Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
2000-04-12
2002-12-17
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
Reexamination Certificate
active
06495086
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of making a part made of a reinforced plastics material by overmolding a sheet, to a device for implementing the method, and to an assembly and to a production line including said device.
It is already known that single-layer sheets can be used to make parts made of plastics materials and having a certain stiffness, in particular for making structural parts of motor vehicles.
For example, with the material known as stampable reinforced thermoplastic (SRT), which is polypropylene reinforced with glass fibers, the method consists in heating sheets of SRT, then in depositing them in an open mold, and then in closing the mold to cause the plastics material to flow and to fill the cavity of the mold.
It is also known that multi-layer materials can be used that are obtained by superposing sheets of SRT and sheets of Twintex (a trademark of Verotex), Twintex being a woven sheet of commingled glass fibers and polypropylene fibers.
The Twintex sheets become soft during the heating prior to placing the lay-up of superposed sheets in the mold, but the SRT sheets are stiff enough to enable the heated material to be handled.
In contrast, when one or more sheets of Twintex only are to be overmolded, it is difficult to place them in the mold because the heated Twintex sheets are too soft and therefore difficult to handle.
As a result, the only known methods of overmolding sheets of Twintex consist in conveying the sheets horizontally from a heating station to the mold, which mold is mounted on a vertical press so that the portion of it that is to receive the sheet(s) of Twintex is horizontal.
This difficulty of handling heated sheets of Twintex therefore imposes, as a first limit to their being overmolded, the obligation of using molds that are mounted on vertical presses.
In addition, conveying the sheet of Twintex does not enable it to be positioned accurately enough in the mold. As a result, it is preferred to leave a safety margin by cutting the sheet of Twintex larger than necessary so as to make sure that it extends over the entire desired area of the part to be made, even if the edges of the sheet of Twintex that project beyond the periphery of the part then need to be cut off after the part has been molded.
A second limit to overmolding sheets of Twintex lies in the fact that the resulting parts must be trimmed after they have been molded.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method that solves all or some of the above-mentioned problems.
The present invention provides, in particular, a method of making a part made of a reinforced plastics material in a mold comprising at least two portions and from a reinforced sheet or from a lay-up of reinforced sheets comprising at least one reinforced sheet, in which method the reinforced sheet is pre-heated, said method being characterized by the fact that it comprises the following steps:
the reinforced sheet or said lay-up of reinforced sheets is presented to a first portion of the open mold by means of a picking-up device including pressers;
at least a region of the reinforced sheet or of said lay-up is applied against a corresponding region of the first mold portion by means of pressers on the picking-up device;
the remainder of its surface is applied against said first mold portion while holding stationary said region of the reinforced sheet or of said lay-up;
the mold is closed; and
the resulting part is removed from the mold.
In the description below, the term “application portion” is used to designate that portion of the mold against which the reinforced sheet is applied.
The picking-up device may optionally be used to apply the remainder of the surface of the sheet or of said lay-up against the first portion of the mold.
It is possible to superpose a plurality of sheets in the mold, optionally with local reinforcements sandwiched between the sheets.
The above-mentioned region may correspond to at least one edge, and preferably both edges of the reinforced sheet or of said lay-up, or, in a variant, to a central zone.
The method of the invention offers the essential advantage of making it possible to automate positioning of the sheet or of said lay-up.
It can also make it possible to omit the trimming step consisting in cutting off the edges of the sheet or of said lay-up that project beyond the part obtained after overmolding. This is achieved because the edges of the sheet or of said lay-up can be positioned accurately relative to the mold. Once this positioning has been performed, the remainder of the sheet or of said lay-up is applied against the remainder of the first portion of the mold.
Use is thus made of the absence of stiffness of the sheet or of said lay-up to press it against the first portion of the mold, without it projecting from the periphery of the mold.
In a particular implementation, pressers are used that comprise rigid chocks mounted on actuators.
In a variant, a rigid chock comprises a plurality of elements separated by inflatable inserts that space them apart so that the chock hugs the shape of the first mold portion as well as possible.
The pressers may also be constituted by inflatable cases which, in the inflated state, exactly match the shape of the first mold portion.
In order to position it accurately on the first mold portion, the sheet or said lay-up is advantageously retained by needles disposed on the picking-up device.
When sheets and/or local reinforcements are superposed, such needles advantageously serve to hold the various superposed layers in position relative to one another, by being inserted into the lay-up.
Preferably, the needles are mounted on the same support as the pressers.
In a particular implementation, the needles are substantially parallel to the direction in which the mold closes.
Preferably, certain needles may be suitable for moving sideways to accommodate the deformations of the sheet or of said lay-up, when said sheet or said lay-up adapts its surface to fit the real surface of the application portion of the mold.
This adaptation may also be referred to as “draping”, the initial surface of the sheet or of said lay-up being plane and corresponding to the developed surface area of the application portion of the mold, while the final surface of the sheet or of said lay-up has all of the relief of the application portion of the mold.
The needles mounted to move sideways are particularly useful when the sheet or said lay-up is not pre-shaped to the relief of the first portion of the mold.
In order to preform the sheet or said lay-up, it is possible, in a particular implementation, to deposit it on a rack of suitable shape and to heat it, e.g. by inserting it in an oven.
Pre-forming the sheet or said lay-up may further be supplemented prior to being put in place in the mold, by acting on the sheet or said lay-up at an intermediate station lying between the place at which the sheets are picked up and the mold.
In a particular implementation, the mold has a join plane that is substantially vertical.
The picking-up device may be carried by a manipulator arm which exerts the mechanical forces necessary to apply the sheet or said lay-up against the first portion of the mold.
In a variant, the picking-up device may be pulled towards the first mold portion to press the sheet or said lay-up thereagainst by means of a base mounted to move relative to the first mold portion.
This makes it possible to relieve the manipulator arm and to use a manipulator arm that is less powerful and therefore less costly.
Advantageously, abutments mounted to move relative to the base are used to entrain the picking-up device, these abutments being disposed to come into engagement over the picking-up device when the base is in the “out” position, and then remaining in place when the base is displaced to pull on the picking-up device.
In a particular implementation, the sheet or said lay-up is overmolded as applied against the first mold portion, i.e. a complementary quantity of plastics material is inserted i
Blanchon Charles-Guillaume
Charpy Robert
Chene Anthony
Uytterhaeghe Luc
Compagnie & Plastic Omnium
Oliff & Berridg,e PLC
Tentoni Leo B.
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