A manufacturer buys some parts and makes some parts for its assemblies. The supp

Question

A manufacturer buys some parts and makes some parts for its assemblies. The supplier of the purchased parts aims to always meet the specs. The supplier conducts inspections before shipping. They checked 25 samples, each containing 5 parts and found the following results:

Xdoublebar = 0.3175cm    Rbar = 0.00508cm

1. Create the appropriate control charts for this process.

2. If the specs are 0.3100+-0.005, is this process capable?

3. What is the probability that a sample with a mean of 0.305 would be out of control?

Explanation / Answer

Xdoublebar = 0.3175cm

Rbar = 0.00508cm

Upper control limit: UCLx = Xdoublebar + A2 *Rbar

Lower control limit: LCLx = Xdoublebar - A2 *Rbar

From fig.1 we find A2 = 0.153

since we have the number of observations in each sample as 5, and the number of samples as 25. Therefore subgroup size = 25

UCLx = 0.3175 + 0.153*0.00508

= 0.3175+ 0.0008

= 0.3183

LCLx = 0.3175 - 0.153*0.00508

= 0.3167

For range UCLr = D4 *Rbar

= 1.541*0.00508 ....................... from fig1, D4 for 25 subgroup = 1.541

= 0.0078

For range LCLr = D3 *Rbar

= 0.459*0.00508 ..... from fig1 D3 = 0.459 for subgroup size 25

= 0.0023

2. for specs of 0.3100 +- 0.005 it is completely out of range from LCLx and much below it. Hence the process is not capable.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.