Uneven Density of Pre-pressed Preforms

The tightness of various parts of the preform is inconsistent. When this defect occurs in products of Process No. 3, it is usually related to a specific process parameter range or equipment status. If it persists, it will directly affect the product qualification rate and production cycle, increasing material loss and rework costs. Timely diagnosis and elimination is a basic requirement for ensuring stable production.

1. Process parameter factors: uneven pressure distribution of the pre-pressing machine, uneven material bulk density, wear of the pre-pressing mold, and material moisture content affecting molding. 2. Preheating factors: The preheating temperature and time of the material (especially thermosetting molding compounds) directly affect its fluidity and curing behavior; improper preheating leads to poor filling or uneven curing, and is a key control point unique to compression molding.

1. Process parameter optimization and adjustment: Calibrate the pressure distribution of the pre-pressing machine, uniformize the material bulk density, repair the pre-pressing mold, and control the material moisture content. 2. Systematic troubleshooting method: Troubleshooting of compression molding problems follows the order of "material -> temperature -> pressure -> mold". First check the preheating and fluidity 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 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 uneven density of pre-pressed preforms in compression molding. The core of the solution lies in the reasonable preheating of the material and the guarantee of fluidity, as well as the precise matching of mold temperature and molding pressure. It is recommended to make coordinated adjustments from both the material state and process parameters.