Statistical Quality Control
Uses statistical techniques and sampling in monitoring and testing of quality of goods and services
Acceptance Sampling
It relies primarly on inspection/test of previously produced items. It determins weather to accept or reject a product.
Statistical Process Control
It is a statistical quality control that occurs during production. It determins if the process is operating within acceptable limits.
Inspection
Apraisal of a good or service against a standard.
3 Stages of Inspection
Statistical Process Control Planning Process
Where to inspect
On Site VS In Lab
Random Variation
Natural variations in the output of processes created by countless minor errors
Assignable Variations
A variation whose source can be identified
Control chart
A time ordered plot of a sample statistic that is used to distinguish between random and assignable variation.
Control Limits
The deviding lines between random and non random variations
Type I Error
Concluding that a process changes whan it has not
Type II error
Concluding that a process is in control when it is actualy not
5 Steps in designing a control Chart
- Determine a sample size
- Obtain 20 to 25 samples
- Establish and graph preliminar control limits
- Plot sample stats values on control chart
- if any point are outside the control limits, investigate and correct
Control Charts for Variables
Sample mean
Monitor the mean of a process
Sample Range
Monitor the dispersion of a process
Control Charts for attributs
p-Chart
- Measure the proportion of deffects in a process
- from a binomial distribution: measure success or failure
c-Chart
- Measurs the number of deffect per unit
- From a poisson distribution
Design Specification
A range of acceptable values established by engineering design or customer requierment
Process Variability
Actual variability in a process for a product
Process Capability
The ability of a process to meet design spacifications
Capability analysis
determins wether the process output falls within the design specifications
Capable process
The output falls within specifications
4 possible strategies if a process is incapable
- Redesign process or reduce variability
- Use an alternative process
- use 100% inspection
- Relax design specifications
six sigma quality
A more advance version of problem solving/ Continuous improvement. It also refers to the goal of acheiving process variability so small that the half width of the design specification is 6 sigma
