5-axis CNC machining - A detailed guide

5 axis CNC machining is among the most misunderstood manufacturing process out there and because of its rarity, it has several myths floating around about it. That is what we hope to break with this article. First, when saying 5-axis machining, we refer strictly to the continuous 5-axis machines. We will separately discuss the indexed 5-axis machines (3+2). They are a little less sophisticated than a continuous machine.

3-axis machines (Conventional VMC machines) can actually machine most geometries. In fact, with additional jigs and fixtures, these machines can machine almost all possible machinable geometries. So, the question is why, where and when one should think about using 5-axis machining?

Before diving into that, let us come to a good understanding of what 5-axis machining is. 5-axis machining, as the name suggests, can work on 5 of the usual 6 axes coordinate system (X, Y, Z, X-rotation or A, Y-rotation or B, and Z-rotation or C) in the same set-up. In other words, the machine can work on 5 of the 6 sides of a part (other than the base), in a single set-up.

In a typical 3-axis machine, the bed can move along the X and Y axis, and the tool moves vertically (Z-axis). But in a 5-axis machine, several configurations are possible to make the 5-axis movement possible. The most common ones are illustrated in the below figure.

The most important feature of the 5 axis machines is that the machine can operate all the 6 axes at the same time. A three-axis or a 5-axis indexed machine can only operate 3 axes at the same time. The implication is that this machine can carve 3D contours with impeccable precision and continuity.

A 5-axis machine can also remove material on every surface except for the clamping area and the bottom. When working on contoured parts or parts that require machining on several planes, you need a few setups on the 3-axis machine to achieve the complex geometry through the manual rotations. 5-axis technology completes the job in a single setup, reducing the number of fixtures and part manipulation and helping you save time.

Other than these features, the operations of all the VMCs are quite similar. Most CAM software can program for 5 axis machines. Modern 5 axis machines are quite easy to use too. Only thing is that the machine’s initial cost is much higher than the other machines which invariably costs more per hour machining time. But when used properly, this machine can more than compensate for that.

Complex contours

The ability of the 5 axis CNC machine to simultaneously control five axes makes the machine manufacture highly intricate contours that are extremely difficult to machine in a 3-axis machine. Even in the case, that surface is machined with a 3-axis machine, it cannot be as precise or smooth as a surface machined by a 5-axis machine. These machines can even machine a perfect sphere

Geometries with features on multiple planes

These machines can also access all the surfaces of a part, other than the base and clamping area, in a single setup. A wide variety of geometries can be readily manufactured in these machines with high levels of precision.

Higher rotational accuracy

Every time we change the setup of the workpiece, there is be at least a positional error, however cautiously one does that. unlike 3-axis machining, 5-axis mills increase accuracy by allowing you to complete a part in a single setup. Therefore, you create multiple and complex shapes without losing the precision required to maintain tight tolerances.

Higher throughput

Since there is no need for additional setups, any part can be machined much faster in a 5-axis machine when compared to a 3-axis machine. So, it can improve your throughput substantially for geometrically intricate parts.

Expensive machinery and tooling

All these additional advantages come with a cost. So the machine is substantially more expensive to buy and operate than a 3-axis VMC. So, if you need to get your part machined with a 5-axis machine, it might be more accurate, but it is going to cost more too.

Deciding on choosing a manufacturing process for a part should be always based on the economics of manufacturing. For 5-axis machines, there are several cases where using this machine makes economic sense. The thumb rule is that if your part meets two or more of the requirements mentioned below, you can go for 5-axis machining.

Complex parts with features on many planes can be manufactured economically in a 5-axis machine for low to medium production runs. For example, the part above can be manufactured with DMLS, 3-axis and 5 axis machining too. But one has to choose 5 axes only for low to medium production runs. For high production runs, a 3-axis machine with specialized jigs will make better sense, and for one-off parts, DMLS might prove to be a more economic choice.

Irrespective of the order quantity, if you need your parts with complex contours to be manufactured accurately, with a good surface finish, you have to go with 5-axis machines. This can be attributed to the ability of the machine to control 5 axes at the same time. No other process can match this machine in for these requirements.

Both DMLS and 3-axis machines can be used to manufacture complex geometries, but they cannot manufacture with the same levels of accuracy as a 5-axis machine. DMLS, being an additive manufacturing process, has lower machine tolerance capability. And in a 3-axis machine, changing setups cause small misalignments, which in turn reduces the achievable tolerance.

5-axis machines can manufacture most CNC machinable parts much faster than a 3-axis machine because of lesser setup changes required. So, if it is more important for you to manufacture parts fast than cheap, go with 5-axis machines.