Shenzhen Alu Rapid Prototype Precision Co., Ltd.

Creating an injection mold is a high-precision engineering task that balances material science, thermodynamics, and mechanical design. It’s essentially a high-stakes game of "how do I get hot plastic in and a perfect part out" as quickly as possible.

Here is the step-by-step breakdown of the process.

1. Part Design and DFMA

Before touching any metal, you must optimize the part for the molding process (Design for Manufacturing and Assembly).

Draft Angles: You need a slight taper (usually 1° to 2°) on vertical walls so the part can slide out without scraping the mold.

Wall Thickness: Keep walls uniform. If one section is significantly thicker than another, it will cool slower and cause "sink marks" (dimples in the plastic).

Radii: Avoid sharp 90-degree corners; they create stress concentrations and restrict plastic flow.

2. Mold Base and Cavity Design

The mold is more than just a hollow shape; it’s a complex assembly of plates.

The Cavity and Core: The "Cavity" (A-side) is the hollow side that forms the exterior, and the "Core" (B-side) is the protruding side that forms the interior.

The Gate and Runner System: This is the plumbing. Plastic enters through a sprue, travels through runners, and enters the part via a gate.

Cooling Channels: Holes are drilled through the mold plates to circulate water. Since cooling accounts for about 90% of the cycle time, efficient thermal management is key.

3. Material Selection

The "life" of your mold depends on what you build it from:

Aluminum: Great for prototyping or short runs (1,000–5,000 parts). It’s easy to machine and cools quickly.

P20 Steel: The industry standard for general production. It’s pre-hardened and durable.

H13 Steel: Used for high-volume or abrasive plastics (like those with glass filler). It requires heat treatment to reach maximum hardness.

4. Machining the Mold

This is where the CAD design becomes physical reality.

CNC Milling: High-speed mills carve out the primary shape of the cavities and runners.

EDM (Electrical Discharge Machining): For deep, thin ribs or sharp internal corners that a circular drill bit can't reach, an electrode (usually graphite) "burns" the shape into the steel using electrical sparks.

Polishing: The finish of the mold determines the finish of the part. A "mirror finish" requires hours of hand-polishing with diamond paste.

5. The Ejection System

Once the plastic is hard, you have to get it out.

Ejector Pins: These sit behind the part on the B-side. When the mold opens, a mechanical bar pushes these pins forward to "pop" the part off the core.

Side Actions (Sliders): If your part has a hole or a feature on the side (an "undercut"), you need moving pieces that slide out of the way before the mold opens.

6. T1 Sampling and Iteration

Rarely is the first part perfect.

The "T1" Hit: The first time resin is shot into the mold.

Debugging: Engineers look for flash (plastic leaking), short shots (mold didn't fill), or warping.

Mold Tuning: The mold is taken back to the shop for final adjustments before moving into full production.