INJECTION MOULDING TOOL AND METHOD FOR THE PRODUCTION THEREOF

OUTIL DE MOULAGE PAR INJECTION ET PROCEDE DE FABRICATION DUDIT OUTIL

English Abstract

The inventive method for the production of a metal mould in order to
manufacture a limited amount of mass-produced injection moulded parts (2)
consists in producing a moulded part (7) by means of injected powder moulding
based on a model for said injection moulded part (2) and in producing a tool
therefrom by means of debinding and sintering.

French Abstract

Procédé de fabrication d'un moule de moulage par injection en métal pour la production en série limitée de pièces (2) moulées par injection, qui consiste, sur la base d'un modèle (1) de la pièce (2) à mouler par injection, à fabriquer une pièce de moulage (7) par moulage par injection de poudre, et à fabriquer un outil de moulage à partir de cette pièce de moulage par élimination du liant et frittage.

Claims

4
Claims
1. Method for the production of a metal injection mould for the limited mass
production of injection moulded parts with dimensions typically greater than 1
mm,
characterized in that:
(a) a model of the injection moulded part to be manufactured is placed in a
standard casting mould,
(b) powder is injected into the mould with the model in position,
(c) the moulded part formed is debound and
(d) the debound moulded part is sintered.
2. Method for the production of an injection mould according to Claim 1,
characterized in that the moulded part is finished prior to debinding.
3. Method for the production of an injection mould according to Claim 1,
characterized in that the model is produced by the so-called rapid prototyping
method, e.g. by means of stereolithography.
4. Metal injection mould for the limited mass production of injection moulded
parts, characterized in that it is produced by a method according to one of
Claims
1-3.
5. Application of the injected powder moulding method to the production of a
metal injection mould for the limited mass production of injection moulded
parts.

Description

CA 02332798 2000-11-14
English Translation of PCT-Publication WO 99/5970
WO 99/59790 PCT/CH99/00211
1
Injection moulding tool and method for the production thereof
T'he invention relates to a method for the production of a metal injection
moulding
tool for the limited mass production of injection moulded parts with
dimensions
S typically greater than 1 mm. For the purpose of this description, the
expression
"limited mass production" is used for the manufacture of injection moulded
parts
in runs preferably in the order of 1000 to 100,000. For comparison,
conventional
injection moulding tools allow runs of about ten times the size, whereas the
so-
called rapid tooling or rapid prototyping method is suitable for runs of about
one
tenth the size.
Conventional injection moulding tools for the mass production of injection
moulded parts are very laborious to produce and hence very expensive. This
applies especially to finishing in cases where modifications are subsequently
required, so they are only economic for the true mass production of millions
of
pieces.
Temporary tools made of diverse materials are therefore often used for the
production of small numbers of prototypes or the production of pilot runs and
small
runs. Thus, for example, casting resin tools or even wooden moulds have
already
been in conventional use for a relatively long time in the casting mould or
thermoforming technique.
Because of the high pressures in the tool, the injection moulding process has
always meant that said temporary materials can only be used for a short time.
More recently, there has been a growing interest in tools which can be
produced
rapidly and inexpensively. The object of the invention is therefore to produce
an
injection moulding tool which on the one hand can be produced rapidly and
inexpensively and on the other hand allows larger production runs than do
tools
made of "soft materials".
This is achieved according to the invention by a method of the type mentioned
at
the outset which is characterized in that a model of the injection moulded
part to be
manufactured is placed in a standard casting mould, powder is injected into
the

CA 02332798 2000-11-14
WO 99/59790 PCT/CH99/00211
2
mould with the model in position, and the moulded part formed is debound and
then sintered.
An Example of the invention is described below with the aid of the attached
drawings, in which:
Fig. 1 is a schematic representation of the steps of the method for the
production
of an injection moulding tool for the manufacture of a plastic cog, and
Fig. 2 is a detail of the production method.
A model 1 of the injection moulded part 2 to be manufactured - a plastic cog
in the
present case - can be produced in various ways. The extra amounts necessary to
compensate for the shrinkage on sintering are known from injected powder
moulding technology. In the present Example, a mould of the model is produced
on the basis of CAD worksheets 3 by means of the known stereolithography 4 and
the synthetic resin model 1 is cast in said mould in a casting process 5, also
known
per se.
In the next step, this model is placed or mounted in a standard casting mould
6.
The mould is then closed and powder is injected into it. The resulting moulded
part 7 constitutes a so-called green body and in this state is very easy to
work.
The next step is the debinding of the moulded part, which can be carried out
in
various ways, e.g. by thermal decomposition, solvent extraction, catalytic
debinding, etc. The final step is sintering, i.e. pressureless compaction of
the
moulded part, to reach approximately the theoretical density of the metallic
material. The result is a metal injection moulding tool 8 which allows the
manufacture of injection moulded parts in runs in the order of 100,000.
The advantages of this method are firstly the relatively short time required
from the
design drawing to the finished tool, a typical duration being no more than two
weeks. Secondly, the method is extremely inexpensive. A tool produced by this
method is about 20 to 30% of the cost of a conventional production tool.
Finally, a
further advantage is the possibility, illustrated in Fig. 2, of producing
several

CA 02332798 2000-11-14
WO 99/59790 PCT/CH99/00211
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identical moulded parts 9, 10, 11 and keeping them in the green body state.
Because they can easily be finished in this state, they can be modified very
rapidly
as required. Thus the tool retouching operations, modifications or repairs
feared in
conventional injection moulding technology no longer present a problem.
The material used for the tool is preferably steel, but it is also conceivable
to use
other materials, e.g. ceramic, which can be processed by injected powder
moulding.

Representative Drawing