Machining of engineering plastics

Engineering plastic can be easily machined on any ordinary metalworking machineries. However, there are some points that are worth to consider in order obtaining good machining result.

Cutting engineering plastic required lesser clamping force than for machining metal. As engineering plastics are not as rigid as metal. It is always advise to support the work adequately during the machining process in order to prevent deflection or deformation. For example, thin wall tubes require the use of internal plug or support in order to allow accurate machining with respect to roundness and it tolerances.

Cutting tools

High-speed tool steels (HSS) are usually used for cutting engineering plastic. High speed steels works well on glass filled fiber reinforced material. Diamond coating tooling is sometime used to provide optimum tooling life.

Cutting coolants

Coolants are not typically necessary for thermoplastic machining operation, gentle compressed air blow are usually use to clean the machining areas and keep the cutting area cool to improves surface finish and maintain good tolerance.

If coolants are required, water-soluble coolants general do very well. However, the part after machining should be thoroughly cleaned with isopropyl alcohol and rinsed with water to reduce the risk of stress cracking.

Due to the poor thermal conductivity of plastics, provision has to be made for good heat dissipation. Heat is best dissipated via the chips.

1. Machining by lathe. ( Turning )

In general, large rake angle and large side clearance are required for turning of engineering plastics. For particularly high quality surface finishes, the tip of the cutting tool is to be shaped as a broad-nosed profile.
A "V" shape cutting edge is required for parting off plastic to prevent remaining stump.
Some time, it is better to work with tools that are ground to a knifelike cutting geometry on thin-walled and particularly flexible workpieces.

2. Milling

For plane surfaces, face milling is more economical than peripheral milling. For peripheral milling and profiling, conventional end mill is not suitable. Single lip cutting tool or double edges slot drill are normally used. The cutting tools should not have more than two cutting edges. Higher spindle speed is recommenced.

Usually, optimum removal rates and surface finish are obtained with single-point tools.

3. Drilling and boring

Twist drills can be used for drilling of engineering plastic. In general, the drill have an angle of twist of 12-16° and very smooth helical flutes for good chip removal. Larger holes should be rough-drilled or produced by internal turning if possible.
Drill must be proper sharpened, otherwise, the developing compressive strain can build up and cause the material to split.