Shenzhen Alu Rapid Prototype Precision Co., Ltd.

Injection molding is a high-volume manufacturing process where molten plastic is injected into a mold cavity to form precise parts. Effective design ensures manufacturability, minimizes defects (like warping or sink marks), reduces costs, and speeds up production. The key is to follow Design for Manufacturability (DFM) principles early in the process. This guide covers essential guidelines, drawing from industry best practices.

1. Material Selection

Choose a thermoplastic resin based on the part's functional requirements, such as strength, flexibility, chemical resistance, and environmental exposure. Common materials include ABS (for impact resistance), polycarbonate (for transparency), and nylon (for toughness).Tip: Consider shrinkage rates (typically 0.5–2%) when designing tolerances, as different materials shrink differently.

Consult material datasheets for properties like melt flow index to ensure fillability.

2. Wall Thickness

Uniform wall thickness is critical to prevent uneven cooling, which causes warping or voids. Aim for consistent thickness across the part to promote even flow and solidification.Recommended Range: 1.5–3 mm for most parts; thinner for small features (0.8–1 mm) or thicker for structural needs (up to 6 mm).

Best Practice: Avoid thick sections (>4 mm) without gussets or ribs; use coring (hollowing) to reduce weight and cooling time.

3. Draft Angles

Draft angles allow the part to eject cleanly from the mold without sticking or damaging surfaces.Standard: 0.5–2° per side for most materials; increase to 1–3° for deeper parts or textured surfaces.

Rule of Thumb: Add 1° of draft for every 25 mm of depth.

4. Corners and Transitions

Sharp corners cause stress concentrations and poor flow; rounded transitions improve strength and mold release.Fillets and Radii: Use minimum 0.5 mm radius on internal corners; external radii can be sharper but avoid 90° angles.

Transitions: Taper changes in wall thickness gradually (e.g., 45° angle) to avoid knit lines.

5. Ribs and Bosses

Ribs add stiffness without increasing wall thickness; bosses provide mounting points for screws or inserts.Ribs: Height 2–3x wall thickness; thickness 50–70% of nominal wall; space ribs 2x their thickness apart to avoid sink marks.

Bosses: Wall thickness 50–60% of main wall; add gussets for support if >4 mm deep.

6. Undercuts and Features

Minimize undercuts (features that prevent straight pull from the mold) to avoid complex, costly side-actions.Alternatives: Use generous radii or redesign for straight pulls; for unavoidable undercuts, limit to <1% of part depth.

Textures and Letters: Emboss (raised) features for easier molding; avoid deep engravings without draft.

7. Tolerances and Dimensions

Injection molding offers tight tolerances (±0.05–0.1 mm standard), but factor in material shrinkage and process variation.Critical Dimensions: Specify tolerances only where needed; use GD&T (Geometric Dimensioning and Tolerancing) for complex geometries.

Gate Location: Place gates at thickest sections to ensure uniform fill; simulate flow if possible.

8. Parting Line and Ejection

The parting line (where mold halves meet) affects aesthetics and flash.Placement: Position on non-visible edges; avoid across critical dimensions.

Ejection Pins: Design flat areas for pin contact to prevent marks.