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
Determine the stress in the meridional direction: A doubly curved shell of thickness 8 mm is filled through a liquid under an internal pressure of 2.0 N/mm 2 . At a specific p

a)What are methods used in rating for time study. Illustrate them. b) Write down principles of motion economy.


Represent moment Graphically: How you represent moment Graphically? Sol.: Consider force F which is represented in magnitude and direction, by   line AB . L

Schedule Evaluation Each continuations of a partial schedule that are produced in step 1 are ranked as per to their respective cost function. This cost function might be dissim

Determine the slopes at free end - cantilever beam: A cantilever beam of length l carries a point load W at a distance l  /4 from free end. Determine the slopes at free end

Q. Show Mass energy Relation? Until the time of Einstein, mass and energy were considered as two different physical quantities. But in 1905, with the help of postulates of the

Compressio n Ignition Engines (or C.I. Engine): It works on the basis of dieses cycle. In diesel engines, energy addition occurs at constant pressure but energy rejection at

PRINCIPLE OF SUBMERGED ARC WELDING In submerged arc welding, the arc zone is submerged beneath the molten flux and hence there is no visible signature of the arc. Welding current

the jet transport B is flying at the velocity of 600km/h when a smaller aircraft A passes underneath the transport headed in the 60 degree direction. To passengers in B, however ap