Demolding cracks

Cracks appear on the product during demolding. When demolding is difficult, a 'hissing' adhesion tearing sound can be heard at the moment of mold opening, the product surface shows whitening or tear marks, and obvious ejection whitening or depression occurs at the ejector rod positions. In severe mold sticking, part of the material of the product remains in the cavity and needs to be manually cleaned after shutdown, which not only prolongs the production cycle but may also damage the cavity surface. For multi-cavity molds, mold sticking of individual cavities will also cause abnormal filling of the remaining cavities.

1. Mold design factors: demolding force too large, insufficient draft angle, product over-cured and brittle, mold surface damaged. 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: reduce the demolding force, increase the draft angle, control the curing time to avoid over-curing, repair the mold surface. 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 demolding cracks 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.