Gear Cutting Tools

High-speed
cutting (HSC)
The advantages of high-speed
cutting are:
■ High surface quality and short
machining times
(depending upon the machining
application)
■ Low cutting forces, with
resulting benefits for the
dimensional accuracy of the
workpiece and the tool life
Owing to the low contact time
between the chip and the cutting
edge, the heat which is generated
does not have time to flow into the
tool or the workpiece. The tool and
the workpiece thus remain relatively
cold. By contrast, the chips
are heated very strongly and must
be removed very quickly in order
to prevent the machine from heating
up.
In an example application, HSC
machining without cooling lubricant
led to the workpieces being
heated to approximately 50-60 °C.
At the point of chip generation,
however, far higher temperatures
occur which under certain circumstances
may rise to approximately
900 °C, as indicated by incandescent
individual chips. Based upon
these observations, a transverse
microsection from a workpiece
subjected to the dry machining
process under optimum machining
conditions for the HSC hobbing
process was examined for possible
changes to the microstructure.
The tooth flanks machined by the
HSC process and the reference
samples of a turned blank analysed
for the purpose of comparison
revealed no changes to the
microstructure attributable to the
machining process.
As already mentioned, HSC machining
must be considered in
conjunction with dry machining.
The first studies were performed
on HSC hobbing machines in the
early 1990s. This process now
permits dry machining of gears in
a secure process at cutting
speeds of up to 350 m/min.
Applications and
cutting data
The proven applications for solid
carbide tools for gear and pinion
manufacture lie in a module range
from m = 0.5 to m = 4. The tools
are generally manufactured as
stable monoblocs with bore- or
shank-type mounting arrangement.
The shank type is recommended
for smaller tools. The
cutting speeds are in the range
from 150 to 350 m/min, according
to the module size and process
(dry or wet machining).
The diagram shows the difference
in cutting speeds for dry and wet
hobbing of materials with a range
of tensile strengths. The values in
the diagram apply to a solid carbide
hob, m = 2.
Substantially higher cutting speeds
can be achieved with dry hobbing
than with wet hobbing.
320
300
Cutting speed v c [m/min]
280
260
240
220
200
180
160
140
Dry machining
Wet machining
120
600 700 800 900 1000 1100
Tensile strength [N/mm2 ]
Cutting speeds for a range of material tensile strengths, carbide hobbing, dry and wet, module 2
29