5-Axis Machining

Multi-Point Method

Multi-Point Machining (MPM) is a 5-axis tool positioning strategy that stems from a simple observation. If a cylindrical coin, that represents a rotating tool is thrown into a premachined die or mold it will contact the die or mold surface at more than one point. Depending on the surface the contact points could be two, three or more. If the die surface is a sphere, the contact will be along the entire perimeter of the circular edge. However, the axis of the cylinder will be inclined. If it is possible to touch the die or mold surface at two or more points, than why limit our tool positioning strategies to just one point of contact? More points could mean reduce machining time, better surface finish etc.

This basic idea was the premise behind the MPM strategy. This strategy utilises the flexibility of a 5-axis machine to tilt the tool along a direction that will result in two points of contacts between tool and surface. The MPM method was first develoiped to machine spherical cavities. A sphere is a special case in which the tool can contact the surface at infinite points, when positioned properly. Further, the MPM method was developed for Bezier and other parametrically defined surfaces. In MPM the method begins by identifying a single point of contact and than moving the tool axis about this point of contact until another contact point is found. As the tool is moved it can gouge into the surface, such movements must be avoided. Thus, MPM has inbuilt gouge checking, which is performed whenever the tool is repositioned. This, however, increases the computational time for determining tool positions.

The MPM method was developed by A. Warkentin. To conclude his work he compared the performance of MPM with 3-axis machining, Sturz method, and with PAM. MPM was found to be the best method. The details can be found in the following publication:

Last updated on: September 19, 2014
Warkentin, A., F. Ismail, S. Bedi
Int. J. of Machine Tools and Manufacture, Vol. 40, 2000, pg. 185-208

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