Chapter 9

Question 1

The Seven Tools of Quality Control

Answer 1

Flowchart

Cause and Effect

Check Sheet

Scatter Diagram

Histogram

Control Chart

Pareto Chart

Question 2

Flow Charts

Answer 2

Understanding the process and identifying possible problem areas

Question 3

Check Sheets

Answer 3

Tabulating data on the problem area

Question 4

Histograms

Answer 4

Illustrating the frequency of occurrence of measures

Question 5

Pareto Diagrams

Answer 5

Identifying the most important problems

Question 6

Cause and Effect Diagrams

Answer 6

Showing possible causes of the problem

Question 7

Scatter Diagram

Answer 7

Investigating causes and effects

Question 8

Control Charts

Answer 8

Holding the gains from process improvement

Question 9

Specification limits

Answer 9

deal with individual product characteristics

Question 10

Control limits

Answer 10

deal with sample process characteristics (i.e., means and ranges)

Question 11

Control Limits and Specification Limits

Answer 11

Should never be plotted on the same graph

Question 12

Process Quality Control

Answer 12

Assignable causes
   -Can be identified and corrected
Common (random) causes
   -Occur randomly
   -Cannot be changed unless process is redesigned

Question 13

Basic assumptions of Process Quality Control:

Answer 13

Every process has random variation in it.

Production processes are not usually found in a state of control (they have assignable causes of variation present).

Question 14

“State of Control”; what does it mean?

Answer 14

Sources of unnecessary variation (assignable causes) have been eliminated

Remaining variation is due to random causes

Question 15

Steps in Designing a Statistical Process Control System

Answer 15

1. Identify critical points to apply control (where data should be collected)
2. Identify the critical quality characteristics of that aspect of the process & Decide on the type of measurement (what)
3. Decide on the amount of data to be collected (how much)
4. Decide who should collect the data, construct the charts, and apply the charts (who)

Question 16

Identify critical points to apply control (where data should be collected)

Answer 16

Processes impacting incoming materials & services

Internal processes (especially prior to high cost processes and processes that are “sensitive”)

Question 17

Identify the critical quality characteristics of that aspect of the process
& Decide on the type of measurement (what)

Answer 17

Variable data

Attribute data

Question 18

Variable data

Answer 18

Process (or product/service) characteristic that can be measured on a continuous scale:
-Length, size, weight, height, time, velocity, temperature, etc.

Typically mean & range or standard deviation

Question 19

Attribute data

Answer 19

Process (or product /service) characteristic evaluated with a discrete choice:
-Good/bad, yes/no, 0/1, ratings, counts, proportions

Question 20

Decide on the amount of data to be collected (how much)

Answer 20

Sample size

• Large enough to detect deviations
• Variable data allow for a smaller sample size

How often to sample?
-Depends upon inherent variability of the process, cost, production rate

Question 21

x-bar Chart

Answer 21

Used to control the mean value of a particular characteristic of a process

Question 22

R Chart

Answer 22

Used to control the variability of that same characteristic of the same process for which the x-bar chart is being used to control the mean

Question 23

SPC - Variables - Example

Answer 23

Characteristic: Critical dimension of a process

Before collecting the data, make sure the process is “in control”!

Question 24

Action Required for Out-of-Control Indicators - Variables

Answer 24

1. Stop the process
2. Conduct an investigation to determine the assignable cause*
3. Take corrective action to remove the assignable cause
4. Resume the process
   * If no assignable cause is found, assume a Type I error has occurred & jump to Step #4

Question 25

Type I error

Answer 25

(a.k.a. producer’s risk and a error) - The control chart for a process indicates the process is “out-of-control” when the process is actually “in-control” and, thus, the process is stopped unnecessarily

Question 26

Type II error

Answer 26

(a.k.a. consumer’s risk and b error) - The control chart for a process indicates the process is “in control” when the process is actually “out-of-control” and, thus, the process is allowed to continue when it should be stopped.

Question 27

Action Required for Out-of-Control Indicators - Attributes

Answer 27

1.Stop the process1
2.Conduct an investigation to determine the assignable cause
3.Take corrective action to remove the assignable cause2,3
4.Resume the process
1If sample value falls below the LCL, only if needed to conduct the investigation for assignable cause
2If no assignable cause is found in Step #2, assume a Type I error has occurred & skip this step
3If downward shift is indicated, attempt to ingrain assignable cause into the process

Question 28

Acceptance Sampling - General

Answer 28

A random sample is drawn from a lot (population)

The sample is inspected to determine the number of defective items in it

The number of defective items found is compared to a cut-off value

The result from the (representative) sample is applied to the entire lot

Question 29

Quality Control in Industry

Answer 29

75% use process control charts

More use of variable (x-bar and R) charts than attribute (p and c) charts

“The Seven Tools of Quality Control”

Quality control in the service industry

Question 30

The Seven “M’s” of a Process

Answer 30

Material
Manpower
Methods
Machines
Measurement
Maintenance
Management