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Simulation Based Production

Planning, Scheduling, andControl

Johannes Krauth

Sim-Serv

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Overview

Planning Steps

Methods Applied

The Contribution of SimulationExamples

The Future

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Planning Steps

Production Programme Planning /

Plant or Process Design

(time horizon: years)Production Planning (months / weeks)

Detailed Scheduling (days / hours)

Control

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Overall Planning Objectives

Maximise Capacity Utilisation

Minimise DelaysMinimise Throughput Times

Minimise Work in Progress

Note: Conflicting Objectives!!

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Facility Planning

Based on assumed demand

Searches optimal match of needed

and available capacityPlanning horizon: years

Not an ongoing activity

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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 h5 workers = 10080 h

?

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Limitations

no interdependencies taken intoaccount

based on estimated / experienceddegrees of capacity utilisation

adequate for strategic, long-termplanning, when little information isavailable

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Production Planning

Based on (expected) customer orders

Using fixed throughput times per step

(based on experience or assumptions)Accepts / rejects orders and fixes startand end dates

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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

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Limitations

Capacity assumed available

Actual shop floor status not taken into

accountWaiting times included and thereforefixed

Applicable only when long deliverytimes are acceptable

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Production Scheduling

Planning Horizon: 1 week 1 day

Based on confirmed orders and

actually available resourcesMust take into account technicalrestrictions

Finds exact sequence of operations perwork station

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Production Scheduling

Must be fit for reality!

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Contribution of Simulation

Detailed models

Exact representation of all processes,

all needed resourcesRealistic transition times, based oncurrent shop floor status

All kinds of rules and constraints canbe taken into account

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Ways to Use Simulation:

MRP /ERP

System

Simulation Modelcontrols

feeds

back

1. Offline, from outside

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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

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Typical Leitstand / APS tool

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Contribution of Optimisation

Can use a large variety of criteria foroptimal solutions

Finds very good schedules quicklyTakes away hours of routine work fromthe planners

Allows them to focus on the essentials

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Examples

2 Examples: Simulation helps optimise

planning tool and process4 Examples: Simulation andOptimisation modules as part ofplanning toolbox

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Conclusion from Examples:

Broad range of industry sectors

Leitstand / APS tools can complementexisting 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!!

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Summary

Simulation Based Scheduling andControl offers substantial advantages

Many approaches available for differentspecial requirements

Also useful for SMEs

Sim-Serv assists with selection of bestsuited approach