TOOLING FOR INJECTION-MOLDING A PART
The present invention relates to tooling for
injection-molding a part, in particular a wax model.
Such a model is used in a lost wax molding method,
5 in particular for molding high pressure turbine blades
for a turbine engine such as a turboprop or a turbojet.
In this method, one or more blades are injectionmolded
by using injection-molding tooling that has a
cavity of shape corresponding to the shape of the model
10 that is to be obtained. When the model has cooling
channels, it is possible to use a core. In this event,
the wax is injected into the cavity, around the core.
Below, it is assumed that no core is used and that the
model is solid.
15 The wax models as obtained in this way are then
mounted as a cluster on a support.
The cluster is then dipped in a bath of ceramic,
referred to as a slip, and then dusted with a ceramic
powder (stuccoworking). Dipping and stuccoworking are
20 repeated several times until a layer of ceramic is
obtained that is sufficiently thick and that forms a
shell around the cluster.
The wax is then removed from the ceramic shell by
passing the assembly in an autoclave where steam under
25 pressure and al, hightemperature causes the wax to melt
(dewaxing).
The shell is then baked in an oven in order to
acquire sufficient mechanical strength for it to be used
as a mold.
30 Metal, e.g. a nickel-based alloy, is then cast into
the shell. After cooling, the shell is knocked out and
then the various parts are removed from the cluster, i.e.
they are separated from their common support.
The parts are then trimmed, ground, and then
35 inspected,
As a general rule, tooling for injection-molding the
wax model comprises two cavity blocks having a cavity
2
formed therein of shape that matches the shape of the
part that is to be molded once the cavity blocks are
superposed. One of the cavity blocks has ejection means
for ejecting the molded part and comprising at least one
5 ejector movable between a molding position in which it
lies outside the corresponding cavity and an ejection
position in which it projects into the cavity. In the
prior art, the ejectors are movable along a rectilinear
path.
10 The part for molding, e.g. a blade, includes a
portion, e.g. a platform, having a radially outer surface
that is not plane, but curved. The same applies Io the
corresponding wax model.
During ejection of the model from the recess, the
15 rectilinear paths of the ejectors do not follow the
curvature of the platform of the model and can cause this
platform of the model to be deformed, running the risk of
a portion of the platform being scratched or torn away.
A particular object of the invention is to provide a
20 solution to this problem that is simple, effective, and
inexpensive.
To this end, the invention provides tooling for
injection-molding a part, the tooling comprising two
cavity blocks each having a cavity formed therein of a
25 shape corresponding to the shape of the part that is to
be molded once the cavity blocks have been superposed, at
least one of the cavity blocks being fitted with ejection
means for ejecting the molded part and comprising at
least one ejector movable between a molding position in
30 which it lies outside the corresponding cavity and an
ejection position in which it projects into the cavity,
the tooling being characterized in that the ejector is
guided to move between its two positions along a curved
path, e.g. a circular arc, of shape that corresponds to
35 the shape of a portion of the molded part to be extracted
from the cavity.
Thus, this portion of a part is not damaged while it
is being unmolded. When the part corresponds to the
curvature of the platform of a wax model of a blade, the
platform is not deformed or damaged during unmolding,
5 thus enabling the blade to be subsequently fabricated
accurately and thereby reducing the amount of manual
reworking required on metal parts.
Advantageously, the ejector is curved in shape.
According to another characteristic of the
10 invention, the two cavity blocks are mounted to pivot
relative to each other about a pin between a molding
position in which the two cavity blocks are superposed,
and an unmolding position in which the two cavity blocks
are spaced apart, and the ejection means include an
15 ejector support having one end mounted to pivot about the
pivot pin of the cavity block and having its other end
fitted with the ejector.
Preferably, the ejector is actuated with the help of
a cam and/or a handle.
20 Turning the handle or the cam causes the ejector to
be moved.
In one possibility of the invention, the cam bears
against a support face of an ejector at a point that is
spaced apart from the pivot axis, so as to lift the
25 support andthe ejector when the cam is turned.
In preferred manner, the ejection means include two
ejectors that are parallel or concentric and spaced apart
from each other.
Advantageously, the injection-molding tooling
30 includes a stationary bottom cavity block and a movable
top cavity block, the ejector being arranged in the
bottom cavity block.
Furthermore, at least one of the cavity blocks may
be mounted to pivot about the pin via at least one
35 rolling bearing, e.g. a ball bearing.
The invention can be better understood and other
details, characteristics, and advantages of the invention
4
appear on reading the following description made by way
of non-limiting example and with reference to the
accompanying drawings, in-which:
Figure 1 is a perspective view of tooling of the
5 invention for injection-molding a part, shown in the
closed position;
Figure 2 is a longitudinal section view of the
injection-molding tooling shown in the open position, the
ejection means being shown in the molding position;
10 . Figure 3 is a view corresponding to Figure 2, with
the ejection means being shown in the ejection position;
and
Figures 4 and 5 are perspective views showing a
bottom portion of the mold, respectively in the molding
15 position and in the position for ejecting the ejection
means.
Figures 1 to 5 show injection-molding tooling of the
invention comprising a top portion 1 and a bottom portion
2, which portions are mounted to pivot relative to each
20 other about a pin 3.
More particularly, the bottom portion 2 comprises a
cavity block 4 of generally rectangular shape, having a
cavity 5 and an injection channel 6 formed therein, as
can be seen more clearly in Figures 4 and 5, and mounted
25 by means of a screw 7 on an elongate and plane bottom
plate 8, likewise of rectangular shape. The two opposite
ends of the plate 8 are fitted with handles 9. The plate
8 also has two lateral lugs 10 arranged on either side of
a longitudinal midplane and forming a clevis in which the
30 pin 3 is mounted. More particularly, the pin 3 is guided
by two ball bearings 11 mounted in the lugs 10, and is
perpendicular to the above-mentioned midplane.
The bottom portion 2 has means for ejecting the
molded part, said means comprising a generally L-shaped
35 support 12 having a first portion 13 with its end mounted
on the pivot pin 3 and a second portion 14 that is
substantially perpendicular to the first portion 13 and
5
from which there extend first and second ejectors 15 and
16 of curved shape. The first ejector 15 extends from
the free end of the second portion 14, while the second
ejector 16 extends between the first ejector 15 and the
5 first portion 13. More particularly, the ejectors 15 and
16 are of circularly arcuate shape centered on the pivot
pin 3. The ejection means extend in the above-mentioned
midplane.
The bottom cavity block 4 has two curved openings of
10 shapes complementary to the shapes of the ejectors and
having the ejectors passing therethrough, which openings
lead to a bottom empty zone 17 (Figure 2). The empty
zone together with the curved openings allows the
ejection means to pivot through a determined angular
15 range, as is described in greater detail below.
A cam 18 is housed in an opening 19 in the plate 8,
under the support 12 for the ejection means, the cam 18
being connected to a rod extending through the plate 8
and having its end fitted with a handle 20. Turning the
20 handle 20 thus causes the cam 18 to turn so that it can
be moved between a molding position in which it is
completely received inside the plate 8, and an ejection
position in which it projects from the plate 8 and pushes
against the bottom face of the support 14 so as to cause
-25--_ it-to pivot about the pin 3.
The ejection means are then moved between a molding
position in which the ejectors 15 and 16 are outside the
cavity 5 and are housed entirely in the cavity block
(Figures 2 and 4), and an ejection position in which the
30 ejectors project upwards inside the cavity (Figures 3 and
5).
The top portion 1 of the injection-molding tooling
includes, in the same manner, a cavity block 21 in which
there is formed a cavity 22, which block is fastened to a
35 top plate 23. The top plate 23 has two lugs 24 arranged
on either side of the longitudinal midplane of the plate
23, forming a clevis that is mounted on the pin 3. More
6
particularly, each lug 24 of the top plate 23 is mounted
between the first portion 13 of the support 12 of the
ejection means and one of the lugs 10 of the bottom plate
8.
5 The end of the top plate 23 that is remote from the
pivot pin 3 is fitted with a handle 25.
There follows a description in greater detail of the
method of molding a blade model 26 out of wax.
When the model 26 includes a hollow portion, such as
10 a cooling circuit, a ceramic core (not shown) is mounted
in the cavity 5 of the bottom cavity block 4, it being
possible for the core to be positioned with the help of
abutments and for it to be held with the help of a
presser screw 27, in known manner.
15 The injection-molding tooling is then closed, i.e.
the top and bottom portions 1 and 2 are pivoted so as to
superpose the two cavity blocks 21 and 4, and thus also
the two cavities 22 and 5. The shape defined by the
cavities 5 and 22, when situated facing each other,
20 corresponds to the shape to be given to the part 26 that
is to be molded. In particular, the cavities 5 and 22
define the shape of a blade comprising an airfoil and a
platform. At least concerning the zone formed by the
cavity 5 in the bottom cavity block 4, the platform
25 presents a shape that is-curved-and o-f section that is
substantially in the form of a circular arc centered on
the pivot pin 3.
A press (not shown) then presses against each of the
outside faces of the plates 8 and 23, and wax is injected
30, into the cavities 5 and 22 via the injection channel 6,
and then cooled so as to solidify and form a wax blade
model 26 (Figures 2 and 3).
The injection-molding tooling is then opened, by
pivoting the top portion about the pin (Figure 2).
35 In order to eject the wax model 26 out from the
cavity 5 of the bottom cavity block 4, the handle 20 is
actuated so as to cause the cam 18 to pivot, thereby
7
causing the ejection means to pivot. The ejectors 15 and
16 then move along respective curvilinear paths of shape
that corresponds to the shape of the platform, and more
precisely to the shape of the zone to be extracted from
5 the cavity 5.
This serves to avoid any damage or deformation of
the platform. This guarantees that the blade obtained by
lost-wax casting, using the method described above,
complies with specifications.
10 The injection-molding tooling is described herein
for molding a wax model 26, however it could be used for
molding other types of part, in order to solve the same
technical problem, i.e. to avoid damaging parts when they
are ejected.
15
CLAIMS
1. Tooling for injection-molding a part (26), the tooling
comprising two cavity blocks (4, 21) each having a cavity
(5, 22) formed therein of a shape corresponding to the
5 shape of the part (26) that is to be molded once the
cavity blocks (4, 21) have been superposed, at least one
of the cavity blocks (4) being fitted with ejection means
for ejecting the molded part and comprising at least one
ejector (15, 16) movable between a molding position in
10 which it lies outside the corresponding cavity (5) and an
ejection position in which it projects into the cavity
(5), the tooling being characterized in that the eojector
(15, 16) is guided to move between its two positions
along a curved path, e.g. a circular arc, of shape that
15 corresponds to the shape of a portion of the molded part
(26) to be extracted from the cavity (5).
2. Tooling according to claim 1, characterized in that
the ejector (15, 16) is curved in shape.
20
3. Tooling according to claim I or claim 2, characterized
in that the two cavity blocks (4, 21) are mounted to
pivot relative to each other about a pin (3) between a
molding position in which the two cavity blocks (4, 21)
25 are superposed, and anunmolding position in which the
two cavity blocks (4, 21) are spaced apart, and in that
the ejection means include an ejector support (12) having
one end (13) mounted to pivot about the pivot pin (3) of
the cavity block (4, 21) and having its other end fitted
30 with the ejector (15).
4. Tooling according to claim 3, characterized in that
the ejector (15, 16) is actuated with the help of a cam
(18) and/or a handle (20).
35
5. Tooling according to claim 4, characterized in that
the cam (18) bears against a support face (12) of the
9
ejector (15, 16) at a point that is spaced apart from the
pivot axis (3), so as to lift the support (12) and the
ejector (15, 16) when the cam is turned.
5 6. Tooling according to any one of claims 1 to 5,
characterized in that the ejection means include two
ejectors (15, 16) that are parallel or concentric and
spaced apart from each other,
10 7. Tooling according to any one of claims 1 to 6,
characterized in that it includes a stationary bottom
cavity block (4) and a movable top cavity block (21), the
ejector (15, 16) being arranged in the bottom cavity
block (4).
15
8. Tooling according to claim 3, characterized in that at
least one of the cavity blocks is mounted to pivot about
the pin (3) via at least one rolling bearing, e.g. a ball.
bearing (11).