Shenzhen Alu Rapid Prototype Precision Co., Ltd.

Designing an injection mold is a complex engineering task that balances part geometry, material science, and mechanical design. The process is generally divided into two stages: Part Design (DFM) and Mold Tool Design.

1. Part Design for Manufacturability (DFM)

Before designing the metal tool, the plastic part itself must be optimized to ensure it can actually be molded without defects.

A.Uniform Wall Thickness: Aim for a thickness between 1.5 mm and 3 mm. Non-uniform walls cause uneven cooling, leading to "sink marks" (depressions) or warping.

B.Draft Angles: All vertical walls must have a slight taper (draft) so the part can slide out of the mold.

Smooth surfaces: 0.5° to 1° minimum.

Textured surfaces: 3° to 5° to prevent the texture from "grabbing" the mold.

C.Radii and Fillets: Avoid sharp 90° corners. Sharp corners restrict plastic flow and create stress concentrations. Use an internal radius of at least 0.5 times the wall thickness.

D.Rib Design: To add strength without increasing thickness, use ribs. They should be 50-60% as thick as the main wall to prevent sink marks on the opposite side.

2. Key Components of the Mold Tool

Once the part is ready, you design the "Tooling"—the steel or aluminum block that forms the part.

3. Step-by-Step Design Workflow

Step 1: Material Selection & Shrinkage

Different plastics shrink at different rates as they cool (e.g., ABS shrinks ~0.5%, while PE can shrink up to 3%). You must scale your CAD model up by the material's specific shrinkage factor before designing the cavity.

Step 2: Establish the Parting Line

Determine where the mold will split. This is usually the widest point of the part. If your part has holes or tabs on the side that prevent it from pulling straight out, you will need Side Actions or Lifters—moving parts within the mold that retract before ejection.

Step 3: Gate and Runner Layout

Decide where the plastic enters.

Gate Location: Place it at the thickest section of the part so the plastic flows toward the thinner areas.

Venting: Add tiny grooves (0.01 mm – 0.03 mm deep) at the end of the flow path to let trapped air escape. Without vents, the air will compress and burn the plastic.

Step 4: Cooling System Design

Design water lines to wrap around the cavity. The goal is isothermal cooling—making sure every part of the plastic cools at the same rate to prevent the part from twisting or bowing.

Step 5: Simulation (Moldflow)

Use software like Autodesk Moldflow or SolidWorks Plastics to simulate the injection. This tells you if the part will fill completely, where "weld lines" (where two flows meet) will occur, and if the part will warp.