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Gerhard Pahl and Wolfgang Beitzʹs

Theory of Systematic Engineering Design & Practice

Synopsis

The need for a systematic approach

The design of complex, complicated or a family of products is usually beyond theintuitive skills alone of a designer or design team. Gerhard Pahl and Wolfgang Beitz[1] have set out a strategy for the development of solutions which aims to increasethe probability of technical and economic success of product design. This is done by

creating a dependable approach which allows careful planning and systematicexecution so that the whole design task reduces to a logical and comprehensibleexercise and also allows recovery from inevitable errors. It also  allocates a timeschedule for the design stages which in turn leads to a predictable projecttimetable. Systematic design is general enough to be applied in any branch of engineering.

However they have not recommended that this method be automatically applied  toall designs nor all aspects of a design. Work should never be done just for the sakeof being systematic or for pedantic reasons. This is because tasks and problemswill differ from product to product and also designers will have variousbackgrounds, experience, skill and preferences. Therefore a des igner shouldassess the situation they are faced with and choose their own appropriate methodfor any particular design step. The authors also do not discount the role of 

inventiveness and intuition in developing solutions. Complex task s are solved onestep at a time and in each such step a designer has to find a balance between thesystematic and the intuitive. Also intuitive inventiveness is one way technical oreconomic advantage can be introduced into products.

Wallace and Blessing [2] lend some perspective to systematic design by noting twocontrasting ways in which design can be approached. The systematic generation of solutions set out by Pahl and Beitz is a problem-orientated approach and this isfavoured in central Europe. In contrast, in the UK and the USA, a more product-oriented approach is evident in which an initial product idea is continuallyelaborated during the design process.

The steps which make up systematic design

Pahl and Beitz divided their method into a number of broad phases, each with a setof basic steps.

1. Start off with product planning and a clarification of the task 

1.1 Clarify the task and build out the specification and requirements

The specification as presented to the designer may not be comprehensive andoften will require clarification and additional information. The designer will alsoneed to determine the clear aims which the solution needs to achieve. He or shealso needs to be sure that there will be the requisite commercial motivation andintellectual stimulation to carry the design through to fruition. At the end of thisphase the specification will be fully developed and requirements and constraints

compiled.

2. Conceptual design phase

Before the conceptual design stage is started a decision is needed as to whether aconceptual elaboration is really needed or whether known solutions allow the

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designer to proceed directly to the embodiment and detail design phase. If not,then a conceptual design phase needs to be undertaken.

2.1 Abstract the task to identify the essential problem

 Abstracting the task means describing it in the broadest way. This makes clearwhat the overall function should be. Too narrow a view of the task, or a quick prejudged one, may well lead the designer down a path to a non-optimum solution;one which would ultimately detract from the technical and economic success of theproduct.

2.2 Establish the functional structures

This is both an articulation of the boundaries of the solution (what is in and out of the design) and the functional way in which energy, material and signals(information) flow (are processed or converted) from input to output to meet thespecification. It involves breaking down the overall function into sub-functions untilthe sub-function task becomes clear and simple. In essence, the development of functional structures aims to assist in discovering solutions.

2.3 Search for solution principles

There may be many means and ways in which a solution to a sub-function can beachieved and the designer seeking an optimum technical and economic solution will

need to elaborate a wider rang of possible solutions in order to be able to assessthe comparative merits of each possibility. Pahl and Beitz note that a successfulsolution is more likely to spring from the choice of the most appropriate principlethan an exaggerated concentration on the finer points.

2.4 Combine the solution principles into concept variants

The larger product is built up from smaller solutions proving the sub-functions. As aresult there is likely to be a number of product concepts or variants which can bederived in this way. This development of solution options is the strength of thesystematic approach.

2.5 Evaluation of concept variants using technical and economic criteria

The designer needs to first draw up a set of evaluation criteria and then assess therelative merits of a solution using a bottom up approach starting from the sub-functions which make up each concept variant. In this way a comparative technicaland economic evaluation can be built up for each concept variant and allows adecision to be made as to which particular solution should be manufactured.

 An additional purpose of such an evaluation is to select one or two back-up solutionwhich, while not as cost-effective, could nevertheless be deployed in place of thefirst choice should this turn out to be necessary.

3. Embodiment design

The authors realistically point out that in the embodiment design stage, many

details and will need to be clarified, confirmed or optimised and as this is done itwill become more obvious whether the right solution concept has been chosen. Ona salutary note they comment that no embodiment design can hope to correct apoor solution concept. The final general observation is that the end of theembodiment design is the very latest to which assessment of financial viability of the project can be left.

3.1 Develop a definitive layout and check that the requirements are met

For each concept solution variant the designer will need to determine the layoutwhich will end up being the technical product or system and check that function,strength and spatial compatibility requirements are met.

4. Carry out a detail design

4.1 Detail design

The exploration of options does not finish with a conceptual solution but extends tothe physical realisation of the products. Again the principle of systematic designshould be applied to make the choice of suitable components, materials, forms and

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finishes.

4.2 Documentation

Detail design also includes the production of final design drawings which can beused to manufacture the product. This firms up each possible product conceptsolution into a potentially manufacturable design. At this stage, a designer can saythat they have explored all of the factors which potentially could significantlyimpact on the design, ending up with one or more potentially manufacturabledesigns.

Would all of this take too much time?

Pahl and Beitz note that the steps which they have described in any case will needto be examined at least implicitly as a designer prepares a design. It is thereforemuch better to be systematic about it rather than leave to chance whether or notsome aspect of the design has been properly covered.

Later edition

The third English language edition updates and expands the material covered [3]. Also new chapters have been added on:

mechanical inter-connections,

mechatronics (integration of mechanics, electronics and information technologyto create new and improved products and new ways to produce and assemblethese),

adaptronics (adaptive structures with electronics so the structures continuallyfulfil their task by actively adapting to disturbances and to changes in loading orrequired functionality),

designing for quality, and

designing for minimum cost.

References

[1] G. Pahl and W. Beitz  Engineering Design: A Systematic Approach  Translated by Arnold Pomerans and Ken Wallace,  Edited by Ken Wallace  The Design Council London, 1988  ISBN 0 85072 239x 

Original German Edition  Konstruktionslehre: Handbuch für Stadium und Praxis  Springer-Verlag, 1977

[2] Ken M. Wallace and Luciënne T. M. Blessing  Observations on Some German Contributions to Engineering Design:  In Memory of Professor Wolfgang Beitz

  Research in Engineering Design (2000)

[3] G. Pahl, W. Beitz, J. Feldhusen and K.H. Grote  Engineering Design: A Systematic Approach, Third Edition  Translators and Editors: Ken Wallace and Luciënne T. M. Blessing  Springer-Verlag London Limited, 2007  ISBN-10: 1846283183

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