Block 3 - lecture 1 Flashcards
3 categories of variation?
- within-piece variation
- piece-to-piece variation
- time-to-time variation
assignable sources of variation?
- equipment
- material
- operators
- methods
- environment
- measurements
examples for variation from equipment?
- tool wear
- machine vibration
- electrical fluctuations
examples of variation from material?
- tensile strength
- ductility
- thickness
examples of variation from environment?
- temperature
- light
- radiation
- humidity
examples of variation from operators?
- personal problems
- physical problem
- lack of training
Size of variation due to inspection vs from other sources?
should be 1/10th of other sources
causes of variation?
random or assignable
control charts for variable data?
- Xbar and R-charts
- Xbar and s-charts
- charts for individuals (x-charts)
Xbar charts?
used to plot averages for each subgroup
Xbar chart advantage?
quick way to show variation
solid line in the centre of an Xbar chart?
Could be:
- average of averages (X double bar)
- reference value (Xbar0)
- population mean (mu)
dashed upper and lower lines on an Xbar chart?
control limits
used to judge the variation
Control limits vs Specification limits?
- control limits are used to measure variation
- Spec limits are the product requirements
How are the control limits positioned?
±3 standard deviations
99.73% within them
How to determine if a process is out of control?
if a subgroup is out of the control limits on an Xbar chart
R chart?
used to plot the range of each subgroup
when would more/less inspections be needed?
More inspections are needed when the process is out of control
what does it mean if an individual value is out of the control limits?
nothing, they refer to the averages
what does it mean if a subgroup has an average out of the control limits?
the process is out of control
uses of a control chart?
- quality improvement
- determining process capability
- deciding on specifications
- production improvement decisions
- product release/upscaling
