ABS Injection Mold Material Selection Guide

ABS (Acrylonitrile Butadiene Styrene) is a widely used thermoplastic known for its balanced mechanical properties, good flowability, and low shrinkage (0.4%–0.7%). When selecting mold materials for ABS, the primary considerations are polishability, wear resistance, dimensional stability, and cost. The choice depends heavily on the production volume and surface finish requirements of the parts.

1. Core Selection Principles

Material Compatibility: Standard ABS is non-corrosive, but glass fiber reinforced ABS (ABS-GF) requires high wear resistance. Transparent ABS demands excellent polishability.

Production Volume: Material hardness and cost increase with the expected number of shots (units produced).

Machinability: Pre-hardened steels are preferred for most applications to avoid heat treatment distortion and reduce lead time.

2. Recommended Materials by Production Scale

A. Low Volume / Prototyping (≤ 10,000 shots)

Focus: Cost-effectiveness and quick turnaround.

45# Steel (Carbon Steel):

Hardness: HRC 22–25 (after quenching/tempering).

Pros: Low cost, excellent machinability.

Cons: Poor wear resistance; surface scratches easily.

Use Case: Prototypes, low-precision parts (toys, simple components).

Q235 Steel:

Use Case: Extreme low-cost trials only (not suitable for production).

B. Medium Volume / Standard Parts (10,000 – 500,000 shots)

Focus: Balance of performance, polishability, and cost (Industry Standard).

P20 (3Cr2Mo - Pre-hardened):

Hardness: HRC 28–32.

Pros: Good polishability (Ra 0.2–0.4μm), stable dimensions, widely available.

Modification: For ABS-GF, nitriding is recommended to improve surface hardness.

Use Case: Most standard ABS parts (home appliances, auto interiors, electronics).

718H (P20 Modification - Pre-hardened):

Hardness: HRC 30–35.

Pros: Superior polishability (Ra 0.1–0.2μm) due to higher purity, better for plating/painting.

Use Case: Parts requiring high-quality surface finishes.

C. High Volume / High Precision (≥ 500,000 shots)

Focus: Durability, mirror finishes, and resistance to abrasive wear.

H13 (4Cr5MoSiV1 - Heat-treated):

Hardness: HRC 48–52.

Pros: Excellent wear resistance and thermal fatigue resistance. Ideal for withstanding the abrasion of glass fibers.

Use Case: Mass production runs, especially for ABS-GF components.

S136 (4Cr13 - Stainless Steel - Heat-treated):

Hardness: HRC 48–52.

Pros: Exceptional mirror polishability (Ra ≤ 0.05μm), corrosion resistant.

Use Case: Transparent ABS parts (lenses, clear enclosures) and medical devices.

3. Key Component Materials

Cavity & Core: Follow the above selection based on volume.

Guide Pins/Bushes: GCr15 (HRC 60–62) for high wear resistance and guiding precision.

Ejector Pins: SKD61 (HRC 50–52) for toughness and resistance to bending/fracture.

4. Critical Notes

ABS-GF Warning: Always use H13 or apply a nitriding treatment to the mold surface. Glass fibers will rapidly erode softer steels like P20.

Transparency: Only S136 or high-grade 718H can achieve the necessary clarity for transparent ABS.

Heat Treatment: Avoid over-hardening; balance hardness with toughness to prevent cracking during machining or use.