IMPROVEMENT PROJECT FOR THE

AUTOMOTIVE A/C MUFFLE ASSEMBLY

Project Leader Denis Sexton

Page 2

D CIAM

In late 2000, after a Pareto Analysis at a automotive A/C

manufacturing plant, the first time quality reject rate (FTQ)

was the highest and most costly in the brazing furnace cell.

A cross functional team was initiated to investigate the

problem.

Team members & roles

CM : Production Team Leader

SR : Manufacturing Engineer

RT : Production Manager

DN : Quality Manager

DS : Engineering Black Belt / Mentor

Introduction

Page 3

Pareto of FTQ Problems in Manufacturing Plant -

2000

05

10152025303540

Muf

fler B

raze

Are

a

Crim

p Diam

eter A

C 1

Crim

p Diam

eter A

C 2

Valve

Inse

rtion

Crim

p Diam

eter P

S 1

Crim

p Diam

eter P

S 2

Oth

er

Source

% D

efe

cti

ve o

f P

lan

t

To

tal

0

20

40

60

80

100

120

Cu

m.F

req

%.

FREQUEN.

CUM.FREQ.

D CIAMStep A: Identify Project CTQs

CTQ = FTQ = Cost Reduction

Page 4

Step A: Identify Project CTQs D CIAM

Pareto of FTQ Problems in Muffler Brasing Process -

2000

05

1015202530354045

Muf

fler j

oint lea

ks

Exc

ess

braz

e us

ed

Hand

ling

Dam

age

Maint

enanc

e Issu

es

Sup

pler I

ssue

A

Sup

pler I

ssue

B

Oth

er

Source

% D

efe

cti

ve o

f P

rocess

To

tal

0

20

40

60

80

100

120

Cu

m.F

req

%.

FREQUEN.

CUM.FREQ.

CTQ = FTQ = Cost Reduction

Page 5

D CIAMStep A: Identify Project CTQs

Muffle

Assembly

unit in situ

on vehicle.

A good muffle unit was defined as one which passed leak test after the first pass in the oven. A bad part was defined as one which failed leak test after the first pass and had to be passed through the oven twice or more. This higher the FTQ, the higher the costs in rework, (meaning more overtime, more brazing paste consumption, more electricity used, and greater maintenance costs due to additional wear and tear on furnace) . The high FTQ also resulted in pressure to keep up with the next operations demand. FTQ became the project “critical to quality” (or CTQ) characteristic.

D CIAMStep A: Identify Project CTQs

Page 7

Step B: Team Charter

Business Case: (BIG Y – Net Sales, Customer Satisfaction, Compliance/Legal, Employee Satisfaction).

All muffle assemblies require 100% in line leak test. This testing can create high costs in the

process if the FTQ is excessive. In addition, the added handling increases the opportunities for

defects and damage.

Problem Statement: With higher FTQ’s it requires greater operator time to rework muffler in

furnace and re leak test. The burden of this rework and inspections is estimated at, USD $35000

or the cost of one permanent head count resource. This does not include hidden additional costs

(see slide 9).

Goal statement: To reduce the FTQ from brazing furnace to half the current level. This will

provide the opportunity to eliminate a permanent rework head count resource and save USD

$35000. In addition, indirect labour savings can be made as well as savings in gas and additional

unnecessary wear and tear on furnace which will result in reduction in downtime and spare parts

cost from the additional maintenance.

Timeline: Define (Oct 00), Measure (Jan 01), Analyse (Feb 01), Improve (March 01), Control (April

01)

D CIAM

Page 8

Step C: Process Map SIPOC D CIAMSuppliers Inputs Outputs

(Providers of the

required resources)

(Resources

required by the

process)

(Deliverables from

the process)

Requirements Requirements

Internal supplied Operators Training

parts from press shop Experience

Units per hour Zero defect from

next operation Internal Customer

(next operation)

Braze Paste Type Complete volume

Quantity in prescribed time. Final Customer

Location

Cycle Time

Furnace Running conditions

Maintenance

FTQ Data and

Work instructions Correct Recordkeeping

Current

Understood

Process Customers

(Top level description of the activity) (Stakeholders who place the

requirements on the outputs)

Prepare

Part for

Brazing

Furnace

(add

braze).

Pass parts

through Furnace

Muffler is

leak tested

and

passed to

plating

area.

Customer View

Page 9

Step 1: Select CTQ Characteristics

Project CTQ (Y) = Cost Reduction

Project y = FTQCost Reduction

Product Labour Machine

Rework Scrap Direct Indirect Uptime Productivity

Cycle

Times

Efficiency

StoppagesReliability

Quality Maintenance

INCREASED COST $$$$$$

D CIAM

Page 10

Step 2: Determine Performance Standard.

Defect Definition CTQ Elements: D CIAM

Output Unit COST

REDUCTION (BIG Y)

Output Characteristic. DELIVERY

OF PARTS WITHOUT LEAK.

Operational Definition MUFFLE ASSEMBLY

Project Y measure FTQ

TARGET 20,500 PPM LEAKS

Defect Definition LEAK FROM MUFFLE AT FIRST TEST

Number of Defect Opportunities ONE PER UNIT

NB. Muffle leak is measured after furnace

by two small Leak decay units.

At this stage, an internal specification

was determined as a pass/fail based on the

requirements of the final assembly.

At final assembly, the leak rate becomes

a significant customer characteristic so the

“after furnace” muffle leak test was initiated

to stop rejection at final assembly.

Page 11

Step 3: Validate Measurement System On Y Kappa

(Cross tabulation) Study for Attribute Leak data. D CIAM

Number of

Part/Samples/Questions n = 50

Number of Judges/Raters m = 2

ENTER CATEGORY INFORMTION

Categories 1 Leak 4 7 10 13

2 No Leak 5 8 11 14

3 6 9 12 15

More than two judges? No

Two judges only? Yes RAW DATA FOR 2 JUDGES

Multiple Judges (> 2) Two Judges

sum x2ij = Pobserved = 1.0

sum p*q = Pchance = 0.500

Koverall = Koverall or Individual = 0.96

Kappacategory for 2 judges

Category Kappa

#REF! #DIV/0!

#DIV/0!

#DIV/0!

#DIV/0!

#DIV/0!

#DIV/0!

#DIV/0!

#DIV/0!

#DIV/0!

#DIV/0!

ENTER INFORMATION IN COLUNMS BELOW

CALCULATIONS WILL APPEAR BELOW ONCE DATA IS ENTERED IN THE APPROPRIATE WORKSHEET

Step 1: Clear any categories values previously entered

Step 2: Enter Information

Step 3 Enter Data into this Worksheet:

Advanced Integrated

Technologies Group, Inc.

Copyright 1999, AIT Group Inc. All rights reserved.

Kappa Value of 0.96. This means that on a sample of

50 parts tested twice by two different operators, on two

readings the operators disagree on “good” and “bad” assemblies.

This was later Found to be a seal issue which was fixed. In general

Kappa values Greater than 0.75 are considered acceptable for inter-rater

agreement.

It should be remembered though that in the case of attribute studies applied,

any disagreement between raters is investigated to ensure no nonconforming

Parts are passed. In this case the next operations will assemble the muffler

into an AC system, which is leak tested automatically prior to final customer.

The purpose of this process is to reduce occurrence of high FTQ at Final

Assembly. Assemblies which pass muffle leak test nearly always pass at

Final assembly unless the leak is elsewhere in the A/C system.

Page 12

D CIAM

As data from muffler leak test is attribute (leak/not leak), the data is collected on

P charts. The current capability of the process is measured by “P Bar” which is

in percent defective. This in turn can then be translated into FTQ PPM for the

leak test operation.

The current year to date Capability (or DPMO) for the braze furnace (which is a

single in-process operation), is 42,000 PPM and needs to be Improved

drastically. The Raw data taken for the 60 days prior to the trials was compiled

onto a P Chart and showed 41,361 DPMO (as shown on next slide).

Although ideally a target of zero would be a long term goal, it is not a realistic

target. For the purpose of the project, a target of 20,500 DPMO has been set as

the benchmark.

Step 4: Define Performance Objectives

Page 13

D CIAMStep 5: Establish Process Capability

Mean FTQ is just over 41,000 PPM for the 60 days prior to the start of Improvement trials

P Chart for production Data prior to Experimental trials

0

0.02

0.04

0.06

0.08

0 10 20 30 40 50 60 70

Production Day Number

Fra

cti

on

De

fec

tiv

e

Page 14

Step 5: Establish Process Capability.

Comparison of FTQ with Process Capability

(Ppk or Cpk)D CIAM

Cpk Ppk Sigma DPMO Cpk Ppk Sigma DPMO Cpk Ppk Sigma DPMO

1 3 66810 1.34 4 6210 1.68 5 233

1.034 3.1 54800 1.374 4.1 4661 1.714 5.1 159

1.068 3.2 44570 1.408 4.2 3467 1.748 5.2 108

1.102 3.3 35930 1.442 4.3 2555 1.782 5.3 72

1.136 3.4 28720 1.476 4.4 1866 1.816 5.4 48

1.17 3.5 22750 1.51 4.5 1350 1.85 5.5 32

1.204 3.6 17860 1.544 4.6 968 1.884 5.6 21

1.238 3.7 13900 1.578 4.7 687 1.918 5.7 13.4

1.272 3.8 10720 1.612 4.8 484 1.952 5.8 8.6

1.306 3.9 8198 1.646 4.9 337 1.986 5.9 5.4

2.02 6 3.4

Page 15

D CIAMStep 5: Establish Process Capability

• From the P chart data:

• P bar = 0.0413

• Process Capability currently is 41,300 DPMO failures of the functional check.

• Customer is protected from receiving nonconforming product by 100% test on final A/C assembly but the failure rate is wasteful. Develop an action plan to reduce failure rate at furnace.

Page 16

Step 6: Identify Variation Sources Potential X’s D CIAM

Press 3

components

together to

make muffle

assembly .

Paste to

outside of

joint.

Pass

Assembl

y through

furnace.

Leak test

muffle and

pass to Store.

Plate

Muffle

Assembly.

Crimp

Hydraulic A/C

Lines to

Muffle.

Final

Assembl

y and

Leak Test

S/C.

Page 17

Step 7: Screen Potential Causes D CIAM

FTQ

Environment

Measurements

Methods

Material

Machines

Personnel

Team Leader

Maintenance

O perator

Leak Test Unit

Paste Dispenser

Furnace

Paste Ty pe

Muffle A ssembly

Paste A pplication

Belt Speed

Leak / No Leak

O v en Temp

Time in O v en

Time to O v en

Feet per Min

Wind gusts

Temperature

A fternoon Shift

Day Shift

Cause and Effect of Factors related to Muffle Leak FTQ

Page 18

Step 7: Screen Potential Causes D CIAM

• An screening trial was carried out on the muffle assembly with

the aim of reducing the occurrence of leakage between the centre

and end sections.

• The trial plan was developed to try different combinations of

paste, copper rings, and different methods of applying the paste,

with the aim of finding the best method that would provide the

highest first time “no leak” condition.

• The set up of samples is shown. There were 36 samples per

group. The other parameters such as belt speed and zone

temperatures were considered less important but were kept

constant throughout the trials.

Page 19

Step 7: DOE Screening Trial Initial results D CIAM

Group No Method Description Total Leaks

1 New Paste inner top cap 36 3

2 Old Wire on Centre 36 9

3 New Double paste on top 36 3

4 Old Old Caps 36 4

5 Old Wire on Cap 36 9

6 Old Different Paste Copper/Tin 20% 36 9

7 Old Different Paste Copper/Tin10% 36 21

8 Old Different Paste B Bronze 36 9

9 Old Different Paste Copper/Tin(other) 36 6

10 Old Double Line on Centre Can 36 9

11 New Paste on Centre Can - Top 36 3

Page 20

D CIAM

• There must be an adequate sample- the expected (not

obtained) frequency in each category must be at least 5.

Three assumptions must be met to use the Chi Square test:

• All observations must be independent, that is counted only once.

• Each observation must fit in only one category.

Step 7: DOE Chi Square Assumptions

Page 21

D CIAM

Good Leaks All

1 33 3 36

28.273 7.727

2 27 9 36

28.273 7.727

3 33 3 36

28.273 7.727

4 32 4 36

28.273 7.727

5 27 9 36

28.273 7.727

6 27 9 36

28.273 7.727

Chi-Square DF P-Value

Pearson 44.191 10 0.000

7 15 21 36

28.273 7.727

8 27 9 36

28.273 7.727

9 30 6 36

28.273 7.727

10 27 9 36

28.273 7.727

11 33 3 36

28.273 7.727

All 311 85 396

Good Leaks All

Step 8: Analysis between Groups.

Group difference is significant (p=<0.05)

Page 22

1110987654321

20

15

10

5

Group

Leaks

Interval Plot of Leaks95% CI for the Mean

Individual standard deviations are used to calculate the intervals.

D CIAMStep 8: Analysis between Groups.

Page 23

D CIAM

• The Main Conclusions that was drawn from this trial was that with

existing parameters and existing paste, the application of the paste to

the inside of the joint prior to press assembly (new) shows an

significant improvement from the existing (old) method. This was

further confirmed when a full Day’s production was run with the

change in paste application.

Step 8: Discover Variable Relationships.

• Different paste combinations should be used with the “new” method.

• Cost v FTQ benefit of different paste to be investigated. Initial P

Chart comparison for before and after (slides 26 and 27) shows

production data with same paste type .

Page 24

D CIAMStep 9: Establish New Assembly Process

Paste to

INSIDE of

joint.

Press 3

components

together to

make muffle

assembly.

Pass

Assembl

y through

furnace.

Leak test

muffle and pass

to store.

Swap Order of

Operations

Page 25

• Paste to be applied to the inside of the end can joints prior to pressing

operation.

• Muffle assembly to be pressed together within 4 hours of applying

paste.

• Muffle assembly to be passed through furnace within 72 hours of

pressing.

• Different types of paste to be trialed under these conditions.

D CIAMStep 9: Establish Operating Tolerances

Page 26

Step 10: Comparison from 60 days BEFORE

to after from validated Measurement System. D CIAM

Mean FTQ is just over 41,000 PPM for the 60 days prior to the start of Improvement trials

P Chart for production Data prior to Experimental trials

0

0.02

0.04

0.06

0.08

0 10 20 30 40 50 60 70

Production Day Number

Fra

cti

on

De

fec

tiv

e

Page 27

Step 10: Comparison from 60 days before to

AFTER from validated Measurement System. D CIAM

Mean FTQ is just under 10,000 PPM for the 60 days after the start of Improvement trials

P Chart for Production Data after process changes implemented.

-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0.03

0 10 20 30 40 50 60 70

Production Day Number

Fra

cti

on

De

fec

tiv

e

Page 28

Step 11: Determine Process Capability Improved

Performance – BEFORE PROJECT D CIAM

Step 11: Determine Process capability Improved

Performance – AFTER PROJECT

P Bar WAS 0.0413 which equates to

41,300 PPM

P Bar IS 0.00985 which equates to

9850 PPM

• Introduce New Paste (from group 9) as running change into

production with new paste application method and monitor FTQ

Page 29

Step 12: Implement Process Controls

To Maintain Performance D CIAM

P Bar = 7612 ppm. Ongoing monitoring via P Chart will ensure improvements have been

maintained and any positive or negative fine tuning can be evaluated moving forward.

P Chart for ongoing production 2001

-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0 10 20 30 40 50 60 70

Shift or Day number

Fra

cti

on

De

fec

tiv

e

Page 30

• FTQ may be improved further by upgrades in hardware and/or

adjustments to other Process Parameters which may need to be

evaluated separately for a cost/ benefit analysis. Longer term design

analysis (DFSS) may be utilised.

• What has been achieved from this project is a reduction in FTQ (and

thus hours saved in overtime, maintenance and downtime) on the

furnace due to additional hours in service for rework, without

any additional capital investment.

• Dedicated rework person was removed from line and used

elsewhere on more value adding activities.

D CIAMStep 12: Implement Process Controls

To Maintain Performance