Mar 07, 2002
For small lots, the typical assembly line comprises two or three pick-and-place machines, and the leading cause of loss of efficiency is the setup time. Off-line reel kitting and sequential setup starting with screen print as soon as the last board of the previous lot has been screened are well known techniques for shortening the nonproductive time. Less common is the storage of complete part setups on racks which can be installed for a new lot in a matter of a few minutes. This implies keeping the inventory at the foot of the machines most likely in vertical storage. Of course, this line management approach requires investing in a large number of feeders, but this is less expensive than adding more line capacity.
For high volume assemblies, setup is also a most common cause of loss of efficiency, but it should not be so. The only lengthy operation should be the first article assembly and in-circuit test prior to starting the full lot, which can take around thirty minutes on a double flow line. When the intricacies of setup have been mastered, it is part shortages which is most likely to become a cause of inefficiency. Then the efficiency of logistics or lack thereof directly impacts the shop floor. It is a strong reminder that board assembly is fundamentally a material management activity of which the transformation of a bare board into a good populated board is only one step.
These are some of the issues raised by CEERIS' report on line efficiency which is presented at http://www.ceeris.com/efficiency.htm. An important asset of the report is to present detailed statistics on what degrades efficiency. This is the knowledge on which factory managers can benchmark their performance and design an improvement strategy. It is certainly financially more efficient to increase the output of existing assembly resources than invest in new lines.
For further information, contact Charles-Henri Mangin at CEERIS International, Inc., at ceeris@aol.com or by telephone at (860)434-8740.
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