Product surface 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: material temperature low and flowability poor, uneven transfer speed, low mold temperature, material jetting at the gate. 2. Feeding factor: The volume of the feeding chamber, the feeding 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: raise the material and mold temperature, stabilize the transfer speed, optimize the gate design to reduce jetting. 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 feeding 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 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 product surface flow marks in transfer molding; the core of the solution lies in the rational 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.