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March 2016 • SMT Magazine 21 are to be placed relative to their pickup position on the feeder table to minimize the travel time during placement operation. When creating op- timized SMT programs with a fixed material set- up common to a group of products, that aspect of the machine program optimization is com- promised. The result is a significant reduction in program efficiency for each product in the group, reducing line throughput accordingly. This loss was deemed acceptable in cases where grouped products were nearly identical, but as lot sizes have decreased further, the variation in the groups of products has increased, which has reduced program efficiency significantly. Unlike down-time at changeover, this loss is hidden from the casual observer because it appears that the SMT machine is working full time. However, the throughput of the machine is likely to have been reduced by around 5% in the best case, to around 80% in some exception- al cases where the common material setup has severely compromised the machine operation. Productivity reports are based on the machine run-time per PCB produced, which is derived from the machine program. The program has this inefficiency built in already, and it is often not compared to what should be the raw ma- chine capability so these losses are not included in management reports. For companies that have recognized this is- sue, another alternative has been explored where trolleys of materials can be used to support the exchange of materials between products, which avoids the need for common material setups thE buyEr'S guIdE to autoMatIon

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