G. Boothroyd

Design for Assembly and Disassembly

Summary A review is made of design for assembly (DFA) methods developed over the last fifteen years. It is found that implementation of DFA at the early conceptual stage of design has led to enormous benefits including simplification of products, lower assembly and manufacturing costs, reduced overheads, improved quality and reduced time to market. DFA is now being broadened to include consideration of the difficulty of manufacture of the individual parts to be assembled and is providing the necessary basis for teamwork and simultaneous engineering. More recently, environmental concerns are requiring that disassembly for service and recycling be considered during product design - in fact, total life cycle costs for a product are becoming an essential part of simultaneous engineering. This keynote paper concludes with a discussion of current developments of design for disassembly (DFD).

Design for disassembly and the environment

Abstract The financial and environmental consequences of disassembly and recycling at the end of a products life are studied. Analyses of a small coffee maker and some large domestic appliances are presented. It is shown that redesign proposals resulting from Design for Assembly analysis are compatible with Design for Disassembly and that significant improvements are achievable. It is also shown that optimization of the disassembly sequence is important in order to maximize any financial benefits, but that to minimize environmental impact considerations additional to Design for Disassembly should be taken into account. Criteria to determine the point at which disassembly should cease are discussed

Early cost estimating in product design

Abstract This paper describes product costing procedures which are intended to form the basis for a design analysis method for product design for efficient manufacture (DFM). This DFM method, presently being developed by the writers, will form a logical extension of their design for assembly procedures. Design for efficient manufacture will consist of two steps. The first step is the identification of the appropriate materials and manufacturing processes for the component parts of a new product design. The second step is the detailed design of the individual components consistent with the capabilities and limitations of the material-process combinations. A prerequisite for making sound judgments in the choice of materials and processes is the availability of manufacturing cost information at the early product concept design stage. This implies the need to estimate manufacturing costs before component part designs are fully detailed and without full knowledge of the manufacturing processing plans. Such cost estimates must therefore be based on assumed optimum manufacturing methods irrespective of the processes and equipment which will actually be used. The present paper illustrates this approach for two important manufacturing processes; namely, machining and injection molding.

Design for assembly—The key to design for manufacture

The results of the applications of design for assembly techniques to two typical designs are presented. Consideration is given to the total product cost and it is found that major cost reductions can be achieved even when assembly costs are relatively small. It is also found that assembly automation becomes more difficult to justify as a product design is gradually improved.

Economics of assembly systems

Abstract This paper presents a description of typical assembly systems including manual, special-purpose automatic and programmable assembly systems. For each case, mathematical models are developed to describe economic performance. Comparisons of the economics of the various systems are also made and the future role for programmable assembly robots discussed.

Approximate cost estimates for typical turned parts

Abstract A model is derived for the cost of typical rotational components machined from bar in a CNC turret lathe. It is found that for components having a finished volume greater than 20 cubic inches the work material costs contribute more than 80% to the total component cost. For smaller components, however, the machining costs—particularly the nonproductive costs associated with workpiece handling—become increasingly important. This phenomenon results in rapidly increasing costs per unit weight (or costs per unit volume) for smaller components. It is also found that by using a cost model, such as the one developed here, it is possible to provide information for the product designer who wishes to make trade-off decisions regarding the materials and manufacturing methods for proposed components.

Economics of General-Purpose Assembly Robots

Summary A study of the comparative economics of various automatic assembly systems using general-purpose assembly robots is described. In the study, use is made of a “typical” candidate assembly whose profile is obtained from statistical analysis of actual products submitted by interested companies. It is shown that the choice of assembly system and the various parts presentation methods depends on three main factors, namely: the annual production volume per shift, the number of parts in the product and the equipment payback period.

Assembly times for electrical connections and wire harnesses

This paper presents the results of a study of assembly times for electrical connections and wire harnesses. The various types of electrical connection are described, together with the assembly of wires and wire harnesses. Comparisons are made of the times for the assembly operations associated with each type of connection, obtained from a variety of sources. From these comparisons, estimates are made of average or recommended assembly times. Finally, the recommended times are presented in the form of classification schemes for use by designers during the early stages of design.

Research program on the selection of materials and processes for component parts

It is now widely accepted that the final cost of a manufactured product is largely determined at the design stage. The research programme described in this paper addresses decisions that must be made early in the design procedure, namely the selection of suitable processes and materials for the proposed component parts of the product. Generally, designers will tend to conceive parts in terms of the processes and materials with which they are familiar and may, as a consequence, exclude from consideration process and process/material combinations that may have proved more economic.A satisfactory method for the systematic selection of suitable process/material combinations for part manufacture is not currently available. Such a method is being developed and implemented in a computer environment for use during the early stages of product design.

Automatic Handling of Parts for Robot Assembly

Summary It is now widely recognized that one of the main obstacles to the economic application of robots in batch assembly work is the lack of flexible parts presentation devices. Current research in the Robot Assembly Laboratory at the University of Massachusetts demonstrates the potential of belt feeding devices as a possible solution to overcome this obstacle for a wide range of parts. This paper discusses the requirements for flexible parts handling and the merits of alternative strategies which are presently being applied. For belt feeding purposes parts are classified as stable or non-stable. Two main developments are reported: (i) a feeding concept employing simple adjustable tooling and a remote sensor for presentation and assembly of a wide class of non-stable parts; (ii) a low cost hopper-type belt feeder which utilizes a single discrete sensor for orientation of stable parts.