Flashcards in Chapter 40 Deck (12):
Define: Quality Control
Past: Concerned with detecting poor quality in manufactured products and taking corrective action to eliminate it.
Current: Encompasses broader range of activities, including various quality programs such as statistical process control and Six Sigma as well as modern inspection technologies.
Define: Random vs. Assignable (special) Variation
Random: Caused by many factors; generally form normal statistical distribution (bell curve).
- Human variability within each operation cycle
- Variations in raw materials
- Machine vibration
Assignable: an exception from normal operating conditions; No longer in statistical control:
- Operator mistakes
- Defective Raw materials
- Tool Failures
- Machine Malfunctions
Define: Statistical Control
When only variation in a process is due to random variations, it is said to be in statistical control. This kind of variability will continue so long as the process is operating normally.
Define: Process Capability
Relates to the normal variations inherent in the output when the process is in statistical control. Equals +/- 3 standard deviations about the mean output value. Often unknown therefore experiments must be conducted to assess it.
Define: Natural Tolerance Limits
Design tolerances can be specified as being equal to process capability. The upper and lower boundaries of this range are known as the natural tolerance limits. 99.73% of parts allowed, 0.27% not.
Define: Control Charts for Variables (Xbar, R)
A graphical technique in which statistics computed from measured values of a certain process characteristic are plotted over time to determine if the process remains in statistical control.
Xbar: Used to plot the average measured value of a certain quality characteristic for each of a series of samples taken from the production process. indicates process mean changes over time.
R chart: Plots the range of each sample, thus monitoring the variability of the process and indicating whether it changes over time.
Management approach to quality that pursues three main goals:
1) Achieving customer satisfaction
2) Encouraging the involvement of the entire workforce
3) Continuous improvement
Define: Six Sigma
Quality program that assumes that defects in any process can be measured and quantified. Once quantified, the causes can be identified and improvements made to eliminate or reduce the defects.
Define: Loss Function
Loss, sometimes seen as the cost a product takes on society after shipment, includes costs to operate, failure to function, maintenance and repair costs, customer dissatisfaction, injuries caused by poor design, and similar costs.
Loss function = k (x-N) ^2; where x is the quality characteristic of interest, N is it's nominal value, and k is a constant of proportionality.
Define: Robust Design
One in which the product's functions and performance are relatively insensitive to variations in design and manufacturing parameters. Involves the design of both the product and process so that the manufactured product will be relatively unaffected by all noise factors.
Define: Noise Factors
Noise Factors are source of variation that is impossible or difficult to control and that affects the functional characteristics of the product. Three types:
1) Unit-to-Unit- related to variation in raw materials, machinery and human involvement
2) Internal- related to time dependent factors such as wear of mechanical components, spoilage of raw materials, and fatigue of metal parts
3) External- related to outside temperature, humidity, input voltage, and raw material supply