Injection molding allows the creation of parts with very complex shapes. However, various defects can occur during the process, affecting the aesthetics or functionality of the finished products. Below is an overview of the most common defects, their main causes, and potential solutions.
Common Defects in Plastics Processing
Defect | Description | Main Causes | Recommended Solutions |
|---|---|---|---|
Sink Marks | Depressions or indentations on the surface of the part (often in thick areas). | – Uneven cooling between the outside and the inside of the part. – Insufficient holding pressure. – Non-uniform wall thicknesses. | – Modify the design to reduce or make wall thickness more uniform. – Increase holding pressure and time. – Optimize mold and polymer temperature. – Avoid thick sections and abrupt changes in wall thickness. |
Short Shots (Incomplete Filling) | Partially formed part, with unfilled areas. | – Melt temperature too low. – Insufficient injection pressure or speed. – Trapped air in the mold. – Too thin or poorly designed sections. | – Increase melt and mold temperatures. – Increase injection pressure and speed. – Improve mold design to facilitate flow. – Check if wall thickness is too thin and optimize if needed. |
Trapped Air (Bubbles) | Presence of bubbles or voids in the part. | – Insufficient mold venting. – Injection speed too high. – Inadequate mold design. – Mold temperature too low. | – Add or enlarge vents in the mold. – Reduce injection speed. – Redesign the mold to avoid air entrapment zones. – Increase mold temperature. |
Warping | Distortion or twisting of the part after ejection. | – Uneven cooling. – Internal stresses due to varying thicknesses. – Premature or improper ejection. | – Design with thin and uniform walls. – Optimize mold cooling system. – Adjust injection parameters to reduce internal stresses. |
Burn Marks | Dark spots or discoloration on the part’s surface. | – Ignition of trapped air or gas under pressure. – Injection speed too high. – Excessive melt temperature. | – Improve mold venting. – Reduce injection speed. – Lower melt temperature. |
Weld Lines | Visible lines where two melt fronts meet. | – Melt or mold temperature too low. – Injection speed too low. | – Increase melt and mold temperatures. – Increase injection speed. – Redesign the mold, especially gate placement, to minimize flow convergence areas. |
Delamination | Layer separation in the material, resulting in a flaky appearance. | – Material contamination. – Mixing of incompatible resins. – Excessive moisture in the material. | – Use clean and compatible materials. – Properly dry the material before molding. – Minimize use of release agents. |
Jetting | Flow marks or lines caused by overly rapid injection. | – Injection speed too high. – Poor gate design. | – Reduce injection speed. – Use a “fan gate” or “tab gate” design and increase gate area as much as possible. – Adjust the injection profile for a smoother transition. |
Surface Defects (Wrinkles, Waviness) | Aesthetic imperfections on the surface of the part. | – Melt or mold temperature too low. – Injection speed too low. | – Increase melt and mold temperatures. – Increase injection speed. – Improve mold polishing. |
Flash (Burrs) | Excess material leaking out of mold parting lines. | – Insufficient clamping force. – Mold wear or damage. | – Increase mold clamping force. – Repair or replace worn mold components. – Adjust injection parameters to reduce excessive pressure. |
Our technical sales team is ready to listen to your needs.