Written by Muqi Wulan.
The material provides the information on design for manufacture (DFM) at Level 2. Before starting this content, it would be better to have gone through the DFA materials at L1 and L2.
Why are DFM and DFA needed?
Manufacture means, by certain processes and tools, to transform raw materials and convert the design of the desired product into physical reality in an efficient way (El Wakil 1998: 1). Traditionally design and manufacture were divided into separate functions in developing a product. The attitude of designers towards manufacture was “we design it, you build it”. This situation was described as “over-the-wall” shown in Figure 1 (Boothroyd, Dewhurst & Knight 2011: 9). Therefore the lack of early involvement of manufacturing engineers and their interaction with the product designers resulted in bad products, and late market release (Pugh 1991: 136).
Figure 1 – Over-the-wall design
Design for manufacture and assembly (DFMA) is a systematic approach to avoid the schism between design and manufacture, and enable integrating the considerations of manufacture and assembly into product design. Design for manufacture (DFM) means the design for the ease of manufacture of the collection of parts that form the product after assembly. Design for assembly (DFA) means the design of the product for the ease of assembly (Boothroyd, Dewhurst & Knight 2011: 1).
Roles of DFM and DFA in product design
Figure 2 summarises the steps taken when using DFM and DFA during design. “DFA analysis is conducted first, leading to a simplification of the product structure. Then, early cost estimates for the parts are obtained for both the original design and the new design in order to make trade-off decisions. During this process, the best materials and processes to be used for the parts are considered. For example, would it be better to manufacture a cover from plastic or sheet metal? Once the materials and processes have been finally selected, a more thorough analysis for DFM can be carried out for the detail design of the parts”. (Boothroyd 1996: 21)
Figure 2 – DFMA used in product design and manufacture
Design for manufacture (DFM)
DFM concerns the cost and difficulty of making a product. So it aims to minimise component and assembly cost, minimise development cycles, and enable high-quality products to be made. In DFM there are two aspects to be considered (Pugh 1991: 137):
• Design for assembly (DFA);
• Design for piece-part producibility (DFP).
As to the information on DFA, please refer to the materials provided under the topic of DFA.
Design for piece-part producibility (DFP)
Due to many different types of manufacturing processes for making piece-parts, DFP is more complicated than DFA. The essential part of DFP is the early selection of process and material combinations for the manufacture of parts at the stage of product design.
Choosing appropriate processes for making a particular part is based on a matching of the required attributes and the various process capabilities. Once the overall function of a part is determined, its engineering attributes can be formulated giving geometrical features and material properties with other required attributes. Most piece-parts are not produced by a single process, but a sequence of diverse processes is required to achieve all the engineering attributes of the part. The sequence of processes has a natural order of shape generation, followed by feature addition or refinement by material removal and then material property or surface enhancement. So processes are categorised as (Boothroyd, Dewhurst & Knight 2011: 31):
• Primary processes – forming and shaping processes like casting, forging, injection moulding, and so on.
• Primary/secondary process – generating the main shape of the part, form features on the part. Material removal processes are included such as machining, grinding and broaching.
• Tertiary process – finishing processes such as surface treatment and heat treatment. They do not affect the geometry of the part which is produced from primary and primary/secondary processes.
Figure 3 shows the available combinations for a selected range of processes and material types. We can see that many processes and materials are not compatible.
Figure 3 – Compatibility between processes and materials (Boothroyd, Dewhurst & Knight 2011: 33)
Summary
The objective of design for manufacture (DFM) is to integrate manufacturing knowledge into product design, lower the production cost, and deliver high-quality products. DFM can be achieved through design for assembly (DFA) and design for piece-part producibilty (DFP). DFA is the design for the easy and low-cost assembly. Compared to DFA, DFM is more diverse and closely related to the selection of adequate processes and materials for manufacturing the parts.
Selected References
Boothroyd, G. (1996) ‘Design for manufacture and assembly: the Boothroyd-Dewhurst experience’. in Design for X: concurrent engineering imperatives. ed. by Huang, G. Q. London: Chapman & Hall
Boothroyd, G., Dewhurst, P., Knight, W. A. (2011) Product design for manufacture and assembly. 3rd edn. Boca Raton: CRC Press, Taylor & Francis Group
El Wakil, S. D. (1998) Processes and design for manufacturing. 2nd edn. Boston: PWS Publishing Company
Pugh, S. (1991) Total design: integrated methods for successful product engineering. Harlow: Pearson Education
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