FORM ERROR CORRECTION OF BEVEL GEARS BY … · FORM ERROR CORRECTION OF BEVEL GEARS BY ELECTROCHEMICAL HONING PROCESS 472-2 network for its mathematical modeling. Naik et al (2008)

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT

Guwahati, Assam, India

472-1

FORM ERROR CORRECTION OF BEVEL GEARS BY

ELECTROCHEMICAL HONING PROCESS

Shaikh Javed Habib1*

, Neelesh Kumar Jain2

1*Department of Mechanical Engineering, RSSOER, JSPM Narhe Technical Campus, Pune (MS), India, [email protected]

2Discipline of Mechanical Engineering, Indian Institute of Technology Indore (India), [email protected]

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 (Ra) and maximum surface roughness (Rmax) 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 Ra and Rmax 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

FORM ERROR CORRECTION OF BEVEL GEARS BY ELECTROCHEMICAL HONING PROCESS

472-2

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 (Ra) and maximum surface roughness

(Rtm) 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 NaNo3

in a ratio of 3:1. Ning et al (2011) reported the

improvements in surface roughness i.e. Rz 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.

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT


472-3

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 L27 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% NaNO3 + 25% 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-cum-

surface 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 Ra and Rmax from 1.79 µm

and 10.0 µm to 1.09 µm and 8.42 µm respectively for

the optimum ECH process parameters.

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 3: Pitch error ‘fu’ and adjacent pitch error ‘

parameters (a) before ECH; (b) after ECH.

Figure 4: Cumulative pitch error ‘Fp’

parameters (a) before ECH; (b) after ECH.


Figure 3 (a)

Figure 3 (b)

djacent pitch error ‘fp’ of bevel gear tooth for the optimum combina

after ECH.

Figure 4 (a)

Figure 4 (b)

’ and Runout ‘Fr’ of bevel gear tooth for the optimum combination of ECH

after ECH.

472-4

of bevel gear tooth for the optimum combination of ECH

of bevel gear tooth for the optimum combination of ECH

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12


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 ca

achieved by selecting accurate and super

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., Rmax 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 5 (a)

Figure 5 (b)

Figure 5: Surface roughness profile of gear

ECH (b) After ECH

Figs. 6(a) and 6(b) shows the bearing area

(BAC) for the depth of 0.5 µm before 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

All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12

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

accurate and super-finished

cathode gear along with the optimum process

parameters and finishing stock on the workpiece gear,

s 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

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

ses such as gears,

is a crucial parameter because

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

r finishing processes, rather than achieving

better surface finish, which can be considered as a

Surface roughness profile of gear (a) Before

Figs. 6(a) and 6(b) shows the bearing area curve

(BAC) for the depth of 0.5 µm before 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 6 (a)

Figure 6: Bearing area curve on the gear surface

before ECH; (b) after ECH

Figs. 7 (a) and 7 (b) show the SEM micrographs

unfinished and finished gear by ECH

the SEM micrograph of unfinished gear the micro

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 7 (a)

Figure 7 (b)

Figure 7: Scanning electron microscopy (SEM)

micrographs (1000×) for (a) unfinished gear;

finished gear, for the optimum combination of ECH

parameters.

All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT

472-5

Figure 6 (b)

Bearing area curve on the gear surface (a)

SEM micrographs for an

finished gear by ECH respectively. From

the SEM micrograph of unfinished gear the micro-pits

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.

Scanning electron microscopy (SEM)

unfinished gear; (b) ECH

finished gear, for the optimum combination of ECH


472-6

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. 103–

107.

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. 103–

106.

Goch, G. (2003), Gear metrology, Annals of CIRP, Vol.

52(2), pp. 659-695.

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. 1817-1830.

Naik, L. R., Jain, N. K. and Sharma, A. K. (2008),

Investigation on precision finishing of spur gears by

electrochemical honing. Proceedings of the 2nd

International and 23rd

AIMTDR Conference, IIT

Madras, India, 509–514.

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. 979-

986.

Wei, G. Q., Wang, Z. B. and Chen, C. P. (1987), Field

controlled electrochemical honing of gears. Precision

Engg, Vol. 9(4), pp. 218–221.

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. 102–

105.

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. 8-13.

Documents

FORM ERROR CORRECTION OF BEVEL GEARS BY … · FORM ERROR CORRECTION OF BEVEL GEARS BY ELECTROCHEMICAL HONING PROCESS 472-2 network for its mathematical modeling. Naik et al (2008)