connected to one of the mold sections, the at least one clamping cylinder including a second retraction chamber, a second extension chamber and a second cylinder rod having a second cylinder rod end releasably mounted to the other of the mold sections, the method comprising the steps of: heating the mold set; placing a charge of material to be formed on one of the first and second mold sections; moving one of the mold sections towards the other mold section; actuating the second cylinder rod to meet the one mold section and actuating a lock member to releasably hold the second cylinder rod end to the one mold section; and pressing the mold sections together at a predetermined pressure for a predetermined time to mold the charge of material.

27. The method of claim 26, wherein the step of moving one of the mold sections includes pumping fluid out of the extension chamber and into the retraction chamber of the at least one activation cylinder.

28. The method of claim 26, wherein the charge of material is molded at a force of 75 to 350 psi.

29. The method of claim 26, further comprising the step of: releasing the lock member thereby releasing the second cylinder rod from said one mold section.

30. The method of claim 29 further comprising the step of: moving the one mold section away from the other mold section.

31. The method of claim 30, wherein the step of moving the one mold section away from the other mold section includes evacuating the fluid from the retraction chamber of the activation cylinder and pumping the fluid back into the extension chamber.

32. The method of claim 31 further comprising the step of: removing the formed material.

33. The method of claim 32 further comprising the step of: retracting the clamping cylinder rod thereby increasing accessibility to the formed material.

34. A method of compression molding using an apparatus including a mold set having first and second mold sections, a means to heat the mold set, and at least one activation cylinder mounted to one of the first and second mold sections, the activation cylinder including a retraction chamber and an extension chamber and further including a cylinder rod having a cylinder rod end mounted to the other of the first and second mold sections, the method comprising the steps of: heating the mold set; placing a charge of material to be formed on the one of the mold sections; moving one mold section towards the other mold section; pressing the mold sections together at a predetermined pressure for a predetermined time to mold the charge of material.

35. The method of claim 34, wherein the charge of material is molded at a force of 75 to 350 psi.

36. The method of claim 34, wherein the step of moving the one mold section towards the other mold section includes pumping fluid out of the extension chamber and into the retraction chamber of the at least one activation cylinder.

37. The method of claim 34 further comprising the step of: moving the one mold section away from the other mold section.

38. The method of claim 37, wherein the step of moving the one mold section away from the other mold section includes evacuating the fluid from the retraction chamber of the at least one activation cylinder and pumping the fluid back into the extension chamber.

39. The method of claim 38 further comprising the step of: removing the formed material.