For most shops, the question is no longer whether or not to use CNC (computer numerical control) machining. It’s what form of CNC machining to use and how best to take advantage of it. In this blog, we will go over the three most common types of CNC machining, how to choose one, and how to optimize it for difficult parts and materials.
What are the different types of CNC machining strategies?
CNC Milling
CNC milling is the most widely used machining strategy in the vast majority of shops. With this process, a rotating cutting tool is advanced into stock material to cut away the excess. In 3-axis milling, the CNC milling unit can move either the tool or the material along three axes: X, Y, and Z – or left and right, up and down, and forward and back. Some machines can even move in up to nine axes, though machining in anything more than four axes is referred to as multiaxis machining. The more axes a machine can use, the fewer setups and less stock handling is required for production because the tool is more maneuverable.
CNC Turning
CNC turning uses a lathe unit to spin the stock material at high speeds as the cutting tool is advanced into it. Turning is most effective for cylindrical or radially symmetrical parts, like screws, pins, and drive shafts.
Electrical Discharge Machining
Wire EDM relies on an electrically-charged strand of wire to cut through material instead of a cutting tool. EDM is exceptionally accurate and precise and can be used on a wide variety of materials. Because the cutting wire is attached to the machine at both ends, this method is best for jobs such as extrusion dies, blanking dies, or other parts that are cut entirely through the stock.
Choosing a CNC machining strategy based on your part
The shape of your part will often decide which machining strategy will work best. Sometimes the best first step to take is to decide whether or not it can be efficiently turned on a lathe. If the part is more radially symmetrical than not, consider using CNC turning. If not, then it is time to decide between CNC milling and wire EDM. Review the expected tolerances, size, and shape of the part. Wire EDM is better suited to making small, intricate parts with tight tolerances. CNC milling, the workhorse of the machining family, can usually take whatever doesn’t fall into either category. For milled parts with complex geometries, consider multiaxis machining.
Fine-tuning a machining strategy based on your material
Currently, the most commonly used materials in the average machining shop are steel, cast iron, and aluminum. All are fairly easy to manipulate and rarely require extra thought. However, the aerospace and medical industries often demand parts made from hardened steel families, titanium, and nickel alloys, all of which are more frangible or just plain harder to cut.
The first step to take when dealing with more difficult materials is reducing vibration. The more imbalances the tool or the material has, the more chatter there will be, and the less accurate cutting will be. It may even end in shattered material. To reduce this risk, analyze your fixturing setup to confirm that it offers the most stability possible. For example, many shops have success using strong dovetail fixtures when using multiaxis machining.
Next, take a look at your cutting tools. Your tooling should be coated – often with carbide or zinc – to work through material more efficiently and without sacrificing tool life. Leaf through your available tools and find the ones most likely to hold up to the additional wear, like ball end mills.
Finally, review your CAM program. Harder materials often do best with slower, shallower cuts and light stepovers that reduce heat. Plan out machining so that the cutting tools is engaged with the material for shorter amounts of time to reduce heat and stress. Plan for multiple stages of machining, and even multiple stages of finishing. Keep in mind that you can also consider rough machining your material in a softened state before heat-treating it and then finishing.
This content was first published on the Mastercam website.
