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.); = h (2 shifts) __________________ 4 workers = 8400 h 5 workers = 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 DepartmentEstimated Throughput Time Process Time Lathing20 days1 hour Machining5 days20 hours Surface Treatm.7 days1.5 hours Polishing7 days10 hours Assembly15 days20 hours Total54 days52.5 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: MRP /ERP System Simulation Model controls feeds back 1. Offline, from outside

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