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Unformatted text preview: 1 MGMT 361 Operations Management (OM) Chapter 6 Quality Management  3 Prof. Julia A. Kalish 2 Quality Control (QC) 1. Acceptance sampling : For incoming material (and sometime outgoing) 2. Process control: During process 3. Process Capability Acceptance sampling Process control Acceptance sampling 3 Process Capability Suppose we are making a component using a certain process. Our internal standard (or the customers) requires that we produce at least 99.5% good components. No matter what we do, we find that we can produce only 98% good components. Then we say that our process is not capable . Suppose we find that we can produce 99.5% (or more) acceptable products i.e. the process is capable. Due to many reasons (such as worn out tool), the process may not perform up to expectations at a particular time. Here are two questions we want to answer. 1. Is the process capable? 2. Even if the process is capable, what is the current status? Answer to the first question is expressed in a measure called process capability ratio [ C P ] . For the second question, we use process capability index [ C pk ] . Again Is the process capable? process capability ratio [ C P ] What is the current status of the process? process capability index [ C pk ] . 4 5 Process Capability Analysis: The methodology used for finding C p and C PK is called process capability analysis. Here we make certain assumptions When we do the analysis, we collect random samples to estimate mean and standard deviation and to ensure that the process is stable. We are measuring only one critical dimension X. X is normally distributed. Process is stable. The specification for this dimension is A B where A + B is the Upper Tolerance Limit [UTL] A is the nominal value and A B is the Lower Tolerance Limit [LTL] If the dimension of the component produced falls between LTL and UTL, we accept the component. If it falls outside, we reject. AB A A+B 6 AB A A+B Process Capability Ratio (C P ): The formula for the process capability ratio is given by C p = (UTL LTL) / (6 ). Here are the specifications A B Now we will superimpose normal distribution on the specifications. It is assumed that the process mean is at the nominal value A. Red area shows probability of rejection....
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 Spring '10
 panwalker
 Management

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