Session 5 - Quality Management Tools 2

Question 1

What is the Process Capability Index?

Answer 1

Cp

The process capability index, or process capability ratio, is a statistical measure of process capability: the ability of an engineering process to produce an output within specification limits.

Can tell whether a process is capable.

Question 2

What are the the measures used in find the Cp?

Answer 2

1- UCL
2- LCL
3- Process Mean (µ)
4- LSL
5- USL

Question 3

How do you find Cp?

Answer 3

Cp = ( USL - LSL ) / 6σ

can also be worded as =
New Requirement / Current Process

Question 4

What are the rules when it comes to whether the process is capable in Cp?

Answer 4

All of the process variation has to be capable for the entire process to be capable

Cp < 1 , process “not capable” of fulfilling the requirements

Cp = 1 , process is “borderline capable” of fulfilling the requirements

Cp > 1 , the process is capable of fulfilling the requirements

Question 5

How far are the UCL and LCL from the process mean (µ)?

Answer 5

3σ
- 3 standard deviations

Question 6

What happens when the process is not capable and Cp < 1?

Answer 6

In this case, the new specifications are stricter than the current process variations

• There are “Higher” level of requirements from the new spec

Question 7

In order for the current process to be capable of and meet the new specs, what must a firm do?

Answer 7

Needs to redesign the process in order to meet the new requirements

Question 8

What is the rule when it comes to meeting the new specification requirements when the process was initially not capable?

Answer 8

USL - LSL < 6σ

Question 9

What happens when the process was barely capable?

Cp = 1

Answer 9

In this case, the current process variation “exactly meets” the new specification and the current process is borderline/barely capable of meeting the new specs

Question 10

What is the general rule when Cp = 1?

Answer 10

USL - LCL = 6σ

Question 11

What happens when the process is capable?

Cp > 1

Answer 11

The current process is stricter than new specifications

It means any process variations will fall within the new spec limits

Question 12

What can a firm do when the current process is capable of meeting the new specification?

Answer 12

The firm can fulfill the new requirements

Question 13

What is the general rule when Cp > 1?

Answer 13

USL - LSL > 6σ

Question 14

How do you find whether a process is capable according to Cp?

Answer 14

Cp = ( USL - LSL ) / 6σ

Question 15

What happens when you increase process variance?

Answer 15

It reduces process capability

Question 16

What is a limitation of Cp (when Cp =1) when the process mean is the same as the mean of the new spec?

Answer 16

The process is barely capable according to the Cp value

Question 17

What is a limitation of Cp (when Cp =1) when the process mean is not in line with the mean of the new specs?

aka the process mean is lower than the spec mean

Answer 17

The process is not capable even when the Cp =1

Question 18

What is another way to measure process capability other than Cp?

Answer 18

Cpk

Question 19

What does Cpk do?

Answer 19

Takes into account distances between process mean (µ) and two spec limits (LSL and USL) separately

Question 20

What is the rule when calculating Cpk?

Answer 20

Cpk < 1 , Process is not capable

Cpk = 1 , Process is borderline capable

Cpk > 1 , Process is capable

Question 21

How do you calculate Cpk?

Answer 21

Cpk = min { (USL - µ / 3σ) , (µ - LSL / 3σ) }

it’s the minimum between the upper spec limit minus the process mean divided by 3 times process standard deviation and the process mean minus the lower spec limit divided by 3 times process standard deviation

Question 22

What is a summary for Cp?

Answer 22

is a good process capability measure only when the process mean does not skew from the center of the specification limits

Question 23

What is a summary for Cpk?

Answer 23

Takes into account the process mean, thereby is not susceptible to a skewed process mean (in relation to the center of the spec limits)

Question 24

What is Six Sigma used for?

Answer 24

To achieve near perfect products

Question 25

What are the key concepts when it comes to Six Sigma?

Answer 25

1- Processes need to be designed to minimize variability
2- Customers perception of quality is not just driven by the average quality, but by the variation in quality each time the customer interacts with the company

Question 26

What is a tool used in Six Sigma and what does it stand for?

Answer 26

DMAIC Cycle

D - Define
M - Measure
A - Analyze
I - Improve
C - Control

Question 27

What is the DMAIC cycle?

Answer 27

Data driven methodology for process improvement to meet customer specifications

Question 28

What do each stages of DMAIC do?

Answer 28

Define - Define the problem (process flowchart)

Measure - Quantify the Problem (Cp, Cpk)

Analyze - Identify the cause of the problem (lean operations)

Improve - Implement and Verify the solution

Control - Maintain the solution (control charts)