Flow lines/flow marks

Flow marks appear on the product surface. Flow marks spread outward from the gate as the center, in the form of concentric circles or wave-like ring patterns, similar to water surface ripples. The formation of flow marks originates from the 'stick-slip' behavior of the melt flow front on the cavity wall——after the front melt contacts the cold mold wall, its viscosity rises and it temporarily stagnates, and the subsequent high-pressure melt pushes it forward, repeating this to form ripple marks. Although flow marks mainly affect appearance, in severe cases they also imply that the melt front temperature is too low, affecting weld strength.

1. Process parameter factors: poor material flowability, uneven mold closing speed, low mold temperature, uneven material preheating. 2. 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: improve material flowability, close the mold smoothly, raise the mold temperature, preheat the material uniformly. 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 flow lines/flow marks 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.