How to solve the injection molding welding line, flash and short shot issues

Various defects frequently occur during injection molding, such as weld lines, flash and short shots. Weld lines form fine streaks on product surfaces and spoil appearance quality. Flash refers to excess thin plastic protruding along component edges, which requires secondary trimming and raises labor costs. Among these issues, short shots are the most critical: molded parts turn incomplete due to insufficient material filling and have to be scrapped directly, failing to pass quality inspection. So how do we prevent these defects? Let’s find out.

1. Solve Welding Line

Welding lines appear when multiple melt flows meet and fail to fuse sufficiently. We properly raise the mold temperature and barrel temperature to improve plastic fluidity, and adjust injection speed to make the melt fuse fully. Meanwhile, we optimize gate positions, runner structure and mold exhaust to reduce melt convergence traces and eliminate obvious welding lines on the product surface.

2.Solve Flash

Flash is mainly caused by insufficient clamping force, excessive injection pressure or poor mold fitting. We increase the clamping force reasonably and lower the overhigh injection pressure and filling speed. In addition, we inspect and repair mold parting surfaces, eliminate mold gaps, and control material feeding volume to prevent plastic overflow and ensure neat product edges.

3.Solve Short Shot issue

Short shots result from poor melt fluidity, insufficient injection volume or blocked air exhaust. We optimize molding temperature to enhance plastic fluidity, appropriately increase injection pressure and injection volume, and expand and clean mold exhaust slots to release trapped air. These operations ensure the plastic melt fully fills the entire mold cavity to complete full product molding without missing material.

Master these troubleshooting tips to avoid common injection molding flaws and achieve consistent high-quality finished products. Go ahead and give them a try!

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