Vacuum molding apparatus

Abstract: Kicker cylinders (62) are used in a vacuum compression molding apparatus to initially break the seal between two members (14, 20) of the mold in order to facilitate quick opeing of the mold to thereby increase part cycle time.

Description: The invention relates to a vacuum molding apparatus having a pair of mold members moveable relative to each other under the action of a ram, the apparatus including a sealing ring surrounding one of the mold members that is in sealing engagement therewith and carries a second seal for creating a sealed vacuum chamber around the two mold members thereby enabling a vacuum to be formed between the mold members during molding of the part. Such vacuum molding apparatus used for compression molding of parts under vacuum are described in US-A-4 488 862, 4 511 085, and 4 612 149. With such an apparatus a sealing ring surrounds the upper die and it makes a seal with a fixed lower member surrounding the lower die. When the upper die is lowered into place the seal between the lower die and upper die is made before the upper die contacts the charge. Thus, a vacuum chamber is defined around the mold cavity. A vacuum is then drawn and the upper die proceeds downwardly to cooperate with the lower die to define and cure the part. It has been found that is is sometimes desireable to maintain the mold cavity under vacuum until the part has cured and the dies are ready to open. Under these circumstances, the vacuum created during the molding operating has been found to make it difficult to break the seal when it is later desired to open the molding apparatus and remove the part. It is the object of the invention to assist the separation of the mold members which have been temporarily sealed together to define a vacuum chamber around the mold cavity. This object is achieved with the vacuum molding apparatus of the generic kind by separating means positioned around the second mold member and being separate from the sealing ring and the ram, and means for activating said separating means such that the separating means pushes away the sealing ring to thereby break the sealed vacuum chamber after the part has been formed. Preferably said seperating means comprises at least one kicker cylinder having a reciprocating piston rod aligned with a portion of the sealing ring, said kicker cylinder being activated to cause the piston rod to force the sealing ring away from the other member to thereby break the seal therebetween. Conveniently said sealing ring has a wiping seal device mounted thereon providing a wiping seal against one of said members, said seal device including a housing for carrying a resilient seal, and adjustment means for horizontally adjusting the position of the seal relative to the housing thereby adjusting for wear of the seal to ensure a good sealing engagement with the mold member. The said seal wipes against an outer side surface of one of the members, with the seal housing including a threaded bore therein for receiving an adjustment screw accessible for adjustment by an operator. Advantageously the said sealing ring includes a plurality of air cylinders normally causing piston rods thereof to be fully extended, and wherein the kicker cylinders provide sufficient force to partially retract the piston rods of the sealing ring cylinders during breaking of the seal. Usually said kicker cylinders are hydraulic cylinders and the cylinders of the sealing ring are air cylinders. If the apparatus is used for compression molding a charge into a part, it comprises preferably a moveable upper die; a sealing ring surrounding the upper die, said sealing ring having a plurality of first cylinders having normally downwardly extending piston rods the ends of which carry a first sealing device making wiping sealing engagement with an outer side surface of the upper die, the ends of the piston rods further carrying a second seal; a lower die cooperating with the upper die to form a mold cavity in the shape of the desired part; ram means for moving the upper die and sealing ring downwardly until the second seal abuts a fixed member surrounding the lower die thereby defining a vacuum chamber encompassing the mold cavity; vacuum means for evacuating the vacuum chamber; said ram means being further adapted to continue downward movement of the upper die until the mold cavity is defined; and kicker cylinder means surrounding the lower die and being vertically in line with a portion of the sealing ring, said kicker cylinder means having piston rods that raise upwardly to overcome the force of the sealing ring cylinders to thereby break the seal provided by the second seal after the part has been formed thereby facilitating quick opening of the mold. The method of compression molding a part according to the invention comprises the steps of placing a charge on a lower die of a compression molding apparatus; using a ram to move an upper die into a position wherein a seal is made between the upper and lower dies; creating a vacuum; forming the part; and using a plurality of kicker cylinders to break the seal between the upper and lower die so that the dies can be quickly opened. Preferably the kicker cylinders are activated to break the seal before the ram is used to lift the upper die during opening of the mold. With the method according to the invention an automotive body panel can be formed having a surface area exceeding 0,1 m² (1 ft²). The invention is further explained with the aid of drawings in which Fig. 1 is a partly cross-sectioned side views of the vacuum molding apparatus with open dies, Fig. 2 shows in the side view of Fig. 1 the apparatus with closed dies, Fig. 3 shows in the side view of Fig. 1 the apparatus in a stage between open and closed dies, Fig. 4 is a plan view looking down on a portion of the wiping seal shown in Fig. 3, and Fig. 5 is a cross-sectional view taken along the lines 4-4 of Fig. 4. Fig. 1 essentially shows the molding apparatus 10 as it would appear during the beginning and ending of the part cycle. The only major difference is that part 12 shown in Fig. 1 would not yet have been formed during the beginning part of the cycle but instead it would be replaced with a suitable charge of fiber-reinforced plastic from which the part is formed. As discussed in the above-referenced patents, the present invention finds particular utility in forming automotive body panels having large surfaces which exceed about 1 ft² (0,1 m²) and which must have extremely smooth finishes. The piston rods 64 of the kicker cylinders 62 would also be retracted instead of extended as shown in Fig. 1 at the beginning of the part cycle. More will be said about the kicker cylinders later herein. In the beginning of the molding cycle the upper die 14 and sealing ring 16 are moved downwardly under the operation of a suitable ram 18 towards the lower die 20. The sealing ring 16 includes several air cylinders 22 connected at their upper ends via brackets 24 to upper die 14 and, hence, to ram 18. The cylinders 22 include depending piston rods 26 which are substantially fully extended during the beginning of the part cycle under the constantly applied air pressure to the cylinders. The lower end of the piston rods 26 are coupled to an annular tubular member 28 which presents a lower surface 30 and upper surface 32. Attached to the upper surface 32 is a sealing device 34 shown most clearly in Figures 4 and 5. Sealing device 34 includes a housing 40 having an inner edge 36 spaced from the outer side wall 38 of the upper die 14. The housing 40 has a horizontally extending threaded bore 42 therein for receiving adjustment screw 44. The inner end of adjustment screw 44 is mounted to a Teflon wiper seal 46 designed to make a wiping sealing engagement with the smooth vertical wall 38 of the upper die 14. As the seal 46 wears, the operator can overcome this wear by suitably rotating adjustment screw 44 to maintain the proper engagement between the seal 46 and walls of upper die 14. The lower surface 30 of member 28 carries an annular tubular seal 50 which is aligned with an annular member 52 fixed to the lower die 20. As the ram 18 brings the upper die 14 and sealing ring 16 downwardly, the seal 50 first becomes in contact with the upper surface of member 52. A vacuum chamber is thus formed that surrounds the mold cavity which shall later be more precisely defined when the upper and lower dies fully nest. The vacuum chamber which is generally designated by the numeral 54 in Figure 2 is defined by the seal 50 between the upper and lower die, and the seal 46 between the ring 16 and upper die 14. This vacuum chamber 54 is formed before the upper die 14 touches the charge (not shown) lying on the lower die 20. At this time a vacuum is quickly drawn from the vacuum chamber through a suitable vacuum source 55 which communicates with vacuum chamber 54 through the hollow tubular member 52 and openings 56 therein. The ram 18 continues its downward movement to bring the dies into the position shown in Figure 2 wherein the stops 58, 60 come into contact. It should be noted that the piston rods 26 retract into their respective cylinders 22 as a result of the further downward movement of the upper die 14, the large force of ram 18 overcoming the much smaller force provided by the air pressure in cylinders 22. After the part has been sufficiently formed (e.g., by sufficient heat, time and pressure to cure the charge), the mold must be opened to enable the part to be removed. It is a feature of this invention that the mold can be opened very quickly and with a minimal amount of maintenance problems that might otherwise occur. By doing so, the part cycle time can be kept to a minimum thereby increasing the throughput for a given machine. To this end, a plurality of kicker cylinders 62 are provided to enhance quick opening of the mold members. Cylinders 62 are preferably spaced substantially equally around the mold 10 underneath the sealing ring 16. Each cylinder 62 has its piston rod 64 vertically aligned with an apron portion 66 of the sealing ring 16. With special reference to Figure 3, cylinders 62 are designed to provide an upward thrust or "kick" which is sufficient to overcome the downward pressure provided by cylinders 22 and the additional adhesion of seal 50 created by the vacuum. In this specific embodiment, the cylinders 62 are hydraulic and are activated at the beginning of the mold opening step before ram 18 begins lifting. In such manner the seal between the upper and lower dies is first broken. Otherwise, the ram 18 must overcome the vacuum seal between the dies that has been created. By first using the kicker cylinders 62 to break the seal, the ram 18 can be raised very quickly thereby increasing the part cycle. After the part 12 has been removed, the kicker piston rods 64 are retracted and a new part cycle can be begun.

Claims: A vacuum molding apparatus having a pair of mold members (14, 20) moveable relative to each other under the action of a ram (18), the apparatus including a sealing ring (16) surrounding one of the mold members (14) that is in sealing engagement therewith and carries a second seal (50) for creating a sealed vacuum chamber around the two mold members (14, 20) thereby enabling a vacuum to be formed between the mold members (14, 20) during molding of the part, characterized by separating means (62, 64) positioned around the second mold member (20) and being separate from the sealing ring (16) and the ram (18), and means for activating said separating means (62, 64) such that the separating means (62, 64) pushes away the sealing ring (16) to thereby break the sealed vacuum chamber after the part (12) has been formed. An apparatus according to claim 1 characterized in that said separating means comprises at least one kicker cylinder (62) having a reciprocating piston rod (64) aligned with a portion of the sealing ring (16), said kicker cylinder (62) being activated to cause the piston rod (64) to force the sealing ring (16) away from the other member (20) to thereby break the seal therebetween. An apparatus according to claim 1 or 2 characterized in that said sealing ring (16) has a wiping seal device (34) mounted thereon providing a wiping seal against one of said members (14), said seal device (34) including a housing (40) for carrying a resilient seal (46), and adjustment means (42, 44) for horizontally adjusting the position of the seal (46) relative to the housing (40) thereby adjusting for wear of the seal (46) to ensure a good sealing engagement with the mold member (14, 20). An apparatus according to claim 3 characterized in that the seal (46) wipes against an outer side surface (38) of one of the members (14), with the seal housing (40) including a threaded bore (42) therein for receiving an adjustment screw (44) accessible for adjustment by an operator. An apparatus according to one of the claims 1 to 4 characterized in that said sealing ring (16) includes a plurality of air cylinders (22) normally causing piston rod (26) thereof to be fully extended, and wherein the kicker cylinders (62) provide sufficient force to partially retract the piston rods (26) of the sealing ring cylinders (22) during breaking of the seal. An apparatus according to one of the claims 1 to 5 characterized in that said kicker cylinders (62) are hydraulic cylinders and the cylinders (22) of the sealing ring (16) are air cylinders. An apparatus according to one of the claims 1 to 5 used for compression molding a charge into a part, said apparatus comprising a moveable upper die (14) a sealing ring (16) surrounding the upper die (14), and sealing ring (16) having a plurality of first cylinders (22) having normally downwardly extending piston rods (26) the ends of which carry a first sealing device (46) making wiping sealing engagement with an outer side surface (38) of the upper die (14), the ends of the piston rods (26) further carrying a second seal (50); a lower die (20) cooperating with the upper die (14) to form a mold cavity in the shape of the desired part (12); ram means (18) for moving the upper die (14) and sealing ring (16) downwardly until the second seal (50) abuts a fixed member (52) surrounding the lower die (20) thereby defining a vacuum chamber (54) encompassing the mold cavity; vacuum means for evacuating the vacuum chamber (54); said ram means (18) being further adapted to continue downward movement of the upper die (14) until the mold cavity is defined; and kicker cylinder means (64) surrounding the lower die (20) and being vertically in line with a portion of the sealing ring (16), said kicker cylinder means (64) having piston rods (62) that raise upwardly to overcome the force of the sealing ring cylinders (22) to thereby break the seal provided by the second seal (50) after the part (12) has been formed thereby facilitating quick opening of the mold. A method of compression molding a part with an apparatus according to one of the claims 1 to 7 characterized by placing a charge on a lower die (20) of a compression molding apparatus (10); using a ram (18) to move an upper die (14) into a position wherein a seal is made between the upper and lower dies (14, 20); creating a vacuum; forming the part (12); and using a plurality of kicker cylinders (62) to break the seal between the upper and lower die (14, 20) so that the dies (14, 20) can be quickly opened. The method of claim 8 characterized in that the kicker cylinders (62) are activated to break the seal before the ram (18) is used to lift the upper die (14) during opening of the mold (10). The method of claim 8 or 9 characterized in that an automotive body panel is formed having a surface area exceeding 0,1 m².

Inventors: HAMNER JAMES RICHARD, SCHILKEY DANIEL PATRICK, HAMNER, JAMES RICHARD, SCHILKEY, DANIEL PATRICK
Applicants: BUDD CO, THE BUDD COMPANY
Application year: 1989
Main classification: B29C43
IPC codes: B29C43, B30B11