How to make PLA plastic injection mold ?

How to Make a Mold for PLA Plastic Injection Moldin

PLA (Polylactic Acid) is a biodegradable thermoplastic that can be injection molded, but it requires lower temperatures than most plastics (typically 180–220°C melt, mold temperature 20–60°C). The mold itself is almost always made from metal (aluminum or steel), not from PLA, because PLA would melt or deform under injection pressures and temperatures.

Below is a practical step-by-step guide to creating a real injection mold suitable for PLA (or any other plastic).

1. Choose the Mold Type and Complexity

For PLA you can perfectly use an aluminum mold — it dissipates heat fast, which helps PLA cool and crystallize nicely.

2. Design the Part for Injection Molding

• Uniform wall thickness (1.5–3 mm ideal for PLA)

• Draft angles 0.5–2° per side

• Avoid undercuts or use side-actions/lifters

• Add proper radii (minimum 0.5 mm) to avoid stress concentration

3. Create the Mold Design

• Core and cavity inserts

• Runner system (cold runner is fine for PLA)

• Cooling channels (very important for PLA cycle time)

• Ejector pins

• Alignment pins, parting line, venting (0.02–0.05 mm vents)

4. Manufacturing Routes

• Professional Mold Maker (recommended for anything beyond prototype)

• DIY / Low-Volume with CNC or 3D-Printed Master + Cast Aluminum

• Desktop CNC Route (most practical DIY)

• 3D-Printed Mold Inserts (only for very low pressure or wax/PLA testing)

5. Essential Mold Features for PLA

• Mold temperature: 20–60°C (use water lines; higher temp → better clarity, lower temp → faster cycle time)

• Generous venting (PLA releases gases)

• Polished surfaces (PLA sticks more than PP or ABS)

• Slightly larger gate (PLA is more viscous when not fully dried)

6. Drying PLA Before Injection

PLA must be bone-dry (<0.02% moisture) or you get bubbles, splay, and hydrolysis.

Dry 4–6 h at 60–70°C in a desiccant dryer.

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