PROCESS CAPABILITY ANALYSIS

FOR CHEMISTRY CONTROL

A PROJECT BY GRADUATE STUDENTS OF LAMAR UNIVERSITY FALL 2001

NORTH STAR STEEL , BEAUMONT

AT

TEAM-1Course: ENGR 5312- Quality Assurance Submitted on: Dec 3,2001

Project title: Control charts and process capability by crew- for meeting guideline aim ranges of controllable elements C, Mn and Si of steel, a study carried out at NSS.

Team members:

Anshu Srivastava E-mail: anshu_lamar@yahoo.com Suresh Putcha E-mail: sureshputcha@yahoo.com

Project Sponsor at NSS: Pete Power E-mail: Pete_Power@Cargill.com

PROBLEM DEFINITION

At North Star Steel, four crews namely A, B, C & D are working on a large number of grades .

They try to achieve the constituents of steel set by the customer to the closest standards. i.e. they try to hit the target set for each element(C, Mn, Si…).

In this project we quantify the success achieved by each crew in attaining this objective.

TERMINOLOGY

•Grade: specifies type of steel based on the percentage of C, Mn, Si…. present in it.

Grade1012KZ-1 : C-0.135%, Mn0.55%, Si-0.14%)

Target or AIM: It is the exact percentage of a constituent to be achieved in a specified grade of steel.

SPEC: This is customer specified limit or range within which the crew has to hit the target. USL-upper limit, LSL-lower limit

DATA COLLECTED

SPEC and AIM values for 57 grades of steel

The heat chemistry analysis report that shows the percentage of each element actually achieved by a crew in a heat was collected.

This log of steel chemistry was printed for all the heats for three months August, September and October

2001.

DATA COLLECTEDGRADE C-AIM Mn-AIM Si-AIM

1006M6-2 0.050 0.35 0.101008A2-1 0.080 0.35 0.111008A39-1 0.060 0.35 0.101008A4-1 0.060 0.37 0.111008AISI1 0.060 0.35 0.091008AISI1 0.060 0.35 0.091008AS-2 0.090 0.45 0.111008AZB 0.045 0.35 0.121008M10-2 0.070 0.40 0.251008M11-2 0.090 0.33 0.091008M12-2 0.070 0.35 0.101008M13-1 0.060 0.44 0.101008M14-2 0.065 0.33 0.171008M15-1 0.060 0.44 0.131008M16-1 0.090 0.35 0.141008M-19-1 0.070 0.35 0.131008M20-1 0.070 0.13 0.131008M21-2 0.080 0.40 0.101008M22-2 0.080 0.42 0.201008M23-2 0.090 0.47 0.201008M4-1 0.080 0.40 0.111008M5-2 0.090 0.45 0.111008M6-1 0.070 0.33 0.101008M7-2 0.070 0.35 0.101008M9-2 0.060 0.35 0.101008MA-2 0.060 0.35 0.131008MB-2 0.050 0.33 0.131008MBR-3 0.100 0.60 0.181010A2-1 0.090 0.35 0.131010M11-2 0.090 0.35 0.131010M4-1 0.095 0.35 0.121010M5-1 0.090 0.35 0.101010M7-1 0.090 0.35 0.171010M8-1 0.090 0.50 0.101010M9-1 0.090 0.45 0.111012A3-2 0.125 0.50 0.201012AZB 0.135 0.50 0.151012B2 0.070 0.45 0.141012KZ-1 0.135 0.55 0.141012KZ-1 0.135 0.56 0.141012M11-2 0.130 0.50 0.181012M1-2 0.135 0.50 0.201012M12-2 0.130 0.55 0.091012M3-2 0.120 0.50 0.031012M7-3 0.120 0.47 0.031012M9-1 0.130 0.50 0.121013A1-2 0.130 0.70 0.131013AISI1 0.130 0.70 0.131013M4-1 0.120 0.45 0.141013M5-1 0.140 0.62 0.171013M6-2 0.120 0.54 0.181015A1-1 0.160 0.55 0.181015AISI1 0.140 0.55 0.151015KZ-1 0.150 0.53 0.121015M4-1 0.140 0.45 0.14DW170 0.810 0.70 0.24WXW10WZ-1 0.085 0.83 0.10

The AIM targets for % carbon % manganese % silicon

Assumption : the SPEC limits for the percentage error graph to be spread around 25% on either side of the Aim.

DATA COLLECTEDC C-AIM Mn Mn-AIM Si Si-AIM Group0.125 0.135 0.58 0.55 0.12 0.14 A0.131 0.135 0.60 0.55 0.16 0.14 A0.133 0.135 0.56 0.55 0.14 0.14 A0.133 0.135 0.64 0.55 0.14 0.14 A0.133 0.135 0.58 0.55 0.17 0.14 A0.126 0.135 0.60 0.55 0.19 0.14 A0.143 0.135 0.59 0.55 0.17 0.14 A0.121 0.120 0.48 0.45 0.15 0.14 A0.120 0.120 0.44 0.45 0.15 0.14 C0.079 0.080 0.41 0.42 0.18 0.20 D0.092 0.080 0.38 0.42 0.17 0.20 D0.074 0.080 0.40 0.42 0.20 0.20 D0.035 0.060 0.38 0.35 0.08 0.09 B0.039 0.060 0.34 0.35 0.09 0.09 B0.045 0.060 0.37 0.35 0.09 0.09 B0.044 0.060 0.35 0.35 0.10 0.09 B0.048 0.060 0.33 0.35 0.09 0.09 D0.048 0.060 0.34 0.35 0.15 0.09 D0.048 0.060 0.33 0.35 0.14 0.09 D0.079 0.060 0.36 0.35 0.11 0.09 D0.057 0.060 0.35 0.35 0.09 0.09 D0.043 0.060 0.36 0.35 0.08 0.09 D0.038 0.060 0.35 0.35 0.08 0.09 D0.045 0.060 0.33 0.35 0.09 0.09 D0.119 0.120 0.44 0.47 0.15 0.03 B0.112 0.120 0.46 0.47 0.14 0.03 B0.112 0.120 0.44 0.47 0.14 0.03 B0.117 0.120 0.46 0.47 0.14 0.03 D0.116 0.120 0.40 0.47 0.14 0.03 D0.112 0.120 0.43 0.47 0.16 0.03 D0.112 0.120 0.46 0.47 0.16 0.03 D0.110 0.120 0.46 0.47 0.15 0.03 D0.070 0.070 0.44 0.45 0.14 0.14 C0.073 0.070 0.44 0.45 0.13 0.14 C0.077 0.070 0.46 0.45 0.14 0.14 C0.060 0.060 0.38 0.37 0.09 0.11 A0.058 0.060 0.38 0.37 0.12 0.11 A0.054 0.060 0.36 0.37 0.12 0.11 A0.054 0.060 0.38 0.37 0.10 0.11 A0.060 0.060 0.36 0.37 0.12 0.11 A0.137 0.130 0.55 0.55 0.11 0.09 C0.138 0.130 0.56 0.55 0.11 0.09 C0.137 0.130 0.54 0.55 0.09 0.09 C0.129 0.130 0.60 0.55 0.11 0.09 C0.129 0.130 0.60 0.55 0.11 0.09 C0.138 0.130 0.57 0.55 0.10 0.09 C0.142 0.130 0.57 0.55 0.09 0.09 C0.132 0.130 0.60 0.55 0.12 0.09 C0.126 0.130 0.66 0.55 0.10 0.09 A

• Heat chemistry for three months – August , Sept. and October 2001 were taken for analysis .

• A sample size of 125 heats for each crew was analyzed .

PROCESS CAPABILITY

Cpk : Capability Analysis index.

It compares natural tolerances (6) of the process with the specification range.

It is a ratio of the tolerance (the width of the specification limits) to the actual spread.

DATA ANALYSIS

Assumption :

SPEC limits for the percentage error graph to be spread around 25% on either side of the target AIM.

RESULTS -Carbon

-0.50 -0.25 0.00 0.25 0.50

LSL USLTarget

CAPABILITY ANALYSIS FOR CARBON(PERCENTAGE ERROR)

USLTargetLSL

Cpk

0.250000 0.000000-0.250000

ProcessData

0.500.73 0.640.87 > > >

D A C B

BC

A

D

CREW

RESULTS -Manganese

0.500.250.00-0.25-0.50

Target USLLSL

CAPABILITY ANALYSIS FOR Mn(PERCENTAGE ERROR)

LSLTargetUSL

-0.250000 0.000000 0.250000Data

Process

Cpk 1.201.48 1.531.68 > > >

C B A DCREW

C

B

A

D

RESULTS - Silicon

0.500.250.00-0.25-0.50

Target USLLSL

CAPABILITY ANALYSIS FOR Si(PERCENTAGE ERROR)

LSLTargetUSL

-0.250000 0.000000 0.250000Data

Process

Cpk 0.510.58 0.56> >

A C BCREW

0.36>

D

AC

B

D

RESULTS – CREW -A

0.500.250.00-0.25-0.50

Target USLLSL

CAPABILITY ANALYSIS FOR CREW-A

LSLTargetUSL

-0.250000 0.000000 0.250000Data

Process

SiC

Mn

SiMn

C

Cpk

0.581.53

0.73

RESULTS – CREW -B

-0.50 -0.25 0.00 0.25 0.50

LSL USLTarget

CAPABILITY ANALYSIS FOR CREW-B

USLTargetLSL

0.250000 0.000000-0.250000

ProcessData

Si

CMn

SiMn

C

Cpk

0.511.48

0.50

RESULTS – CREW -C

-0.50 -0.25 0.00 0.25 0.50

LSL USLTarget

CAPABILITY ANALYSIS FOR CREW-C

USLTargetLSL

0.250000 0.000000-0.250000

ProcessData

Si

C

Mn

SiMn

C

Cpk

0.561.68

0.64

RESULTS – CREW -D

0.500.250.00-0.25-0.50

Target USLLSL

CAPABILITY ANALYSIS FOR CREW-D

LSLTargetUSL

-0.250000 0.000000 0.250000Data

Process

Si

C

Mn

C Si

Mn

Cpk

0.361.20

0.87

RESULTS

We have graded the crews on a 4-point scale.

CREW CARBON MANGANESE SILICON Total Points

A 3 2 4 9

B 1 3 2 6

C 2 4 3 9

D 4 1 1 6

Ranking can be awarded as A >C > D > BRanking can be awarded as A >C > D > B

CONCLUSIONS

•A hits the target very well .

•D is good in hitting carbon only .

•B is average across all the grades .

•C has to improve on hitting carbon %

•Looks like Silicon % is a low priority across crews .

THANK YOU !