"Simulation Based Production Planning Scheduling and Control Johannes Krauth Sim Serv Overview Planning Steps Methods Applied The Contribution of Simulation Examples The Future Planning Steps"
Simulation Based Production Planning, Scheduling, and Control Johannes Krauth Sim-Serv Overview Planning Steps Methods Applied The Contribution of Simulation Examples The Future Planning Steps Production Programme Planning / Plant or Process Design (time horizon: years) Production Planning (months / weeks) Detailed Scheduling (days / hours) Control Overall Planning Objectives Maximise Capacity Utilisation Minimise Delays Minimise Throughput Times Minimise Work in Progress Note: Conflicting Objectives!! Facility Planning Based on assumed demand Searches “optimal” match of needed and available capacity Planning horizon: years Not an ongoing activity Optimal Match Needed per year: Available per year: 10,400 h milling 4 machines = 5376 h (1 shift, 80% utilis.); = 10752 h (2 shifts) ______________ __________________ 8,500 h welding ? 4 workers = 8400 h 5 workers = 10080 h … … Limitations no interdependencies taken into account based on estimated / experienced degrees of capacity utilisation adequate for strategic, long-term planning, when little information is available Production Planning Based on (expected) customer orders Using fixed throughput times per step (based on experience or assumptions) Accepts / rejects orders and fixes start and end dates Example: Assumed and Real Durations Department Estimated Process Throughput Time Time Lathing 20 days 1 hour Machining 5 days 20 hours Surface Treatm. 7 days 1.5 hours Polishing 7 days 10 hours Assembly 15 days 20 hours Total 54 days 52.5 hours Limitations Capacity assumed available Actual shop floor status not taken into account Waiting times included and therefore fixed Applicable only when long delivery times are acceptable Production Scheduling Planning Horizon: 1 week – 1 day Based on confirmed orders and actually available resources Must take into account technical restrictions Finds exact sequence of operations per work station Production Scheduling Must be “fit for reality”! Contribution of Simulation Detailed models Exact representation of all processes, all needed resources Realistic transition times, based on current shop floor status All kinds of rules and constraints can be taken into account Ways to Use Simulation: 1. Offline, from outside Simulation Model controls MRP /ERP feeds System back Ways to Use Simulation 2. Online, as part of planning toolbox MRP / ERP System: Long Term Planning Module_____________________ Medium Term Planning Module___________________ Simulation Model Scheduling Module: Shop Floor Typical “Leitstand” / APS tool Contribution of Optimisation Can use a large variety of criteria for “optimal” solutions Finds very good schedules quickly Takes away hours of routine work from the planners Allows them to focus on the essentials Examples 2 Examples: Simulation helps optimise planning tool and process 4 Examples: Simulation and Optimisation modules as part of planning toolbox Conclusion from Examples: Broad range of industry sectors Leitstand / APS tools can complement existing MRP / ERP tools or run stand-alone Typical benefits include Higher capacity utilisation Less WiP Less delays, shorter throughput times Payback often within a few months!! Summary Simulation Based Scheduling and Control offers substantial advantages Many approaches available for different special requirements Also useful for SMEs Sim-Serv assists with selection of best suited approach