Difference Between Extruder and Injection Molding

Both extruder and injection molding machine plastify plastics and process them into certain shapes. The extruder is required to create continuous linear, two-dimensional shapes. The injection molding machine produces three-dimensional shapes that do not remain constant in a parallel line. Although they have similar functions, their differences still exist.

For structure, screw and barrel are used in both machines to plastify and convey plastics. However, for extruders, the screw has a bigger diameter and L/D ratio.

For the procedure, extruders continuously extrude plastics through a die head to form products, for example, plastic pipes, sheets/profiles, and bars. The injection molding machine is not continuously working. Plastics will be injected into a closed mold cavity. When the cavity is filled, the machine will stop working and plastics in the mold will be cooled and shaped. The machine will work again after shaped plastic was taken out from the opening mold. The products produced by injection molding machines have a relatively complex structure, for example, plastic cup, pot, and shell.

Both machines can process most of the plastics. The difference between the materials used is that material used by extruder can have higher viscosity. The reason is injection molding machine requires plastics flowing inside the mold and the flow channel inside the mold is usually curved and narrow.

When starting both machines, the current will be 3 to 4 times or maximum 6 to 7 times as current when machines operate normally.

For end-product differences and advantages. While the final shape required for a part often dictates the process used, both extrusion and injection molding have their advantages.

Injection molding typically has a higher, initial design cost due to the complexity of the mold structure. Its cyclical production, however, typically creates a finished piece that often does not require further assembly or secondary processing.

The extruder can create complex cross-sections such as multi-lumen tubing used in medical devices or food processing. The surfaces of extruded materials are smooth and do not require post-production “clean-up.”Extrusion is ideal when a variety of lengths of the same profile shape is required. By producing a stock product with a continuous production process and cutting to length post-process per demand, setup, and die/design costs are reduced for similar items.

These are general differences and similarities between extruder and mold injection machine.