May, 2018
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What Does Lean Production Planning Really Look Like? Continued from previous page
the planning optimization process, it would not have an accurate model of what the resultant cycle time would be, nor the specific changeover time required at the start and end of any work order. Therefore, such decisions, without the provision of huge amounts of reference data from SMT programming, are nearly impossible. These are some of the main reasons why
scheduling and planning in SMT production has remained a “dark art” over the years. These issues have to be addressed to create a lean planning system.
Turning the Process Upside Down For the principles of lean to work, the engi-
neering flow needs to be turned upside down. Decisions about product assignment to production lines or how to create common material setup groups are done as part of the planning opti- mization, rather than by SMT pro- gramming. The product model is processed by the programming tool, for design data import, merge of the BOM, and management of a central material shape library, but it makes no assignments to machines or lines. Then the planning optimization
engine models the material assign- ments to machines, program times, line balances, and changeover times. The planning system does not create optimized SMT programs, because each iteration could take hours. However, with a good model of the machine capability and timing and the ability to create groups of prod- ucts that have common material setups based on actual completion requirements, SMT programming is done more quickly per iteration. Next, replace the advance prepa-
ration of material kits “push” approach with a lean material “pull” flow. With direct connections to the SMT machines through real-time communication interfaces, informa- tion about the consumption of materi- als and completion of products is gath- ered continuously. Because the quan- tity of materials originally on each reel and the sequence of production is known, computerization is used to create a “pull” signal that is generated based on the expected need for replen- ishment of each material or the provi- sion of materials for changeover. Instructions for moving materials to and from the warehouse are created just in time (JIT). By using unique barcodes to identify material units and their locations within the ware- house, the integrity of physical mate- rial inventory is maintained, avoiding the risk of unexpected material star- vation at the machine. This eliminates almost all
unused materials, as it provides accurate inventory and communi- cates where to find materials when needed. This way, no buffer of mate- rials is necessary between the ware- house and the shop floor. In a lean process, however, there is no over- commitment of material because the production plan is able to change to anything at any time, without the need for extensive material realloca- tion. The moratorium for schedule change is now reduced, basically to whatever is already running. The physical barrier to making short- term planning changes is gone.
Lean Planning In a lean operation, the factory
consists of lean production cells that can be reconfigured to assemble or
See at SMT Hybrid Pkg., Booth 5-212
test a range of products at short notice. A lean pro- duction plan tool, such as Valor Production Planning, starts with product shipping require- ments and works backward, so that each prior pool of cells takes as its completion requirement the next set of cells in the process. In the SMT area, things are more complex.
The production plan tool knows the existing sched- ule for all processes in the area, including the printing, component placement, reflow, AOI, ICT, and hand assembly. The production plan tool also has access to the real-time status of the machines and processes, using the same data from the direct machine interfaces used by the JIT materials logistics system. Simulating a model of each machine, the pro-
duction plan software optimizes the sequence of work orders and creates the common feeder setups
Page 71
that reduce changeover time. The last piece of optimization is to create the
final SMT programs for the machines, which is done with a third-party, multi-vendor process preparation tool, or by using the software supplied by the machine vendor. Programming optimization happens after planning optimization, not before. However, the daily cycle may not fit all customer needs, so it can be adjusted to every shift, or less often, such as weekly or even monthly. Lean production planning opens up the
opportunity in SMT for computerization of multi- ple automated processes as defined by Industry 4.0. Following this approach, factories can make only what is needed, when it is needed. Contact: Mentor — A Siemens Business, 8005
SW Boeckman Road, Wilsonville, OR 97070 % 503-685-7000 E-mail:
tessent@mentor.com
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