COMPLEXITY OF ASSEMBLY

Boothroyd and Dewhurst have suggested a DFA index aimed at assessing the complexity of assembly. This is the ratio of (the theoretical minimum number of parts x 3 seconds) to the estimated total assembly time The theoretically minimum number of parts can he calculated by having each theoretical part meet at least one of the following:

• Does the part need to move relative to the rest of the assembly?

• Must the part be made of a different material?

• Does the part have to be physically separated for access, replacement, or repair?

If not theoretically necessary, then the designer should consider the physical integration with one or more other parts. And why 3 seconds? Merely because that is a good average unit assembly time. Once this is done, then Boothroyd and Dewhurst suggest further rules for maximum ease of assembly. These are:

Assembly Support Costs should be considered at the design stage. This includes consideration of:

• Inventory management and sourcing
• The necessity for new vendors
• A requirement for new tools to be used
• A requirement for new operator skills to be acquired
• The possibility of failsafing