cv-joint remanufacturing parameter optimization

International Journal of Automotive Technology, Vol. 15, No. 4, pp. 603−610 (2014)

DOI 10.1007/s12239−014−0063−1

Copyright © 2014 KSAE/ 078−10

pISSN 1229−9138/ eISSN 1976−3832

603

CV-JOINT REMANUFACTURING PARAMETER OPTIMIZATION

Y. K. SEO1), S. YU2) and A. GAFUROV1)*

1)Reliability Research Department, Korea Automotive Technology Institute, 303 Pungse-ro, Pungse-myeon, Dongnam-gu, Cheonan-si, Chungnam 330-912, Korea

2)Mechanical Engineering Department, Chungnam National University, Daejeon 305-764, Korea

(Received 15 February 2013; Revised 4 June 2013; Accepted 15 July 2013)

ABSTRACT−Quality assessment process is based on a standard procedure. These standards are developed as a combined

effort. It requires deep knowledge about structural material in addition to component`s behavior under external loads.

Remanufactured components pose another difficulty to assess their quality in the form of unknown usage rate. This paper

represents optimization of quality assessment criteria for remanufactured CV-joints. Working surface hardness of the CV-joint

elements is measured at certain depth interval. A minimum acceptable surface hardness value for the BJ-outer joint elements

is suggested based on existing research. Remanufactured CV-joint Housing, Inner race and Cage surface machining steps are

studied and machining parameter optimization is performed through laboratory based durability test results. The test results

of optimized machining parameters are compared with the test results of unmachined test samples. Mean-time-to-failure is

calculated along with Weibull distribution parameters. Also, Birfield joint inner race bending and rotating torque are measured

and standard parameters for remanufactured CV-joint are determined. Those quality assessment criteria for remanufactured

CV-joints are developed.

KEY WORDS : BJ, Durability, Reliability, Remanufactured CV-joint, Surface hardness depth

1. INTRODUCTION

Generally, a product must pass certain quality inspection

procedure. Reliability/durability assessment standard

procedures exist and are in use for newly manufactured

products. However, these existing standards cannot be

applied for quality assessment of the remanufactured

components due to these components already being used

and damage is done to the component. In this case a

remaining service life is estimated instead of expected

service life. Obviously, it is complicated procedure as a

result of the unknown usage conditions of components

(Jung et al., 2008; Jung et al., 2009).

Recent research studies underline the reliability as the

core issue when it comes to reuse and remanufacturing. They

describe a methodology to estimate the technical reusability

of component at the end of their life. However, these

methodologies are based on statistical parameters like time-

to-failure record, maintenance data, lifetime monitoring data

to make quantitative judgment of reliability (Anitsayari and

Kaebernick 2008; Kara et al., 2005). Lack of established

core collection system makes it nearly impossible to track

the maintenance and lifetime monitoring data (Mok et al.,

2008; Guide, 2000).

In practice, the collected core elements are disassembled

at remanufacturing company’s facilities and visually

observed for presence of wear. As the primary failure mode

is understood to be a wear of contact surfaces of housing

and inner race, their surface hardness becomes main

parameter to focus on. Remanufacturing companies use the

surface condition as a tool to make decision whether to

reuse or recycle the core element. If slightly worn, it could

be reused as it stands. Moderate and severely worn core

elements are decided to recondition or scrap and replace

(Philpott et al., 1996). The need for standardized

reconditioning/machining procedure is clear. This paper

introduces development and optimization of the quality

assurance parameters for the remanufactured CV-joint with

unknown usage rate based on surface hardness study.

2. THEORETICAL BACKGROUND

To facilitate an understanding of durability estimation and

statistical analysis, a brief introduction will be presented.

For a deeper understanding of derivation the reader is

referred to the reference works (Jeong et al., 2007; Seherr-

Thoss et al., 2006).

2.1. CV-Joint Durability Estimation

Durability of the CV-joint is directly related to the ball

bearing life. According to the research, durability life of the

outer joint BJ (BJ – Birfield joint) is estimated using

Equation 1 (a) and 1 (b), whereas the inner joint TJ (TJ-

tripod joint) durability is estimated using Equation (2).*Corresponding author. e-mail: [email protected]

604 Y. K. SEO, S. YU and A. GAFUROV

(1a)

(1b)

(2)

where Lhx – service life, n – rated rpm, Md – dynamic torque

capacity, Mx – rated torque, Ax = (1-sinβx)-cos2βx ; β −articulation angle.

2.2. Statistical Parameter Estimation

Durability test results analysis is carried out using Weibull

distribution theory. The Weibull distribution is most

commonly used in life data analysis. It is considered to be

one of the most important prediction methods, since it fits

many different failure distributions.

The Weibull cumulative density function F(t) is given in

Equation (3).

(3)

The first derivative of Eq.3 with respect to t gives the

Weibull probability density function f(t) as Equation (4).

(4)

where b – shape parameter or Weibull slope, θ – scale

parameter, t – time.

A shape and scale parameters are a kind of numerical

parameter of probability distribution. Their estimation is

widely available in literature (Elsayed, 1996).

The mean time to failure (MTTF) is estimated as in

Equation (5).

(5)

where ⎡(n) – gamma function.

3. SURFACE HARDNESS ANALYSIS AND RESULTS

3.1. Surface Hardness Depth Measurement Test

Failure mode and effect analysis (not covered in this paper)

indicates that BJ appears to be the most often damaged part

whereas TJ is slightly worn. Usually only BJ is subjected to

reconditioning/machining process. TJ shape complexity and

wall thickness makes it extremely difficult to recondition.

That is why TJ is either reused as it is or replaced with a new

one. The decision is based on naked eye observations by an

experienced remanufacturing engineer.

Surface micro-hardness depth measurement is performed

using a Mitutoyo MicroWizard (HM-221) hardness testing

machine at ambient temperature of 20oC and load of

0.2 kgf (Figure 1). Measurement direction is shown with

yellow arrow in Figure 2 (b), 2 (d) and 2 (f), starting from

the edge (top surface) towards inside (depth) of the

samples. Distinctive dark colored layer starting from the

edge of samples in Figure 2 (b), 2 (d), and 2 (f) is the

indication of heat treatment layer. The BJ housing is high

frequency inductive heat treated whereas the Inner race and

Cage are carburized.

Randomly selected new and remanufactured CV-joints are

taken to prepare cut-off section to perform hardness

measurement tests. Test samples are cut as close as possible

to local contact surfaces using wire-cutting technique. In

order to provide stable positioning and easily move across

the surface depth while measuring hardness the cut-off

samples are inserted into circular-shaped silicone block. The

samples with measuring side facing top are polished to

achieve smooth surface. Ready-to-measure samples are cross

sections of the core element’s contact surfaces (Figure 2).

A question of vital importance is the minimum

acceptable level of hardness. Available standard AISI 4140

for high tensile steel, which is widely used in automobile

axle shafts, shows that typical induction hardened surface

hardness is up to HRc54. Practical analysis of an automobile

rear axle shaft surface hardness also demonstrates

compliance with the standard specification (Asi, 2006). In

case of remanufactured CV-joint, the surface hardness

Lhk

25 339,nx

0.577-----------------

AxMd

Mx

------------⎝ ⎠⎛ ⎞

3

for n 1,000rpm≤ =

Lhx

470 756,nx

--------------------AxMd

Mx

------------⎝ ⎠⎛ ⎞

3

for n 1 000 rpm,>=

Lhx

365 000,nx

--------------------Md

Mx

------⎝ ⎠⎛ ⎞

3

=

F t( ) 1t

θ---⎝ ⎠⎛ ⎞

b

–exp–=

f t( ) btb 1–

θb----------

t

θ---⎝ ⎠⎛ ⎞

b

–exp= b 0 θ 0 t 0≥,>,>

MTTF θ1

b---Γ

11

b---+⎝ ⎠

⎛ ⎞=

Figure 1. Mitutoyo MicroWizard (HM-221) Vickers

hardness measuring equipment.

Figure 2. Surface hardness measurement test samples: (a)

BJ housing; (b) BJ housing cut-off sample; (c) Inner race;

(d) Inner race cut-off sample; (e) Cage; (f) Cage cut-off

sample.

CV-JOINT REMANUFACTURING PARAMETER OPTIMIZATION 605

derived from AISI 4140 and minimum acceptable surface

hardness of 513 Hv (HRc50) is suggested (Kim, 2006).

Acceptability of the derived hardness level is proved by

durability tests. Test results are discussed in Chapter 4.

Table 1 summarizes the surface hardness depth of the

newly manufactured BJ-side elements of the CV-joint.

Exact depths corresponding to surface micro-hardness of

513 Hv is estimated and given in above mentioned table.

Measured depth is a guide to the machining process. It

shows how much of surface layer can be cut-off while still

keeping the surface hard enough and maintain the

reliability/durability target for remanufactured CV-joint.

3.2. BJ Housing Surface Hardness Depth Measurement

Results

For measurement a randomly chosen new BJ housing is

used. Two samples are prepared to perform hardness

measurement. The samples are cut-off from two different

locations of the housing raceways.

Figure 3 shows that the BJ-housing surface hardness is

within the range of 653~746 Hv (HRc 58~62). This value is

in compliance with the standard requirement. Intersecting

line indicating the derived minimum acceptable hardness

(513 Hv) level is also shown. Vertical lines, drawn down to

the depth scale axis from the intersecting points of

measured hardness curve line and minimum acceptable

hardness level, reveal the maximum permissible surface

thickness which can be processed (machined, polished,

ground, etc.). In case of housing it is found out to be around

1.9~2.2 mm.

3.3. BJ Inner Race Surface Hardness Depth Measurement

Results

Two different samples are cut-off from the same Inner race

to conduct surface hardness depth measurements. The

samples are prepared and hardness depth is measured as

described in Chapter 3.1. Figure 4 shows the measurement

results. It can be seen that surface hardness is within the

specified range of 653~800 Hv. By applying the same

method as in the case of BJ Housing, it is possible to

identify that the maximum permissible surface thickness

which can be machined is about 1.2~1.8 mm.

3.4. BJ Cage Surface Hardness Depth Measurement

Results

Similar to BJ Housing and Inner race the Cage is also

tested for the surface hardness depth after proper

procedures to prepare the test samples. Test results are

shown in Figure 5. From the graph it is visible that

maximum permissible machining thickness is about

0.73~0.8 mm.

4. SURFACE MACHINING PROCEDURE AND DURABILITY TEST RESULTS

4.1. Manual to Surface Machining Process and Hardness

Measurement Results

Until recently, the remanufacturing companies were

Table 1. Surface micro-hardness depth analysis of the BJ

components.

Item

Derived hardness standard,

[Hv (HRc)]

Heat treatment

depth, [mm]

Heat treatment method

BJ Housing

513 (50)

1.9~2.2High frequency

induction hardening

BJ Inner race

1.2~1.8 Carburization

BJ Cage 0.73~0.8 Carburization

Figure 3. Surface hardness depth measurement results of

the new BJ housing raceway.


the new BJ Inner race.


the new BJ Cage.


rebuilding the CV-joints solely based on visual inspection

for presence of wear. If there was a sign of wear, then

Housing, Inner race and Cage used to be machined without

established standard for cut-off depth. The decision was

intuitive and visual. That means treating the surface until

any sign of wear disappears.

After the surface hardness depth of the new CV-joint is

measured and minimum allowable hardness value is

derived, the remanufactured CV-joints are also measured for

surface hardness depth in the manner as described in Chapter

3. For that the BJ is machined according to the manual used

by remanufacturing companies to remanufacture CV-joints

(Table 2). Total 36 samples are selected. Among them 6

samples were not machined, i.e., used-as-stands, only by

replacing the grease and boot. Then, the remaining 30

samples are divided into 3 groups and machined according

to the manual. The size measurement method is shown in

Figure 6.

According to the manual, collected core elements are

sorted, disassembled, rinsed and visually observed for their

current condition. If the elements are in reusable condition,

they transferred to the machining process. Otherwise sent

to recycling. Depending on the processing step and

geometrical dimensions a remanufactured CV-joint is

machined according to the manual given in Table 2.

Selected remanufactured CV-joints are machined and

surface hardness depth measurements of Housing, Inner

and Cage are performed. Only the BJ housing measurement

result is shown in Figure 7. Due to the close proximity of

measured results, only two samples from each group are

shown in the graph.

According to the graph in Figure 7, the hardness level of

the CV-joint which are reused without surface machining

reaches the established minimum value of 513 Hv at around

1.3 mm. Processed CV-joints had a surface hardness of

513 Hv at 0.8~1.1 mm depth. These values are about

42~60% of the hardness depth of a new CV-joint Housing.

4.2. Durability Test Results of Remanufactured CV-joints

After the surface hardness depth measurements the

samples are tested for durability according to the developed

procedure (Gafurov and Jung, 2012). The test bench is

shown in Figure 8 and its technical specifications are given

Table 2. BJ (Outer joint) surface machining manual used by remanufacturing companies.

Reman. CV-joint elements

Size prior to machining

[mm],(Group-A)

1st step machining [mm],(Group-B)

2nd step machining [mm],(Group-C)

3rd step machining [mm],(Group-D)

Size after machining

[mm]

Cut-off volume [mm]


[mm]

Cut-off volume [mm]


[mm]

Cut-off volume [mm]

BJ Housing 82.70 83.26 0.56 83.28 0.58 83.30 0.60

BJ Inner race 44.15 43.76 0.39 43.79 0.36 43.84 0.31

BJ Cage 19.10 19.55 0.45 19.55 0.45 19.55 0.45

Ball size ∅19.050 mm ∅19.558 mm ∅19.558 mm ∅19.558 mm

Sample size 6ea. 10ea. 10ea. 10ea.

Figure 6. BJ elements dimension measurement method: (a)

Housing; (b) Inner Race; (c) Cage.


Remanufactured CV-joint (BJ-Outer joint).

Figure 8. 4 channel driveshaft and axle simulator test

bench.


in Table 3. The target test duration for the remanufactured

CV-joint is 40,000 km, which is equal to 25 cycles. Note,

that for a new CV-joint the target mileage is 65,492 km of

real driving distance, which is equal to 40 cycles. The cycle

number is calculated based on the tire size, rolling distance

and standard mileage distance for the remanufactured CV-

joints (Table 4).

The test cycle duration is evaluated for a vehicle with

tire outer diameter of 627 mm. So, one rotation is equal to

1.97 m. Having the test duration in minutes and number of

revolutions, it is simple to estimate that one test cycle is

equal to 1637.3 km of real driving. Therefore, total 25 test

cycles are equal to 41,000 km of real driving distance.

During the test procedure the unmachined test samples

successfully completed the test, but machined samples

failed to pass the target of 25 cycles. Test results are

analyzed using Weibull distribution to find out statistical

parameters (Figure 9) and shown in Table 5. Precise

detection of time-to-failure was possible due to the constant

visual monitoring of the test procedure.

4.3. BJ-Outer Joint Surface Machining Parameter

Improvement

The inner race rotation and bending torque measurement

results (discussed in Chapter 5) confirmed that the

machining parameters must be reconsidered. By analyzing

the durability results of unmachined and machined

samples, it is suggested to increase the curvature radius of

the Inner race. In this way the excessive friction is reduced

due to increased backlash. Modified machining parameters

are given in Table 6.

Durability test procedure is performed using CV-joints

which are remanufactured following the modified

machining parameters. After 25th cycle, which is equal to

41,000 km of real driving distance, the samples were in

normal condition without any functional abnormalities. So,

Table 3. Driveshaft test bench technical specifications.

Maximum torqueJounce motionVehicle velocityAngular accelerationSteering angleMaximum power in loopMeasuring accuracy

- ±3000 Nm - Max. 400 mm- 300 km/h- 150 rpm/sec- 0~55o

- 300 HP- 0.1%

Table 4. Durability test specification, total 25 cycles

(1cycle: 590.6min).

Phase 1 2 3 4 5

Loading torque [Nm]

1568 1255 843 490 245

Revolution [rpm] 250 370 570 990 1690

Actual vehicle speed [km/h]

30 45 65 120 200

Test time [min] 12.24 8.91 55.80 107.42 406.29

Total test duration [hour]

8.16 5.94 37.2 71.61 270.86

Drive angle [DEG] 7

Standard temperature

Fixed Joint : 55~85oC with air-cooledPlunging Joint : without air-cooling

Figure 9. Weibull analysis graph of the failure data.

Table 5. Durability test results of remanufactured CV-joint.

Sample Type

Shape parame-

ter

Scale parame-

ter

MTTF, [km]

B10 Life, [km]

Lower Median Upper

Machined 3.02 22089 19,731 7,768 10,484 14,149

Unma-chined

2.72 71682 63,762 19,933 31,341 49,278

Figure 10. Boot temperature measurement: (a) test method

(b) measurement results comparison.


they are taken off from the testing and marked as nonfailed

samples.

As the main failure during durability test is a boot

rupture, the boot temperature measurement is performed

using a laser gun during the test (Figure 10 (a)). To do that,

the gun is pointed to the rotating CV-joint boot at safe

distance and measured temperature is read from the

display.

Comparative analysis results are given in Figure 10 (b).

There are two groups of data shown in graph. The

comparison must be made between the intuitively machined,

unmachined and improved sample. Intuitively machined

samples are the ones that use an old approach from

remanufacturing companies. Unmachined samples are those

which used as-it-stands, by replacing the grease and boot.

Lastly, improved samples are those which machined using

modified parameters. Ideally, the temperature measurement

results between two groups should be in close range.

However, due to technical reasons, like limited precision

machining, deviations in cooling air blow vector and

temperature measuring points, the results differ from one

set to another. Nevertheless, the main focus must be on the

temperature difference within a certain set of samples, not

between the sets. It is clear that improved machining

parameters give the same temperature results as unmachined

samples.

Table 6. Modified machining parameters for CV-joint remanufacturing.

Reman. CV-joint elements

Size prior to machining [mm],

(Group-A)

4th step machining [mm], (Group-E) 5th step machining [mm], (Group-F)

Size after machining [mm]

Cut-off volume [mm]

Size after machin-ing [mm]

Cut-off volume [mm]

BJ Housing 82.70 83.26 0.56 83.30 0.60

BJ Inner race 44.15 43.73 0.42 43.73 0.42

BJ Cage 19.10 19.55 0.45 19.55 0.45

Ball size ∅19.050 mm ∅19.558 mm ∅19.558 mm

Sample size 0ea. 2ea. 2ea.

Figure 11. BJ-Outer joint rotation and bending torque

measurement test bench: (a) Overview; (b) Inner race

bending torque measurement.

Table 7. Bending and Rotating torque measurement results.

Sample type Sample #Rotating

torque, [Nm]

Bending torque, [Nm]

Measuringangle

At 0o At 60o At 120o

+Peak -Peak +Peak -Peak +Peak -Peak

Prior to improvement

B1 26.82

±45o more than 40 NmB2 33.93

D1 39.6

D2 32.4

Improved samples

E1 18.73

±45o

35.43 38.32 29.34 28.31 36.14 36.94

E2 17.98 27.85 17.85 16.5 13.67 18.15 18.75

F1 17.12 31.43 33.88 26.19 26.38 35.9 31.48

F2 19.7 35.74 32.87 24.98 25.92 26.04 32.41


5. BJ ROTATING TORQUE ANALYSIS

Observations revealed that mostly grease leakage and boot

ruptures are the main cause of failure. It suggests that

temperature of BJ-outer joint is above the permissible limit.

It is understood that temperature elevation is due to

excessive friction between the housing-ball-inner race

assemblies. Analysis of the interaction surface of failed

samples after the test proved the reason of excessive wear.

Another proof was a rotation torque measurement of the

inner race inside the housing. It is performed by a

dedicated and newly developed test bench (Figure 11).

A shaft is inserted into the Inner-race and bent until it

reaches 45o angle. Then, the shaft is rotated in clockwise

direction and resistive torque is measured. Also, this test

bench allows measuring a bending torque. This procedure

is done at three angle locations (0o; 60o and 90o) and from

peak-to-peak, i.e. from maximum positive to minimum

negative angles. During the peak-to-peak travel a bending

torque is measured. Final results of measurement compared

with improved results are given in Table 7.

Analysis of rotating and bending torque results show

that modified machining parameters are beneficial in both

cases by significantly reducing the value comparing to old

machining parameters. The rotation torque below 20 Nm

and the bending torque below 40 Nm are achieved.

6. CONCLUSION

Until recently the remanufacturing companies operated

based on their own remanufacturing procedure. Absence of

the quality compliance certificate and certification procedure

for remanufactured products was one of the obstacles to

convince the end-users to purchase such products. This

paper investigates the remanufacturing method of CV-joint

in attempt to develop assessment criteria for certification.

Newly manufactured and remanufactured CV-joints are

analyzed for surface hardness depth. A minimum limit of

the surface hardness is determined and permissible

machining depths for the remanufacturing of BJ elements

are given. Also, intuitive remanufacturing procedure

parameters which were used by local remanufacturing

companies are studied. Durability tests are performed using

CV-joints remanufactured following the intuitive parameters.

Their inappropriateness is proved by unsuccessful test results.

Then, intuitive machining parameters are optimized using

measured surface hardness depth results. Second time

durability test results with optimized machining parameters

proved to be acceptable as results satisfied the standard

requirement of 40,000 km driving distance. Based on all

performed tests and analysis following conclusions can be

underlined:

(1) Minimum acceptable surface hardness of the BJ

elements is 513 Hv (50HRc);

(2) Previously used intuitive surface machining parameters

are unacceptable. They may result in large backlash or

increased friction due to tight fit;

(3) Maximum allowable surface machining depth for BJ

Housing is 1.9~2.2 mm, for BJ Inner race is 1.2~1.8 mm

and for BJ Cage is 0.73~0.8 mm;

(4) As the main failure during durability tests is a boot

rupture, the boot temperature must be maintained

below 85oC;

(5) Boot temperature reduction is achieved by optimized

surface machining parameters. BJ Inner race bending

torque must be below 40 Nm and rotating torque must

be below 20 Nm. By this way the excessive friction is

avoided and low boot temperature is maintained.

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cv-joint remanufacturing parameter optimization

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