Stress Cracking

Cracks appear in the part at stress concentration locations. Cracks may appear on the surface or inside the part; surface cracks are visible to the naked eye as fine filaments, while internal cracks need to be found by X-ray or ultrasonic testing. Stress cracking is concentrated at geometric sudden changes (sharp corners, hole edges, around inserts), while environmental stress cracking occurs at locations in contact with chemical media. Once a crack appears, it is irreversible; even if it looks small, it will expand rapidly during use.

1. Comprehensive factors: excessive residual internal stress, low weld line strength, stress concentration around metal inserts, environmental stress cracking. 2. Temperature factors: the settings of barrel temperature and mold temperature directly affect melt fluidity, cooling rate, and crystallization behavior; low temperature is a common cause of filling and molding quality problems, and precise control is required according to the material's recommended processing window. 3. Mold comprehensive factors: in addition to venting, mold design parameters such as cooling water channel layout, gate position and size, and demolding draft angle all have a systematic impact on part quality, and optimization is required from the source of mold design.

1. Process parameter optimization and adjustment: increase melt temperature to reduce internal stress, increase the fusion temperature at weld lines, preheat inserts, avoid stress concentration design. 2. Systematic troubleshooting method: troubleshoot item by item in the order of "parameters -> material -> mold -> equipment". First adjust the parameters that are easiest to change, such as injection pressure and temperature, and observe the effect; if there is no improvement, check the drying and fluidity of the raw material; further check mold venting and gate design; finally check the mechanical condition of the equipment (check ring, screw). Change only one variable at a time to determine the root cause. 3. Preventive management: establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluation. For recurring problems, use fishbone diagram or 5Why analysis to trace the root cause, and fix the countermeasures as PFMEA control points.

This problem is a typical manifestation of stress cracking in '2079851475616104452; the core of the solution lies in eliminating the root cause of the defect through systematic optimization of process parameters (temperature, pressure, speed) and rationality checks of mold design. It is recommended to start with process parameter adjustment and gradually go deeper into the equipment and mold levels.