Injection Molding Terminology and Process Quality Test
Injection molding requires precise control of mold design, material flow, temperature, and pressure. A typical injection mold consists of a cavity, core, runner system, gate, cooling channels, and ejector pins. Each component affects the quality and consistency of molded plastic parts.
During the filling stage, molten plastic flows through the sprue and runner before entering the cavity through the gate. The gate location and gate size influence flow patterns, weld lines, air traps, and filling balance. An incorrect gate design may cause short shots, burn marks, or excessive shear heating.
After filling, packing pressure and holding pressure compensate for material shrinkage. Insufficient packing pressure may produce sink marks near thick ribs or screw bosses. Excessive holding pressure can increase residual stress and cause dimensional variation.
Cooling time, mold temperature, and cooling channel layout also influence the injection molding cycle. Uneven cooling may cause warpage, differential shrinkage, and dimensional instability.
Mold construction is equally important. The parting line must fit correctly to prevent flash. Slides and lifters release undercuts, while ejector pins push the molded part away from the core side. An inadequate draft angle may cause sticking, scratches, or deformation during ejection.
Quality inspection should include critical dimensions, surface defects, and functional assembly requirements. First article inspection helps verify important characteristics before mass production. Engineers should also evaluate cycle time, scrap rate, and process stability.
For OEM buyers, a reliable injection molding supplier should provide DFM feedback, mold trial reports, material specifications, and clear acceptance criteria. These documents help reduce tooling risk, improve part quality, and support consistent production.
During injection molding, the gate connects the runner to the cavity. The mold uses PA66 at 280 °C. A poorly designed gate can cause sink marks, weld lines, and short shots.
