Cracking at product fillets

Cracks appear at the corners of the product. Cracks may appear on the surface or inside of the product; surface cracks are visible to the naked eye as fine filaments, and internal cracks need to be found by X-ray or ultrasonic testing. Stress cracking is concentrated at geometric mutations (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 small in appearance it will rapidly expand during use.

1. Cooling factors: fillet radius too small causing stress concentration, demolding force too large, over-cured and brittle, cooling too fast. 2. Preheating factor: The preheating temperature and time of the material (especially thermosetting molding compounds) directly affect its flowability and curing behavior; improper preheating will lead to poor filling or uneven curing, and it is a key control point unique to compression molding. 3. Molding pressure factor: In compression molding, pressure is not only used to overcome flow resistance, but also directly affects the compactness of the product and the degree of fiber impregnation; insufficient pressure is an important cause of product looseness and insufficient strength.

1. Process parameter optimization and adjustment: increase the fillet radius, reduce the demolding force, control the curing time, cool slowly. 2. Systematic troubleshooting method: Troubleshooting of compression molding problems follows the order of 'material -> temperature -> pressure -> mold'. First check the preheating and flowability of the material, then verify the mold temperature distribution and curing time, then adjust the molding pressure and mold closing speed, and finally check the mold venting and demolding conditions. 3. Preventive management: Establish standardized process parameter cards and quality control limits for each set of 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 the countermeasures as PFMEA control points.

This problem is a typical manifestation of cracking at product fillets in compression molding; the core of the solution lies in proper preheating of the material and assurance of flowability, as well as precise matching of mold temperature and molding pressure. It is recommended to adjust coordinately from both aspects of material state and process parameters.