determination of the optimal parameters in resistance ... · • by comparing various welding...

1

Determination of the Optimal Parameters

in Resistance Projection Welding for a

Wheel Starter of Motorcycle Engines

Dr.Chuckaphun Aramphongphun Mr.Suriya Salikul

Department of Industrial Engineering,

Faculty of Engineering, Kasetsart University THAILAND

2 Operation of the start system of the motorcycle engine

• A case study factory is an automotive and motorcycle part manufacturer. Forming and welding of sheet metals are the main manufacturing processes.

• The factory would like to reduce the manufacturing cost and time by developing alternative welding process and also maintain the same quality of the welded wheel starter.

1. Introduction

Motor Start System

Wheel Starter

(Pulley Starter)

3

1. Introduction (cont.)

• A wheel starter (or pulley starter) is a main component in the motor start system of the motorcycle engine.

• It serves as a driving gear to start the engine of motorcycle.

A wheel starter of the motorcycle engine

4


A Flow Process Chart

BOSS GEAR

RESISTANCE

PROJECTION

WELDING

SURFACE HARDENING

MACHINING

CIRCLIP &

BEARING

STORAGE

5

The wheel starter installation in the engine

A location of the wheel starter in the motor start system


6

• Plasma Arc Welding (PAW) is originally used to join the boss

and gear to make the wheel starter.

The welded part after Plasma Arc Welding

Plasma Arc Welding (Original Welding Process)


7

Comparison of various welding processes


Electron Beam Welding (EBW)

Plasma Arc Welding (PAW)

Resistance Projection Welding (RPW)

Welding cycle time = 30 sec Welding cycle time = 47 sec Welding cycle time = 9 sec

8

Comparison between PAW and RPW


Features Types of Welding Process

PAW RPW

Welding Depth 2 1

Torsion Torque 2 2

Welding Height 1 2

Welding Bead 1 2

Machine Cost 1 2

Electric Cost 2 1

Welding Wire Cost 0 2

Shield Gas Cost 0 2

Cycle Time 1 2

2 = Very good, 1 = Good, 0 = Poor

9

• By comparing various welding processes in terms of reduced cost, time, and quality of the part, Resistance Projection Welding (RPW) is the most suitable welding process used to form the wheel starter.

Resistance Projection Welding used in the experiment

Comparison among welding processes


10

An example shows the macro section of a weld

nugget after the welding time has ended.

1->2 Lowering of the top electrode

2->3 Application of the adjusted electrode force Set-up time tpre, sequence

3->4 Switching-on of the adjusted welding current for the period of the welding time tw.

Formation of the weld nugget in the joining zone of both workpieces.

4->5 Maintaining the electrode force for the period of the set post-weld holding time th.

5->6 Switching-off the force generating system and lifting the electrodes off the workpiece.

Cycle of Resistance Welding


11

• To study and analyze the factors that significantly

affect the quality of the wheel starter using

Resistance Projection Welding

• To determine the optimal parameters in Resistance

Projection Welding and set it as the production

standard

• To study the microstructure and hardness in Heat

Affected Zone after Resistance Projection Welding

2. Research Objectives

12

3. Design of Experiments

A Flow Chart of the Design of Experiments

Start

Full Factorial

Design with

Center Points

RSM Design

(CCD)

2nd Experiments

1st Experiments

Statistical

Analysis Confirm Run

Summary

Statistical

Analysis

13

RPW

Resistance welding machine used in the experiments

3. Design of Experiments (cont.)

14

Note: 1 Cycle = 50 Hz = 1/50 sec

Levels of each factor used in the experiments

3. Design of Experiments (cont.)

Factors Low (-1)

Middle (0)

High (+1)

Current (kA) 44.5 45.0 45.5

Time (Cycle) 19 20 21

Pressure (MPa) 0.35 0.40 0.45

Margin (mm) 0.500 0.5275 0.555

15

- Full Factorial design: 24 x 2 = 32 runs

- Center points = 4 runs

- Total runs = 36 runs (32 + 4)

Number of the Full Factorial experiments

3. Design of Experiment (cont.)

16

4. Results and Analysis Factorial Fit: Torque versus Current, Time, Pressure, Margin Estimated Effects and Coefficients for Torque (coded units)

Term Effect Coef SE Coef T P

Constant 1524.44 7.589 200.87 0.000

Current 16.62 8.31 7.589 1.10 0.287

Time -18.87 -9.44 7.589 -1.24 0.229

Pressure 2.75 1.37 7.589 0.18 0.858

Margin 24.37 12.19 7.589 1.61 0.125

Current*Time 15.63 7.81 7.589 1.03 0.316

Current*Pressure 1.00 0.50 7.589 0.07 0.948

Current*Margin -14.38 -7.19 7.589 -0.95 0.355

Time*Pressure 12.50 6.25 7.589 0.82 0.420

Time*Margin 10.38 5.19 7.589 0.68 0.503

Pressure*Margin -13.00 -6.50 7.589 -0.86 0.402

Current*Time*Pressure -7.50 -3.75 7.589 -0.49 0.627

Current*Time*Margin 32.38 16.19 7.589 2.13 0.046

Current*Pressure*Margin 11.25 5.63 7.589 0.74 0.468

Time*Pressure*Margin 3.00 1.50 7.589 0.20 0.845

Current*Time*Pressure*Margin -12.00 -6.00 7.589 -0.79 0.439

Ct Pt -52.19 22.768 -2.29 0.033

S = 42.9312 PRESS = 135202

R-Sq = 51.85% R-Sq(pred) = 0.00% R-Sq(adj) = 11.30%

17

80400-40-80

99

90

50

10

1

Residual

Pe

rce

nt

160015501500

50

25

0

-25

-50

Fitted Value

Re

sid

ua

l

6040200-20-40-60

10.0

7.5

5.0

2.5

0.0

Residual

Fre

qu

en

cy

35302520151051

50

25

0

-25

-50

Observation Order

Re

sid

ua

l

Normal Probability Plot Versus Fits

Histogram Versus Order

Residual Plots for TorqueNormality

Constant Variance

Independence Normal curve

4. Results and Analysis (cont.)

18

Factorial Fit: Torque versus Current, Time, Margin Estimated Effects and Coefficients for Torque (coded units)

Term Effect Coef SE Coef T P

Constant 1524.44 6.835 223.05 0.000

Current 16.63 8.31 6.835 1.22 0.233

Time -18.87 -9.44 6.835 -1.38 0.178

Margin 24.38 12.19 6.835 1.78 0.085

Current*Time*Margin 32.37 16.19 6.835 2.37 0.025

Ct Pt -52.19 20.504 -2.55 0.016

S = 38.6623 PRESS = 63807.7



19

100500-50-100

99

90

50

10

1

Residual

Pe

rce

nt

15601540152015001480

80

40

0

-40

-80

Fitted Value

Re

sid

ua

l

806040200-20-40-60

8

6

4

2

0

Residual

Fre

qu

en

cy

35302520151051

80

40

0

-40

-80

Observation Order

Re

sid

ua

l

Normal Probability Plot Versus Fits

Histogram Versus Order

Residual Plots for TorqueNormality

Constant Variance

Independence Normal curve


20

0.555

0.5

21

1945.544.5

Margin

Time

Current

1472.25

1557.50

1518.001563.75

1507.25

1504.75

1550.751503.00

1490.50

Centerpoint

Factorial Point

Cube Plot (data means) for Torque

Level of the factors that provides the highest torque is as follows: Current = 44.5 kA, Time = 19 cycle, Margin = 0.555 mm


21

Response Surface Regression: Torque versus Block, Current, Time, Margin The analysis was done using coded units.

Estimated Regression Coefficients for Torque

Term Coef SE Coef T P

Constant 1536.40 10.845 141.673 0.000

Block -60.36 7.071 -8.536 0.000

Current 2.05 7.081 0.290 0.775

Time -4.60 7.081 -0.650 0.522

Margin 11.50 7.081 1.624 0.118

Current*Current 38.03 14.142 2.689 0.013

Time*Time -3.97 14.142 -0.281 0.781

Margin*Margin 12.53 14.142 0.886 0.385

Current*Time 11.88 7.917 1.500 0.147

Current*Margin -3.12 7.917 -0.395 0.697

Time*Margin 4.31 7.917 0.545 0.591

S = 31.6677 PRESS = 56396.5



22

The optimal condition that provides the maximum torque based on the RSM model


23

The Surface Plot of the RSM Model


1550

1575

1600

2144.5

2045.0

1945.5

ue

TimeCurrent

Margin 0.555

Hold Values

Surface Plot of Torque vs Time, Current

Torque

24

The Contour Plot of the RSM Model

Current

Tim

e

45.5045.2545.0044.7544.50

21.0

20.5

20.0

19.5

19.0

Margin 0.555

Hold Values

>

–

–

–

–

< 1560

1560 1570

1570 1580

1580 1590

1590 1600

1600

Torque

Contour Plot of Torque vs Time, Current


25

Confirmation Runs at the Optimal Parameter


Factors Optimal Level

Current (kA) 44.5

Time (Cycle) 19

Margin (mm) 0.555

26

Confirmation Runs at the Optimal Parameter (cont.)


Tests Measured Torque (N.m)

1 1607.62

2 1610.14

3 1607.59

4 1605.10

5 1602.60

6 1607.13

7 1612.12

8 1604.42

9 1610.18

10 1609.91

27

Hypothesis Testing of the Confirmation Runs


28

One-Sample T: Confirm Run Test of mu = 1600 vs > 1600

95% Lower

Variable N Mean StDev SE Mean Bound T P

Confirm Run 10 1607.68 2.99 0.94 1605.95 8.13 0.000

P-value < (0.05), thus reject H0

According to results of the confirmation runs, it was found that

the average torque was greater than 1,600 N-m. A 95% confidence

interval was greater than 1,605.95 N-m. Therefore, the result of the experiments agreed with the values obtained from the RSM analysis.


29

5. A Study of Microstructure in Heat Affected Zone

Microstructure in Heat Affected Zone (HAZ) after

Resistance Projection Welding was studied and viewed by a

microscope. This study compared (i) the microstructure in HAZ and

(ii) hardness in Plasma Arc Welding (PAW) and Resistance

Projection Welding (RPW).

30

A microstructure in HAZ of the boss at a distance of 0.2 mm from the welded joint with magnification of 2,000x

(a) Plasma Arc Welding and (b) Resistance Projection Welding

(a) (b)

5. A Study of Microstructure in Heat Affected Zone (cont.)

31

(a) (b)

A microstructure in HAZ of the boss at a distance of 0.4 mm from the welded joint with magnification of 2,000x



32

(a) (b)

A microstructure in HAZ of the gear at a distance of 0.2 mm from the welded joint with magnification of 2,000x



33

(a) (b)

A microstructure in HAZ of the gear at a distance of 0.4 mm from the welded joint with magnification of 2,000x



34

Hardness in Heat Affected Zone after Plasma Arc Welding

Boss

(S

35C

)

Gear

(S

PH

C)

HAZ

6. A Study of Hardness in Heat Affected Zone

35

Gear (SPHC)

Boss (S35C)

HAZ

6. A Study of Hardness in Heat Affected Zone (cont.)

Hardness in Heat Affected Zone after Resistance Projection Welding

36

• The Resistance Projection Welding (RPW) has been

recently developed to join the wheel starter. • Process parameters (factors) in RPW that significantly

affected the torsion torque of the welded wheel starter

were: (i) Current, (ii) Time, and (iii) Margin.

• The pressure used in the experiments was not significant.

• The optimal setting of the significant parameters was as

follows:

Current = 44.5 kA

Time = 19 cycle

Margin = 0.555 mm

7. Summary

37

• According to results of the confirmation runs, it was found

that the average torque was greater than 1,600 N-m. (Target

specification is greater than 1,600 N-m.)

• A 95% confidence interval was greater than 1,605.95 N-m.

Therefore, the result of the experiments agreed well with the

values obtained from the RSM model.

• Moreover, RPW also significantly reduced (i) the welding

cycle time from 47 to 9 sec (-81%) and (ii) the welding cost.

7. Summary (cont.)

38

• The welded joint has experienced high temperature

and resulted in the residual stress. Microstructure in

Heat Affected Zone was therefore different from that

in the unaffected base metal zone.

• Microstructure changes resulted from Plasma Arc

Welding were more severe than those resulted from

Resistance Projection Welding and led to the non-

uniform microstructure. In addition, too high

hardness could result in brittle structure.

7. Summary (cont.)

39

Thank you for your attention.

QUESTIONS?

determination of the optimal parameters in resistance ... · • by comparing various welding...

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