Mumbai university > mechanical engineering > sem 7 > cad/cam/cae

Marks: 5M

Difficulty: Medium

•Design for assembly (DFA) has received much attention in recent years because assembly operations constitute a high labour cost for many manufacturing companies. The key to successful design for assembly can be simply stated: (1) design the product with as few parts as possible, and (2) design the remaining parts so they are easy to assemble.

•The cost of assembly is determined largely during product design, because that is when the number of components in the product is determined, and decisions are made about how these components will be assembled. Once these decisions have been made, there is little that can be done in manufacturing to influence assembly costs.

Some of the general principles for Design for Assembly are:

•Use the fewest number of parts possible to reduce the amount of assembly required. This principle is implemented by combining functions within the same part that might otherwise be accomplished by separate components; for example, using a plastic moulded part instead of an assembly consisting of sheet metal parts.

•Reduce the number of threaded fasteners required. Instead of using separate threaded fasteners, design the components to be assembled using snap fits, retaining rings, integral fasteners, and similar fastening mechanisms that can be accomplished more rapidly. Use threaded fasteners only where justified (e.g., where disassembly or adjustment is required).

•Standardize fasteners. This is intended to reduce the number of sizes and styles of fasteners required in the product. Ordering and inventory problems are reduced, the assembly worker does not have to distinguish between so many separate fasteners, the workstation is simplified, and the variety of separate fastening tools is reduced.

•Reduce parts orientation difficulties. Orientation problems are generally reduced by designing parts to be symmetrical or minimizing the number of asymmetric features. This allows easier handling and insertion during assembly.

•Avoid parts that tangle. Certain part configurations are more likely to become entangled in parts bins, frustrating assembly workers or jamming automatic feeders. Parts with hooks, holes, slots, and curls exhibit more of this tendency than parts without these features.