EP3086913A2

EP3086913A2 - Membrane-assisted preforming of plastic semi-finished product

Info

Publication number: EP3086913A2
Application number: EP14833518.5A
Authority: EP
Inventors: Damien BOISSON; Emilien HUMMER
Original assignee: Plastic Omnium SE
Current assignee: Plastic Omnium SE
Priority date: 2013-12-24
Filing date: 2014-12-22
Publication date: 2016-11-02
Also published as: WO2015097397A3; CN106132657A; FR3015339A1; FR3015339B1; US20170001339A1; WO2015097397A2

Abstract

Process for preforming a semi-finished product (SP) made of plastic, in which: at least one anti-adhesive membrane (PM) is positioned facing a wall of a preforming mould (MP); the plastic semi-finished product (SP) is positioned facing the anti-adhesive membrane (PM), so that the anti-adhesive membrane (PM) is positioned between the semi-finished product (SP) and the wall; pressure is applied in order to press the semi-finished product (SP) against the wall of the preforming mould (MP), in order to give a shape to the semi-finished products (SP); the pressure ceases to be applied and the thus preformed part (PF) is injected from the wall; and the thus preformed part (PF) is removed from the mould.

Description

Preforming of plastic semi-finished product with membranes

The invention relates to the field of manufacturing composite materials by molding processes employing closed molds.

In particular, the invention relates to a method of preforming a semi-finished plastic product used to manufacture a plastic product.

In the automotive field for example, many parts must combine mechanical strength and low weight.

To do this, it is known to replace steel parts by plastic parts, thermosetting or thermoplastic.

Various molding processes of plastic parts are known:

• compression process (for thermosetting materials such as SMC);

• thermoforming process (compression with a thermoplastic material);

· Injection process (for thermoplastics).

• Resin transfer process (RTM)

It is known to use reinforced plastics (thermosetting or thermoplastic). These materials consist of reinforcing fibers mixed with a polymer resin. These reinforcements comprise glass or carbon fibers, for example. These fibers can be cut or continuous.

Depending on the plastics used and the molding process used, it may be necessary to preform the part by preforming the semi-finished product before it is introduced into the production mold.

For example, it is known to use SMC with a high degree of reinforcement, especially greater than or equal to 50% by weight, to manufacture semi-structural composite parts.

However, since these SMC flanks are more loaded with fiber than conventional SMC flanks, the plastic (resin) flows less well into the manufacturing mold. There is therefore a need to preform these flanks of SMC to make pieces of complex shapes. Thus, between the cutting of the sidewall of SMC and the molding to obtain the finished part, a step of preforming the sidewall of SMC is introduced.

The preforming consists in giving a rough shape to the semi-finished product by means of a specific equipment, different from the equipment necessary for molding the finished part. For example, the preforming equipment does not necessarily incorporate the definitive shapes of the part, unlike the manufacturing mold. Moreover, the preforming equipment usually operates under conditions of pressure, temperature, and time different from those used for molding the finished part. For example the temperature for the preforming of the preform is less than that used during the molding of the finished part. Due to a lower temperature than in the manufacturing mold, there is no creep or polymerization of the resin.

Various preforming techniques are known. For example, a preforming process known as "vacuum preforming" is known. This process uses a membrane, called a vacuum tarpaulin, placed on the side of SMC. Then the air is evacuated, resulting in the plating of the sheet against the wall of the mold, bringing with it the side of SMC placed between the sheet and the mold.

Another known method of compression preforming (called cold stamping) in which a semi-product made of plastic material is placed in punch-die type preforming equipment. Then the equipment is closed to apply pressure on the semi-product, while remaining at a moderate temperature, such as the ambient temperature.

However, whatever the method used, this preforming step has a major disadvantage: the preform adheres to the surface of the preforming means after shaping. This adhesion makes it difficult for the robot to pick up the preform and insert it into the manufacturing mold. This adhesion makes it difficult to eject the preform out of the mold. In addition, this adhesion causes a fouling of the preforming means.

Finally, in the case of preforming by means of punch-die type equipment, the SMC flank may tear.

The object of the invention is to remedy these drawbacks by providing a method for preforming a semi-finished product made of plastic material, in which non-stick membranes are inserted between the semi-finished product and the mold walls. The method according to the invention thus comprises the following steps:

at least one nonstick membrane is arranged opposite a wall of a preform mold;

the semi-product made of plastic material is placed opposite the non-stick membrane, so that the release membrane is positioned between the semi-finished product and the wall;

applying a pressure to press the semi-product against the wall of the preforming mold, to give a shape to the semi-finished product;

the pressure is stopped and the preformed part is ejected from the wall ; and

the mold thus preformed is removed from the mold.

By interposing membranes between the mold and the semi-product, it prevents the preformed semi-product from adhering to the walls of the preform mold.

Finally, the use of membrane according to the method makes it possible to limit the damage of the preforms during compression.

It is also possible to use spare membranes to clean or repair used membranes without mobilizing the preform mold.

Preferably, the release membrane is nonstick vis-à-vis the wall of the preform mold and vis-a-vis the semi-product.

The membrane may contain silicone and / or stearates and / or fatty substances and / or maleic anhydrides.

The part thus preformed can be ejected from the wall of the mold by detaching the membrane from the wall.

For example, the membrane can be peeled off the wall by applying a pressure between the membrane and the wall. It is also possible to detach the membrane from the wall by reshaping the membrane.

According to one embodiment, the air gap is produced between the membrane and the wall before closing the mold in order to press the membrane on the wall, then the membrane is taken off the wall by reintroducing air between the membrane. and the wall.

The membrane may be flat or have the shape of the wall.

According to one embodiment, a punch-die type preform mold is used, the first membrane being located between the semi-finished product and a first wall of the mold, and a second non-stick membrane being located between the semi-finished product and a second wall of the mold.

The second membrane may contain silicone and / or stearates and / or fatty substances and / or maleic anhydrides.

According to one embodiment, the temperature inside the preforming mold is the ambient temperature.

Finally, according to the invention, a thermosetting material of the SMC type can be used as a plastic material.

The invention will be better understood on reading the appended figures, which are provided by way of examples and are in no way limiting, in which:

FIG. 1 illustrates, for a first embodiment, the introduction into the preforming mold (MP) of the semi-finished product (SP) made of plastic material and a release membrane (PM).

FIG. 2 illustrates, for a second embodiment, the introduction into the mold preforming (MP) of the semi-finished product (SP) made of plastic material and the two non-stick membranes (PM, SM).

FIG. 3 illustrates the closed state of the preforming mold (MP), when the punch (PO) presses the die (MA).

Figure 4 illustrates the opening start of the preform mold (MP).

Figure 5 illustrates the preform (PF) output of the preform mold (MP).

FIG. 6 illustrates the embodiment in which the preformed part (PF) is ejected from the matrix (MA) by detaching the first membrane (PM) from the matrix (MA). Referring now to Figure 1 which describes the various steps of the method according to the invention. This method of preforming a semi-finished product (SP) made of plastic material comprises the following steps:

at least one nonstick membrane (PM) is arranged opposite a wall of a preforming mold (MP);

the semi-finished product (SP) is placed in plastic material facing the non-stick membrane (PM), so that the release membrane (PM) is positioned between the semi-finished product (SP) and the wall;

a pressure is applied to press the semi-finished product (SP) against the wall of the preforming mold (MP), to give a shape to the semi-finished product (SP);

the pressure is stopped and the part (PF) thus preformed is ejected from the wall; and

the part thus preformed and called the preform (PF) is removed from the mold.

The nonstick membrane (PM) is attached to a membrane support (SU). It can be a frame to which the membrane is fixed (by means of metal eyelets for example).

This support (SU) can be fixed on the mold. It can also be mobile vertically and / or horizontally. The support (SU) can for example be mounted on moving means, to be moved. Thus during production, it is possible to load the frame with a semi product (SP) and a membrane, while the mold preforms another sidewall of semi-product (SP). When the mold is opened, or when the air gap has stopped under the vacuum cover, the support is moved so as to remove the preform on the membrane from the mold. Another support comprising a semifinal flank and a membrane is then taken to introduce the semi-finished product and the membrane into the mold.

The release membrane (PM) may be arranged facing the wall of the preforming mold (MP) at each molding cycle, either on a fixed support to the mold, or on a mobile support.

In a preferred embodiment, the release membrane (PM) is permanently positioned on or above the wall of the mold.

The non-stick membrane (PM) can be introduced into the mold (MP) with a flat shape. It is then deformed during pressurization (closure of the mold or when an air gap is applied).

The release membrane (PM) can also be introduced into the mold (MP) having the same shape as that of the wall of the mold with which it is in contact.

According to a first embodiment (FIG. 1), a "vacuum preforming" method is used, in which the pressure is applied by carrying out the vacuum under a tarpaulin (BV) placed against the semi-finished product on the side opposite to the wall of the mold, so that the tarpaulin slates the semi-product against the wall of the mold. According to this embodiment, the pressure is ceased by ceasing the vacuum.

FIG. 1 illustrates the introduction into the preforming mold (MP) of the semi-finished product (SP) made of plastic material and the non-stick membrane (MP).

According to a second embodiment (FIGS. 2 to 5), a "compression preforming" method is used in which the pressure is applied by closing the punch-die mold. According to this embodiment, the pressure is stopped by opening the punch-die type mold.

According to this embodiment, it is also preferable to use a second membrane (SM) insofar as each face of the semi-product is in contact with a wall of the mold: the first membrane (PM) being located between the semi-product product (SP) and a first wall (PO) of the mold (MP), and the second non-stick membrane (SM) being located between the semi-finished product (SP) and a second wall (MA) of the mold (MP).

The compression preforming method according to this second embodiment thus comprises the following steps:

at least the first non-stick membrane (PM) is arranged opposite the punch (PO) of the preforming mold (MP);

at least the second nonstick membrane (SM) is arranged facing the matrix (MA) of the preforming mold (MP);

the semi-finished product (SP) is placed in plastic material opposite the two non-stick membranes (PM, SM), so that the semi-finished product (SP) is inserted between the two membranes (PM, SM);

the preforming mold (MP) is closed;

the mold is opened and the piece (PF) thus preformed is ejected; and the part thus preformed and called the preform (PF) is removed from the mold.

Figure 2 illustrates the introduction into the preform mold (MP) of the plastic semi-finished product (SP) and the two non-stick membranes (PM, SM).

According to a variant of the second embodiment, the second membrane (SM) is introduced into the mold permanently.

The second non-stick membrane (SM) is also attached to a membrane support (SU) of the same type as that of the first membrane (PM).

The second non-stick membrane (SM) can be inserted between the wall of the preform mold (MP) and the semi-finished product (SP) at each use of the mold, either on a fixed support to the mold or on a mobile support.

In a preferred embodiment, the second non-stick membrane (SM) is permanently positioned in the mold.

The second non-stick membrane (SM) can be introduced into the mold (MP) with a flat shape. It is then deformed during pressurization (closing of the mold).

The second release membrane (SM) can also be introduced into the mold (MP) in the same shape as the wall of the mold with which it is in contact.

Figure 4 illustrates the opening start of the preform mold (MP).

Figure 5 illustrates the preform (PF) output of the preform mold (MP).

A preform mold (MP) is an equipment comprising a fixed matrix (MA) and a movable punch (PO). Such a mold does not necessarily include a heating element, insofar as it is not a question of molding the finished part, but of forming a preform intended to be introduced into a manufacturing mold.

The PM and SM membranes have a percentage of elongation allowing them to conform to the shapes of the mold.

The use of membrane having the capacity to lengthen when subjected to the same constraints as the semi-product in the preforming equipment makes it easier to demold the preform, allowing the part to be ejected after opening. of the mold.

Preferably, the MP membrane has a return elasticity, allowing it to resume its original shape.

PM and SM membranes are nonstick membranes for preforming temperatures and semiproduct (SP) materials. These temperatures are generally between 0 ° C and 150 ° C, preferably between room temperature and 100 ° C, and more preferably between room temperature and δΟ 'Ό). So :

these membranes do not adhere to the walls of the mold;

these membranes do not adhere to the semi-finished flank.

Adhesion is the set of physico-chemical phenomena that occur when two materials are brought into intimate contact, to create a mechanical resistance to separation. Once the contact is established, the energy needed to achieve the separation is called adhesion energy.

In a manner known per se, adhesion is governed by four types of phenomena: physical, mechanical, chemical and diffusive.

Thus, the specialist knows, depending on the semi-product used and the material forming the wall of the mold, to determine a material to meet this non-stick need.

For example, membranes (PM, SM) containing silicone can be used in the process according to the invention, because they are known for their non-stick properties with respect to plastic resins and plastic preform molds.

These membranes may also contain, as non-sticking agent, stearates, fatty substances (soaps, etc.), maleic anhydrides, etc.

According to an exemplary embodiment, the membranes are silicone membranes having a thickness of 1 mm and 5 mm.

According to a third embodiment, the PM membrane is used to eject the preform (PF) from the mold (MP), as illustrated in FIG. 6 for the second embodiment.

Thus, according to this embodiment, the method comprises a step during which the matrix (MA) is ejected from the preformed part (PF) by detaching the PM membrane from the matrix (MA). In Figure 6 it is observed that the first membrane (PM) is detached from the matrix (MA), ejecting the preform (PF).

According to an exemplary embodiment, the membranes are membranes containing silicone and having an elongation percentage of between 100 and 800%.

This PM membrane can be detached from the wall of the mold by applying a pressure between the membrane (PM) and the wall (MA, PO) with which it is in contact.

The pressure can be applied by local ejectors, the membrane then distributing the forces applied by these ejectors.

The pressure can also be applied by injecting a gas, such as air, between the mold wall and the PM membrane. Due to its elastic property, the membrane hangs, ejecting the preform from the mold.

This membrane (PM) can also be detached from the matrix (MA) by recovering the shape of the first membrane (PM). The PM membrane must also have the following property: a return to rest of the membrane allows the membrane to return to its original shape. Elastomeric, silicone or latex membranes are membranes having this property.

According to a variant of this embodiment, the air gap is produced between the first membrane (PM) and the matrix (MA) before closing the mold (MP). Unlike the air vacuum preforming method, it is not a matter of deforming the semi-product (SP) to be preformed. This operation is intended to press the first membrane (PM) on the matrix (MA), thus preventing the piece from sticking to the mold. In this variant of the invention, this operation also makes it possible to predict the ejection of the preform (PF). Indeed, after opening the mold, the first membrane (PM) is removed from the matrix (MA) by reintroducing air between the first membrane (PM) and the matrix (MA).

According to one embodiment, and depending on the type of semi-product (SP) of plastic material, there is kept inside the preforming mold (MP) an ambient temperature during the preforming of the part.

The semi-product (SP) made of plastic material may be of thermoplastic material or thermosetting material. For example, it may be thermosetting material type SMC.

According to a preferred mode of preform production, the following steps are carried out:

i. a loading plan is made outside the mold, by stacking at least a semi-product and a first non-stick membrane (PM) on a mobile support;

ii. introducing the semi-finished product and the first non-stick membrane (PM) by moving the support, so that the first non-stick membrane (PM) is positioned between one of the mold walls and the semi-finished product;

iii. a second non-stick membrane (SM) is permanently disposed between the other movable wall of the preforming mold (MP) and the semi-finished product; iv. the preforming mold (MP) is closed, and at least part of a new loading plan outside the mold is simultaneously produced on a second support (a new loading plan is made at least partially in masked time of the molding) ;

v. the mold is opened and the piece (PF) thus preformed is ejected;

vi. removing the mold thus preformed, and called preform (PF); then vii. repeating in step iii with the second support.

Claims

1. A method for preforming a semi-finished product (SP) made of plastic, characterized in that:

the mold thus preformed (PF) is removed from the mold.

2. Method according to claim 1, wherein the release membrane (PM) is nonstick vis-à-vis the wall of the preform mold and vis-a-vis the semi-product.

3. The method of claim 2, wherein the membrane (PM) contains silicone and / or stearates and / or fatty substances and / or maleic anhydrides.

4. Method according to one of the preceding claims, wherein is ejected the wall of the mold part (PF) thus preformed by peeling the membrane (PM) from the wall.

5. Method according to claim 4, wherein the membrane (PM) is peeled off the wall by applying a pressure between the membrane (PM) and the wall.

6. The method of claim 4, wherein the membrane (PM) is peeled off the wall by recovery of the membrane (PM).

7. The method of claim 4, wherein the vacuum is air between the membrane (PM) and the wall before closing the mold to press the membrane (PM) on the wall, then the membrane is removed (PM ) of the wall by reintroducing air between the membrane (PM) and the wall.

8. Method according to one of the preceding claims, wherein the membrane (PM) is flat or in the shape of the wall.

9. Method according to one of the preceding claims, wherein using a punch-matrix type preforming mold (MP), the first membrane (PM) being located between the semi-finished product (SP) and a first wall (PO). ) of the mold (MP), and a second nonstick membrane (SM) being located between the semi-product (SP) and a second wall (MA) of the mold (MP).

The method of claim 9, wherein the second membrane (SM) contains silicone and / or stearates and / or fatty substances and / or maleic anhydrides.

11. Method according to one of the preceding claims, wherein the temperature inside the preform mold (MP) is the ambient temperature.

12. Process according to one of the preceding claims, in which a thermosetting material of the SMC type is used as plastic material.