Example of process capability, Mechanical Engineering

Assignment Help:

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%.


Related Discussions:- Example of process capability

Resistance welding processes, RESISTANCE WELDING PROCESSES The followin...

RESISTANCE WELDING PROCESSES The following five are the main types of resistance welding: 1. Spot welding 2. Seam welding 3. Projection welding 4. Upset butt we

Matter, Matter, particle and body: Matter is anything which occupies s...

Matter, particle and body: Matter is anything which occupies space, possesses mass provides resistance to any stress, example Iron, air, stone, Water. A body of negligible

Calculate the force - pulley, Calculate the force - pulley: A string i...

Calculate the force - pulley: A string is passing over a smooth pulley. The string supports the mass m on one side which is to be pulled up with acceleration a. calculate the

Properties of aluminium alloys, Properties of Aluminium Alloys: Among...

Properties of Aluminium Alloys: Among the different properties of aluminium alloys given are notable as: (a) Low density as 2.7 gm/cc (b) Elevated electrical and therma

Bench vices tool and equipment , Bench Vices: Bench vice is used to hold a...

Bench Vices: Bench vice is used to hold a job on a bench. It consists of a movable jaw, a fixed jaw, spindle and a lever. Figure shows a bench vice. The movable jaw is in the fron

What are the instructions to charge a battery?, (a) How is specific gravity...

(a) How is specific gravity of electrolyte (battery water) measured and what should be the value of specific gravity? (b) How would you measure battery voltage and what is its reco

Throttling process - thermodynamics, Throttling Process: The expansion...

Throttling Process: The expansion of gas through an orifice or partly opened valve is called as throttling. q 1 -2 = 0 and w 1 -2  = 0 Now              The throt

Mechanics of solid, determine crippling load for T section dims 12cm??12cm?...

determine crippling load for T section dims 12cm??12cm??2m and of length 6m it used as colum with one of its end fixed and other hinged E=2??10 power 5 N/mm2

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd