CNC machining is a subtractive manufacturing process since it starts with a block of material (metal or plastic mainly) and removes materials using different tools to reach the final shape.
The full name is Computer Numerical Controlled as the machines are following specific instructions programmed by an operator. Once the instructions are set, the production process doesn’t involve manual operators. There are two main processes for CNC machining: milling and turning. Most CNC machines work on 3 axis: X, Y and the Z. Sometimes, 3 axis is not enough to make complex geometries. More advanced machines are used, such as 4 axis or 5 axis, allowing the bed and or the cutting tool to move on additional on the A and the B axis.
Process : milling and turning
There is two different way to shape material. First one, the machine moves and works around the piece. It’s the milling process, which is more popular compared to the turning process. On the turning process, the piece turns on an axle and the cutter is stationary. In the industry, when we mention CNC machining, we often think about the milling process by default.
Step 1: input data into the machine
The first step is designing a CAD model. Then with the help of the CAD file, the operator is converting the file to a CNC program. He inputs the data through a series of commands that can be interpreted by the CNC machine.
Step 2: place the material block
We prepare the material and cut it into the correct size. Once ready, we place the block of material (the workpiece), on the built platform (the bed). In order to have the best manufacturing accuracy, positioning and alignment are crucial.
Step 3: material is milled
We can then use different set of cutting tools to remove the material from the workpiece, make and thread holes or create radius. There are different passes necessary to create the final part. The first ones we use special tools that remove a lot of material. Then we change them to use some that remove less material but are very accurate to reach the desired tolerances and roughness.
Once the machining is finished, we take the part then remove burrs from sharp edges and drilled holes. After that, a thorough inspection is done to check dimensions and metrology compared with specifications, with a micrometer and MMT tools.