Balakrishnan, A: Setup Optimization and Workload Balancing

Excerpt from Setup Optimization and Workload Balancing: For Mixed-Model Electronics Assembly Operations

This paper addresses a medium-term, tactical decision facing high mix, low volume electronics assembly facilities containing several surface mount assembly modules (one or more placement machines in series, see Section Operating in parallel, possibly at different sites. We consider facilities in which each module can assemble several different products (with appropriate setups), and modules have overlapping capabilities, i.e for each product, we have a choice Of modules to assemble that product. Furthermore, the demand for individual products is not adequate to justify using dedicated, single-product modules. Operations with these characteristics, which we refer to as mixed-model assembly operations, are common in companies producing electronic subsystems for applications such as telecommunications, computer peripherals, consumer electronics, and medical systems. We will focus on the component placement Operation since the automatic placement machines are very expensive and also require considerable setup time. For convenience, we use the words machine, module, and line interchangeably. Given the equipment configuration and capacity of each machine, and the projected demand for various products, the tactical plan determines which products to assemble on each machine.

In making this tactical decision, managers must address two conflicting objectives reducing the setup or changeover times, and distributing the workload evenly across the parallel machines (relative to their available capacities). When lot sizes are small (say, tens or hundreds of boards per lot), equipment changeover times can equal or exceed the actual processing (placement) times. For instance, the time to change over production from one board type to another on a placement machine can vary from 15 minutes to over an hourdepending on the number of new components to be loaded, whereas placing all the components for a batch of 50 boards with, say, 200 placements per board, might require less than an hour of processing time. Reducing setup times is, therefore, an important concern both to increase productive capacity, and to provide quick response with minimal inventories. On the other hand, balancing the workload has several benefits including reducing overtime expenses, decreasing the lead time to supply board sets multiple board types that are assembled into a single unit) for final assembly, and providing safety capacity on each machine to accommodate contingencies. These two Objectives can be contradictory. To minimize total setup time, we might assign products that share many common components to the same machine; however, this strategy of grouping products solely based on component commonality can result in imbalances due to uneven group sizes.

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