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Gundrill life improvement for deep-hole drilling on manganese steel
International Journal of Machine Tools & Manufacture 44 (2004) 327–331
Gundrill life improvement for deep-hole drilling on manganese steel Wei Zhang ∗, Fengbao He, Dilin Xiong Department of Mechanical Engineering, Dalian Institute of Light Industry, 1 Qinggongyuan Road, Ganjingzi District, Dalian 116034, China Received 10 June 2003; received in revised form 2 September 2003; accepted 3 September 2003
Abstract Problems of heat dissipation and drill tip strengthening become intensified when deep-hole drilling on manganese steel, due to the higher cutting resistance and poorer heat conductivity of this material. The characteristics of manganese steel drilling are investigated and a novel drill point is developed. Industrial on-line tests, for drilling a slant oil hole on a crankshaft of manganese steel, confirm that drill life is improved by 33% in comparison with that of a conventional drill point. 2003 Elsevier Ltd. All rights reserved. Keywords: Drill; Deep-hole drilling; Drill life improvement; Manganese steel drilling
1. Introduction Gundrills have been in use for a long time in firearm manufacturing. They are extensively used as a useful means of deep and precision-hole drilling [1–4]. Many gundrill production companies have developed different types and series of gundrills to meet the large market requirements; yet, there is much work to be done in improving drill life, increasing productivity, and lowering cost [5–7]. These problems become serious when drilling slant oil holes on crankshafts of manganese steel (Fig. 1), with a depth/diameter ratio of typically 2:4. In this circumstance, by using the conventional gundrill
Fig. 1.
∗
(Fig. 2), the drill life in terms of pieces’ for re-sharpening is reduced from 120 for common carbon steel to 60 for manganese steel. To improve drill life in accordance with the characteristics of the cutting process, a novel gun drill point has been developed. On-line tests demonstrate that the drill life increases from 60 to 75.
Slant deep-hole on the crankshaft.
Corresponding author. Tel./fax: +86-411-632-3806. E-mail address: [email protected] (W. Zhang).
0890-6955/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmachtools.2003.09.004
Fig. 2.
Drill point of conventional gundrill.
328
W. Zhang et al. / International Journal of Machine Tools & Manufacture 44 (2004) 327–331
Table 1 Chemical composition and mechanical properties Material
Common carbon steel Manganese steel
Chemical composition (wt.%)
Mechanical properties
C
Si
Mn
Yield (kgf/mm2) Tensile (kgf/mm2)
Elongation (%)
Hardness (BHN)
0.48 0.48
0.25 0.30
1.05 1.45
47.0 60.0
31.2 20.0
189 250
63.9 80.0
2. Characteristics of drilling process by using conventional gundrill Comparisons of chemical compositions and mechanical properties of manganese steel and common carbon steel used for crankshaft manufacturing are shown in Table 1. Manganese content, strength, and hardness of the former are higher than those of the latter. Elevated strength and hardness make the manganese steel more resistant to drilling. Increase of the manganese content also results in reduced drillability. Because the heat conductivity of manganese steel is much lower than that of common carbon steel, the heat generated in intensified drilling is liable to accumulate on the drill tip and thus its durability is reduced significantly. With Fig. 3 as a reference, the characteristics of wear in drilling for two different kinds of material are summarized as follows: For common carbon steel: 앫 Small circumferential relief angle along the inner edge causes localized flank wear on the inner edge. 앫 Great plasticity of the material leads to crater wear with a clearly defined shelf. 앫 Small point angle of conventional gun drill reduces the heat dissipation from drill tip, causing severe wear and tip breakage. For manganese steel:
Fig. 3.
앫 High strength and hardness of the material cause 20% higher cutting force and generate more heat. 앫 Poor heat conductivity and small point angle of conventional gun drill lead to heat build-up in the tip, causing tip breakage and lip chipping. 앫 High temperature accelerates the diffusion and alloying processes.
3. Improvement of gundrill point design To improve the gundrill point design for drilling manganese steel, aimed at increasing heat dissipation space, strengthening cutting edge and drill tip, and promoting cooling of tip area, a series of effective measures are adopted (Fig. 4): 앫 Double outer edge increases the point angle to 128°, enlarging heat dissipation space and improving tip strength. The first outer edge with increased outer angle (15° more than that of the second outer edge) decreases the axial thrust. 앫 Smaller normal relief angles accompanied with a 45° outer angle result in sufficient circumferential relief angle, ensuring sufficient strength for cutting edge and reducing flank wear. 앫 A honed round tip, 0.4 mm in diameter, prevents tip chipping. Secondary flank facilitates coolant supply to the cutting edge.
Wear comparison.
W. Zhang et al. / International Journal of Machine Tools & Manufacture 44 (2004) 327–331
329
In accordance with the mathematical models, the drill point is ground by using a 5-axis CNC grinder. Grinding parameters pertinent to each model are determined by a large number of proof tests.
5. Drilling tests and results On-line tests for drilling deep-hole on manganese steel crankshaft by using conventional gundrill and the newly designed drill point were performed. The cutting condition, tests, and results were as follows: Cutting condition:
Fig. 4.
Drill point of the newly designed gundrill.
앫 Small dub-off angle, 1° smaller than usual, intensifies coolant pressure in the cutting area.
4. Drill point configuration In order to put the design ideas into manufacturing practice, the drill point is divided into seven segments (Fig. 5): (a) (b) (c) (d) (e) (f) (g)
Primary flank of the first outer edge; Secondary flank of the first outer edge; Primary flank of the second outer edge; Secondary flank of the second outer edge; Honed surface of the tip; Inner flank; Dub-off surface.
Their mathematical models are described in Appendix A, and detailed derivations are omitted.
앫 Coolant: Castrol Syntilo 9904 water based coolant, 10% of dilution. 앫 Coolant pressure: 55–60 kg/cm2; 앫 Hole depth: 149.0 mm; 앫 Spindle speed: 6000 rpm; 앫 Feed: 116 mm/min (3 mm from inlet of the drilling), 250 mm/min (from 3 to 149 mm in depth). Tests and results (Fig. 6): Two sets of drills, 50 pieces in each, were used. The drill point of the first set was conventional and that of the second set was newly designed. The number of crankshafts drilled before examination for every drill in the first set was 60 and that in the second set was 75. Microscopic inspection of wear for the two sets of drills is summarized below. The crater wear of the former is obviously shallower than that of the latter. (a) For new drill point: 앫 Flank wear distributes evenly along the cutting edge with a maximum value of 0.7561 mm, mean value 0.70 mm, and deviation 0.09 mm. 앫 This wear does not exceed the allowable value and more pieces, no less than 80, are sustainable. (b) For conventional drill points: 앫 Flank wear distribution is uneven, with a maximum value of 1.0591 mm, mean value 0.98 mm, and deviation 0.20 mm. 앫 This wear is beyond the allowable limit. A 3.7% of breakage is bound to occur.
6. Concluding remarks
Fig. 5. Seven segments of the drill point.
The test results mentioned above verify that the newly designed drill has good anti-wear capability, especially appropriate for machining high strength and poor heat conductivity materials. Double outer cutting edges and honed tip improve both tip strength and heat dissipation
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W. Zhang et al. / International Journal of Machine Tools & Manufacture 44 (2004) 327–331
Fig. 6.
effectively. The secondary flank benefits cooling of the cutting area. Thus, the drill point configuration improves drill life by 33%. The paper proves that the geometry optimization of drill point has great potential for tool life improvement.
Test results.
aon, normal relief angle of the first outer edge, xA1, yA1, zA1, coordinates of the point A1. (b) Secondary flank of the first outer edge R(u,v) ⫽ (usinj1cosw ⫹ rosinw)i ⫹ (usinj1sinw⫺rocosw)j ⫹ (T1(w⫺wo)π / 2 (A2)
Appendix A. Mathematical models of the drill point
⫹ ucosj1)k in which
The newly designed drill point surface is divided into seven segments as shown in Fig. 5 with the following characteristic points: A drill tip; A1 intersecting point between the first outer edge and the second outer edge; B point of the first outer edge on the drill diameter; C point of inner edge on the flute; M2 common point of the three surfaces, a design requirement: the primary flank of the first outer edge, the primary flank of the second outer edge, and the secondary flank of the first outer edge. Each surface is expressed in a parametric equation, with unit vectors i, j, and k in Cartesian coordinate system, as follows:
R(uo,vo) ⫽ (xA1 ⫹ uocos⌽o ⫹ (zA1 ⫹ uosin⌽o ⫹ vosinaoncos⌽o)k where ⌽o, outer angle of the first outer edge,
⫽ tan⫺1(tanaon / sin⌽o)ro ⫽ T1tanj1 / (2π) where j1, grinding angle of the wheel, wo, the original angle of grinding, T1, lead of the involute helical surface. (c) Primary flank of the second outer edge R(uo2,vo2) ⫽ (xA ⫹ uo2cos⌽o2 ⫺vo2sinaon2sin⌽o2)i ⫹ (yA ⫹ vo2cosaon2)j
(A3)
⫹ (zA ⫹ uo2sin⌽o2 ⫹ vo2sinaon2cos⌽o2)k where ⌽o2, outer angle of the second outer edge, aon2, normal relief angle of the second outer edge, xA, yA, zA, coordinates of the point A.
(a) Primary flank of the first outer edge ⫺vosinaonsin⌽o)i ⫹ (yA1 ⫹ vocosaon)j
j1 ⫽ 90⫺cos⫺1(cos⌽ocosaon)wo
(A1)
(d) Secondary flank of the second outer edge R(uo3,vo3) ⫽ (xM2 ⫹ uo3cos⌽o2 ⫺vo3sinaon3sin⌽o2)i ⫹ (yM2 ⫹ vo3cosaon3)j (A4) ⫹ (zM2 ⫹ uo3sin⌽o2 ⫹ vo3sinaon3cos⌽o2)k
W. Zhang et al. / International Journal of Machine Tools & Manufacture 44 (2004) 327–331
ain, normal relief angle of the inner edge.
where aon3, normal relief angle of the secondary flank of the second outer edge, xM2, yM2, zM2, coordinates of the point M2. (e) Honed surface of the tip
xto ⫽ xA ⫹ rt(cos⌽o2 / tanq⫺sin⌽o2)yto ⫽ yAzto ⫽ zA ⫺rt(sin⌽o2 / tanq ⫹ cos⌽o2)
(A7)
⌽e, oil clearance angle, dub-off, dub-off angle, xC, yC, zC, coordinates of the point C.
References
where q = (π⫺⌽o2⫺⌽t) / 2 rt, arc radius of the honed round surface on the rake face, aton, normal relief angle of the honed round tip, ⌽i, inner angle. (f) Inner flank R(ui,vi) ⫽ (xA ⫹ vicos⌽i⫺uisinainsin⌽i)i
where
⫺ offsin⌽e)i ⫹ (yC⫺uecosdub ⫺ off)j
where
in which
⫹ uisinaincos⌽i)k
R(ue,ve) ⫽ (xC ⫹ vecos⌽e⫺uesinainsindub
(A5)
⫹ utsinaton)sinwt)k
⫹ (yA ⫹ uicosain)j ⫹ (zA ⫹ visin⌽i
(g) dub-off surface
⫹ (zC ⫹ vesin⌽e ⫹ uesindub ⫺ offcos⌽e)k
R(ut,wt) ⫽ (xto ⫹ (rt⫺utsinaton)coswt)i ⫹ (yto ⫹ utcosaton)j ⫹ (zto⫺(rt
331
(A6)
[1] A. Katsuki, K. Sakuma, H. Onikura, Axial hole deviation in deep drilling—the influence of the shape of the cutting edge, Nihon Kikai Gakkai 54 (502) (1988) 1350–1356. [2] G. Mason, Deep hole drills cut out equipment needs, Machinery and Production Engineering 137 (3540) (1980) 53–54. [3] H. Hinchcliffe, Tooling up for precision gundrilling, Tooling and Production 45 (1) (1979) 92–94. [4] T. Hoshi, High productivity machining research in Japan, Journal of Applied Metal Working 4 (3) (1986) 226–237. [5] P.M. Noaker, Gundrills at the cutting edge, Manufacturing Engineering 104 (5) (1990) 56–59. [6] P.M. Noaker, Gundrill for precision holes, Manufacturing Engineering 116 (5) (1996) 71–74. [7] J. Augustine, Gundrilling small holes with solid carbide drills, Modern Machine Shop 68 (1) (1995) 76–82.
Gundrill life improvement for deep-hole drilling on manganese steel Wei Zhang ∗, Fengbao He, Dilin Xiong Department of Mechanical Engineering, Dalian Institute of Light Industry, 1 Qinggongyuan Road, Ganjingzi District, Dalian 116034, China Received 10 June 2003; received in revised form 2 September 2003; accepted 3 September 2003
Abstract Problems of heat dissipation and drill tip strengthening become intensified when deep-hole drilling on manganese steel, due to the higher cutting resistance and poorer heat conductivity of this material. The characteristics of manganese steel drilling are investigated and a novel drill point is developed. Industrial on-line tests, for drilling a slant oil hole on a crankshaft of manganese steel, confirm that drill life is improved by 33% in comparison with that of a conventional drill point. 2003 Elsevier Ltd. All rights reserved. Keywords: Drill; Deep-hole drilling; Drill life improvement; Manganese steel drilling
1. Introduction Gundrills have been in use for a long time in firearm manufacturing. They are extensively used as a useful means of deep and precision-hole drilling [1–4]. Many gundrill production companies have developed different types and series of gundrills to meet the large market requirements; yet, there is much work to be done in improving drill life, increasing productivity, and lowering cost [5–7]. These problems become serious when drilling slant oil holes on crankshafts of manganese steel (Fig. 1), with a depth/diameter ratio of typically 2:4. In this circumstance, by using the conventional gundrill
Fig. 1.
∗
(Fig. 2), the drill life in terms of pieces’ for re-sharpening is reduced from 120 for common carbon steel to 60 for manganese steel. To improve drill life in accordance with the characteristics of the cutting process, a novel gun drill point has been developed. On-line tests demonstrate that the drill life increases from 60 to 75.
Slant deep-hole on the crankshaft.
Corresponding author. Tel./fax: +86-411-632-3806. E-mail address: [email protected] (W. Zhang).
0890-6955/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmachtools.2003.09.004
Fig. 2.
Drill point of conventional gundrill.
328
W. Zhang et al. / International Journal of Machine Tools & Manufacture 44 (2004) 327–331
Table 1 Chemical composition and mechanical properties Material
Common carbon steel Manganese steel
Chemical composition (wt.%)
Mechanical properties
C
Si
Mn
Yield (kgf/mm2) Tensile (kgf/mm2)
Elongation (%)
Hardness (BHN)
0.48 0.48
0.25 0.30
1.05 1.45
47.0 60.0
31.2 20.0
189 250
63.9 80.0
2. Characteristics of drilling process by using conventional gundrill Comparisons of chemical compositions and mechanical properties of manganese steel and common carbon steel used for crankshaft manufacturing are shown in Table 1. Manganese content, strength, and hardness of the former are higher than those of the latter. Elevated strength and hardness make the manganese steel more resistant to drilling. Increase of the manganese content also results in reduced drillability. Because the heat conductivity of manganese steel is much lower than that of common carbon steel, the heat generated in intensified drilling is liable to accumulate on the drill tip and thus its durability is reduced significantly. With Fig. 3 as a reference, the characteristics of wear in drilling for two different kinds of material are summarized as follows: For common carbon steel: 앫 Small circumferential relief angle along the inner edge causes localized flank wear on the inner edge. 앫 Great plasticity of the material leads to crater wear with a clearly defined shelf. 앫 Small point angle of conventional gun drill reduces the heat dissipation from drill tip, causing severe wear and tip breakage. For manganese steel:
Fig. 3.
앫 High strength and hardness of the material cause 20% higher cutting force and generate more heat. 앫 Poor heat conductivity and small point angle of conventional gun drill lead to heat build-up in the tip, causing tip breakage and lip chipping. 앫 High temperature accelerates the diffusion and alloying processes.
3. Improvement of gundrill point design To improve the gundrill point design for drilling manganese steel, aimed at increasing heat dissipation space, strengthening cutting edge and drill tip, and promoting cooling of tip area, a series of effective measures are adopted (Fig. 4): 앫 Double outer edge increases the point angle to 128°, enlarging heat dissipation space and improving tip strength. The first outer edge with increased outer angle (15° more than that of the second outer edge) decreases the axial thrust. 앫 Smaller normal relief angles accompanied with a 45° outer angle result in sufficient circumferential relief angle, ensuring sufficient strength for cutting edge and reducing flank wear. 앫 A honed round tip, 0.4 mm in diameter, prevents tip chipping. Secondary flank facilitates coolant supply to the cutting edge.
Wear comparison.
W. Zhang et al. / International Journal of Machine Tools & Manufacture 44 (2004) 327–331
329
In accordance with the mathematical models, the drill point is ground by using a 5-axis CNC grinder. Grinding parameters pertinent to each model are determined by a large number of proof tests.
5. Drilling tests and results On-line tests for drilling deep-hole on manganese steel crankshaft by using conventional gundrill and the newly designed drill point were performed. The cutting condition, tests, and results were as follows: Cutting condition:
Fig. 4.
Drill point of the newly designed gundrill.
앫 Small dub-off angle, 1° smaller than usual, intensifies coolant pressure in the cutting area.
4. Drill point configuration In order to put the design ideas into manufacturing practice, the drill point is divided into seven segments (Fig. 5): (a) (b) (c) (d) (e) (f) (g)
Primary flank of the first outer edge; Secondary flank of the first outer edge; Primary flank of the second outer edge; Secondary flank of the second outer edge; Honed surface of the tip; Inner flank; Dub-off surface.
Their mathematical models are described in Appendix A, and detailed derivations are omitted.
앫 Coolant: Castrol Syntilo 9904 water based coolant, 10% of dilution. 앫 Coolant pressure: 55–60 kg/cm2; 앫 Hole depth: 149.0 mm; 앫 Spindle speed: 6000 rpm; 앫 Feed: 116 mm/min (3 mm from inlet of the drilling), 250 mm/min (from 3 to 149 mm in depth). Tests and results (Fig. 6): Two sets of drills, 50 pieces in each, were used. The drill point of the first set was conventional and that of the second set was newly designed. The number of crankshafts drilled before examination for every drill in the first set was 60 and that in the second set was 75. Microscopic inspection of wear for the two sets of drills is summarized below. The crater wear of the former is obviously shallower than that of the latter. (a) For new drill point: 앫 Flank wear distributes evenly along the cutting edge with a maximum value of 0.7561 mm, mean value 0.70 mm, and deviation 0.09 mm. 앫 This wear does not exceed the allowable value and more pieces, no less than 80, are sustainable. (b) For conventional drill points: 앫 Flank wear distribution is uneven, with a maximum value of 1.0591 mm, mean value 0.98 mm, and deviation 0.20 mm. 앫 This wear is beyond the allowable limit. A 3.7% of breakage is bound to occur.
6. Concluding remarks
Fig. 5. Seven segments of the drill point.
The test results mentioned above verify that the newly designed drill has good anti-wear capability, especially appropriate for machining high strength and poor heat conductivity materials. Double outer cutting edges and honed tip improve both tip strength and heat dissipation
330
W. Zhang et al. / International Journal of Machine Tools & Manufacture 44 (2004) 327–331
Fig. 6.
effectively. The secondary flank benefits cooling of the cutting area. Thus, the drill point configuration improves drill life by 33%. The paper proves that the geometry optimization of drill point has great potential for tool life improvement.
Test results.
aon, normal relief angle of the first outer edge, xA1, yA1, zA1, coordinates of the point A1. (b) Secondary flank of the first outer edge R(u,v) ⫽ (usinj1cosw ⫹ rosinw)i ⫹ (usinj1sinw⫺rocosw)j ⫹ (T1(w⫺wo)π / 2 (A2)
Appendix A. Mathematical models of the drill point
⫹ ucosj1)k in which
The newly designed drill point surface is divided into seven segments as shown in Fig. 5 with the following characteristic points: A drill tip; A1 intersecting point between the first outer edge and the second outer edge; B point of the first outer edge on the drill diameter; C point of inner edge on the flute; M2 common point of the three surfaces, a design requirement: the primary flank of the first outer edge, the primary flank of the second outer edge, and the secondary flank of the first outer edge. Each surface is expressed in a parametric equation, with unit vectors i, j, and k in Cartesian coordinate system, as follows:
R(uo,vo) ⫽ (xA1 ⫹ uocos⌽o ⫹ (zA1 ⫹ uosin⌽o ⫹ vosinaoncos⌽o)k where ⌽o, outer angle of the first outer edge,
⫽ tan⫺1(tanaon / sin⌽o)ro ⫽ T1tanj1 / (2π) where j1, grinding angle of the wheel, wo, the original angle of grinding, T1, lead of the involute helical surface. (c) Primary flank of the second outer edge R(uo2,vo2) ⫽ (xA ⫹ uo2cos⌽o2 ⫺vo2sinaon2sin⌽o2)i ⫹ (yA ⫹ vo2cosaon2)j
(A3)
⫹ (zA ⫹ uo2sin⌽o2 ⫹ vo2sinaon2cos⌽o2)k where ⌽o2, outer angle of the second outer edge, aon2, normal relief angle of the second outer edge, xA, yA, zA, coordinates of the point A.
(a) Primary flank of the first outer edge ⫺vosinaonsin⌽o)i ⫹ (yA1 ⫹ vocosaon)j
j1 ⫽ 90⫺cos⫺1(cos⌽ocosaon)wo
(A1)
(d) Secondary flank of the second outer edge R(uo3,vo3) ⫽ (xM2 ⫹ uo3cos⌽o2 ⫺vo3sinaon3sin⌽o2)i ⫹ (yM2 ⫹ vo3cosaon3)j (A4) ⫹ (zM2 ⫹ uo3sin⌽o2 ⫹ vo3sinaon3cos⌽o2)k
W. Zhang et al. / International Journal of Machine Tools & Manufacture 44 (2004) 327–331
ain, normal relief angle of the inner edge.
where aon3, normal relief angle of the secondary flank of the second outer edge, xM2, yM2, zM2, coordinates of the point M2. (e) Honed surface of the tip
xto ⫽ xA ⫹ rt(cos⌽o2 / tanq⫺sin⌽o2)yto ⫽ yAzto ⫽ zA ⫺rt(sin⌽o2 / tanq ⫹ cos⌽o2)
(A7)
⌽e, oil clearance angle, dub-off, dub-off angle, xC, yC, zC, coordinates of the point C.
References
where q = (π⫺⌽o2⫺⌽t) / 2 rt, arc radius of the honed round surface on the rake face, aton, normal relief angle of the honed round tip, ⌽i, inner angle. (f) Inner flank R(ui,vi) ⫽ (xA ⫹ vicos⌽i⫺uisinainsin⌽i)i
where
⫺ offsin⌽e)i ⫹ (yC⫺uecosdub ⫺ off)j
where
in which
⫹ uisinaincos⌽i)k
R(ue,ve) ⫽ (xC ⫹ vecos⌽e⫺uesinainsindub
(A5)
⫹ utsinaton)sinwt)k
⫹ (yA ⫹ uicosain)j ⫹ (zA ⫹ visin⌽i
(g) dub-off surface
⫹ (zC ⫹ vesin⌽e ⫹ uesindub ⫺ offcos⌽e)k
R(ut,wt) ⫽ (xto ⫹ (rt⫺utsinaton)coswt)i ⫹ (yto ⫹ utcosaton)j ⫹ (zto⫺(rt
331
(A6)
[1] A. Katsuki, K. Sakuma, H. Onikura, Axial hole deviation in deep drilling—the influence of the shape of the cutting edge, Nihon Kikai Gakkai 54 (502) (1988) 1350–1356. [2] G. Mason, Deep hole drills cut out equipment needs, Machinery and Production Engineering 137 (3540) (1980) 53–54. [3] H. Hinchcliffe, Tooling up for precision gundrilling, Tooling and Production 45 (1) (1979) 92–94. [4] T. Hoshi, High productivity machining research in Japan, Journal of Applied Metal Working 4 (3) (1986) 226–237. [5] P.M. Noaker, Gundrills at the cutting edge, Manufacturing Engineering 104 (5) (1990) 56–59. [6] P.M. Noaker, Gundrill for precision holes, Manufacturing Engineering 116 (5) (1996) 71–74. [7] J. Augustine, Gundrilling small holes with solid carbide drills, Modern Machine Shop 68 (1) (1995) 76–82.