FR2763879A1 - Production of mould with internal detachable skin protecting against deterioration in mass production - Google Patents

Abstract

This novel method produces a mould. The inventive feature is its internal skin or shell (3) which is detachable, and which confers the finished appearance to the moulding. Preferably, the shells (3) are replaceable and are made by low pressure resin transfer moulding (RTM). They are made with the same mould half (1) which is used to produce the mouldings themselves. The other mould half producing the mouldings, differs from that (2) producing the shells.

Description

 The present invention relates to a process for producing molds with replaceable shells for the production of parts made of composite materials.

The transformation of composite materials based on synthetic resins and reinforcing fibers is usually carried out according to 3 families of processes
manuals (contact or simultaneous projection)
These are cold pressless manufacturing, with simple mold (1 side only), the main characteristics of which are:
- very low level of investment
- very slow production rate
These processes are used for unit productions or for very small series (10 to 200 pieces).

highly industrialized (SMC-BMC)
These are high pressure hot manufacturing with closed molds (2 sides) whose main characteristics are:
- very high level of investment
- very fast production rate
These processes are used for mass production (over 10,000 pieces).

moderately industrialized (low pressure injection / RTM vacuum injection,
cold compression)
These are cold manufacturing, closed molds (2 sides) whose main characteristics are:
- average level of investment
- average production rate
These processes were used for productions ranging from a few hundred to a few thousand pieces. The upper limit of a few thousand was due to the fact that the molds used are made themselves of composite materials and that their surface deteriorates after one or even a few thousand pieces.

 The deterioration is characterized by cracks, splinters, which leads to reject the mold, because the parts produced no longer have the desired surface appearance, while only the interior skin of the mold is deteriorated (it is she who is in contact with the molded part and which gives the appearance of the part produced).

 The rest of the mold, framework, general shape, peripheral equipment is still perfectly usable.

 In the traditional RTM process, once the mold is closed on the fiber reinforcements, the liquid resin, mixed with the catalyst, is injected.

 After a curing time (polymerization) between 3 and 4 times the injection time, the part is rigid enough to be able to be removed from the mold.

 The method according to the invention overcomes these drawbacks.

 It consists of making molds from composite materials, but the inner skin of which is independent of the rest of the mold, and can therefore be replaced.

The molds are normally made up of two parts:
- A female part (matrix) and a male part (punch) which, once closed against each other, delimit the volume of the part to be produced.

- In the method, according to the invention, the skin of the matrix, or that of the punch, or both are independent shells which are produced separately by injection
RTM.

The drawings presented in the appendix illustrate the invention:
Figure 1 shows in section the first phase which is the production of shells.

 With reference to this drawing, the matrix (1) is fixed with a first specific punch (2) for the production by RTM injection of the shells.

 The final surface of the matrix mold (matrix + shell) is produced.

 Figure 2 shows in section, the second phase which is the mass production of molded parts.

 With reference to this drawing, the matrix (1) is the same as that used to make the shells, one of these being placed on it (3).

 On this die (1) with shell (3) is fixed a second punch (4) for the production by RTM injection of the molded parts.

 The difference between the punch (2) for injection of the shells and the punch (4) for injection of the parts is the place representing the part to be molded.

 According to a variant not illustrated, the shell can be produced on the punch, in this case, 2 dies are used (one to produce the shell and one to produce the parts) and a single punch.

 According to another variant not illustrated, shells are made both on the die and on the punch, in this case, 2 dies and 2 punches are used.

The method according to the invention allows:
- a much longer lifetime of the molds (by replacing the shells)
- a significant increase in production rates, the parts being able to be demolded with the shell much earlier, when they are not yet rigid enough to be able to be demolded alone (without the shell).

 And therefore an increase in the possibilities of the RTM, making it possible to use this technique to produce series between a few thousand to ten thousand while maintaining a very good surface condition, which was not achievable with traditional molds .

 The method according to the invention is particularly intended for the production of molded parts made of composite materials by RTM injection in the plastics industry.

Nomenclature used in the figures: 1-Matrix
2 - Shell injection punch
3 - Shell
4 - Punch injection piece
5 - Injection nozzle
6 - Tightening
7 - Metal frame
8 - 2 vent nozzles

Claims (5)

 1) A method of making molds characterized in that the inner part (skin) of these molds giving the final appearance of the part produced is a removable shell (3).  2) Method according to claim n "1 characterized in that these shells (3) are replaceable.  3) Method according to claim n "2 characterized in that these shells (3) are made by RTM injection.  4) Method according to claim No. 3 characterized in that these shells are made with a half part of the mold (1) serving also to produce the molded parts.  5) Method according to claims n "3 and 4 characterized in that the other half part (4) for producing the molded parts is different from that (2) for making the shells.