Common Defects in Injection Molding and How to Prevent Them
Injection molding is a popular manufacturing process used for producing plastic products of various shapes and sizes. However, like any other manufacturing process, injection molding is prone to defects. These defects can result in rework, scrap, and, ultimately, higher production costs. In this article, we will discuss common defects in injection molding and how to prevent them.
1. Sink Marks
Sink marks are depressions on the surface of the molded part caused by uneven cooling. They usually occur near thick areas of the part and can be unsightly. To prevent sink marks, one can increase holding pressure, reduce cycle time, or adjust cooling time and temperature.
2. Warpage
Warpage is the distortion of the molded part caused by uneven cooling or internal stresses. It can cause the part to become unusable. To prevent warpage, one can optimize the gate location and size, adjust cooling time and temperature, and reduce the packing pressure if possible.
3. Weld lines
Weld lines occur when two or more flow fronts converge at a joint. They can weaken the part and make it look unsightly. To prevent weld lines, one can optimize the gate location and size, increase the temperature and pressure, and use flow aids, such as mold coatings and mold inserts.
4. Short shots
Short shots occur when the plastic does not completely fill the mold cavity. This can result in incomplete parts. To prevent short shots, one can adjust the holding pressure, increase the injection speed and time, and optimize the gate location and size.
5. Flash
Flash is the excess plastic that protrudes from the parting line or the ejector pins. It is caused by the excessive clamping force or the poor alignment of the mold. To prevent flash, one can reduce the clamping force, improve the alignment of the mold, and adjust the molding conditions, such as cooling time and temperature.
6. Jetting
Jetting is the visible streaks on the surface of the molded part caused by turbulent flow. It can be caused by the high injection speed or the poor gate design. To prevent jetting, one can reduce the injection speed, optimize the gate location and size, and use flow aids, such as mold coatings and mold inserts.
7. Burn marks
Burn marks are the discoloration or blackening of the surface of the molded part caused by overheating. They can be unsightly and weaken the part. To prevent burn marks, one can reduce the melt temperature, adjust the cooling time and temperature, and use mold coatings and mold inserts.
8. Air traps
Air traps are the voids or bubbles in the molded part caused by the trapped air. They can weaken the part and affect its appearance. To prevent air traps, one can increase the injection speed, reduce the hold time, and use venting devices, such as ejector pins and vacuum ports.
9. Flow marks
Flow marks are the visible lines or streaks on the surface of the molded part caused by the uneven flow of the plastic. They can be unsightly and affect the part's appearance. To prevent flow marks, one can increase the temperature and pressure, optimize the gate location and size, and use mold coatings and mold inserts.
10. Contamination
Contamination is the inclusion of foreign materials, such as dust and debris, in the molded part. This can result in rejected parts and production delays. To prevent contamination, one can use clean materials and equipment, properly store and handle the materials, and clean the equipment regularly.