Based on part geometry, gate location(s) will determine how the polymer fills the cavity. If the cavity doesn’t fill in a balanced/uniform fashion, the internal stresses will be anisotropic- meaning non-uniform properties. So it is important to place a gate in a location such that the polymer flowfront fills the cavity at a uniform rate and reaches the end of the cavity at all locations, including weld line locations, simultaneously.
With simple part geometry, identifying an ideal gate location may be possible by using experience and examining the part. However, with more complex geometry and gating limitations (cooling line interference, ejector pin interference, slides, etc.), it is nearly impossible to determine the appropriate gate location(s) without using FEA(flow simulation). Not only can FEA(flow simulation) produce actual deflection results(warpage), it can also provide data that is a precursor to warpage-such as volumetric shrinkage and frozen-in stress which is typically due to a response from forcing the material into the cavity while the material is trying to freeze.
Gate location(s) will determine polymer orientation. Based on that location, it will ultimately determine polymer shrinkage. Also, different regions of the part will cool at different rates(regions of the cavity near the gate that were first to fill will cool before regions furthest from the gate).
Why is this important? Because there are 3 major components that contribute to warpage:
✔ Polymer Orientation
✔ Polymer Shrinkage
✔ Cooling Effects
Shrinkage and orientation are both directly correlated to injection location(s) on a part as it relates to processing conditions. Warpage due to cooling effects is based on the rate of how the polymer cools on one side of the cavity relative to the other side. Non-uniform cooling through the thickness will create warpage.
Because gate location(s) directly correlates to the contributors of warpage, gate location is therefore extremely important in the tool creation process and ultimately the quality of the part.
The injection molding professionals at Bozilla Corporation have over 20 years of experience assisting OEM’s, Tier 1 & Tier 2 suppliers, and Tool Shops to create quality parts that meet timing and goals.
About the author
Chris Czeczuga is a Plastics Engineer, Injection molding expert, Military Veteran and the President of Bozilla Corporation. He has proven success with many OEM’s Tier 1’s, Tier 2’s, Tool Shops, Molding shops, Part Designers, Processors and Fortune 500 companies throughout the injection molding industry. A graduate from UMass Lowell, he is Expert Certified with Autodesk, has 20+ years of field experience, intimate knowledge of injection molding part, tool and feed system design. Bozilla Corporation’s success is built on providing the highest level of injection molding simulation and consulting advice to businesses who have short lead times, require an efficient, cost-effective molding process, and desire to produce a correct part before mold steel is cut.