Thermal Fatigue Cracking of Products

The product cracks during repeated thermal cycles. Cracks may appear on the surface or inside of the product; surface cracks are visible to the naked eye as fine filaments, while internal cracks need to be detected by X-ray or ultrasonic testing. Stress cracking is concentrated at geometric discontinuities (sharp corners, hole edges, around inserts), while environmental stress cracking occurs at parts in contact with chemical media. Once a crack appears, it is irreversible, and even if it is small in appearance, it will expand rapidly during use.

1. Material factors: uneven product wall thickness causing thermal stress concentration, large material thermal expansion coefficient, insufficient interfacial bonding force, and incomplete curing. 2. Runner and gate design factors: In transfer molding, the material must enter the cavity through runners and gates; the runner length, cross-sectional shape, and gate size directly affect pressure loss, fiber breakage, and filling balance; unreasonable design is the root of many quality problems. 3. Feeding factors: The volume of the loading chamber, the loading amount, and the preheating state of the material directly determine the transfer pressure and filling effect, and are key variables unique to transfer molding.

1. Process parameter optimization and adjustment: Optimize wall thickness design for uniformity, select materials with low thermal expansion coefficient, improve interfacial bonding, and ensure complete curing. 2. Systematic troubleshooting method: Troubleshooting of transfer molding problems follows the order of "runner -> feeding -> parameters -> mold". First check whether the runners and gates are blocked or worn, then verify the loading amount and material preheating, then adjust the transfer pressure and speed, and finally check the mold venting and temperature uniformity. 3. Preventive management: Establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluations. For recurring problems, use fishbone diagrams or 5Why analysis to trace the root cause, and solidify countermeasures as PFMEA control points.

This problem is a typical manifestation of thermal fatigue cracking of products in transfer molding. The core of the solution lies in the reasonable design of the runner and gate system, the effective transmission of transfer pressure, and the uniform control of mold temperature. It is recommended to start troubleshooting from the runner system and transfer parameters.