Determination of the Real Cutting Edge Wear Contact Area on the Tool-Workpiece Interface in the Light of Cutting Forces Variations

1. Determination of the Real Cutting Edge Wear Contact Area on the
Tool-Workpiece Interface in the Light of Cutting Forces Variations
SAMY E. ORABY
Department of Mechanical Production Technology, College of Technological Studies, PAAET, P. O.
Box. 42325 Shuwaikh 70654, KUWAIT
Email: se.oraby@paaet.edu.kwmail
Keywords: Cutting edge wear and deformation; Wear contact area, Tool-workpiece interface;
cutting forces.
Abstract. The determination of actual stresses over the tool-workpiece interface has long been a
matter of debate among researchers. Evaluation of the nature and the geometry of the wear contact
area were always associated with many, sometime impractical, assumptions. The indeterministic
fashion of edge wear and deformation requires a more realistic way to predict the actual wear contact
area. In the current study, many wear area patterns are proposed considering the different wear modes
of the cutting edge. The selection of the most correlated pattern to a specific edge deformation is
justified using the relevant variations in the radial and the axial force components. For a regular wear
over the entire cutting edge, a wear pattern that considers nose and/or flank is justified. When the
cutting edge plastically fails, a pattern that considers only nose wear is preferred. As the cutting edge
is subjected to many types of irregular disturbances of edge fracture and chipping, a wear pattern
considering both flank and nose wear is selected.
Introduction
In machining, the tool edge exhibits many wear forms such as flank wear, crater wear, nose wear,
chipping, etc, Fig. 1. The flank wear has long been used as a criterion measure to determine the tool
useful time. Usually the flank wear is assessed by its direct measurement as specified by
ANSI/ASME B94.55M-1985 standard, Fig. 2. However, such a direct measurement usually involves
the frequent interruption of the machining process and this is no longer accepted when the advanced
fully automated processes are considered. This called for a more efficient indirect assessment of edge
performance through the inherent variations in one or more of the measures cutting output; cutting
force, system dynamic characteristics, cutting temperature, consumed power, etc. [1,2].
The edge deformation on the tool-workpiece interface is a result of thermal-mechanical-chemical
interaction with a severe friction and plastic-elastic contact. In such situations, the contact bearing
area is usually a matter of interest since it determines the extent of the induced stresses. According to
Waldorf [3], the contact is so complex that the ratio of the normal and contact forces does not follow
those obtained in standard mechanical tests [4]. One unrealistic approach was the assumption of a
constant wear width along the flank contact area [3]. Moreover, a dispute still on [4-6] regarding the
nature of the contact and the induced stresses on the flank interface. One of the reasons behind such a
disagreement is the lack of a realistic approach to determine the actual pattern of the stresses bearing
contact area. Unfortunately, the edge wear and deformation has rarely been with an even distributed
area. In most cases several wear and deformation modes exist over different locations on the
tool-workpiece contact interface. Online or, in-process monitoring of the state of the cutting edge for
possible replacement decision requires a better understanding of the mutual interrelationship between
the wear topography on the flank interface and the corresponding variations in the measured cutting
force components. In more simple words, it is thought that the use of the wear area rather than wear
land width may produce an accurate measure to judge the state of the cutting edge and its
performance. Changes in the contact area as wear propagates can be monitored inprocess through the
corresponding variations in the measured cutting force. Verification of such an approach is the main
objective of the current study.
Applied Mechanics and Materials Vols. 325-326 (2013) pp 1406-1411
Online available since 2013/Jun/13 at www.scientific.net
© (2013) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMM.325-326.1406
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,
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2. a) Edge wear and deformation b) ANSI/ASME B94.55M-1985 standard
Figure 1 Cutting edge wear topography and standard
Geometrical Considerations of the Wear Contact Area on the Flank Face
Various Patterns of Wear Contact Area. Many possible patterns for wear contact area are
proposed as schematically described in Fig. 3. First wear contact area pattern Aw1 is proposed
considering the nomenclatures assigned by ANSI/ASME B94.55M-1985 standard, Fig. 1.b, where
the edge is of zero radius. As shown by Fig. 3.a, the wear contact area is:
( )
( )





++==
r
NBCavc1w
sin
ap
.VBmaxVBVB.
3
1
VB.bA
κ
(1)
where bc is the cutting length considering zero nose radius, ap is the depth of cut, κr is the main edge
(approach) angle and VBav is the arithmetic average wear of the three wear measures on flank face.
With a rounded nose, Fig. 2, the contact length usually comprises of two length parts; the straight
bs and the rounded br. The second patterns Aw2 is proposed, Fig. 3.b considering the nose wear
domination with a linear decrement toward the contact end points at the notch and the round nose:
( ) ( )
( ) 



















−+




 −
=+=+= rn
r
n
CrsCrs2w
2
.r
sin
rap
.VB.
2
1
bb.VB.
2
1
aaA κ
π
κ
(2)
in which rn is the nose radius while bs and br are the straight and the rounded part of the contact length.
The third pattern Aw3, Fig. 3.c, considers the nose wear along with the notch and the end_nose:
( ) ( )
( ) 



















−+




 −
=+=+= rn
r
n
CrsCrs3w
2
.r
sin
rap
.VB.
4
3
bb.VB.
4
3
aaA κ
π
κ
(3)
Finally, the pattern Aw4, Fig. 3.d, is assumed to include both the max flank wear and the nose:
( )
( )
( ) 





−++




 −
=++= rnCBC
r
n
r2_s41_4s4w
2
.r.VB.
2
1
maxVB.2VB.
sin
rap
.
4
1
aaaA κ
π
κ
(4)
Applied Mechanics and Materials Vols. 325-326 1407

3. Figure 2 Real wear land on the conventional tool-workpiece interface
Figure 3 Various assumptions of wear contact area on tool-workpiece interface
Experimental Procedures and Evaluation
A set of turning experiments were carried out using multicoated carbide inserts to cut 709M40 alloy
steel. Inserts configuration was 6°, 5°, 0°, 60°, 30° normal rake, clearance, inclination, approach and
side approach angles respectively. For each experiment, wear land measured sequentially at three
regions: nose VBC, flank VBBmax, and notch VBN, Fig. 1.b. Three cutting force components: main Ft,
feed (axial) Fa and radial Fr, Fig. 1.b, were measured using a three-component dynamometer.
Regular Evenly Distributed Wear Land. Figure 4 shows the wear and the force experimental
results using 100 m/min, 0.6 mm/rev and 2.25 mm speed, feed and depth of cut respectively. Both
SEM micrograph, Fig. 4.a and wear-time graph, Fig. 4.b, show an almost regular wear on both the
edge flank and nose. The radial force component Fr, Fig. 4.c, is observed to be more sensitive for
wear land than the axial force Fa one [7]. In this case, wear pattern resembles that proposed by Aw2,
Fig. 3.b. As shown in Fig. 4.d, the wear pattern Aw1 proposed by ANSI/ASME B94.55M-1985
standard overestimated the real contact area and, consequently produced a misleading values of the
normal stresses on the flank face. Also, it is observed that the pattern Aw3 did not comply with the
case where there no notch wear developed. Generally, the regular evenly distributed wear may by
represented either by pattern Aw2 or Aw4.
1408 Manufacturing Engineering and Process II

4. a) SEM micrograph of the edge wear b) Wear-time plot
c) Force-time plot d) Wear area according to different patterns
Figure 4 Testing results and data evaluation for evenly deformed cutting edge
Edge Failure due to Softening. The use of a high cutting speed of 206 m/min led to the failure of
the cutting edge due to material softening and plastic deformation, Fig. 5.a. Failure eventually
occurred at the nose and extended to the flank zone. Again, the edge deformation was detected well
by the radial force component. While the proposed wear patterns Aw2 and Aw4 conformed well to the
experimental results, the other proposed patterns especially Aw1 overestimated the wear contact area.
Combined Nose and Flank Wear together with Edge Fracture. For a cutting speed, feed and
depth of cut were 145 m/min, 0.12 mm/rev and 2.0 mm respectively, wear-time plot, Fig. 6.b,
indicated that the cutting edge practiced a sudden fracture at the flank zone at an early stage followed
by a nose fracture after about 16 min. These were detected by the radial and the axial force
components, Fig. 6.c. Wear-force-time plots, Fig. 6.b&c, show a good correlation between the edge
deformation and corresponding force variation using Aw1 and Aw4 patterns. This is basically because
the patterns Aw2 and Aw3 do not involve the flank wear. Besides, the notch wear VBN is found
insignificant to invoke itself in the pattern Aw3. Although the pattern Aw1 seems to qualitatively
represents the case, the SEM micrograph of the cutting edge, Fig. 6.a, strongly suggests that its values
are overestimated. Generally, whenever similar radial and axial magnitudes with fluctuated nature is
observed, it is probably better to suggest a wear pattern of the type Aw4.
a) SEM micrograph of the plastic deformed cutting edge
VBN
VBBmax
VBc
0,1
0,2
0,3
0,4
2 5,17 8,84
Wear(mm)
Time (min)
Fr
Fa
Fra
0
500
1000
1500
2 5,17 8,84
Force(N)
Time (min)
Aw2
Aw4
Aw3
Aw1
0
50
100
2 5,17 8,84
Weararea(x100mm2)
Time (min)
Applied Mechanics and Materials Vols. 325-326 1409

5. b) Force-time graph b) Wear area for different patterns
Figure 5 Testing results and data evaluation for plastically deformed cutting edge
a) SEM micrograph shows nose and flank wear b) Wear-time plot
c) Force-time graph d) Wear area for different patterns
Figure 6 Testing results and data evaluation for combined edge wear and fracture
Edge Fracture at Nose, Flank and Notch Zones. Low cutting speed of 72 m/min in combination
with large values of feed and depth of cut of 0.3 mm/rev and 2.5 mm led to a sequential edge fracture
on notch, flank and nose zones, fig. 7.a. The radial force component responded very well to edge
fracture especially at the end of the experiment when nose fracture dominated. Considering the
presence of the notch deformation, it is shown; Fig. 7, that force and wear may be expressed by either
Aw1 or Aw3 patterns. Before the nose failure, both the axial and the radial force components were of
almost equal values with much greater magnitude of Aw1. The sudden increase of Aw3 at the final
failure stage suggests that the earlier values of Aw1 overestimated the contact area. Generally,
whenever multiple random disturbances are observed with minor effect on force signals, the case may
be attributed to either Aw2 or Aw3 patterns. Escalated rate of increase of the radial force component
suggests the wear extraversion over the nose zone.
a) SEM micrograph of multi fractured edge b) Force-time plot
Fr
Fa
Fra
0
2000
4000
6000
8000
2 4 6
Force(N)
Time (min)
Aw2
Aw4
Aw3
Aw1
0
200
400
2 4 6
Weararea(x100
mm2)
Time (min)
0,00
0,20
0,40
0,60
2 11 22 33 45 57 67
Wear(mm)
Time (min)
VBN VBBmax VBN
Fa
Fr
Far
0
500
1000
1500
2 11 22 33 45 57 67
Force(N)
Time (min) Aw2
Aw4
Aw3
Aw1
0
50
100
2 11 22 33 45 57 67
Weararea(x100
mm2)
Time (min)
0
1000
2000
3000
2 13 23 33
Force(N)
Time (min)
Fa Fr Far
1410 Manufacturing Engineering and Process II

6. c) Wear contact areas according to different proposed patterns
Figure 7 Testing results and data evaluation for edge fracture at nose, flank and nose
Conclusions
In metal cutting, there are always much disagreement between the analytical and the experimental
results regarding the nature of contact over the tool-workpiece interface. Among factors behind such
a conflict is the incorrect estimation of the real wear contact area. In this study, the determination of
the most appropriate wear area pattern is verified in the light of the variations encountered in the
cutting forces. A pattern depending on the proposed tool life standard with zero nose radius is found
to produce overestimate values of the wear contact area. For a regular wear mode over the entire
cutting edge, a wear pattern that considers nose and/or flank is justified. When the cutting edge
plastically fails, a pattern that considers only nose wear is preferred. As the cutting edge is subjected
to many types of irregular disturbances of edge fracture and chipping, a wear pattern considering both
flank and nose wear is selected. However, in practice, the notch wear is found to have a diminishing
influence on either the cutting force or on the wear contact area.
Acknowledgements
The author would like to thank the Public Authority for Applied Education and Training PAAET,
KUWAIT for supporting this study under the research support agreement: TS-11-11. Also, author
thanks the Kuwait Foundation for the Advancement in Sciences (KFAS) for their support.
References
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0
50
100
150
2 13 23 33
Weararea(x100
mm2)
Aw4 Aw2 Aw3 Aw1
Applied Mechanics and Materials Vols. 325-326 1411

7. Manufacturing Engineering and Process II
10.4028/www.scientific.net/AMM.325-326
Determination of the Real Cutting Edge Wear Contact Area on the Tool-Workpiece Interface in the
Light of Cutting Forces Variations
10.4028/www.scientific.net/AMM.325-326.1406