control limits

Submitted by vijayavadrevu on Mon, 05/27/2013 - 19:19

 You are involved in manufacturing ball bearings using lathe machines. The ball bearings should have a diameter of 5.0 cms - allowable control limits are 4.95 cms to 5.05 cms. Measurements made after the end of the process for the bearings produced are: 4.96, 4.98, 5.01, 5.03, 5.02, 5.01,5.03,5.04, 5.02, 4.96, 4.98, 5.00. 


What is your conclusion about the process?


1.    

Process is out of control and needs to be investigated


2.    

Process is in control and adjustments are not required


3.    

The tool needs to be changed or re-calibrated


4.    

Process should be further measured using a run chart

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sanskrit

Mon, 05/27/2013 - 22:57

 1. Process is out of control and needs to be investigated

Rule of Seven , Seven consecutive readings are on one side of mean (mean is 5 Here) 

vijayavadrevu

Tue, 05/28/2013 - 02:00

 Yes, correct. Sometimes instead of taking mean into consideration, people may look at the readings , and go for option A since all of them are within control limits. Hence posted the question

sriram.mukundan's picture

sriram.mukundan

Tue, 05/28/2013 - 04:03

  Hi Vijayavadrevu,

considering the mean as 5, seven consecutive points above the mean which means out of process and needs investigation.

Your comments:

Yes, correct. Sometimes instead of taking mean into consideration, people may look at the readings , and go for option B INSTEAD OF A since all of them are within control limits. Hence posted the question

-Sri

vijayavadrevu

Tue, 05/28/2013 - 08:06

Yes, I should have written as B INSTEAD OF A

Thank you for correcting me

 

Regards

Vijaya

vijayavadrevu

Tue, 05/28/2013 - 08:06

Yes, I should have written as B INSTEAD OF A

Thank you for correcting me

 

Regards

Vijaya