© J. Christopher Beck 2005 1

Lecture 28: Supply Chain Scheduling 2

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Outline Discrete Manufacturing vs

Continuous Manufacturing What Difference Does It Make?

A Typical Framework for Supply Chain Optimization Medium Term Planning Short Term Scheduling Information System Issues

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Supply Chain Scheduling

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Discrete vs. Continuous Manufacturing

Continuous (process) production Main inventory/products are finely

divisible Steel, shampoo, paper

Discrete production Main inventory/products are individually

countable Cars, computers, consumer electronics

Scheduling problems are different

© J. Christopher Beck 2005 5

Continuous:1. Main Processing

Raw materials aretransformed to intermediate products

Machines have high start-up/shutdown costs and

High changeover costs Often fixed batch sizes Usually run 24/7

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Continuous:2. Finishing

Products of mainprocesses are “specialized” Cut, bent, extruded, painted, printed, …

Often these are commodities Many clients Mix of make-to-stock, make-to-order

Due dates, sequence dependent changeovers, and inventory management are important

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Discrete:1. Primary Conversion

Like finishing in continuous Stamping, bending, cutting

Process is generally pretty simple

Output is often a part Car body part, computer case, …

Schedule is often integrated with downstream processes

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Discrete:2. Main Production

Many differentoperations of many tools 100 step process for semiconductors!

Machines are very expensive Often organized like a job shop Each order has its own route,

quantity, due date Sequence dependent changeovers

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Discrete:3. Assembly

Put together parts Machines are cheap but material

handling is important Assembly lines

cars or consumer electronics Due dates, changeovers,

sequencing, …

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Table 8.1

Segment Process Horizon Clock Speed

Differentiation

Continuous: Main

Planning Long-medium

Low Very low

Continuous: Finishing

Planning/scheduling

Medium-short

Medium/High

Medium/low

Discrete: Conversion

Planning/scheduling

Medium-short

Medium Very low

Discrete: Main

Planning/scheduling

Medium-short

Medium Medium/low

Discrete: Assembly

Scheduling Short High High

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Table 8.2Segment Optimization

ProblemSolution Technique

Continuous: Main Lot-sizing, cyclic scheduling

MIP

Continuous: Finishing

Single machine, parallel machine

Batch scheduling, inventory control, dispatch rules

Discrete: Conversion

Single machine, parallel machine

Batch scheduling, dispatch rules, CP

Discrete: Main Flow shop, job shop

IP, CP, shifting bottleneck, LS

Discrete: Assembly

Assembly line Grouping, spacing, sequencing techniques, CP, LS

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Supply Chain Decomposition

Medium-term plannin

g

Short-term

sched-uling

Stage 1 Stage 2 Stage 3 Stage 4

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Medium-term Aggregation

Time abstraction 1 unit = 1 day or 1 week

Product abstraction Work at product “family” level

e.g., Tuborg beer, not 6-pack, 12, 24, keg, …

Cost/job/capacity abstraction Average processing times Sequence dependencies ignored Factory treated as a single resource

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Medium-term Planning Results

Daily or weekly Demand for product families at each

facility Inventory levels Transportation requirements

No detailed scheduling has been done!

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Medium-term Constrains Short-term

Medium-term plannin

g

Short-term

sched-uling

Stage 1 Stage 2 Stage 3 Stage 4

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Medium-term Decouples Short-term

Medium-term plannin

g

Short-term

sched-uling

Stage 1 Stage 2 Stage 3 Stage 4

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Short-term Scheduling Uses More Precise Data

Time in minutes or seconds Horizon ≈ week, 2 weeks Jobs and resources are detailed Set-up time/cost are taken into

account Products not just product families

Demand for each product is represented

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Problem

Short term schedule solution may not exist! Why?

May require feedback of information to the medium-term and a resolve Carlsberg takes 10-12 hours for a

medium-term solve …

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Feedback Mechanism Needed

Medium-term plannin

g

Short-term

sched-uling

Stage 1 Stage 2 Stage 3 Stage 4

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Information Infrastructure Requirements

Medium-term plannin

g

Short-term

sched-uling

Stage 1 Stage 2 Stage 3 Stage 4