six sigma application on rivet production

Application Of Six Sigma Methodology On Production Process of Rivets

A I C MD

Measure

Analyze

Improve

Control

Define

Measure

Analyze

Improve

Control

Six Sigma Roadmap

Problem Statement: The rejection percentage of rivets manufactured in an engineering company (Turbo India), at Bangalore is 0.466%.

Goal/Objective: To achieve six sigma level in the process of manufacturing rivets in order to reduce the variation in critical height.

Problem Statement and Goal

In Scope: Production, Inspection, Operator, Performance, Machine efficiency, Raw Material Quality.

Out of Scope: Logistics and Material Handling.

Scope of our project

Project Champion: Johanan Daniel

Project Team Leader: Muthuraman AR

Project Core Team Member: i) Divyank R Jain

ii) Apoorva iii) Suyash Kashyap

Project Team Membership

High Level Process Map (SIPOC)SUPPLIERS INPUT PROCESS OUTPUT CUSTOME

RSAkash Steels Raw Material

(Brass rods)

Manufacturing the rivets

Rivets according to specification

ADM MotorsBESCOM Electricity

Mrini Tools

Supervisor CAMS

Rajiv Lubricants

Working Fluid (Oil)

Possible factor

Potential failure

Severity Rating

Potential causes

Occurrence Rating

Control Detection Rating

RPN

Worker Error Defective component

9 • Unskilled Worker

• Lazy attitude

3 • inspection error 3 81

Oil Defective component

8 • Wrong oil• Fluid

properties

2 • Tool marks 2 32

Raw Material

Defective component

9 • Bent rods• Poor

specification & quality

5 • Inspection & QC

2 90

CAM Design Defective component

10 • CAM not designed properly

• Unskilled designer

2 • Inspection & QC 4 80

Collet (uncleaned)

Defective component

4 • Collet not cleaned by worker


7 196

Tools Defective component

6 • Wrong tool• Tool not

sharpened


Measurement errors

Wrong Measurement

8 • Wrong measurement tool

• Instrument not calibrated


9 448

Failure Mode Effect Analysis (FMEA)

Measure

Analyze

Improve

Control

Define

Six Sigma Roadmap

Project Y (or Ys) in Y=f(x)

Variation in height of the rivet which is critical to quality (CTQ) for the customer.

Critical Height Specification is 1.00±0.1 mm. Y’s can not be controlled but they can only be

monitored. It is the X’s or the input factors that can be controlled in order to achieve CTQ. So, we will try to find out all possible X’s (factors) in the project.

Note: All dimensions are measured in millimeter (mm)

Sample Measure1 0.952 1.033 0.964 1.015 0.986 1.067 1.018 1.019 1.05

10 1.0511 1.0412 0.9613 1.0214 1.0315 1.0216 117 1.0818 1.0219 120 121 1.0522 1.0823 0.9824 1.0525 1.0426 1.0427 1.0328 1.0129 1.0330 1.03

1.081.041.000.960.92

LSL 0.9Target *USL 1.1Sample Mean 1.02067Sample N 30StDev(Overall) 0.032688StDev(Within) 0.032404

Process Data

Pp 1.02PPL 1.23PPU 0.81Ppk 0.81Cpm *

Cp 1.03CPL 1.24CPU 0.82Cpk 0.82

Potential (Within) Capability

Overall Capability

PPM < LSL 0.00 111.48 98.12PPM > USL 0.00 7612.42 7177.47PPM Total 0.00 7723.90 7275.58

Observed Expected Overall Expected WithinPerformance

LSL USLOverallWithin

Process Capability Report for Measure

Flow Process DiagramStart

Customer sends order

Procure Raw Materials

CAM design

M/C Setting Machining Cleaning

Inspection

Stop

Dispatch

YEAR MONTH INSPECTED (QTY) ACCEPTED (QTY) REJECTED (QTY) % REJECTION DPMO SIGMA LEVEL[2016] JANUARY 368215 367991 224 0.060834024 608.340236 4.7[2016] FEBRUARY 508446 508131 315 0.061953482 619.5348179 4.7[2016] MARCH 306979 306854 125 0.040719398 407.1939774 4.8[2016] APRIL 633594 633164 430 0.067866804 678.6680429 4.7[2016] MAY 555200 554165 1035 0.186419308 1864.193084 4.4[2016] JUNE 428419 427573 846 0.197470234 1974.702336 4.4

Descriptive Analysis

Mean 4.616666667Standard Error 0.070316744

Median 4.7Mode 4.7

Standard Deviation 0.172240142Sample Variance 0.029666667

Kurtosis -1.730842065Skewness -0.730623505

Range 0.4Minimum 4.4Maximum 4.8

Sum 27.7Count 6

Confidence Level(95.0%) 0.180754944

Measure Baseline Performance

Current:

PPM (or DPMO): 1025.43

Sigma Level: 4.61

Goal:

PPM (or DPMO): 3.4

Sigma Level: 6

Rivet Height

Variation

Tools Machine

Operator Raw Materials

Chamfer Tool

Blunt Drill Bit Limit

switch

Centering Tool Holder

Collet Open/ Close Timing

Collet CleaningRaw Material

insertion timing Dead

WeightBar Straightness

Cause and Effect Diagram

Measure

Analyze

Improve

Control

Define

Six Sigma Roadmap

Potential Xs – Theories To Be Tested

X1: Measuring Error

X2: Collet Cleanliness

X3: Raw Material Defects

Theory: Measuring error could be one of the reasons for the current DPMO and sigma level. So, we need to test this by a proper comparison technique.

H0: Mean difference between population is zero.H1: Mean difference between the population is not zero.

Theory 1

Sample

Machine Measure

Manual Measure

1 1.00 1.032 1.02 1.063 1.01 1.054 1.02 1.085 1.01 1.036 1.00 1.047 1.03 1.058 1.03 1.049 1.03 1.0410 1.04 1.04

Theory 1 : Data Collected

N Mean StDev SE MeanManual Measure 10 1.0460 0.0151 0.0048Machine Measure 10 1.0190 0.0137 0.0043

Difference = μ (Manual Measure) - μ (Machine Measure)Estimate for difference: 0.0270095% CI for difference: (0.01342, 0.04058)T-Test of difference = 0 (vs ≠): T-Value = 4.19 P-Value = 0.001 DF = 17

ConclusionSince, p value is less than 0.05 the null hypothesis is rejected. Therefore, there is difference between the two populations. Measuring error can be reduced with the use of testing machines.

Theory 2 Theory: Unclean collet is suspected to be the cause of deviation in the critical height of the rivets. So, we need to test this by appropriate comparison technique.

H0: Difference between the mean of two processes is zero.H1: Difference between the mean of two processes is not zero.

Theory 2: Data Collected

SL.N0 Before Cleaning

After Cleaning

1 1.02 0.992 1.08 1.013 1.08 1.004 0.98 0.995 1.06 0.996 1.07 0.997 1.03 1.008 0.98 1.019 1.04 1.0010 1.00 0.99

Two-sample T for before cleaning vs after cleaning

N Mean StDev SE MeanBefore cleaning 10 1.0340 0.0386 0.012After cleaning 10 0.99700 0.00823 0.0026

Difference = μ (before cleaning) - μ (after cleaning)Estimate for difference: 0.037095% CI for difference: (0.0087, 0.0653)T-Test of difference = 0 (vs ≠): T-Value = 2.96 P-Value = 0.016 DF = 9

ConclusionSince, p value is less than 0.05 the null hypothesis is rejected.There is a difference between the two means. Therefore, collet cleaning reduces the variability in the critical height of rivets.

Measure

Analyze

Improve

Control

Define

Six Sigma Roadmap

Improvement Strategies for Proven XsProven Xs (Causes): Strategies:

1) Measurement Error

We try to improve measurement standards by focusing on mechanizedInspection of rivets.If the measurement is done manually highly calibrated and maintained measurement instruments should be used.

2) Unclean collet Since in our study we found that unclean collet is a major reason for rivet height deviations so, workers should ensure cleanliness of collet regularly checked by an appropriate time plan by the supervisor.

3) Raw Material Defects R.M straightness is checked before usage. Inspection chart is used for this purpose.

Descriptions of Possible Solutions (Pros and Cons)

Possible Solution: Strengths (Pros): Weaknesses (Cons):

Measurement should be done by inspection machines.

Eliminates any kind of error in measurement compared to manual measures.

Skilled and technically trained staffs required.Machines are susceptible to software errors.

Make a measurement schedule in which operator has to mention the readings.

Measurement can be ensured at regular intervals and effective control on them can be established.

Time consuming.

Prepare a regular collet clean schedule and it must be administered by a senior technical staff of organization.

Reduction in variation of rivet height.

Time consuming.Supervisor’s concentration gets deviated.

Updated Flow Process DiagramStart

Customer sends order

Procure Raw Materials

CAM design M/C Setting

Machining

Component Cleaning

Inspection using automated system

Stop

Dispatch

Check straightness of RM Collet cleaning

Possible factor

Potential failure

Severity Rating

Potential causes

Occurrence Rating

Control Detection Rating

RPN

Raw Material Defective component

6 • Bent rods• Poor

specification & quality


Collet (uncleaned)

Defective component

3 • Collet not cleaned by worker


Measurement errors

Wrong Measurement

8 • Wrong measurement tool

• Instrument not calibrated


Updated Failure Mode Effect Analysis (FMEA)

Raw Material Inspection Chart

• Raw material ovality is a vital reason for defects in the rivets. It can be eliminated by careful examination of each Raw material, whether it is straight or not.

• A Raw material inspection chart is used to monitor the straightness of raw material.

• The chart is prepared date-wise in which quantity of raw material is recorded by the assigned person. Then he is supposed to inspect all the materials and record the no. of accepted quantity and the no. of rejected quantity. Then the corresponding dates are to be signed by the person and by the supervisor.

• This method ensures that only straightened raw materials are accepted for manufacturing thereby reducing the no. of defectives. The model of raw material chart is in the subsequent slide.

SL.NO Date Qty(no. of rods)

Accepted (QTY)

Rejected (QTY)

Inspectors Sign

Supervisor Sign

Raw Material Inspection Chart

Collet Cleaning Schedule Chart• Unclean collet is also an important reason behind the

deviation of critical height of the rivet. Due to constant rotation of brass rods in the lathes, brass particles wear out and when dirt is stuck in the collet during production of rivets, the Raw materials aren't held properly between the jaws of the collet. So due to the presence of dirt in collet the raw material cant be fed properly in the lathe and deviation in critical height of rivets would occur.

• To avoid this the operators should clean the collet at regular intervals (every alternate days) using kerosene and ensure that there isn’t any presence of dirt in collet. This would reduce the number of defectives considerably.

• Day-wise cleaning schedule chart can be maintained. In this chart, operator’s name is mentioned with the respective machines he is working on. The collet is cleaned by the operator and puts a signature at the authorized place. The supervisor reviews the same.

COLLET CLEANING SCHEDULEM/C OPERATOR NAME 1 3 5 7 9 11 13 15

OS SS OS SS OS SS OS SS OS SS OS SS OS SS OS SS

GT-9

GT-10

GT-11

GT-12

GT-13

GT-14

M/C OPERATOR NAME 17 19 21 23 25 27 29 31OS SS OS SS OS SS OS SS OS SS OS SS OS SS OS SS

GT-9

GT-10

GT-11

GT-12

GT-13

GT-14

Measure

Analyze

Improve

Control

Define

Six Sigma Roadmap

Training Plans No special operator training is required for the

control phase, they need to follow the Raw Material Inspection Chart and Collet Cleaning Schedule to achieve the desired sigma level.

Operators also need to make sure that Automated Inspection System is used to measure rivet height. Usage of Vernier Calipers should be avoided since it leads to variation in the readings.

We sincerely believe that if mentioned plans are

followed then it will lead to high process capability with respect to process of manufacturing rivets.

Updated Process CapabilitySample MEASURE

1 0.982 0.963 0.994 1.025 16 1.017 1.018 1.039 1.01

10 1.0211 1.0112 1.0313 0.9714 0.9815 116 117 0.9718 119 0.9820 121 0.9922 1.0423 1.0124 125 0.9726 1.0227 0.9928 0.9829 1.0630 0.99

• From the updated process capability chart we find the Cpk value to be equal to 1.44 which can be used to calculate the improved sigma level.

• Current Sigma level = Cpk ×3+ 1.5 Sigma Level = 1.44(3)+1.5=5.82

• From the updated histogram, we see the variation is controlled within the specification limits.

• The achieved mean is 1.00067 is much closer to expected mean of 1.0000 compared to the earlier mean of 1.02067

Updated Run Chart

Project Baseline: Project Target: Project Actual:

DPMO= 1025.43 DPMO= 3.4 DPMO= 8

Sigma Level=

4.61 Sigma Level=

6 Sigma Level=

5.82

Project Results

Project Start Date: 6/5/2016

Project End Date: 10/6/2016

We learned many concepts of manufacturing processes in an industry. Though we have theoretical knowledge about the subject, witnessing the operations in front of our eyes in real-time was once in a life time experience.

The project helped us better as an individual in dealing with different people in varied number of situations. We learned to find effective solutions to the problems that would help us in accomplishing our future endeavors in life.

We would like to thank all the people involved directly or indirectly in this project. Without you this project wouldn’t have been possible.

Lessons Learned

six sigma application on rivet production

Small Business & Entrepreneurship