example 33, three-plate injection mold with stripping ... · example 33, three-plate injection mold...

Example 33, Three-Plate Injection Mold with Stripping Device for aPrecision Magazine

Integrated circuits (IC) are generally mountedautomatically during production of electronic devi-ces. This requires that they be stored in magazines.The magazine shown in Fig. 1 has an undercut U-shaped groove to hold the ICs and a recessed bottomthat is reinforced by transverse ribs. Snap fits andmounting holes are located at either end of themagazine.

Mold

In the mold (Figs. 2 to 11), the longitudinal axis ofthe molded part is transverse to the opening direc-tion of the mold. The ribbed bottom faces the runnersystem. The cavity is filled via two pinpoint gatesfrom a runner system and a heated sprue bushing(16) in a 3-plate design.

Mold Operation

Parting Line IAfter a partial opening stroke of approx. 7 mm, thespring-loaded bolts (69) cause the gate to shear off.The sucker pins (22) hold the runner in the runnerplate (5), and the snap fits as well as the mountingholes of the molded part are released by retraction ofthe slides (33). Mold plates (3) and (4) remainclosed during this time.

Parting Line II (mold opening)Parting line II (between plates 3 and 4) is openedduring further opening of the injection mold. Thisphase of opening is concluded after a distance of80 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 thehook-shaped detent on the molded part so that it cansubsequently be stripped off the mold core.

Parting Line IIIAfter a further opening stroke of 60 mm, parting lineI opens completely through the action of stripperbolt (67). Two further stripper bolts (66) engagemold plate (4), pulling the runner plate (5) forward.

The complete runner system is now pulled off thesucker pins (22) and away from the heated spruebushing (16), dropping out of the mold. The spring-loaded strippers (72) prevent the runner from stick-ing to the runner plate (5). Shoulder bolts (68)prevent the mold plates from being pulled off theguide pins completely. They do not, however, serveas a mechanical stop. This is found on the moldingmachine.

Ejection (Stripping) of the Molded Part

During the opening sequence of the mold, thestripping device, which is mounted on the movinghalf of the mold, has moved into the ejection posi-tion. Only in this position will the limit switchinitiate operation of the stripping device.During the inward movement, the guide blocks (56)glide under the guide strips (31), the carefullyadjusted latches (54) slide over the transverse stif-fening ribs of the molded part and, once the strip-ping device is fully inserted, engage behind two ofthese ribs. A limit switch (58) is actuated simulta-neously in this position to initiate the strippingoperation. The molded part is now stripped off theentire length of the mold core (27), which is 162 mmlong, and then drops out of the mold. Once thestripping device has returned to its starting position,limit switch (59) is actuated and another cycle canstart if the infrared mold safety has also cleared thestart.The infrared mold safety monitors the lower moldhalf and checks whether the molded part and strip-ping device have cleared the tool area. Only whenboth conditions have been fulfilled are the machinecontrols able to initiate another molding cycle.

Figure 1 Precision magazine to hold 50 integrated circuitstop: view from above with undercut groove to hold the ICs; bottom;view from below showing the stiffening ribs by which the magazine ispulled off the groove-forming core

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88 3 Examples – Example 33

Example 33: Three-Plate Injection Mold with Stripping Device for a Precision Magazine 89

Example 125, Single-Cavity Injection Compression Mold for ThermosetV-Belt Pulley (Injection Transfer Mold)

The pulley (Fig. 1) for a Poly-V belt in a car enginehas a diameter of 91.5 mm. It is located via its boreon a shaft and mounted with three bolts. The mold

(Fig. 2), which measures 344 mm in diameter and350 mm in height, is a core-embossing type.The unique feature of this mold involves actuationof the compression core (1) by the yoke-shaped slide(2) with the aid of hydraulic cylinder (3). Beforemolding compound is injected, the core is retracted,so that the transfer chamber is considerably larger(Section A-A, bottom). After the metered amount ofmolding compound is injected, the core is moved tothe right, forcing the molding compound into theactual cavity (Section A-A, top). The flange holesare formed without any flow lines.After the part cures at a mold temperature of about180�C (356�F), the mold opens. The radially guidedsplits (7) on the moving mold half are opened by thecam pins (8). The cured gate remnant is pulled outof the sprue bushing (4). After the mold opens, thepulley is pushed off the core by the stripper ring (9);pin (10) ejects any cull remnant.Figure 1 Thermoset V-belt pulley


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Example 125: Single-Cavity Injection Compression Mold for Thermoset 301

Example 127, Single-Cavity Injection Mold for a PE-HD Clothes HangerProduced via Gas-Assisted Injection Molding

The clothes hanger (Fig. 1) is basically a bent roundrod 16 mm in diameter with a hook at one end. An I-beam-shaped cross piece with a wall thickness of2.2 mm connects the two ends of the rod. Twobutton-shaped projections for hanging women’sskirts are located on the bottom cross piece.

Mold (Fig. 2)

To save material, reduce cycle time and prevent sinkmarks, the mold (dimensions: 546 mm� 346 mm �297 mm shut height) was designed for gas-assistedinjection molding.The mold cavity and runner channel, which entersthe cavity close to the connecting cross piece, arelocated between the mold plates (1, 2). The gasinjection pin, consisting of injection pin body (4)and gas injection needle (5), is located immediatelyadjacent to the gate.

Molding Sequence

Molding of the clothes hanger begins with injectionof a metered amount of resin. The injection pressurerequired is relatively low, because the mold is filledonly partially and the large cross-section of the partdoes not create any significant resistance to flow. Forthe same reason, no resin flows into the air gapbetween the injection pin body (4) and gas injectionneedle (5).Next, nitrogen gas at a pressure of about150 bar=2175 psi is introduced into the runner, andfrom there into the still-molten resin in the cavity,via the gas injection pin. An ever-larger bubbleforms in the resin, while the still-molten coreadvances via fountain flow to the ends of the flowpaths leading away from the gate. The result is a partwith a tubular cross-section 16 mm in diameter and awall thickness of 2.5 mm.

Part Release=Ejection

As the mold opens, the two loosely fitted moldinserts (6) release the bottom cross piece of thehanger from the stationary-side mold plate (2) underthe action of springs (7). The sprue is pulled out ofthe sprue bushing and the hollow runner stem ispulled out of the gas injection pin. Once the moldhas opened completely, the profiled ejector pins (8)and the runner ejector pins (9, 10) eject the moldedpart and runner, respectively. After the molded parthas been degated, a hole about 3 mm in diameter thatwas formed by the nitrogen gas remains at the gate.


Figure 1 PE-HD clothes hanger

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Example 127: Single-Cavity Injection Mold for a PE-HD Clothes Hanger 305

Example 128, Single-Cavity Injection Mold for a Syringe Shield Producedvia Metal Injection Molding (MIM)

The pellets of molding compound used for metalinjection molding (MIM) consist of a mixture ofmetal powder and a thermoplastic resin. The resincomponent imparts to the molding compound theflow characteristics of a highly filled thermoplastic.This means that injection molding machines canprocess the molding compound in molds withcomplex part-forming geometries.With the MIM process, a plastic resin-containingpart (‘‘green part’’) is obtained from the initial stepof injection molding. In a second step, heat andchemical means are employed to remove the resinbinder from the injection molded part. The resultingpart (‘‘brown part’’) is then converted into a densemetal part by means of sintering – as in conventionalpowder metallurgy. In the course of this latter step,volumetric shrinkage occurs, resulting in a linearshrinkage of from 10 to over 15%. The injectionmolded item (Fig. 1) is the ‘‘green part’’. Thefinished item is a syringe shield in the metal alloyIMET N 200 comprising 1.5–2.5% Ni and the re-mainder Fe.

Mold

As Fig. 2 shows, the two mold inserts (1, 2) form theouter surface of the injection molded part, while thecores (3, 5) and slide (7) form the inner surface. Thecore (3) is actuated by the hydraulic cylinder (4).The end of the core seats and locates itself in themating core (5), which is actuated by the cam pin(6). The opening in the side of the molded part hasrounded edges on the outside, necessitating the useof slide (7), which is actuated by cam pin (9). Whenthe mold is closed, the core (3) is held in place bythe 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

processing metal injection molding compounds, thegate is placed so that the incoming material im-pinges 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, thecore (3) is pulled and the molded part is carefullyremoved and deposited by means of a part handlingdevice. The runner simply drops and, after beingregranulated, is proportioned back into the virginmolding compound. The ball detents (10, 11) securethe 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 ofMIM. PM World Congress 1994=Paris

3. R.M. German: Powder Injection Molding. Metal Powder IndustriesFederation, Priceton. NJ, MPIF, 1990.


Figure 1 Syringe shield

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Example 128: Single-Cavity Injection Mold for a Syringe Shield Produced via Metal Injection Molding (MIM) 307

example 33, three-plate injection mold with stripping ... · example 33, three-plate injection mold...

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