chapter 2 line balancing no pics

7/29/2019 Chapter 2 Line Balancing No Pics

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Chapter 2: Line BalancingChapter 2: Line Balancing

IE 5511 Human Factors

Professor Hayes


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Line BalancingLine Balancing

Line: an assembly line composed of several

work stations, at which specific operations

are performed.To work effectively, with no work pile-ups

between stations, the line must be balanced,

e.g. work must get through eachworkstation in roughly the same amount of

time.


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Line BalancingLine Balancing

Goals: To meet production goals,

Maximize output.

Common Approaches to Line Balancing:

1. Estimating the number of operators for a givennumber of stations,

2. Work element sharing: grouping activities perwork elements into stations or jobs performed

by a single person (some times multiple peoplework in concert at a single station or machine)


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Estimating theEstimating the

number of operatorsnumber of operatorsIn a perfectly balanced line, alloperations

at allstation would take identicaltime.

Efficiency would be 100 %

However, this rarely happens!!

100 % efficiency is rarely achievable,

A more reasonable goal is 95 % efficiency.

(However, even that may not be achievable

depending on the nature of the operations).


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Estimating the number ofEstimating the number of

OperatorsOperatorsTo achieve a given rate of production, R,

N operators are needed (total).

(1) N = R x AM = R x SM

EDesired

Rate of Production

Number of

Operators

Needed

Allowed Minutes: total time

between pieces (e.g. AM =

time of slowest operation)

Efficiency

(expressed as fraction)

Standard Minutes:

Time it actually takes

to complete an operation

on average


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Procedure for DeterminingProcedure for Determining

the Number of Operatorsthe Number of Operators

needed to meet production goals.needed to meet production goals.

Assumptions. You have already determined:

the numberof workstations, theirsequence

the operations that will be performed at each one.

Goals. To:

Meetproduction goals given to you by your management,

Balance the workloadbetween stations by putting more

workers at the slower stations,

Reduce idle time


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Procedure: Estimating the Number of OperatorsProcedure: Estimating the Number of Operators

Givens: Production goal, operation sequence.

Step 0: (Prior to the analysis) Perform time studies for eachoperation using experienced operators in order to obtainstandard times (SM).

Step 1: Convert theproduction rate, R, into the sametime units as your standard times.

Step 2: (optional) Estimate the total number ofoperators for the line using Equation (1) (see previousslides)

Step 3: Estimate the number of operators needed foreach operation,

Step 4: Identify theslowestoperation given the numberof operators computed in previous step,

Step 5: Test: have you met the production goal?Step 6: Adjust. Add more operators, negotiate to

reduce the production goal, or try additional methods.


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Example: Estimating the Number of OperatorsExample: Estimating the Number of Operators

Givens: Production goal: 700 units/day where 1 day =

8 hours.

Operation sequence: Op1, Op2, Op3, Op4,

Op5, Op6, Op7, Op8.

Step 0: (Prior to the analysis) Perform time

studies for each operation using

experienced operators in order to obtainstandard times in minutes (SM).


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Example:Example:

Estimating the Number of OperatorsEstimating the Number of OperatorsStep 1: Convert theproduction rate, R, into the

same time units as your standard times.

The standard times, SM, have been expressed inminutes, while R is in days, so:

R = 700 units/day = 1.458 units/min

480 min/day

Also compute the desired cycle time (rate at whichunits exitline)

cycle time = 1 = 0.685 min/unit

R


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Example:Example:

Estimating the Number of OperatorsEstimating the Number of Operators

Step 2:(optional) Estimate the total number

of operators, N, required to meet production

goal, using Equation (1) :


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Example:Example:

Estimating the Number of OperatorsEstimating the Number of OperatorsStep 3: Estimate the number of operators

needed foreach operation,

Step 4: Identify theslowestoperation given

the number of operators computed in

previous step,

Step 5: Test: have you met the productiongoal?


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Number of operators neededNumber of operators needed

for each operationfor each operation

to achieve production goalsto achieve production goals

Cycle time = 1/R


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Calculate reduced cycle times atCalculate reduced cycle times at

each station when using multipleeach station when using multiple

operatorsoperators

SM / Number of Operators

New cycle time at

station when using

multiple operators


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Calculate reduced cycle times atCalculate reduced cycle times at

each station when using multipleeach station when using multiple

operatorsoperators

SM / Number of Operators

New cycle time at

station when using

multiple operators

Your production line will only be as fast as your slowest worker.Does this line meet the desired cycle time (0.685)?


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Work Element SharingWork Element Sharing

A line can sometimes be balanced with less

costby rearranging the sub-work elements

(e.g. activities composing a work element)For example, by giving activities from the

busiestelement to elements with idle time.


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Properties of Work ElementsProperties of Work Elements

What is a work element?How big should a work element be?

Assemble items in

box

Load Styrofoam

block

Load book

Grasp

block

Move block

to box

Orient

Block

Release

Block

Work Element

Sub-work elements

Sub-sub work elements


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Work Element PropertiesWork Element Properties

Work elements can be represented atvarious levels of abstraction or detail

Work elements can almost always be sub-divided into smaller elements.

The appropriate representation depends onthe task and situation.


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Work Element Sharing:Work Element Sharing:

GEs Line BalancingGEs Line Balancing

A Procedure for AssigningA Procedure for AssigningWork Elements to StationsWork Elements to Stations

Given:

Precedence graph Production goal (e.g. 300 units per shift)

Shift duration (e.g. 450 minutes)

Number of workstations (e.g. 6 workstations)

Decided how to assign elements to workstations so

as to meet production goals withoutviolating

precedence constraints!


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A Precedence Graph forA Precedence Graph for

Assembly OperationsAssembly Operations

The graph should only contain necessary orderings.

Any unnecessary constraints make it harder to achieve

efficiency.

P d l ti 1 i b f


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Precedence relations: 1 = y is before x


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Compute positional weighs,Compute positional weighs,

Record immediate predecessors,Record immediate predecessors,

Sort from biggest positional weightSort from biggest positional weight


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The Final Assembly LineThe Final Assembly Line

A streamlined version:A streamlined version:

(00) (02)

(01) (03)

(05) (06)

(04)

(08) (07) (09) (10)

Station 1

Station 2

Station 3

Station 4 Station 5Station 6


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A stream-lined version of theA stream-lined version of the

Assembly lineAssembly line

(00) (02)

(01) (03)

(05) (06)

(04)

(08) (07) (09) (10)

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