RPM Industries LLC
Injection Molded Plastic

3 Common Challenges Associated with Injection Molded Plastic Manufacturing

For plastic molded parts, the injection molded plastic process is essential. With high-quality machinery, manufacturers can create a multitude of plastic molded products used by many different industries, including food and drink, cosmetics, aerospace, medical, automotive, pharmaceutical, and more. Although this method produces excellent finished products, there are some challenges associated with the manufacturing aspect. Following are the three most common issues that arise.

1. Flow Lines – Otherwise known as streaks or patterns, flow lines are typically off in color and show up on a prototype part or component. Flow lines occur when molten plastic takes a physical path through a section of the machine called the “gate.” Usually, this defect is caused by the varying speeds of the molten plastic when it shifts direction going through the bends of the mold tool. The correction for this problem is to increase the injection speed and pressure to the optimal levels.
2. Sink Marks – Sink marks are the second challenge seen with manufacturing injected molded plastic. These small depressions develop in the thicker parts of the prototype due to shrinkage within the interior portions of the final product. In most cases, sink marks occur because of an insufficient cooling mechanism or cooling time required for the plastic to fully cool and cure while still in the mold. To correct this problem, experts need to lower the mold temperature, as well as increase the holding pressure and time.
3. Vacuum Voids – These pockets of trapped air appear within or close to the surface of a prototype. The cause is usually uneven solidification between the prototype’s inner section and surface. The fix for this problem involves choosing a less viscous plastic, making sure the mold parts are aligned properly, and increasing the holding pressure and time.

Along with these three common issues seen when producing injected molded plastics, there are several others, including surface delamination, weld lines, short shot, jetting, warping, and burn marks. Achieving the highest-quality plastic prototypes and finished products starts by using the best injection molding machines and superior manufacturing.


At RPM Industries, we offer exemplary services to our customers. Please visit our website to learn more or contact us by phone today. For all of your injected molded needs, we guarantee outstanding results.