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Transcript of Facility Design
Topic 10
Facility Design and Line Balancing
Facility Layout Design
Facility Layout: Determine the Relative Positions of each Unit
(Department/Process Function/Machine Center) within the Facility
(Plant/Shop).
Facility Layout will determine the Work Flow Patterns
(Job/Material/Worker) in the Facility.
Layout Design: has a significant impact on most Operational
Performance Measures, especially on:
--Materials Handling Costs
--Production Cost
--Production Leadtime
--Inventory Level
--Quality Control
Topic 10 - 1
Major Objectives of Facility Layout Design
1. Simplify Work Flow Pattern within the Facility.
2. Reduce Material-Handling Costs.
3. Increase Utilization of Resources (Machine/Labor/Space/..)
4. Provide Flexibility that Required.
Topic 10 - 2
Some Objectives of Facility Layouts
Topic 10 - 3
Facility LayoutFacility layout means planning:
for location of all machines, utilities, employee workstations, customer service areas, material storage areas, aisles, restrooms, lunchrooms, internal walls, offices and computer rooms
for the flow pattern of materials and people around, into and within buildings
Characteristics of the Facility Layout Decision Location of these various area impacts the flow through
the system The layout can affect productivity and costs generated
by the system Layout alternatives are limited by
o The amount and type of space required for various areas
o The amount and type of space available]o The operations strategy
Layout decisions tend to be:o Infrequento Expensive to implemento Studied and evaluated extensivelyo Long-term commitments
Topic 10 - 4
Material Handling in Layout Design
o The central focus of most manufacturing layouts is to minimize the cost of processing, transporting, and storing materials throughout the production system.
o Materials used in manufacturing include:o Raw materialo Purchased componentso Work-in-processo Finished goodso Packaging materialo Maintenance, repair, and operating supplies
A material-handling system is the entire network of transportation that:
o Receives materialo Stores material in inventorieso Moves material between products into vehicles for delivery
to customers
Material-Handling Principleso Move directly (no zigzagging/backtracking)o Minimize human effort requiredo Move heavy/bulky items the shortest distanceo Minimize number of times same item is movedo MH systems should be flexibleo Mobile equipment should carry full load
Material-Handling Equipment
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o Automatic transfer devices/Containers/pallets/hand cartso Conveyers/Cranes/Elevators/Pipelines/Turntables/AGVS
Types of Facility Layout
1. Process Layout: Similar Machines are Grouped together as
Specific Work Centers (WC). (Functional/Departmental Layout)
(e.g., Job Shop)
2. Product Layout: Machines are installed According to Operations
Sequence through which designed Product is made.
(Line Layout)
(e.g., Assembly Line/Continuous Process)
3. Project Layout: Equipments are fixed at Specified Position.
(Fixed Position Layout)
(e.g., Project Shop: Aircraft Plant/Ship Building Yard)
4. Cellular Layout: Selected Machines are grouped to form several
Manufacturing Cells, each produces a specific group of products.
(GT Layout, GT- Group Technology)
(e.g., Cellular Shop)
Topic 10 - 6
What is Layout Planning?
Key Design Choices:a. What centers should we include?b. How much space and capacity for each center?c. How to configure the space?d. Where should each be located?
Relative Location : can affect travel time, material handling cost, and communication
Absolute Location : can affect cost to change layout and customer reactions
Four Major Layout Types:a. Process layout : organizes resources around the process and
groups workstations or departments according to functionb. Product (Line) layout : dedicates resources to a product or
closely related product family Challenge in designing product layouts—balance tasks,
equalize the workload assigned to resoucesc. Hybrid layout (Cellular layout—Group technology): combines
elements of both a flexible flow and line flow facility with both fabrication and assembly operations
d. Fixed-position layout : product is fixed in place; resources come to the product, minimizing number of times product must be moved
Group Technology (GT) Group parts into families that have identical processing steps Changeover from producing one part to another requires only
minor setup adjustments
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Product family volume justifies dedication of machines, which are arranged into flow lines called “cells”
Topic 10 - 8
Group Technology/Cellular Manufacturing
o Group Technology
o Each part produced receives a multi-digit code that
describes the physical characteristics of the part.
o Parts with similar characteristics are grouped into part
families
o Parts in a part family are typically made on the same
machines with similar tools
o Cellular Manufacturing
o Some part families (those requiring significant batch
sizes) can be assigned to manufacturing cells.
o The organization of the shop floor into cells is referred to
as cellular manufacturing
o Flow of parts within cells tend to be more like product-
focused systems.
o Advantages (relative to a job shop)
o Process changeovers simplified
o Variability of tasks reduced (less training needed)
o More direct routes through the system
o Production planning and control simpler
o Automation simpler
Topic 10 - 9
Process Layout vs. Product Layout
Process Layout Product Layout
Product Mix: Large & Dynamic Small & Stable
Product Volume: Low to Medium High
Machine Type General/Non-Dedicated
Special/Dedicated
Flexibility High Low
Work Flow Pattern Batch Flow/Random Continuous/Linear
Automation: Low High
Initial Cost Low High
Variable Cost High Low
Plan & Control Order Based/Complex
Flow Rate Based
Leadtime Very Long Short
WIP Level: High Very Low
MGT Concerns: Scheduling, Leadtime, Costs
Efficiency, Line Balancing
Topic 10 - 10
Layout Design in Service
Process Layout and Product Layout are also two major
facility layout designs in Service operations.
Some Examples:
Process Layout:
Product Layout:
Some Specific Considerations in Service Layout Design:
Must provide entryways to customer.
Must provide waiting space for customers.
Need separation of rooms for customer privacy.
Topic 10 - 11
Process Layout Design Procedure
1. Collect Required Data: (Product Mix/Production
Volume/....)
2. Determine the Number of Work Centers.
3. Determine Space Requirement for Each Work Center.
4. Examine Relationships among Work Centers based on:
Material Handling Costs,
Transportation Capability,
Supportive Factors (Loading & Unloading/Closeness to
Computer Center/......)
Specific Requirement.
5. Develop Layout Alternative Plans.
6. Evaluate Alternative Plans and Make Final Selection.
Topic 10 - 12
Layout by Process
Topic 10 - 13
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Process Layout Design Methods
1. Small Size Problems (Theoretical): Optimizing Techniques.
(Linear Programming/Integer Programming/Transportation
Model/...)
(N < 10)
2. Medium Size Problems (Practical): Computerized Software
Packages of Various Solution Heuristics.
(CRAFT/BDA/ALDEP/CORELAP/SLP/PLANPAK/..)
(N = 10 - 50)
3. Large Size Problems (Most Practical): Computer Simulation.
(Special Language: GPSS)
(N > 50)
Topic 10 - 14
Service Operations Layout
Office (Service) Layouts:
Recent Poll: a 1400 service worker poll revealed that 75% felt a better layout would improve their productivity
Management indirectly used layout as a “spatial language” to say: You are special/Out of supervisor’s watchful eyes/Satisfied social needs
Proximity :a. The usual approach is to design office layouts around
work flows and communication patternsb. The assumption is that proximity helps with
understanding mutual interests, and even friendship Privacy :
a. Crowding and noise can hurt performance and attitudes
Options in office layout: Privacy is expensive; the capital investment in open-plan
layouts is about 40% less; an open plan maximizes flexibility A trade-off between privacy and proximity is possible Traditional layouts
Closed offices for some Open areas for others
Office landscaping Everyone in the open: plants, screens, and portable
partitions for semiprivate space Activity settings
Home base: a personal nook; position no longer means place
Multiple workplaces Telecommuting or electronic cottages
Topic 10 - 15
Product Layout Design
Line Layout:
All Work Stations (WS) are Located along Production Line in
a Pre-Specified Sequence.
A Series of Operations Performed in the Same Order.
A Transportation Device Connecting all WSs to Form a Line.
All Machines are dedicated to Perform certain operations
tasks.
Design Questions:
How Many Work Stations in the Line?
How Operation Tasks are assigned to Each Work Station?
There is No "Relative Position" Issue in Line Layout Design.
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Why Line Need Be Balanced?
Example: (Assign 10 Operation Tasks to 5 Work Stations)
Tasks: A B C D E F G H I J
Op eration Time : 2 3 9 1 14 16 4 1 7 13
Work Station: (1), (2), (3), (4), (5)
Precedence Requirement:
(A) → (B) → (C) → (D) → (E) → (F) → (G) → (H) → (I) → (J)
Initial Assignment:
Tasks: (A,B) (C,D) (E,F) (G,H) (I,J)
WSs : (1) (2) (3) (4) (5)
Question: How About the Performance of This Production Line?
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1. Shortest Time Interval a Finished Product out off Line = ?
(Cycle Time ≥ Maximum of Individual Task Operation
Time)
2. Stable Output Rate of this Line = ?
3. Idle (Slack) Time at Each WS = ?
4. Total Slack Time of the Line = ?
5. Is this Line Balanced ?
Objectives of Line Balancing: To Minimize Total Slack Time
(Two Types of Problems)
1. Given the Number of WS - Minimize the Cycle Time
(Maximize Output Rate)
2. Given the Cycle Time - Minimize the Number of WS
(Maximize Utilization)
Topic 10 - 18
Elements of Line Balancing Problem
1. Task: Smallest Work Element.
2. Task Processing Time: Time Required to Complete a Task.
3. Work Station (WS): A Location along the Line Where Tasks
Are Processed. (Operator/Machine/Robotic/....)
4. Work Load of A WS: The Sum of the Processing Times of All
Tasks Assigned to A Work Station.
5. Cycle Time: A Fixed Time Interval for Feeding Two Consecutive
Units into the Line.
6. Production Rate: (Output Rate = Input Rate) At Which Work
Materials (RM/Subassemblies/Parts) are Fed into the Line.
(Production Rate = 1/Cycle Time)
Topic 10 - 19
Line Balancing: Constraints & Assumptions
Constraints:
1. Precedence Requirements: Technical Processing Requirements
(e.g., Task B only can be processed after Task A is completed.)
(Represented by a Precedence Network/Diagram)
2. Zoning Limitations: Certain Tasks can not be processed at
Same Work Station (e.g., Welding vs. Painting).
3. Other Constraints: (Engineering/Behavioral/Environmental).
General Assumptions:
1. A Task can not be Split Among Two or More Work Stations.
2. All Tasks must be processed to complete a Finished Product.
3. Processing Time for a Task will be same at All Work Stations.
Topic 10 - 20
How to Balance a Production Line
1. Collect All Required Information:
(Tasks/Processing Times/Precedence Requirements/WS/.....)
2. Draw A Precedence Network/Diagram.
3. Determine:
a) The Number of Work Stations - Under Given Cycle Time, or
b) The Cycle Time - Under Given Number of Work Stations
4. Select Task-Assignment Methods:
(Optimizing: LP/Heuristics/Computer Simulation/.....)
5. Assign Tasks to Work Stations.
6. Evaluate Assignment Solution:
(Efficiency/Total Slack Time/Utilization Level/ Production
Rate)
Topic 10 - 21
Planning Product (Line) Layouts
Line Balancing Procedure1. Determine the task involved in completing I unit2. Determine the order in which tasks must be done3. Draw a precedence diagram4. Estimate task times5. Calculate the cycle time6. Calculate the minimum number of workstations7. Use a heuristic to assign tasks to workstations
Line Balancing Heuristics Heuristic methods, based on simple rules, have
been developed to provide good (not optimal) solutions to line balancing problems
Heuristic methods include: Shortest-Task-Time (SPT) method Longest-task-time (LPT) method .. and many others
Rebalancing a Production LineChanges that can lead to production lines being out of balance or having insufficient/excess capacity are:
Change in demand Machine modifications Variations in employee learning and training
Topic 10 - 22
Task Assignment Heuristics
1. LPT (Next Longest Processing Time Task first): Select the Task
that has the Largest Processing Time but still fit to the WS
Available Time.
2. SPT (Next Shortest Processing Time Task first): Select the Task
that has the Shortest Processing Time and still fit to the WS
Available Time.
3. MSF (Most Successors Task first): Select the Task that has the
Most Successors and still fit to the WS Available Time.
4. LSPT (Largest Successor's Processing Time Task First): Select
the Task that has the Largest Successor's Processing Time and still
fit to the WS Available Time.
Topic 10 - 23
How to Select Line Balancing Heuristics
For a specific problem - How to select?
Random?
Try all heuristics?
Guidelines:
1. Job Structure: More branches, high flexibility for assignment,
and a large task available pool.
2. Task Processing Time distribution: Small Variation, Easy to
Balance.
Computer Expert Systems have been developed for Line balancing
problems.
"Bottleneck" of the Line: Improving on the "bottleneck" work
stations will improve the entire production line.
Topic 10 - 24
LINE BALANCING PROBLEM
(Single-Model vs. Mixed-Model)
1. Single-Model Line: Only one product is processed on the line.
All items are Identical - No Job Sequencing Issue.
Major Management Concern: Balancing the Line Only.
(Advantages: Simple and Easy to Planning, Scheduling, and
Controlling)
2. Mixed-Model Line: More than two products are processed on the
same Line. Items are Different.
Major Management Concern: Both Item Sequencing & Line
Balancing are to be Considered together to Achieve Better
Performance.
(Advantages: High Utilization/Eliminate line Changeovers/...)
Why Mixed: Capacity of Line > Demand of A Single Product
Topic 10 - 25
Subjective Considerations in
Assembly Line Balancing Problems
Job enlargement vs. Job specialization—employee motivation
Choice of cycle time—speed of line vs. balance delay
Reliability of time estimates for work tasks
Space requirements
Task decomposition—can a major task be broken down?
Segregation of worker skills
Special materials handling considerations
Supervision problems
Safety
Quality control
Special equipment or services
Flexibility of design
Interface with scheduling—critical if products can vary
Task “relatedness”
In-process inventory
Topic 10 - 26
Production Lines: Western versus Japanese
Western JapaneseTop Priorities; line balance Top priority: flexibilityStrategy: stability- long production runs so that the need to rebalance seldom occurs
Strategy: flexibility- expect to rebalance often to match output to changing demand
Assume fixed labor assignments Flexible labor: move to the problems or to where the current workload is
Use inventory buffers to cushion effects of equipment failure
Employ maximal preventive maintenance to keep equipment from breaking down
Need sophisticated analysis (e.g., using computers) to evaluate and cull the many options
Need human ingenuity to provide flexibility and ways around bottlenecks
Planned by staff Supervisor may lead design effort and will adjust plan as needed
Plan to run at fixed rate; send quality problems off line
Slow for quality problems, speed up when quality is rights
Linear of L-shaped lines U-shaped or parallel linesConveyorized material movement is desirable
Put stations close together and avoid conveyors
Buy “supermachines” and keep them busy
Make (or buy) small machines, add more copies as needed
Applied on labor-intensive final assembly
Applied even to capital-intensive subassembly and fabrication work
Run mixed models where labor content is similar from model to model
Strive for mixed-model production, even in subassembly and fabrication
Line Balancing Problems
Topic 10 - 27
1. The Baud Electronics Company produces electronic calculators and is planning to begin production of a new model. An assembly line is to be developed that will produce 500 units per 7.5 hour workday. The tasks, task times, and precedence requirements are given below.
Task Time (seconds) PredecessorA 32 NoneB 35 AC 15 AD 22 AE 35 BF 38 BG 12 DH 16 GI 31 GJ 20 I
a) Group the tasks into work stations by selecting the shortest remaining time, from the available list at each selection, so long as that time will fit within the remaining available time at the work station.
b) How well balanced is the line? How many work stations are used?
c) Balance the line by selecting the longest task time that will fit within the available time for the work station. Is this assignment much different from a)? Why, or why not?
2. The Montana Appliance Company is installing as assembly line to produce one of its small appliances, and you have been asked to
Topic 10 - 28
balance the line. The tasks that are to be performed are listed below, along with the time required to perform each task and its immediate predecessor(s). The line is to produce 300 units in a full 8 hours of work.
Task Time (seconds) Predecessor(s)A 51 NoneB 22 AC 28 AD 32 AE 39 AF 20 BG 20 CH 16 DI 12 EJ 42 F, GK 44 H, IL 20 JM 20 KN 12 I, M
a) Assign tasks to work stations by selecting the longest task that can be assigned at each opportunity.
b) Assign tasks to work stations by selecting the shortest task that can be assigned at each opportunity.
c) Assign task to work stations by incremental utilization heuristic d) Compare the performance of the above three heuristics.
Line-Balancing Solution SheetProblem: #1 (Supplement)
Topic 10 - 29
a) Assign Tasks by <SPT> Heuristics Given: Cycle-Time = 54
Work Task Task Task TimeStation Available Assigned Time Remaining
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
_____________________________________________________________________________
______________________________________________________________________________
Number of Work Stations =
Total Slack Time =
Efficiency = (Total Time – Total Slack Time)/Total Time = Problem: #1 (Supplement)
a) Assign Tasks by <LPT> Heuristics Given: Cycle-Time = 54
Topic 10 - 30
Work Task Task Task TimeStation Available Assigned Time Remaining
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Number of Work Stations =
Total Slack Time =
Efficiency = (Total Time – Total Slack Time)/Total Time = Problem: #2 (Supplement)
a) Assign Tasks by <LPT> Heuristics Given: Cycle-Time = 96
Topic 10 - 31
Work Task Task Task TimeStation Available Assigned Time Remaining
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Number of Work Stations =
Total Slack Time =
Efficiency = (Total Time – Total Slack Time)/Total Time = Problem: #2 (Supplement)
a) Assign Tasks by <SPT> Heuristics Given: Cycle-Time = 96
Topic 10 - 32
Work Task Task Task TimeStation Available Assigned Time Remaining
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Number of Work Stations =
Total Slack Time =
Efficiency = (Total Time – Total Slack Time)/Total Time = Example: Line-Balance in Service Operations
State Automobile License Renewals Operations
Topic 10 - 33
Jessica, the manager of an Atlanta branch office of the state Department of Motor Vehicles, attempted to perform an analysis of the driver's license renewal operations. Several procedural steps were to be performed in the process. After examining the license renewal process, she identified the six steps and associated times required to perform each step, as shown in the following table:
State Automobile License Renewals Process Times
STEP AVERAGE TIME (in seconds)-----------------------------------------------------------------------------------------------------------------1. Review renewal application for correctness 152. Process and record payment 303. Check file for violations and restrictions 604. Conduct eye test 405. Photograph applicant 206. Issue temporary license 30-----------------------------------------------------------------------------------------------------------------
Jessica found that each step was assigned to a different person. Each application was through a same process in the sequence shown above. Jessica determined that her office should be prepared to accommodate the maximum demand of processing 120 renewal applicants per hour.
She observed that the work was unevenly divided among the clerks, and the clerk who was responsible for checking violations tended to shortcut her task to keep up with the other clerks. Long lines built up during the maximum demand periods. She also found that first 4 steps were handled by general clerks who were each paid $6.00 per hour, while Step-5 was performed by a photographer paid $8 per hour. Step 6, the issuing of a temporary license, was required by state policy to be handled by a uniformed motor vehicle officer. Officers were paid $9.00 per hour, but they could be assigned to any other job except photography.
A review of the jobs indicated that Step-1, reviewing the application for correctness, must be performed before any other step could be taken. Similarly, Step-6, issuing the temporary license, could not be performed until all the other steps were completed. The branch offices were charged $5 per hour for each camera to perform photography. Jessica was under severe pressure to increase productivity and reduce costs, but she was also told by the regional director of the Department of' Motor Vehicles that she had better accommodate the demand for renewals. Otherwise, "heads would roll."
DISCUSSION QUESTIONS:
1. What is the maximum number of applications per hour that can be handled by the present configuration of the process?
2. How many applications can be processed per hour if a second clerk is added to check for violations? (Make the assumptions you need for your answer.)
3. Assuming the addition of one more clerk, what is the maximum number of applications the process can handle?
4. How would you suggest modifying the process in order to accommodate 120 applications per hour?
Review Questions for Topic - 10
<Facility Layout Design>
Topic 10 - 34
Be prepared to discuss the following cases:(a) State Auto License Renew Operations (Supplement: p.10-33)
(1) Define product layout vs. process layout. What is a departmental layout? A project layout?(2) Describe the quantitative approach (using flow matrix) that was used in the process
analysis. What is SLP?(3) Define the objective function and constraints in assembly line balancing. How is the cycle
time computed? Using the heuristic algorithm given in class, be prepared to balance an assembly line configuration and compute the efficiency of your solution.
(4) Describe several non-quantitative considerations in the assembly line balancing problem.(5) What is meant by the term "heuristic?" Provide an example of a heuristic algorithm used in
operations management.(6) Explain the use of "balance delay" in determining the efficiency of an assembly line design.
Explain the relationship between the "balance delay" and the "efficiency" of an assembly line design.
(7) What is "over-cycling" in assembly line design? How can over-cycling be related to the sequencing of products on the assembly line during operation?
(8) Explain the group technology approach to facility layout.(9) Based on p.10-26 (Supplement), summarize a few key differences in U.S. and Japanese
production line management.10) Explain the description of the differences in product and process layout in the services.11) What is the essential requirement for mixed-model production lines to be practical?
Topic 10 - 35