Two Different Types of Injection Molding

Injection molding is a manufacturing process for producing high volumes of finished parts at a low cost per part. Various plastic or rubber parts are produced in a wide range of colors. The injection molding machine injects heated molding material to the part mold through input channels. The two principal types of injection molding machines use either a cold runner channel or a hot runner channel.

Cold Runner Machines

Cold channel injection molding machines cool the entry channel, or runner, after each part is molded and ejected. During each molding cycle a part is produced with material in the runner channel. After the part is ejected, the runner is waste material and must be separated from the molded part. Runner waste is reground and reused or thrown away. Disposed material affects part cost. Reground and reprocessed material may affect part quality. Changing part colors in a cold runner machine is fairly easy since each ejected parts carries the material with it. Cold runner machines offer the advantages of cheaper mold designs, lower maintenance costs and lower operator skills.

Hot Runner Machines

Hot runner injection machines keep the runner portion of the mold hot. This reduces or eliminates runner scrap material, which may reduce part costs. Hot runnermachines are more expensive than cold runner machines. Hot machines require more skilled operators and require costly maintenance. Changing colors in hot runner machines is difficult because material is hard to remove from the runners. Hot runner machines eliminate wasteful runner scrap and the need to separate them from molded parts.

Changing Injection Molding Technology

Until recently, all injection molding machines were hydraulic devices. Newer machines are operated by an all-electric process or a hybrid combination of both technologies. Each injection molding process has an advantage. Hydraulic injectors offer high injection rates. Electric injection machines produce precision parts accurately and consistently. Hybrid machines are best suited to part positioning accuracy and repetitive parts. In a paper presented in May of 2008 to the Energy Technology Conference at New Orleans, Amit Kanungo and Eric Swan, senior engineers for RLW Analytics stated, "though it is a challenge to choose a right machine for molder's processing needs, by most accounts in the near future, all-electric machines will dominate the injection molding industry in the U.S."

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