Design for assembly (DFA) has received much attention in recent years because
Assembly operations constitute a high labor cost for several manufacturing companies. The key to successful design for assembly will be simply stated [3]: (1) design
The product with as few parts as possible, and (2) design the remaining parts so that they are easy to assemble. The price of assembly is decided largely during product
Design, because that’s when the quantity of separate components within the product
Is determined, and decisions are made about how these components are going to be assembled. Once these decisions are made, there’s little that may be worn out
Manufacturing to influence assembly costs (except, of course, to manage the operations well).
This section considers a number of the principles which will be applied during product design to facilitate assembly. Most of the principles are developed within the context of mechanical assembly, although a number of them apply to the opposite assembly and joining processes. Much of the research in design for assembly has been motivated by the increasing use of automated assembly systems in industry.
Accordingly, our discussion is split into two sections, the fi rst coping with general principles of DFA, and also the second concerned specifically with design for automated assembly.
GENERAL PRINCIPLES OF DFA
Most of the final principles apply to both manual and automatic assembly. Their Goal is to attain the desired design function by the best and lowest cost means.
➢ Use the fewest number of parts possible to scale back the quantity of assembly required . This principle is implemented by combining functions within the identical part which may preferably be accomplished by separate components (e.g., employing a plastic molded part rather than an assembly of flat solid parts).
➢ Reduce the amount of threaded fasteners required . rather than using separate
Threaded fasteners, design the component to utilize snap fits, retaining rings,
Integral fasteners, and similar fastening mechanisms that may be accomplished more rapidly. Use threaded fasteners only where justified (e.g., where disassembly or adjustment is required).
➢ Standardize fasteners. This is often intended to cut back the quantity of sizes and designs of fasteners required within the product.
Ordering and inventory problems are reduced, the assembly worker doesn’t must distinguish between such a big amount of separate fasteners, the workstation is simplified, and also the type of separate fastening tools is reduced.
➢ Reduce parts orientation difficulties. Orientation problems are generally reduced by designing an element to be symmetrical and minimizing the amount of asymmetric features. This enables 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.
DESIGN FOR AUTOMATED ASSEMBLY
Methods suitable for manual assembly aren’t necessarily the simplest methods for automated assembly. Some assembly operations readily performed by a personality’s worker are quite difficult to automate (e.g., assembly using bolts and nuts). To automate the assembly process, parts fastening methods must be specified during product design that lend themselves to machine insertion and joining techniques and don’t require the senses, dexterity, and intelligence of human assembly workers.
Following are some recommendations and principles that may be applied in product design to facilitate automated assembly.
➢ Use modularity in product design . Increasing the quantity of separate tasks that are accomplished by an automatic assembly system will reduce the reliability of the system. To alleviate the reliability problem, Riley suggests that the planning of the merchandise be modular within which each module or subassembly includes a maximum of 12 or 13 parts to be produced on one assembly system. Also, the subassembly should be designed around a base part to which other components are added.
➢ Reduce the necessity for multiple components to be handled directly . the popular practice for automated assembly is to separate the operations at different stations instead of to simultaneously handle and fasten multiple components at the same workstation.
➢ Limit the specified directions of access. This implies that the quantity of directions in which new components are added to the present subassembly should be minimized. Ideally, all components should be added vertically from above, if possible.
➢ High-quality components. High performance of an automatic assembly system requires that consistently good-quality components are added at each workstation. Poor quality components cause jams in feeding and assembly mechanisms that lead to downtime.
➢ Use of snap fit assembly. This eliminates the necessity for threaded fasteners; assembly is by simple insertion, usually from above. It requires that the parts be designed with special positive and negative features to facilitate insertion and fastening.
