Shenzhen Alu Rapid Prototype Precision Co., Ltd.

An injection mold is a precision tool (typically made of metal or high-performance polymers) that shapes molten plastic into a desired part by cooling it in a cavity. The mold-making process can range from DIY methods using 3D printing for prototypes and low-volume runs (10–1,000 parts) to professional machining for high-volume production. DIY approaches are cost-effective and accessible with basic equipment, while professional molds require specialized tools and expertise but offer greater durability (up to millions of cycles). Below, I'll outline step-by-step guides for both, focusing on key considerations like design, materials, and testing.

DIY 3D-Printed Molds

This method uses stereolithography (SLA) or similar 3D printing for quick iterations. It's ideal for small parts and prototyping, but molds may only last 100–500 cycles depending on the resin and plastic used.

Professional Metal Molds

For production runs (thousands to millions of parts), molds are machined from steel or aluminum for longevity and precision. This process is more expensive ($5,000–$100,000+) and typically outsourced to shops.

Step-by-Step Guide

1.Design the Mold

Create a detailed 3D CAD model of the part, then build the full mold assembly. Include cooling channels (for uniform temperature control), side actions (for undercuts), and lifters. Simulate flow using software like Moldflow to predict fill times and defects. Account for shrinkage (0.5–2% for plastics) by scaling the cavity slightly larger.

2.Select Materials  

Aluminum: Softer, cheaper ($2,000–$10,000), faster to machine; good for prototypes (10,000–100,000 cycles).  

Steel (e.g., P20 or H13): Harder, more durable (500,000+ cycles); ideal for high-volume but costlier and slower to produce.

Consider the plastic type—e.g., abrasive materials like glass-filled nylon require harder steels.

3.Fabricate the Mold  

CNC Machining: Mill the cavity and core from a solid block using multi-axis CNC mills for complex shapes.  

EDM (Electrical Discharge Machining): For fine details or hard materials.  

Assembly: Add inserts, align pins, and polish surfaces (Ra 0.8–3.2 μm for smooth finishes). Build in a frame with hydraulic clamping.

4.Test the Mold

Perform pressure testing (fill with liquid to check for leaks) and fit testing (insert a prototype part). Dry-run cycles without plastic to verify mechanics. Inject sample parts and measure tolerances (e.g., ±0.1 mm). Refine via grinding or re-machining if defects occur.

5.Production Setup

Integrate into an industrial press (100–5,000 tons clamping force). Monitor for wear and maintain with polishing.