Shenzhen Alu Rapid Prototype Precision Co., Ltd.

When making PLA (Polylactic Acid) plastic molds, several key issues require attention to ensure quality, efficiency, and durability. PLA is a biodegradable thermoplastic with unique properties, so the molding process differs from traditional plastics like ABS or PP. Below are the critical considerations:

 Material Properties of PLA

Low Heat Resistance: PLA has a low glass transition temperature (55–60°C) and melting point (150–180°C). Molds must maintain precise temperature control to prevent deformation or sticking.

Shrinkage Rate: PLA typically has a shrinkage rate of 0.3–0.8%, which is lower than many plastics. Mold design must account for this to ensure dimensional accuracy.

Brittleness: PLA is relatively brittle compared to other plastics. Mold designs should minimize sharp corners or thin sections to avoid cracking during demolding.

Moisture Sensitivity: PLA is hygroscopic and can absorb moisture, leading to hydrolysis during processing. Ensure the resin is dried (typically at 45–60°C for 2–4 hours) before molding to prevent defects like bubbles or weak parts.

Mold Design Considerations

Draft Angles: Incorporate adequate draft angles (1–3°) to facilitate easy demolding, as PLA can stick to mold surfaces due to its adhesive nature.

Surface Finish: Use polished mold surfaces to reduce friction and improve part release, as PLA can adhere to rough surfaces. Consider coatings like PTFE or nickel to enhance release properties.

Venting: Proper venting is critical to avoid trapped air, which can cause burn marks or incomplete filling, especially given PLA’s viscosity.

Cooling Channels: Design efficient cooling channels to maintain consistent mold temperatures (typically 20–40°C). PLA requires rapid and uniform cooling to prevent warping or internal stresses.

Gate Design: Use small gates (e.g., pinpoint or submarine gates) to minimize shear stress, as PLA is sensitive to high shear rates, which can degrade the material.

Temperature Control:

Barrel Temperature: Set between 180–210°C to avoid thermal degradation. Start with lower temperatures and adjust based on flow.

Mold Temperature: Keep at 20–40°C to ensure proper crystallization and reduce cycle time.

Nozzle Temperature: Slightly lower than the barrel (170–190°C) to prevent drooling.

Injection Pressure and Speed: Use moderate pressure (50–100 MPa) and speed to avoid shear heating, which can degrade PLA and cause defects like flashing or yellowing.

Cycle Time: PLA requires shorter cooling times than other plastics due to its low heat resistance. Optimize cycle times (20–40 seconds) to balance quality and productivity.

Screw Speed: Keep screw speed low to medium (50–100 RPM) to minimize shear and ensure uniform melting.

 Sustainability Considerations

Recyclability: PLA is biodegradable, but recycling requires specific conditions. Plan for scrap management and consider regrinding sprues and runners for reuse, ensuring they are free of moisture and contaminants.

Energy Efficiency: Optimize molding parameters to reduce energy consumption, aligning with PLA’s eco-friendly profile.

Request prototypes to test mold performance before full-scale production, leveraging our rapid prototyping services.By addressing these issues, you can achieve high-quality PLA molded parts with minimal defects and efficient production.