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Module 3: Quality Assurance Tools

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Page 1: 7 quality tools

Module 3:

Quality Assurance Tools

Page 2: 7 quality tools

Learning Objectives

• Learn the theory and method of use of the

seven tools of quality needed in process

analysis and problem-solving techniques

• Seven tools of quality• Pareto charts• Flow charts• Cause-and-effect diagram• Check sheet• Histograms• Control charts• Scatter diagrams

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Pareto Chart

• Method of prioritizing problems or causes by frequency of occurrence or cost • Based in the 80-20 rule:

• 80% of the problem is caused by 20% of the sources• “Vital few” and “trivial many”

• Depicted by a vertical bar graph arranged from left to right descending order

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• Focuses efforts on problems with greatest

potential for improvement

• Distinguishes the critical causes from the less

significant causes

• Helps prevent “shifting the problem” where the

solution removes some causes but worsens

others

Advantages of a Pareto Chart

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• Measure the impact of improvement projects

when comparing charts “before” and “after”

• The chart shows the relative importance of

problems in a simple, quickly interpreted,

visual format.

• Progress is measured in a highly visible format

that provides incentive to push on for more

improvement.

Advantages of a Pareto Chart (cont.)

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Steps to Build a Pareto Chart

• Identify problem

• Choose categories that will be monitored

• Choose the most meaningful unit of measurement

• Frequency

• Cost

• Determine time period

• Long enough to represent situation

• Scheduled time to collect data is typical of a workday

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• Collect data

• Compare the frequency of each category

• Draw chart:

• List the categories on the horizontal line

• Descending order, from left to right

• Frequencies on the vertical line

Steps to Build a Pareto Chart (cont.)

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• Draw the cumulative percentage line showing

categories contribution

• Optional

• Draw vertical line on the right side of the chart

• Plot cumulative values from left to right

• Interpret results

• Tallest bar represents biggest contributor

• Perform analysis of category that has the “most

impact”

Steps to Build a Pareto Chart (cont.)

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2418

128

4 20

10

20

30

Latedelivery

Wrongproduct

Missingparts

Damagedcontainer

Wrongaddress

Not received

Delivery complains

35%

61%

79%

91%

97%100 %

50 %

Frequency

Cum %Example of a Pareto Chart

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Further analysis using Pareto charts

• Major cause breakdown:• Tallest bar is broken down into sub-causes

2418

128

4 20

10

20

30

Late delivery Wrong product Missing parts Damagedcontainer

Wrongaddress

Not received

86 4 4

2

0

2

4

6

8

Missing address Driver mistake Latedocumentation

Transportationproblems

Administrativedelays

Late delivery

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Further analysis using Pareto charts

•Before and after:• New Pareto bars are drawn side-by-side with the original Pareto showing effect of change

24

10

18

8

1210

8

4 43 2 1

0

5

10

15

20

25

Latedelivery

Wrongproduct

Missingparts

Damagedcontainer

Wrongaddress

Notreceived

Before After

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Further analysis using Pareto charts

•Change measurement scale:• Same categories are used but measured differently. Typically cost and frequency.• This exercise defines the category of “most impact”.

24

18

128

4 20

5

10

15

20

25

30

Latedelivery

Wrongproduct

Missingparts

Damagedcontainer

Wrongaddress

Not received

Delivery complains

$2,500

$1,850

$1,200$800

$220 $200$0

$500

$1,000

$1,500

$2,000

$2,500

$3,000

Wrong product Not received Missing parts Wrongaddress

Damagedcontainer

Late delivery

Cost/month

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Flow Charts

• Pictorial representation of the steps and decision

points in a process.

• Flow charts are used to identify the actual path

of a product or service.

• Flow charts show:

• Sequential work activities

• Inputs for each action• Outputs from each activity

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Advantages of a Flow Chart

• Provide common understanding of how a process works. • Identifies problem areas, unexpected complexity, redundancies, and areas of potential improvement • Serves as a training aid • Provides basis for documentation. • Identifies location where additional data can be collected and investigated

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Symbols of a Flow Chart

Shows an activity performed in the process

Shows a point in the process where a Yes/Noquestion is being asked or a decision is required

AIdentifies a break in the flow chart and is continuedelsewhere on the same page or another page

Shows the flow of the process

Shows the beginning and end process

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Steps to Build a Flow Chart

• List the basic steps of the process.

• Determine the logical sequence of the steps.

• Identify the inputs of each step.

• Determine the outputs of each step.

• Draw the chart using the symbols to show the

actions and decisions.

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Team is given task to write procedure

Develop outline

Completedraft

Review draft

Revise Draft with changes

CompleteFinal

version

Send toRelease

Dept.

Draftapproved

Releaseprocedure

yes

No

Example of a Flow Chart

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Cause and Effect Analysis

• Pictorial representation of all possible causes contributing to a problem.

• Developed by Dr.Kaoru Ishikawa•Also known as “Fishbone” or “Ishikawa” diagrams

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Advantages of a Cause and Effect Diagram

• Clearly illustrates the various causes affecting a

process:• Relationship between these causes• Where are they occurring

• Helps in finding the most basic cause of the

problem

• Motivates team members participation

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Steps to Build a Cause and Effect Diagram

• Place problem statement in a box to the right-hand side of the paper. • Select the major cause or categories and place them to the left of the problem statement.

• 4 M’s (Production process):• Materials• Manpower• Machinery/equipment• Method

• 4 P’s (Service process):• Policies• Procedures• People• Plant / equipment

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Steps to Build a Cause and Effect Diagram(cont.)

• Draw a box around each category and connect to a line pointing out towards the problem statement.

• Using the brainstorming technique, generate ideas of causes, on the major categories. • Record these ideas on a line off the applicable major category line.

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Steps to Build a Cause and Effect Diagram(cont.)

• For each cause listed on the diagram, ask “why

does this happen?”.

• For each response, ask the same question.

• Each successive answer is another possible cause

• Look for causes that repeat across major cause

categories.

• Ensure all team members agree on the problem

and causes statements.

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Late deliveries

Method Material

ManpowerMachinery/equipment

Drivers get lost

Drivers don’tShow upUnreliable trucks

Not enough trucks

Poor dispatching

Poor handling of large orders

Run out of products

Not capacity for peak periods

Wrong address on shipper

Database Input error

Poor planning

Lack of trainingLack of

training

Example of a Cause and Effect Diagram

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Check Sheets

• Tool used to record and compile frequency of

observations as they occur

• Used for Pareto charts and histograms

• Design varies depending on information needed

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Advantages of a Check Sheet

• Patterns of information are clearly detected

and shown

• Easy-to-understand data from a simple process

• Based on facts, not opinions

• Forces agreement on the definition of each

condition

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Steps to Build a Check Sheet

• Agree on the definition of the events or conditions to observe.

• Decide who will collect the data. • Determine the time period.

• Design a check sheet form that is clear and easy to use.

• Define Source of information.• Determine Content of information.

• Collect data consistently and accurately.

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Project: Defects on fastener installation Performed by: John Doe

Location: Cost Center 727 Reason: Defect reduction

Time period: W/E 4/23/04

4/19 4/20 4/21 4/22 4/23 Total

Gapped fasteners 15 15 12 10 14 66

Missing fasteners 3 0 0 1 1 5

Damaged fasteners 8 3 12 8 4 35

Defective fasteners 12 3 5 3 6 29

Total 38 21 29 22 25 135

Type of defects

Example of a Check Sheet

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Histograms

• Graphical representations of the frequency

distribution of data in bar form.

• Summarizes data from a process that has been

collected over a period of time

• Provide a quick representation of the “spread”

and “centering” of a process

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• Histogram Defined– A histogram is a bar graph that shows

frequency data.– Histograms provide the easiest way to evaluate

the distribution of data.

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Advantages of a Histogram

• Display large amounts of data that are difficult to interpret in a tabular form

• Show the relative frequency of occurrences of the various data values

• Reveal the variation, centering, and distribution shape of the data

• Very useful when calculating capability of a process

• Helps predict future performance of a process

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Steps to Build a Histogram

• Collect data for analysis.• At least 50 to 100 data points• Use historical data to find patterns or to use as a baseline for past performance

• Determine the range of the data set.• Smallest value subtracted from largest value

• Determine quantity of categories.• Take the square root of total number of data points and round to nearest whole number

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• Determine each category’s data point.

• Mid-point of each category

• Plot data on a vertical bar-graph.

• Frequency on Y-axis

• Categories on X-axis

• For each class interval, draw bar with the

the height equal to frequency count

Steps to Build a Histogram (cont.)

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1

6

12

86

3

0

2

4

6

8

10

12

14

10.00 -10.19

10.20 -10.39

10.40 -10.59

10.60 -10.79

10.80 -10.99

11.00-11.19

CategoryClass

boundaryMid-point Frequency

1 10.00 - 10.19 10.1 12 10.20 - 10.39 10.3 63 10.40 - 10.59 10.5 124 10.60 - 10.79 10.7 85 10.80 - 10.99 10.9 66 11.00- 11.19 11.1 3

Example of a Histogram

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Control Charts

• Line graph of measurements of a process overtime that has statistically based control limits placed on it

• Process control charts monitor and display variations in a process output. • Control limits are based on process variation

• Define expected variation range due to common causes• +/- three standard deviations from centerline

• Centerline represents the average of all measurements used

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Types of Control Charts

• Two primary types are:• Control charts for variables:

• Most used: X –R

• X is average values• R is range

• Others: Run charts, moving range charts (MX –MR charts)

• Control charts for attributes:• p chart: fraction defective

• np chart: number of defectives• c chart: number of defects

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Advantages of Control Charts

• Focuses attention on detecting and monitoring process variation over time

• Distinguishes “special” from “common” causes

• Helps predict performance of a process

• Helps improve a process to perform consistently

• Provides a common language to discuss process behavior

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Steps to Build a Control Chart

• Select the process to be charted.

• Determine type of chart.

• Determine sampling method and plan.

• Initiate data collection.

• Calculate control limits and centerline.

• Build the control chart.

• Plot data.

• Interpret results.

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Upper control limit

Lower control limit

Centerline

3 std.deviations

3 std.deviations

Data plot

Point out-of-control(out of the control limits boundaries)

Example of a Control Chart

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Scatter Diagrams

• Chart used to identify the possible relationship between two process characteristics

• Advantages of the scatter diagram

• Provides visual and statistical means to test the strength of a potential relationship

• Provides a good follow-up to the cause and effect diagram to find out if there is a connection between the cause and the effect

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Steps to Build a Scatter Diagram

• Collect 50 – 100 paired samples of data.

• Construct a data sheet.

• Draw the Y-axis and the X-axis of the diagram.

• Plot the data on the diagram.

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Variable 1

Var

iab

le 2

Example of a Scatter Diagram

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Summary

• The seven tools of quality discussed in this module

are considered to make up the fundamental

continuous improvement toolkit.

• It is the intent of this course to touch basis on these

tools and not to study them in depth.

• Depth analysis of these theories is considered subject

for another course.

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RUN CHARTS

• Run Charts Defined– Run charts are used to

analyze processes according to time or order.

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RUN CHARTS

• Creating a Run Chart– Gathering Data

• Some type of process or operation must be available to take measurements for analysis.

– Organizing Data• Data must be divided into two sets of values X and Y. X values represent

time and values of Y represent the measurements taken from the manufacturing process or operation.

– Charting Data• Plot the Y values versus the X values.

– Interpreting Data• Interpret the data and draw any conclusions that will be beneficial to the

process or operation.

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RUN CHART

• An Example of Using a Run Chart– An organization’s desire is

to have their product arrive to their customers on time, but they have noticed that it doesn’t take the same amount of time each day of the week. They decided to monitor the amount of time it takes to deliver their product over the next few weeks.