What is CNC Manufacturing?

If you’ve ever been involved in the manufacturing of a product, you’ve likely heard the term CNC used. This stands for computer numerical control and is a very common method of manufacturing parts, still used today. CNC manufacturing is a method of subtractive machining in which a blank piece of material is milled away to create a desired part. This is commonly done with the use of CNC milling or CNC turning.

CNC Milling

CNC milling is likely the first thing that would come to mind when picturing the manufacturing method.

With this process, a cutting bit is placed into the machine and the workpiece is clamped to a stationary bed. The machine then rotates the bit at a high speed, which allows the material to be milled away. The basic mills are known as 3-axis, which allows them to move in the x-y-z directions. There is also a process known as 5-axis milling with which the machine can still move in the x-y-z directions, with the additional ability to move with two rotational axes, while increasing the cost of the part. CNC milling is best used for parts with relatively simple geometry but results in accurate parts with tight tolerances (±0.125 mm on average, up to ±0.025 mm). Even though the tolerances are very tight, be cautioned when including fine features in your design, as the vibrational nature of the machines can result in them breaking.

When designing a part for CNC milling, it must be kept in mind that the bit being used to cut is the biggest limitation. Certain geometries may not allow for the access of a bit. This is especially true for 3-axis mills. It is possible to rotate the orientation of a part to add features, however, this increases labor costs. The size of the bit is another limitation. A bit can only get so small, which means vertical internal corners must be rounded to at least match the radius of the smallest available bit.

This manufacturing method can be used with numerous materials, from metals such as aluminum and steel, to plastics such as ABS and nylon. The choice in material does affect the cost. The cost of the blank piece of material must be accounted for, along with the difference in machining costs, as certain materials, such as steel, are more difficult to machine. Restrictions on part size max out at 2000x800x1000 mm or 78”x32”x40”.

CNC Turning

CNC turning is another method commonly used for relatively simple parts with rotational symmetry. This process is completed with a machine known as a lathe.

In this process, the workpiece is placed in a spindle and is rotated at a high speed. The cutting piece typically moves along the radial direction, as well as along the length of the part. The bit generally does not rotate around the part. The manufacturing process is the lowest in cost among the CNC processes, while it is quite limited to parts with rotational symmetry. This can be overcome somewhat by using a mill-turning CNC machine. This allows a part to be cut with traditional lathe capabilities, along with positioning it at specific angles to have material removed with CNC milling tools. This presents the lowest cost of 5-axis CNC technologies. The same materials and tolerances can be found with CNC turning as those with CNC milling, along with the same design concerns. Restrictions on part size max out at a diameter of approximately 500 mm or 20”.

Summary

CNC machining has been used for a long time and is still commonly used today. It is best used for parts with relatively simple geometry and features. It can be used with a variety of materials; however, the cost is directly affected by the level of difficulty of milling. The parts created with this method are very accurate have tight tolerances. It is best used for relatively low quantities of production (<1000 parts). While it can be used for one-off, or extremely low quantity production, additive manufacturing such as 3D printing is often a more cost-efficient solution, especially for plastics.

Thank you for taking the time to read our blog. If you have any questions or require our contract services, please don't hesitate to contact us.