Answer all the following questions The specification limits of a certain quality

Question

Answer all the following questions The specification limits of a certain quality characteristics are 100 plusminus 10 units. A process being considered for producing this product has a variance of 9 units. A. WHAT can you say (quantitatively) about the process capability? B. Suppose that the process average shifts to 91 units. CALCULATE the process quality level in terms of the Part/Million (PPM). C. What is the percentage of increase or decrease in the number of nonconforming items due to the shift

Explanation / Answer

Answer:

1.

Process Capability can be described as a comparison of your process performance against its process specifications using various capability indices.

To better understand these concepts I’ve broken this section down into 3 sub-sections.

In the first two sections we will define Process Performance & Process Specifications.

Then the third section explains their relationship with Process Capability Analysis, which at the end of the day looks like this:

Process Capability Analysis = Process Specifications/Process Performance

                                                = Product Design Tolerance/ Natural Process Variation

Variance = 9, USL=100, LSL=10, Average = 91

Process Capability = Process Specifications/Process Performance

                                = USL-LSL/6

Process Capability = 100-10/6*9 = 90/54 = 1.66

2.

PPM (Parts per million) is a measurement used today by many customers to measure quality performance.

Definition: One PPM means one (defect or event) in a million or 1/1,000,000

There was a time when you were considered a pretty good supplier when your defect rate was less than 1%, (10,000 PPM), then the expectation was increased to 0.1% or 1,000 PPM.

=91/100= 0.91=0.91*100000= 91,000 PPM

Centered Process= Min (USL-Average/3, LSL-Average/3 )

= Min (100-91/3*9, 10-91/3*9)= Min (9/27, -81/27) = Min (1/3, -3) = -3

3.

Nonconforming Unit : A unit with one or more nonconformities or defects. Also called a reject.

Nonconforming units = USL-Average/3 = 100-91/3*9= 9/27=1/3= 0.33

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