04 Master Scheduling 2011spring

8/11/2019 04 Master Scheduling 2011spring

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MASTER SCHEDULING: An Overview

The sections entitled: Uncertainty & Promisesand Closed-Loop Planningdescribedproduction planning and resource requirements planning, which are aggregate plans of

production and capacity generally taing one to ten years to complete e!ecution" Theseplans combine #aggregate$ similar products into product groups, combine demand intomonthly totals, and often group personnel requirements across departments" The timecomes when indi%idual products and ser%ices must be scheduled at specific wor centers"This is accomplished by master scheduling---producing a plan to manufacture specificitems or pro%ide specific ser%ices within a gi%en time period"

ough cut capacity planning#CCP$ is the process of determining if the plan is feasible' itdetermines whether the organi(ation has sufficient capacity to carry out the plan" )lthoughCCP is more refined than resource requirements planning #P$, it is called *rough cut+because it is less refined than capacity requirements planning #CP$"

igure illustrates how master scheduling and rough cut capacity planning relate to thecorporate and operations planning"

Figure 1
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This section presents a general picture of master scheduling, the master productionschedule #.P/$ and its relationship to rough cut capacity planning, the pro0ected on hand#P12$ in%entory and order promising using the a%ailable-to-promise #)TP$ quantity" /incethese terms and processes are used primarily in manufacturing, we describe them in thatconte!t" 2owe%er, their counterparts e!ist in many ser%ice organi(ations, ) description of

the de%elopment of the master schedule including the )TP, the P12 in%entory, and the.P/ and its relationship to CCP follows"

MASTER SCHEDULING & THE MPS

The master schedule #./$ is a presentation of the demand, including the forecast and thebaclog #customer orders recei%ed$, the master production schedule #the supply plan$, thepro0ected on hand #P12$ in%entory, and the a%ailable-to-promise #)TP$ quantity" Themaster production schedule #.P/$ is the primary output of the master scheduling process"The .P/ specifies the end items the organi(ation anticipates manufacturing each period"

3nd items are either final products or the items from which final assemblies #products$ aremade' as described later in this section" Thus, the .P/ is the plan for pro%iding the supplyto meet the demand" )n e!ample of a master schedule only including the .P/ and thebaclog is shown in Table " This e!ample is de%eloped further in the section"

Tabe 1

INTERFACES

The master schedule #./$ is a ey lin in the manufacturing planning and control chain"The ./ interfaces with mareting, distribution planning, production planning, and capacityplanning" 4t also dri%es the material requirements planning #.P$ system as shown inFigure 1"
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.aster scheduling calculates the quantity required to meet demand requirements from allsources" Tabe !shows a case in which the distribution requirements are the grossrequirements for the ./" .aterial requirements planning is used to calculate the quantityrequired" or e!ample, the 5 units in in%entory at the end of 6ee 7 are subtracted fromthe gross requirements, 85 units, of 6ee 9 to determine the net requirements of ; units

for 6ee 9"

Tabe !

The ./ enables mareting to mae legitimate deli%ery commitments to field warehousesand final customers" 4t enables production to e%aluate capacity requirements in a moredetailed manner" 4t also pro%ides the necessary information for production and mareting toagree on a course of action when customer requests cannot be met by normal capacity"inally, it pro%ides to management the opportunity to ascertain whether the business planand its strategic ob0ecti%es will be achie%ed"


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THE EN'IRONMENT

The competiti%e strategy of an organi(ation may be any of the following:

" .ae finished items to stoc #sell from finished goods in%entory$

>" )ssemble final products to order and mae components, >; subassemblies, and optionsto stoc

7" Custom design and mae-to-order

The competiti%e nature of the maret and the strategy of the organi(ation determine whichof the ./ alternati%e it should use" 4t is not unusual for an organi(ation to ha%e differentstrategies for different product lines and, thus, use different ./ approaches"

Ma(e)#*)S#*"(

The competiti%e strategy of mae-to-stoc emphasi(es immediate deli%ery of reasonablypriced off-the-shelf standard items" 4n this en%ironment the .P/ is the anticipated buildschedule of the items required to maintain the finished goods at the desired le%el"?uantities on the schedule are based on manufacturing economics and the forecastdemand as well as desired safety stoc le%els" )n end item bill of material #


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Figure !

The ad%antage of this approach is that many different final products can be produced fromrelati%ely few subassemblies and components" This reduces in%entory substantially" Figure- represents such a situation" 3ach final product contains four ma0or subassemblies and acomponent" 2owe%er, each subassembly and the component has different %ariations#alternates$" There are four different %ariations of /), two of /)>, four of /)7, three of/)9, and fi%e of C, which results in 9 ! > ! 9 ! 7 ! 5 or 98; final product configurations"

)ssembling to order enables the firm to stoc 9 A > A 9 A 7 A 5 or 8 different items ratherthan 98;"


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Figure -

Cu+#*% De+ign & Ma(e)#*)Or$er

4n many situations the final design of an item is part of what is purchased" The final productis usually a combination of standard items and items custom designed to meet the specialneeds of the customer, Combined material handling and manufacturing processingsystems are an e!ample, special trucs for off-the-road wor on utility lines and facilitiesare another" Thus, there is one .P/ for the raw material and the standard items that arepurchased, fabricated, or built to stoc and another .P/ for the custom engineering,fabrication, and final assembly" Case 444 in Figure ! represents this situation"

)s we proceed with the discussion of the policies and procedures of master scheduling andits relationship to rough cut capacity planning #CCP$, we will e!amine further therelationship of these en%ironments to the .P/ tas"

THE .ILL OF MATERIAL

)n inclusi%e definition of a final product includes a list of the items, ingredients, or materialsneeded to assemble, mi!, or produce that end product" This list is called a bill of material#


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of the design process and is used by manufacturing engineers to determine which itemsshould be purchased and which items should be manufactured" Production control andin%entory planning uses the


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Mu#i)Leve Tree S#ru"#ure an$ Leve+

6hile the single le%el


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Tabe 0

Tabe


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To illustrate this and se%eral other real-life comple!ities, let=s assume that we manufacturelamps with three different shades, two alternate base plates, and two types of socets" 1uroriginal lamp was designated L);l" 6oring with the different components, we now canha%e > different final products" To clarify this, we can produce a common parts bill in amatri! format, as shown in Tabe 2" )n e!amination of the matri! shows that some parts

are common to alt models" To ease the planning tas, we could group together the wiringassembly and the finished shaft with a new part number, say 9;;;, on the bill of material")lthough these components are produced independently of one another, they can begrouped as common parts on the


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the matri! form of the summary bill #Tabe 2$, a simplified product structure diagram#Figure $ can be created for the family of lamps that consisted of pseudo subassemblies-base assemblies, shades, and socet assemblies" or each of these, in place of thequantity for each unit assembled, the percentage split for each type of component is stated"@ow, as we plan for a total of ;,;;; lamps for each month, this planning bill can be used

to deri%e the number of each type of component to build" urthermore, if we decide tochange to, say, a B-inch green shade, only this single


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Figure 2

THE PLANNING HORI4ON

) principle of planning is that a plan must co%er a period at least equal to the time requiredto accomplish it" This means that the ./ planning hori(on must be at least as long as the

lead time required to fabricate the ./ items" This includes production and procurementtime as well as engineering time in a custom design en%ironment" eli%ery-to-customerresponse times #lead times$ in the different production en%ironments are illustrated inFigure 56

.any organi(ations di%ide the planning hori(on into periods with different controls onschedule changes" The closer a period is to the present, the tighter are the controls onschedule changes" or e!ample, rime fences #boundaries between different periods$ maybe established at the fourth wee and the eighth wee #two months$, as shown in Tabe 5 AThe location of the time fences and the nature of the appro%al required depend on thesituation" Darying lead times, maret conditions, and processing fle!ibility mae for different

time fences, sometimes at different plants within the same firm, Time fences should betailored to specific product groups as lead time may %ary widely between groups" 4n allcases, the ./ is the %ehicle for coordinating the achie%ement of mareting andmanufacturing goals"


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Figure 5

Tabe 5


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In Peri*$ C#a time hori(on beyond two months in Tabe 5$ the .P/ is consistent with theproduction plan" ) good production plan will mae preparation of the ./ straightforward inthis time frame"

In Peri*$ .#a time hori(on of four to eight wees in Tabe 5$ things become a bit sticy

when operating at full capacity" ) (ero sum game e!ists' that is, any additions to theschedule must be counterbalanced by comparable deletions or increases in capacity"Changes in demand patterns, unusual orders, or equipment failures may warrant changesin the .P/" These changes are usually negotiated between mareting and manufacturingwith the master scheduler determining their feasibility before the final decision" The productmi! may change but not the production rate"

In Peri*$ A#a time hori(on of (ero to four wees in Tabe 5$ only an act of Eod or topmanagement can change the .P/"

)s the time for order e!ecution and manufacturing approaches, labor and material are

committed" ) change in the schedule can be disrupti%e and costly, and the costs must becompared with the benefits of the change" ollowing time-fence-control guidelines, whichreflect realistic lead time constraints and competiti%e factors, will result in an .P/ thatpromotes manufacturing stability and producti%ity while pro%iding reasonable fle!ibility inmeeting mareting demands" 2owe%er, the competiti%e en%ironment may force decisions torestructure the


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7" etermine the planning hori(on, the time fences, and the related operational guides"

9" /elect the method for calculating and presenting the a%ailable-to-promise #)TP$information"

.6 Crea#ing #e MS in"u$e+ #e /**wing +#e3+:

" 1btain the necessary informational inputs, including the forecast, the baclog #customercommitments$, and the in%entory on hand"

>" Prepare the initial draft of the master production schedule #.P/$"

7" e%elop the rough cut capacity requirements plan #CC=$"

9" 4f required, increase capacity or re%ise the initial draft of the .P/ to obtain a feasibleschedule"

C6 C*n#r*ing #e MS in"u$e+ #e /**wing a"#ivi#ie+:

" Trac actual production and compare it to planned production to determine if theplanned .P/ quantities and deli%ery promises are being met"

>" Calculate the a%ailable-to-promise to determine if an incoming order can be promised ina specific period"

7" Calculate the pro0ected on hand to determine if planned production is sufficient to fille!pected future orders"

9" Use the results of the preceding acti%ities to determine if the .P/ or capacity should bere%ised"

Up to this point, this section has emphasi(ed ./ design factors and practices" @ow we areready to discuss preparing the initial draft of the master schedule-creating the ./"2owe%er, as you will note, creating and controlling acti%ities are interwo%en, emember,the .P/ lists by period the planned quantity of each .P/ item to be built" The ./ includesthe demand, the a%ailable-to-promise, the pro0ected on hand, and the .P/ quantity byperiod"

Crea#ing #e Ma+#er S"e$ue

Let=s consider creating the ./ in a mae-to-stoc en%ironment with no safety stoc" Tabe7pro%ides the type of information a%ailable for a product group" 4t re%eals that Product 7has sufficient in%entory to co%er the requirements of 6ees 7>, 77, and 79 but not 6ee75" Product > has sufficient in%entory to co%er the requirements for 6ees 7> and 77 butnot 6ee 79, Product 4 must be produced in 6ee 7>" )t this point there is no production


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Tabe 7

scheduled yet, so the P16 merely equals the P12 of the preceding period minus theforecast requirements" )n .P/ quantity should be planned in the first wee that an itemhas a negati%e P;9" Thus, Product 4 must be scheduled in 6ee 7>, Product > in 6ee79, and Product 7 in 6ee 75" 4n some situations an organi(ation may decide that an .P/quantity should be scheduled whene%er the P12 reaches some safety le%el, >5 units fore!ample" 4n the latter case, production is planned in the first period that the P;9 is lessthan the safety stoc le%el"

and 77, manufacturing Product > in 6ee 79 and thefirst part of 6ee 75, and manufacturing Product 7 in the last part of 6ee 75, as shown inTabe 8" Calculation of the P12 quantities demonstrates that the plan will co%er forecastrequirements"


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Tabe 8

The P12 for the first wee equals the beginning in%entory plus the .P/ quantity minus theforecast, and, for all remaining wees, it equals the P12 of the preceding period plus the.P/ quantity minus the forecast requirements of the current period" Thus, the P12 ofProduct 4 in 6ee 7> equals ; A 8; - 5; F 9; units' and in 6ee 77 it equals 9; A 8;

G ;; F >;" The other P12 quantities are calculated in the same manner, The ne!tquestion is, +4s there sufficient capacity to produce the .P/ quantitiesH+

R*ug Cu# Ca3a"i#9 Panning RCCP;: CCP calculates the critical wor centercapacity requirements for all items on the .P/" 4t pro%ides an early warning of insufficient

capacity and the need for capacity actions" Capacity in some wor centers---the paint shop,for e!ample may be well beyond that e%er required, while capacity in other wor centers---welding and heat treating, for e!ample---may be relati%ely low and a frequent bottlenec"Planning should focus attention on the potential bottlenec wor centers, Capacity actionsis the term used to describe rectifying a situation in which the a%ailable capacity is lessthan the required capacity
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Figure 7 shows the relationship of the %arious stages of capacity planning resourcecapacity planning #CP$, rough cut capacity planning #CCP$, and capacity requirementsplanning #CP$-to the specific production processes of a product group" #CP wasdescribed in the Closed-Loop Planningsection, CCP and CP are described in theCCP/ection"$ Table ;highlights the salient characteristics of these different stages of

capacity planning"

Figure 7

Tabe 1


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Te 3ri%ar9 $i//eren"e+ be#ween RCP an$ RCCP 3anning arethat the latter plans insmaller time increments, usually weely rather than monthly, and considers the productionlead time of the %arious components and subassemblies required to produce the products

on the .P/"

Revi+ing #e MPS: This section re%eals" once again that control taes place in theplanning process" )n initial .P/ is de%eloped for Products , >, and 7 of Product Eroup )from the production plan for Product Eroup ) as shown in Table " The capacity requiredby this initial .P/ is shown in Table >" Calculation of these requirements is described inthe CCP/ection"

Tabe 11

The comparison of capacity requirements to a%ailable capacity re%eals ii the present .P/is feasible" Tabe 1! shows a shortfall 7"5B hours of assembly= capacity in both 6ees 7>and 77 and surplus capacity in 6ees 79 and 75" This presents the master scheduler withthe following options:

" 4ncrease capacity in 6ees 7> and 77"
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>" educe production quantities in 6ees 7> and 77 and increase production quantities in6ees 79 and 75"

7" /ome combination of 1ptions 4 and >,

Tabe 1!

Tabe 1-


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4n this case the choice is 1ption >, as shown inTabe 1-, which also re%eals that sufficientcapacity is a%ailable with the re%ised .P/" The re%ise# .P/ quantities were obtained byscheduling the ma!imum possible quantity ; Product in 6ees 7> and 77 and completingthose requirements in 6ee 79 The remaining requirements for Products > and 7 wereroughly balanced between 6ees 79 and 75, producing Product > first" The resulting P12

%alue are shown in Tabe 10, which re%eals that sufficient units will be a%ailable to co%erforecast demand for Product " /imilar calculations will re%eal that the forecast demandsfor Products > and 7 are also co%ered" Later, as orders arri%e, it may be necessary tore%ise the .P/ again if actual orders are substantially different from the forecast on whichthe production plan and the .P/ are based"

Tabe 10

.any organi(ations ha%e computeri(ed the calculation of rough cut capacity requirementswhile others ha%e standard forms and procedures that= facilitate manual computations" 4nany e%ent the rough cut capacity require to implement the .P/ must be compared toa%ailable capacity to determine if any capacity actions are required" Tabe 1- re%eals thatthe .P/ is within the capacity constraints of the assembly department" 4t is also necessaryto %erify that the plan does not require more than the a%ailable capacity in the departmentsused in the manufacture of subassemblies and components"

)t first glance this may seem to be a rather complicated procedure" 2owe%er, once it isunderstood and the appropriate software obtained or de%eloped, it readily pro%ides

information e!tremely %aluable for planning" 1nce this initial re%ised feasible .P/ isde%eloped, creating the master schedule is completed"


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C*n#r*ing #e Ma+#er S"e$ue

The ./ ser%es as a control in three distinct ways" )ctual production is compared to the.P/ to determine if the plan is being met" The a%ailable-to-promise is calculated todetermine if an incoming order can be promised for deli%ery in a specific period" Thepro0ected on hand is calculated to determine if the supply is sufficient to fill e!pected futureorders"

The )%ailable-to-Promise #)TP$: Promising deli%ery to customers should be based on whatis or will be a%ailable #not committed$")%ailable-to-promise #)TP$ is defined by the )P4C/ictionary #I8$ as +The uncommitted portion of a company=s in%entory or plannedproduction" This figure is normally calculated from the master production schedule and ismaintained as a tool for customer order promising"+ 2owe%er, when one is informed that

there are +>5 units a%ailable-to-promise in 6ee and >; units a%ailable-to-promise in6ee 8,+ the meanings are not clear until the method of calculation is nown, The threebasic methods of computing the )TP are the discrete, the cumulati%e without loo-ahead,and the cumulati%e with loo-ahead, escriptions of these methods follow"

Ca"ua#ing #e Di+"re#e ATP: The discrete a%ailable-to-promise #)TP: $ iscomputed as follows:

" or the first period, the a%ailable-to-promise is the sum of the beginning in%entory plusthe .P/ for the first period #in this case (ero$ minus customer commitments for the firstperiod and all periods following the first period up to, but not including, the ne!t period for

which an .P/ quantity has been planned"

>" or all periods after the first, there are two possibilities:

a" 4f a master production quantity has been scheduled for the period the a%ailable-to-promise is the quantity scheduled minus all customer commitments for the period and forall following periods up to but not including, the ne!t period for which a master productionquantity has been scheduled"

b" 4f no master production quantity has been scheduled for the period the a%ailable-to-promise is (ero, e%en if deli%eries in the period ha%e been promised" The promised

shipments often are shown as baclog #customer commitments$ in the period with the mostrecent production #.P/$"

)s an e!ample, suppose after the .P/ has been constructed, total actual orders recei%ed#total customer commitments$ for Product 4 are as follows: ; units for deli%ery by the endof 6ee 7>, 8; units for deli%ery by the end of 6ee 77, 5 units for deli%ery by the end of6ee 79, and 5 units for deli%ery by the end of 6ee 75" The discrete )TP of Product in6ee 7> equals ; A BI G ;F BI units" The discrete )TP in 6ee 79 equals >>->F


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units" There is no .P/ in 6ee 75 so )TP F ; units" The discrete )TPs for all product=, areshown in Tabe 1"

4f in addition to the ; units of Product that had already been promised for deli%ery in6ee 7>, an order for 5 more units was recei%ed for deli%ery in 6ee 7>, the )TP would

be 59 in 6ee 7> and all the other )TPs would remain the same"

Tabe 1

@ote that in computing the )TP: it is not necessary to ha%e the forecast and thepro0ected on hand in%entory in the master schedule, That is because at this time themaster scheduler is not creating a master schedule, but is, instead, managing an e!istingschedule" The master scheduler is promising deli%ery to customers of units that will be

a%ailable either from units already on hand when construction of the master schedulebegan or from units scheduled to be built in accordance with the master productionschedule, Therefore, the forecast and P12 are not included in the tables that follow"

Ca"ua#ing #e Cu%ua#ive ATP: The cumulati%e method can be used without or withthe +loo-ahead+ calculation" 6e describe both methods" Table Bis an e!ample of thecumulati%e calculation of the )TP without loo-ahead #)TP:61L$ for Products , >, and 7"


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The cumulati%e )TP without loo-ahead equals the )TP in the preceding period plus the.P/, minus the baclog #customer commitments$ in the period being considered" Thus, in6ee 7> the )TP:61L for Product is

; A BI -; F BI"

4n 6ee 77 it equals

BI A BI-8;F58"

Tabe 12

The salient difference between this method and the discrete method is that the )TP in anyperiod is liely to include units also included in the )TP of other periods" or e!ample, the58 unit )TP of 6ee 77 includes the BI units in the )TP of 6ee 7>, which are alsoincluded in the )TP of all other wees" urthermore, when there is no loo-aheadprocedure, the )TP for a wee may include units committed to fill requirements for a laterwee" or e!ample, 5 of the units in the )TP of 6ee 79 are committed to customer


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orders promised in 6ee 75, )lthough some planners may function well with such asystem because they understand the data and are able to e!tract accurate informationfrom it, the data is misleading" The loo-ahead approach resol%es this problem" Table isan e!ample of the cumulati%e with loo-ahead calculation of the )TP #)TP: 6L$"

Tabe 15

The difference between this method and the cumulati%e )TP without loo-ahead is thatunits produced in one period and committed for use in a future period are omitted from the

)TP in all periods preceding that in which they are promised"The )TP of Tabe 15 gi%es a%ery clear picture: there are B> units of Product 7 that can be promised for any of the6ees 7> through 79, and a total of ;> units, including the B> a%ailable earlier" that canbe promised for deli%ery in 6ee 75, The )TP:6L of a period equals the )TP:6L of the


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preceding period plus the .P/ of the period minus the baclog of the period minus thesum of the differences between the baclogs and master production schedules of all futureperiods until, but not including, the period from which point production e!ceeds thebaclogs" This is shown by the following model" )lthough this description and the followingmodel seem cumbersome, the actual calculations usually are not" This is because proper

management of the ./, including the .P/ and promises to customers, usually will pre%entthe baclog from e!ceeding the .P/ for an e!tended time"

C*n+u%ing #e F*re"a+#: This section pre%iously described how to calculate the P12without changing the forecast or the .P/" Under the consuming-the-forecast concept, themaster schedule presents the forecast as only the quantity yet to be ordered by customers,as opposed to the initial forecast" Thus, each time an order is recei%ed, the forecastquantity on the ./ may be changed" Two different situations e!ist when using thisapproach"

4n the first case, the e!isting total sales forecast still is seen as an accurate forecast of the

total e%entual units to be sold for deli%ery in the period" The re%ised forecast equals theoriginal forecast minus the orders recei%ed #the baclog$ for the period' the forecast is+consumed+ by the orders recei%ed"

This situation is illustrated in 6ees 7>,77, and 79 of Tabe 17" The orders recei%ed ha%ebeen subtracted from the forecast" or e!ample, the forecast for 6ee 7> now equals 5;#the initial forecast$ - ; F 9;" The forecast now represents the remaining orderse!pected, and the P12 equals the P12 of the preceding wee plus the .P/ minus thesum of the forecast and the baclog #


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Tabe 17

The second situation differs in that the e!isting total forecast no longer is %iewed asaccurate, or e!ample, suppose an une!pected order is recei%ed from a new customer andthere is no reason to belie%e that the regular customers will not order as forecast" Thissituation is illustrated in 6ee 75 of Tabe 17" Ten of the units ordered for deli%ery in 6ee75 come from a new customer' the planner decides that there will still be additional ordersfor 95 units" Thus, only J units of the 5 ordered are subtracted from the forecast" This alsorequires that another ; units be subtracted from the P12 in 6ee 75 as the originalforecast for 6ee 75 has effecti%ely been increased by ; units" or e!ample, the P12 of6ee 75 now equals ; A ; - #95 A 5$ F ;, Thus, the P12 for 6ee 75 is different fromthat shown in Tabe 10" Consuming the forecast is an effecti%e method of recogni(ingeither potential stoc-outs or e!cessi%e in%entory and the need to re%ise the .P/" Thelielihood of e!cessi%e in%entory would be spotted when present sales suggest thate%entual total orders will be less than the e!isting forecast"

THE FINAL ASSEM.L= SCHEDULE

The final assembly schedule #)/$ is a statement of those final products that are to beassembled from .P/ items in specific time periods" 4n some organi(ations--thoseproducing power tools, for e!ample-.P/ items and final products are identical, and onedocument ser%es as both the .P/ and the )/" 4n many other situations, especially whenthere are many more final products than there are items at the first


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4n some cases final products differ only by the labeling or pacaging of the same .P/item" 4n others painting or finishes may constitute the difference" 4n still others a %astdifference may e!ist in the transformation of items into a %ariety of final products" 4n each ofthese cases an )/ that is distinct from but consistent with the .P/ must be prepared" 4nthe manufacture of automatic washers, for e!ample, the motor, transmissions, control units,

consoles, tubs, sets of assembly hardware, and %arious optional accessories would be.P/ items, and the different models a%ailable to the customer would be final assemblies"Thus, the manufacture of motors can be authori(ed long before each motor is committed tothe assembly of a particular model" /ince the )/ is constrained by the a%ailability of thoseitems scheduled on the .P/ plus those in in%entory, the .P/ and the )/ must becoordinated, This is true for both purchased and manufactured components"

Tabe 18is an e!ample showing the relationship between the )/ for an assembly, ),made-to-order, and an .P/ for two optional subassemblies, /)l and /)>, which aremade-to-stoc with option o%er-planning" The assembly may be ordered with either an /)or an /)> subassembly" /ales records re%eal that each has an equal probability of being

selected' each has recei%ed a ma!imum of B; percent of the orders in any wee" Thus,with an )/ for a ma!imum of ten )=s in 6ee >, no beginning in%entory for any item, anda lead time of one wee for subassemblies, the .P/ calls for si! each of /)l and /)> in6ee 4" Three possible demand combinations e!ist: fi%e each of /)l and /)>, four of /)land si! of /)>, and si! of /)l and four of /)>" Two subassemblies will not be usedimmediately' they will be carried in stoc to the ne!t wee"

>ee( 1 3a++e+: )ctual orders are for ten )=s, four with /)l and si! with /)>" Two /)l=s arein in%entory at the end of the wee" This results in an .P/ calling for producing four /)l=sand si! /)>=s in 6ee > to assemble a ma!imum of ten )=s in 6ee 7" The )/ and the.P/ are coordinated"

4n an assemble-to-order en%ironment, the )/ frequently is stated in terms of indi%idualcustomer orders and must be consistent with the shipping schedule" 4n a mae-to-stocen%ironment, the )/ is a commitment to produce specific quantities of catalog finalproducts" The shipping schedule depends on a%ailable in%entory and a%ailable capacity"Capacity is required for assembly and for any items that may be controlled by the )/ andnot the .P/" 3!amples are painting, pacaging, crating, and preparing shippingdocuments"

4n any e%ent, authori(ation of the final assembly schedule should be held to the lastpossible moment" This pro%ides the greatest fle!ibility in meeting actual demand andimpro%es customer ser%ice" /ince assembly lead time and .P/ item a%ailability constrainthe )/, any planning and design to reduce this lead time and increase fle!ibility, aid inachie%ing customer ser%ice ob0ecti%es"

Preparation, measuring of actual output, and control of the )/ should rest with the masterscheduler" This enables one indi%idual to control all demands on resources and coordinate.P/ items and the )/, order entry items, and order-promising acti%ities"


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Te Ma+#er S"e$uer

.ost organi(ations should ha%e a master scheduler, This indi%idual is the lin betweenmareting, distribution, engineering, manufacturing, and planning" The tass of the master

scheduler include the following:

" Pro%ide deli%ery promise dates for incoming orders' match actual requirements withthe master schedule as they materiali(e,

>" 3%aluate the impact of top-down inputs, such as a request for the introduction of anew product in much less than the normal deli%ery time"

7" 3%aluate the impact of bottom-up inputs, such as anticipated delay reports from theshop or purchasing indicating that particular components will not be a%ailable asscheduled or that planned production rates are not being attained,

9" e%ise the master schedule when necessary because of lac of material or lac ofcapacity"

5" Call basic conflicts of demand and capacity to the attention of other members ofmanagement, especially mareting and manufacturing, who need to participate inresol%ing the problems"

6hether or not a firm has someone formally designated as the master scheduler, the tassare essential" Combining them under the 0urisdiction of one indi%idual impro%es thelielihood that they will be coordinated and managed properly" .ost importantly, it pro%idesa focal point for the required coordination of mareting, manufacturing, distribution, and

planning as well as a place to loo for answers when things are not going as planned"

MPS In/*r%a#i*n S9+#e%+ an$ Ana9+i+

The comple!ity of most manufacturing en%ironments requires a computeri(ed productionplanning and control system with human interfaces at appropriate decision points" )s notedpre%iously, the master scheduler requires such as interface" The requirement for computerassisted planning is due to a combination of the number of items on the .P/, the largenumber of subassemblies=" and components, and the magnitude of recording andprocessing in%entory transactions, material requirements, and capacity requirements"

Today, there are literally hundreds of commercial software /ystems a%ailable" /ome are foruse with mainframe computers, others for use with minicomputers, and a growing numberfor use with personal computers"

The installation and a%ailability of such a computer system often allows the organi(ation toperform what-if analyses to answer questions such as:

#$ 6hat will be the effect of a shift in product mi! on capacity requirementsH


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#>$ 6hat will be the effect of a ; percent increase in demand on capacity requirementsH

)nswers to these questions, a%ailable from a computeri(ed simulation run, will enablemanagement to prepare plans for such contingencies"

SUMMAR= AND COMMENTS

)lthough the preparation and maintenance of all the elements of the master' schedule maybe comple! in some situations, the principles and concepts an not" )ll ha%e beende%eloped in practice and are well documented in the literature and ha%e been discussedin this section"

The .P/ is a %ital lin in the operations planning and control systems in .anufacturing,production, mareting, and engineering #product and process design$" The items on the.P/, in particular their le%el in the

04 Master Scheduling 2011spring

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