j o ur nal ho me p age: www.elsev ier .com/ locate /wear
hort communication
mproving wear resistance of sprocket parts using a fine-blanking process
. Thipprakmas ∗
ing Mongkut’s University of Technology Thonburi, 126 Prachautid, Bangmod, Thungkru, Bangkok, Thailand
r t i c l e i n f o
rticle history:eceived 1 September 2010eceived in revised form2 December 2010ccepted 22 December 2010
eywords:ear
procket
a b s t r a c t
A sprocket is a toothed wheel, commonly used in drive systems, to which the strength and wear resis-tance of the teeth are important. Sprockets are conventionally fashioned by hobbing, followed by heattreatment. However, the fine-blanking process has recently seen increasing use by sprocket manufac-turers. The process of fine-blanking has the possibility of reducing the number of process operations,thus reducing production time and cost, as well as improving part quality and process repeatability.Because of the severe plastic deformation in fine-blanking process, the strength, hardness and wearresistance of parts can be improved. In this work, the surface hardness and wear resistance of a fine-blanked sprocket are compared with those of a sprocket made using the hobbing process. The source ofthe wear resistance improvement was identified via examination of the microstructure. The microstruc-
ine-blankingobbingardness
ture of the fine-blanked sprocket revealed an increasingly compressed and elongated grain structure, inwhich grain flow and orientation resulted in pronounced hardening across the tooth width. The wearresistance of the fine-blanked sprocket, as measured by the distance between the teeth and the radius atthe tooth bottom, was greater than that of the hobbed and heat-treated sprocket. Based on the results,the material cost of the sprocket could be reduced by using low carbon steel (SS400) instead of mediumcarbon steel (S50C), and further savings in production time would be realized by eliminating the need
ment
for subsequent heat treat
. Introduction
A sprocket is a profiled wheel with teeth used in the drive sys-ems of machinery and equipment, such as bicycles, motorcycles,anks, movie projectors, and printers. Sprockets are mainly usedor the transmission of rotary motion between two shafts. Fig. 1hows an example of a rear sprocket for a motorcycle. The strengthnd wear resistance of a sprocket are important concerns over itsifetime. Therefore, sprockets are conventionally fabricated usinghe hobbing process to form the teeth, followed by heat treatingo improve the hardness. This sprocket fabrication process is timeonsuming and results in high production costs. Much research haseen done to improve sprocket fabrication efficiency as well as toevelop a process for more complicated sprocket shapes. Liu et al.
nvestigated the effect of geometrical parameters, such as cutoutength and height, inner diameter and the number of teeth, onhe distortion of S45C mid-carbon steel sprockets using numeri-
al simulations during the heat-treatment process [1]. Takagi et al.eveloped a CNC multilevel compacting press designed to pro-uce complicated shapes and achieve tight dimensional tolerancesithout a sizing operation for housing sprockets [2]. Fine-blanking
technology has been applied to sprocket manufacturing to improvehardness and wear resistance [3,4]. With the advantages of thefine-blanking process, a smooth clean-cut surface across an entirethickness could be achieved, and the production cost and timecould be reduced. In addition, the severe plastic deformation thattakes place under cold working conditions caused changes in thematerial properties of the parts, especially hardness properties[4–8]. However, the changes in wear resistance in the fine-blankedparts appear to only have been investigated in commercial stud-ies [9]. Wear resistance is an important system property that isrelated to sliding forces applied to the surface of parts, as is seenin sprocket use. Therefore, it is important to consider the effects ofthe fine-blanking process on wear resistance when considering theapplication of this process to sprocket manufacturing. In order toreplace the conventional sprocket manufacturing process with thefine-blanking process, it be must be shown that the wear resistanceof fine-blanked sprockets is greater than that of the convention-ally manufactured sprockets. Although the fine-blanking process iscurrently used to fabricate sprockets, the effects on wear resistanceand its underlying mechanism have not been clearly investigated
or explained. In this study, the wear resistance of the fine-blankedsprocket was compared with that of the commercial sprocket,and the improved wear resistance observed in the fine-blankedsprocket was explained by examination of the microstructure ofthe material.
Cl clearanceFB blankholder forceFC counterpunch forcet material thickness
2
pcttt(sb(tfst
3
f
Table 1Chemical compositions of SS400.
Alloys C Si Mn P S% 0.066 0.207 0.360 0.008 0.003
Table 2Chemical compositions of S50C.
Fig. 1. An example of rear sprocket for motorcycles.
. Principle of the fine-blanking process
The fine-blanking process is an advanced and precise blankingrocess by which a cut surface with exact geometry and smooth,rack-free cut surface can be created. Fig. 2 outlines the principle ofhe fine-blanking process. The fine-blanking principle is based onhe application of a hydrostatic pressure on the work piece throughhe use of a high blankholder force (FB) and a counterpunch forceFC). The V-ring indenter is also formed on the blankholder andometimes on the die in order to firmly tighten the work pieceefore the blanking operation. In addition, the blanking clearanceCl) of the fine-blanking process is approximately ten times lesshan that of the conventional blanking process. With these specialeatures, the plastic deformation generated in the work piece iseverely increased within the shearing zone, resulting in changeso the material properties, particularly on the cut surface.
. Experimental procedure
The sprocket investigated in this study was the rear sprocketor a motorcycle (model 428-36T) with 36 teeth and a thickness
Fig. 2. Principle of the fin
Alloys C Si Mn P S% 0.491 0.287 0.572 0.028 0.023
of 7 mm. Low carbon steel SS400 (JIS) was used for the fine-blanked sprocket and the hobbed sprocket. A commercial rearsprocket made of medium carbon steel S50C (JIS) with inductionheat-treatment applied after the hobbing process was completedwas also investigated. The chemical compositions of SS400 andS50C are listed in Tables 1 and 2, respectively. An 800-ton, fine-blanking press machine with a blankholder force of 1500 kN andcounterpunch force of 1000 kN was used for the experiments. Theblanking clearance was set to 0.5% of material thickness (t), andthe tool-cutting edge radii were set at 0.01 mm and 0.5 mm onpunch and die, respectively. The V-ring indenter height was 0.7 mmand 1.0 mm formed on the blankholder and the die, respectively,with a 90◦ angle, and located 3 mm from the punch side. The SS400fine-blanked and hobbed sprockets were sectioned and further pro-cessed by subsequent mounting, polishing, and etching with 3%nitric acid solution. Optical microscopy was used to observe andcapture microstructure images for microscopic examinations. Inaddition, the surface hardness was measured using the Vickersmicrohardness test method. In this study, two samples, the fine-blanked sprocket SS400 and the commercial sprocket S50C, wereinvestigated. The surface hardness was measured at six observationpoints on each sprocket and measured across the tooth width every1 mm at each observation point. The driving test (conditions listedin Table 3) was performed to investigate the wear resistance onboth the fine-blanked sprocket SS400 and the commercial sprocketS50C. In this study, no lubrication was applied (dry condition) inorder to reduce the testing time. The counterface material surfacehardness and roughness were examined as listed in Table 3. Again,the fine-blanked sprocket SS400 and commercial sprocket S50Cwere tested for wear resistance. The twelve observation points oneach sprocket were inspected for wear formation. The wear at thebottom radius and the distance between teeth, as shown in Fig. 3,were inspected. Concerning the sprocket lifetime, due to the wear,formation was not uniform across the tooth width, especially for thefine-blanked sprocket SS400; therefore, the least wear formation
over the tooth width was considered. The least wear was calculatedby creating a shadow and measuring it with a circle comparator.
Driving system Drive: 17T/1900 rpm × 36TChain tension: 1.47 kN
4
4fi
SWtdttap
Chain of links: 116 RESliding distance: 342 kmSliding speed: 2.37 m/sSliding distance per tooth: 9.5 km
. Experimental results and discussion
.1. Comparison of SS400 microstructure between hobbed andne-blanked sprockets
Fig. 4 shows the comparison of the microstructure for materialS400 on a tooth from both the hobbed and fine-blanked sprockets.ith the hobbing process, the sprocket teeth were formed by cut-
ing and removing the unwanted material. This cutting mechanism
id not result in compression or elongation of the microstruc-ure; thus, the microstructure was unchanged across the materialhickness, as shown in Fig. 4(a). On the other hand, the special char-cteristic features of the fine-blanking process resulted in severelastic deformation within the shearing zone [10–14]. This resulted
Fig. 4. Comparison of SS400 microstructure on the tooth
Fig. 3. Inspection point of wear on sprocket teeth.
in a more compressed and elongated grain structure along the con-tributed grain flow, as shown in Fig. 4(b). It was observed thatthe compressed and elongated grain structure increased in thethrough-thickness direction.
4.2. Comparison of SS400 surface hardness across the tooth widthbetween hobbed and fine-blanked sprockets
To investigate the changes in material properties on the hobbedand fine-blanked sprockets, the surface hardness was measured.The surface hardness value of the initial work piece, SS400,was approximately 130 HV. With the different contributed grainflow, the material properties, especially surface hardness, differedbetween the hobbed and fine-blanked sprockets. Fig. 5 shows thecomparison of surface hardness across the tooth width betweenthe hobbed and fine-blanked sprockets. The 0 corresponds to thecounterpunch side (face surface), and the 7 corresponds to thepunch side (back surface). In the case of the hobbed sprocket, the
grain structure was not compressed or elongated, the surface hard-ness was approximately constant over the material thickness, andits surface hardness value was unchanged from that of the initialwork piece. In contrast, the fine-blanked sprocket had a compressed
between the hobbed and fine-blanked sprockets.
S. Thipprakmas / Wear 271 (2011) 2396– 2401 2399
tooth width between the hobbed and fine-blanked sprockets.
ain
4s
tutpscSmSctam
wssecshichecfi
Fig. 5. Comparison of SS400 surface hardness across the
nd elongated grain structure along the contributed grain flow thatncreased in the through-thickness direction, and the surface hard-ess increased sharply in the through-thickness direction.
.3. Comparison of wear resistance between the commercialprocket S50C and the fine-blanked sprocket SS400
The most important property considered in sprocket fabrica-ion is wear resistance. Commercial sprockets are usually fabricatedsing medium carbon steel S50C, for which the induction heat-reatment can be applied after tooth formation from the hobbingrocess. To investigate the possibility of replacing conventionalprocket fabrication with the fine-blanking process, the commer-ial sprocket S50C was compared with the fine-blanked sprocketS400 in terms of wear resistance as well as surface hardness. Theicrostructure and surface hardness of the commercial sprocket
50C were examined. The induction heat-treatment to the surfaceaused increased surface hardness compared with that of the ini-ial surface hardness of S50C. After the induction heat-treatment,
surface hardness of approximately 310 HV was observed. Theicrostructure was ferrite and pearlite as shown in Fig. 6.Fig. 7 shows the comparison of surface hardness across the tooth
idth between the commercial sprocket S50C and the fine-blankedprocket SS400. In the case of the commercial sprocket S50C, theurface hardness was approximately 310 HV. This result could bexplained by the hobbing process used to fabricate the commer-ial sprocket S50C causing no compressed and elongated graintructure along the contributed grain flow. However, the surfaceardness across the tooth width was higher compared with the
nitial S50C, due to the induction heat-treatment process. In the
ase of the fine-blanked SS400, although there was no inductioneat-treatment process, the surface hardness was increased by theffects of the compressed and elongated grain structure along theontributed grain flow. As shown in Fig. 7, the surface hardness ofne-blanked sprocket SS400 was slightly lower than that of com-
Fig. 7. Comparison of surface hardness across the tooth width between th
Fig. 6. Microstructure of commercial sprocket S50C.
mercial sprocket S50C from the face surface to approximately 40%t depth. However, over the 40% t depth, the surface hardness of thefine-blanked sprocket SS400 was increasingly higher than that ofthe commercial sprocket S50C. This change in material propertiesresulted in a non-uniform wear formation across the tooth width.Therefore, the least amount of wear was formed on the back surfaceside, where the surface hardness was largest.
Fig. 8 shows the comparison of wear resistance between thecommercial sprocket S50C and the fine-blanked sprocket SS400.Due to the variation in the surface hardness along the tooth width,as shown in Fig. 7, the wear on the back surface side (larger surface
hardness side), where the least wear was formed, was inspected.Fig. 8(a) shows the increase in distance between teeth due to wearand Fig. 8(b) shows the increase in bottom radius due to wear. Theseresults showed that the wear increased as the driving test time
e commercial sprocket S50C and the fine-blanked sprocket SS400.
2400 S. Thipprakmas / Wear 271 (2011) 2396– 2401
(a) Distance between teeth
(b) Bottom radius
0.000
0.050
0.100
0.150
0.200
0.250
0.300
0.350
0.400
484032241680
Testing time (Hrs.)
Wea
r bet
wee
n t
eeth
(m
m) Fine-blanked sprocket SS400
Hobbed sprocket S50C
0.000
0.020
0.040
0.060
0.080
0.100
0.120
0.140
484032241680
Testing time (Hrs.)
Wea
r at
bott
om
rad
ius
(mm
)
Fine-blanked sprocket SS400
Hobbed sprocket S50C
Ffi
ibsooosttouraaitriobriAbiotcact
mance concerns, Met. Powder Rep. 64 (2009) 25–29.
ig. 8. Comparison of the wear between the commercial sprocket S50C and thene-blanked SS400.
ncreased. It was observed that the wear resistance of the fine-lanked sprocket SS400 was better than that of the commercialprocket S50C. Specifically, the increase in distance between teethf the fine-blanked sprocket SS400 was approximately half thatf the commercial sprocket S50C. The increase in bottom radiusf the fine-blanked sprocket SS400 was approximately 3 timesmaller than that of the commercial sprocket S50C. In addition,o investigate the effects of variation in surface hardness alonghe tooth width, the wear formation, with a material thicknessf approximately 3.5 mm, was examined. The sprocket was cutsing the wire-EDM, and the wear was measured. With the mate-ial thickness of 3.5 mm, the increase in distance between teethnd the increase in bottom radius were approximately 0.315 mmnd 0.092 mm, respectively. These results confirmed that the wearncreased as the surface hardness decreased. After the driving test,he surface hardness was also examined on both sprockets. Theesults showed that due to work hardening, the surface hardnessncreased slightly in both cases. Specifically, the surface hardnessn the back surface of the commercial sprocket S50C and the fine-lanked sprocket SS400 were approximately 332 HV and 468 HV,espectively. Fig. 9 shows an example of a tooth profile compar-son for the commercial sprocket S50C before and after testing.s the results show, the special characteristic features in the fine-lanking process resulted in an increase in surface hardness. An
ncrease in surface hardness to a level significantly higher than thatf the commercial sprocket S50C, leading to a wear resistance forhe fine-blanked sprocket SS400 that was better than that of the
ommercial sprocket S50C. Moreover, based on these results, withpplication of the fine-blanking process, the low carbon steel SS400ould be used instead of the medium carbon steel S50C, reducinghe material cost.
Fig. 9. Comparison of a single pair of tooth profiles for the commercial sprocketS50C before and after testing.
5. Conclusions
With the advantages of the fine-blanking process, a smoothclean-cut surface across the entire thickness could be produced;this process could be applied by the manufacturer, resulting in areduction in production costs and time. In this study, the wearresistance of the fine-blanked sprocket was investigated becauseit is considered to be important for sprocket lifetime. The changesin material properties were also explained as changes in themicrostructure of the material. With the special characteristic fea-tures of the fine-blanking process, a compressed and elongatedgrain structure along the contributed grain flow was generatedwithin the shearing zone, resulting in an increase in surface hard-ness. By contrast, this compressed and elongated grain structurefeature was not generated in the sprocket fabricated by the hob-bing process; therefore, the additional induction of heat-treatmentwas necessary to increase the surface hardness. The increase in sur-face hardness resulted in an improvement in wear resistance. Thisincrease in surface hardness and improved wear resistance for thefine-blanked sprocket SS400 was better than that of the commer-cial sprocket S50C. Therefore, the application of the fine-blankingprocess on sprocket fabrication not only reduced production costsand time, but also improved the surface hardness and wear resis-tance of the sprocket. The material cost was also reduced by usinglow carbon steel SS400 instead of medium carbon steel S50C.
Acknowledgements
The presented research is partially supported by a grant fromthe Thai Research Fund (TRF) under grant No. TRF-MRG5380117,the National University Research Project of Thailand (NRU Project),and the Center of Excellence in Sheet and Bulk Metal Forming Tech-nology (SBMFT). The author would like to express gratitude to Mr.Komdech Vichitjarusgul, Diamond Dimension Co., Ltd., for his sup-port for the experiments. The author also thanks Miss WasanaThongthing (undergraduate student) and Miss Wiriyakorn Phan-itwong (graduate student) for their assistance to this study.
References
[1] P. Liu, Y.Y. Wang, J. Li, C. Lu, K.P. Quek, G.R. Liu, Parametric study of a sprocketsystem during heat-treatment process, Finite Elem. Anal. Des. 40 (2003) 25–40.
[2] M. Takagi, K. Suganaga, T. Nagata, New PM sprocket meets auto cost, perfor-
[3] Y.H Seo, B.K. Kim, H.D. Son, Application of fine-blanking to the manufacture of asprocket with stainless steel sheet, Key Eng. Mater. 261–263 (2004) 1665–1670.
[4] S. Thipprakmas, C. Chanchay, N. Hanwach, W. Wongjan, K. Vichitjarusgul, Inves-tigation on the increasing material hardness on fineblanked sprocket, Adv.Mater. Res. 83–86 (2010) 1099–1106.
ar 271
[
[
[
S. Thipprakmas / We
[5] S.S.M. Tavares, M.R. Silva, J.M. Pardal, H.F.G. Abreu, A.M. Gomes, Microstructuralchanges produced by plastic deformation in the UNS S31803 duplex stainlesssteel, J. Mater. Proc. Technol. 180 (2006) 318–322.
[6] F.O. Sonmez, A. Demir, Analytical relations between hardness and strain forcold formed parts, J. Mater. Proc. Technol. 186 (2007) 163–173.
[7] W. Zhang, Z. Luo, W. Xia, Y. Li, Effect of plastic deformation on microstructureand hardness of AlSi/Al gradient composites, Trans. Nonferrous Met. Soc. China
17 (2007) 1186–1193.
[8] M. Milad, N. Zreiba, F. Elhalouani, C. Baradai, The effect of cold work on structureand properties of AISI 304 stainless steel, J. Mater. Proc. Technol. 203 (2008)80–85.
[9] Feintool Training: Module BT/2—Introduction into the Fineblanking Technol-ogy, Feintool Technologie AG Lyss, Switzerland, 2003.
[
[
(2011) 2396– 2401 2401
10] S. Thipprakmas, M. Jin, M. Murakawa, An investigation of material flowanalysis in fineblanking process, J. Mater. Proc. Technol. 192–193 (2007)237–242.
11] S. Thipprakmas, M. Jin, K. Tomokazu, Y. Katsuhiro, M. Murakawa, Prediction offineblanked surface characteristics using the finite element method (FEM), J.Mater. Proc. Technol. 198 (2008) 391–398.
12] S. Thipprakmas, Finite-element analysis of V-ring indenter mechanism in fine-
blanking process, J. Mater. Des. 30 (2009) 526–531.
13] S. Thipprakmas, M. Jin, Investigation mechanism of V-ring indenter geometryin fine-blanking process, Key Eng. Mater. 410–411 (2009) 305–312.
14] S. Yiemchaiyaphum, M. Jin, S. Thipprakmas, Die design in fine-piercingprocess by chamfering cutting edge, Key Eng. Mater. 443 (2010)219–224.
