《CP-CPK-PP-PPK》.ppt

Section 1Variation, Tolerances and Dimensional Control Two Types of Processes All processes have: Natural (random) variability= due to common causes The Two Causes of Variation Common Causes: Causes that are implemented in the process due to the design of the process, and affect all outcomes of the process Identifying these types of causes requires methods such as Design of Experiment (DOE), etc. Special Causes: Causes that are not present in the process all the time and do not affect all outcomes, but arise because of specific circumstances Special causes can be identified using Statistical Process Control (SPC) Tolerances A tolerance is a allowed maximum variation of a dimension. Measurement Report Example of Capability Analysis Data For some critical dimensions we need to measure more than 1 part For capability data we usually measure 5 pcs 2 times/hour=100 pcs (but sampling plan needs to be made on the basis of production quantity, run duration and cycle time) Why Make Process Capability Studies The Nokia Process Verification Process Section 2.Population, Sample and Normal Distribution Population versus Sample Population An entire group of objects that have been made or will be made containing a characteristic of interest The Normal Distribution Defining Cp and Pp Section 3.Cp and Cpk Concept Defining Cpk and Ppk What is the Difference Between Cp and Cpk? Cp and Cpk Indices and Defects(both tails of the normal distribution) The Effects of Cpk and Cp on FFR Section 4.Confidence Intervals Confidence of Cpk Cpk values are not definite numbers as they are based on relatively small samples of a population. The 95% confidence interval determines the interval which includes the true Cpk value with a probability of 95%, i.e. there is a probability of 5% that Cpk is either lower or higher than this confidence interval. Confidence Intervals Cpk Confidence Limits with a sample size of 100 and a nominal Cpk of 1.67 Exercise : Cp and Cpk Determine the