Handbook of Industrial Automation - Richard L. Shell and Ernest L. Hall Part 13 pptx

Material handling and storage systems planning anddesign are subsets of facilities planning and design.. In the facilities design process the material ment determines the ¯ow paths.. The

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Material handling and storage systems planning and

design are subsets of facilities planning and design

Material ¯ow has both internal and external e€ects

on a site There are in¯uences for the site plan and

the operations space plan Conversely, the material

handling system impacts the facility plans, as

illu-strated inFig 1

In the facilities design process the material

ment determines the ¯ow paths The material

move-ment origins and destinations are layout locations

The storage locations and steps are e€ects of the

opera-tions strategy and thus the organization structure A

lean manufacturing system may have material delivery

direct to point of use replenished daily and a pull

sys-tem cellular manufacturing process that produces to

order with a TAKT* time of 5 min Such a system

could have inventory turns of 300 per year A more

traditional system would have a receiving inspection

hold area, a raw material/purchased parts warehouse,

a single shift functional layout batch manufacturing

system, inspection and test with 90% yield, a separate

packing department, and a policy of one month's

®n-ished goods inventory The space plans for the tional system should be very di€erent from the leanapproach and so should the material handling and sto-rage plans and systems A ``pull '' system also indicatesunnecessary material in the system If it does not pull itshould not be there

tradi-Material handling determines the capacity of a ufacturing plant From the receiving dock to the ship-ping platform the material ¯ow routes are thecirculation system Flow restrictions can act as capa-city limiters The material handling and storage plandetermines handling and storage methods, unit loadsand containerization to support the operations andbusiness strategy

man-The product volume plotÐthe plot of tities of materials by product typically shows a nega-tive exponential distribution, the important few andthe trivial many Pareto distribution The plot can beoverlaid with the most suitable production mode asillustrated in the product volume (PV)/mode curve,

These seven steps provide an understanding of the

material ¯ows in the facility The calibrated ¯ows are

used to develop anity ratings These initial steps are

also the basis for subsequent evaluation of layout

options and material handling system design

Step 1 Classify Materials Most manufacturing and

warehouse operations have a large variety of products

and materials Situations with 20,000 or more distinct

items are not unusual To analyze ¯ow or design amaterial handling system around so many individualitems is not practical Classi®cation reduces materials

to a manageable number of items so that the classesthen become the basis for determining ¯ow rates, con-tainers, and handling equipment

The initial classi®cations stratify materials for mon handling methods and container design Weight,size, shape, ``stackability,'' and special features are

Figure 3 Material varieties

de®ning criteria Figure 5shows a classi®cation based

on handling characteristics for a four-drawer cabinet

In addition, similarities in product, process

sequence, and raw material are bases for grouping

items that move over the same routes

Step 2 Identify Flow Units Material ¯ow is measured

in units of material over a unit of time and the analyst

chooses appropriate units for both parameters The

time unit is usually a matter of convenience and

depends largely on data availability Typical examples

are cases per hour, tons per day, pallets per week

Selection of the material ¯ow unit is more

proble-matic Where only one type of material moves, the

selection is straightforward, for example, the bushel

for a grain mill But few facilities have only a single

material or material type A wide variety of size, shape,

weight, and other handling characteristics must be

con-sidered, as illustrated earlier in Fig 3 For example,

integrated circuits are tiny, delicate, expensive, and

highly sensitive to electrostatic discharge (ESD), but

the operations that use integrated circuits also use

large metal cabinets Between these extremes is a

wide range of diverse items to move

Various items of the same size may have di€erent

handling requirements and costs A resistor and an

integrated circuit (IC) are very close in size But

resis-tors are moved in bulk, in ordinary containers, and

without special precautions The individual IC is sitive to ESD It requires an enclosed, conductive andexpensive container It may have a special tube or bag

sen-to further protect it Humans may sen-touch it only if theywear a grounded wrist strap and a conductive smock.Individual items or materials are seldom handledseparately Most items are in boxes, tote boxes, car-tons, bundles, bales or other containers These contain-ers then are what need to be handled But layout designrequires a standard unit of ¯ow This is the equivalent

¯ow unit (EFU) which should have the following acteristics:

char-Applicable to all materials and routesEasily visualized by the users

Independent of the handling method

The equivalent ¯ow unit should account for weight,bulk, shape, fragility, value, special conditions andother factors:

Weight is a common unit for most materials and isusually available in a central database

Bulk, or density, relates weight and size Overalldimensions determine bulk density

Shape impacts handling diculty Compact regularshapes such as boxes stack and handle mosteasily Round and irregular shapes stack with

Figure 4 Material ¯ow analysis

Tree trunks may be received and newsprint shipped.

Bulk liquids and gases may be received but

pharma-ceutical intravenous packs or bottles of tablets

Wood pulp and naphtha are received, chemicals,

textiles, and plastics are shipped

What seems a minor change in the item sometimes

brings a dramatic change in the equivalent ¯ow units

Figure 6 is a schematic ¯ow diagram that illustrates

changes in ¯ow intensity as the material is processed

for a four-drawer cabinet

Figure 7is a river diagram illustrating material ¯ow

for all products in an entire plant The diagram shows

how ¯ow intensity increases after the material ispainted and decreases after the parts are assembled.Painted sheet metal parts are easily damaged and di-cult to handle Once assembled and packaged, the unitsbecome protected, compact, and stackable and their

¯ow in equivalent ¯ow units decreases dramaticallyfor the same quantity and weight

When a decision is made on an equivalent ¯ow unit,convenience and familiarity often take precedence overaccuracy The primary purpose of this analysis is torate ¯ow intensities into one of four categories Weuse the vowel letter rating system A, E, I, and O.Accuracy of the order of 20% is therefore sucient.For this level of accuracy, the following procedure isused:

Review potential data sources

Interview production and support personnel

Figure 6 Equivalent unit ¯ow analysis

represent the largest volumes and are representative of

others, data from the top 20±30% should be used

Where groups of products have similar processes

and ¯ows, a representative item might portray an

entire group When the product mix is very large and

diverse, random sampling may be appropriate Figure

9 illustrates data selection guidelines

Process charts map the sequence of processes

graph-ically; routing sheets often have much the same

infor-mation in text form With either source, each operation

must be examined to determine in which SPU thatoperation will occur This determines the route Fromthe product volume analysis or other information, theraw ¯ow is determined which is then converted toequivalent ¯ow units, as illustrated inFig 10

This procedure is used directly if there are only afew products and where processes and ¯ows are similarand a single item represents a larger product group.For large numbers of items, process charts with arandom sample are used

Figure 8 Equivalent ¯ow units

Figure 9 Data selection guidelines

size, type, and class codes uses the same process and

follows the same route Field 8 is the number of

equiva-lent ¯ow units per day for each route and size These

subtotals are the basis for subsequent anity ratings,

stang, and for material-handling-system design

Other possible ®elds might contain information on

the time required per trip, distance for each route and

speed of the equipment From this the database

man-ager can derive the numbers and types of equipment

and containers required

Step 6 Calibrate Flows This step includes the lation of material ¯ow from each route origin to eachdestination It also includes conversion of calculated

calcu-¯ows to a step-function calibration for use in layoutplanning The calibration scale can be alphabetical ornumerical The vowel rating convention AEIO is usedhere The intensities of ¯ow distribution may indicatethe important few and trivial many The calibrationscan be used for relative capacity of material-handling-system selection

Figure 11 Material ¯ows from±to chart

For the calibration the ¯ow rates are ranked on a

bar chart, as shown inFig 13

The breakpoints are a matter of judgment and

should be made near natural breaks Experience from

a range of projects suggests that the following

propor-tions are a useful guideline:

A 5±10%

E 10±20%

I 20±40%

O 40±80%

Transport work Total material handling cost is

roughly proportional to the product of ¯ow intensity

and distance In physics force multiplied by distance

de®nes work For layout planning, material ¯ow

inten-sity I multiplied by distance D equals ``transport

work'' TW:

TW ˆ DI

In an ideal layout all SPUs with anities would be

adjacent Since an SPU occupies ®nite space, proximity

but not necessarily adjacency is possible Placing two

particular SPUs together forces other SPUs fartheraway The theoretical optimum relative locationsoccur with equal transport work on all routes wheretotal transport work is at the theoretical minimum.Transport work, then, is a metric for evaluating thelayout For evaluation, transport work is calculatedalong every path on a layout and the summationmade Layout options may be evaluated by comparingtheir total transport work

Transport work is useful in another way InFig 14

distance is plotted on the horizontal axis and ¯owintensity on the vertical axis Each route on the layoutplots as a point As mentioned above, the ideal layoutwould have constant (or iso-) transport work, such acurve being a hyperbola Routes with low intensityhave long distances; those with high intensity, shortdistances The product of distance and intensity foreither is then equal

A ``good'' layout, from strictly a material ¯ow spective, is one which has most or all points close tothe same hyperbolic isotransport work curve Routeswhich are signi®cantly distant from the hyperbola indi-cate an anomaly in the layout

Figure 12 Material ¯ow report

Three-dimensional

Distance±intensity plot

Animated

Figure 15 is a schematic diagram The blocks represent

locations on the layout and the arrows are material

move routes In this example a single arrow represents

all materials But di€erent line styles or colors might

show di€erent materials, or separate diagrams might

represent di€erent material classes Schematic grams are most useful in the early stages of a projectwhen they help the analyst and others to document,visualize, and understand the material ¯ows

dia-Figure 16 is a quanti®ed schematic diagram Inaddition to routes it illustrates ¯ow intensity by thethickness of shaded paths The thicker the path, thehigher the ¯ow intensity The quanti®ed schematicmay derive from the schematic as the project pro-gresses and data become known

Figure 15 Schematic ¯ow diagram

and ¯ow patterns It can also assist in designing certain

types of handling systems, such as automatic guided

vehicles (AGVs)

Macrolevel ¯ow patterns The facility layout

affects sequence and characteristics of material ¯ow

Indeed, the ¯ow pattern dictates the shape or

arrange-ment within a facility.Figure 22 shows the basic ¯ow

patterns: straight-through ¯ow, L-shape, U-shape or

circular, and hybrids

With straight-through or linear ¯ow, material entersand exits at opposite ends of the site or building.Flow deviates little from the shortest straight linepath Material movement is progressive Receivingand shipping areas (entrances and exits) are physicallyseparate

Straight-through ¯ow is simple and encourageshigh material velocity Operations are typicallysequential This ¯ow pattern has been a hallmark of

Figure 17 Locational ¯ow diagram (shaded lines)

Figure 18 Locational ¯ow diagram (multiple lines) Figure 19 River diagram

mass production With this type of ¯ow, material

tracking and handling are relatively simple In fact,

Henry Ford and Charles Sorensen invented the

assembly line to solve a material ¯ow problem

Straight-through ¯ow can also be vertical movement

in a high or multistory building This ¯ow pattern

was used in some of the ®rst water-powered textilefactories in England

L-shape ¯ow has a 908 directional change Thispattern results from multiple material entry pointsalong the ¯ow path and a need for direct access It is

a ¯ow pattern sometimes used in paint shops

U-shape or circular ¯ow is an extension of the shape ¯ow The loop may be open or closed.Materials return to their starting vicinity Thesepatterns combine receiving and shipping docks withshared personnel and handling equipment.Conversely, one set of truck docks in a building cancreate a U or circular ¯ow, for example, morningreceiving and afternoon shipping patterns

L-The use of common receiving and shipping nel is not conducive to good security In pharmaceuti-cal manufacturing regulations may require strictseparation of receiving and shipping facilities.Incoming material handling, storage, and materialphysical characteristic di€erences may also require dif-ferent personnel skills from those required at shipping.Hybrids, such as X, Y, Z, or star, are combinations

person-or variations of the basic ¯ow patterns

Flow complexity Simple material ¯ow patternshave fewer routes, fewer intersections and shorter dis-tances River and locational diagrams show ¯ow com-plexity These can be used to evaluate the relativecomplexity inherent in various layouts

Figure 20 String diagram

Figure 21 Three-dimensional material ¯ow diagram

convenient in that respect However, the convenience

for the designer becomes a high-cost system that

encourages large lots and high inventories It seldom

supports just-in-time and world-class manufacturing

strategies

The macrolevel handling plan speci®es the route,container and equipment for each move It then accu-mulates the total moves by equipment type and calcu-lates equipment requirements To prepare a handlingplan:

Figure 23 Transport work material ¯ow evaluation

(a)

(b)

1 Assemble ¯ow analysis output:

a Routes and intensities

b Material ¯ow diagrams

3 Calculate equipment requirements

4 Evaluate and select equipment

1.3.1 Containers

Materials in industrial and commercial facilities move

in three basic forms: singles, bulk, and contained

Singles are individual items handled and tracked as

such Bulk materials, liquids, and gases assume the

form or shape of their container Fine solids such as

¯owable powders are also bulk In containerized

hand-ling, one or more items are in or on a box, pallet,

board, tank, bottle, or other contrivance The

con-tainer restrains the items within and, for handling

pur-poses, the container then dominates

Some materials take several forms Nails and screws

can move on belt conveyors almost like powders Later

in the process, handling may be individually or in

con-tainers Containers o€er several advantages:

Protecting the contents

Improving handling attributes

Improved use of cube

Standardizing unit loads

Assisting inventory control

Assisting security

Pallet and palletlike containers have in the past been

the most widely used In many industries they still

are

``Tote pans'' and ``shop boxes'' have evolved into

sophisticated container families They are versatile for

internal and external distribution and are an important

feature of kanban systems Because of their wide use

they should be standardized and selected with great

care

Just-in-time, cellular manufacturing and time-based

competition strategies require moving small lot sizes to

point of use, which calls for smaller containers

For broad use in large plants, a family of

inter-modular units is important The International

Organization for Standardization (ISO) and the

American National Standards Institute (ANSI) have

set size standards The most popular families use

48 in:  40 in: and 48 in:  32 in: pallet sizes Figure

24 shows one system

Larger-than-pallet containers are primarily forinternational trade and ISO standardized unit havebeen designed There is, of course, a large variety ofnonstandard loads and containers

The key to container selection is integration.Container, route structure, and equipment are inti-mately connected; they should ®t with and complementeach other Other issues such as process equipmentand lot size also in¯uence container selection.Unfortunately, most container selections occur bydefault Certain containers pre-exist and new products

or items get thrown into them Existing route tures may also dictate container selection

struc-Manufacturing strategy should in¯uence containerselection Conventional cost-based strategies indicatelarge containers corresponding to large lot sizes; con-temporary strategies emphasize variety and responsetime The smallest feasible container corresponding

to small process and movement lot sizes should beselected

Figure 24 Box con®gurations for standard pallets

1.3.2 Route Structure

Route structure in¯uences container and equipment

selection It impacts costs, timing and other design

issues Figure 25 shows the three basic route structures:

direct, channel, and terminal In a direct system,

mate-rials move separately and directly from origin to

desti-nation In a channel system which has a pre-established

route, loads move along it, often comingled with other

loads In a terminal system, endpoints have been

estab-lished where the ¯ow is broken Materials may be

sorted, consolidated, inspected, or transferred at

these terminals In practice, many hybrids and

varia-tions of these basic route structures occur, as Fig 26

shows

1.3.2.1 Direct Systems

Direct systems using fork trucks are common In

operation, a pallet of material needs moving to another

department; the foreman hails a fork truck driver who

moves it to the next department An analogy for a

direct system is how taxis operate, taking their

custo-mers directly from one location to another without

®xed routes or schedules

Direct systems are appropriate for high ¯ow sities and full loads They also have the least transittime and are appropriate when time is a key factor,provided there is no queuing for transit requests.1.3.2.2 Channel Systems

inten-Channel systems use a predetermined path andschedule In manufacturing some automatic guidedvehicle systems work this way Manned trailer trainsand industrial trucks ®t channel systems They follow a

®xed route, often circular At designated points theystop to load and unload whatever is originating orreaching a destination at that point City bus systemsand subway systems use the channel structure.Channel systems are compatible with just-in-time(JIT) and world class manufacturing strategies ManyJIT plants need to make frequent moves of small quan-tities in tote boxes They may use a channel systemwith electric industrial trucks or golf carts Thesecarts operate on a ®xed route, picking up materialand dropping o€ loads as required Externally, overthe road trucks make several stops at di€erent suppli-ers to accumulate a full load for delivery.Simultaneously, they return kanban signals andempty containers for re®ll

Lower ¯ow intensities, less-than-full loads and longdistances with load consolidation bene®t from channelsystems Standardized loads also indicate the use of achannel system

1.3.2.3 Terminal Systems

In terminal systems loads move from origin to ultimatedestination through one or more terminals At the

Figure 25 Basic route structures

Figure 26 Hybrid route structures