Statistical quality control

Question 2

attributes

Answer 2

define the product

Question 3

CONFORMANCE

Answer 3

means the attributes and features
are the same and at similar levels every time

Question 3

features

Answer 3

distinguish like products from one
another

Question 4

SPECIFICATIONS

Answer 4

MEASURABLE

Question 5

Controlled variation

Answer 5

results from chance or
common causes
* Causes that are present because of the system or
process
* Always present
* Exist because of the manufacturing system or way it
is managed
* Responsibility of those who own the process

Question 6

Uncontrolled variation

Answer 6

results from assignable
or special causes
* Not part of the system or process
* Abnormality
* Localized to a specific machine, operator, ingredient,

Question 7

Two ways to control variation and improve a process

Answer 7

• With controlled variation, the only way to reduce variation is to change the process itself
• With uncontrolled variation you must identify and remove the assignable causes from the process

Question 8

Statistical process control

Answer 8

the continual removal of variation from a process using data

Question 9

Sampling for Acceptance/Rejection

Answer 9

Appropriate sample size you need to inspect (based on lot size)
o The maximum number of defects you will accept in the order (based
on AQL)
o AQL: Acceptable Quality Level
o Levels of inspection (expensive test, destructive/nondestructive test)

Question 10

GI level

Answer 10

• You have strict budgetary constraints
• Products are of low value
• Suppliers have a strong quality management system

Question 11

GII level

Answer 11

a “normal” sample size, used by importers

Question 12

GIII level

Answer 12

• Your supplier has a history of poor quality
• This is your first order with a supplier
• This is the first order of a newly developed product
• The product is of particularly high value (e.g., luxury goods) or poses
  particularly high risk (e.g., medical devices)

Question 13

Special Sampling Levels

Answer 13

• Special inspection levels generally point to much
  smaller sample sizes
• Typically reserved for on-site tests that are:
• Destructive to the product, rendering it unsellable
• Expensive or tedious to perform
• Likely to yield similar results across all pieces in the
  order

Question 14

Acceptable Quality Level

Answer 14

0% for critical defects (totally unacceptable: a user might get harmed, or regulations are not respected).
2.5% for major defects (these products would usually not be considered acceptable by the end-user).
4.0% for minor defects (there is some departure from specifications, but most users would not mind it).

Question 15

Statistical Process Control (SPC)

Answer 15

– Monitoring production process to detect and prevent poor quality

Question 16

Sample

Answer 16

subset of items produced to use for inspection

Question 17

Control Charts

Answer 17

process is within statistical control limits

Question 18

Quality Measures

Answer 18

attribute and variables

Question 19

Attributes

Answer 19

A product characteristic that can be evaluated with a discrete response (good – bad; yes – no)

Question 20

Variables

Answer 20

A product characteristic that is continuous and can be measured (weight, length, %)

Question 21

Types of Control Charts

Answer 21

– Attributes
* p-chart
* c-chart
– Variables
* mean (𝑥 -chart)
* range (R -chart)

Question 22

UCL X CHART

Answer 22

x + A2 R

Question 23

LCL X CHART

Answer 23

x − A2 R

Question 24

UCL R CHART

Answer 24

D4R

Question 25

LCL R CHART

Answer 25

D3R

Question 26

A Process Is in Control If …

Answer 26

1. No sample points outside limits 2. Most points near process average 3. About equal number of points above and below centerline 4. Points appear randomly distributed