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The effect of varying the workpiece diameter on the cutting tool clearance angle in tool-life testing
WEAR ELSEVIER
Wear 195 (1996) 201-205
The effect of varying the workpiece diameter on the cutting tool clearance angle in tool-life testing M.A. El Baradie School of Mechanical and Manufacturing Engineering, Dublin City University, Dublin 9, Ireland
Received 18 April 1995; accepted 9 November 1995
Abstract The effect of varying the workpiece diameter on the cutting tool effective clearance angle has been investigated. Theoretical analysis of the relationship between the workpiece diameter and the cutting tool clearance angle is presented. To simulate this relationship experimentally, the cutting tool working normal clearance angle was kept constant, while varying the workpiece diameter, cutting speed and feed-rate. Tool-
life cutting tests of cast iron bars were performed under dry cutting conditions using carbide tipped cutting tools. The experimental results revealed the existence of an optimum tool-life relationship under the above cutting conditions, indicating that the effective clearance angle varies with the varying of the workpiece diameter. Keywords: Tool-life; Cutting tool; Clearance angle; Workpiece diameter
1. Introduction
The influence of tool point material upon tool life speed depends on the resistance of the material to high cutting temperature and the resulting changes of strength, friction and abrasion [ 11. The flank wear land is usually the limiting factor in determining the life of the cutting tool. It has been shown [ 21 that the physical conditions of stress, temperature, and speed that determine the wear rate on the tool flank are sensibly constant along the wear land, and for reasonably small wear lands these physical conditions are not greatly affected by changes in the wear-land width. Hence, it would be expected that the wear rate of the tool material normal to the resultant cutting direction would be constant and independent of the normal clearance angle [ 21. However, the influence of clearance angle on tool life, as illustrated in Fig. 1, indicates that if the clearance angle is increased, the volume of wear required to reach a particular width of flank wear land (VB) is also increased. Hence longer tool life values are obtained. On the other hand, the larger the clearance angle the weaker is the mechanical strength of the cutting edge, and the more liable the tool is to chipping or fracture. It is also suggested [ 1,3] that as the clearance angle increases, the area of tool to conduct the heat away from the cutting edge is reduced and the temperature and wear rate 0043-1648/96/$15.00 0 1996 Elsevier Science S.A. All rights reserved SSDIOO43-1648(95)06858-9
Fig. 1. Effect of clearance angle on tool life: (a) large clearance small clearance angle.
angle; (b)
increase. Thus an optimum clearance angle may occur, since the tool wear volume, as well as the wear rate increase as the clearance angle increases. Small clearance angles Fig. 1 (b) lead to opposite results. Experience has shown that with most work materials, clearance angles in the range of 5-8” with high-speed steel tools and 5-l 1” with carbides give the best compromise between these conflicting requirements [ 41. The objective of this paper is to investigate the effect of varying the workpiece diameter on the cutting tool effective clearance angle in a similar way. From Fig. 2 it can be noticed that as the tool wear develops during cutting, for a small workpiece diameter (Fig. 2(a) ) , the effective clearance angle increases as cutting progresses to reach a fixed width of flank wear land (VB) . The volume of wear required to reach this fixed width of flank wear is
M.A.E. Baradie/
202
Wear 195 (1996) 201-205
Fig, 2. Effect of workpiece diameter on effective clearance angle: (a) small workpiece diameter; (b) large workpiece diameter.
large compared with that of Fig. 2(b) , Therefore longer tool life values are obtained in the case of smaller workpiece diameters. Larger workpiece diameters (Fig. 2 (b) ) lead to the opposite results. However, on the other hand, the larger the effective clearance angle, the smaller the area of tool to conduct the heat away from the cutting edge and the temperature and wear rate increase. Consequently these conflicting requirements lead to an optimum value-with respect to tool life-of clearance angles for various workpiece diameters.
2. Analysis Fig. 3 shows that the rate of increase of flank wear-land width is dependent on the flank clearance angle [ 33 and the workpiece diameter. From the figure with zero tool rake angle VB = NB cot CY,,
(la)
VB VB NB=s=
( lb)
cot ff,,
where VB =rate of increase of flank wear-land length; $JB = rate of removal of tool material normal to the cutting direction; (Y,, = the working normal clearance angle. But, from Fig. 3, NB=NBl
+NB2
(2)
o
2
4
6
CLEARANCE
Fig. 3. Effect of workpiece
8 ANGEL
10 CL,,
DEG.
diameter on effective clearance
angle.
Eq. (6) is illustrated graphically in Fig. 3 for an assumed constant flank-wear length VB = 0.6 mm, which shows the relationship between the ratio VBINB and the working normal clearance angle, for a range of workpiece diameters D = 10 mm, 20 mm etc. It can be noticed from the workpiece diameter’s family curves illustrated in the figure, that for small values of (Y,,, an increase in (Y,, or a decrease in the workpiece diameter, will give a significantly reduced wear rate, as represented by the ratio (VB /NB) . The effect due to the decrease in the workpiece diameter, is attributed to actual increase in the effective clearance angle. It is clear, however, that the effective clearance angle is dependent on the workpiece diameter range. As the diameter increases the component (NB2) decreases, and for larger diameter (D > 100 mm), (NB2) reduces to zero, and consequently the workpiece diameter has a negligible effect.
and NB 1= VB tan (Y,,
(3) 3. Experimental
NB2=&&Dz/4)
- (VB)’
Squaring both sides of Eq. (4) and adding to Eq. (3) after neglecting the higher order terms of NB2, Eq. (2) yields NB=VB
tan a,,,+ (VB)‘ID
(5)
Hence, Eq. (5) can be written as VB E=tan
1 (Y,, + VBID
where D is the workpiece diameter
procedure
(4)
(6)
Tool-life cutting tests were carried out to simulate the effect of varying the workpiece diameter on the effective clearance angle. All tests were carried out under single point cutting conditions on a 10 hp centre lathe. Three cutting speeds were used: 110, 195 and 350 m min- ‘. At each cutting speed three feed rates were used, 0.47, 0.63 and 0.84 m mini. For each cutting speed/ feed-rate combination, a workpiece diameter was selected in the range 32-178 mm. Table 1 summarizes the cutting conditions used in the experiment.
M.A.E. Baradie/Wear195(1996)201-205
Table 1 Workpiece diameter combinations
(mm)
for
Cutting speed (m min-‘)
the
various
Feed-rate
110 195 350
cutting
The tool material grade KlO.
Feed
I
speed/feed-rate
0.47
0.63
0.84
55 100 178
41 75 130
32 55 100
0
0
~~~n’~~~~‘ ~lr~‘~i 5
15 TIME
Imins)
rate - 0.84 mlmin
/f/
LEGEND o speed D speed ?? speed
_
0
~~**‘***I’**~fi’.*
5
10
110 mlmin 195 mlmin 350 mlmin
TIEE
(mins)
Fig. 6. Increase of flank wear with time for a feed-rate of 0.84 m mm’.
used was cemented
Feed rate
carbide
uncoated
-0.47
mlmin
E 0:
0.3
I 4
2 0.2
LEGEND a speed o speed ?? speed
5
10
Feed
0
90” 7” 0” 1 lo
The average flank wear values as plotted against cutting time, for the three feed-rates, 0.47, 0.63 and 0.84 m min-‘, are shown in Fig. 4, Fig. 5 and Fig. 6, respectively. A flank wear land of VB = 0.3 mm in accordance with B.S. 5623 [ 51 was taken as the tool life criteria, and applied to the flank wear graphs. Table 2 gives a summary of these tool-life values.
01 ““““““““’ 0
m/min
Fig. 5. Increase of flank wear with time for a feed-rate of 0.63 m min-‘.
Table 2 Tool-life values (mm) for the various cutting speed/feed-rate
4. Experimental results and discussions
3
-0.63
0.1
Cutting speed (m min-‘)
d
rote
(m min- ’)
Grey cast iron was used, the workpieces were cast in the form of cylindrical bars approximately 500 mm long and 200 mm diameter. The bars were manufactured to BS 1452: 1977 Grade 260. After centring the bars, 4 mm depth of cut was removed from the outside surface to ensure total removal of any cast skin. The hardness of the material was found to be between 145 and 154 BHN. In all experiments the feed/rev was maintained constant at 0.74 mm rev-‘, while the feed-rate was varied by varying the spindle rotation (rpm) . All tests were carried out with a fixed depth of cut 1 .O mm, under dry cutting conditions. The tool tips used in the experiments had an IS0 shape designation TPMR 09 0204. The inserts had the following geometry: Approach angle Side rake angle Back rake angle All clearance angles
203
IO
110 mlmin 195mlmin 350mlmin
15 TIME
lmins)
Fig. 4. Increase of flank wear with time for a feed-rate of 0.47 m mm-‘.
110 195 350
Feed-rate
combinations
(m mm-‘)
0.47
0.63
0.84
13.80 2.16 1.33
15.83 4.66 2.00
15.41 4.08 1.66
From Table 2, it can be noticed that 0.63 m min- ’ feedrate gives the highest tool-life values, at each of the three cutting speeds 110, 195 and 350 m min- ‘. Fig. 7 shows the Taylor curves for the tool-life values against the cutting speeds, for the three feed-rates 0.47,0.63 and 0.84 m min- ‘. By examining these curves it is clear that feed-rate has an influence on tool-life values, with 0.63 m min-’ feed-rate giving the highest tool-life value. The optimum feed-rate range would appear to be between 0.6 and 0.8 m min- ‘. This is mainly due to a variation in the workpiece diameter/effective clearance angle combination, at this particular feed-rate, as illustrated earlier in Fig. 3. As in the experimental procedure the workpiece was varied at each cutting speed/ feed-rate combination as shown in Table 1. It is also important to mention that the feed-rate (m min- ‘) was used during the cutting tests rather than the feed (mmrev-I). Th e reason was to avoid the effect of varying the feed (mm rev-‘) on the helix angle of the cut, and con-
204
M.A.E. Baradie/
1.0 100
200
It appears that as the workpiece diameter decreases, the rate of VB/NB decreases as shown by Fig. 3, suggesting that an increase in the effective clearance angle has taken place. It may be argued that the larger the effective clearance angle, the greater the volume of tool wear and the greater the time required to reach this wear-land value (i.e. the longer the tool life). On the other hand the larger the effective clearance angle, the smaller is the area of tool to conduct the heat away from the cutting edge, and hence, the temperature and wear rate increase. Thus, an optimum tool life may occur, since the tool wear volume, as well as the wear rate increase as the effective clearance angle increases. The increase in the effective clearance angle due to the decrease in the workpiece diameters, as indicated in Fig. 3, may be very small, in the range of 2-3” only. However, experiments [6] and experience [4] indicate that the optimum range of clearance angles is very narrow. Clearance angles in the range of 5-8” with high-speed steel tools, and 5” to 11” with carbides, are usually recommended for optimum cutting conditions.
1000
500 CUTTING
Wear 195 (1996) 201-205
SPEEDIm/min)
Fig. 7. V-T curves for feed rates.
5. Conclusions
Speed
20
40
60
80 Workpiece
100 Diameter
120
140
160
180
(mm)
Fig. 8. Variation of tool life with workpiece diameter.
sequently its effect on the side clearance angle and hence tool-life results. Hence, feed-rate 0.63 m min-’ and workpiece diameter range 41-130 mm give the optimum tool-life values. From the data presented in Table 1 and Table 2, Fig. 8 has been constructed showing the relationship between the workpiece diameter and the tool-life for the three cutting speeds 110, 195 and 350 m min- ’ at the three feed-rates 0.47, 0.63 and 0.84 m min-‘. For all the three cutting speeds, the tool-life increases as the feed-rate increases up to 0.63 m min- I and then decreases with further increases in the feed-rate. For example, it can be noticed from the figure that the largest increase in tool-life occurs at speed 195 m mini’. The toollife increases from 2.16 min at 0.47 m min- ’ feed-rate to 4.66 min-’ at 0.63 m min- ’ feed-rate, which represents an increase of over 100%. Then the tool-life decreases to increase in the feed-rate to 4.08 min, with further 0.84 m min-‘, while at the same cutting speed 195 m min- ‘, the workpiece diameter decreases from 100 mm at 0.47 m min- ’ to 75 mm at 0.63 m min- ’ and further decreases to 55 mm at 0.84 m min- ’feed-rate as shown in Fig. 8 and Table 1.
Further experimental work on other materials is required before the results can be generalized. However, the following conclusions can be drawn for the specific case of cutting cast iron with uncoated carbide tipped tools. The variation in the effective clearance angle is dependent on the ratio VB/NB, and as the workpiece diameter decreases, the ratio VB/NB decreases, giving a significant reduction in tool wear rate. The change in the effective clearance angle due to the decrease in the workpiece diameter is very small, but the rate of change increases significantly as the diameter decreases. This change is in the range between 2 and 3”. However, in general, recommended clearance angle ranges are very narrow. With high speed steel tools 5-8” are recommended. The experimental results revealed the existence of an optimal tool life for a specific feed-rate/workpiece diameter combination, at three different cutting speeds (Fig. S), indicating a variation in the effective clearance angle. The effect of the workpiece on the effective clearance angle is more pronounced for small workpiece diameters, i.e. D < 100 mm. This investigation is of direct interest for the tooling design of automatic bar machines, which produce components from bar stocks (i.e. automatic turret and the Swiss-type automatic lathes). Many of these machines usually operate on very small diameter bars 5-20 mm, where tolerances of 5-15 km are common on these machines.
M.A.E. Baradie/ Wear I95 (1996) 201-205
Appendix
D NB NB VB VB (Y“e
A. Nomenclature
Workpiece diameter (mm) Tool material normal to the cutting direction Rate of removal of tool material normal to the cutting direction Flank wear-land length Rate of increase of flank wear-land length The working normal clearance angle
References [ l] MC. Shaw, Metal Cutfing Princi&x, Clarendon Press, Oxford, 1986. [2] G. Boothroyd and W.A. Knight, Funaizmentals of Machining and Machine Tools, Mercel Dekker, New York, 1989.
205
[ 31 E.J.A. Armarego and R.H. Brown, The Machining of Metals, PrenticeHall, Enflewood Cliffs, NJ, 1967. [4] Metcut Research Associates Inc., Machining Data Handbook, 3rd Edn, Vols 1 and 2, Cincinnati, OH, 1980. [5] British Standard, Specification for tool-life testing with single-point turning tools, B.S. 5623, 1979. [ 61 M.Es. Abdel Moneim, Effect of the clearance angle on the wear of high speed steel tools, Wear, 72 ( 198 1) l-l 1.
Biographies M.A. El Baradie: is a Senior Lecturer in the School of Mechanical and Manufacturing Engineering, Dublin City University. He has attained the academic degrees BSc., M.Sc., M.A., Ph.D. and belongs to the professional societies: C.Eng., MI. Mech.E., M.I. EE.
Wear 195 (1996) 201-205
The effect of varying the workpiece diameter on the cutting tool clearance angle in tool-life testing M.A. El Baradie School of Mechanical and Manufacturing Engineering, Dublin City University, Dublin 9, Ireland
Received 18 April 1995; accepted 9 November 1995
Abstract The effect of varying the workpiece diameter on the cutting tool effective clearance angle has been investigated. Theoretical analysis of the relationship between the workpiece diameter and the cutting tool clearance angle is presented. To simulate this relationship experimentally, the cutting tool working normal clearance angle was kept constant, while varying the workpiece diameter, cutting speed and feed-rate. Tool-
life cutting tests of cast iron bars were performed under dry cutting conditions using carbide tipped cutting tools. The experimental results revealed the existence of an optimum tool-life relationship under the above cutting conditions, indicating that the effective clearance angle varies with the varying of the workpiece diameter. Keywords: Tool-life; Cutting tool; Clearance angle; Workpiece diameter
1. Introduction
The influence of tool point material upon tool life speed depends on the resistance of the material to high cutting temperature and the resulting changes of strength, friction and abrasion [ 11. The flank wear land is usually the limiting factor in determining the life of the cutting tool. It has been shown [ 21 that the physical conditions of stress, temperature, and speed that determine the wear rate on the tool flank are sensibly constant along the wear land, and for reasonably small wear lands these physical conditions are not greatly affected by changes in the wear-land width. Hence, it would be expected that the wear rate of the tool material normal to the resultant cutting direction would be constant and independent of the normal clearance angle [ 21. However, the influence of clearance angle on tool life, as illustrated in Fig. 1, indicates that if the clearance angle is increased, the volume of wear required to reach a particular width of flank wear land (VB) is also increased. Hence longer tool life values are obtained. On the other hand, the larger the clearance angle the weaker is the mechanical strength of the cutting edge, and the more liable the tool is to chipping or fracture. It is also suggested [ 1,3] that as the clearance angle increases, the area of tool to conduct the heat away from the cutting edge is reduced and the temperature and wear rate 0043-1648/96/$15.00 0 1996 Elsevier Science S.A. All rights reserved SSDIOO43-1648(95)06858-9
Fig. 1. Effect of clearance angle on tool life: (a) large clearance small clearance angle.
angle; (b)
increase. Thus an optimum clearance angle may occur, since the tool wear volume, as well as the wear rate increase as the clearance angle increases. Small clearance angles Fig. 1 (b) lead to opposite results. Experience has shown that with most work materials, clearance angles in the range of 5-8” with high-speed steel tools and 5-l 1” with carbides give the best compromise between these conflicting requirements [ 41. The objective of this paper is to investigate the effect of varying the workpiece diameter on the cutting tool effective clearance angle in a similar way. From Fig. 2 it can be noticed that as the tool wear develops during cutting, for a small workpiece diameter (Fig. 2(a) ) , the effective clearance angle increases as cutting progresses to reach a fixed width of flank wear land (VB) . The volume of wear required to reach this fixed width of flank wear is
M.A.E. Baradie/
202
Wear 195 (1996) 201-205
Fig, 2. Effect of workpiece diameter on effective clearance angle: (a) small workpiece diameter; (b) large workpiece diameter.
large compared with that of Fig. 2(b) , Therefore longer tool life values are obtained in the case of smaller workpiece diameters. Larger workpiece diameters (Fig. 2 (b) ) lead to the opposite results. However, on the other hand, the larger the effective clearance angle, the smaller the area of tool to conduct the heat away from the cutting edge and the temperature and wear rate increase. Consequently these conflicting requirements lead to an optimum value-with respect to tool life-of clearance angles for various workpiece diameters.
2. Analysis Fig. 3 shows that the rate of increase of flank wear-land width is dependent on the flank clearance angle [ 33 and the workpiece diameter. From the figure with zero tool rake angle VB = NB cot CY,,
(la)
VB VB NB=s=
( lb)
cot ff,,
where VB =rate of increase of flank wear-land length; $JB = rate of removal of tool material normal to the cutting direction; (Y,, = the working normal clearance angle. But, from Fig. 3, NB=NBl
+NB2
(2)
o
2
4
6
CLEARANCE
Fig. 3. Effect of workpiece
8 ANGEL
10 CL,,
DEG.
diameter on effective clearance
angle.
Eq. (6) is illustrated graphically in Fig. 3 for an assumed constant flank-wear length VB = 0.6 mm, which shows the relationship between the ratio VBINB and the working normal clearance angle, for a range of workpiece diameters D = 10 mm, 20 mm etc. It can be noticed from the workpiece diameter’s family curves illustrated in the figure, that for small values of (Y,,, an increase in (Y,, or a decrease in the workpiece diameter, will give a significantly reduced wear rate, as represented by the ratio (VB /NB) . The effect due to the decrease in the workpiece diameter, is attributed to actual increase in the effective clearance angle. It is clear, however, that the effective clearance angle is dependent on the workpiece diameter range. As the diameter increases the component (NB2) decreases, and for larger diameter (D > 100 mm), (NB2) reduces to zero, and consequently the workpiece diameter has a negligible effect.
and NB 1= VB tan (Y,,
(3) 3. Experimental
NB2=&&Dz/4)
- (VB)’
Squaring both sides of Eq. (4) and adding to Eq. (3) after neglecting the higher order terms of NB2, Eq. (2) yields NB=VB
tan a,,,+ (VB)‘ID
(5)
Hence, Eq. (5) can be written as VB E=tan
1 (Y,, + VBID
where D is the workpiece diameter
procedure
(4)
(6)
Tool-life cutting tests were carried out to simulate the effect of varying the workpiece diameter on the effective clearance angle. All tests were carried out under single point cutting conditions on a 10 hp centre lathe. Three cutting speeds were used: 110, 195 and 350 m min- ‘. At each cutting speed three feed rates were used, 0.47, 0.63 and 0.84 m mini. For each cutting speed/ feed-rate combination, a workpiece diameter was selected in the range 32-178 mm. Table 1 summarizes the cutting conditions used in the experiment.
M.A.E. Baradie/Wear195(1996)201-205
Table 1 Workpiece diameter combinations
(mm)
for
Cutting speed (m min-‘)
the
various
Feed-rate
110 195 350
cutting
The tool material grade KlO.
Feed
I
speed/feed-rate
0.47
0.63
0.84
55 100 178
41 75 130
32 55 100
0
0
~~~n’~~~~‘ ~lr~‘~i 5
15 TIME
Imins)
rate - 0.84 mlmin
/f/
LEGEND o speed D speed ?? speed
_
0
~~**‘***I’**~fi’.*
5
10
110 mlmin 195 mlmin 350 mlmin
TIEE
(mins)
Fig. 6. Increase of flank wear with time for a feed-rate of 0.84 m mm’.
used was cemented
Feed rate
carbide
uncoated
-0.47
mlmin
E 0:
0.3
I 4
2 0.2
LEGEND a speed o speed ?? speed
5
10
Feed
0
90” 7” 0” 1 lo
The average flank wear values as plotted against cutting time, for the three feed-rates, 0.47, 0.63 and 0.84 m min-‘, are shown in Fig. 4, Fig. 5 and Fig. 6, respectively. A flank wear land of VB = 0.3 mm in accordance with B.S. 5623 [ 51 was taken as the tool life criteria, and applied to the flank wear graphs. Table 2 gives a summary of these tool-life values.
01 ““““““““’ 0
m/min
Fig. 5. Increase of flank wear with time for a feed-rate of 0.63 m min-‘.
Table 2 Tool-life values (mm) for the various cutting speed/feed-rate
4. Experimental results and discussions
3
-0.63
0.1
Cutting speed (m min-‘)
d
rote
(m min- ’)
Grey cast iron was used, the workpieces were cast in the form of cylindrical bars approximately 500 mm long and 200 mm diameter. The bars were manufactured to BS 1452: 1977 Grade 260. After centring the bars, 4 mm depth of cut was removed from the outside surface to ensure total removal of any cast skin. The hardness of the material was found to be between 145 and 154 BHN. In all experiments the feed/rev was maintained constant at 0.74 mm rev-‘, while the feed-rate was varied by varying the spindle rotation (rpm) . All tests were carried out with a fixed depth of cut 1 .O mm, under dry cutting conditions. The tool tips used in the experiments had an IS0 shape designation TPMR 09 0204. The inserts had the following geometry: Approach angle Side rake angle Back rake angle All clearance angles
203
IO
110 mlmin 195mlmin 350mlmin
15 TIME
lmins)
Fig. 4. Increase of flank wear with time for a feed-rate of 0.47 m mm-‘.
110 195 350
Feed-rate
combinations
(m mm-‘)
0.47
0.63
0.84
13.80 2.16 1.33
15.83 4.66 2.00
15.41 4.08 1.66
From Table 2, it can be noticed that 0.63 m min- ’ feedrate gives the highest tool-life values, at each of the three cutting speeds 110, 195 and 350 m min- ‘. Fig. 7 shows the Taylor curves for the tool-life values against the cutting speeds, for the three feed-rates 0.47,0.63 and 0.84 m min- ‘. By examining these curves it is clear that feed-rate has an influence on tool-life values, with 0.63 m min-’ feed-rate giving the highest tool-life value. The optimum feed-rate range would appear to be between 0.6 and 0.8 m min- ‘. This is mainly due to a variation in the workpiece diameter/effective clearance angle combination, at this particular feed-rate, as illustrated earlier in Fig. 3. As in the experimental procedure the workpiece was varied at each cutting speed/ feed-rate combination as shown in Table 1. It is also important to mention that the feed-rate (m min- ‘) was used during the cutting tests rather than the feed (mmrev-I). Th e reason was to avoid the effect of varying the feed (mm rev-‘) on the helix angle of the cut, and con-
204
M.A.E. Baradie/
1.0 100
200
It appears that as the workpiece diameter decreases, the rate of VB/NB decreases as shown by Fig. 3, suggesting that an increase in the effective clearance angle has taken place. It may be argued that the larger the effective clearance angle, the greater the volume of tool wear and the greater the time required to reach this wear-land value (i.e. the longer the tool life). On the other hand the larger the effective clearance angle, the smaller is the area of tool to conduct the heat away from the cutting edge, and hence, the temperature and wear rate increase. Thus, an optimum tool life may occur, since the tool wear volume, as well as the wear rate increase as the effective clearance angle increases. The increase in the effective clearance angle due to the decrease in the workpiece diameters, as indicated in Fig. 3, may be very small, in the range of 2-3” only. However, experiments [6] and experience [4] indicate that the optimum range of clearance angles is very narrow. Clearance angles in the range of 5-8” with high-speed steel tools, and 5” to 11” with carbides, are usually recommended for optimum cutting conditions.
1000
500 CUTTING
Wear 195 (1996) 201-205
SPEEDIm/min)
Fig. 7. V-T curves for feed rates.
5. Conclusions
Speed
20
40
60
80 Workpiece
100 Diameter
120
140
160
180
(mm)
Fig. 8. Variation of tool life with workpiece diameter.
sequently its effect on the side clearance angle and hence tool-life results. Hence, feed-rate 0.63 m min-’ and workpiece diameter range 41-130 mm give the optimum tool-life values. From the data presented in Table 1 and Table 2, Fig. 8 has been constructed showing the relationship between the workpiece diameter and the tool-life for the three cutting speeds 110, 195 and 350 m min- ’ at the three feed-rates 0.47, 0.63 and 0.84 m min-‘. For all the three cutting speeds, the tool-life increases as the feed-rate increases up to 0.63 m min- I and then decreases with further increases in the feed-rate. For example, it can be noticed from the figure that the largest increase in tool-life occurs at speed 195 m mini’. The toollife increases from 2.16 min at 0.47 m min- ’ feed-rate to 4.66 min-’ at 0.63 m min- ’ feed-rate, which represents an increase of over 100%. Then the tool-life decreases to increase in the feed-rate to 4.08 min, with further 0.84 m min-‘, while at the same cutting speed 195 m min- ‘, the workpiece diameter decreases from 100 mm at 0.47 m min- ’ to 75 mm at 0.63 m min- ’ and further decreases to 55 mm at 0.84 m min- ’feed-rate as shown in Fig. 8 and Table 1.
Further experimental work on other materials is required before the results can be generalized. However, the following conclusions can be drawn for the specific case of cutting cast iron with uncoated carbide tipped tools. The variation in the effective clearance angle is dependent on the ratio VB/NB, and as the workpiece diameter decreases, the ratio VB/NB decreases, giving a significant reduction in tool wear rate. The change in the effective clearance angle due to the decrease in the workpiece diameter is very small, but the rate of change increases significantly as the diameter decreases. This change is in the range between 2 and 3”. However, in general, recommended clearance angle ranges are very narrow. With high speed steel tools 5-8” are recommended. The experimental results revealed the existence of an optimal tool life for a specific feed-rate/workpiece diameter combination, at three different cutting speeds (Fig. S), indicating a variation in the effective clearance angle. The effect of the workpiece on the effective clearance angle is more pronounced for small workpiece diameters, i.e. D < 100 mm. This investigation is of direct interest for the tooling design of automatic bar machines, which produce components from bar stocks (i.e. automatic turret and the Swiss-type automatic lathes). Many of these machines usually operate on very small diameter bars 5-20 mm, where tolerances of 5-15 km are common on these machines.
M.A.E. Baradie/ Wear I95 (1996) 201-205
Appendix
D NB NB VB VB (Y“e
A. Nomenclature
Workpiece diameter (mm) Tool material normal to the cutting direction Rate of removal of tool material normal to the cutting direction Flank wear-land length Rate of increase of flank wear-land length The working normal clearance angle
References [ l] MC. Shaw, Metal Cutfing Princi&x, Clarendon Press, Oxford, 1986. [2] G. Boothroyd and W.A. Knight, Funaizmentals of Machining and Machine Tools, Mercel Dekker, New York, 1989.
205
[ 31 E.J.A. Armarego and R.H. Brown, The Machining of Metals, PrenticeHall, Enflewood Cliffs, NJ, 1967. [4] Metcut Research Associates Inc., Machining Data Handbook, 3rd Edn, Vols 1 and 2, Cincinnati, OH, 1980. [5] British Standard, Specification for tool-life testing with single-point turning tools, B.S. 5623, 1979. [ 61 M.Es. Abdel Moneim, Effect of the clearance angle on the wear of high speed steel tools, Wear, 72 ( 198 1) l-l 1.
Biographies M.A. El Baradie: is a Senior Lecturer in the School of Mechanical and Manufacturing Engineering, Dublin City University. He has attained the academic degrees BSc., M.Sc., M.A., Ph.D. and belongs to the professional societies: C.Eng., MI. Mech.E., M.I. EE.