Question

You work for Harley-Davidson, manufacturer of popular a motorcycle in the U.S. You have been assigned to a corporate cross-functional team tasked with finding the best supplier of metal stampings to ensure a quality product. Your engineering department has provided specifications on a piston ring produced by suppliers, such that the USL = 82.9500 mm and the LSL = 82.8900 mm. The design center target is 82.9200 mm. The industry standard for Cp is 1.33 or higher (for capability).

One supplier, Metals Inc., has provided SPC charts of their manufacturing process, and you have determined from studying them that the estimated standard deviation is 0.006 mm, while the process mean is 82.9110 mm. Another supplier, Rings Inc., also wants to supply the product. Rings, Inc. representatives have provided detailed process data showing their process capability indexes to be Cp = 1.00 and their Cpk to be 0.50.

Below are the answers I put, not sure if they are correct or not.

Question 1

What is the Cp for Metal Inc.? Do not round your result, keep at least three significant digits.

1.666

Question 2

What is the Cpk for Metal Inc.? Keep at least three significant digits when reporting your result

1.166

Question 3

What is your interpretation of Cp and Cpk for Metal Inc?

c. The process is not capable and not centered

d. The process is capable but not centered

b. The process is centered but not capable

I answered, e. The process is capable and centered

a. The process is capable of meeting 6-sigma requirements

Question 4

What is your interpretation of Cp and Cpk for the other supplier, Ring Inc?

e. The process is capable and centered

b. The process is centered but not capable

I answered, d. The process is capable but not centered

a. The process is capable of meeting 6-sigma requirements

c. The process is not capable and not centered

Question 5

How many defects per million is Metal Inc. capable of?

22700

Question 6

How many defects per million is Ring Inc. capable of?

50000

Question 7

Based on your previous finding, what recommendation would you suggest for Harley-Davidson?

a. They should unconditionally order from Ring Inc.

b. They should unconditionally order from Metal Inc.

e. They should order from Ring Inc. but recommend that they center their process

I answered, d. They should order from Metal Inc. but recommend that they center their process

c. They should unconditionally order 50% from Ring Inc. and 50% from Metal Inc.

Answer 1