A comprehensive tool-wear/tool-life performance model in the ...

ARTICLE IN PRESS
P.W. Marksberry, I.S. Jawahir / International Journal of Machine Tools & Manufacture 48 (2008) 878–886 881
3. The new tool-wear/tool-life relationship for NDM
A recent advance in tool-wear/tool-life modeling for
dry machining is the work of Jawahir et al. [31] and Li
et al. [32]:
km V ð1=nc Þ
R
T ¼ T R
f n 1
d n , (1)
2
V
where T is tool-life or tool-wear, T R is the reference
tool-life or tool-wear for 1 min, V is the cutting speed,
V R is the reference cutting speed for 1 min of tool-life
or tool-wear, n c is the coating effect factor and W g is
the chip-groove effect factor, represented as km=f n 1
d n 2
. W g
is a function of feed (f), depth of cut (d), tool nose radius,
chip breaker configurations and the type of machining
operation (m) with m ¼ 1 for turning. n 1 , n 2 and k are
empirical constants. Outputs and constants of this model
can be easily generated using a series of machining trials
(o10) while varying depth of cut, feed, and cutting speed
while achieving accuracies on the order of 90%.
Modifications to the tool-coating effect factor, n c , is
possible by including NDM parameters to the series of
trial experiments.
Extension to the dry machining model is shown
below:
km V ð1=nc Þð1=N NDM Þ
R
T ¼ T R
f n 1
d n , (2)
2
V
where N NDM is the NDM effect factor and is expressed as
N NDM ¼ n mist
n c
, (3)
where n mist is the modified coating factor for NDM mist
spray. n mist can be defined as the following:
log V 1 log V 2
n mist ¼
, (4)
logðG F;W;N;MZX ;M ZY
Þ log T 1
where G F;W;N;MZX ;N ZY
is the new modified tool-wear/tool-life
value in NDM, empirically derived while varying MWF type,
MWF volumetric flow rate and nozzle(s) position. Subscripts
of the G function: F, W, N, M ZX and M ZY each represent a
modified tool-wear value that is empirically derived. Table 3
explains each mapping function and how it is derived.
3.1. Derivations of the M ZX and M ZY effect factors
M ZX and M ZY effect factors can be solved by linearization
of actual tool-wear/tool-life results as shown in Fig. 1.
MWF rate (denoted X rate in units ml/h along the X-axis)
represents the actual volumetric flow rate of the MWF. The
performance and linkage of MWF type can be accomplished
by using a standard MWF evaluation method. In
this work, a standard tapping torque test method was used
(denoted as Y typ in units N cm along the Y-axis). Variations
of the standard method were also developed to characterize
cooling and lubrication behaviors of MWFs.
Having obtained M ZX and M ZY , G F;W;N;MZX ;M ZY
can be
solved using Eq. (5):
G F;W;N;MZX ;M ZY
¼ T NDM ½ðM ZX ÞðX rate b min Þ
þðY type a min ÞðM ZY ÞþZ 1 Š, ð5Þ
where G F;W;N;MZX ;M ZY
40, T NDM is the predominate toollife
of the cutting tool, Z 1 is the intercept of the effect
Table 3
G function explanation
Mapping
function
(subscript)
Definition Comment Categories Method to calculate
F Ideal MWF function MWFs are often classified as
‘‘coolants’’ or ‘‘lubricants’’
W
Dominant tool-wear
pattern
Tool-wear pattern responsible for
catastrophic failure or end of life
N Nozzle(s) position MWF source direction and
distance to cutting zone
M ZX MWF rate effect factor Linearization of tool-wear and
MWF vol. flow rate data
M ZY MWF type effect factor Linearization of tool-wear and
tapping torque data from MWF
G C , cooling (water
miscible); G L , lubrication
(non-water miscible)
W BL , length of groove
backwall wear
Single nozzle: R, rake
face; F, flank face; C, chip
M ZX
M ZY
Collect torque test data (N m) for
each MWF using the ASTM D 5619
tapping torque test standard with
reamed holes at 5.48 and 5.55 mm.
Measurements using new method for
assessing tool-wear.
Vector representation of nozzle to
cutting zone (include three
dimensional angle and distance to
cutting zone from nozzle tip)
Calculate slope of axis:
1. Tool-wear
2. MWF volume flow rate
Calculate slope of axis:
1. Tool-wear
2. Tapping torque results from
MWF