Precision Plastic Injection Molding

Precision plastic injection molding has challenges beyond regular projects. Small parts are used in medical devices, electronics, the auto industry, and dozens of other industries. Just like their big brothers, micro plastic injected parts must still be carefully finished, fit together, and still have the designated materials characteristics.  Just because they are small doesn’t mean they are less complex; they are just smaller.

Micro-molding plastic parts have their own problems, just because they are so small. Micro-precision molds have additional challenges that include thin walls, small diameter and multiple prongs, very small multicomponent fit, and the nature of very small tooling.

Tooling, the building of the molds and injection tubes themselves (called runners) is an additional issue of the precision necessary for the mold.  Molding small parts normally includes injecting into multi-cavity molds. Each cavity is the three dimensional void, mirror opposite of the physical part. Several parts can be injected at one time with a multi-cavity tool.  To do this, the tool must have runners from the injection machine “running” to each part cavity. The more cavities, the higher the complexity of the tool. Complex parts may require more than one runner to get the liquid plastic to all areas of the piece, adding even more complexity.

In addition, the tool must line up with the injection machine, and allow overflow space and a way for air to escape. Proper fittings (bolds, screws, fasteners) must also be included to fit the particular machine.

Finally, the tool must come apart in a way that the hardened plastic part can be taken from the cavity undamaged. Pillars align with holes called a bush.  The tool parts must easily come apart so the micro-parts, can be removed from the tool, and the tool immediately reused and filled with more plastic. Then the overflow and plastic pieces that were formed by the runners must be carefully cut or ground from the edges of the part.

While the plastic injection machine is standard for each use, the tool for molding is custom built for each part shape. The smaller the piece, the more care is required to maintain tolerances. Tools are made of metal. So these heavy metal blocks must be milled with metal forming machines.  Today CMC metal mills are computerized for many of the shapes to be milled into solid blocks of metal. But additional pieces of the tool are still manually built to meet all the specifications mentioned above.

This is similar to making a custom all-metal product, which is very expensive. Making very small parts that may cost a few pennies each requires a custom tool that may cost over $100,000. Therefore, each precision plastic molded piece must have additional cost added to cover the tool and setup costs. This means that very small micro plastic parts be made in relatively large quantities to keep the price low. Many specialty plastic molded medical parts do not require large quantities; therefore, they may be very expensive to cover the tooling costs.

Certain types of precision injected molded pieces must be so precise that clean rooms are needed for certain operations to keep them absolutely clean and sterile. This is especially true of medical devices that are used on humans. This adds some incremental costs where a clean room is required. Reasons for sterile parts includes devices that are invasive or implanted in the body.  Other non-invasive parts that contain liquids or medicine also require a sterile environment. Microdyne is very familiar with these special clean room needs and has worked on major products and new medical device inventors to create precision plastic injection medical devises.

Microdyne also has decades of experience in micro molding, and in fact, Microdyne is a company name that recalls our founding in the 1970s as a specialty micro-injection molding company. We’ve expanded into a variety of other injection and blow-molded areas over the years, but we cut our teeth on precision plastic injection molding.

If your business uses lots of very small plastic parts, please give us a call or fill out our quote form to start a conversation.


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