CONTROL CHARTSCONTROL CHARTSCONTROL CHARTSCONTROL CHARTS

Cliya JacksonCliya Jackson S6 E2S6 E2

Roll No 22Roll No 22

Definition• Control chart is a graphical

representation of the collected information.

• collected information – implies measured characteristics of the items or samples.

• Dynamic in nature – it is kept current and up – to – date as per the changes in processing conditions .

Purpose and advantages

• Depicts any change in the characteristics of items since the start of the production.

• It determines whether the process is in control or out of control.

• It detects unusual variations taking place in a process.

• It ensures product quality level.

Contd…..• It warns in time and if the process is

rectified at that time , scrap or percentage rejection can be reduced.

• It builds up the reputation of the organization through customer’s satisfaction.

Types of control charts

Control charts

Attribute Variables

p np C U X bar R σ

chart

• Most commonly used variables chart.

• Chart for measure of central tendency.

• Shows changes in process average and is affected by changes in process variability.

X

R chart

• Controls general variability of the process

• Chart for measure of spread

• Use along with chartX

ExampleExampleSample no. R

1 7.0 2

2 7.5 3

3 8.5 2

4 10.0 2

5 9.5 3

6 11.0 4

7 11.5 3

8 4.0 2

9 3.5

3

10 4.0 2

∑ =76

∑ R = 26

X

X

• and and RR Control Control Chart ConstantsChart Constants

n A 2 D 3 D 4

2 1.88 0 3.267

3 1.023 0 2.575

4 0.729 0 2.282

5 0.577 0 2.115

6 0.483 0 2.004

8 0.37 0.14 1.86

10 0.31 0.22 1.78

12 0.27 0.28 1.72

X

0

6.2*0

6.2

48.5

6.2*11.2

3

4

RDLCL

RCL

RDUCL

R

R

R

09.6

)6.2*58.0(6.7

6.7

11.9

)6.2*58.0(6.7

2

2

RAXLCL

XCL

RAXUCL

X

X

X

Control chart calculations

Plotting chartX

Plotting R chart