Unit Iii Statistical Process Control

UNIT III STATISTICAL PROCESS CONTROL

Meaning and significance of statistical process control (SPC) – construction of control charts forvariables and attributed.

Process capability – meaning, significance and measurement – Six sigma - concepts of processcapability.

Reliability concepts – definitions, reliability in series and parallel, product life characteristicscurve.Total productive maintenance (TMP), Terotechnology.

Business process Improvement (BPI)– principles, applications, reengineering process, benefits and limitations.

Control Chart:

Meaning:

It is a graph that displays data taken over time and the variations of this data.

It is used to check whether the process is controlled statically or not.

It is a graphical representation of measured actual process performance relative to computed control limits.

It is a statistical technique for controlling the quality of a product being manufactured.

It was first developed by Dr. Walter A.Shewart.

Steps in Construction of control chart:

1. Checking for errors

2. Selection of Sub Sample

3. Calculation of relevant Statistics tools.

4. Setting the control limits

5. Constructing the control chart

Types of control charts:-

Control chart for variables
Control chart for attributes

I. Attribute

a product characteristic that can be evaluated with a discrete response

Ex: good – bad; yes - no

II.Variable:

Product characteristic that is continuous and can be measured

Ex: weight – length

I. Control chart for variables:-

A single measurable quality characteristic such as dimension, weight, volume, pressure, temperature, strength & hardness are called variables. Control chart for variables requires a measurement of the quality characteristic of the continuously varying magnitude. These variables can be measured and expressed in terms of units. Types of control chart for variables are;

i) Average (or) x Chart

ii) Range (or) R Chart

iii) Standard deviation (or) chart

iv)X – Chart

v) MR (or) Moring Range Chart

II. Control chart for attributes:-

2. Control chart for attributes

It is very difficult to represent many quality characteristics numerically. For example, colour, scratches, blow holes and damage in a component. The characteristics cannot be measured numerically but can be classified based on conforming items or non conforming items to the given specifications.

Types of control chart for attributes are;

i)P – Chart

ii)np – Chart

iii)C – Chart

iv)U – Chart

1. P &np charts are called control charts for number of defectives where as

2.C &u chart are called as control chart for number of defects.

What are the types of Control Chart Patterns?

1. Cycle

2. Oscillation

3. Instability

4. Level shift

5. Trend

6. Mixture

Objectives of control chart:

1. It determine whether process meet specifications or not.

2. To provide a basis for current decisions on acceptance or rejection of manufactured.

3. It determine the Quality of process

Types of Control Charts for Variable Data:

Chart Name / Central Line / Control Limits / Remarks
- Chart / / Control limits are:

i.e.,UCL =
LCL = /

R – Chart / / UCL =
LCL = / Where D3 & D4 are statistical factors (constants) obtained from table.
X – Chart / /
i.e.,UCL =
LCL = / Where is the average of moving ranges.
0 (or) SD chart / / (a)If sample SD is known:
UCL =
LCL = / Where B1, B2, B3 & B4 are statistical factors (constants) obtained from table and
(b)If population SD 1 is known:
UCL =
LCL =
MR - Chart / / UCL = 3.276 
LCL = 0 /

Types of Control Charts for Attribute Data:

Chart Name / Central Line / Control Limits / Remarks
np – Chart / n / Control limits are:

i.e.,UCL =
LCL = /
p = , Fraction Defective
np – No. of defectives
n – No. of items inspected in a subgroup
p – Chart / / Control limits are:

i.e.,UCL =
LCL =
c – Chart / / Control limits are:

i.e., UCL =
LCL = / c – No. of defects
n – No. of samples
, Average no. of defects
u – Chart / / Control limits are:

i.e., UCL =
LCL = / u – No. of defectives per unit in a sample
=
i.e., =

When to use ?

I.For variable:

1.X and R charts are used for sample size less than 10 where as

2. X-S.D charts are used for Large Sample size.

For attribute:

The ‘p’ chart is a fraction defective chart for variable sample size.

4. ‘np’ chart is number of defectives chart for constant sample size only.

5.The ‘c’ chart is the Total number of defects chart for constant sample size

6. ‘u’ chart is the Average number of defects per unit chart for variable sample size

III.Numbers of defective items are taken in different samples---- p, np chart

Number of defects in one item--- c chart used.

Sample control Chart:

SPC –Statistical Process control

It means using statistical techniques to measures and analyze the variation in process.

S- Using statistical tools

P- Understanding the present process capability& Quality specifications.

C- Control the quality to meet the specification with minimum variation.

Importance & Advantages of SPC:

1. Improve product quality

2. Reduce Scrap and Rework

3. Increase manufacturing efficiency

4. To meet customer requirements.

5. Simple and Effective

6. Predictable’

7. Communicative Performance tool

8. Process Improvement.

Process Capability (PC)

What do you mean by Process Capability?

The term Process capability refers to the inherent variability of process output relative to the variation allowed by the specifications.

Process capability is a Measure of variability of a process only due to common causes.

Process capability is a scientific and Systematic procedure that uses control chart to detect and eliminate the unnatural causes variation.

Process capability= Specification width/ Process width Interpretation Process capability Index:

PC < 1= Process variation exceeds specification.

PC=1 Process is just meeting specification.

PC>=1 Process variation less than specification

What are the factors affecting Process Capability Index: (5 Ms)

1. Organizational factors

Environment b. Manpower c. Measurement

2. Technological factors

a. Material b. Machine c. Method

3.5 M’s

List out various Steps in Process Capability:

Step:1 Select critical parameters

2. Collect data

3. Establish control over the process

4. Analyse process data

5. Aanalyse source of variation

6. Establish process monitoring system ( SPC)

Types of Process variability:

1. Common cause of Process variability

2. Special cause variability

Process Capability Measures:

I. Computing Cp Index (Maximum):

= Upper specification- Lower Specification

6σ

II.Calculation of CP index (Minimum)

Example:

New Cutting Machine

New process mean x = .250 inches

Process standard deviation s = .0005 inches

Upper Specification Limit = .251 inches

Lower Specification Limit = .249 inches

SIX SIGMA

What is Six Sigma?

Sig Sigma may be defined as “ a vision of quality which equates with only 3.4 defects per million opportunities (DPMO) for each product or service transaction and strives for Perfection.

First Six sigma concept implemented in Motorola company.

It is One of the Process capability techniques.

Sigma / Defects per Million / Product status
6 Sigma / 3.4 / World Class
5 Sigma / 233 / World Class
4 Sigma / 6,210 / Industry average
3 Sigma / 66,807 / Industry average
2 Sigma / 3,08,537 / Non-competitive
1 Sigma / 6,90,000 / Non-competitive

STEPS IN SIX SIGMA PROCESS:

DMAIC-APPROACH

Step: 1 D- Define and Identify the Process

2 M- Measure

3 A- Analyze

4 I- Improvement

5 C-Control

Elements of six sigma:

1. Customer 2.Process 3.Employees 4.Top mgt commitment 5.Measurment system 6.Improvement methodology

Tools & Techniques of Six Sigma

1.Process Mapping

2.Measurement Systems Analysis

3.Multivariate study

4.Failure Mode Effect Analysis (FMEA)

5.House of Quality (xy matrix)

6.Process capability Index

7.Hypothesis Testing

8.Control chart

Benefits or Advantages of Six Sigma

1.Design Better Products

2.Improve Quality

3.Top Down approach

4.Rapid and Radical Improvements

5.Transform the entire Organist ion

6.Focuses on Customer

7.Continuous Improvement

8.To reduce the number of defects

Six sigma Implementation

•Business level

•Operations level

•Process level

1.Master black belt- Technical side (Master)

2.Black belts-Technical side (Master)

3. Green belt -They should have technical and support background

Reliability

What is reliability?

According to Hollenbeck “ Reliability is the accuracy and stability of measures as well as actual conditions under which Observation are made.

Define Reliability:

Probability product performs intended function for specified length of time

Measurement of Reliability

1. Mean Time Between Failures (MTBF)

-It is denoted by µ .

2. Mean Time To repair(MTTR)

3. Avialability (A)= MTBF/MTBF+MTTR

4. Failure Rate (ƛ)

= Number of failures

No of units tested X Total length of time

Types of Reliability system

1. Series system

2. Parallel system

3. Combination of Series and Parallel

I.Series ReliabilitySystem

For a series systems, the reliability is the product of the individual components

RS = R1 R2 ... Rn

As components are added to the series, the system reliability decreases

II.Parallel ReliabilitySystem

Rs = 1 - (1 - R1) (1 - R2)... (1 - Rn)

When a component does not function, the product continues to function, using another component, until all parallel components do not function

III.Combinations of Series-Parallel System

Convert to equivalent series system

Product Life Cyclecharters tics Curve:

1. Debugging (Infant mortality) Phase

rapid decrease in failure rate

Weibull distribution with shape parameter  < 1 is used to describe the occurrences of failure

Usually covered by warranty period

2. Chance failure phase

Constant failure rate – failure occur in random manner

Exponential and also Weibull with  =1 can be used to describe this phase

3. Wear-out phase

Sharp rise in failure rate – fatigue, corrosion (old age)

Normal distribution is one that best describes this phase

Also can use Weibull with shape parameter  > 1

TOTAL PRODUCTIVE MAINTAINENCE-(TPM)

What is Total Productive Maintenance?

TPM is a plant improvement methodology which enables continuous and rapid improvement of the manufacturing process through use of employee involvement, employee empowerment, and closed-loop measurement of results

Breakdown of TPM

•TOTAL = All encompassing by maintenance and production individuals working together

•PRODUCTIVE = Production goods and services that meet or exceed customers’ expectations

•MAINTENANCE = Keeping equipment and plant in as good as or better than the original conditions at all times

TPM – History

•Productive maintenance (PM) originated in the U.S. in late 1940’s & early 1950’s

•Japanese companies modified and enhanced it to fit the Japanese industrial environment

•The first use the term TPM was in 1961 by Nippondenso, a Japanese auto components manufacturer

•Seiichi Nakajima – head of JIPM, one of the earliest proponents, known as the Father of TPM

What are the types of Major Losses?

i. Planned Downtime losses

•Start-ups

•shift changes

•coffee and lunch breaks

•planned maintenance shutdowns

ii. Unplanned Downtime Losses

•Equipment breakdown

•Changeovers

•Lack of material

iii.Reduced Speed Losses

•Idling and minor stoppages

•Slow-downs

iv. Poor Quality Losses

•Process non-conformities

•Scrap

What are the various Types of Maintenance?

•Breakdown maintenance

•Periodical Maintenance

•Preventive maintenance (PM)

•Productive maintenance

•Total productive maintenance

Objectives of TPM

1. Aims at getting the most effective use of equipment

2. Builds a comprehensive Plant Maintain system

3. Brings together people from all departments concerned with equipment

4. Requires the support and cooperation of everyone from top managers down

Promotes and implements PM activities based on autonomous small group activities.
Maintaining Equipment for life
Encouraging input from all employees
Using teams for continuous improvement

Three Principles of TPM:

•Maintenance of normal conditions

•Early discovery of abnormalities

•Prompt response

List out 8 Pillars of TQM with neat diagram?

What is OEE?

•OEE (overall equipment efficiency) is a “best practices” way to monitor and improve the efficiency of your manufacturing processes

–Machines manufacturing cells

–assembly lines

OEE = Availability X Performance X Quality

TPM BENEFITS

Improved equipment eliminates the root cause of defects
Defects are prevented through planned maintenance
Preventive maintenance costs are reduced
equipment operators conduct autonomous maintenance
Improved equipment designs ensure
Simplified products designs and a redesigned process produce with few defects
Engineers, technicians and managers are trained in maintenance and quality

Difference between TQM AND TPM

Basis of difference / TQM / TPM
Scope / Quality of Product &Process basis / Machinery or Equipment basis
Origin / SQC / Preventive Maintenance
Approach / Inductive / Deductive
Fundamental / To improve Quality / To reduce Breakdowns
Implement / Quality circle / Autonomous Maintenance
concept / Six Sigma,Kaizen,5s / Terotechnology
1.Managerial,Financial,Engineerial aspect

Terotechnology concept in TPM

Tero- a word derived from greek meaning “I CARE”.

What do you mean by terotechnology?

It is concerned with the application of Managerial,financial, engineering and other skills to extend the operational life of and increase efficiency of equipment and machinery.

Draw tero technology diagramme:

Business Process Improvement (BPI)

Business ProcessImprovement (BPI) focuses on Changing Business Processes to improve their effectiveness.

DEFINITION OF BPR

“The fundamental RETHINKING and RADICAL redesign to business processes to achieve DRAMATIC IMPROVEMENTS in critical. The contemporary measures of performance , such as quality , service and speed. A PROCESS is a set of activities that ,taken together produce a result of VALUE to the CUSTOMER.

------MICHAEL HAMMER

INTRODUCTION

FATHER OF BPR:MICHAEL HAMMER

BPR is a problem solving techniques.
It provides a sustainable competitive advantage.

3 R’s of re enginnering:

1. Rethink

2. Redesign

3. Retol

Principles of BPI:
1. Lean thinking
2. Change Process
3. Team work
4. Business Process redesign
5. Process Improvement techniques
6. Kaizen- Continuous change Improvement
7. Benchmarking

Step in BUSINESS PROCESS:

Steps or Phases IN BPR

FOCUS PHASE
DESIGN PHASE
IMPLEMENTATION PHASE

STAGES (OR) PHASES IN BPR

1.FOCUS STAGE:

Top management as a group
Individual interviews
Group presentation
Analysis of level of process
Identification of critical activities
Re discussion with top management

2.DESIGN PHASE:

Task Force Designs A System Which Results Existing Activities Being Done “ Faster & Better”

3. IMPLEMENTATION PHASE:

Work should be organized for around outcome s.
A few people are needed in performance of process.
Utilization of information technology

BPR IMPLEMENTATION STEPS:

STEP1: Developing Process and determining process objectives:

STEP: 2Defining the process to be re-engineered.

Step: 3 Understanding & measuring existing process step.

4. Identifying the “Information Technology Levels”

STEP: 5 Designing & Building PrototypeOf New Process.

Business Process Flowchart Symbols

- AN ACTIVITY - A DOCUMENT

- A DECISION -DATA(INPUT AS OUTUTS)

Business Process Flowchart Symbols

- PRE DEFINED PROCESS

- THE START OF A PROCESS

- THE END OF A PROCESS

- REPRESTING THE RELATION

Business Process Flowchart Symbols

Continuation of the process at the same page at an equal symbol with the same number. Used when a relation arrow crosses another relation arrow

Off-Page Connector - Process will continue on the next page

Integration Relation - A relation to another module is identified and described

I.Advantages or Merits of BPR

Systems Philosophy
Global Perspective on Business Processes
Radical Improvement
Integrated Change
People Centred
Focus on End-Customers
Process-Based
Change Process

II.Limitations of BPR

1.Lack of authority

2.It is based on historical data

3.Difficulty in new process

4.Lack of unexpected change

5.High cost

6.Time consuming Process

III.BPR Applications:

1. Railway reservation system

2. Bank Automatic teller machine (ATM concept)

3. Online education

4. Online valuation

5. Viedo conferencing

6. Employee punch card system

7. Automobile industry (Nano technology)

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