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58 The PCB Magazine • October 2015 uct family, which creates a near homogeneous product flow. Another method is using theory of constraints (TOC), where a critical work center is identified and work is introduced into the sys- tem based on the output of that constraint. Some companies simply have a Kanban based on what goes into finished goods. Material is introduced at the front end based on what gets completed into stock. While all these methods will control WIP, they tend to struggle when a high product mix goes through the same work centers; this situa- tion is very common for manufacturing that re- quires chemical processes and high capital cost equipment. The problem is that as product mix changes, the WIP will accumulate at different processes. The constraint moves around, while other critical work centers are starved for work. In this case cycle time reduction comes at the expense of overall throughput. Product Mix Control A hybrid system uses Kanban with a product mix control. The factory is divided into process "loops." Material is introduced into a loop based on the completion of a lot going through that loop, but with a "twist"—each product family has its own Kanban card. When a single-sided circuit is completed in the loop, another lot of single-sided product is introduced. Likewise, when a double-sided lot is completed in the loop, another lot of double-sided is introduced, and so on for the various product families. Lot size for each product family is determined by impact on the loop capacity. This system con- trols WIP and keeps the product mix constant, making it easier to manage overall capacity and maximize throughput. Short Term Capacity/Workflow Planning Of course the above technique would break down as demand changes and the product mix changes to meet the demand. This is where ca- pacity/work flow planning comes into play. The product mix control system can be adjusted weekly to accommodate changes in demand. An essential requirement is a good MRP system with accurate capacity loads. The Kanban sys- tem of each loop is adjusted as needed, based on changes in product mix. Daily Management The above tools fall into the "necessary but not sufficient" category. A strong daily manage- ment system that involves management, opera- tors, engineers and planners reviewing critical shop floor metrics is a final piece of the puzzle. Cycle time and WIP are reviewed, along with quality and safety metrics. Any metric outside predetermined control points requires an action plan with follow up. Action plans and results are reported monthly at the management qual- ity review meetings, where all critical metrics and performances are reviewed and discussed with top management. This system incorporates the "plan-do- check-act" principles made popular by W. Ed- wards Deming back in the late 80s. Short term capacity/flow planning system establishes the product mix control (plan). The Kanban sys- tem executes the shop floor flow (do). The daily management system checks results and creates action plans to adjust (check-act). The key to successful implementation of any cycle time reduction program is making sure it fits, or is tailored to, an individual situation. Some factories build relatively homogeneous prod- uct, others a wide variety. And that can change with the variability of customer product mix. The adoption of the above methods will be most successful when tailored, and continuously im- proved, based on the changing environment. PCB CyCLE TIME REDUCTION IN A FLExIBLE CIRCUIT FACILITy All AbouT Flex Dave Becker is vice president of sales and marketing at all Flex Flexible circuits llc. " some companies simply have a Kanban based on what goes into finished goods. "

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