1. Lot size in batch production Slovak University of Technology Faculty of Material Science and Technology in Trnava

2. What is the lot size? Lot size is number of parts that is processed on one workstation at the same time, when the set up costs are spent only once. Lot size is one of norms of production that markedly influences production costs.

3. Problem of correct lot size Advantages of big lot size  Decline of set up time  Reductiom of the number of arrangement  The existence of inventories allows usage of capacity proportionally Disadvantages  High inventories  Long flow time  High production costs

4. Classic methods for determination of lot size These methods use different mathematical models  Minimal lot size (capacity)  Optimal lot size  Empirically determined lot size  Periodic lot size None of classic methods is not able to involve many real factors, that influences lot size.

5. How to set up lot size? Conflict between systems, which go out from MRP and JIT Use reductionistic alebo holistic approach? It is possible to expect more complex aproach such as simulation optimization

6. Simulation? Simulation allows predicate reactions of production system on selected lot size It is possible to include crucial factors that influence on lot size into simulation model. Values of goal parameters of production system are gained directly by simulation:  system performance  flow time  work in process  costs  capacity utilisation

7. Usage of simulation optimization The solving for determination of accurate (optimal) lot size offers simulation optimization

8. Simulation model of production system in Witness Skupiny pracovísk Workstation groups

9. Workstation

10. IF No_out_parts () default value of flow time Unit_Costs = SumCosts / No_out_parts RETURN Unit_Costs ELSE Unit_Costs = SumCosts / No_out_parts + constant RETURN Unit_Costs ENDIF quantitative values of goals Definition of objective function

11. Preparatory experiments model verification; set up simulation and warm up period; find out lower and upper limit of system loading; determination of quantitative values of production goals.

12. Optimizer Window

13. Otpimization results Optimal lot size Values of the others goals: · flow time (42,26 min ); · machine utilisation (76%); · number of finished parts (1344). 2 1

14. Final evaluation It is possible to set up optimal lot size by simulation optimization, while the factors that influence lot size in real are respected. Simulation optimization is possible to use also for opposite production goals

15. Final evaluation However, simulation model have to be created. Simulation optimization requires special software aid (plug in module) Optimization process can take long time.