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DIFFICULT TO MACHINE MATERIALS
There are number of materials which are generally regarded as
being difficult to machine. In general terms the material being
worked is considered to be difficult when it does not respond
readily to normal machining techniques. Among these “difficult’
materials are aluminium alloys, stainless steel and work harden-
ing steels.
Aluminium Alloys
require relatively high speeds and feeds.
They respond best to cutters with few teeth and correspond-
ingly wide chip spaces, and can be worked very effectively by
using two flute end mills, which have the advantage of fewer
teeth engaged in the cut. In many cases coolant may not be
needed to cool the cutter although it is of benefit in lubricating
and particularly in removing chips. Climb milling gives definite
advantages and shows significant benefits where a good qual-
ity surface finish is needed. These materials can be worked
quite effectively with regular tooling, although benefits would
be obtained from custom tools in the event of large volume
production being the norm.
Stainless Steels
require lower speeds and higher feed rates
and often benefits are obtained from using corner radii and
chamfers. These materials respond well to the conventional
cutting method but rigidity of machine and setup are critical.
Light finishing cuts are to avoided but where necessary should
be taken at a feed rate as high as possible to meet with sur-
face finishing requirements. It is crucial that these materials be
“worked”, and “rubbing” of the cutter against the workpiece
should be avoided. Selection of speed and feed rates is of
great importance. Coolant must be used in large volume and be
directed at the cutting area. Benefits are often obtained from a
higer coolant concentration or from using cutting oils.
Work Hardening Steels
such as some stainless and manga-
nese steels can be successfully machined by using the same
techniques as described for stainless steels above.
