I. Optimize Injection Molding Process Parameters

1. Reduce Injection Pressure
   High injection pressure can cause mold expansion. Adjust the injection molding machine's pressure based on product structure, size, and plastic properties. For small, thin - walled, simple - structured products, if 120MPa causes expansion, reduce it by 5 - 10MPa increments until an optimal value (e.g., around 90MPa) ensuring complete filling without expansion is found. Record adjustments for future reference.

   
   

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3. Reduce Injection Speed
   Fast injection speeds can lead to mold expansion. Slow it down to let the plastic melt fill the cavity smoothly. For a large, complex part with an 80mm3/s initial speed, reduce it to 50mm3/s or lower. But beware, too slow a speed may cause early cooling and short - shot defects. Balance all product - quality aspects during adjustment.

4. Adjust Holding Pressure and Time
   Excessive holding pressure or time can result in mold expansion. Consider product wall - thickness distribution, dimensional accuracy, and plastic shrinkage when setting these parameters. For an uneven - wall - thickness product, start with an initial setting (e.g., 60MPa for 10s), then fine - tune. Adjust pressure by about 5MPa and time by 1 - 2s each time until the right combination (e.g., 50MPa for 8s) eliminates expansion and meets quality standards.

II. Improve Mold Design and Maintenance

1. Increase Mold Wall Thickness
   For mold parts prone to expansion, use CAD to analyze and increase wall thickness. For example, if the 25mm - thick side of a mold cavity is at risk, increase it to 30mm. This boosts strength and lifespan, but weigh the pros and cons of increased weight and longer cooling times.

2. Strengthen the Mold Support Structure
   Add support columns and reinforcing ribs. Arrange support columns evenly at key mold parts based on size, shape, and injection pressure. For a large flat - plate mold, use 30mm - diameter columns with 200 - 300mm spacing. Design reinforcing ribs with a thickness 0.6 - 0.8 times the cavity wall thickness to enhance mold rigidity.

   
   

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4. Check the Mold Clamping Accuracy
   Poor mold clamping can cause expansion. Regularly inspect the guiding mechanism. Replace guide columns (if diameter reduces > 0.1mm) or loose guide sleeves. Ensure the parting surface is flat and free of foreign matter for proper clamping.

III. Select Appropriate Materials

1. Selection of Mold Materials
   Choose mold materials considering production batch, accuracy, plastic type, and cost. For high - volume, high - precision, high - pressure products, pick high - strength alloy steels like P20 or H13. For example, use H13 for automotive - part molds. For small - batch or cost - sensitive products, consider pre - hardened mold steel.

2. Optimization of Plastic Materials
   Optimize plastic materials. Replace high - fluidity plastics with those of lower fluidity if product performance allows. Add fillers like glass fiber (20% - 30% in PP) to reduce fluidity, enhance strength, and improve dimensional stability, thus reducing mold expansion risk.