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ORIGINAL PAPER

The flexibility of manufacturingsystems

Nigel SlackBrunel University, London, UK

Abstract

Purpose Many of the pressures from the manufacturing environment are turning manufacturingmanagers attention to the virtues of developing a flexible manufacturing function. This paper,originally published in 1987, focuses on flexibility in manufacturing.

Design/methodology/approach Assessses how managers in 10 companies view manufacturingflexibility in terms of how they see the contribution of manufacturing flexibility to overall company

performance; what types of flexibility they regard as important; and what their desired degree offlexibility is.

Findings Flexibility has different meanings for different managers and several perfectly legitimatealternative paths exist towards flexible manufacturing. The results of the investigations in these tencompanies are summarised in the form of ten empirical observations. Based on these observationsa check-list of prescriptions is presented and a hierarchical framework developed into which thevarious issues raised by the observations can be incorporated.

Originality/value Provides a focus on flexibility in manufacturing, as determined in 1987.

Keywords Flexible manufacturing systems, Manufacturing industries

Paper type Conceptual paper

IntroductionFlexibility is fashionable. As customers demand faster response and a wider variety ofupdated products and as competitors achieve levels of performance above that whichwas considered feasible a few years ago flexibility, above all other measures ofmanufacturing performance, is cited as a solution. More flexibility in manufacturingoperations, it is held, means more ability to move with customer needs, respond tocompetitive pressures and be closer to the market. Yet for all its new found popularity,flexibility seems to be the least understood of manufacturing objectives; the very wordflexibility is used by different managers to mean different things.

The literature on manufacturing flexibility treated as a broad managementobjective, is sparse. Zelenovic (1982), Buzacott (1982), Gerwin (1982) and Slack (1983),

amongst others, all developed some form of flexibility typology. Adler (1985) providesan excellent summary of the work on flexibility classifications and some of theemergent issues, while Gerwin (1983) and Graham (1986) develop methodologies for alimited comparison of the flexibility of alternative manufacturing systems. As yet,though, no totally satisfactory methods exist for assessing a companys flexibilityneeds, auditing its flexibility capability or (perhaps of most immediate use) evaluating

The Emerald Research Register for this journal is available at The current issue and full text archive of this journal is available at

www.emeraldinsight.com/researchregister www.emeraldinsight.com/0144-3577.htm

This paper was first published in IJOPMVolume 7 Issue 4 (1987) pp. 35-45. It has been includedhere as part of the 25th anniversary issue of the journal.

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International Journal of Operations &

Production Management

Vol. 25 No. 12, 2005

pp. 1190-1200

q Emerald Group Publishing Limited

0144-3577

DOI 10.1108/01443570510633594


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in a broad sense change or in-vestment proposals involving the enhanced flexibility ofproduction systems.

The intention of this article is to take the area at least one step further towards anevaluative procedure by contributing in two ways to the growing debate on the

importance, nature and analysis of manufacturing flexibility. It presents:(1) the results of a study which sought managers views on manufacturing

flexibility; and

(2) an hierarchical framework which can be used for conceptualising and analysingthe flexibility needs of manufacturing organisations.

Managers perceptions of manufacturing flexibilityA study was made of how managers view the flexibility of their manufacturingsystems. It was not intended to be a comprehensive survey, rather it was intended toprovide an empirical basis for the development of a framework useful for the analysisof broad manufacturing flexibility. More especially it had the objective of developingpropositions relating to a number of issues, namely:

. Was flexibility regarded as intrinsically desirable under all or mostcircumstances, or was it viewed as an attribute of the production systemuseful only under certain circumstances?

. Where flexibility was regarded as important, why was it so regarded?

. What types of flexibility were recognised, and which were seen as beingimportant?

. How was the desirable degree of flexibility articulated, assessed or informallyjudged?

. How (if at all) was flexibility formally evaluated, for example for capital

budgeting purposes?

Ten manufacturing organisations were studied. Three of these were in theprocess/mass production area, three were mass/batch producers of consumerdurables, one a large batch producer of industrial products and three werebatch/jobbing producers of industrial products. Depending on the companysmanagement structure and the availability of key executives, several managers ineach company were interviewed. In all cases the manufacturing director, worksmanager or whoever bore overall responsibility for the manufacturing function wasinterviewed. Also interviewed, where possible, were other managers in the broadmanufacturing area, for example engineering, production control, industrialengineering and quality control. In addition, senior managers outside the

manufacturing area were questioned in all of the companies visited. Usually theseincluded the Chief Executive Officer (CEO) and the Marketing Director and, in six ofthe companies, either the Purchasing or Personnel Managers or both.

The interviews were conducted on an informal basis although the same topics wereraised, usually in a similar sequence, in all cases. These roughly corresponded with thepreviously described research objectives. In all but two of the organisations some of theinterviewees were given notice of the subject of the discussion and the type ofquestions which would be raised.

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The results 10 observations on manufacturing flexibilityGiven such a small sample and a wide spread of companies, and given the relativelyloose methodology of the investigation no definitive conclusions can be drawn; but thiswas never the intention. What did emerge were several generalisations about how

managers view manufacturing flexibility. These can be summarised in the form of tenobservations which will be used later to develop a framework for manufacturingflexibility.

Observation 1. Managers had a partial rather than a comprehensive view ofmanufacturing flexibilityThere was a tendency amongst most managers to restrict their perception of flexibilityin two ways. First, most managers focused more on flexibility as it applied to theindividual resources of manufacture as opposed to the flexibility of the productionsystem as a whole (Figure 1).

Using Buzacotts distinction Buzacott (1982), they focused on machine rather thansystem flexibility Gerwin draws a similar distinction Gerwin (1982). This tendencywas especially marked amongst managers in the production function below directorlevel, where there seemed to be little voluntary discussion of how resource flexibilitycontributed to the overall performance of the manufacturing function. The managerswho were least likely to discuss flexibility exclusively at the individual resource levelwere those in the marketing area (and to a slightly lesser extent the CEOs) who oftenactively sought system flexibility as a solution to unpredictable market conditions.Second, not only was perception frequently limited to the resource level but also it oftenfocused exclusively on one particular resource. So flexibility was synonymous withmachine flexibility or alternatively labour flexibility in many managersvocabulary.

Figure 1.

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Observation 2. Different types of manufacturing are concerned with the flexibility ofdifferent resourcesAcross all companies there was a tendency to concentrate on flexibility at the resourcerather than the system level. Amongst the companies studied, this tendency was most

marked in the jobbing/batch manufacturers for whom flexibility equated withmachine flexibility, and for process manufacturers where flexibility usually meantlabour flexibility. Companies in the batch/mass production area seemed toconcentrate either on machine flexibility or alternatively both machine and labourflexibility. In only one company was the issue of infrastructural flexibility raised; thisin relation to the ability of the companys production control system to rescheduleproduction at short notice.

Observation 3. At the total manufacturing system level, managers identify four maintypes of flexibilityWhen managers volunteered views on system flexibility or when discussion was thus

guided, four distinct types of flexibility emerged as important.(1) Product flexibility: the ability to introduce novel products, or to modify existing

ones.

(2) Mix flexibility: the ability to change the range of products made within a giventime period.

(3) Volume flexibility: the ability to change the level of aggregated output.

(4) Delivery flexibility: the ability to change planned or assumed delivery dates.

These types are similar to a previously published typology Slack (1983) with theomission of quality flexibility the ability to change planned product quality levels.No support was found in the sample for the idea that companies might want to vary the

quality of their products improve maybe, but not vary.

Observation 4. Volume flexibility and delivery flexibility have some degree ofinterchangeability determined by the type of manufacturing systemAll the companies studied were concerned with mix flexibility and product flexibilitybut volume and delivery flexibility seemed to be interchangeable to some extent.Process and mass producers were more concerned with volume flexibility whereasbatch and especially jobbing companies were more concerned with delivery flexibility.The various functional managers interest in the types of flexibility was predictable;product engineers focused on product flexibility, process and industrial engineers onmix flexibility and production controllers on volume and/or delivery flexibility.

Marketing, purchasing and general managers were interested in all four types.

Observation 5. Managers seek to limit the need to be flexibleManagers questioned in the study did not usually regard flexibility as something to bepromoted indiscriminately throughout the production system. In fact, they seemed totry and reduce the need for flexibility by using one or more of three broad strategies,controlling the external stance, controlling the internal need generally, and confiningthe internal need to a limited part of the manufacturing system:


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. Moving the companys (external) market stance towards competing on anon-flexible basis involved, for example, adopting strict limits on product range,attempting to stabilise demand fluctuations or discouraging frequent productionmodifications.

. Reducing the overall (internal) need for flexibility throughout the organisationinvolved, for example, adopting modular product design principles or making forstock rather than following demand variations.

. Confining the need for flexibility to selected parts of the manufacturing systemusually involved matching market segmentation with segmentation of theproduction system often to restrict a significant proportion of the product rangeto a limited part of the manufacturing system.

Observation 6. Managers accept that the word flexibility is used in two senses to meanrange and to mean responseThere was widespread support in the organisations studied for the differentiation

between these distinct dimensions of flexibility. It had been suggested previously(Slack 1983) that flexibility has two dimensions. One dimension involves the range ofstates a production system can adopt. Thus one production system is more flexibilethan another if it can exhibit a wider range of states or behaviours, for example, make agreater variety of products, manufacture at different output levels or delivery leadtimes, and so on. However the range of states a production system can adopt does nottotally describe its flexibility. The ease, with which it moves from one state to another,in terms of cost, time or organisational disruption, is also important. A productionsystem which moves quickly, smoothly and cheaply from one state to another shouldbe considered more flexible than a system which can only achieve the same change atgreat cost and/or organisational disruption. Both cost and time can be regarded as thefriction elements of flexibility which constrain the response of the system. They

are the manifestations of the difficulty of making a change.

Observation 7. Differentiating between range and response flexibility helps managers toarticulate their flexibility needsAfter initial discussions with most of the managers interviewed the distinctionbetween range and response flexibility was introduced. The concepts were defined as:

. Range flexibility, the total envelope of capability or range of states which theproduction system or resource is capable of achieving.

. Response flexibility, the ease (in terms of cost, time, or both) with which changescan be made within the capability envelope.

It became clear that failure to distinguish between range and response flexibility was amajor cause of confusion between managers in the same organisation. For example, inone of the sample companies a new flexible machining centre was installed whichconsiderably enhanced the production functions response flexibility (giving majorbenefits in terms of shorter throughput times, lower work in progress, etc.) but whichactually reduced the range of (differently sized) products which the company couldproduce. Not surprisingly the marketing manager could not understand why the newflexible technology seemed less flexible (in terms of range flexibility) than the old

jobbing shop which it had replaced.

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Observation 8. Response flexibility is of more immediate concern to most managers thanrange flexibilityThere was in most organisations a distinct tendency to view response and rangeflexibility as short-term and long-term problems, respectively. In other words, the most

pressing issues of flexibility improvement which could reasonably be resolved in theshort-term were nearly always concerned with improving response, i.e. the time or(more rarely) cost of making changes. So, for example, short-term flexibility problemsincluded machine changeover times, new product lead times, purchasing lead times,limiting volume changes, and so on. Issues of range flexibility on the other hand, wereusually long-term in nature and involved extra or improved resources. For example,the range of products or parts capable of being produced in the manufacturing systemis usually determined by the capabilities of the technology and labour resources in thesystem. Changing the possible range of products means changing or adding to theseresources in the longer term.

Observation 9. Managers see flexibility not as an end in itself but as a means to

other endsSurprisingly the interviews seemed to indicate that managers see little intrinsic meritin flexibility per se, rather that they want to be flexible in order to improve some otheraspect of production. In other words the justification for enhancing flexibility wasusually instrumental, and indeed often expressed in terms of other attributes ofproduction performance. Companies did not see themselves as selling flexibilitydirectly, they considered themselves to be selling what a flexible manufacturingfunction can give. This was usually:

. better product availability, i.e. shorter delivery lead time or a wider orcustomised product range;

. more dependable delivery, i.e. processing the part or product on schedule even in

the face of unreliable supply or uncertain process reliability; and. increased productivity, i.e. better utilisation of process technology, labour or

material resources.

So, flexibility was often judged in terms of how it enhanced other measures ofmanufacturing performance, namely dependability, productivity and availability.

Which of these was regarded as being most important was governed by theperceived competitive position of the company, but also seemed to be stronglyinfluenced by functional responsibility.

Managers on the supply side of companies such as purchasing (suppliers ofmaterial) and personnel (suppliers of labour) managers had a tendency to stressflexibility as an answer to dependability problems. For example in-house

manufacturing capability (mix flexibility) helps to overcome slow vendor response,transferability of labour between departments (labour flexibility) helps cope withtemporary skill shortages and so on.

Manufacturing managers, in the middle of the material chain, were more likely to seeflexibility as contributing to overall productivity. Manufacturing systems which wereflexible were seen as overcoming such problems as,for example,long machine changeovertimes, excessive work in progress, fluctuating demand between product groups and so on,all of which adversly affected resource utilisation and therefore manufacturing cost.


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Sales and marketing managers on the demand side of the company seemed to focuson flexibility as a solution to problems of availability. The major advantages of aflexible manufacturing function were seen as reducing delivery lead times, reducingnew product introduction lead times, the ability to offer customisation, and so on.

It should be stressed that there was not an exclusive preoccupation by any class ofmanager on dependability, productivity or availability alone. Most managers cited allthree justifications but in perceived importance the focus was as described (Figure 2).

Observation 10. The types and dimensions of flexibility which most concernmanufacturing organisations are determined by variety and uncertaintyIt is perhaps traditional to leave the more speculative observations until last, and thisfinal point certainly is presented with less empirical support from the study. However,as well as an intuitive attraction the idea does have some support from the researchdata and was not directly contradicted in any of the sample companies.

In searching for some predictor of which types of flexibility were of interest to the

companies in the sample it seemed that two factors more than any other were at theroot of the need to be flexible. These two factors were:

(1) the variety of products, processes and activities with which the system has tocope; and

(2) the ability of the system to predict the demands on it, i.e. the degree ofuncertainty under which it operates.

Puttick (1980) uses a similar device to categorise manufacturing systems.In the short term, variety in manufacturing operations increases the need to

change the mix of products loaded on the system (mix flexibility response) andthe need to readjust due dates since there are many different due dates

(delivery flexibility response). In the long term the likely product design turbulence

Figure 2.

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increases the need to be able to introduce a wide range of new products (productflexibility range).

High levels of uncertainty in the market mean that in the short term emphasiswill be placed on responding to unexpected changes in demand (volume flexibility

response), introducing new or modified products at short notice (product flexibility response) and rearranging due dates (delivery flexibility response). Longer term, thelikelihood of continued market uncertainty will prompt concern over the limits to howmuch or how little needs to be produced (volume flexibility range), what can beproduced using current technology and labour (mix flexibility range) and by howmuch orders can be expedited (delivery flexibility range).

Figure 3 shows the effect of these two factors. Concurrent high levels both of varietyand uncertainty will presumably result in the whole field of flexibility types beingrelevant.

The ten observations presented above are essentially descriptive in nature even allowing for occasional interpretive lapses by the researcher. It is not toolarge a step however to framing a set of prescriptions useful for any organisationwhich wants to understand its own broad flexibility requirements. Such a listcould be:

. Flexibility is about the ability to change. Think of how the wholemanufacturing system can change what it does, as well as how individualparts of it can change.

. All resources contribute to flexibility. Flexible technology cannot be totallyeffective without flexible labour and vice versa. Neither can be effective without aset of procedures, systems and controls which are themselves capable of copingwith the flexibility of the physical processes.

. Think of flexibility in four areas:

Figure 3.


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(1) introducing product changes;

(2) making different mixes of products;

(3) adjusting the volume of output; and

(4) changing delivery dates.. Not all of these will be equally important. Consider priorities, based on the type

of manufacturing engaged in and the competitive position.

. Flexibility costs money. Try to focus flexibility where it is needed to enhancecompetitiveness.

. Do not make life unnecessarily difficult. It is bad enough that the marketdemands flexibility without bad design, poor communication, lack of focus,excessive routing complexity, with year-end spurts making things even worse.

. Always distinguish between the range and response dimensions of flexibility, i.e.between what changes are possible and how easily they can be made.

. Getting better response flexibility is likely to give immediate benefit, but withoutdecisions on range flexibility resources cannot be effectively developed over thelong term.

. Think of flexibility in terms of how it can improve manufacturing performance especially in terms of dependability of delivery (between different parts of theproduction system or to the customer), productivity of resources, and availabilityof products (either lead time or range).

. If possible, try and separate the parts of the business which have to cope withhigh variety from those which operate under uncertainty. When both cometogether the need for flexibility is maximised.

It is also useful to link some of these ideas together; behind much of the perceived

confusion surrounding manufacturing flexibility is the lack of any model or frameworkwhich links the various aspects and types of flexibility discussed above. In an attemptto provide a suitable framework, a flexibility hierarchy is presented which can be usedto clarify the contribution and role of flexibility in overall manufacturing strategy.The central argument is that flexibility should be considered at four levels.

(1) the production resources themselves;

(2) the tasks which the production function needs to manage;

(3) the overall performance of the production function; and

(4) the competitive performance of the whole company (Figure 4).

Structural and infrastructural resources determine the degree of flexibility (measured

in terms of both range and response) of the four types of manufacturing flexibility atthe task level new product flexibility, mix flexibility, volume flexibility and deliveryflexibility. Enhanced flexibility in these four areas gives better production performancein terms of availability, dependability and productivity. Improved productionperformance in turn increases overall company competitiveness.

The hierarchy is presented not to assess the effect of enhanced production resourceson company competitiveness by working up through the four levels but to help defineguidelines for the development of appropriately flexible production resources by

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working down through the levels. In other words a companys chosen competitiveposition should define the desired levels of availability, dependability andproductivity. This will indicate the necessary range and response characteristics for

the four types of flexibility which in turn will set goals for the development ofappropriately flexible resources.

SummaryManagers views on manufacturing flexibility seem to be partly influenced by theirfunctional responsibilities and partly by their organisational position. However, mostmanagers have only a limited view of their companys flexibility needs. Rarely do theyconsider all the facets of manufacturing flexibility, nor do they recognise that allmanufacturing structural and infrastructural resources contribute to flexibility.

As regards functional responsibility, managers who supply resources to themanufacturing core of the organisation such as personnel and purchasing managersstress flexibility as a means of coping with unplanned disturbance. A flexible

organisation is one, which can accommodate such disturbances and thus ensuredependability of supply. Manufacturing managers see flexibility as an aid to greaterproductivity because flexible resources can be utilised more readily without costpenalties. Managers on the demand side of the organisation see enhanced availabilityof supply, either by widening the range of what can be made or by shortening supplylead time, as being the main benefit of a flexible manufacturing function.

Support was found for a modified version of a previously presented typology offlexibility Slack (1983) with additional observations that response flexibility is largely

Figure 4.The flexibility hierarchy


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a short-term concern and range flexibility a long-term concern. Further it wastentatively suggested that the variety and uncertainty under which a companyoperates will determine the most relevant types of flexibility.

Finally, it is suggested that availability, productivity and dependability be formally

incorporated into a flexibility hierarchy which links overall company competitivenesswith resource level decisions concerning operational flexibility. This hierarchy couldthen form the basis of a procedure for assessing the broad flexibility needs of theorganisation.

References

Adler, P. (1985), Managing flexibility: a selective review of the challenges of managing the newproduction technologies potential for flexibility, A Report to the Organisation forEconomic Cooperation and Development, Stanford University, July.

Buzacott, J.A. (1982), Principles of flexibility in manufacturing systems, Proceedings of the 1stInternational Conference on Flexible Manufacturing Systems.

Gerwin, D. (1982), Dos and donts of computerised manufacture,Harvard Business Review

,March-April.

Gerwin, D. (1983), A Framework for Analysing the Flexibility of Manufacturing Processes, Schoolof Business and Administration, University of Wisconsin, Milwaukee.

Graham, M.B.W. (1986), A tale of two FMSs, in Voss, C. (Ed.), Managing AdvancedManufacturing Technologies, IPS (Publications) Ltd, Thessaloniki.

Puttick, J. (1980), The design of flexible manufacturing systems, B.P.I.C.S. Proceedings.

Slack, N. (1983), Flexibility as a manufacturing objective, International Journal of Operationsand Production Management, Vol. 3 No. 3.

Zelenovic, D.M. (1982), Flexibility: a condition for effective production systems, International Journal of Production Research, Vol. 20 No. 3.

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