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 / Remarksnp – 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 status6 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 / TPMScope / 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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