Презентация на тему Quality management. Chapter 10

Control is an activity that evaluates quality characteristics relative

to a standard, and takes corrective action when they do not meet standards
How is quality control accomplished?
by monitoring and inspecting the product during process (but not preventing bad quality from happening)

during a process (reactive)
Quality Assurance focuses on proactive actions

to eliminate quality defects during processes

customer
Only shows a picture of the existing situation
We inspect

because we expect to find defects
We cannot trust the reliability of our process

Inspection: appraisal of goods or services against standards

the impact upon the customer (and Liability) if we

do not inspect?

purchased parts that arrive from suppliers- before we accept
Finished

products after final process step
Finished product (packaged) before shipment to customer
Before a costly operation
Before an irreversible process (cannot undo once done)
Before a covering process (painting)

of a process during production
Statistical Process Control
Quality Control Steps
Type

of Variations
Control Charts
Designing Control Charts
Individual Unit and Moving Range Charts
Control Charts for Attributes
Managerial Considerations

– ex. Product dimensions

Measure the characteristics – determine

how often Ex. every 10th piece

Compare to a standard (engineering drawing or physical “perfect” sample) and evaluate

Take corrective action when necessary

Evaluate the effectiveness of the corrective action – should result in fewer defects going forward

length: 25mm+/- 3mm means:

25 is the

optimal desired
22 is the smallest we will allow
28 is the largest we will allow

Any part whose measurement is higher or lower than these numbers are considered defective

The tighter the tolerance – the more difficult and costly it will be to meet that tolerance. Allow as great a tolerance without impacting product performance or appearance

output of process, created by countless minor factors
Assignable variation:

A variation whose source can be identified

Most desirable – closest to the Mean as possible – all samples inspected

UCL to be considered acceptable quality
The lower the

spread between LCL and UCL the more difficult to meet quality standards

many samples outside allowable range
BEST – samples well

within allowable range

sample statistics, used to distinguish between random and non

random variability

Control Limits: The dividing lines (upper and lower limits) from the desired mean of the sampling distribution

Every x piece the operator measures and record on the Control Chart. Chart is kept beside the machine, visible to anyone

sample piece
Establish LCL and UCL control limits
Plot the

inspected sample values on the control chart, and note whether any points fall outside control limits (CL)
If no points outside CL assume there is no assignable cause. If points are outside CL investigate and correct
Operators use control chart by recording the value of sample statistic which is periodically taken
Determine when to take action if a series of sample values trend in a certain direction (up or down)

design or customer requirements
Control limits
Statistical limits plotted against LCL

and UCL
Process variability
Natural or inherent variability in a process (process varies)
Process capability
The inherent variability of process output relative to the variation allowed by the design specification

Process Capability

to lots or batches of items before or after

a process, to judge conformance with predetermined standards. Ex. Receive a box of 1000, randomly check 25, and based on results, infer to the entire amount

Conditions for Acceptance Sampling
A large number of items must be processed in a short time
Destructive testing may be required Ex. Air tanks
Fatigue or boredom caused by inspecting large numbers of items leads to inspection errors

sample size, number of samples, and acceptance/rejection criteria
Types:
Single-sampling: one

random sample is drawn from each lot
Double-sampling: a second sample could be taken
Multiple-sampling: more than two different samples may be required
Choose a plan in terms of cost and time for inspection