CNC machining has changed the world of manufacturing. While milling machines — devices that use rotary cutters to cut material away from an unshaped “workpiece” — have existed since the nineteenth century, the emergence of CNC (computer numerical control) technology in the mid-twentieth century has made machining much faster and more accurate.
Today’s CNC machines, which use computers to control the movement of the cutter and/or table, are highly advanced pieces of equipment that allow manufacturers to create complex parts with extremely low tolerances.
However, with all the different CNC machining options out there, it can be difficult to know where to start. Different parts require different machining processes depending on their shape, size, quantity and end purpose, so choosing the right CNC process is rarely a straightforward task.
One of the biggest questions for companies using CNC machines concerns the number of axes offered by the machine. 3-axis, 4-axis and 5-axis machines are all frequently used, but what is the practical difference between them? And more importantly, which should you use for your part?
What are the CNC machine “axes”?
Getting your head around the multiple “axes” of machining can be confusing — and for good reason.
The concept is confusing because, intuitively, it seems that three axes could cover all possible shapes. By having a cutter that can move along the X, Y and Z axes (side to side, back and forth, up and down), a machine should be able to cut a workpiece at any point on its surface. By manually reorienting the workpiece on the table at certain intervals (creating a new “set-up”), the machine operator can also allow the cutting tool access to any side of the workpiece.
But while many CNC machines use only three axes, and while the kind of three-axis CNC machining described above can be sufficient for many projects, there are other axes to be exploited too.
These extra axes are the result of rotation around one or two of the X, Y and Z axes, taking account of not just position, but orientation as well. In practical terms, these axes can be exploited by either rotating the cutting tool or tilting the table holding the workpiece.
Why are 4-axis and 5-axis CNC machines useful?
Having a CNC machine with these extra axes presents many advantages. Since they can cut the workpiece from different angles, 4-axis and 5-axis machines can complete a part in a shorter timeframe, with less of a need for multiple set-ups. This has the knock-on benefit of eliminating incorrect alignment — a risk every time the workpiece has to be manually reoriented for a new set-up.
Another related benefit of multi-axis machining is how it eliminates the need for complex fixtures, generally needed to hold parts in place on 3-axis machines.
From a client’s perspective, however, the biggest advantage of 4-axis and 5-axis CNC machining is how it can produce extremely complex shapes to a very high standard. With the extra axes, the machine can move in new arcs and angles with greater reach and flexibility. This ultimately results in the ability to create a wide range of unusual geometries.
Additionally, by having a machine that can orient its cutter at any angle, the job can be programmed to cut the workpiece in the most efficient manner — coming at an angle that will provide optimal cutting speed and chip removal, resulting in a higher quality of finished part.
The arrangement is also ideal for producing contoured surfaces. With a 3-axis machine, a curved edge requires multiple small cuts which can take a long time to carry out and which rarely leave the perfect finish. But with a multi-axis machine, gradual rotation — adjustment of the fourth or fifth axis — can produce near-perfect contours with a smooth finish.
Which process is right for me?
Since 4-axis and 5-axis machines can produce highly complex parts, they are often favored by clients in high-budget, high-stakes industries like the aerospace sector. However, a multi-axis setup is not necessary for every job.
If cost is the number one priority, 3-axis machining is likely the best option. 3-axis machines are cheaper to purchase and require less skill to operate, so 3-axis machining of a part tends to be cheaper than one of the more advanced processes. And even if cost is no concern, extremely simple shapes are sometimes best left to 3-axis machines as well.
When neither of those criteria apply, the decision becomes trickier. And that’s why it’s often best to consult an expert in CNC machining for advice on what kind of machine is appropriate for a given job.
Prototyping specialist 3ERP is one of China’s leading CNC machining companies, and one of a select number that can offer 4-axis and 5-axis machining in addition to the more common 3-axis variety. Its HAAS CNC milling machines are some of the best available, and the company’s engineers have many years of experience in the field. 3ERP also offers a wide range of materials, including plastics like ABS, Teflon and PEEK, and metals like Aluminum, Steel and Titanium.