Experimental investigation on precision finishing of spur gears by pulse electrochemical honing (PECH) process.

Misra, Joy Prakash ; Jain, Pramod Kumar

1. INTRODUCTION

Gears running at high speed and transmitting large forces are subjected to additional dynamic forces due to poor surface quality of gear tooth profile. Therefore, the gear teeth must be error-free for smooth noiseless motion transmission. The surface quality of gear tooth profile can be improved significantly by the gear finishing processes. Commonly used conventional gear finishing processes such as gear grinding, gear shaving, gear honing, gear lapping are costly, have low productivity, and gear material hardness limitation. This necessitates exploration of electrochemical honing (ECH) process which has capabilities and potential to be developed as an alternative to conventional gear finishing processes. It is reported that ECH is faster than conventional gear finishing processes and can provide surface finish up to 300 nm to the gear tooth profile (Misra et al., 2009). Moreover, the pulse assistance in ECH provides the relaxation period to the system during off time to discharge the dregs out of the electrodes' gap and thus improves the process capability.

There are very few references available on ECH of gears. Jain et al. (2009) have done a state-of art review of past work on ECH of internal cylinder and gears. According to the best knowledge of the authors, the application of ECH for gear teeth finishing was first reported by Chen et al. (1981). Wei et al. (1987) used a current-control method by varying the intensity of the electric field to control the intensity of electrolytic dissolution steplessly along the full profile of the gear using a newly developed gear-shaped cathode in the field-controlled ECH (FC-ECH) of gears. While, He et al. (2000) used the time-control method to correct the gear tooth profile errors very efficiently in a process that they called as slow-scanning field controlled ECH (SSFC-ECH) of gears. Ramlal et al. (2008) have investigated on ECH of spur gears using different combinations of NaNO3 and NaCl as electrolyte. In recent work, Misra et al. (2009) explained the effects of voltage, rotating speed of workpiece and electrolyte concentration on precision finishing of helical gears by ECH. The study of precision finishing of gears by ECH under pulse current condition has not been explored significantly.

2. EXPERIMENTATION

The present study emphases the effect of finishing time on precision finishing of spur gears by PECH process and thus it helps to realize the different aspects of the process. For the present study, PECH experimental setup incorporating several unique features to exercise a precise control over the operational kinematics and process input parameters with a good parameter range was designed and developed indigenously as shown in Fig. 1. It consists of five major subsystems namely pulse power supply system, electrolyte supply system, tooling system, tool motion system, and machining chamber. Pulse power supply system consists of a constant voltage (0-110 V) and pulse-setting DC (up to 100 A) supplying units. Electrolyte supply system consists of electrolyte storage and settling tanks, pump, heat exchanger, flow meter, flow valves. The tooling system contains three types of gears: cathode gear, workpiece gear and honing gear. For the purpose, a special type of cathode gear has been designed having the capability of varying the rate of electrolytic dissolution steplessly along the full profile of the workpiece gear. All gears are mounted on special type of axles made of stainless steel. Brackets are used for holding the gear axles of cathode and honing gears. The tool-motion system comprises of a DC induction motor to provide rotary motion to the workpiece gear and a programmable stepper motor to provide reciprocating motion. The entire tooling system with axles and brackets are enclosed in a machining chamber made of perspex for better visibility and corrosion-resistance. In the present work, finishing time is used as input process parameter to investigate its effect on finishing of gear tooth profile by analysing the surface roughness values before and after the process. The surface roughness values before and after ECH, is measured by a Wyko NT 1100 optical profilometer interfaced with Vision[R]32 software. Ten separate measurements each at tip, middle and root of one particular gear tooth are taken along the face-width of the gear and the average value is used. Percentage improvement in average/maximum surface roughness value (PIRa / PIRtm) is defined as follows:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1)

3. RESULTS AND DISCUSSIONS

Table 1 and 2 presents the percentage improvement of average and maximum surface roughness values for different finishing times respectively. Table 3 and Table 4 shows the change in [PIR.sub.a] and [PIRt.sub.tm] value for different finishing time durations. Fig. 2(a) and 2(b) show variation of [PIR.sub.a] and [PIRt.sub.tm] with finishing time. From these graphs, it is evident that [PIR.sub.a] and [PIRt.sub.tm] increase with the finishing time but at a decreasing rate because intensity of EC dissolution deceases as the surface gets smoothened. Therefore, increments in [PIR.sub.a] and [PIRt.sub.tm] for first two time periods are most significant but for the time period from 24 min to 32 min it is insignificant. Therefore, in present study, finishing time of 24 min is found the most appropriate for PECH of spur gears.

[FIGURE 1 OMITTED]

4. CONCLUSION AND FUTURE SCOPE

The present study established the feasibility of using PECH for precision finishing of spur gears. An experimental setup for the same has been designed and developed. Based on the results, 24 min is found optimum for precision finishing of spur gears. PECH is capable of greatly reducing the irregularities of the gear tooth profile. However, like most of the hybrid machining processes (HMPs), PECH is also in the development phase and therefore a sustained global research is required to transform it into a matured manufacturing technology and for its successful industrial applications and commercialization. It is very evident that very few attempts have been made to analyse and mature the process and hence, the process has plenty of scope for future work. In the present study, only the effect of finishing time has been investigated. The effects of other parameters on precision finishing of spur gears by PECH yet to be explored.

[FIGURE 2 OMITTED]

5. REFERENCES

Chen. C. P.; Liu. J., Wei. G. C., Wan. C. B. & Wan. J. (1981). Electrochemical honing of gears: a new method of gear finishing. Annls CIRP, 30(1), pp. 103-106.

He, F.; Zhang, W. & Nezu, K. A. (2000). Precision machining of gears: slow scanning field controlled electrochemical honing. JSME Int. J. Ser. C, 43(2), pp. 486-491.

Jain. N. K.; Naik. L. R., Dubey. A. K., & Shan. H. S. (2009). State-of-art-review of electrochemical honing of internal cylinders and gears. Proc. IMechE, PartB: J. Engineering Manufacture, 223(6), pp. 665-681, 09544054.

Naik. L. R.; Jain. N. K., & Sharma. A. K. (2008). Investigation on Precision Finishing of Spur Gears by Electrochemical Honing. Proc. of 2nd International and 23rd AAIMTDR Conference, Shunmugam, M. S. & Ramesh Babu, N. (Eds.), pp. 509-514, I.I.T. Madras, India.

Misra, J. P.; Jain, N. K., & Jain, P. K. (2010). Investigations on Precision Finishing of Helical Gears by Electrochemical Honing (ECH) Process. Proc. IMechE, Part B: J. Engineering Manufacture (in press).

Wei. G. Q.; Wang. Z. B., & Chen. C. P. (1987). Field controlled electrochemical honing of gears. Precision Engg. 9(4), pp. 218-221, 0141-6359.

Tab. 1. [PIR.sub.a] values for different finishing times

Finishing At Tip of At Middle of At Root of
Time (in Min) gear profile gear profile gear profile

8 min 26.95 31.79 35.93
16 min 44.45 34.41 49.91
24 min 63.09 58.67 71.64
32 min 64.19 58.62 72.77

Tab. 2. [PIR.sub.tm] values for different finishing times

Finishing At Tip of At Middle of At Root of
Time (in Min) gear profile gear profile gear profile

8 min 35.97 62.35 49.68
16 min 46.39 68.70 57.12
24 min 58.61 76.87 70.28
32 min 58.86 72.35 71.31

Tab. 3. Increment of [PIR.sub.a] for different finishing time duration

Finishing Time
Duration At Tip of gear At Middle of At Root of
(in Min) profile gear profile gear profile

8 - 16 35.97 62.35 49.68
16 - 24 46.39 68.70 57.12
24 - 32 58.61 76.87 70.28

Tab. 4. Increment of [PIR.sub.tm] for different finishing time duration

Finishing Time
Duration At Tip of gear At Middle of At Root of
(in Min) profile gear profile gear profile

8 - 16 35.97 62.35 49.68
16 - 24 46.39 68.70 57.12
24 -32 58.61 76.87 70.28