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

Department Estimated Throughput Time

Process 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:

MRP /ERP

System

Simulation Modelcontrols

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