How many times you were in need to design some plastic part that needed to be machined, be it because of low quality, unusual shape, or close tolerance? Too many, right?! Even though not common, when it comes to plastic CNC machining is usually the only left solution, but trying to do it yourself with the help of some handbook and manual is not the best option you have. Material selection, polishing, tolerating, handling, and annealing, all these challenges will be successfully done in a specialized shop for CNC machining plastic, performed by a skilled individual.
The first and most important thing you need to do is to find shops that specialize in CNC machining plastic, but not any, the most reputable ones. Call them, ask some questions about your particular job, as well as some other basic ones regarding the whole procedure. If they cannot give you an exact answer to all these questions, contact another shop. Be persistent, and stick to what you are looking for. You will surely find a reliable and reputable store that will give you the answer to what you are looking for.
Machining processes are usually used as secondary operations on moulded and formed parts, but they are mainly used in the fabrication of flat plastic sheet, bar stock, or rod into finished products. Since there is a wide range of plastic materials, they respond differently to machining. They are usually divided into three categories:
- Soft plastics (polypropylene and polyethylene) that can produce long curly chips when machined;
- Hard plastics like, polycarbonate and Acrylonitrile Butadiene Styrene (ABS) which can produce short crystal when machined;
- Reinforced plastics – they contain abrasive fibres that require very sharp tooling.
Plastic CNC machining includes the following processes:
- Waterjet Cutting
- Laser Cutting
This type of process is usually used to reduce in size plastic sheet stock, as well as bar and rod stock for subsequent machining.
Milling is a versatile machining process in which is used a relative motion between the multi-edge cutter that rotates and the workpiece in order to cut both curved and flat surfaces.
This is a type of milling operation which can be used for machining flat plastic sheet stock. This process is usually performed by using an end-mill cutter, and can be done automatically and manually with CNC machine tools or routers.
This process can be accomplished with fixed or rotating workpieces presented to the drill bit which can be helically fluted, straight flute, carbide or diamond tipped.
In this type of process, the plastic workpiece is usually rotated about its axis on a lathe, wherein a single-point cutting tools are fed into the workpiece in order to cut unwanted material while creating the desired cylindrical, axially symmetric shape.
In this type of process a high pressure stream of water, or abrasive particles in water are being used in order to cut plastics. Speaking of which, the typical waterjet pressures range from 20,000 to 60,000 psi.
Laser cutting is needed when plastics require a fine and polished cut.
When it comes to plastics assembly, there are many methods of assembling, plastic-to-plastic, and plastic-to-metal parts together.
Snap-Fits – Integral fasteners which are moulded into plastic parts held into place. Snap fits are pretty easy to use when assembly and disassembly is required.
Hinges – This mechanical bearing is used in assemblies that require repeated opening and closing.
Mechanical Fasteners – Mechanical fasteners include rivets, screws, and eyelet which can be installed manually or automatically.
Bonding – If you want to effect strong and permanent joints, use bonding. There are two principle bonding methods like adhesive bonding which requires specific adhesive materials, and solvent bonding wherein the surfaces can be joined by melting.
Welding – Welding includes fusion, or coalescence of thermoplastic components, and includes several other welding methods like, spin welding, hot-gas welding, vibration welding, ultrasonic welding and staking.