Core Details That Must Be Emphasized in Plastic Mold Design

Details in plastic mold design directly determine mold processing cycle, mass production stability, product appearance and convenience for later maintenance. Many failures emerging in production root from negligence in design phase. Multiple core details need to be checked one by one during design review.

Draft Angle and Fillet Design of Products

Draft angle is the first item to verify in mold design. Insufficient draft angle causes scratching and whitening during product ejection, and thin-wall parts may crack under ejection force. Distinguish draft angle for visible and non-visible surfaces. Increase draft angle for high-gloss and texture surfaces. Deeper texture requires larger draft angle. Set fillets for all corners of products as much as possible. Sharp corners cause stress concentration, raise melt flow resistance during injection, and mold sharp edges tend to chip, shortening mold service life. Avoid sharp right angles on molded areas.

Shrinkage Compensation and Dimension Allowance

Before designing cavity size, select molding shrinkage rate according to plastic material, product thickness and molding pressure. Glass-filled materials have smaller shrinkage fluctuation, while amorphous materials show larger variation. Keep consistent shrinkage compensation for each cavity in multi-cavity molds to prevent dimension difference between cavities. Reserve proper mold modification allowance during machining, especially for assembly sizes. Fine adjustment can be realized by polishing and insert trimming after trial molding to avoid re-steel processing. Refer to GB/T 14486 tolerance standard, allocate machining tolerance reasonably according to different dimensional segments of products.

Parting Line Selection and Seal Design

Select parting surfaces away from visible appearance areas to make flash easy to clean. Set seal width properly according to product size and injection pressure. Too narrow seal surface easily causes flash while too wide seal increases clamping load. Perform relief treatment on stepped parting surfaces to prevent mold crush during mold closing. Arrange exhaust at the final melt filling position together with parting surfaces to discharge air inside cavity and reduce weld line and burning defects.

Gating System and Gate Layout Planning

Gate position affects melt flow direction, weld line location and internal stress of products, which cannot be arranged randomly. Place gates on non-appearance areas to avoid obvious marks after gate removal. Evaluate gate quantity for long flow and thin-wall products to prevent short shot. Optimize runner cross-section to reduce runner waste and shorten cooling time under the premise of filling guarantee. Balance runner length for multi-cavity molds to realize synchronous filling and avoid inconsistent product weight and dimension.

Cooling Channel Layout Design

Mold cooling system decides molding cycle and product deformation. Arrange channels close to molded surface and keep uniform distance between channels and cavity. Uneven distance causes unstable mold temperature and product warpage. Follow product contour when laying cooling pipes, use arc joints at corners to reduce pipe block risk. Separate cooling pipelines for thick rubber areas and large inserts to reduce local heat accumulation. Place pipe connectors on non-operation side of mold to avoid interference with manipulator and mold clamp. Seal water channels thoroughly to stop water leakage.

Balanced Ejection Mechanism Design

Ejector pins, flat ejectors and ejector blocks should be arranged for uniform force. Add ejection components at thick rubber positions with high wrapping force to prevent whitening and penetration during ejection. Avoid placing ejector pins on assembly and appearance areas. Ejection components must have enough strength. Add guide protection for slender ejector pins. Reserve safety margin for ejection stroke, set ejection limit and reset mechanism to prevent ejector pin crush during mold closing. Calculate slide core pulling stroke and lock block strength for lifter and slide structures, install replaceable wear plates to reduce gap caused by long-term wear.

Convenience of Mold Structure Maintenance

Adopt split insert structure in design stage. Make easily worn and flash-prone areas into separate inserts. Worn inserts can be replaced individually instead of whole mold core replacement. Use standard guide parts for easy procurement and replacement. Design lifting holes and lock screw positions for safe hoisting and assembly space. Reserve lubrication positions for moving parts and use replaceable wear plates to reduce daily maintenance difficulty.