Control Charts 1

Question 1

In order to succeed, SPC requires

Answer 1

1 Leadership
2 Teamwork
3 Well educated employees at all levels
4 Emphasis on Variability reduction
5 Measuring success in quantitative terms
6 Effectively communicating all the successes thoughout the company

Question 2

What indicates assignable (special) causes of variation?

Answer 2

A situation of instability

Question 3

A process with only common causes of variation present is said to be:

Answer 3

in statistical control

Question 4

A process in the presence of assignable causes of variation is said to be

Answer 4

out of control

Question 5

What is the fundamental objective of control charts?

Answer 5

..to indentify assignable causes of variation marking the moments when they occur.

Question 6

The expected variation due to common causes is graphically represented by the

Answer 6

control limits

Question 7

What are the two steps in order to achieve a stable and more capable process?

Answer 7

1 Eliminate ACV (assignable causes..)

2 Reduce CCV

Question 8

Calculation of Process Capability Ratio Cp

Answer 8

Cp = (USL-LSL)/6*Sigma

Question 9

Interpretation of
Cp>1
Cp=1
Cp<1
What is the ideal Cp?

Answer 9

low number of nonconforming items will be produced

Assuming a normal distribution, 0,27% nonconforming are being produced

large number of nonconforming items will be produced

in Practice, we opt for Cp of 1,3

Question 10

What is the chosen significance level and why?

Answer 10

alpha = 0,27 (k=3) is chosen because an alpha=5% (as usual would lead to an excessive number of false alarms

Question 11

What are the seven pattern types that indicate assignable causes?

Answer 11

1 One point beyond CL
2 4/5 points below the 1 sigma line
3 2/3 points above the 2sigma line
4 seven or more points going up or down
5 big oscillations: three consecutive points in +-2 sigma regions
6 proximity to the center line (within +- 1,5sigma)
7 Cyclic patterns (seasonality)