Plastic Injection Molding Defects: Causes and Possible Solutions

Plastic injection molding manufacturing method is considered both science and art. The injection molding process can be described as heating plastic pallets to molten state, injecting molten plastic tin the cavities then cooling the plastic to solidify the plastic. The injection molding process does have some drawback in the form of defects. The defects can be observed on the components. The defects in plastic injection molding can be attributed to material selection, part design, tool/mold design and process settings or any combination of material, part, tool and process. The defects can be first observed during the tool/mold verification/validation trials. The defects can also be observed during production. The defects can be resolved by modifications to part, tool, process settings or any combination of material, part, tool and process. Resolving defects by changes in process settings is very cost effective.

Process settings in the plastic injection molding process involves very good understanding of material properties, tool design and capabilities of injection molding machine/press. Most of the defects are caused due to thermal imbalances in the molten material flow path. This article discusses causes and possible solutions to some of the plastic injection molding defects that can be observed on a part.

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Injection molding gate, blessing or a nightmare?

Executive summary

Injection molding is used for mass production for plastic parts. Molten plastic is forced in to cavities and solidified to produce parts. Injection molded plastic parts are considerably cheaper than parts produced with conventional manufacturing processes. The molten plastic takes shape of the cavities before solidifying. The molten plastic enters the cavity through a gate. A gate is a critical portion in the plastic injection molding mold/tool. Any error during the selection of type, design and manufacturing of the plastic injection mold/tool are magnified in the form of injection molding flaws. Gate modifications require precision work and is usually expensive and time consuming. The selection of type, size and location of injection molding gate limits injection molding process setting or process window.

A good gate design reduces time required to validate the mold/tool, improves part quality and widens the process window.

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How the cold runner system can work wonders!

What is a Runner System?

Runner system is defined by molten plastic flow path from the sprue of the injection molding press to the cavity gate. The runner system incorporated in the mold without insulation is called a cold runner system. The hot runner system consists of heated and insulated flow path from sprue of injection molding press to the gate or cold runner.

Either hot or cold runner system is an integral part of the injection mold/tool. Hot or cold runner system is selected during the tool design. The selection of type of runner system depends on several factors including cost, time and maintenance. The selection of runner system can be very cost effective. The runner system change is very difficult and costly.

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