ABS/TPU 2K Mold Case Study: Rotating Stripper Plate Mold Mechanism

• Product Application: Industrial Equipment Component
• Resin Combination: 1st Shot: ABS (Hard plastic) | 2nd Shot: TPU (Soft plastic elastomer)
• Cavitation: 4 Cavities total (1st Shot: 2 cavities | 2nd Shot: 2 cavities)
• Machine Compatibility: Parallel two-shot injection molding machine
• Gating System: Full hot runner system

Standard two-shot molding typically relies on the injection machine's rotating platen to switch the substrate from the first to the second injection station. However, for this specific project, the mold itself houses the rotational mechanism. The mold relies on a rotary stripper plate to facilitate the transition between the ABS and TPU shots.

The rotary stripper plate is mounted within the core plate assembly. After the first shot (ABS) is injected, the semi-finished part remains securely held on the stripper plate. Instead of ejecting the part, the stripper plate is pushed forward, rotates 180 degrees via an integrated rack and pinion gear mechanism, and retracts back into the second-shot position.

Utilizing an in-mold rotary stripper plate offers distinct mechanical advantages over traditional two-shot tooling. It allows manufacturers to utilize parallel injection machines without requiring massive, heavy machine-side rotary tables. The rack and pinion setup ensures precise 180° indexing, preventing misalignment during the critical TPU overmolding phase. Furthermore, keeping the first-shot ABS part on the stripper plate rather than transferring it via robotics guarantees zero positioning errors, resulting in a flawless chemical and mechanical bond between the ABS and TPU boundary.

The synchronization of hydraulic cylinders and machine ejector rods must be meticulously timed to prevent mechanical collision. The operational sequence of this rotary stripper plate injection mold is divided into two continuous cycles:

1. Mold Close: Tool locks under tonnage.
2. First Shot Injection: ABS (hard plastic) is injected into the primary two cavities.
3. Mold Open: Parting line separates.
4. Hydraulic Ejection (Phase 1): The hard plastic hydraulic cylinder drives forward 30mm, pushing the stripper plate out simultaneously.
5. Machine Ejection (Phase 2): The injection machine's ejector rod fires to 68.5mm, extending the stripper plate an additional 38.5mm to clear the core geometry.
6. Ejector Plate Reset: The hydraulic cylinder retracts the ejector plate back to its home position, leaving the stripper plate suspended and stationary.
7. Plate Rotation: A dedicated hydraulic cylinder actuates the rack, turning the pinion gear and rotating the entire stripper plate exactly 180°.
8. Stripper Plate Reset: The injection machine's ejector rod retracts, pulling the rotated stripper plate (with the ABS substrate) back into the mold base.
9. Mold Close: Tool locks for the second cycle.

1. Simultaneous Injection: TPU (soft plastic) is injected over the ABS substrate in the secondary cavities, while a new batch of ABS is simultaneously injected into the primary cavities.
2. Soft Plastic Ejection & Part Demold: The soft plastic hydraulic cylinder ejects 30mm. The finished ABS+TPU composite parts are ejected and removed (via robot or operator).
3. Soft Plastic Cylinder Reset: The cylinder retracts to its home position.
4. Hydraulic Ejection (Phase 1): The hard plastic cylinder ejects 30mm (bringing the new ABS substrates forward on the stripper plate).
5. Machine Ejection (Phase 2): The machine ejector rod fires to 68.5mm, extending the stripper plate another 38.5mm.
6. Ejector Plate Reset: The hard plastic cylinder resets the ejector plate, keeping the stripper plate in the extended position.
7. Plate Rotation: The rack-and-pinion cylinder rotates the stripper plate 180° again.
8. Stripper Plate Reset: The machine ejector rod retracts, seating the stripper plate back in place.
9. Mold Close: The continuous cycle repeats.

This ABS+TPU two-shot mold case study demonstrates a compact and reliable alternative to conventional rotary platen tooling. The design uses a full hot runner system, a 2+2 cavity layout, and a rack-and-pinion-driven rotating stripper plate to transfer first-shot ABS substrates into the TPU overmolding station.

The 18-step sequence clearly shows how the mold opens, ejects, rotates, resets, and closes in steady production. For mold designers and process engineers, this concept offers a practical reference for two-shot applications where space, cost, and precise part transfer are critical factors.