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3 Examples – Example 33
Example 33, Three-Plate Injection Mold with Stripping Device for a
Precision Magazine
Integrated circuits (IC) are generally mounted
automatically during production of electronic devices. This requires that they be stored in magazines.
The magazine shown in Fig. 1 has an undercut Ushaped groove to hold the ICs and a recessed bottom
that is reinforced by transverse ribs. Snap fits and
mounting holes are located at either end of the
magazine.
The complete runner system is now pulled off the
sucker pins (22) and away from the heated sprue
bushing (16), dropping out of the mold. The springloaded strippers (72) prevent the runner from sticking to the runner plate (5). Shoulder bolts (68)
prevent the mold plates from being pulled off the
guide pins completely. They do not, however, serve
as a mechanical stop. This is found on the molding
machine.
Ejection (Stripping) of the Molded Part
Mold
In the mold (Figs. 2 to 11), the longitudinal axis of
the molded part is transverse to the opening direction of the mold. The ribbed bottom faces the runner
system. The cavity is filled via two pinpoint gates
from a runner system and a heated sprue bushing
(16) in a 3-plate design.
Mold Operation
Parting Line I
After a partial opening stroke of approx. 7 mm, the
spring-loaded bolts (69) cause the gate to shear off.
The sucker pins (22) hold the runner in the runner
plate (5), and the snap fits as well as the mounting
holes of the molded part are released by retraction of
the slides (33). Mold plates (3) and (4) remain
closed during this time.
Parting Line II (mold opening)
Parting line II (between plates 3 and 4) is opened
during further opening of the injection mold. This
phase of opening is concluded after a distance of
80 mm. During this opening motion, the ejector pin
(36) is pushed into the eject position by the lever
(29) with the aid of a stripper bolt (38). This lifts the
hook-shaped detent on the molded part so that it can
subsequently be stripped off the mold core.
Parting Line III
After a further opening stroke of 60 mm, parting line
I opens completely through the action of stripper
bolt (67). Two further stripper bolts (66) engage
mold plate (4), pulling the runner plate (5) forward.
Figures 2 to 11 Three-plate injection mold with stripping
device for a precision magazine
1: movable-side mold base plate; 2: spacer plate; 3, 4: mold plate;
5: runner plate; 6: cam pin retainer plate; 7: stationary-side mold
base plate; 8, 9: leader pins; 10, 11, 12, 13, 14, 15: guide bushings;
16: heated sprue bushing; 17: movable-side locating ring; 18:
insulating plate; 19: junction box for heated sprue bushing; 20:
locating sleeve; 21: cam pin; 22: sucker pins; 23: spring; 24: mold
core; 25, 26: core insert; 27: core; 28: wedge; 29: lever; 30: cavity
end insert; 31: guide strip; 32: slide guide; 33: slide; 34: core; 35:
articulated head and guide for ejector pin 36; 36: ejector pin; 37:
fulcrum for lever 29; 38: stripper bolt; 39: spring-loaded bolt; 40:
spring; 41: pivot pin; 42: housing for sensor; 43: sensor; 44:
microswitch; 45: housing for microswitch 44; 46: mechanical
stop for slide 33; 47: spring; 48: stripper head; 49: base plate for
stripping device; 50: bearing support for guide; 51: sheet metal
reinforcement; 52: support plate for stripping device; 53: outboard
bearing for guide; 54: latch; 55: latch spring; 56: guide block; 57:
mechanical limit for inward movement; 58, 59: limit switches; 60:
cylinder connection; 61: spring; 62: hydraulic cylinder; 63: linear
bearing; 64: guide rod; 65: circlip; 66, 67, 68: stripper bolts; 69:
spring-loaded bolt; 70: runner ejector; 71: adjustment screw; 72:
stripper; 73: stationary-side locating ring
!
Figure 1 Precision magazine to hold 50 integrated circuits
top: view from above with undercut groove to hold the ICs; bottom;
view from below showing the stiffening ribs by which the magazine is
pulled off the groove-forming core
During the opening sequence of the mold, the
stripping device, which is mounted on the moving
half of the mold, has moved into the ejection position. Only in this position will the limit switch
initiate operation of the stripping device.
During the inward movement, the guide blocks (56)
glide under the guide strips (31), the carefully
adjusted latches (54) slide over the transverse stiffening ribs of the molded part and, once the stripping device is fully inserted, engage behind two of
these ribs. A limit switch (58) is actuated simultaneously in this position to initiate the stripping
operation. The molded part is now stripped off the
entire length of the mold core (27), which is 162 mm
long, and then drops out of the mold. Once the
stripping device has returned to its starting position,
limit switch (59) is actuated and another cycle can
start if the infrared mold safety has also cleared the
start.
The infrared mold safety monitors the lower mold
half and checks whether the molded part and stripping device have cleared the tool area. Only when
both conditions have been fulfilled are the machine
controls able to initiate another molding cycle.
Example 33: Three-Plate Injection Mold with Stripping Device for a Precision Magazine
89
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Examples – Example 125
Example 125, Single-Cavity Injection Compression Mold for Thermoset
V-Belt Pulley (Injection Transfer Mold)
The pulley (Fig. 1) for a Poly-V belt in a car engine
has a diameter of 91.5 mm. It is located via its bore
on a shaft and mounted with three bolts. The mold
Figure 1
Thermoset V-belt pulley
(Fig. 2), which measures 344 mm in diameter and
350 mm in height, is a core-embossing type.
The unique feature of this mold involves actuation
of the compression core (1) by the yoke-shaped slide
(2) with the aid of hydraulic cylinder (3). Before
molding compound is injected, the core is retracted,
so that the transfer chamber is considerably larger
(Section A-A, bottom). After the metered amount of
molding compound is injected, the core is moved to
the right, forcing the molding compound into the
actual cavity (Section A-A, top). The flange holes
are formed without any flow lines.
After the part cures at a mold temperature of about
180 C (356 F), the mold opens. The radially guided
splits (7) on the moving mold half are opened by the
cam pins (8). The cured gate remnant is pulled out
of the sprue bushing (4). After the mold opens, the
pulley is pushed off the core by the stripper ring (9);
pin (10) ejects any cull remnant.
Figure 2 Single-cavity injection transfer mold for thermoset Vbelt pulley
1: core; 2: tapered slide; 3: hydraulic cylinder; 4: sprue bushing; 5:
cartridge heater; 6: insulating plate; 7: split; 8: cam pin; 9: stripper
ring; 10: cull ejector pin; 11: guide; 12: ball detent (spring-loaded);
13: ejector plates; 14: push-back pin
Company illustrations: Hasco Normalien, Lüdenscheid, Germany
Example 125: Single-Cavity Injection Compression Mold for Thermoset
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Examples – Example 127
Example 127, Single-Cavity Injection Mold for a PE-HD Clothes Hanger
Produced via Gas-Assisted Injection Molding
The clothes hanger (Fig. 1) is basically a bent round
rod 16 mm in diameter with a hook at one end. An Ibeam-shaped cross piece with a wall thickness of
2.2 mm connects the two ends of the rod. Two
button-shaped projections for hanging women’s
skirts are located on the bottom cross piece.
Figure 1
PE-HD clothes hanger
Molding Sequence
Molding of the clothes hanger begins with injection
of a metered amount of resin. The injection pressure
required is relatively low, because the mold is filled
only partially and the large cross-section of the part
does not create any significant resistance to flow. For
the same reason, no resin flows into the air gap
between the injection pin body (4) and gas injection
needle (5).
Next, nitrogen gas at a pressure of about
150 bar=2175 psi is introduced into the runner, and
from there into the still-molten resin in the cavity,
via the gas injection pin. An ever-larger bubble
forms in the resin, while the still-molten core
advances via fountain flow to the ends of the flow
paths leading away from the gate. The result is a part
with a tubular cross-section 16 mm in diameter and a
wall thickness of 2.5 mm.
Mold (Fig. 2)
Part Release=Ejection
To save material, reduce cycle time and prevent sink
marks, the mold (dimensions: 546 mm 346 mm 297 mm shut height) was designed for gas-assisted
injection molding.
The mold cavity and runner channel, which enters
the cavity close to the connecting cross piece, are
located between the mold plates (1, 2). The gas
injection pin, consisting of injection pin body (4)
and gas injection needle (5), is located immediately
adjacent to the gate.
As the mold opens, the two loosely fitted mold
inserts (6) release the bottom cross piece of the
hanger from the stationary-side mold plate (2) under
the action of springs (7). The sprue is pulled out of
the sprue bushing and the hollow runner stem is
pulled out of the gas injection pin. Once the mold
has opened completely, the profiled ejector pins (8)
and the runner ejector pins (9, 10) eject the molded
part and runner, respectively. After the molded part
has been degated, a hole about 3 mm in diameter that
was formed by the nitrogen gas remains at the gate.
Figure 2 Single-cavity injection mold for an HDPE clothes
hanger produced via gas-assisted injection molding
1, 2: mold plates; 3: locators; 4: injection pin body; 5: gas injection
needle; 6: mold insert; 8: profiled ejector pin; 9, 10: runner ejector
pins; 11, 12: ejector plates; 13: thermocouple; 14, 15: sealing rings
16: insulating plate
Company illustrations: Arburg, Loßburg; FH Aalen, Germany
Example 127: Single-Cavity Injection Mold for a PE-HD Clothes Hanger
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Examples – Example 128
Example 128, Single-Cavity Injection Mold for a Syringe Shield Produced
via Metal Injection Molding (MIM)
The pellets of molding compound used for metal
injection molding (MIM) consist of a mixture of
metal powder and a thermoplastic resin. The resin
component imparts to the molding compound the
flow characteristics of a highly filled thermoplastic.
This means that injection molding machines can
process the molding compound in molds with
complex part-forming geometries.
With the MIM process, a plastic resin-containing
part (‘‘green part’’) is obtained from the initial step
of injection molding. In a second step, heat and
chemical means are employed to remove the resin
binder from the injection molded part. The resulting
part (‘‘brown part’’) is then converted into a dense
metal part by means of sintering – as in conventional
powder metallurgy. In the course of this latter step,
volumetric shrinkage occurs, resulting in a linear
shrinkage of from 10 to over 15%. The injection
molded item (Fig. 1) is the ‘‘green part’’. The
finished item is a syringe shield in the metal alloy
IMET N 200 comprising 1.5–2.5% Ni and the remainder Fe.
processing metal injection molding compounds, the
gate is placed so that the incoming material impinges directly against the core (5).
Part Release=Ejection
As soon as the mold opens, the core (5) and slide (7)
begin to withdraw from the molded part. Next, the
core (3) is pulled and the molded part is carefully
removed and deposited by means of a part handling
device. The runner simply drops and, after being
regranulated, is proportioned back into the virgin
molding compound. The ball detents (10, 11) secure
the core (5) and slide (7) in the retracted position.
Literature
1. H. Eifert, G. Veltl: Metallspritzguss fuer komplizierte Bauteile.
Metallhandwerk þ Technik. Heft 9=94
2. F. Petzoldt: Advances in Controlling the Critical Process Steps of
MIM. PM World Congress 1994=Paris
3. R.M. German: Powder Injection Molding. Metal Powder Industries
Federation, Priceton. NJ, MPIF, 1990.
Mold
As Fig. 2 shows, the two mold inserts (1, 2) form the
outer surface of the injection molded part, while the
cores (3, 5) and slide (7) form the inner surface. The
core (3) is actuated by the hydraulic cylinder (4).
The end of the core seats and locates itself in the
mating core (5), which is actuated by the cam pin
(6). The opening in the side of the molded part has
rounded edges on the outside, necessitating the use
of slide (7), which is actuated by cam pin (9). When
the mold is closed, the core (3) is held in place by
the side lock (16), while the wedges (8) and (12)
lock the core (5) and slide (7) in position.
Gating=Runner System
The part is filled via a large gate at the lower end.
Since the risk of jetting is especially high when
Figure 1
Syringe shield
Figure 2 Single-cavity injection mold for a syringe shield
produced via metal injection molding (MIM)
1, 2: mold inserts; 3, 5: cores; 4: hydraulic cylinder; 6, 9: cam pins; 7:
slide; 8, 12: wedges; 10, 11: ball detents; 13: sprue bushing; 14: return
pin; 15: ejector pin; 16: side lock
Company illustrations: Fraunhofer Institute IFAM, Bremen; Aicher,
Freilassing, Germany
Example 128: Single-Cavity Injection Mold for a Syringe Shield Produced via Metal Injection Molding (MIM)
307