With the cost of most metals continually on the rise, an increasing number of product designers are trying to find alternative, workable, cost-effective materials. As a result, plastic machined parts are becoming more and more commonplace.
For the most part, the equipment, tools and techniques used for metal machining are identical to those used for precision plastic machining. It should however be noted that cutting one type of plastic is not always the same as cutting another type of plastic, so machine operators need to ensure they are adequately trained in the properties and machinability of different plastics.
The Advantages Of Machining Plastic
There are many advantages, but the main ones are:
* Short lead times
* No mold costs
* Can make low volumes economically
* Can accommodate thicker wall sections
* Low force required
* Swarf (turnings, shavings or filings) can be recycled back into the process
* Plastics normally machine dry
Points To Remember When Starting To Machine Plastic
Just like metal, the cutting tools used in the machining of plastics rely on the rigidity of the component being cut in order to create products with precision end results. Metal has a natural rigidity that resists distortion when the cutting saw, machine bit or drill, hit it.
With plastics, however, as there is not always a natural rigidity, some kinds of plastics are more suited to machining than others. Fiber reinforced thermosetting plastics materials, glass reinforced nylons, acrylic and PEEK all have good relative stiffness.
Plastics that are less rigid are prone to deforming and bending away from the cutter. This makes achieving fine dimensional tolerances difficult.
Achieving Precision Plastic Machining
One of the most important things to remember is that many plastics absorb moisture from the air, or from the coolant used during the machining process. Some plastics only absorb a little moisture on an exposed surface, and will then stabilize. With these plastics, if strict precision and tight tolerances are required, parts should first be rough machined, allowed to stabilize, and then finish machined to their final tolerance.
Other plastics absorb moisture (usually from the coolant) and swell while they are being machined, before shrinking as they dry out. With these plastics, in order to achieve tight tolerances, air should be used for cooling, instead of water or other liquids.
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