Tool life is defined as the duration of actual cutting time before a tool becomes unusable, commonly measured by the maximum flank wear reached. Tool life can be expressed in units of time, number of components machined, or volume of material removed. Cutting speed has a significant inverse effect on tool life and follows a power law relationship defined by Taylor's tool life equation. Other factors like feed rate, depth of cut, tool geometry, work material, and cutting fluids also influence tool life to varying degrees.

1. LECTURE -22
TOPIC- TOOL LIFE
BY-AMIT HAZARI
Machining and Machine
tools

2. Tool life
 The tool life is the duration of actual cutting time
after which the tool is no longer usable. There are
many ways of defining the tool life, and the
common way of quantifying the end of a tool life is
by a limit on the maximum acceptable flank wear.
 Tool life is used to calculate the tool material
performance and machinability of workpiece
material.

3. Methods to specify tool life :
 Time period in minutes between two successive
grindings.
 No. of components machined between two
successive grindings.
 Volume of metal removed between two successive
grindings.

4. Tool life expressions :
 Volume of metal removed per minute = $pi$ . D .t . f . N
$mm^3$ / min
 Total volume of metal removed for tool failure = $pi$ .
D. t . f . N . T $mm^3$
 where,
 D = Workpiece dia in mm
 t = Depth of cut in mm
 f = Feed rate in mm/rev
 N = no. of revolutions of workpiece per minute.
 3) Total vol. of metal removed for tool failure = failure =
V x 1000 x t x f x T $mm^3$

5. Factor affecting tool life :
 cutting speed
 feed and depth of cut
 tool geometry
 tool material
 work material
 nature of cutting
 rigidity of machine tool and work
 cutting fluids
 process parameters

6. Cutting speed :

7.  t is major for affecting tool life.
 It varies inversely with tool life which leads to
parabolic curve as shown.
 Tool life relation is invented by F.W.Taylor.
 VT^n = c (n is power of V)
 V = cutting speed in m/min, C = machining constant
 T = Tool life in min, n = Tool life index

8. Tool geometry :
 As a tool geometry is a variable parameter there is
no quantitative relationship is available between tool
geometry and tool life.
 The relationship depends on the rake angle of tool
 Generally as rake angle increases, the tool life also
increases, But if rake angle is too large results in
reduced strength of tool geometry.

9. Cutting fluid
 when cutting fluid is used during machining, it is
acting as a lubricant at friction region and carrying
away the heat generated during machining.
 with the use of cutting fluid, the tool life increases
approximately by 25 to 40 %

10. Process parameters :
 General process parameters are speed, feed, depth of
cut etc.
 Because of uniqueness in process parameters their
are the attempts showing the relationship between
process parameters and tool life.
 Taylor has assumed that cutting velocity is major
parameter which influences tool life. Hence he
derived equation.
 VT^n = constant

11. Contd……
 where ,
 V = cutting velocity in m/min
 T = volume of material removed
 C = Taylors constant
 n = Taylors exponent (Depend on cutting tool material)
 = 0.05 to 0.1 (HCS)
 = 0.1 to 0.2 (HSS)
 = 0.2 to 0.4 (Carbide)
 = 0.4 to 0.6 (Ceramic)
 = 0.7 to 0.9 diamond

12. Solved numericals
 If in turning of a steel rod by a given cutting tool
(material and geometry) at a given machining
condition (so and t) under a given environment
(cutting fluid application), the tool life decreases
from 80 min to 20 min. due to increase in cutting
velocity, VC from 60 m/min to 120 m/min., then at
what cutting velocity the life of that tool under the
same condition and environment will be 40 min.?

13. solution

14. Solved numericals
 Determine percentage change in cutting speed
required to give 50% reduction in tool life (i.e., to
reduce tool life to 1/5 of its previous value). Take n =
0.2 ?

15. solution

16. Modified Taylor’s Tool Life equation
 In Taylor’s tool life equation, only the effect of
variation of cutting velocity, VC on tool life has been
considered. But practically, the variation in feed (so)
and depth of cut (t) also play role on tool life to some
extent. Taking into account the effects of all those
parameters, the Taylor’s tool life equation has been
modified as.

17. Numericals
 While drilling holes in steel plate by a 20 mm
diameter HSS drill at a given feed, the tool life
decreased from 40 min. to 24 min. when speed was
raised from 250 rpm to 320 rpm. At what speed
(rpm) the life of that drill under the same condition
would be 30 min.?
 Ans. 287 rpm