How many times you were faced with the challenge of designing a plastic part that required to be machined, be it unusual shape, low quantity or close tolerance? Although not common (compared to plastic molding), plastic CNC machining is sometimes the only solution. Attempting to do it yourself with the help of a manual or handbook is not your best approach. Material selection, tolerating, polishing, annealing, and handling, all these challenges will be successfully addressed by a skilled individual. If you choose the right plastic CNC machining shop that is.
First and foremost, identify shops that specialize in plastic CNC machining. Call them and ask questions about your particular job and few basic ones regarding the procedure. If they cannot provide you with such information, contact another shop. But this requires time, research and knowledge of the plastic machining process itself.
Machining process is sometime used as secondary operation on formed and molded parts, but is commonly used in the fabrication of plastic into finished products. There are few differences between machining plastics and metals and those differences require changes in both feed rates and cutting tool speeds. Different plastic materials respond different to CNC machining and they are generally divided into three categories:
Soft plastics, like polypropylene and polyethylene, which will produce long curtly chips.
Hard plastics, including polycarbonate and ABS, which result in short crystal like shards.
Reinforced plastics, which contain abrasive fibers and require very sharp tooling.
The plastic CNC machining include few different processes like:
Sawing
Usually used to reduce in size plastic sheet stock and rod and bar stock for subsequent machining.
Milling
Versatile machining process that uses the motion between the multi-edge cutter, the work-piece and the rotating to cut curved and flat surfaces.
Routing
A type of milling operation used to machine flat plastic. Routing is usually made by using an end-mill cuter and can be performed manually or automatically with CNC machine.
Drilling
Process which is accomplished with either rotating or fixed work-pieces presented to the drill bit. The drill bit may be straight fluted or helically fluted and diamond or carbide tipped.
Turning
Here the plastic piece is rotated about its axis on a lathe. Cutting is performed on internal surfaces and the exposed end.
Water-jet cutting
This process uses high pressure stream of water to cut plastics.
Laser cutting
This process is used in cases when a fine, polished cut is required. The most common types of lasers are CO2, the Neodymium-Doped Yttrium- Aluminum Garner, gas laser, solid-state laser.
When it comes to assembling, there are many methods of joining plastic-to-plastic and plastic-to-metal parts together. All these methods can be accomplished both manually or automatically using:
Snap fits which are integral fasteners molded into plastic components. They are easy and quick to use in permanent assembly and when disassembly is required.
Hinges are used assemblies that require repeated closing and opening. There are three main types of hinges: one-piece integral, two-piece and multi-part hinges.
Common mechanical fasteners include rivets, eyelets and screws. All they can be installed automatically or manually.
Bonding is used to effect permanent and strong joints. The two principle bonding methods are solvent bonding and adhesive bonding.
Welding includes the fusion of thermoplastic parts. Few different welding methods are used, including: spin welding, hot-gas welding, ultrasonic welding, vibration welding and staking.
