WO1998015372A1

WO1998015372A1 - Method and device for making moulds and tools

Info

Publication number: WO1998015372A1
Application number: PCT/DE1996/001916
Authority: WO
Inventors: Ronald I. Simmonds; Henner Schöneborn; Heiner Frohn
Original assignee: Hek Gmbh
Priority date: 1996-10-07
Filing date: 1996-10-07
Publication date: 1998-04-16

Abstract

Disclosed is a method consisting in making from a premaster (generally SLAT, FDM or another rapid prototyping method) an intermediate model in casting resin which remains stable at high temperature when using the vacuum casting process. This model constitutes then the base of the actual mould. The intermediate model is shaped in a cavity retainer up to the mould parting plane. An alloy with low melting point is then cast around the model into the cavity retainer and solidified in an especially developped device. Upon solidification of the first mould half, the structure extending up to the starting line is removed and the second mould half is manufactured by applying the same method.

Description

METHOD AND DEVICE FOR PRODUCING MOLDS AND TOOLS

Metal - Mold - Casting (MMC)

The invention relates to a method and an apparatus for the production of molds and tools from low-melting alloys for the production of plastic parts for the prototype phase and pre-series. According to the current state of the art, it is not possible to use metallic

Manufacture molds quickly and inexpensively. Metallic molds, which have the advantage of longer service life and have better thermal properties than synthetic resin molds, are primarily prefabricated by casting and machined. This procedure is very time and cost intensive. Resin molds can be produced very quickly, but they have the major disadvantage that changes are not possible at all or only to a limited extent. Plastic molds also have a very low thermal conductivity, which results in rapid heating of the tool during part production. The cycle times are extended accordingly. Also, both of the previously described manufacturing processes cannot be fully automated, so that manual rework is necessary.

The object of this invention is therefore to show a faster way compared to the existing methods. Furthermore, the use of low-melting metal alloys is intended to create the opportunity for use in the workshop without including a classic foundry in the chain.

The procedure for solving this task is as follows: The basis is an original model made of any material. This can also be a model from a rapid prototyping system, for example. A silicone mold is now built from this model using the well-known vacuum casting process. The first step to ..shrink compensation "of the intermediate model is now being prepared via the curing temperature of the silicone. Depending on the curing temperature, the later intermediate model either has a shrinkage or a growth Series plastic must be adapted. the silicone rubber should be cured in this way. that the intermediate model is growing. This step is carried out in general and for this special case as is known from the field of VG technology. As a second step, the required intermediate model is now also produced from a high-temperature casting resin using the vacuum casting process. Depending on the requirements of the alloy (150 ° C - 220 ° C), the shrinking behavior of the resin and the shrinking behavior of the plastic to be processed, the casting resin is selected. Practical experience will show which combinations should ultimately be chosen.

After the intermediate model is created. construction of the "actual" mold or tool begins. Here are different ones

Approaches possible. Which method is ultimately used depends on the part geometry and the resulting complexity of the shape or tool.

Possibility 1 {procedure 1).

The intermediate model is made with plaster, molding sand. Gas concrete or similar at the parting level or shape division with multi-part molds, built (Fig. 1.1 to

1.2). Then the complete first part of the parting line structure incl.

Mold the frame and intermediate model in the ..Compression - Casting Machine "with the low-melting alloy (Fig. 1.3 to 1.4).

The detailed description of the "Compression - Casting Machine" follows.

After hardening of the alloy is the first half of the mold or the first

Molding finished. The parting line structure made of gypsum, molding sand, etc. is removed (Figure 1.5), the previously made mold side is cleaned and treated with a release agent to avoid melting with the second mold side to be cast (Figure 1.6). As in the first step, the second page in the

"Compression - casting machine" cast with alloy (Fig. 1.7 to 1.8). After the alloy has hardened, the model is now removed from the finished mold (Figure 1.9) (or, if necessary, the next molded part is manufactured as described above).

Possibility 2 {procedure 2):

Already during the construction of the silicone mold for the intermediate model, the later structure for the tool is taken into account. The existing SLA model or the like is embedded in the silicone mold in such a way that the parting planes for the tool are already defined (Figure 2.1). After the high-temperature intermediate model has been created with the mold, the resulting silicone molded parts serve as a supporting structure for the plaster or sand structure (Figure 2.2) (etc.). The further procedure (pouring the respective molded parts or mold halves) is equivalent to that described in sequence 1 (Fig. 2.3 to 2.9).

Option 3 (procedure 3):

Again, an intermediate model is made from a high-temperature resistant resin (Figure 2.1). The intermediate model is now roughly adapted to the part geometry in a mold half (or a molded part) that is completely filled with alloy and mechanically (milling) (Figure 3.2). The model is now embedded in the milled cavity and fixed with gypsum molding sand (etc.) (Figure 3.3) and fixed. The support structure produced in this way is sealed with a release agent (Figure 3.4). The first mold halves are poured off as described under 1 and 2 (Fig. 3.5 to 3.6). After the first mold half (molded part) has hardened, the support structure is removed (Figure 3.7). The second half of the mold is created as already described (Fig. 3.8 to 3.1 1).

Option 4 (procedure 4):

Here, according to the present CAD model, a surface model (positive) with shape separation is milled from a high temperature tooling plate. The same is prepared for the second half of the mold (negative) (Figures 4.1 and 4.7). The alloy is now poured onto these intermediate models (Figs. 4.2 to 4.4 and 4.8 to 4.10). After curing, the models are removed (Fig. 4.5 and 4.1 1) and the two mold halves (or the molded parts created) are ready for use in the manufacture of plastic parts (Fig. 4.12).

The process in the ..Compression - Casting machine. Runs as follows: The correspondingly prepared mold frame assemblies with support structure and intermediate model are shown in vg. Mold the machine with the low-melting alloy. After reaching the max. Filling level, the still liquid alloy is pressurized (approx. 2 - 6 bar). This ensures that the shape or tool is without voids and that the optimum physical properties of the alloy are achieved. At the same time, the alloy is now cooled using water or another cooling medium (e.g. nitrogen, etc.). The process or the machine can be controlled both manually and automatically. (Drawing 1)

State of the art

The system is based on the manufacturing process of molds for wax cores for investment casting (see brochure from HEK No. 14 - 1/89). Molds made from low-melting alloys are also used here. However, the basis here is always a metallic master model. These metallic master models are very complex to manufacture, but have the advantage that you can pour directly onto the models. By producing an intermediate mold (intermediate model), you are now able to quickly cast additional intermediate models that make it possible to produce several molds in parallel. To date, it has also not been possible to compensate for the shrinkage of the material to be processed. The metallic models are scaled to the required shrinkage. Process description

1. Name

Metal mold casting; Process and device for the production of molds and tools from low-melting alloys for the production of plastic parts for the prototype phase and pre-series.

2. Summary

2.1. Technical problem of the invention = technical task and objective

Nowadays, molds and tools for plastic molding in the prototype phase are usually made of synthetic resin, fine zinc (zamak), or aluminum. For the toolmaker, aluminum and fine zinc mean extensive programming work to generate the milling programs and often long milling times. Furthermore, the milled molded parts have to be reworked. Resin tools are taken from an existing master model, but for injection molding tools this means that in addition to a "0" model, which is available in most cases, a "shrinkage model" must also be available. Furthermore, the molds, which are predominantly made of epoxy resin, are increasingly polluting our environment because they can only be recycled to a limited extent.

2.2. Solution of the problem or the technical problem

The process developed by the HEK is characterized in that:

- The "0" model is used as the basis of the design

- Retired forms can be 100% recycled

- The surface of the mold does not have to be reworked

- Subsequent changes are possible

- Tool temperature control can be integrated - The part size is unlimited

- the molds and tools have a homogeneous metallic structure - first sample parts are possible after approx. 1 - 2 weeks after submission of the usable master model

- Impression qualities of a production tool can be achieved

- Depending on the material and complexity, impression quantities of approx. 250 parts can be achieved even with demanding plastics

In the newly developed process, an intermediate model is produced from a high-temperature-resistant casting resin using the vacuum casting process from a master model (mostly SLT. FDM or other rapid prototyping process). This model now forms the basis for the `` original '' shape.

This intermediate model is built up in a form frame at the parting level. A low-melting alloy is now poured around the model into the mold frame and solidified in a specially developed device. After the first half of the mold has solidified, the parting line structure is removed and the second half is produced according to the same scheme.

In order to be able to easily separate the two mold halves, to be able to remove the model without problems and to avoid the two mold shells from melting together, the model and the “newly” created parting plane are treated with suitable parting agents. Depending on the part geometry, the structure is also a three - or multi-part

Tool necessary. Core pulls or other inserts can be used with vg. Manufacturing technology without further ado. Due to the low casting temperature of the metal, the use of aluminum or brass cores, which can be manufactured mechanically, is also possible.

2.3. field of use

In conclusion, it should be noted that the user of the method and the user of the systems or devices find a new, more effective, faster and environmentally friendly way to manufacture prototype molds for

Offers plastic parts and thus first samples. With the system z. B. at

Split injection molding

Numbers of approx. 250 pieces and more possible. This value is e.g. Currently the number of parts that are required in the automotive industry in the prototype phase.

Claims

claims

1. The process of making molds and tools

Low melting alloys for the production of plastic parts in which, according to any model (e.g. SLA etc.) a) an intermediate model is created from a high temperature resistant casting resin using the vacuum casting process, b) the intermediate model already contains the required shrinkage and for the production of the prototype form or . of the tool is used as an impression model, c) the silicone mold created for the intermediate model is constructed in such a way that the parting planes and molded silicone parts are used as a support structure for the final parting plane construction, d) the temperature-resistant parting plane structure made of plaster etc. is used as a support structure for the impression process Shells to be created from low-melting alloys is used. e) the low-melting alloy is poured onto the prepared intermediate model in a mold frame and then pressurized.

2. The method according to claim 1, characterized in that a hiss model made of high-temperature-resistant synthetic resin (up to about 250 ° C) is made from any model.

3. The method according to claim 1 and 2. characterized in that the intermediate model has a growth and thus compensates for the shrinkage of the material to be processed.

4. The method according to claim 1 to 3, characterized in that the intermediate model is built using the silicone molded shells, the support structure or the intermediate model is fixed in an "intermediate cavity"

5. The method according to claim 1 to 4, characterized in that the Trennebenenaulbau made of plaster. Molding sand, gas concrete or the like exists.

6. The method according to claim 1 to 5, characterized in that the

Intermediate model and the parting line structure within a mold frame is cast with a low-melting alloy.

7. The method according to claim 1 to 6, characterized in that the liquid

Alloy is pressurized.

8. The method according to claim 1 to 7, characterized in that the second and each further molded shell is poured against the shell created according to claim 1 to 7.

9. The method according to claim 1 to 8, characterized in that the

Separation is guaranteed by a temperature-resistant release agent.