Three factors are crucial
When turning, the conditions such as cutting speed, feed and depth of cut affect tool life.
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Depth of cut
Cutting speed has the greatest effect on tool life. As shown in the graph below, when cutting speed increases, cutting temperatures rise and tool life can shorten. Also if the cutting speed is too low, tool life can also be much shorter, this is because welding occurs and can easily cause trouble such as chipping and fracturing. Additionally, machining accuracy worsens in this low speed area also due to welding and the built-up edge formed on the insert.
Workpiece: JIS SNCM1
Tool: P20 cemented carbide
The images below show the surface roughness when facing a ø80 carbon steel disc at a fixed main spindle revolution of 500 min.
JIS S45C 180HB φ80 disc
Insert CVD coated SNMN1204
vcmax = 152.7m / min (n=500minˉ¹)
ap = 0.5mm
f = 0.1mm / rev
When the spindle speed is fixed, and the cutting edge approaches the centre of a disc, the cutting speed decreases. When the cutting edge reaches the lower cutting speed area (a), built-up edge is formed and the surface roughness immediately deteriorates and the workpiece surface finish becomes turbid* or cloudy.
JIS S45C 180HB
vcmax = 200m / min,
f = 0.25mm / rev
ap = 0.5mm,
f = 800minˉ¹
Next to cutting speed, feed has the greatest effect on tool life. At low feed rates, flank wear increases and the tool life shortens, this is because the cutting edge will rub and work harden the workpiece. On the contrary, with higher feed rates, the flank wear increases due to the higher cutting temperature, but in most cases the effect on tool life is smaller than high cutting speeds.
Increasing the feed improves machining efficiency without shortening tool life and is thereby effective in reducing machining costs.
Depth of cut
The depth of cut least affects tool life. However, as with feed rates, a small depth of cut will tend to work harden the workpiece (abrasive phenomenon), causing a shortening of tool life. In addition, for cast surfaces and outer scale, unless the depth of cut is increased to a depth below the surface scale, the cutting edge will cut the hard surface layers’ impurities, leading to chipping and abnormal damage.
vc=200m / min