Product weld lines

The strength at the confluence of multiple material streams is low or the marks are obvious. Weld lines appear as linear marks along the flow confluence direction, with darker or lighter color and poor surface gloss, and fine grooves visible under magnification. Mechanical tests show that the tensile strength at the weld line is only 60%-80% of the parent material, and the notched impact strength can drop below 40%. When the product bears bending or impact loads, fracture often starts at the weld line. For transparent products, the refractive index difference at the weld line makes the area show obvious strip-shaped optical distortion.

1. Process parameter factors: material temperature at the confluence low and fusion poor, poor venting, transfer speed slow, improper gate position. 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, improve the venting at the confluence, speed up the transfer speed, optimize the gate position to reduce confluence. 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.

Weld lines cannot be completely eliminated but can be greatly reduced. The core strategy is to let the two melt streams converge under conditions of high temperature and low gas resistance——raise the mold temperature to slow the front cooling, improve venting to eliminate air cushion blockage, optimize the gate layout to improve the convergence angle.