Impact of Late Design Changes - Six Sigma

Design change proile. (Adapted from Yang and El-Haik, 2003)

Figure is a conceptual plot of how typical and successful companies implement design changes through the product life cycle. Common practice companies tend to start a programme with minimal resources and consequently implement design changes at a low rate until the start of the development phase when prototypes are tested. This is also the time at which full financial approval is given to the project, and the rate of design changes increases until it peaks just short of production when it is too late to make further changes.

However, shortly after the start of production it is realised that there are some changes that are absolutely essential, as shown by the second, slightly lower peak of design activity. This late attempt to get the product right drops of quite quickly because the expense involved means that only the essential changes are justified. In contrast, the best practice company quickly ramps up its design effort by employing multi - disciplinary teams very soon after project start.

As the development phase approaches, the best practice team is experiencing a decreasing rate of design changes. Development is undertaken to prove the design changes made during the previous phase and well before production commences, design activity comes to an end. From previous discussion it can be seen that the cost of design changes to the best practice company is considerably less than for common practice companies. Also, although Figure is shown with a single timescale, the improved right first time rate for the best practice company will enable it to develop products quicker. This diagram is not meant to state that best practice companies never make design changes during the production and in - service phases of a products life; it is a conceptual plot in which the scale of design changes during these phases is so low compared to our performance, that they could be represented by a line co-incident with the x-axis.

Many Western organisations have long recognised the need to increase the up - front effort, thereby improving product quality and reducing the need for large product support functions. The transition phase from old to new - style project management is deficit because products still in service have to be supported while the organisation tries to increase the size and capability of the design function, and usually this has to be attempted without any net increase in the organisations personnel. One of the options that the organisation must consider is to market fewer products during the transition period, but those projects that do gain approval are conducted with a steadfast commitment to early design changes.

It is worth noting that both the ‘good’ and ‘bad’ approaches described above are reinforcing cycles; as long as the existing products have problems to be fixed it will draw resource away from new products, leading to a poor upfront design effort, leading to error and so on. Similarly if we put the right effort in up front we should avoid problems and thus have resource available for future projects.


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