Example of process capability, Mechanical Engineering

Example of Process Capability

The specifications for one characteristic of a part call for its width to be 3.000 + 0.008 centimetres. The procedure has been run under controlled conditions so that no assignable causes of variation have been introduced, & samples have been taken. The standard deviation of the process was calculated to be 0.003 centimeter.

A.    What is Cp for this process? What does this value say regarding the process capability?

B.     What percentage of the units would be outside the specifications for the width of the part if the procedure were operated and centered at 3.000 centimeters? Suppose a normal distribution of measurements.

Solution

(a)     C p   = USL - LSL/6 σ = 3.008 - 2.992/6 (0.003)

                   = 0.016/0.018

                    = 0.889

As the index is less than 1, the process is not capable of generating all the items within the specifications limits, even if the process is operated so that its mean is centered exactly among the specification limits.

 (b)       As the normal distribution is symmetrical and centered among the specification limits, the portion outside the upper & lower limits shall be twice the portion outside one limit. The portion outside the upper limit might be found by converting the upper limit to a Z value and referring to the normal distribution curve  as following:

Z =  x - μ / σ  =  3.008 - 3.000/0.003 =  0.008/0.003 = 2.667 or 2.67

The area to the left of a Z of 2.67 is 0.9962. The area to the right of this value is 1 - 0.9962, or 0.0038. As the curve is symmetrical, an equal amount shall be to the left of the lower specification limit. The overall portion outside the specifications shall be 2 (0.0038) = 0.0076, that is 0.76%.

Posted Date: 12/26/2012 7:56:40 AM | Location : United States







Related Discussions:- Example of process capability, Assignment Help, Ask Question on Example of process capability, Get Answer, Expert's Help, Example of process capability Discussions

Write discussion on Example of process capability
Your posts are moderated
Related Questions
(a) Draw a single point cutting tool and label clearly the several parts of it. Illustrate them in brief. (b) What are the several factors affecting tool life ? (c) List char

Explain about the Raft Foundations The raft foundations are generally used for large loaded area on soils of low bearing capacity. They are of particular use when soils are of

procedure for measuring area of square by planimeter

Determine reactions at supports of loaded beam: Determine reactions at supports A and B of loaded beam as shown in the figure given below.     Sol.: First co


If Motorcycle Pulls to One Side Causes of Problem Remedy Misaligned shock Absorber Front and rear wheels are not alig

Q.  A wooden beam of the rectangular cross section is subjected to bending moment of 5KNm. If the depth of section is to be double the breadth and stress in wood is not to exceed 6

Show that for a flat circular steel plate subjected to uniform pressure on one surface, the maximum stress when the periphery is freely supported is 1.65 times that when the periph


Aluminum-lithium alloys have been developed by the aircraft industry to reduce the weight and improve the performance of its aircraft. A commercial aircraft skin material having a