Successful 5-axis CNC machining

5-axis CNC machines have become more common and designers are increasingly specifying more sophisticated components, especially in the aerospace and toolmaking sectors. The main benefits of 5-axis CNC machining are the ability to use shorter and more rigid cutters, and manufacturing more or all of the part in one setting, hence making it easier to produce complex parts faster and at a reduced cost.

Shorter tools make it possible to machine at higher speed, which will cut cycle times and, at the same time, improve the surface finish of the component. Machining more of the part in one operation improves accuracy, saves setting time and reduces the overall production cycle. Many components require die sinking operations to finish the fine detail. 5-axis CNC machining can reduce or remove the need for EDM operations by machining the shapes directly, significantly reducing costs through taking out whole tasks.

Older machines may not have continuous 5-axis capability, but can go a long way towards one hit machining with 3+2 metal cutting techniques. These will often achieve the same result as 5-axis, but CNC programming is complex and, without extreme care, mismatches between toolpaths can leave marks on the job. CNC programming in 5-axis overcomes these problems but requires powerful CAM software to make it easy to achieve the desired results.

For successful 5-axis CNC programming, the CAM system needs to be able to know exactly where there is material remaining on the job and amalgamate this with the kinematics of the machine tool. It is not sufficient to know when there is a collision as, from the programmer’s point of view, a solution still has to be found. Collision avoidance detects a potential crash, tips the tool and adds unwind or flip movements if these will help. If not, it will suggest new tool lengths which will reach previously inaccessible areas, generating an uncollided toolpath for the existing cutter.

Angular limitations vary considerably from one machine to another, so it is necessary to know which machine is to be used before postprocessing and, ideally, during the programming phase. A 5-axis cutterpath is unlikely to run, collision free, on two different machines as angular movements possible on one machine will cause another to exceed its axis limits and stop.  Similarly, where, for example, available C-axis movement is small or slow, the programmer will want to keep the tool vertical wherever possible, minimising C-axis moves and avoiding unnecessary air cutting. Clearly the programmer needs to know the machining strategies best suited to his components and 5-axis cnc machine. Even so, the calculations in the CAM system are complex as it needs to be able to work within the programmer’s restraints, overriding them where necessary to keep the toolpath smooth, and at the same time deliver a safe collision free result, which will be ideal for high speed manufacturing.

Software such as Sescoi’s WorkNC makes 5-axis CNC machining virtually automatic with its Auto 5 module. This turns 3 and 3+2 axis toolpaths into 5-axis with little more than one mouse click, once the programmer has selected his preferred cutting method. Collision avoidance in the software takes away much of the decision making, bringing 5-axis CNC machining well within the capabilities of the majority of companies, enabling them to get the best from their machinery, improve quality and open up new markets.

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