Design margins: a hidden issue in industry

Abstract

In complex products the values of parameters are rarely exactly the required values, rather they often have a margin that might be designed in deliberately or be the incidental results of other design decisions. These margins play a critical role in design processes in managing engineering change and iteration. While engineers often talk about margins informally, designers and researchers also use other terms for specific margin concepts. This paper reviews the existing literature on related concepts and defines margins formally. It discusses the role margins play in handling uncertainty by distinguishing between buffer and excess. Buffer deals with uncertainty and excess with the remaining overcapacity of the design. Buffer can transition into excess of the design solution if the uncertainty can be reduced. The concepts are applied to the temperature margins of several candidate materials for a non-rotary jet engine component. This shows that a clear understanding of margins can help a company to select design alternatives.

Designing as playing games of make-believe

“…This section discusses designing components of jet engines at a second-tier aerospace supplier in terms of games of make-believe. This example draws on research on how design margins (the amounts by which design parameters exceed their requirements) can drive the dynamics of design iteration, carried out by one of the authors of this paper with a co-author who has worked for many years as a jet engine engineer; the research included interviews with a number of working engineers on margins in jet engine design (Eckert et al 2014(Eckert et al , 2019. It is therefore an illustrative reinterpretation of an existing case study.…”

“…It argues that the notion of games of make-believe (derived from the ideas of Walton (1990)) explicates what designers are doing when they make and discard assumptions to handle the complexity of large-scale design projects and, in particular, how these assumptions are coordinated across large design teams. It illustrates some of its points with an example, the development of non-rotary components of a jet engine, drawing on one of the authors' research on design margins (Eckert, Isaksson & Earl 2014, 2019.…”

An Assumption Network-Based Approach to Support Margin Allocation and Management

“…However, the uncertainty inherent in the assumptions constitutes a risk that has to be mitigated, especially at early-stage design where about 70% of the budget is committed (INCOSE, 2015). In this regard, design margins are traditionally assigned as a risk mitigation strategy in order to account for the different uncertainties in addition to providing flexibility (Eckert et al, 2019). Although the current systems engineering processes (e.g.…”

Models of Margin: From the Mathematical Formulation to an Operational Implementation

“…In these contexts, engineers keep using margins to ensure the reliability of the models, the simulations and the system in general. How-ever, the margins are often implicit or hidden, as they are not monitored [2]. Thus, they cannot be used as indicators to characterize the system.…”

“…To address this problem, some recent works, such as [2], focused on laying the theoretical foundation of the concept of margin in design science. In order to rigorously formulate problems on margins, independently from the engineering field or modeling practice, we proposed a formal mathematical framework to define margins in [3].…”