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
Loading Conditions Non-uniformity of loading has to be considered in the choice of foundations particularly in highly compressible soils. It is not uncommon for buildings with

Explain the Application of Electro Chemical Machining? 1. EBM has been used to perforate holes in glass fiber spinning head made from a heat resistant supper alloy. 2. Slott

Spot welding of different metals-Nickel and monel metal While spot welding these materials, the settings are to be properly maintained. Welding time, in this case, is only 50 %

(a) A 50 mm dia. jet having a velocity of 18 m/sec. impinges without shock on a flat plate inclined at an angle to the axis of jet. If the plate is moving at 5 m/sec in the directi

A biaxial rosette is shown at right. Derive equations to correct for transverse sensitivity effects for the case in which the two strain gage elements exhibit different gage factor

write a notes of system of forces and classified it a/c to orintenssion of forces

We shutdown our furnace and always encountered crack on our piping at the weld joints. I investigated that upon shutdown the furnace cracking, our maintenance immediately remove th

Creep: Creep of rails is the forward movement of rails in the direction of dominant traffic over a period of time. Creep is undesirable because it disturbs the gauge of the t

A triangle ABC with vertices A (30,20), B(90,20), C(30,80) is to be scaled by a factor of 0.5 about a point X(50,40). Calculate :- (i) The composite transformation matrix; and

what are the anti refection coating.expretion for thicknessrefractive index of coating material to act as anti reflacting coating