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Part IIIPerformance evaluation and design

of manufacturing systems

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ObjectivesObjectives

Understanding important performance measures of Understanding important performance measures of manufacturing systems manufacturing systems

Understanding the impact of random perturbation on Understanding the impact of random perturbation on manufacturing systemsmanufacturing systems

Developping a system theory approach for Developping a system theory approach for performance evaluation and design of manufacturing performance evaluation and design of manufacturing systems systems

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ProblemsProblems

Manufacturing systems engineering not as advanced Manufacturing systems engineering not as advanced as other fields of engineeringas other fields of engineering

PractitionPractitioners encouraged to rely on gurus, slogans, ers encouraged to rely on gurus, slogans, and black boxesand black boxes

Gap between theoreticians and practitionersGap between theoreticians and practitioners

Separation of product, process, and system designSeparation of product, process, and system design

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ProblemsProblems

Confusions about objectivesConfusions about objectives

•maximize capacitymaximize capacity

•minimize capacity variabilityminimize capacity variability

•maximize capacity utilizationmaximize capacity utilization

•minimize leadtimeminimize leadtime

•minimize leadtime variabilityminimize leadtime variability

•maximize profitmaximize profit

System issues are often studied last, if at all.System issues are often studied last, if at all.

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ProblemsProblems

Manufacturing gets no respectManufacturing gets no respect

•Systems not designed with engineering methodsSystems not designed with engineering methods

•Product designers and sales staff are not informed Product designers and sales staff are not informed of manufacturing costs and constraintsof manufacturing costs and constraints

Black box thinkingBlack box thinking

•Factories not treated as systems to be analyzed Factories not treated as systems to be analyzed and engineeredand engineered

•Simplistic ideas often used for management and Simplistic ideas often used for management and design.design.

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ProblemsProblems

Reliable systems intuition is lacking. As a Reliable systems intuition is lacking. As a consequence, there is …consequence, there is …

•Management by softwareManagement by software

•managers buy software to make production managers buy software to make production decisions, rather than to aid in making decisionsdecisions, rather than to aid in making decisions

•Management by sloganManagement by slogan

•Gurus provide simple solutions which sometimes Gurus provide simple solutions which sometimes work. Sometimes.work. Sometimes.

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ObservationsObservations

When a system is not well understood, rules When a system is not well understood, rules proliferate.proliferate.

This is because rules are developed to regulate This is because rules are developed to regulate behaviorbehavior

But the rules lead to unexpected, undesirable But the rules lead to unexpected, undesirable behavior.behavior.

New rules are developed to regulate the new behavior.New rules are developed to regulate the new behavior.

Et cetera.Et cetera.

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Observations - exampleObservations - example

A factory starts with one rule: A factory starts with one rule: do th latest jobs firstdo th latest jobs first..

Over time, more and more jobs are later and later.Over time, more and more jobs are later and later.

A new rule is added: A new rule is added: treat the highest priority treat the highest priority customers orders as though their due dates are two customers orders as though their due dates are two weeks earlier than they areweeks earlier than they are..

The low priority customers find other suppliers, but the The low priority customers find other suppliers, but the factory is still late.factory is still late.

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Basic issuesBasic issues

Frequent new product introductionsFrequent new product introductions

Product lifetimes often shortProduct lifetimes often short

Process lifetimes often shortProcess lifetimes often short

This leads to frequent building and rebuilding of This leads to frequent building and rebuilding of factories.factories.

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Basic issues – consequent needsBasic issues – consequent needs

Tools to predict performance of proposed factory Tools to predict performance of proposed factory design.design.

Tools for optimal real-time management (control of Tools for optimal real-time management (control of facories.facories.

Manufacturing systems engieering professionals who Manufacturing systems engieering professionals who understand factories as complex systemsunderstand factories as complex systems

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Basic issues – Quantity, quality and variabilityBasic issues – Quantity, quality and variability

Quantity – how much and whenQuantity – how much and when

Quality – how well.Quality – how well.

We emphasize We emphasize quantityquantity..

General statement: variability is the enemy of General statement: variability is the enemy of manufacturing.manufacturing.

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Basic issues – conceptsBasic issues – concepts

Nothing happens until everything is present.Nothing happens until everything is present.

Operationspart

Consumable

part

waste

operator

machine

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Basic issues – conceptsBasic issues – concepts

Waiting: whatever does not arrive last must wait.Waiting: whatever does not arrive last must wait.

Inventory : parts waitingInventory : parts waiting

Underutilization: machine waitingUnderutilization: machine waiting

Idle work force: operators waiting.Idle work force: operators waiting.

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Kinds of systemsKinds of systems

Flow shop, flow line, tranfer line, production line

machine Buffer ou stock tampon

Traditionally used for high volume, low variety production.

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Kinds of systemsKinds of systems

Assembly system

Assembly systems are trees, and may involve thousands of parts.

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Kinds of systemsKinds of systems

Closed loop lines with limited number of pallets

Pallets or fixtures travel in a closed loop.

empty pallet buffer

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Kinds of systemsKinds of systems

Reentrant systems

Semiconductor fabircation is highly reentrant.

type 1 type2

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Kinds of systemsKinds of systems

Job-shops:

Machines not organized according to process flow.

Often, machines grouped by department

Great variety of products.

Different products follow different paths.

Complex management.

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Two issuesTwo issues

Effient design of systems

Efficient operation of systems after they are built.

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TimeTime

Most factory performance measures are about time.

Production rate: how much is made in a given time.

lead time: how much time before delivery

cycle time: how much time a part spends in the factory (leadtime)

delivery reliability: how often a factory delivers on time

capital pay-back period: the time before the company get its investment back.

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TimeTime

Time appears in two forms

•delay

•capacity utilization

Every action has impact on both.

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Time – Capacity utilizationTime – Capacity utilization

An operation that takes 10 min takes up 10 min of the available time of

a machine

an operator

or other resources

Since there are a limited number of minutes of each resource available, there are a limited number of operations that can be done.

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Time – Production rateTime – Production rate

Operation time: the time that a machine takes to do an operation

Production rate: the average number of parts produced in a time unit (also called throughput)

If nothing interesting happens (no failures, etc)

Production rate = 1 / operation time

… but something interesting always happens.

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Time – CapacityTime – Capacity

Capacity: the maximum possible production rate of a manufacturing system, for systems that are making only one part type.

•Short term capacity: determined by the resources available right now

•Long term capacity: determined by the average resource availability

Capacity is harder to define for systems making several part types. It depends on the product mix.

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Randomness, variability, uncertaintyRandomness, variability, uncertainty

Factories are full of random events:

•machine failures

•changes in orders

•quality failures

•human variability

The economic environment is uncertain

•demand variations

•supplier unreliability

•changes in costs and prices

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Randomness, variability, uncertaintyRandomness, variability, uncertainty

Therefore, factories should be

•designed as reliable as possible, to minimize the creation of variability

•designed with shock absorbers, to minimize the propagation of variability

•operated in a way that minimizes the creation of variability

•operated in a way that minimizes the propagation of variability.