Keywords: critical to quality variables; automotive mission plan; AMP; process mapping; cost of poor quality; response surface methodology; RSM; contour plot; process audit sheet; p-chart; sigma calculator; measurement system analysis; MSA; India; six sigma; foundry operations; make-to-order foundries; die casting foundries; optimisation.

1. Scope of Six Sigma in Indian foundry
operations: a case study
By
Dr. Bikram Jit Singh
Professor
MMDU Mullana

2. CEO/CHAMPION: RA/BJS DATE: 20-01-2011
Project Name: Reduction in scrap of Bajaj classic 5-Port pistons.
1 BUSINESS CASE
Rejection in foundry defect are taking place at two stages,
a) Rejection at foundry stage
b) Rejection detected at final inspection after machining, value addition takes
place during the manufacturing operations, project of improving piston rejection
of BCL5-P has been selected in Piston Foundry
For a particular machined number of blanks due to higher rejection good out put
is reduced , which in certain cases results in plan /customer requirements not
being met in Time.
With Low rejection hence more good out put good result in lower product cost
the actual benefits of 6 lakhs per annum is to be achieved.
The saving are calculated on the basis of benefits observed in manufacturing cost
due to scrap reduction at current level of production.

3. Rejection in foundry are taking place at two stages,
a) Rejection at foundry stage
b) Rejection detected at final inspection after machining, value addition takes
place during the manufacturing operations, project of improving material
rejection in CSA24 applications has been selected in Piston Foundry
For a particular machined number of blanks due to higher rejection good out
put is reduced , which in certain cases results in plan /customer requirements
not being met in time.
With Low rejection hence more good out put good result in lower product
cost the actual benefits of 6 Lakhs per annum is to be achieved.
The saving are calculated on the basis of benefits observed in manufacturing
cost due to scrap reduction at current level of production.

5. 0
10
20
30
40
50
60
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec
Baja Classic5P (Avg. 29.08%)
Baja Classic 5P
(Avg.29.08%)

6. Pareto Analysis Material Scrap of BCL 5 PORT
43.04%
17.72%
11.39%
8.86%
7.59%
6.33%
5.06%
100.00%
81.01%
88.61%
94.94%
72.15%
60.76%
43.04%
0.00%
5.00%
10.00%
15.00%
20.00%
25.00%
30.00%
35.00%
40.00%
45.00%
50.00% ShrinkageonSkirt
S3
ShrinkageonTop
S1
PorosityonSkirt
P3
ShrinkageonTop
B1
Shrinkageinring
zoneS2
blowholeinring
zoneB2
BlowHoleonSkirt
B3
Parameters
%age
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
90.00%
100.00%
Commulative%age

7. Financial Parameters (in Rs) Bajaj Classic 5-port
Scrap /Month 4582
Scrap cost/ Piston 153
Total rejection cost / Month 7,01,046
Total rejection cost / Year 84,12,552

8. Premelt-
ing R & R
Pre
Melting
Chips
Age
Hardening
Burr
Cutting
&
Fettling
Metal
Treatment
Casting
Composition
check through
spectrometer
Visual and
Dimensional
Checking
Visual &
Hardness
checking
Approval of
Brick mould
test & Density
Index
Alloying
Blank
Store
In Goting
Inspection
Storage
Operations

9. Casting

10. Production results of July-2011
Total number of Machined parts 15797
Scrap type Nos.
Shrinkage in Skirt (S3) 1976
Shrinkage on Top (S1) 812
Porosity on Skirt (P3) 519
Porosity on Top (P1) 406
Shrinkage in Ring Zone (S2) 348
Blow holes in Ring Zone (B1) 290
Blow holes on Skirt (B3) 231
Total Scrap in june 4582
Nos. of Oppertunities 7
DPMO 41436
Sigma level of process 3.2
Yield 69%

11. msa
STABILITY TEST
PART NAME : GAUGE NAME &L.C: Vac Tester
TOLERANCE : MM
MASTER VALUE: mm
X=Averrage X UCL= X+A2R= LCL=X - A2R=
R = average R UCL=D4xR LCL=D3xR 0
0.4075
0.3350 0.7645
CSA-18 alloy
0.70
0.16330.6517
0.00
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
0.8000
0.9000
1.0000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
0.0000
0.5000
1.0000
1.5000
2.0000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Oneunit=Oneunit=
ucl
Lcl
ucl
Lcl

12. Date Feb 1 3 4 5 6 7 8 10 11 12 13 14 15 18 19 20 21 22 24 25
Time
X1
X2
X3
X4
N/s
M/s
A/s N/s
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
X1 0.4 0.3 0.4 0.6 0.3 0.4 0.4 0.4 0.5 0.4 0.3 0.3 0.4 0.3 0.4 0.1 0.6 0.4 0.4 0.3
X2 1.2 0.2 0.3 0.4 0.4 0 0.5 0.3 0.3 0.3 0.4 1.2 0 0.4 0.3 0.2 0.4 0.5 0.4 0.4
X3 0.5 0.3 0.4 0.4 0.4 0.2 0.3 0.5 0.4 0.3 0.5 0.2 0.4 0.3 0.5 0.2 0.4 0.4 0.3 0.3
X4 0.2 0.4 0.3 0.4 0.4 0.4 0.4 0.4 0.4 0.6 0.5 2.3 0.5 0.4 0.5 0 0.5 0.4 0.4 0.3
Xbar 0.5750 0.3000 0.3500 0.4500 0.3750 0.2500 0.4000 0.4000 0.4000 0.4000 0.4250 1.0000 0.3250 0.3500 0.4250 0.1250 0.4750 0.4250 0.3750 0.3250
Range 1.000 0.200 0.100 0.200 0.100 0.400 0.200 0.200 0.200 0.300 0.200 2.100 0.500 0.100 0.200 0.200 0.200 0.100 0.100 0.100
Sub Group Size= 4 A2= 0.729 D3= 0 D4= 2.28 D2=
Standard deviation (s) R =
Gauge stability= s X100 %
BIAS CONTROL CHART METHOD BIAS
ULX = d2=
Xdbar = = =
LCLx = d2*=
UCLr = tv,1-a/2 = Lower Limit =
R bar =
LCL = 0 alpha = 0.05 Upper Limit =
Result Gage is not well stable
0.036220294
0.163
0.4075
2.05875
0.3350
0.76
2.06813
2.000
0.479612034
0.40750
0.16198208
28.26765674
0.6517
2.059
0.197873597
0.335388
R
e
a
d
I
n
g
s
Tolerance
*2d
R
r =s
g
r
b
s
s =

13. Analyse
METAL
OPERATORMETHOD
DIE
Temperature
Metal Treatment
1) Gas
2) Nucleation
Composition
Air venting
Flow lines
Cooling cycle
Pre-heating of
die
Good tool paint
Good die paint
Pouring
Filter insertion
Filter size
APPLICATION –BC 5P
Outer mould
relief
Rear side tool paint
Hourly out putPin stick air cooling
Die cleaning
Water
Circulation
SHRINKAGE
POROSITY &
BLOW
HOLES
ON SKIRT &
Top (CROWN)
CAUSE AND EFFECT DIAGRAM
Outer Dia

14. 790 Degree770 Degree750 Degree730 degree
100
90
80
70
60
50
40
30
20
10
Data
Boxplot of 730 degree, 750 Degree, 770 Degree, 790 Degree
790 Degree770 Degree750 Degree730 degree
100
90
80
70
60
50
40
30
20
10
Data
Individual Value Plot of 730 degree, 750 Degree, 770 Degree, 790 Degree

15. 116 Secs90 Secs
60
50
40
30
20
10
Data
Boxplot of 90 Secs, 116 Secs
116 Secs90 Secs
60
50
40
30
20
10
Data
Individual Value Plot of 90 Secs, 116 Secs

16. 700500300
50
40
30
20
10
CL2AR
50
40
30
20
10
Type of Gas
Degassing Time
AR
CL2
of Gas
Type
300
500
700
Time
Degassing
Interaction Plot for Casting Scrap
Data Means

17. Metal Temperature Cooling Time Degassing Time Casting Scrap
750 140 550 10
780 140 450 22
750 100 650 14
750 140 550 11
750 140 550 12
720 140 450 25
750 180 450 12
780 180 550 10
780 140 650 26
750 100 450 20
720 140 650 23
780 180 550 11
720 100 550 16
750 180 650 13
720 180 450 18

18. Response Surface Regression: Casting Scra versus Metal Temper, Cooling Time, ..
The analysis was done using coded units.
Estimated Regression Coefficients for Casting Scrap
Term Coef SE Coef T P
Constant 11.0000 0.7707 14.272 0.000
Metal Temperature -0.1429 0.5641 - 0.253 0.810
Cooling Time -2.3929 0.5641 -4.242 0.008
Degassing Time -0.3750 0.4720 -0.795 0.463
Metal Temperature*Metal Temperature 5.6012 0.8972 6.243 0.002
Cooling Time*Cooling Time -3.6488 0.8972 -4.067 0.010
Degassing Time*Degassing Time 7.3988 1.0731 6.895 0.001
Metal Temperature*Cooling Time 0.2262 1.3852 0.163 0.877
Metal Temperature*Degassing Time 1.5000 0.6675 2.247 0.075
Cooling Time*Degassing Time 1.7500 0.6675 2.622 0.047
S = 1.33497 PRESS = *
R-Sq = 98.03% R-Sq(pred) = *% R-Sq(adj) = 94.48%

19. 28262422201816141210
1.0
0.5
0.0
-0.5
-1.0
Casting Scrap
Residual
Residuals Versus Casting Scrap
(response is Casting Scrap)

20. 5
10
15
100
125
150
100
125
150
15
20
175
600
540
480
660
600
Casting Scrap
Degassing T ime
Cooling T ime
Metal Temperature 750
Hold Values
Surface Plot of Casting Scrap vs Degassing Time, Cooling Time

21. Cooling Time
DegassingTime
180170160150140130120110100
650
600
550
500
450
Metal Temperature 750
Hold Values
>
–
–
–
–
–
< 5.0
5.0 7.5
7.5 10.0
10.0 12.5
12.5 15.0
15.0 17.5
17.5
Scrap
Casting
Contour Plot of Casting Scrap vs Degassing Time, Cooling Time

22. 10
15
20
720720
740
760
720
740740
25
480
780
600
540
480
660
600
Casting Scrap
Degassing T ime
Metal T emperature
Cooling Time 140
Hold Values
Surface Plot of Casting Scrap vs Degassing Time, Metal Temperature

23. Metal Temperature
DegassingTime
776768760752744736728720
650
600
550
500
450
Cooling Time 140
Hold Values
>
–
–
–
–
< 12
12 15
15 18
18 21
21 24
24
Scrap
Casting
Contour Plot of Casting Scrap vs Degassing Time, Metal Temperature

24. 5
10
720
740
760
720
740740
15
780780
150
125
100
175
150
Casting Scrap
Cooling T ime
Metal T emperature
Degassing Time 550
Hold Values
Surface Plot of Casting Scrap vs Cooling Time, Metal Temperature

25. Metal Temperature
CoolingTime
776768760752744736728720
180
170
160
150
140
130
120
110
100
Degassing Time 550
Hold Values
>
–
–
–
–
< 5.0
5.0 7.5
7.5 10.0
10.0 12.5
12.5 15.0
15.0
Scrap
Casting
Contour Plot of Casting Scrap vs Cooling Time, Metal Temperature

26. Cooling Time
DegassingTime
180170160150140130120110100
650
600
550
500
450
Metal Temperature 750
Hold Values
10
29
Scrap
Casting
Contour Plot of Casting Scrap

27. Cur
High
Low0.99997
D
Optimal
d = 0.99997
Targ: 10.0
Casting
y = 10.0005
0.99997
Desirability
Composite
450.0
650.0
100.0
180.0
720.0
780.0
Cooling DegassinMetal Te
[750.9091] [151.7172] [552.9324]

28. Response Optimization
Parameters
Goal Lower Target Upper Weight Import
Casting Scra Target 5 10 29 1 1
Global Solution
Metal Temper = 750.909
Cooling Time = 151.717
Degassing Ti = 552.932
Predicted Responses
Casting Scra = 10.0005 , desirability = 0.999973
Composite Desirability = 0.999973

29. Production results of July-2011
Total number of Machined parts 17252
Scrap type Nos.
Shrinkage in Skirt (S3) 1976
Shrinkage on Top (S1) 812
Porosity on Skirt (P3) 519
Porosity on Top (P1) 406
Shrinkage in Ring Zone (S2) 348
Blow holes in Ring Zone (B1) 290
Blow holes on Skirt (B3) 231
Total Scrap in june 2416
Nos. of Oppertunities 7
DPMO 20006
Sigma level of process 3.6
Yield 85%

30. Financial Parameters (in Rs) Bajaj Classic 5-port
Scrap /Month 2416
Scrap cost/ Piston 153
Total rejection cost / Month 3,69,648
Total rejection cost / Year 44,35,776
Net saving in scrap per month 3,31,398
Net saving in scrap per annum 39,76,776

31. 31st July
28th
July
25th
July
22nd
July
19th
July
16th
July
13th
July
10th
July
7th
July
4th
July
1st July
0.225
0.200
0.175
0.150
0.125
0.100
0.075
0.050
Time
IndividualValue
_
X=0.1406
UCL=0.2178
LCL=0.0635
p chart for scrap monitoring

32. Deptt.: PISTON FDY. Line 3,Cell2
Piston Type: Bajaj Classic 5 Port AC9A ALLOY
Parameter Specification Observation Remarks
Scrapping of crucible walls Clean walls ok was done before tapping of metal in HF
Drossing off with Cov11
MEASURING SPOON
(300gms+50 gms )
WITH MEASURING SPOON YES 329 gms
Holding Furnace Clean from Slag visual clean Not Clean Not ok
Degassing - - Ar 553±10 secs 555 OK
Waiting time 5 MIN MINIMUM 3 Min 50 sec Not ok
Sample probe Visual SAMPLE PISTON TURNED Gas free, ok
Density Index upto 1.0 0.6 Ok
Casting temp. 750±10ºC HF 3 Line 2-759ºC OK
Die cooling cycle 150±10 secs 148 OK
Luff Sticks/air vents Open open
Luff stick not present in left
tool
left tool opened and sent for providing luff stick
Tool wear out No wear NO WEAR OK
Casting Spoon Refer specification Coated ok
Die Paint/ Padding Hatching Lines not Visible NOT OK CASTER called and advised to refill the padding
Core grouping Proper steps No Tool Shifting ok