Method and Apparatus for Compression Molding Under Vacuum

1. Technical Field

This invention relates to molding apparatus and, more particularly, apparatus for compression molding a part under vacuum.

2. Discussion

Commonly-assigned U.S. Pat. Nos. 4,488,862 to Epel et al.; 4,551,085 to Epel et al.; 4,612,149 Iseler et al. disclose methods and apparatus wherein parts are compression molded under vacuum. These patents are hereby incorporated by reference. The present invention is an improvement to the subject matter disclosed in these prior patents.

According to the broad teachings of this invention, provision is made for assisting the separation of the mold members which have been temporarily sealed together to define a vacuum chamber around the mold cavity. In the preferred embodiment, a sealing ring surrounds the upper die and it makes a seal with a fixed lower member surrounding the lower die. The ring also contains a seal which makes wiping engagement with the upper 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. The vacuum created during the molding operation tends to make it difficult to break the seal when it is later desired to open the molding apparatus and remove the part. To facilitate this process, one or more kicker cylinders are provided which thrust upwardly against the sealing ring to thereby break the seal between the upper and lower die. In such manner, quicker part cycle times can be achieved.

These and various other advantages of the present invention will become apparent to those skilled in the art upon studying the following specification and by reference to the drawings in which:

FIGS. 1-3 are side views of molding apparatus made in accordance with the teachings of this invention, with portions thereof shown in cross section, during various stages of the molding operation;

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 (exceeding about 1 square foot) which must have extremely smooth finishes. The piston rods 64 of the kicker cylinder 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 FIGS. 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 FIG. 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 FIG. 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 FIG. 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.

It should be understood that while this invention has been described in connection with a particular example thereof, that no limitation is intended thereby except as defined in the following claims.