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The single machine approach can also be applied to selected machines or processes

within a GT cell, this is incorporated once the general family is known and toolingand fixturing is at a stage where it can be rationalised.

Ideally within this environment ‘line flow’ layout cells are preferred. It is alsointerested to note that some companies also have ‘functional’ layout cells containing

small numbers of similar work centre types.

The families of parts or assemblies chosen can be design or production based (Figure

8 and Figure 9, from [4]).

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2.1 Choosing Cells

Cells can be chosen in a number of ways depending on the data available, the productmix and the company’s requirements.

Three main methods exist as described:

(a)

Empirically or by eye – for a simple product or component mix some geometric

or manufacturing families are obvious.

(b) Using a classification code (see Figures 10 [5] and 11 [3]). Part geometry,

manufacturing method or both can be classified and codes sorted to determine the

preferred part families.


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(c) Using component process plans. A typical process plan showing the relevant

information required for GT analysis is shown in Figure 12 [3].

Information relating to future product requirements is also necessary. This enables

capacity requirements for both human and production resources to be determined.

One of the most common analytical techniques applied in this area is ‘Production

Flow Analysis (PFA)’. This is a progressive analysis based on the application of five

sub-techniques. These are outlined in Figure 13 (adapted from [1]).

Within this approach there is a drive towards flow based manufacturing. PFA can be

carried out manually; however, group analysis in particular lends itself to

computerisation. An example of a manual analysis is illustrated in Figure 14.

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This can become very difficult when the number of process plans analysed increasesto more than, say, one hundred. Computerisation can certainly carry out the process

much more quickly and accurately (Figure 15 [3]), cluster analysis, etc. is possible(see [4]).


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3.0 Advanced Manufacturing Technology and GT

The introduction and utilisation of NC machine tools within a cellular manufacturing

environment helps enhance the GT layout. They act as key work centres serving

secondary machines or processes where required. The same may also apply to robotic

systems feeding manual assembly environments.

A number of operational factors relating to NC machine tools are also relevant to GT,e.g. standardising tooling and fixturing, combining more than one operation into one

set up, increasing throughput and productivity, enabling the manufacture of more

general component families, enhancing any existing ‘design for manufacturing’(DFM) policy.

In the GT context secondary or support work centres must be placed nearby the main

NC machine tools, as they are great work generators. Examples of some typical NC

cell layouts are given in Figure 16.

As product families, tooling and set-ups are standardised and the number ofoperations required decrease, cell systems can be extended in a number of ways:(a)

by introducing automated work handling;

(b) by fitting machines with large standard tooling magazines;

(c) quicker generation of NC machine control data;(d)

standardising on production sequences;

(e) introducing DNC (direct or distributed numerical control);(f)

computerising production control and scheduling procedures.

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Indeed, it was the application of many of these developments to cellular layout which

eventually caused GT systems to evolve into flexible manufacturing systems (FMS)and flexible manufacturing cells (FMC). However, not every company can afford

or justify these modern systems, therefore traditional GT applications are just as

relevant to modern manufacturing facilities.

The flexibilities of various types of manufacturing processes are illustrated

traditionally pre-1990s as shown in Figure 17 (adapted from [7]. As the production

volume increases the trend is towards special purpose machines or processes.


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REFERENCES

(1)

‘The Introduction of Group Technology’

John L BurbidgeHeinemann (1975)

(2) ‘The Scientific Principles of Group Technology’S P Mitrofanov (University of Leningrad)

British National Lending Library (1986) – Translation

(3)

‘The Development of a New Cellular Manufacturing Analysis Technique

and its Application within an Engineering Company’

James M Ritchie

MSc Thesis, Heriot-Watt University (1984)

(4) ‘Group Technology Production Methods in Manufacture’C C Gallagher, W A Knight

Ellis Horwood (1986)

(5)

‘MICLASS Instruction Manual’, MICLASS Ltd., 1993.

(6)

‘Group Technology in the Engineering Industry’

John L Burbidge

MEP, 1979

(7) ‘Manufacturing Technology: Volume 2’R L Timings and S P Wilkinson

Longman, 2000

(8)

‘Manufacturing Engineering and Technology’S Kalpakjian

Addison-Wesley, 1985.

FIGURE 20

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Production Layout Final v2