How a 5-axis Mill Machines an Impeller

Take a moment and think back to the last time you had to machine an impeller from a solid metal cylinder.
Was it this morning? Perhaps it was a few weeks or months ago? For most of us, the occasion has never really come up (or just that one time in University when you said you’d try anything once). Whatever the case, I’m willing to bet that it eventually required a 5-axis milling machine.. Of course, the best way to use such a machine is a complicated matter.
5-Axis
The first step would be to refresh your knowledge on the basic of Impellers

An impeller is a rotating component of a pump which transfers energy from a driveshaft to the fluid by accelerating it outwardly from the centre of rotation by a set of vanes. Usually made of metal, the impeller’s vanes often have compound curves and are tightly spaced, which makes the process of machining a difficult task. Moreover, the area between the blades is often narrow and deep, a bad combination because it requires long, skinny tools.

Machining impellers from a blank generally involves turning and milling the excess material from between the blades, semi-finishing the floor and the blades, then finally finishing the floor and the blades. See the video below, care of gizomodo.com:

With modern computer-aided manufacturing (CAM) systems and 5-axis plunge roughing, the excess material is milled in precisely monitored layers. Additionally, by keeping the cutter’s centre axis aligned with the cutting forces, side-pressure and vibration can be dramatically reduced, greatly prolonging the tool’s life.

Finishing the impeller vanes provides the greatest challenge, as they are often thin, warped and closely-spaced. Cutting the vanes using a tapered-end ballnose cutter in one continuous motion will provide a smooth finish, and will avoid undesired vibration.

Modern 5-axis cutting in combination with CAM systems is a growing and challenging field, but so often what seems difficult at first eventually becomes second-nature with experience. At the very least, it provides us with cool videos like the one above.

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