Process Capability Index - Asymmetrical Positioning of the Process

As stated earlier, the C_p index assumes that the process mean is centred within the tolerance band, but, in practice, this is often an unreasonable assumption. For this reason, alternative indices have been devised which take account of asymmetrical positioning of the process mean relative to mid-tolerance. Consider the process output represented in this next figure, for which the LSL is 10, the USL is 20, the process mean (µ) is 18 and the standard deviation (σ) is 1.166. For this process the C_p index value is 1.43 [i.e. (20 - 10)/ (6 × 1.166)], which might suggest that the output has a very low level of non-conformance. However, as can be seen from the figure, a significant proportion of the output actually lies beyond the upper specification limit. The C_pk index takes account of the asymmetry by relating the spread of one side of the output distribution (3σ) to the difference between the process mean (µ) and the nearest specification limit. Two calculations are performed, and the lowest value (worst case) is taken as the index value.

In the example in the figure above, the C_pk index is 0.57 [ie (20 - 18)/(3 × 1.166)], indicating that the process, as currently set, is not capable of producing to the design specification. The following figure shows the significance of different C_pk values.

Posted Date: 3/16/2013 1:29:37 AM | Location : United States

Ask an Expert

Related Discussions:- Process capability index - asymmetrical positioning, Assignment Help, Ask Question on Process capability index - asymmetrical positioning, Get Answer, Expert's Help, Process capability index - asymmetrical positioning Discussions

Write discussion on Process capability index - asymmetrical positioning
Your posts are moderated

Write your message here..

Related Questions

Explain the economic order quantity, Question 1 In a net change MRP system ... Question 1 In a net change MRP system requirements and schedules are considered rigid and never updated. Question 2 the customer grace period is a time-span having some specifie

Explain what qualities do you think supervisors take, What qualities do you... What qualities do you think supervisors take into consideration when choosing whom to give a promotion to at work?

Features of production and operation management, Features of Production and... Features of Production and Operation Management 1. Production management is the process of making decisions. 2. Decisions are made regarding transformation of inputs outputs. 3

MBA-2, What do you understand by line balancing what happens if balance doe... What do you understand by line balancing what happens if balance doesn''t exist

Explain finite backward scheduling, A process capacity methodology that is ... A process capacity methodology that is used to show how well parts being produced fit into a range specified by design limits is which of the following? a. Finite backward sche

Compute the total relevant cost associated with the eoq, The local technolo... The local technology store WiredIn hired you to manage their inventory, which consists of 2 products configurations, type L and type J. Below are the data for the products. The hol

Explain the various classifications of stakeholders, An Organization: Its M... An Organization: Its Mission and Strategic Intent In this assignment, you will decide on a company's strategic intent, its mission, and the role of stakeholders in developing an

I need to describe forecasting, I need to explain forecasting, also how it ... I need to explain forecasting, also how it is performed at St. Arnold's Brewery (Houston, TX) also what forecasting error is and if there has been any in the past.

Location analysis, explain the series of steps involved and various factor... explain the series of steps involved and various factor effecting location decion?

Explain the business-level strategy, Research the corporate-level of strate... Research the corporate-level of strategies and evaluate the business-level strategy do you believe is appropriate to offset forces in the industry for Victory Motorcycles. Can you