Facility Design-Week 4Material Flow Analysis

By Anastasia L. Maukar

2

Flow Analysis

• Factors that Affect the Flow Pattern

• Flow Analysis Information

• Flow Patterns

a. Flow within Workstations b. Flow within Departments

c. Flow between Departments

• Flow Planning

• Measuring Flow

• Types of Layout

a. Fixed Location b. Product

c. Group Technology d. Process

e. Hybrid

• Flow Dominance Measure

3

Factors that Affect the Flow Pattern

• Number of parts in each product• Number of operations on each part• Sequence of operations in each part• Number of subassemblies• Number of units to be produced• Product versus process type layout• Desired flexibility• Locations of service areas• The building• . . . .

4

Flow Analysis Information

• Assembly Chart• Operation Process

Chart (OPC)• Multi-Product Process

Chart (MPPC)• String Diagram• Process Chart• Flow Process Chart• Flow Diagram

• From-to Chart/Travel Chart

• Triangular Flow Diagram

• Activity Relationship Chart (ARC) dan Activity Relationship Diagram (ARD)

• Procedure Chart• Critical Path Network

5

Assembly Chart

It is an analog model of the assembly process.

Circles with a single link denote basic

components, circles with several links denote

assembly operations/subassemblies, and

squares represent inspection operations. The

easiest method to constructing an assembly

chart is to begin with the original product and to

trace the product disassembly back to its basic

components.

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Operations Process Chart

By superimposing the route sheets and the

assembly chart, a chart results that gives an

overview of the flow within the facility. This

chart is operations process chart.

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Multi-Product Process Chart

This chart is a flow process chart containing

several products.

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String Diagram

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Flow Process Chart

This chart uses circles for operations,

arrows for transports, squares for

inspections, triangles for storage, and

the letter D for delays. Vertical lines

connect these symbols in the sequence

they are performed.

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Other Flow Process Chart

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Flow Diagram

It depicts the probable movement of

materials in the floor plant. The

movement is represented by a line in

the plant drawing.

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From-To Chart

This chart is a matrix that contains

numbers representing a measure

(units, unit loads, etc.) of the material

flow between machines, departments,

buildings, etc.

13

Triangular Flow Diagram

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Flow Patterns: Flow within Workstations

Motion studies and ergonomics considerations are important in establishing the flow within workstations. Flow within workstations should be:

• Simultaneous: coordinated use of hands, arms and feet.• Symmetrical: coordination of movements about the center of the body.• Natural: movements are continuous, curved, and make use of momentum.• Rhythmical and Habitual: flow allows a methodological and automatic

sequence of activities. It should reduce mental, eye and muscle fatigue, and strain.

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Flow Patterns: Flow within Departments

• The flow pattern within departments depends on the type of department.• In a product and/or product family department, the flow follows the product

flow.

1 machine/operator1 machine/operator 2 machines/operator

1 machine/operator

More than 2 machines /operator

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Flow Pat.: Flow within Departments (cont.)

• In a process department, little flow should occur between workstations within departments. Flow occurs between workstations and aisles.

Aisle

Aisle

Aisle

Aisle

Aisle

Dependent on interactions among workstations

available space

size of materials

Uncommon

One way

One way

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Flow Pat.: Flow between Departments

• Flow between departments is a criterion often used to evaluate flow within a facility.

• Flow typically is a combination of the basic horizontal flow patterns shown below. An important consideration in combining the flow patterns is the location of the entrance (receiving department) and exit (shipping department).

Straight

U flow

Serpentine

L flow

S flow

Circularflow

Simplest. Separate receiving/shipping crews

Very popular. Combine receiving /shipping. Simple to administer

When line is too long

Similar to straight. It is not as long.

Terminate flow. Near point of origin

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Flow within a facility considering the locations of entrance and exit

At the same location

On adjacent sides

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Flow within a facility considering the locations of entrance and exit (cont.)

On the same side but at opposite ends

On opposite sides

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Vertical Flow Pattern

Flow between buildings exists and the connection between

buildings is elevated

Ground level ingress (entry) and egress (exit) are required

Ground level ingress (entry) and egress (exit) occur on the

same side of the building

Travel between floors occurs on the same side of the building

Some bucket and belt conveyors and escalators result

in inclined flow

Backtracking occurs due to the return to the top floor

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Flow Planning

• Planning effective flow involves combining the above patterns with adequate isles to obtain progressive movements from origin to destination.

• An effective flow can be achieved by maximizing directed flow paths, reducing flow, and minimizing the costs of flow.

• A directed flow path is an uninterrupted flow path progressing directly from origin to destination: the Figure below illustrates the congestion and undesirable intersections that may occur when flow paths are interrupted.

Uninterrupted flow paths

Interrupted flow paths

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Flow Planning (cont.)

• The reduction of flow can be achieved by work simplification including:

1. Eliminating flow by planning for the delivery of materials, information, or people directly to the point

of ultimate use and eliminate intermediate steps.

2. Minimizing multiple flows by planning for the flow between two consecutive points of use to take

place in as few movements as possible.

3. Combining flows and operations whenever possible by planning for the movement of materials,

information, or people to be combined with a processing step.

• Minimizing the cost of flow can be achieved as follows:

1. Reduction of manual handling by minimizing walking, manual travel distances, and motions.

2. Elimination of manual handling by mechanizing or automating flow.

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Measuring Flow

1. Flow among departments is one of the most important factors in the arrangement of departments

within a facility.

2. Flows may be specified in a quantitative manner or a qualitative manner. Quantitative measures

may include pieces per hour, moves per day, pounds per week. Qualitative measures may range

from an absolute necessity that two departments show be close to each other to a preference that

two departments not being close to each other.

3. In facilities having large volumes of materials, information, a number of people moving between

departments, a quantitative measure of flow will typically be the basis for the arrangement of

departments. On the contrary, in facilities having very little actual movement of materials,

information, and people flowing between departments, but having significant communication and

organizational interrelation, a qualitative measure of flow will typically serve as the basis for the

arrangement of departments.

4. Most often, a facility will have a need for both quantitative and qualitative measures of flow and both

measures should be used.

5. Quantitative flow measure: From-to Chart

Qualitative flow measure: Relationship (REL) Chart

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Quantitative Flow Measurement

• A From-to Chart is constructed as follows:

1. List all departments down the row and across the column following the overall flow pattern.

2. Establish a measure of flow for the facility that accurately indicates equivalent flow volumes. If

the items moved are equivalent with respect to ease of movement, the number of trips may be

recorded in the from-to chart. If the items moved vary in size, weight, value, risk of damage,

shape, and so on, then equivalent items may be established so that the quantities recorded in

the from-to chart represent the proper relationships among the volumes of movement.

3. Based on the flow paths for the items to be moved and the established measure of flow, record

the flow volumes in the from-to chart.

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Example 1

Stores

Turning

Milling

Press

Plate

Assembly

Warehouse

– 6 12 9 1 4 –

– – 3 – 4 – –

– – – – 7 2 –

– – – – 3 1 1

– 1 3 – – 4 3

1 – – – – – 7

– – – – – – –

Sto

res

T

urni

ng

Mil

ling

Pre

ss

Pla

te

Ass

embl

y

War

ehou

se

Stores

Milling

Turning

Press

Plate

Assembly

Warehouse

– 12 6 9 1 4 –

– – – – 7 2 –

– 3 – – 4 – –

– – – – 3 1 1

– 3 1 – – 4 3

1 – – – – – 7

– – – – – – –

Sto

res

Mil

ling

Tur

ning

Pre

ss

Pla

te

Ass

embl

y

War

ehou

se

From-to Chart

Original Flow Pattern Revised Flow Pattern

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Flow PatternsS

tore

Tur

ning

Mil

ling

Pre

ss

Pla

te

Ass

embl

y

War

ehou

se

Stores Turning Milling

Warehouse Assembly Plate

Press

Stores Press Plate Assembly

Turning Milling Warehouse

Stores Milling Warehouse

Turning Press Plate Assembly

Straight-line flow U-shaped flow

W-shaped flowS-shaped flow

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Flow Patterns (cont.)S

tore

Tur

ning

Mil

ling

Pre

ss

Pla

te

Ass

embl

y

War

ehou

se

Stores Turning Milling

Warehouse Assembly Plate

Press

Stores Press Plate Assembly

Turning Milling Warehouse

Stores Milling Warehouse

Turning Press Plate Assembly

Straight-line flow U-shaped flow

W-shaped flowS-shaped flow

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Types of Layout

Volume

High

Medium

Low

Low Medium HighVariety

Product Planning Department

Fixed Materials Location Planning Department

Process Planning Department

Product Family Planning Department

Product Layout

Fixed Location Layout

Group Technology Layout

Process Layout

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Fixed Product Layout

Lathe Press Grind

Weld AssemblyPaint

Storage

Warehouse

Fixed Product Layout

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Fixed Product Layout (cont.)

• Advantages 1. Material movement is reduced.2. Promotes job enlargement by allowing individuals or teams to perform the

“whole job”.3. Continuity of operations and responsibility results from team.4. Highly flexible; can accommodate changes in product design, product mix, and

product volume.5. Independence of production centers allowing scheduling to achieve minimum

total production time.

• Limitations1. Increased movement of personnel and equipment.2. Equipment duplication may occur.3. Higher skill requirements for personnel.4. General supervision required.5. Cumbersome and costly positioning of material and machinery.6. Low equipment utilization.

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Product Layout

Drill Grind Drill

Lathe

Drill

Drill

Storage

Warehouse

Assembly

Lathe

Bend

Lathe

Mill

Press

Drill

Product Layout

33

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Product Layout (cont.)

• Advantages

1. Since the layout corresponds to the sequence of operations, smooth and logical

flow lines result.

2. Since the work from one process is fed directly into the next, small in-process

inventories result.

3. Total production time per unit is short.

4. Since the machines are located so as to minimize distances between consecutive

operations, material handling is reduced.

5. Little skill is usually required by operators at the production line; hence, training is

simple, short, and inexpensive.

6. Simple production planning control systems are possible.

7. Less space is occupied by work in transit and for temporary storage.

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Product Layout (cont.)

• Limitations

1. A breakdown of one machine may lead to a complete stoppage of the line that

follows that machine.

2. Since the layout is determined by the product, a change in product design may

require major alternations in the layout.

3. The “pace” of production is determined by the slowest machine.

4. Supervision is general, rather than specialized.

5. Comparatively high investment is required, as identical machines (a few not fully

utilized) are sometimes distributed along the line.

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Process Layout

Lathe Drill Weld

Mill

Drill

Grind

Storage

Warehouse

Lathe

Lathe

Mill

Mill

Lathe

Mill

Paint

Grind

Assembly

Assembly

Paint

Weld

Process Layout

37

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Process Layout (cont.)

• Advantages 1. Better utilization of machines can result; consequently, fewer machines are

required.2. A high degree of flexibility exists relative to equipment or man power allocation for

specific tasks.3. Comparatively low investment in machines is required.4. The diversity of tasks offers a more interesting and satisfying occupation for the

operator.5. Specialized supervision is possible.

• Limitations1. Since longer flow lines usually exist, material handling is more expensive.2. Production planning and control systems are more involved.3. Total production time is usually longer.4. Comparatively large amounts of in-process inventory result.5. Space and capital are tied up by work in process.6. Because of the diversity of the jobs in specialized departments, higher grades of

skill are required.

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Group Layout

Drill Grind Assembly

Drill

Weld

Assembly

Storage

Warehouse

Lathe

Assembly

Grind

Press

Mill

Lathe

Paint

Drill

Drill

Press

Grind

Assembly

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Group Layout (cont.)

• Advantages 1. Increased machine utilization.2. Team attitude and job enlargement tend to occur.3. Compromise between product layout and process layout, with associated

advantages.4. Supports the use of general purpose equipment.5. Shorter travel distances and smoother flow lines than for process layout.

• Limitations1. General supervision required.2. Higher skill levels required of employees than for product layout.3. Compromise between product layout and process layout, with associated

limitations.4. Depends on balanced material flow through the cell; otherwise, buffers and work-

in-process storage are required.5. Lower machine utilization than for process layout.

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Hybrid Layout

• Combination of the layouts discussed.

• A sample hybrid layout that has characteristics of group, process and product layout is shown in the following figure.

• A combination of group layout in manufacturing cells, product layout in assembly area, and process layout in the general machining and finishing section is used.

TM

TM TM

TM TMDM

BM

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Flow Dominance Measure

• Notations:

M: number of activities.

Nij: number of different types of items moved between activities i and j.

fijk: flow volume between i and j for item k (in moves/time period).

hijk: equivalence factor for moving item k with respect to other items moved

between i and j (dimensionless).

wij: equivalent flow volume specified in from-to chart (in moves/time period),

w = f h .ij ijk ijkk

N ij

1

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Flow Dominance Measure (cont.)

• Flow dominance measure = f =

where

f f

f fU

'

U L

f

w M w

M 1

w, w =

w

M

f MM M 1

(M 1 )(M 1 ), f M

1

(M 1 )(M 1 )

'

ij2 2 2

j 1

M

i 1

M

2

1

2

ijj 1

M

i 1

M

2

U

2

2 L 2

1

21

2

• f is the coefficient of variation.

• fL and fU are lower and upper bounds on f, respectively (fL f fU).

• The upper bound fU is only guaranteed to work when each process plan includes all activities. In this case, 0

f 1.

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Flow Dominance Measure (cont.)

Three cases :

1. f 0 a few dominant flows exist. product layout.

can use operations process chart as starting point for developing layout and

material handling system design.

quantitative measures principal source of activity relationship.

2. f 1 many nearly equal flows exist.

any layout equally good with respect to flows .

qualitative measures principal source of activity relationship.

3. 0 << f << 1 no dominant flows exist. difficult to develop layout.

process or product family layout .

both quantitative and qualitative measures important source of activity

relationship.

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Example 1

• Given three machines (activities) labeled 1, 2 & 3,

Product

A

B

C

Process Plan

1 - 2 - 3

2 - 1

3 - 1 - 2

Quantities/Shift

10

5

15

• Assume Product B is twice as “difficult” to move as A or C hijB = 2 and hijA = hijC = 1

To

From

1

2

3

1

0

2 510

1 1515

2

1101 15

25

0

0

3

0

1 1010

0

Equivalent Flow Volume

From-To Chart

w12 = 25,

w21 = 10, etc

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Example 1 (cont.)

M = 3 and

f3 1

6 .6 7= .3 5 2

f 33 3 1

(3 1 )(3 1 )= 1 .9 8 4 an d f 3

1

(3 1 )(3 1 )

f

'2

U

2

2 L 2

( ) ( . )

.

. .

. ..

2 5 1 0 1 0 1 5 3 6 6 7

1

0 7 5

1 9 8 4 1 3 5 2

1 9 8 4 0 7 50 5 1 2 2

2 2 2 2 2 212

1

21

2

w =(2 5 1 0 1 0 1 5 )

36 .6 72

no dominant flows exist (likely, since 3 different process plans)

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Qualitative Measures

• Closeness values (A, E, I, O, U, X) used to indicate physical proximity requirements

between activities.

• Relationship Chart can only show symmetric relationships, as compared to From-to

Chart (wij wji possible).

• Relationship Chart is starting point for developing layout when 0 << f 1.

– If f 1, then don’t need to consider flow (only qualitative relationship)

– If f <<1, then one can convert equivalent flow volumes to closeness values so that material

flow relationships can be considered along with qualitative relationship.

– If f 0, then can still convert to relationship chart if significant qualitative relationship exists,

otherwise, just use operations process chart.

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Conversion Method

• To convert equivalent flow volumes to closeness values for the example problem,

use wij + wji to make them symmetric.

• Conversion relations :

20 < wij + wji A w12 + w21 = 25 + 15 A

12 < wij + wji 20 E w13 + w31 = 0 + 15 E

5 < wij + wji 12 I w23 + w32 = 10 + 0 I

0 < wij + wji 5 O

wij + wji = 0 U

A

IE

Machine 1

Machine 2

Machine 3