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Nokia生产过程控制全球培训教材.ppt

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Section 1

Variation, Tolerances and Dimensional Control


Two Types of Product Characteristics
Variable: A characteristic measured in physical units, e.g. millimetres, volts, amps, decibel and seconds.
ON
OFF
Attribute: A characteristic that by comparison to some standard is judged “good” or “bad”, e.g. free from scratches (visual quality).
In this training we deal with variables only

The Sources of Process/System Variation
Methods
Operators
Customer Satisfaction
Material
Environment
Equipment
Process

Two Types of Processes
All processes have:
Natural (random) variability => due to common causes
Stable Process: A process in which variation in outcomes arises only from common causes
Unstable Process: A process in which variation is a result of both common and special causes
USL
LSL
nominal value
Defect
USL
LSL
nominal value
Unnatural variability
=> due to special causes

Shewhart (1931)
The Two Causes of Variation
Common Causes:
Causes that are implemented in the process due to the design of the process, and affect all outcomes of the process
Identifying these types of causes requires methods such as Design of Experiment (DOE), etc.
Special Causes:
Causes that are not present in the process all the time and do not affect all outcomes, but arise because of specific circumstances
Special causes can be identified using Statistical Process Control (SPC)
USL
LSL
Nominal value
Defect
USL
LSL
nominal value

Tolerances


LSL (lower specification limit)
10,7
USL (upper specification limit)
10,9
Acceptable part
Rejected Part
Rejected Product
Nominal
10,80,1

Rejected Part


A tolerance is a allowed maximum variation of a dimension.

Measurement Report

In most cases we measure only one part per cavity for measurement report

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