Design for Manufacture and Assembly

In today’s environment manufacturing businesses are facing fierce competition and operating in changing markets. Customer demands for higher quality products at lower costs and shorter product lifecycles are putting additional pressure on the product introduction process.

Cost and quality are essentially designed into products (or not!) in the early stages of the product introduction process. The designer has the great responsibility of ensuring that the product will conform to customer requirements, comply with specification, and ensure quality in every aspect of the product, including its manufacture and assembly, all within compressed time-scales. The company that waits until the product is at the end of the line to measure its conformity, performance and cost will not be competitive. The need to understand and quantify the consequences of design decisions on product manufacture and quality has never been greater.

There is extensive evidence to show that products are often being designed with far too many parts and with complex assembly and manufacturing requirements. It has been found that more than 50% of product development effort can be wasted on rework and it is not uncommon for manufacturing operations to have a “cost of quality” equal to 25% of total sales revenues. Even Fortune 500 quality leaders face intimidating quality losses.

Why do businesses continually face such difficulties? The costs ‘fixed’ at the planning and design stages in product development are between 60 to 85%, while the costs actually incurred at that stage range from only 5 to 7%. Therefore, the more problems prevented early on, through careful design, the fewer problems that have to be corrected later when they are difficult and expensive to change. However, to achieve this it is necessary to reduce the ‘gap in the knowledge’ between design and manufacture.

Competitive Product Introduction and Techniques in DFM

Experience in the introduction of new products over many years has indicated the need to adopt a concurrent engineering approach in new product development, undertaken by enterprise-wide teams, within a professionally managed product introduction process and supported by Design for Manufacture (DFM) tools and techniques. The application of DFM tools and techniques that quantify manufacturing and assembly problems and identify opportunities for redesign are the major means available for bridging the knowledge gap. It has been found that DFM analysis and its problem identification leads to innovative design solutions where considerable benefits accrue including functional performance and large savings in manufacturing and assembly cost. Design for Assembly (DFA) is particularly powerful in this connection and is probably the single most valuable product introduction technique.

Although the use of design for manufacture and assembly techniques requires additional up-front effort when compared with the more conventional design activity, overall the effect is to reduce the time-to-market quite considerably. This is primarily due to fewer engineering changes, fewer parts to detail, document and plan, and a less complex product with good assembly and manufacturing characteristics.

Business Benefits

Very substantial reductions in part count and component manufacture and assembly costs have resulted from using DFM techniques in product development teams. The results of sixty documented applications, carried out recently in a wide variety of industries, show that the average part count reduction was almost 48% and the assembly cost saving was 45%.

The Design for Manufacture and Assembly module in the Executive Masters in Manufacturing Leadership programme at the University of Leeds presents the theoretical considerations and assumptions underpinning the quantitative methods in DFMA used in the above studies. It introduces methods for part-count analysis, assembly sequence design, and the analysis of component fitting, handing and manufacturing processes. Techniques to support innovative product redesign are also covered. Lectures and tutorials provide the students with the knowledge and skills necessary to apply the methods in the product design process. The knowledge gained is further developed through a team-based case study involving the analysis and redesign of an industrial product, and including an assessment of the risks associated with the design changes proposed. In carrying out tutorial examples and the team-based case study the delegates will learn to the use the DFMA technique given in reference (9), and appreciate first hand the benefits that can be obtained.

Sources

1.Brown et al. Manufacturability in the Designers’ Sandpit, Proc. IMechE Vol. 221 Part B J. Engineering Manufacture, 2007
2.Boothroyd G, Dewhurst P. Product Design For Assembly, Boothroyd Dewhurst, Wakefield, Rhode Island, USA 1989
3.Miyakawa S, Ohashi T. “The Hitachi Assemblability Evaluation Method”, Proceedings International Conference on Product Design For Assembly, Newport, RI, 1986
4.Parker, A. New Product Development, Manufacturing Engineer, 76 (6), 1997 pp 267 – 271
5.Myrup, M, Design for Quality, Institute for Engineering Design, Technical University of Denmark, PhD Thesis IK pub 93.134A (1993)
6.Fabrycky, WJ, Modeling and Indirect Experimentation in System Design and Evaluation. Journal of NCOSE, 1 (1), 1994 pp 133-144
7.Miles, BL and Swift, KG. Design for Manufacture and Assembly, Manufacturing Engineer, 77 (5), 1998 pp 221-225
8.Boothroyd, G., Product Design for Manufacture and assembly, CADJ 26 (7), 1994 pp 505-519
9.Swift, KG and Brown, NA. Designers’ Sandpit DFA/DFM Workbook, University of Hull (2005)