The tool life can be defined in three different ways.
- The actual machining time between two successive regrinding of a cutting tool is called tool life. It is most commonly expressed in minutes.
- Volume of material removed in mass production.
- Number of work pieces machined (in mass production).
The life of cutting tool is affected by the various factors mentioned below:
1. Properties of Work Piece Material:
- With the increase in hardness of work piece, forces and power consumption increases and tool wear increases. So tool life decreases.
- When ductility of work piece increases, forces and power consumption decreases, tool wear decreases. So tool life increases.
- But there is no quantitative relationship available between properties of work and tool life.
2. Tool Geometry:
As the tool geometry changes, like when rake angle increases, the tool life will increase. But there is no quantitative relationship between tool geometry and tool life.
3. Use of Cutting Fluid:
- When the cutting fluid is used during machining it is acting as a lubricant in friction zone and carrying away the heat during machining.
- So forces in machining with the use of cutting fluid. It increases by 25 to 40 %.
4. Process Parameters:
- Cutting speed
- Depth of cut
- Because of uniqueness of process parameters, the researchers tried to establish relationship between process parameters and tool life.
- Taylor has assumed that cutting velocity is the major parameter influencing the tool life.
Taylor’s Tool Life Equation:
VTn = constant = C
where, V = Cutting velocity in m/min
T = tool life in minutes
C = Taylor’s constant = Cutting velocity for 1 minute tool
n = Taylor’s exponent depending mainly on cutting tool material
n = 0.05 to 0.1 for H.C steels.
n = 0.1 to 0.2 for H.S.S
n = 0.2 to 0.4 for carbides
n = 0.4 to 0.6 for ceramics
n = 0.7 to 0.9 for diamond
Modified Taylor’s Equation:
f = Feed mm/rev
d = depth of cut in mm
p,q are constants < 1
q < p indicates that tool life is more sensitive to the uncut slip chip thickness than to the width of cut.