High speed machining

This machining type is contrary to the aforementioned traditional concept. Chip section is maintained, i.e. feed per tooth and immersion conditions (radial and axial depths of cut) and to a great extent are even reduced, however, cutting speed is higher than usual. How much is it increased? There is no real academic response, however, it is understood to be higher than ‘traditional’ (x10,x20,...) cutting speed. From the academic viewpoint one could say v _c is increased to the point where the thermophysics of the chipping process varies considerably in relation to that of the conventional process.

This definition implies one or several of these aspects:

- The shearing process deformation speed occurring in the primary shearing area, exceeds 10 ⁵ s ^-1.

- Almost all the heat is evacuated with the chip, the process being close to adiabatic conditions regarding the material. Almost no heat is transmited to the tool, which is optimum in preventing its degradation.

- The effect of chip direction change, which is the material kinetic momentum change, is appreciable and should be considered in the global energy balance.

With this definition we would find almost none of today’s machining processes are high speed, when almost all machine offerers claim that what their milling machines allow is. Why the paradox? Its explanation can be found in the following section. We can advance that only in easily machinable lightweight alloys of magnesium or aluminium, the chipping process differs from that of conventional speeds. However, for this fact to be evident, cutting speeds must be much higher than those applied in today’s industrial HSM processes, which must exceed a cutting speed of 2500 m/min. In the case of steels, castings, difficult-to-machine alloys, titanium, etc., even with today’s cutting speeds being considerably higher than conventional, there is no great variation in intrinsic mechanisms (viscoplastic, thermal, etc.) associated with chipping.High Speed Machining will be abbreviated here to HSM. It should be remembered HSM is recognised worldwide even as a verb (its participle is HSM’ed)