Process capability Premiered by EDOUARD GATETE of The Pennsylvania State University.
Overview • Definition • Measurements of process capability control • How can Process Capability be used in an organization
Overview • A real world example • Exercise • Summary
Definition • Process capability is defined as a how likely a product is going to meet the design specification. • It has been argued whether the specifications are actually set by customers or design engineers.
Measurements of process capability • Most of the times, conventional process capability work quite well, but we have to keep in minds that they will be times when the usual formulas don’t work. • An index that measure potential process capability is used in unusual situation.
Measurements of Process Capability • The formula C sub P is the tolerance divided by six standard deviations (also known as sigma) • C sub P = tolerance/6-sigma Reveals how many six-sigma fits within a specified tolerance In order for a product to meet specifications, at least 99.773% of productions should confirm anticipated operation condition.
Measurement of process capability • Population : a collection of all observation of interest to a decision maker. • Sample: a portion of population • population distribution: a distributions of the entire population • sampling distribution: distributions of sample means.
How to use process capability in an organization • The control chart • bell-shaped curve: as long as all inputs to a process remain constant, the output will always vary
The difference between Stable and capability • A process is capable if a given product meets specifications. • A process is stable if there is a common variation present in the process
The disadvantage of using process capability • Over-correcting: the most common • reducing variation
Factors influencing the tolerance allocation • Statistical aspects of the dimensions and manufacturing processes involved • Assembly requirements and conditions • the cost-tolerance relationship • International Standards Organization's practices for fits.
A real world example • Taking an example of a car manufacture company. The process capability will be used if out of 1000000 cars produced, only 3.4 cars come out defective
Exercise • A certain manufacturing process is producing metal washers that have diameters that are known to be normally distributed with mean 1 inch and standard deviation .006 inch. The process is known to be stable and in control. The specifications for these washers are 1 inch +/- .01. What percentage are within specification limits?
Summary • We have just reviewed process capability. This process is used in production to determine whether a product meets specification on a consistent basis. Even though they are a lot of complex ways to to figured out process capability, it’s more important to understand the basics before we can get in more details.
summary • This presentation has definitely focused on the basics of process capability. It is very important to minimize defects in production if you want to optimize the profit.
summary • A bibliography used to come up with these slides is as follow; • Hart, M. Quality Tools for Decreasing Variation and Defining Process Capability. V33 n2. Second Quarter 1992, p.6-11.
summary • Raouf, A. On developing optimal process capability index. International Journal of Quality & Reliability Management. V9 n7. 1992. P. 17-22 • Bothe, D. R. Measure process capability when Cp won’t work. Quality. V34 n8. Aug 1995. P. 20-22
Summary • Foster, T. S. An integrative approach. Managing Quality 2001. P. 374-376.