Molding defects and they’re preventative Defects = rejects When it comes to injection molding, there is a multitude of reasons parts can be rejected due to parts have defects. Some of the more common defects will be covered in this video, along with the key preventative measures. Sink marks and their preventative measures What causes a sink mark issue? A sink mark is a depression on the surface of the molded part and is generally found where there are bosses or ribs on the underside of the molding. These interchange close in a massive material section and the cooling are not parallel in these areas. As the material cools, the outer surface solidified, the inner molten material begins to cool, solidify and shrink thus pulling on the already solidified surface. The irregular cooling and shrinking of the material around thicker areas in the cause of most sink marks. Sink marks and their preventative measures Key preventative measures

  • Ensure wall diameter are uniform wheresoever possible Make ribs 50% to 80% of the wall thickness it is connected to
  • Select the thickest section of the part to add the injection gate, this allows thickest parts to injected first
  • Do not have the gate area as well small as this will avoid the flawless fill and filling of the mold
  • prevent big massive size in the design, improved to have a banter or punch design if you are watching for toughness and rigor
  • raise the injection pressure during the action this will force more material into the mold and deflate the contraction
  • deflate the injection climate of the element and the mold

Voids and their preventative measures What causes avoid? Voids or air pockets tend to occur in a thicker section of a molded part, this is caused when the surface cools and solidifies faster than the inner material. As the close element is calm it also decreases, but if it is not able to fully decrease, the element fragment will be drag apart thus build voids. Key preventative measures

  • Ensure there are no unnecessary thick section in the part design
  • expand the gate capacity to arrange flawless mold enough
  • Increase shot volume, increase injection pressure, increase screw forward time, reduce melt temperature, or adjust injection speed
  • arrange element is preserved rightly, mist in the element will source voids

Weld lines and their preventative measures What causes a weld line? Weld lines are created when two melt fonts come together but do not bond with each other because they have partially solidified. When the part is fully solidified the weld lines often look like two plastic have come together. Key preventative measures

  • Having a design where the flow is continuous, not split will prevent weld lines
  • If a split in molten plastic is unavoidable, ensure the position of the gate allows the melt fonts to come together evenly at the same time
  • Raising the temperature of the mold or molten plastic will help when the two melt fonts come together
  • Increasing the injection speed will help the melt fonts come together quicker, while still molten.