Introductory Chapter: Overview on Design for Manufacturing and Assembly

1. Introduction

Product design can be defined as a comprehensive process of imagining, ideating, developing, testing and iterating products to solve users’ problems or to address needs in a specific market. The steps of this process are interdependent and should complement each other in order to introduce a successful product. The designers or engineers working on this process have a significant influence on the success of the product. In order to achieve the desired goal, many criteria such as product functions, performance, ergonomics, aesthetics, cost and the launch process must be taken into account by these designers or engineers. With the pandemics, wars and other developments that have blocked logistics routes in the world, especially in the last decade, new criteria have been added, and local sourcing, resilience, agility and production-on-demand subjects started to be considered. While applying many of the criteria listed here contributes to success, ignoring or underestimating them causes the resulting product to have issue(s). In this context, the importance of design for manufacturing and assembly has increased and these guidelines have been implemented by designers and engineers at many steps of the product development process. Moreover, design for manufacturing and assembly rules were included in the concurrent engineering processes, thus saving the total product development time by ensuring that the product development steps were implemented simultaneously instead of a sequential manner. These rules are not only applied in geometric design but are also included as boundary conditions in finite element method, topology optimization and process simulation software. Even though the importance of design for manufacturing and assembly rules has been understood and their application has increased, these rules and related knowledge need to be updated according to emerging manufacturing methods. This book aims to contribute to the required knowledge and, in this context, exhibits the approach to the design of different product groups from a manufacturing perspective.

Design for manufacturing is also known as design for manufacturability and is abbreviated as DFM or DfM. This method simply aims to facilitate the manufacturing, thus reduces the manufacturing times and costs, by changing or refining the product designs. For this process, which is implemented starting from the conceptual design step, product requirements and targeted cost are taken into consideration, and manufacturing methods that can be used to shape the selected product material are investigated [1]. While some products and components can take their final shape with only one manufacturing method, in others it may be necessary to apply more than one method sequentially and/or simultaneously [2]. Regardless of the situation for the related product, as the first step of design for manufacturing, all necessary manufacturing processes must be understood, and their limitations must be revealed [3]. For this appreciation, the designer can refer to the literature on the subject or consult experts in related manufacturing methods. Or alternatively, process modelling software can be utilised, and simulations can be performed.

After understanding the relevant manufacturing method or methods and revealing their limitations, necessary changes are made in the product design. For the current state-of-the-art, design for manufacturing rules is readily available for conventional manufacturing methods like casting, forming, forging, injection moulding, joining and machining [4].

On the other hand, design for manufacturing rules for emerging methods like additive manufacturing is still being developed. While it is still beneficial for design for manufacturing to understand the limitations of additive manufacturing methods, further considerations are needed and improved functionality opportunities should be taken into account such as assembly consolidation, embedded channels/cavities or lightweighting [5]. In addition to these, limitations can be dissimilar to the conventional manufacturing methods and new aspects like minimum wall thickness, minimum hole/cylinder sizes, minimum gap width, the need for support structures and their types and sizes might need to be deliberated [6]. Two different test artefacts are shown in Figure 1 for the evaluation of hole/boss sizes and stair-stepping effect.

Figure 1.

Design for additive manufacturing test artefacts to understand the limitations: (a) hole and boss test artefacts [7], (b) stair-stepping effect test artefact [8].

In contrast to design for manufacturing, design for assembly rules might be followed to reduce assembly costs and one of the common practices of design for assembly is to make the product integral and combine several sub-components so that the number of assembly operations is reduced. This approach may obviously lead to complex product geometries and increased manufacturing costs. Because of this reason, design for manufacturing and assembly are performed simultaneously and in this way the conflict between two mindsets can be avoided. If the integrated design approach is not followed or not fully adopted, other aspects can be visited to ease the assembling of components. In this respect, decreasing the number of manufacturing operations for each product can be aimed. One of the typical practices to be followed is to use snap-fit designs and to reduce the need for screw/nut type fasteners so that drill or tapping operations are not needed. While this is possible for injection moulded parts, attention should be taken and the reverse angles of snap-fit joints should be design in a way to avoid the need of additional mould cores or inserts.

Focusing on different engineering and manufacturing problems, this book will help students, engineers, designers and professionals to understand the potential of design for manufacturing early in the product design.