Statistical process control

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Quality inspection
focus on providing information
Quality control
focus on monitoring and controlling SPC
Quality assurance
management programs aimed at ensuring good product quality
Total quality management
management philosophy about ensuring and improving product quality throughout the entire organization
acceptance sampling
taking a sample of a batch of items and determining whether to accept or reject whole batch based on results. occurs before or after production not during
Statistical process control
to prevent poor product quality, process improvement tool, method of inspecting a sample of goods and deciding if process is in control
Steps in SPC
Step 1: define characteristic to measure
Step 2: set up control chart
Step 3: take a sample and plot results
Step 4: is any sample point outside control limites
Step 5: does a pattern exist
If yes to step 4 or 5, Step 6: process is out of control
Attributes
Measured qualitatively, have discrete values, countable values
Variables
characteristics that are measured quantitatively, thus have continuous values, measuring the difference
Type 1 error
random variation mistaken for abnormal variation
Type 2 error
abnormal variation is not detected
P Chart
measures proportion of defective items, sample size generally 50-100, used when classification is "either or"
C chart
measures defective features per item, sampel size of 1, used when not possible to count defective items
R chart
measures variation in range of results
X chart
variation in average result, measures central tendency of a process
Pattern test
to detect a non random pattern within the control limits. Runs test to check for runs in the sample, Zone test to see if results stay within same area
Process capability
the ability of a process to satisfy a product or services tolerances, process must be in control and meet design specifications
Tolerances
design specifications that reflect customer requriments
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