Machinery's Handbook, 31st Edition
Microcutting Tools 1169 equivalent tool life and equivalent tool speed. The equivalent tool life T e is just the sum of all machining time periods: (7) The equivalent tool speed must produce the same tool damage as a tool after cumulative machining. The total tool damage is given in Equation (6) as: (8a) T t e i i 1 = ∆ = / k Q t V C TV 1 i i i k e e 1 ∆ = = = / n 1 ⁄ n 1 ⁄ n 1 ⁄
Solving for the equivalent cutting speed V e
k
n P OO OO OO OO O N
J L KK KK KK KK K
/
n 1 ⁄
t tV i i ∆
∆
(8b)
1
1
i
V Q e =
=
k
/
i
1
i
=
When Q = 1 then, ( V e ) 1/ n terms, by definition. Mathematical models for cumulative tool wear are now derived for most popular machining operations, namely turning, drilling, facing, and milling. 1/ n is the mathematical average of all ( V i ) • For turning with different cutting speeds, Equation (6) is applied. If turning speeds are kept the same from one pass to another, substitute V = V i into Equation (6) to obtain: (9) • For drilling, tool wear would be most substantial at the cutting lip where cutting speed is at the highest. Since cutting speed is constant during drilling as in turning, the tool wear model for drilling is the same as in Equation (6) for variable speeds, and Equation (9) for constant speed. • For facing, the cutting speed reduces linearly from the maximum V i at the outermost radius to zero at the spindle center. It can be shown that the cumulative tool life model for facing is: (10) • For milling, the actual machining time is the time during which chips are produced. The chip generating time involves geometry of a tool and milling parameters. The cumulative tool life model for face milling is tV i i 1 ∆ = + = / n 1 ⁄ n n QC 1 i k n 1 ⁄ V t QC i i k 1 ∆ = = / n 1 ⁄ n 1 ⁄
D a
1 2 −
cos
1 − `
M
j
k
1 λ
(11)
/
tV i i ∆ = n 1 ⁄
n 1 ⁄
and
QC
=
λ
360
°
1
i
=
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