Unit 36 Statistical Process Control

 

Unit 36:

Statistical Process Control


Unit code:
K/601/1460

QCF level:
5


Credit value:
15






Aim

This unit will enable learners to apply relevant statistical techniques used in process quality control and to evaluate a process against a given specification.

Unit abstract

This unit takes the learner through the statistical techniques used in process control, variables inspection and attribute inspection. It covers the handling of data and the use of process control charts. This will lead learners into the study of process capability and identification of types of variation within a process.

Control charts will be seen as a graphic aid for the detection of quality variations in output. Emphasis is given to their online monitoring function, which provides early warning of deviations from specifications.

The importance of process capability analysis in production planning, processing method, modification and maintenance will also be stressed.

Learning outcomes

On successful completion of this unit a learner will:

1       Understand the basic types, variations and characteristics of statistical techniques used in process control

2       Be able to select data, construct process control charts and initiate a control program for a specified application

3       Be able to evaluate process capability against a given product or component quality requirement using modified control chart limits

4       Be able to analyse types of variation within a process and record information on that variation.




Unit content



1      Understand the basic types, variations and characteristics of statistical techniques used in process control

Basic type: evaluation of basic types – variables inspection eg that concerned with precision measurements of dimensions or other critical characteristics such as weight; attribute inspection eg based on a binary rating (accept – reject); the relative cost and type of equipment involved in the inspection process

Variation: all processes subject to some degree of natural variability that can have a cumulative effect on quality of output eg worn bearings, slides, vibration; these are a function of the accuracy of the process and hence relate to the design specification requirement; assignable causes tend to produce large variations and are traceable to a specific reason eg errors in tool setting, tool wear, materials, operators

Characteristics: frequency, mean, standard deviation; control limits based on areas contained within specified standard deviation values

2      Be able to select data, construct process control charts and initiate a control program for a specified application

Sample data: variables eg weight, length, height, diameter; attributes eg length, diameter, weight, height, circuit boards, defects per unit area/length on paint or cloth; data should be grouped in tabular form and sample means; bulk mean and standard deviation values computed, using appropriate software; p and c charts

Limits: upper and lower control limits based on appropriate BS and ISO standards for all charts

3      Be able to evaluate process capability against a given product or component quality requirement using modified control chart limits

Modified control charts: should allow flexibility to accommodate long-term variation while maintaining control within the specified tolerance

Limits: distinction between specification limits and control chart limits, reduction of variability and its effect on range; high, medium and low precision in terms of standard deviation for a particular component or product should be used to determine the relative precision index for the process and hence its capability; Cp and Cpk


4      Be able to analyse types of variation within a process and record information on that variation

Types of variation: within the process; common cause; special cause

Recording variation: charts eg simple run, tally, bar, box plots time series, run; other information eg histograms, Pareto diagrams, stem and leaf plots



Learning outcomes and assessment criteria




Learning outcomes

Assessment criteria for pass



On successful completion of

The learner can:



this unit a learner will:














LO1 Understand the basic types,

1.1
evaluate the two basic types of inspection used in


variations and characteristics



sampling for process control


of statistical techniques used

1.2
describe the significance of natural and assignable


in process control






causes of variation










1.3
use selected data to construct frequency distribution






and calculate mean, range and standard deviation




1.4
relate the characteristics of the normal curve to the






distribution of the means of small samples








LO2 Be able to select data,

2.1
select and group sample data based on variable


construct process control



inspection and attributable inspection and calculate


charts and initiate a control



appropriate control chart limits


program for a specified

2.2
construct control charts for variables, rejects per unit


application






and percentage defectives per batch










2.3
initiate a control program for a specified application







LO3 Be able to evaluate process

3.1
describe process capability



capability against a given

3.2
investigate the purpose of modified control chart limits



product or component










quality requirement using

3.3
evaluate processes against a given quality requirement



modified control chart limits











LO4 Be able to analyse types of

4.1
analyse a range of processes for types of variation



variation within a process

4.2
record information on variation from a process.



and record information on










that variation



















Guidance



Links

This unit may be delivered individually or as part of a wider project with other relevant production-based units.

The unit can also be linked to the SEMTA Level 4 National Occupational Standards in Business Improvement Techniques, particularly Unit 14: Carrying Out Statistical Process Control Procedures (SPC).

Essential requirements

There are no essential requirements for this unit.


Employer engagement and vocational contexts

Industry links could provide access to alternative resource facilities and learners who are not in work-based settings should have the opportunity to visit industrial organisations to gain knowledge and experience of process control and its function within the total quality system.









Comments