Discussion

This chapter provides a general discussion to the thesis. It also discusses margins from two different perspectives.

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7.1 General Discussion

This thesis argued that margins play an important role across the entire design process. However, margins are not recognised as a unified concept which is clearly communicated and tracked throughout the design process. Rather different people have different notions of margins and do not disclose the rationale behind adding margins or the amount that they have added. This can ultimately lead to products which are more costly to develop than necessary. However, margins also enable designers to avoid design changes as they know the extent to which existing components and systems can accommodate new requirements and thereby saving significant design time. Hence, having a clear picture of the state of the margins on component parameters, together with managing the ways that requirements are met as a product is developed, are important aspects of product development. Understanding margins will be of a great benefit to the company to cope with product optimisation without compromising the platform strategy. Therefore, how well a manufacturing company is able to understand the margins of their design concepts is crucial in successfully dealing with changes that occurs throughout the development process.

Margins are a combination of buffers built into a design to cater for uncertainty and excess which is a genuine surplus in a component, system or design. While different notions of margins favour one or other aspects, it becomes clear that both aspects have to be looked together. As the excess part of a margin provides design flexibility, designers can try to reduce uncertainty, for example by reducing the variability in use, to move parts of the buffer element of the margin into a useable excess.

At a general level, the work presented in this thesis has helped define the concept of design margins. As was described in Chapter 2, there are relatively few publications on the topic and what has been published is usually unlinked and only focuses on specific aspect of margins such

as performance margins. There are very limit references in the available literature that have examined design margins in companies in detail or addressed the concept from a process view. This thesis redresses this by reporting upon an empirical study carried out in Volvo GTT. One of the findings from this study was that there is a clear industrial need for support with design margins and how they are communicated in teams or across teams. An explorative process method grounded in the needs of industry has been proposed to model design margins. The method focused on understanding the product and the connections among different parts in order to capture margins and the role they play throughout the product development process. Without understanding the details of a product, it is difficult to predict its exact behaviour or understand the margins associated to key components or systems.

Margins on key parameters can apply to the whole system, such as the engine design temperature, or as margins for specific parameters, like the temperature a material can handle. Another important group of margins to capture are those on critical components where a company knows that they will not be able to absorb change. However, if they are aware they might be able to compensate through making fundamentally different design choices. These design considerations are highly relevant where alternative configurations and variants are considered, with princely different margins behaviour. This critical margin information can be flagged up and shared across an organisation.

7.2 Knowing and communicating margins

Generally, designers have a sense of the margins some key components have, rather than knowing an explicit value of margins they had a sense of whether their component would be able to absorb more change or be able to be changed easily without requiring a major redesign.

168 However, this knowledge is usually not recorded explicitly. The product planners and designers in the early phases of a new product did not know to which extent a component could still be changed. The designers in later stages where usually not aware that margins have been added to the requirement or had little sense of how much margin was added.

Margins are not communicated explicitly across the organisation, but become part of the discourse in informal negotiations within the company. Some critical margins are flagged up as part of concerns for the longevity of the product, but large margins are often left uncommented. As designers are often aware of the state of the margins of their own components, they often try to protect components with critical margin in the design process from changes. One way of doing this by embedding the parameter values deeply in the sequence in which dependent decisions are being made, so that they parameters and their components cannot be changed without undoing a large part of the design process. For example much of a product in the case study is designed around the harmonic frequencies. If these are changed most components would need to be altered, therefore values from which the harmonic frequencies are derived usually remain unchanged.

7.3 Designing margins into the product

Some major systems are designed explicitly so that a system does not have to be redesigned in the next product generation. For example, the truck company recently redesigned their wiring harness and created a new harness with several unused ports in the expectation of needing them in a future product generation. In this example, the margins are clearly visible to everybody including the customers, as the additional cost is minimal for the current generation but with a clear advantage in the future.

Designers can take active design act steps to generate margins within a product. The obvious one is to overdesign a system or component and thereby generating an excess that can be used up in future changes. This does not mean that all parts of a system are overdesigned, rather than that an engineer designs or redesigns specific components so that the overall system has a greater flexibility. For example, if a system is getting too heavy, it might be enough to redesign one component to make it substantially lighter to a give the whole system a weight margin that they can use for future changes. Usually this can only be justified if there is an immediate benefit for the current system.

Sometimes the design itself can be flexible so that it can be used in different contexts without requiring a change. A simple example is that the engineers designed a fixing where screws where screwed into slides rather can holes, so that they could be moved around without needing to add additional holes. Similar decisions can be taken about far more complex components. In fact, some of the motivation between a move from hardware to software comes from a need for increased flexibility.

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