FORM ERROR CORRECTION OF BEVEL GEARS BY ELECTROCHEMICAL HONING PROCESS

Size: px

Start display at page:

Download "FORM ERROR CORRECTION OF BEVEL GEARS BY ELECTROCHEMICAL HONING PROCESS"

Chrystal Bruce
5 years ago
Views:

1 5 th International & 26 th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12 th 14 th, 2014, IIT Guwahati, Assam, India FORM ERROR CORRECTION OF BEVEL GEARS BY ELECTROCHEMICAL HONING PROCESS Shaikh Javed Habib 1*, Neelesh Kumar Jain 2 1* Department of Mechanical Engineering, RSSOER, JSPM Narhe Technical Campus, Pune (MS), India, shaikhjaved1@gmail.com 2 Discipline of Mechanical Engineering, Indian Institute of Technology Indore (India), nkjain@iiti.ac.in Abstract This paper reports about the correction of form errors of case hardened straight bevel gears (made of 20MnCr5 alloy steel) by the Electrochemical honing (ECH) process using the honing gear made of 20MnCr5 alloy steel, and effects of ECH parameters on the correction of form errors. Surface topography, pitch error and runout have been used to evaluate the form errors whereas average surface roughness (R a ) and maximum surface roughness (R max ) have been used to evaluate the surface finish. An innovative experimental setup has been designed and developed for ECH of bevel gears based on a novel concept of using a set of twin complementary cathode gears. In this, one of the cathode gears has an undercut conducting layer sandwiched between two insulating layers while, in the other cathode gear, the insulating layer is sandwiched between two undercut conducting layers. These two complementary cathode gears ensure finishing of the entire face width of the workpiece gear and at the same time inter-electrode gap required for ECH. The experimental results have shown significant reduction in the form errors i.e. the quality of the bevel gear has improved from standard DIN 8 to DIN 7 for the pitch error, from DIN 9 to DIN 8 for the adjacent pitch error and from DIN 7 to DIN 6 for the runout within an optimized finishing time of 2 minutes as well as improvement in surface finish as R a and R max from 1.79 µm and 10.0 µm to 1.09 µm and 8.42 µm respectively for the optimum process parameters thus ensuring enhanced service life and operating performance. Keywords: Electrochemical Machining, Honing, Gear, Form 1 Introduction Approximately 2 to 2.5 billion gears of all types are produced and consumed annually (Goch, 2003). Bevel gear is one of the crucial components used in the automobiles, machine tools, wind turbines, marine applications, and various industrial machines for transmitting motion and/or power between intersecting shafts. Despite its production and consumption demand, the quality achieved and the operating performance of the gears has not reached its best. There has been continuous demand for a finishing process which will improve the quality, operating performance and the service life of the gears. Electrochemical honing (ECH) a hybrid micro-finishing process combines high material removal capability of electrochemical machining (ECM) and controlled functional surface generating capability of the conventional honing process in a single operation. ECH has the potential to become a viable alternative gear finishing process. The quest for development and exploration of the ECH for finishing of gears started in the early 80 s when Capello and Bertoglio (1979) used it for finishing the tooth face of a hardened helical gear mating with a specially designed cathodic helical gear tool. Their results were not acceptable in terms of improvement in helix and involute profiles but it confirmed the feasibility of using ECH for the gear finishing. Chen et al (1981) further developed a high accuracy gear finishing method based on the ECH principle and reported an improvement in the accuracy of profile as well as in the surface finish of spur gear teeth and reduction in noise level. Wei et al (1987) attempted to improve the accuracy of spur gear profile by varying electric field intensity and time respectively, to control the electrolytic dissolution uniformly along full profile of the gear using a newly developed gear-shaped cathode in the Field-Controlled ECH (FC-ECH) and slow-scanning field controlled ECH (SSFC-ECH) of gears to correct the gear tooth profile errors respectively.they reported that the accuracy of tooth profile can be greatly improved provided the errors in profile of all the teeth are nearly same. Yi et al (2000) used electrochemical process for tooth profile modification of carbonized gears and investigated on the distribution of the current density along the gear tooth profile. They reported that both current and finishing time affect the volume of crown and the amount of modification. Yi et al (2002) used real-time control based electrochemical finishing for tooth profile modification and used artificial neural 472-1

Misra et al (2010) reported the effects of voltage, electrolyte concentration and rotating speed of workpiece gear on the surface finish of the helical gears made of EN8 using EN24 as honing gear

2 FORM ERROR CORRECTION OF BEVEL GEARS BY ELECTROCHEMICAL HONING PROCESS network for its mathematical modeling. Naik et al (2008) investigated on ECH of spur gears reporting percentage improvement up to 80% and 67% in average surface roughness (R a ) and maximum surface roughness (R tm ) respectively. Misra et al (2010) reported the effects of voltage, electrolyte concentration and rotating speed of workpiece gear on the surface finish of the helical gears made of EN8 using EN24 as honing gear material and electrolyte as a mixture of NaCl and NaNo 3 in a ratio of 3:1. Ning et al (2011) reported the improvements in surface roughness i.e. R z improved from 7.13 to 4.32 µm and geometric accuracy i.e. Max. T. S. (Tooth spacing) index error has improved from standard DIN 10 to DIN 8, Max. T.S. error from DIN 10 to DIN 8 and T. S. total index error from DIN 9 to DIN 7 of spiral bevel gears finished using pulse electrochemical finishing (PECF) in which only one gear tooth was finished at a time. For this they used a cathode cutter which rotates and passes through the tooth space of the workpiece gear. After reaching the full depth, the cutter withdraws and the gear is indexed for the finishing of the next tooth. They also developed a mathematical model for total thickness of the material removed and surface roughness produced, and validated it with the experimental results. 2 Working principle of ECH of bevel gears Fig. 1 (a) and (b) respectively depict the working principle and photograph of the proposed concept for ECH of the bevel gears. The anodic workpiece gear 1 is mounted on the spindle of a bench drilling machine. To ensure finishing of the entire face width of bevel gear tooth, a novel concept of using twin complementary cathode gears has been conceived. For this, in one of the cathode gears 4, a layer of the conducting material is sandwiched between two insulating layers while, in the other complimentary cathode gear 3, a layer of an insulating material is sandwitched between two conducting layers. Since, the cathode gears have to be in constant mesh with the anodic workpiece gear in the ECH of bevel gears therefore, to avoid the short circuiting an inter electrode gap (IEG) is to be provided between the cathode and anode gears. For this, the conducting layer is undercut by 1 mm as compared to the insulating layers. A honing gear 2 is mounted on the backside of the workpiece gear. Both cathode and honing gears have the same involute profile as that of the workpiece gear. The axes of the shafts of workpiece gear, cathode gears and honing gear are perpendicular to each other. A full stream of electrolyte 5 is supplied to the IEG, and a DC current is passed through the gap. During the electrochemical process of material removal from the tooth flank an oxide passivating layer is formed on the tooth surface of the workpiece gear which inhibits further electrochemical action. This passivating layer is scraped by the honing gear. A tight meshing between the honing and workpiece gears ensures the pressure required to remove the passivating layer and dual flank contact. The honing gear scraps the passivating oxide layer from the high spots both along the tooth face and profile. Relatively more material is removed from the protruding high spots by the electrochemical action in the next cycle. This cyclic sequence in ECH of bevel gears leads to improvement both in the geometric accuracy and surface finish of all the teeth of the workpiece gear simultaneously. Figure 1 (a) Figure 1 (b) Figure 1. The arrangement for bevel gears for ECH operation (a) Schematic diagram (b) Photograph. The schematic diagram and photograph of the experimental set up are shown in Fig.2 (a) and (b) respectively

5 th International & 26 th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12 th 14 th, 2014, IIT Guwahati, Assam, India 1. DC power source; 2.

First stage filter with magnetic separator; 9. Second stage filter with magnetic separator; 10. Workpiece gear.

3 5 th International & 26 th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12 th 14 th, 2014, IIT Guwahati, Assam, India 1. DC power source; 2. Honing gear; 3. Cathode gears; 4. Carbon brush and slip ring assembly; 5. Electrolyte storage tank; 6. Stainless steel electrolyte supply pump; 7. Flow meter and Pressure gauge; 8. First stage filter with magnetic separator; 9. Second stage filter with magnetic separator; 10. Workpiece gear. Figure 2 (a) Figure 2 (b) Figure 2: Experimental setup for ECH of bevel gears: (a) schematic diagram; (b) photograph. 3 Experimentation Table 1 shows the values and levels of the fixed and variable process parameters used in the main experiments. Three levels of rotary speed of workpiece gear, voltage, concentration, flow rate, and temperature of the electrolyte have been used in the main experiments to study their effects on the bevel gear tooth geometry defining parameters i.e. surface topography, pitch and runout. The levels of the variable parameters were selected on the basis of the trial experiments and literature review while, the values of the fixed parameters were obtained from the pilot experiments and time dependent study. The experiments have been designed using the L 27 orthogonal array of Taguchi approach. Table 1 Details of the selected parameters for the experimentation. Parameter and their levels selected for the Main Experiment 1. Electrolyte Composition (C): 75% NaNO % NaCl ( Fixed from pilot Experiments) 2. Finishing time (t): 2 min. ( Fixed from pilot Experiments) 3. Inter electrode gap: 1 mm (Fixed from literature review) 4. Voltage (V): 3 levels (8 V; 12 V; 16 V) 5. Electrolyte concentration (C): 3 levels (5%; 7.5%; 10% by wt) 6. Electrolyte flow rate (F): 3 levels (20; 40; 60 lpm) 7. Rotary speed of workpiece gear (R): 3 levels (40; 60; 80 rpm) 8. Electrolyte temperature (T): 3 levels (27 C; 32 C; 37 C) The response parameters before and after ECH were measured using CNC gear metrology machine SmartGear 500 from Wenzel GearTec, Germany for geometric accuracy and surface roughness was measured before and after ECH on a contracer-cumsurface roughness tester from KOSAKA, Japan. Two gear teeth were selected for surface topography measurement. For each tooth, two measurements, one on left hand flank and other on the right hand flank were performed for the analysis. 4 Results and discussion The results of main experiment were analyzed for optimization of the ECH process parameters. It was found that the parametric combination of 12V as voltage, 10% electrolyte concentration, 30 lpm electrolyte flow rate, 37 C as electrolyte temperature, and 60 rpm as workpiece gear speed yielded the best results. Fig. 3(a) and Fig. 4(a) present the reports of metrological investigations by the CNC gear metrology machine for pitch error and adjacent pitch error, and cumulative pitch error and runout respectively, before the ECH while, Fig. 3(b) and Fig. 4(b) present the same after the ECH for the optimum combination of ECH parameters. From the figures 3 and 4 it can be seen that the quality of the bevel gear has improved from DIN 8 to DIN 7 for the pitch error, from DIN 9 to DIN 8 for the adjacent pitch error and from DIN 7 to DIN 6 for the runout. Figs. 5(a) and 5(b) depict the profile of the surface finish before and after ECH. The ECH improved the surface finish parameters R a and R max from 1.79 µm and 10.0 µm to 1.09 µm and 8.42 µm respectively for the optimum ECH process parameters

4 FORM ERROR CORRECTION OF BEVEL GEARS BY ELECTROCHEMICAL HONING PROCESS Figure 3 (a) Figure 3 (b) Figure 3: Pitch error fu and adjacent djacent pitch error fp of bevel gear tooth for the optimum combination combina of ECH parameters (a) before ECH; (b) after ECH. Figure 4 (a) Figure 4 (b) Figure 4: Cumulative pitch error Fp and Runout Fr of bevel gear tooth for the optimum combination of ECH parameters (a) before ECH; (b) after ECH

5 5 th International & 26 th All India Manufacturing Guwahati, Assam, India Technology, Design and Research Conference (AIMTDR 2014) December 12 th 14 th, 2014, IIT Enhanced geometric accuracy results in better operating performance in terms of noise, vibration, transmission accuracy and efficiency. In any of the gear finishing processes it is relatively difficult to achieve better geometric accuracy as compared to the surface finish. In ECH, better geometric accuracy can be achieved by selecting accurate and super-finished cathode gear along with the optimum process parameters and finishing stock on the workpiece gear, whereas it is difficult to achieve better geometric accuracy in case of other finishing processes such as gear grinding and gear honing due wear of grinding/honing tools and subsequent dressing, while in case of lapping, longer lapping cycle affects the accuracy of the gear teeth profile severely. Though shaving can correct minute profile errors it has material hardness limitation of 40 HRC. Improvement in surface finish results in increased service life of the gear i.e. for the surfaces subjected to cyclic stresses such as gears, shafts, bearings, etc., R max is a crucial parameter because large peak-to-valley heights are prone to crack propagation and subsequent failure. From above, it is clear that, the main motive of the ECH is to achieve better geometric accuracy, which is difficult to achieve in other gear finishing processes, rather than achieving better surface finish, which can be considered as a byproduct. Figure 6 (a) Figure 6: Bearing area curve on the before ECH; (b) after ECH Figure 6 (b) gear surface (a) Figs. 7 (a) and 7 (b) show the SEM micrographs for an unfinished and finished gear by ECH respectively. From the SEM micrograph of unfinished gear the micro-pits on the tooth flank surface are clearly visible, which may lead to the pitting failure in operating life of the gears. These pits are smoothened by the ECH as shown in Fig. 7 (b). Figure 5 (a) Figure 7 (a) Figure 5 (b) Figure 5: Surface roughness profile of ECH (b) After ECH gear (a) Before Figs. 6(a) and 6(b) shows the bearing area curve (BAC) for the depth of 0.5 µm beforee and after ECH. The improvement in percentage material in BAC after ECH results in larger contact area and hence less noise and vibration during the operation and less wear. Figure 7 (b) Figure 7: Scanning electron microscopy (SEM) micrographs (1000 ) for (a) unfinished gear; (b) ECH finished gear, for the optimum combination of ECH parameters

6 FORM ERROR CORRECTION OF BEVEL GEARS BY ELECTROCHEMICAL HONING PROCESS 5 Conclusions This paper reports about innovatively developed ECH setup for bevel gears based on a novel concept of twin complimentary cathode gears and experimental investigations on the effects of ECH of gear on the form accuracy, surface finish, Bearing area and surface integrity of straight bevel gears. Following are the conclusions which can be drawn based on this study: 1. The ECH process can be used successfully to finish and correct the form errors of the bevel gears with the specially designed complimentary cathode gears. 2. The study confirms ECH being an economical and highly productive alternative finishing process for the bevel gears due to its independence on the gear material hardness and ability to significantly improve the geometric accuracy and surface finish which consequently improve the operating performance and service life of the bevel gears. 3. Finishing time as low as 2 minutes highlights the productivity of the ECH process. 4. The desirable effects such as profile crowning, tip relief and root relief can be achieved by appropriately modifying the profile of the cathode gear. 5. The accuracy and surface finish of the gear tooth profile finished by ECH depends on the accuracy and surface finish of the cathode gear surface apart from the process parameters. A precisely lapped cathode gear may give further better results. 6. It is relatively difficult to correct the form errors than improving the surface finish of the gears by ECH. For better form error correction precise control over the cathode gear tooth profile and in the finishing stock of the workpiece gears is required. Acknowledgements The authors gracefully acknowledge (i) CSIR, New Delhi (India) for the financial support received under the Project No. 22/ (0468)/09/EMR-II, (ii) SnH Gears, Dewas, MP (India) for providing their facilities for fabrication of the bevel gears, and (iii) VE Commercial Vehicles, Pithampur, MP (India) for allowing to use their facilities for surface roughness measurements. References Capello, G. and Bertoglio, S. (1979), A new approach by electrochemical finishing of hardened cylindrical gear tooth face. Annals of CIRP, Vol. 28(1), pp Chen, C. P., Liu, J., Wei, G. C., Wan, C. B. and Wan, J. (1981), Electrochemical honing of gears: a new method of gear finishing. Annals of CIRP, Vol. 30(1), pp Goch, G. (2003), Gear metrology, Annals of CIRP, Vol. 52(2), pp Misra, J. P., Jain, N. K. and Jain P. K. (2010), Investigations on precision finishing of helical gears by electrochemical honing process. Proc. IMechE Vol. 224 Part B: J. Engineering Manufacture, pp Naik, L. R., Jain, N. K. and Sharma, A. K. (2008), Investigation on precision finishing of spur gears by electrochemical honing. Proceedings of the 2 nd International and 23 rd AIMTDR Conference, IIT Madras, India, Ning, M., Wenji, X., Xuyue, W. and Zefei, W. (2011), Mathematical modeling for finishing tooth surfaces of spiral bevel gears using pulse electrochemical dissolution, Int. J. of Ad. Mfg. Tech., Vol. 54, pp Wei, G. Q., Wang, Z. B. and Chen, C. P. (1987), Field controlled electrochemical honing of gears. Precision Engg, Vol. 9(4), pp Eshelman, R. H. (1963), Electrochemical honing reports ready for production jobs, Iron Age, 124. Yi, J., Yang, T. and Zhou, J. (2000), New electrochemical process gear tooth-profile modification, Mfg. Tech. and Modern Machine, Vol. 9(1), pp Yi, J., Zheng, J., Yang, T. Xia, D. and Hu, D. (2002), Solving the control problem for electrochemical gear tooth-profile modification using an artificial neural network, Int. J. of Ad. Mfg. Tech., Vol. 19(1), pp

Performance of pulsed-electrochemical honing and pulsed-electrochemical finishing in improving quality of bevel gears

Performance of pulsed-electrochemical honing and pulsed-electrochemical finishing in improving quality of bevel gears Manufacturing Rev. 5, 14 (2018) S. Pathak and N.K. Jain, Published by EDP Sciences 2018 https://doi.org/10.1051/mfreview/2018012 Available online at: https://mfr.edp-open.org RESEARCH ARTICLE Performance