Simulation Based Production Planning, Scheduling, and Control

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: 10,400 h milling ______________ 8,500 h welding … Available per year: 4 machines = 5376 h (1 shift, 80% utilis.); = 10752 h (2 shifts) __________________ 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

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 System feeds back

Ways to Use Simulation 2. Online, as part of planning toolbox MRP / ERP System: Long Term Planning Module_____________________ Medium Term Planning Module___________________ Scheduling Module: Simulation Model 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

Simulation Based Production Planning, Scheduling, and Control

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