IE 368: FACILITY DESIGN AND OPERATIONS MANAGEMENT

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IE 368 FACILITY DESIGN AND OPERATIONS MANAGEMENT

• Lecture Notes 2
• Production System Design
• Part 1

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Production System Design

• Abstraction of production systems for system
  design purposes
• General concepts/definitions that may be used to
  represent many different systems
• High level qualitative analysis for the selection
  of a general system flow concept

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Production System Design (cont.)

• Part 1
• Calculations for estimating resource requirements
• Equipment fraction calculations
• Extensions
• Machine assignment
• Part 2
• Calculations for evaluating system performance
• Review of relevant probability/statistics
  concepts
• Application of queuing models

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Production System Design (cont.)

• Part 3
• Generalizations of queuing model
• Generalizations of utilization formula
• Multiple linked workstations
• Automated systems
• Batched arrivals and departures

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Generalization/Abstraction of Production Systems
for IE Design/Analysis

• Production system
• A collection of workstations that perform
  operations such as manufacturing, assembly,
  inspection, finishing, testing, etc. to create
  products
• Workstation
• A collection of machines/operators that perform
  the same operation for the same set of products
• A machine/operator may be
• An automated machine
• A machine operated by a human
• A human operator performing a manual operation

Terminology in this area is not standardized
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Generalization/Abstraction of Production Systems
for IE Design/Analysis (cont.)

• The production systems to be addressed are
  discrete part production systems
• Each part produced is a distinct entity
• Vehicle, computer, hamburger, etc.
• This is in contrast to continuous goods
  production such as fluids, powders, etc.
• Often in the domain of chemical process engineers
• Thus, the product being produced will be referred
  to generically as a part or job

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Production System Design

• Production system design
• The general arrangement of workstations,
  dictating the pattern of flow of the products,
  and the resource requirements at each workstation

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Production System Performance Characterization

• At the level of abstraction presented, the
  performance of the production system is evaluated
  by determining the following
• How fast
• Throughput (e.g., jobs/hour, parts/minute)
• How long
• Time-In-System (TIS)
• Flow Time
• Cycle Time (we will not use this term)
• How much
• Work-In-Progress (WIP)

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Examples of Production Systems

• Simulation models
• Truck assembly
• FMS
• Distribution center
• Questions
• What constitutes a job?
• What are the workstations?
• Why are jobs flowing as they are?

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Production System Design Different Perspectives

• Manufacturing engineer
• Designs/selects the processes and operations
  required to produce the product
• e.g., fixturing, tooling, feed rates, cutting
  speeds, etc.
• Human factors engineer
• Design of the individual human operated
  workstation
• e.g., bench heights, lifting angles, placement of
  tools, presentation of visual information, etc.

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Production System Design Different Perspectives
(cont.)

• Higher level IE analysis/business operations
• Supply chain design
• The number, level, and location of suppliers
• Delivery, ordering, inventory policies
• The number of distributors and their locations

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General Production System Flow

• Examine product volume versus variety
• Typically cannot have both

Automation Hard Systems Special Purpose Machines
Volume of Production
General Purpose Equipment
Flexible Systems
Skilled labor
Variety of Products or Parts
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Basic Types of Production System Flow
System Example
Job Shop
Batch Processing
Production Line
Continuous Flow
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Job Shop Characteristics

• Many products low volume
• General purpose machinery
• Operators work at only one department and are
  highly skilled in that operation
• Process Layout
• Equipment of the same type is located in the same
  department
• Unorganized material flow
• High material handling
• High cycle time
• High flexibility

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Job Shop Characteristics (cont.)
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Production Line Characteristics

• Few products high volume (mass production)
• Highly standard parts
• Somewhat similar to continuous production
• Special purpose machinery
• Low skill labor
• Equipment is arranged into a line almost in the
  same order of required production operations
• Low material handling
• Short cycle time
• Well organized material flow

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Production Line Characteristics (cont.)
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Group Technology/Batch Processing Characteristics

• Fewer products than Job Shop higher production
  volume
• Products are produced in batches satisfying a few
  days up to few months of demand
• Less general purpose machinery than job shop
• Process layout cellular layout machines to
  produce family of products are located in the
  same cell
• Large batches have organized material flow
• High to moderate material handling
• Moderate cycle time
• High flexibility

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Group Technology/Batch Processing Characteristics
(cont.)

• Group Technology Cell

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Group Technology/Batch Processing Characteristics
(cont.)

• Batch processing layout

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Product Volume versus Variety

• Product Volume versus Product Variety in
  Production System Design

Volume of Production
Variety of Products or Parts
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Variety-Volume-Flexibility
Product Variety High Moderate Low Vey Low
Equipment Flexibility High Moderate Low Vey Low
Low Volume
Moderate Volume
High Volume
Very High Volume
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Quiz

• For the following situations, would you suggest a
  production line, job shop, or hybrid facility?
  Why?
• The assembly of vehicle bodies for a popular
  sport utility vehicle
• Fabrication and assembly of custom sheet metal
  parts
• Fabrication of computer boxes for a line of
  desktop PCs plus custom sheet metal parts
• Assembly of three distinct families of electronic
  card assemblies for high end printers
• Production of high end office furniture

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Determining Resource Requirements

• Assume you are running a manufacturing facility.
  What information would you need to determine how
  many machines/people are required at each
  workstation?

Text reading Chapter 2 pp. 51-53, 56-63
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Example 2.5

• A machined part has a standard machining time of
  2.8 min per part on a milling machine
• During an 8-hour shift, 200 units are to be
  produced
• Of the 480 min available for production, the
  machine will be operational 80 of the time
• During that time the machine is operational,
  parts are produced at a rate equal to 95 of the
  standard rate
• How many milling machines are required?

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Example 2.5 Common Sense Solution
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Determining Resource Requirements

• Equipment Fraction
• Number of machines required at a workstation
• Where
• F Number of machines required per shift
• S Standard time per job
• Q of jobs to produce over a fixed time period
• E Actual performance expressed as a percentage
  of standard time
• H Amount of time available per machine
• R Reliability of a machine, expressed as a
  percent of uptime

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Determining Resource Requirements (cont.)

• Other considerations
• If shifts are used
• In how many shifts a machine can be used
• Setup times
• Takes away available production time

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Important Observations

• The equipment fraction as presented is helpful
• It is more important to understand the
  fundamentals behind the formula because, as is,
  it is not applicable in all situations
• A specified quantity must be produced in some
  time period and each machine can produce a
  certain amount in that time period
• Efficiency, availability and reliability can be
  expressed in different ways and all these factors
  affect machine capability
• Units must be consistent

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Incorporating the Production of Scrap in the
Equipment Fraction

• Scrap
• Material waste that is generated in the
  manufacturing process
• Affects the number of times an operation must be
  performed to get a specific number of good jobs
• Typically due to geometric or quality
  considerations

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Incorporating the Production of Scrap in the
Equipment Fraction (cont.)

• Nomenclature

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Incorporating the Production of Scrap in the
Equipment Fraction (cont.)
WS1
WS2
WSn
.
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Example 2.1

• 97,000 good parts are required. Three operations
  are used to produce the part with scrap
  percentages of d10.04, d20.01, d30.03. What
  are the required inputs to each operation?

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Incorporating the Production of Scrap in the
Equipment Fraction (cont.)

• Calculations with rework

Rework station
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In-Class Exercise

• Part X requires machining on a milling machine
• Operations A and B are required
• Assume the company will be operating 5 days/week,
  18 hours/day
• The following information is known
• The milling machine requires 30 minutes for tool
  changes and preventive maintenance after every
  400 parts
• Assume that operation A is first and that both
  operations A and B are completed before the next
  part is started
• Find the number of machines required to produce
  2,500 parts per week

Operation Standard Time Efficiency Reliability Scrap
A 2 min 95 95 2
B 4 min 95 90 5
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In-Class Exercise Solution
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In-Class Exercise Solution
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Modifications to the Equipment Fraction Equation

• The equipment fraction equation is applicable to
  machines which can be human operators, a single
  operator running a single machine, and also
  automated machines
• For automated machines, data is often not
  expressed as in the equipment fraction equation
• In some cases a single operator runs gt1 machine
  in which case the machines are not producing at
  their maximum rates (the opposite can occur also)

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Modification for Automated Machines

• Automated Workstation
• A workstation where the movement of jobs in and
  out of the workstation, and the processing of
  jobs is performed by machines
• While the workstation is operating, the move
  times and processing times are predictable

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Modification for Automated Machines (cont.)

• Cycle time
• Represented as C
• Total time required to produce a single job on a
  workstation when it is operating
• Normally C Process time Move time
• Move time
• The time to move a job into and/or out of the
  workstation
• Does the movement of a job into a workstation
  occur at the same time as the movement of a job
  out of the workstation?

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Modification for Automated Machines (cont.)

• Mean (Operating) Time Between Failures (MTBF)
• The average time between unplanned failures of
  the machine
• Excludes scheduled down time or non-operating
  time
• Mean Time To Repair (MTTR)
• The average time to bring the machine back to
  operating status after a failure occurs

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Modification for Automated Machines (cont.)

• Equipment Fraction
• S standard time per job
• Q of jobs to produce over a fixed time period
• E actual performance expressed as a percentage
  of standard time
• H amount of time available per machine
• R Reliability of a machine, expressed as a
  percent of uptime

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Modification for Automated Machines (cont.)
Referred to as Stand Alone Availability
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Modification for Automated Machines (cont.)

• Example
• An automated machine has a move time 10 sec/job
  and a processing time of 1 min/job. The machine
  will be used for a single 8 hr shift and has a
  MTBF 75 min and a MTTR 5 min. What is the
  number of machines required to produce 1,000 jobs
  per shift?

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In-Class Exercise

• Part X requires machining on a CNC milling
  machine
• Operations A and B are required
• Assume the machine will be operating 5 days/week,
  18 hours/day
• The following information is known
• The milling machine requires tool changes and
  preventive maintenance after every 400 parts.
  This takes 30 minutes.
• Assume that operation A is first and that both
  operations A and B are completed before the next
  part is started
• Move times in and out of the machine occur at the
  same time
• Find the number of machines required to produce
  2,500 parts per week

Operation Process Time Move Time MTBF MTTR Scrap
A 5 min 0.5 min 500 min 20 min 2
B 7 min 0.5 min 700 min 30 min 5
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In-Class Exercise Solution
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Rates and Times in Calculations

• No general rules
• Assess the general quantity being calculated,
  then use common sense
• Test calculations in extreme cases
• Example 1 Calculate Average Speed of Vehicle

10 mph
40 mph
5 miles
5 miles
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Rates and Times in Calculations (cont.)

• Example 2 Calculate Average Job Interarrival
  Time
• Example 3 Calculate Average Job Processing Rate
  of M1

10 min
M1
5 min
6 min
Time between job arrivals
Jobs CBACBA
M1
?
M1 processing rates A 20 JPH B 30 JPH C 60
JPH
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Rates and Times in Calculations (cont.)
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Machine Assignment

• There are many cases where multiple machines are
  run by a single operator
• The number of machines running may be limited by
  the number of operators or the number of machines
  may determine how busy the operator is

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Model for the Number of Machines to Assign to an
Operator

• Assumptions
• All machines are identical and perform the same
  task
• All times are known and constant
• Use this model as a starting point or
  approximation

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Model for the Number of Machines to Assign to an
Operator (cont.)
Figure 2.19 from Tompkins
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Model for the Number of Machines to Assign to an
Operator (cont.)

• Notation for machine assignment

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Model for the Number of Machines to Assign to an
Operator (cont.)
L Load UL Unload T Transport IP
Inspect Pack
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Figure 2.18 Multiple activity chart
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Model for the Number of Machines to Assign to an
Operator (cont.)

• A machine uses (a t) minutes (use min for
  clarity) per job
• An operator devotes (a b) minutes to each
  machine per job

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Model for the Number of Machines to Assign to an
Operator (cont.)

• Since m must be an integer
• See Figure 2.18 (slide 53)

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Model for the Number of Machines to Assign to an
Operator (cont.)

• See Figure 2.18
• Idle time per machine in steady state 1 minute
• Im m(ab) - (at) 3(21) (26) 1 minute

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Model for the Number of Machines to Assign to an
Operator (cont.)

• For the example in Figure 2.18
• 3 parts are produced every 9 minutes ? 20
  jobs/hour
• Not 22.5 jobs/hour with no idle time
• Examine the operation of a single machine
• For a single machine, 1 part is produced every
• 6 minutes 1 minute 1 minute 1 minute 9
  minutes
• (Machining load unload idle
  )

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Machine Assignment Impact on Cost Per Job

• Machine assignment decisions affect the cost per
  job produced

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Machine Assignment Impact on Cost Per Job (cont.)
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Machine Assignment Impact on Cost Per Job (cont.)

• Let then either TC(n) or TC(n1)
  will minimize cost per job
• It is straightforward to show that

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Example

• Problem 2.38
• Suppose 5 identical machines are to be used to
  produce two different products
• The operating parameters for the two products are
  as follows a1 2 min, a2 2.5 min, b1 1 min,
  b2 1.5 min, t1 6 min, and t2 8 min
• The cost parameters are the same for each
  operator-machine combination Co 15/hr and Cm
  50/hr
• Determine the method of assigning operators to
  machines that minimizes the cost per unit produced

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Example
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Example
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In-Class Exercise

• Semiautomatic mixers are used in a paint plant.
  It takes 6 min for an operator to load the
  appropriate pigments and paint base into a mixer.
  Mixers run automatically and then automatically
  dispense paint into 50-gallon drums. Mixing and
  unloading take 30 min. Mixers are cleaned
  automatically between batches it takes 4 min to
  clean a mixer. Between batches, an operator
  places empty drums in a magazine to position them
  for filling. It takes 6 min to load the drums
  into the magazine. Filled drums are transported
  automatically by conveyor to a test area before
  being stored. Mixers are located close enough for
  travel between mixers to be negligible.
• What is the maximum number of mixers that can be
  assigned to an operator without mixer idle time?
• If Co 12/hr and Cm25/hr, what assignment of
  mixers to operators will minimize cost per batch?

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In-Class Exercise Solution