Facility Design and Line Balancing

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

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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.

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Some Objectives of Facility Layouts

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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

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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)

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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”

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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

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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

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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.

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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.

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Layout by Process

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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)

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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

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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)

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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)

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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.

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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)

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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

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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.

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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.

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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

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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

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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

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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

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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)

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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

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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

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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

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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

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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>

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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?

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