CNC Machining:
How the process works:
CNC Machining uses a, computer controlled, robotic arm that removes material from a piece of stock using data from CAD files to create parts quickly and precisely. CNC machines are basically a computerized machinist that cuts material away from a standard size piece of material until the desired product is achieved. CNC Machines come in two basic forms: The CNC mill and the CNC lathe. On a CNC milling machine, the robotic arm manipulates a spinning mill bit to remove material from a piece of stock that is clamped in place. CNC lathes use lathe bits and spin the work piece to remove material from the work piece. CNC lathes are best suited to creating parts that have axial symmetry such as shafts and rods. Some CNC machines have more axis than others. With more axis more complex designs can be produced since the robotic arm can articulate in more directions.
CNC Vertical Machining Center CNC lathe close-up CNC lathe
How is design information transmitted to the manufacturing process?
What materials does the process use?
CNC machining is a very popular method of rapid prototype construction because it can use any machinable material. This includes most common metals (steel, aluminum, copper, titanium, etc.) as well as many plastics (acrylic, polycarbonate, and many other thermoplastics and resins)
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Metal CNC made parts Plastic CNC made parts
What are the size and shape limitations on the parts?
The size of CNC made parts is primarily limited by the size of the actual machine and the bits it uses. Most machines cannot manufacture any part that is over about 3 feet in any dimension although large machines do exist and produce much larger parts for special applications. Another problem with large parts is that the amount of material that must be removed from the piece of stock is significantly increased. This means that it will take longer to produce and puts more wear on the machine. Small parts are also hard to produce since very small milling bits must be used and milling bits are not produced in extremely small sizes because of the lack of applications and the fact that the strength of the bit decreases with size. The shape of parts is limited by the ablility to hold the part in some sort of clamp while the part is machined. Multi-axis machines can be used for very complicated geometries and intricate parts. Very small, and intricate parts may be hard to clamp and may be so small that the stress induced in the part during the machining process cannot be withstood by very small parts.
How much do parts cost? How quickly can parts be manufactured?
One of the major advantages to CNC is how quickly and cheaply parts can be produced. Simple parts can be produced in under an hour while more complex designs will take up to a few days. Parts can be produced at a price similar to what a machinist would charge. Exact pricing varies widely from part to part and shop to shop.
Advantages to CNC: