breakdowns happen: factoring downtime into your simulation

Breakdowns Happen:

How to Factor Downtime

into your Simulation

Simulation expert Brian Harrington explains the key learning points simulation modelers should consider when working with downtime.

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Introductions

Brian Harrington, CSSBB

- 20 years in simulation at

Ford Motor Company

- Experienced Six

Sigma Blackbelt and

SIMUL8 Manufacturing Consultant

- Director of MTN-SIM, a

simulation specialist consulting firm

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MTBF & MTTR

1. How often does a machine fail (MTBF)?

2. How long does it take to repair it (MTTR)?

These two questions may seem simple, however

are often abstracted within the forest of machinery

and clouded by human behavior.

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One of the most debatable pieces of data

that goes into a simulation is the stochastic

behavior of machine downtime.

• Introducing new equipment • Collecting downtime data • Summarizing downtime data • Catastrophic downtimes • Lock-out procedures • Time to react, travel, and repair • Distributions to represent downtimes • Limited skilled trades • Simultaneous faults • Protective capacity • Equations (MTBF, MTTF, MTBC, MTTR, etc…)

Plants perspective

Designer’s perspective

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Availability

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SIMUL8 Efficiency… Prove it

MTBF

MTTR

Availability

Efficiency

Go to MTBF MTTR Defined.S8

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Capture downtime at station or line level?

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Math behind the Spreadsheet

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Equivalent Results

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Advantages of Aggregate Values

• Used for predicting station/cell level

downtime based on components

• Reduces large data files

• Ease of communicating downtime figures

• Aligned with scope of model

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Distributions for MTBF & MTTR?

Exponential

Erlang

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Stat::Fit (View your data!)

• Data tables (Input data)

• Input Graph

• Descriptive Statistics

• Auto::Fit

• Distribution Viewer

Go to View Dist.S8

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Time to React & Travel?

Named Distributions and the Combination Distribution can capture some of this behavior.

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Lock-out Procedure

A safety protocol which protects skilled trades when entering a station or work cell. Each skilled trade will have a named-lock, which will be “locked” on an electrical panel before entering a work cell for a repair. The protocol will have several required steps to assure that all power is off, assuring no machinery, robot, etc. movement.

A typical lock-out procedure might take 3 to 7 minutes to complete!

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How do we account for the Lockout

Procedure?

A lockout procedure might be assumed to be followed on the lengthier repairs

such as repair times that take 10 minutes or more.

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VL for creating a Bimodal Distribution

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Skilled Trades on Repairs

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TimeView

Improve Performance

Downtimes cause Performance issues!

(Wait & Blocks)

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Design Facilities to Absorb Downtime

• Protective Capacity

– Resides in an over-speed (Push)

– Resides in buffers

– Preventative maintenance

– Skilled trades available

– Material handling systems

• Power & Free

• Electric Monorail Systems

• Power Friction

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Questions

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