Page 1 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

Quality Control

Course Objective: The main objective of this course is to introduce the students to the principles of quality

used in the field of Mechanical Engineering and enable them to promote businesses amidst stiff global

competition.

Course contents: INTRODUCTION - Definition of Quality, Quality costs, Quality Planning , Quality

circles, STATISTICAL PROCESS CONTROL (SPC) - The seven tools of quality, Normal Curve,

Control Charts for variables and attributes, Process capability, Concept of six sigma, TOTAL QUALITY

MANAGEMENT (TQM) -Basic concepts of Total Quality Management, Customer Perception of Quality,

Employee Involvement – Motivation, Empowerment, Total Productive Maintenance (TPM), Continuous

Process Improvement, Kaizen, QUALITY SYSTEMS- Need for ISO 9000 and Other Quality Systems,

ISO 9000:2000 Quality System , Quality Auditing, QS 9000, ISO 14000

Introduction Defining Quality

• In technical usage, quality can have two meanings:

– the characteristics of a product or service that bear on its ability to satisfy stated or

implied needs, and

– a product or service free of deficiencies or defects

Latest view of quality control

99.9% Quality not good enough

6-sigma --> less cost of failures

Cost of failure underestimated

Cost of Quality not understood

Increased Quality Eliminates Waste.

Why should we study Quality Control or Improvement?

Global Competition

• Economic and political boundaries are slowly vanishing

• The 1950’s slogan “Built by Americans for Americans” is very far from reality in

the 2000’s.

It pays

• Less rework, fewer mistakes, fewer delays, and better use of time and materials

• In United States today, 15 to 20% of the production costs are incurred in finding

and correcting mistakes.

Examples of quality services in the 21st century

99.9% is not good enough :

1 hour of unsafe drinking water every month

2 unsafe plane landings per day at O’Hare Airport in Chicago

16,000 pieces of mail lost by the U.S. Post Office every hour.

20,000 incorrect prescriptions every year

500 incorrect operations each week

50 babies dropped at birth every day

22,000 checks deducted from the wrong bank account each hour

32,000 missed heart beats per person each year

Page 2 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

Six sigma quality control process (Latest concept)

The goal of six sigma quality control process aims at obtaining 3.4 defects for every 1 million

products.

This means:

There are only 3.4 Pepsi bottles rejected for every 1000,000 bottles produced

Your car would not start only 3.4 times for every 1000,000 attempts

Only 3.4 patients die out of 1000,000 patients admitted

Only 3.4 students fail for only 1000,000 students admitted into graduating schools.

This list goes on and on….

Quality Costs

A quality cost is considered to be any cost that the company would not have incurred if the quality of the

product or service were perfect.

• Prevention costs – Costs associated with Customer requirements/expectations market research , Product

design, Quality education programs

• Appraisal costs – Testing/inspection costs , Audits

• Internal failure costs – Rework, scrap, repair

• External failure costs – Returned goods, warranty costs, liability costs, penalties

• Intangible costs – Customer dissatisfaction, company image, lost sales, loss of customer goodwill

Total quality costs are the sum of prevention costs, appraisal costs, and

internal and external failure costs.

Quality planning It is a systematic process that translates quality policy of an organization into measurable objectives and

requirements. It lays down a sequence of steps for realizing them within a specified timeframe.

Quality Circle (QC)

Quality Circles are (informal) groups of employees who voluntarily meet together on a regular basis to

identify, define, analyze and solve work related problems.

Usually the members of a particular team (quality circle) should be from the same work area or who do

similar work so that the problems they select will be familiar to all of them.

In addition, interdepartmental or cross functional quality circles may also be formed. An ideal size of

quality circle is seven to eight members. But the number of members in a quality circle can vary.

Page 3 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

STATISTICAL PROCESS CONTROL (SPC)

Statistical process control (SPC) deals with controlling quality of various processes ranging from

industrial processes, business processes and any other kind of processes using statistical techniques and

their applications. Apart from many tools, the SPC also makes use of the following:

The seven tools of quality,

Normal Curve,

Control Charts for variables and attributes,

Process capability,

Six sigma,

7 Tools of Quality

Pareto chart or Pareto diagram

Histogram

Process flow diagram

Check sheet

Scatter diagram

Control chart

Cause and effect diagram

7 Tools of Quality

1. Pareto Chart or Pareto diagram

Pareto Principle

According to Vilfredo Pareto (1848-1923), an Italian economist , 20% of the population has 80%

of the wealth. He used the term “vital few, trivial many” and stated that 20% of the quality

problems caused 80% of the costs of the industry or organization.In 1897, he presented a formula

that showed that income was distributed unevenly, with about 80% of the wealth in the hands of

about 20% of the people.

What can it do for you?

There are so many aspects of work that can be improved, knowing where to begin is often difficult.

Pareto analysis will help you:

Graphically display your results so that the significant few problems emerge from the general

background.

How do you do it?

1. Decide how to classify your problems. This may involve looking at the reasons cited for

returned or rejected material, talking to your customer, or examining the rework aspects of your

process.

Page 4 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

2. Create a preliminary list of problem categories. Try to keep this list to no more than six or

seven. (You may find yourself modifying this list as you continue your analysis.)

3. Decide on a time frame or other scope limitations on the material you will consider. The time

frame or scope you choose should be representative of the whole process you are examining.

4. Tally the occurrences in each problem classification. (If cost or time is an issue, you may wish

to tally the cost or time involved in each problem classification.) If a problem does not fit in

any of your classifications, tally it as “other.”

5. Determine the total occurrences (or total cost or total time) in each classification. Add these

totals to produce a grand total.

6. Divide each classification total by the grand total to determine the percentage that each

individual problem classification represents of all the problems.

7. Arrange the problem classifications in order from highest value or most frequent to lowest

value or least frequent. The “other” category should always be put last even if it is larger than

some of the others.

8. Draw a horizontal axis and two vertical axes. Mark the left vertical axis in increments from

zero to the grand total of all the problem classifications. Mark the right vertical axis in

increments from zero to 100%.

9. Construct the vertical bar diagram beginning on the left with the highest percentage

classification and progressing to the lowest and ending with “other.” The height of each bar

should correspond with the value or number of occurrences on the left axis and the percentage

of the total on the right axis. The width of the bars should be the same and they should be

touching.

10. Label the bars under the horizontal axis.

11. Beginning at the left zero point, plot a line showing the cumulative percentage total reached

with the addition of each problem classification. The line should end at the 100% mark on the

right axis.

Page 5 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

12. Title the chart. It is also a good idea to write a brief summary telling how and when you

collected the data you used to produce your Pareto chart.

NOTE: The first pass at a Pareto chart may identify a significant problem that is still too big to work on.

A second Pareto analysis may be necessary to break this most significant problem into workable pieces.

Pareto charts can be used to identify problems to work on. They can help you produce greater efficiency,

conserve materials, reduce costs or increase safety. They are most meaningful, however, if your

customer–the person or organization that receives your work and helps define the problem categories.

Page 6 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

Home work 1 : Pareto analysis

Construct a Pareto diagram for the following problems and analyze them to find the vital few defects that

contribute to 80 % of the quality problems.

Problem 3:

Mini Project one : Draw Pareto chart using excel on the computer and show it to the instructor

Problem 1: The following table gives various defects

namely door, motor, track, vinyl and T-lock and their

frequency of occurrences.

Problem 2: The following table gives various defects

and number of complaints related to a Pizza

restaurant.

Problem 3: Analyze the following pareto diagram

and draw a table representing number of defects,

their percentage and cumulative percentage.

Problem 4: The following diagram shows various

defects of a refrigerator and the number of

complaints associate with them. Draw and analize

the pareto diagram.

Page 7 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

Quality tool 2 : Histogram

Page 8 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

Quality tool 3 : Process flow chart or Process flow diagram

What Is a Flowchart? A diagram that uses graphic symbols to describe the nature and flow of the steps in a process.

A flow diagram is a graphical means of presenting, describing, or analyzing a process. This is

done by drawing small boxes which represent steps or decisions in a chain of steps or decisions.

These boxes are connected to other boxes by lines and arrows which represent sequence and

dependency relationships (i.e., X must be done before Y can be done).

Benefits of Using Flowcharts

Promote process understanding

Provide tool for training

Identify problem areas and improvement opportunities

“Draw a flowchart for whatever you do. Until you do, you do not know what you are doing,

you just have a job.” -- Dr. W. Edwards Deming.

How to construct a process flow chart ?

Steps

Start with the big picture

Observe the current process

An example flow diagram explaining the process of

taking a decision as to whether to get up after an

alarm bell rings !

Page 9 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

Record process steps

Arrange the sequence of steps

Draw the Flowchart

Home work 2:

1. You started from your house and went to a restaurant to take lunch. You asked the waiter whether

a chicken pizza is available to eat. If he says it is available you order it and eat and then go back

home. If he says, chicken pizza is not available then you order one chicken rice and then eat it

there and go home. If chicken rice also not available, you order a drink and then go home. Draw a

simple process flow chart to explain this process.

2. Consider any one of the manufacturing processes you are aware of and draw a process flow

diagram. Each student should choose a different process. Assume the following events :

a. A Starting event

b. At least five processing steps

c. At least 2 decision making events

d. A Stopping event.

Quality tool 4 : Check sheets

A check sheet is a simple form you can use to collect data in an organized manner and easily convert it

into readily useful information. With a check sheet, you can:

• Collect data with minimal effort.

• Convert raw data into useful information.

An Example check sheet:

Check sheets are extremely useful process-improvement and problem-solving tools. Their power is

greatly enhanced when they are used in conjunction with other simple tools, such as histograms and

Pareto analysis. Ishikawa estimated that 80% to 90% of all workplace problems could be solved using

only the simple quality improvement tools.

Page 10 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

Quality tool 5 : Scattergrams

What it is:

A scatter diagram is a tool for analyzing relationships between two variables. One variable is

plotted on the horizontal axis and the other is plotted on the vertical axis. Most often a scatter diagram is

used to prove or disprove cause-and-effect relationships.

When to use it:

Use a scatter diagram to examine theories about cause-and-effect relationships and to search for

root causes of an identified problem.

How to use it:

Collect data. Gather 50 to 100 paired samples of data that show a possible relationship.

Draw the diagram. Draw roughly equal horizontal and vertical axes of the diagram, creating a

square plotting area. Label the axes in convenient multiples (1, 2, 5, etc.) increasing on the

horizontal axes from left to right and on the vertical axis from bottom to top. Label both axes.

Plot the paired data. Plot the data on the chart, using concentric circles to indicate repeated data

points.

Title and label the diagram.

Interpret the data. Scatter diagrams will generally show one of six possible correlations between the

variables:

Strong Positive Correlation: The value of Y clearly increases as the value of X increases.

Strong Negative Correlation: The value of Y clearly decreases as the value of X increases.

Weak Positive Correlation: The value of Y increases slightly as the value of X increases.

Weak Negative Correlation: The value of Y decreases slightly as the value of X increases.

Complex Correlation: The value of Y seems to be related to the value of X, but the

relationship is not easily determined.

No Correlation: There is no demonstrated connection between the two variables

Scatter Diagram Example

Strong Positive Correlation

Page 11 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

Home work 2 : Draw a scattergram for the following problems and identify the kind of

relationship between the given variables

Problem 1 :

John Betty Sarah Peter Fiona Charlie Tim Gerry Martine Rachel

Maths score 72 65 80 36 50 21 79 64 44 55

English score 78 70 81 31 55 29 74 64 47 53

Problem 2 :

John Betty Sarah Peter Fiona Charlie Tim Gerry Martine Rachel

English score 78 70 81 31 55 29 74 64 47 53

Time 12 32 19 31 30 15 22 10 17 16

Problem 3 :

John Betty Sarah Peter Fiona Charlie Tim Gerry Martine Rachel

Maths score 72 65 80 36 50 21 79 64 44 55

Absences 4 6 0 13 8 15 2 3 9 5

Page 12 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

Quality tool 6 : Cause & Effect diagram or Fish bone diagram

Fishbone analysis also known as cause and effect analysis was created by Kaoru Ishikawa. The analysis

suggests that in order to solve a problem (or effect) an organization should try to find out the causes

behind the effect. Discovering all of the causes will help an organization solve the problem and plan how

to prevent the problem from reoccurring.

Fishbone Diagram

Fishbone analysis involves drawing a diagram (showing the effect and each of its causes) in a fish

skeleton shape. The problem is written at the head of the fish skeleton and each cause is recorded next to

a fishbone. Recording each cause as a bone and add a title to each bone . Later add small bones to each

big bones to find the root cause of the actual problem.

A cause and effect diagram is a tool that shows the relationship between an effect and possible sources of

variation for this effect (causes).

The causes are most commonly categorized as machines, methods, environment, materials, measurement,

and people (the 4 M's, a P and an E). This is particularly true for manufacturing applications. You can

pick your own categories. Cause and effect diagrams can be used for any problem in any department

(manufacturing, administration, controllers, supply and transportation, marketing, etc.).

Analyzing Cause and Effect Diagrams

What causes variation in things we do?

Why don't we arrive at work at the same time every day?

Why isn't the monthly report error-free each month?

Why can't we produce the same product day in and day out?

Page 13 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

An example of a cause and effect diagram on reasons for downtime is shown in the following figure.

Another example fish bone diagram to find the causes of why the car will not start is given below:

The next step is to eliminate the ideas that everyone agrees would really not cause the problem. Everyone

must agree. If one person does not agree, it must stay on the diagram as a possible cause.

Page 14 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

For example, suppose we know we have the key to the car. We could simply strike through that cause as

shown in the fishbone. We have decided a couple of other "potential" causes of the car are not really

causes. A line is drawn through those causes as well.

A word of caution: even though an idea is eliminated as a possible cause, it is best to leave it on the

fishbone diagram. You may circle it or strike through it. However, always keep the fishbone diagram with

all the ideas on it. This will allow you to return at a later date to determine if you have eliminated true

causes of the problem.

How Likely?

The next step is to examine each idea and determine the degree to which the idea is an actual cause of the

problem. For each idea on the fishbone, each team member "votes" one of the following for how likely

the listed idea is to be a cause of the problem:

* Very likely (V)

* Somewhat likely (S)

* Not likely (N)

Whichever answer receives the most votes, the corresponding letter (V, S or N) is noted beside that cause

on the fishbone diagram.

For example, the team decided that "No gas" was not a likely cause because they knew gas was in the car.

So, "No gas" gets a "N" for not likely. This process is repeated for each item on the fishbone.

Page 15 Quality control study material Prepared by Mr. Suresh Makkena, Department of Mechanical Engineering, Faculty of Engg, Omar Mukhtar university, Albeida, Libya

How Easy?

The next step is to determine how easy it is to check or verify the cause. For each item on the fishbone,

team members decide how easy it is to verify that item as the cause of the problem, using the following

rating scale:

* Very easy (V)

* Somewhat easy (S)

* Not easy (N)

Again, the answer receiving the most votes is noted beside the first response. The causes that receive VV

responses are investigated first since these are most likely to be the cause of the problem and are the

easiest to check. In this case, the "Battery" received the only VV.

Data should be collected to verify that the selected idea is the actual cause of the problem. How this is

done depends on the cause and effect relationship you are investigating. A scatter diagram may be

appropriate, for example. Once the data have been collected and analyzed, it can be determined if the idea

is the actual cause of the problem. If it is, a solution should be developed and implemented.

Quality Tool 7: Control Chart

Control chart is used to control quality of a manufactured product. There are many control charts in use

today. Some of the control charts are X bar chart, R chart, P chart, np chart , C chart and U chart. We will

discuss all these charts in the next chapter.