Ch. 6 (Statistical Process Control-SPC)

Question 1

Statistical process control (SPC)

Answer 1

Statistical process control (SPC)

A process used to monitor standards by taking measurements and corrective action as a product or service is being produced.

Question 2

Control chart

Answer 2

Control chart

A graphical presentation of process data over time.

Question 3

Natural variations

Answer 3

Natural variations

Variability that affects every production process to some degree and is to be expected; also known as common cause.

Question 4

Assignable variation

Answer 4

Assignable variation

Variation in a production process that can be traced to specific causes.

Question 5

x-bar chart

Answer 5

x-bar chart

A quality control chart for variables that indicates when changes occur in the central tendency of a production process.

Question 6

R-chart

Answer 6

R-chart

A control chart that tracks the “range” within a sample; it indicates that a gain or loss in uniformity has occurred in dispersion of a production process.

Question 7

Central limit theorem

Answer 7

Central limit theorem

The theoretical foundation for x-bar charts, which states that regardless of the distribution of the population of all parts or services, the distribution of x-bars (averages) tends to follow a normal curve as the number of samples increases.

Question 8

calculate standard deviation

Answer 8

1. find average of the sample means. = x-dblbar
2. UCL: add 3*(1/sqrt(N))
3. LCL: subtract 3*(1/sqrt(N))
4. Plot points

Question 9

calculate standard deviation with range values

Answer 9

1. find average of the sample means. = x-dblbar
2. 2. UCL: add (A2 based on sample size*range mean)
3. LCL: subtract (A2 based on sample size*range mean)
4. Plot points

Question 10

calculate R-chart limits

Answer 10

UCL: d4R-bar
Mean: R-bar
LCL: d3R-bar

Question 11

percent defective- p-chart

Answer 11

1. calculate mean of defectives. p-bar
2. p-bar*(1 - p-bar)
3. divide by size of each sample (100 data in one sample)
4. sqrt root of everything
5. multiply by 3 and add to/subtract from p-bar for UCL/LCL

Question 12

number of defective- c-chart

Answer 12

1. average of complaints. c-bar

2. add or subtract 3*sqrt(c-bar)

Question 13

When to use each chart

Answer 13

1. x-bar or R-bar chart are used with variables
2. p-chart is a yes or no and percentage of one.
3. c-chart is the # of an occurrence