Page 112 - Die_and_Molds_User_Guide_7861458_2017

3.4. Special Methods: High Speed Machining (HSM)
and Milling of Hardened Steel

The term “High Speed Machining” and the abbreviation “HSM” are well-known in industry, and in
particular, in die and mold making. High speed machining, what is it? Why is HSM so relevant for
up-to-date die and mold manufacturing?

Even up to now a generally accepted definition of high speed machining does not exist. Obviously,
HSM can mean:
• High cutting speed machining
• High spindle speed machining
• High feed speed machining
HSM is often emphasized that it is “…a high-efficiency method of modern machining with high spindle
and feed speeds…” that allows for various advantages.
It is clear that cutting, spindle and feed speeds are interrelated. More spindle speed = more feed speed,
etc. How to define the cutting speed?

In the example of machining steel with hardness HRC 55 to the section “Solid carbide ball nose cutters”
Milling Tools
the real cutting speed related to the effective diameter was 50 m/min, and the speed with respect to
the nominal diameter – 182 m/min. More illustrative is a case of milling with 0.1 mm depth of cut by ball
nose cutters of different diameters (Table 83). The table shows distinctly that in profile milling with
shallow depths of cut, even small cutting speeds can require considerable spindle speed, which in turn
causes a cutter to run fast.
Assume that 4 mm diameter ball nose cutter in Table 83 has 2 teeth and it cuts with feed
0.04 mm/tooth. The feed speed will be 815 mm/min, 1222 mm/min and 1630 mm/min for cutting speed
40 m/min, 60 m/min and 80 m/min correspondingly!

Shallow, light cuts combined with high spindle speeds are classical attributes of high speed machining.
HSM, as a metalcutting method, demands very specific cutting techniques and dedicated machine
tools, toolholding devices and of course, cutting tools, that will ensure acceptable tool life. Being
applied to manufacturing process HSM can dramatically cut cycle time.
It is worthy of note that HSM not always a process with high spindle speed; and many HSM operations
do not need high rotational velocity.

History: HSM
In the twenties-thirties Dr.-Ing. Carl Salomon, a German researcher, did a series of experiments for
measuring cutting temperatures against the corresponding cutting speeds during machining of
some engineering materials. The results, which have been represented graphically, allowed the
researcher to assume that the cutting temperature rises with increasing the cutting speed, until
the speed reaches some specific critical value, and then comes down, in spite of further the speed
growth (Fig. 53). Hence, Salomon concluded, there is an area of cutting speeds much more than
usual for which the cutting temperature is similar to those that are observed in conventional cutting.
By hypothesis the area related to speeds is 5-10 times as much as common values.

112