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Scheduling Optimization in FlexSim

Introduction

manufacturing, production planning and scheduling is a daily task. Thus, the cost of productiondepends to a great deal on scheduling decisions; e.g. the scheduling of order sequence or setup

work. Most scheduling decisions are often characterized by complex constraints, which make it

very difficult to find an optimum solution. In FlexSim, a user can optimize the production schedule

via a tool called OptQuest.

OptQuest uses an advanced technique called metaheuristics, a type of search algorithm which leads

the user towards better solutions. It combines Tabu search, scatter search, integer programming,

and neural networks into a single, composite search algorithm which gives very accurate optimal

solutions.

Figure 1: The Product Manufacturing Sequence

Scheduling Optimization Example

Assume we have to manufacture 10 different products that require 3 machining steps and each

product has a different process time for each of the three machine steps. A simple 10 job 3 machine

problem is built in FlexSim, with two Global Tables that store the Product Sequence and Processing

Times.

The objective is to find the optimal job sequence, which will provide the minimum Fabrication or

lead time to manufacture all 10 products. Since we have to determine the optimal sequence and

thus the minimum lead time we assume each row of ‘Product Sequence’ table as a variable in

Experimenter tab. The objective function is to minimize the Fabrication Time and there are no

constraints.

Once the Optimizer is configured, the user runs the optimization by clicking on the ‘Optimize’ button

to generate the results. All results with the best solution can be viewed in Optimizer results tab by

using the Export to CSV option.

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Figure 2: Creating variables in OptQuest

Figure 3: Optimization results

Initial Sequence for

products

Optimum Sequence

for products

1st

  1 52

nd  2 3

3rd

  3 8

4th

  4 4

5th

  5 6

6th

  6 1

7th

  7 2

8th

  8 7

9th

  9 9

10th

  10 10

Fabrication time

(Make Span)(min)182.17

163.26(10.38 %

decrease)

Table 1: Result from Optimization