Mold element retaining and releasing mechanism

Details Mold element retaining and releasing mechanism Mold element retaining and releasing mechanism

1999-04-21

2001-12-04

Pyon, Harold (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

With apparatus assembly or dismantling means or with idle part

For extrusion or injection type shaping means

C425S4360RM, C425S444000, C425S810000

Reexamination Certificate

active

06325614

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method and system for retaining a replaceable mold element in place on a molding machine. More specifically, the present invention relates to a retaining and releasing mechanism and actuation system located in a mold half which can engage spigots of various sizes and designs that are attached to a mold element. Preferred embodiments are disclosed in detail wherein a CD or DVD stamper plate or a CD or DVD mold half are retained in an accurate and secure operative position on a molding machine. This method and system allows exchange of a mold element for another in a novel and effective manner.
BACKGROUND OF THE INVENTION
In the manufacture of a wide variety of molded articles it is desired to change one or more elements of a mold from time to time for production changes and/or maintenance purposes. Conventionally, mold elements such as mold inserts, the mold cavity and/or the mold core plates have been retained in place on the mold machine via manually activated retaining and releasing means such as bolts, etc. While such means provide good mechanical strength and can be inexpensive to employ, mold elements retained by them are generally not easily or quickly removed from the mold machine.
The use of conventional fasteners is especially problematic in the molding of articles which require frequent and/or prompt removal and replacement of one or mold elements. For example, in molding automotive bumpers, an element in a mold may need to be changed during a production run to allow different configurations of the bumper to be molded as necessary. A standard bumper may be molded for the majority of cars but an optional lighting package may require that the bumpers molded for some cars include receptacles for fog lamps, or the like. With conventional means of retaining the mold elements, changing the mold elements to allow production of the bumper for optional lighting packages can be onerous and/or time consuming.
The mold element that has to be changed rapidly can be the entire mold, or just one mold half. Reference is made in this regard to the U.S. Pat. No. 5,486,101 to Guyon that shows a mold clamping mechanism including a transverse cylinder and a wedge that interacts with a peg attached to the mold half to be retained. The mold half is thus removable connected to an injection molding machine platen. Unfortunately, the design of Guyon requires a lot of space due to the fact that the cylinder is in a transverse position in order to move the wedge laterally with respect to the peg. Also, if many changes of the mold half are required, the working surfaces of the wedge and of the peg can be worn out due to the high friction they are exposed to in use. This can cause the peg to become loosely connected to the machine platen after a certain time. Therefore the design concept of Guyon is not applicable to applications which require many changes and which require accurate positioning, such as the retention of the stamper plate in a CD mold. The stamper plate has to be replaced very fast, accurately and typically tens of times during a 24 hours manufacturing cycle.
Information carrier articles such as CDs (compact discs) or DVDs (digital versatile discs) are typically molded in a three part mold, comprising a stationary mold plate, a movable mold plate and a stamper plate. The stamper plate is a removable mold element which is maintained in the mold cavity formed between the stationary and the movable mold plates. The stamper is a plate-like disc element with upstanding bosses responsible for forming the encoded digital information carrier pits in the molded final article. Each time a different information title is to be molded, the stamper is changed appropriately.
The technical and patent literature disclose several ways to retain the stamper plate in a CD mold. The first way is to hold directly the stamper plate using vacuum or magnetic clamping means as shown for example in the U.S. Pat. No. 5,552,098 to Kudo and more recently in the U.S. Pat. No. 5,612,062 to Takahashi. The second way is to use a central holder attached to the stamper plate that is retained using either mechanical means or vacuum means. U.S. Pat. No. 5,116,210 of Watanabe et al. shows the mechanical approach and U.S. Pat. No. 5,297,951 of Asai shows the vacuum approach. A third way is to use a combination of the direct and the central holding means. The direct means can be a ring pressing the outer diameter of the stamper plate which is employed with a central holding means. This combined approach is disclosed amongst other in the U.S. Pat. No. 4,917,833 of Cools and U.S. Pat. No. 5,297,951 of Asai.
While under ideal circumstances the run size of each information title is sufficiently large to mitigate the frequency with which the stamper must be changed (to, for example, once a day), often this is not the case and it is desired to change a stamper several times a day. In most instances the stamper plate is changed using manual means to release the central holder, as shown in the U.S. Pat. No. 5,116,210 of Watanabe, U.S. Pat. No. 5,466,145 of Takahashi and more recently in the U.S. Pat. No. 5,607,705 of Asai. In other instances, automatic means are used to release the stamper plate from the outer ring as shown in U.S. Pat. No. 4,917,833 of Cools.
In addition to the inconvenience of frequent stamper changes, such systems are very slow and thus suffer from the problem that the resin used to mold the information carriers undergoes an undesired crystallisation when it remains in the hot runner of the molding machine for more than a short period of time. Thus, as the change of the stamper in systems such as that shown in the above-mentioned Watanabe, Takahashi, and Asai references can take a significant time to accomplish, the crystallised resin must be purged from the mold machine after each stamper change. This results in a significant amount of waste material and additional manufacturing down time. In addition, a dedicated person is required to select the new stamper plate and to handle the removal and storage of the previous stamper plate and the loading of the new stamper plate.
Previous attempts have been made to address this problem. In this regard, reference is made to Swiss Patent CH 663 929 to Muller et al., the U.S. Pat. No. 5,374,177 to Hehl, PCT publication WO/94/19166 to De Graaf and the Japanese Patent 62-286717 to Shuji et al. While both Muller and De Graaf show known spigot means, robotics systems and stamper storage magazines used during the stamper change process, all of these patents fail to teach enabling designs of the mold itself and, more importantly, fail to teach the actual means used to retain the stamper plate.
Attempts have been made in the past to provide systems for changing a mold element such as a stamper plate in an efficient manner by improving the retaining and releasing means of the stamper plate. For example, U.S. Pat. No. 4,789,320 to Sasamura et al. assigned to the assignee of the present invention and U.S. Pat. No. 4,917,833 to Cools teach an all mechanical stamper plate retention means employing a central spigot attached to the stamper plate and an outer ring independent to the stamper plate that is used to hold the periphery of the stamper disc. In both embodiments, the outer ring has to be firstly disengaged prior to releasing the stamper plate and the spigot from the mold in order to change it.
More specifically, Cools shows a spring based stamper releasing mechanism comprising in the mold half a movable thrust plate connected to a ball bushing. This ball bushing further comprises several circumferential bores wherein balls are located to engage changer sleeve through the annular groove adapted to catch the balls. An outer bushing also has groove adapted to release the balls when they come in alignment. To retain the stamper plate and its support, thrust pins attached to the thrust plate are pushed backward by a guard ring. The guard ring remains attached to the mold plate in the molding position. To replace the stamp

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