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7/18/2019 Chap006 Mrp
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Copyright 2011 by The McGraw-Hill Companies, Inc. ll rights reser!e".McGraw-Hill#Irwin
Manufacturing
Planning and Control
MPC 6thEdition
Chapter 6
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Material Requirements
Planning (MRP)
Material Requirements Planning(MRP) has the managerial objective
of providing the right part at theright time to meet the schedulesfor completed products!
MRP provides a formal plan for eachpart number"ra# materials$components$ and finished products!
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%genda
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6-4
Resource
planning
&ales and operations
planning
'emand
management
Master productionscheduling
'etailed capacit
planning
'etailed material
planning
Material and
capacit plans
&hopfloor
sstems
&upplier
sstems
EnterpriseResourc
ePlanning(ERP
)&stem
Front End
Engine
Back End
Manufacturing Planning and Control System
*imephased
requirement (MRP)
records
Routing
file
+ills of
material
,nventor
status
data
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6-5
+asic MRP Record
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6-6
+asic MRP Record
-n hand
Period
. / 0 1 2
3ross requirements .4 14 .4
&cheduled receipts 24
Projected available balance 1 21 11 11 1 11
Planned order releases 24
5ead time . period5ot si7e 24
% previousl
released order
due in period .
% unreleased
order due in
period 2
Requirements
from all
sources
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+ill of Materials
*he +-M sho#s thecomponents and
subassemblies
required to produce
a product
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Product &tructure 'iagram
&ubassemblies
are represented
b separate
levels
8inished product is
located at the top$
components belo#
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E9plosion
E9plosion"the process of translating product
requirements into component part requirements
Considers e9isting inventories and scheduled
receipts
Calculating the quantities of all components
needed to satisf requirements for an given part!
Continued until all parts have been considered$leading to e9act requirements for all purchased
and:or ra# material parts
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3ross and ;et
Requirements 3ross requirements represent the total planned usage for the part
;et requirements account for e9isting inventor and:or scheduled
receipts
.44 req
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'emand *pes in MRP
'ependent"component or subassembl
demand driven b net requirements from the
ne9t higher level (e!g! scoop demand causedb net requirements for scoop assemblies)
,ndependent"demand driven b requirements
from outside the firm (e!g! customer orders)
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5ead *ime -ffsetting
3ross to net e9plosion sho#s ho# much of each
part is required$ but not #hen
*iming requires consideration of t#o factors5ead times"ho# long does it ta?e to obtain the
component or subassembl
Precedent relationships"the order in #hich parts
must be assembled MRP considers both factors #hen developing the
plan
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&cheduling 5ogic
*#o common approaches to scheduling e9ist
8ront schedule"schedule each step as earl as
possible
+ac? schedule"schedule each step as late as
possible
MRP combines bac? scheduling and gross to net
e9plosionReduced inventories
Minimi7ed storage time
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+ac? &cheduling
*op handle
assembl has the
longest duration of
an subassembl
&coop assemblmust be complete
before final
assembl can begin
-nl #hen all sub
assemblies and
components are
available can final
assembl begin
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MRP RecordsPlanned order release
for top handle assembl
becomes gross
requirement for top
handle component andnail (note / nails required
per assembl)
5otforlot order polic
e9actl matches suppl
to net requirements
8i9ed lot si7e order
polic requires orders in
multiples of lot si7e
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MRP *echnical ,ssues
Processing frequenc"recalculating all records and
requirements is called regeneration *his is a computationall intensive process so it is often run
in the bac?ground and during periods of lo# sstem demand ;et change approach onl recalculates those records
that have e9perienced changes
5ess frequent processing results in an outofdate
picture More frequent processing increases computer costs
and ma lead to sstem nervousness
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&afet &toc? and &afet
5ead *ime
&afet stoc? is buffer stoc? over and above the
quantit needed to satisf gross requirements
@sed #hen quantit uncertaint is the issue &afet lead time changes both the release and
due date of shop and:or purchase orders to
provide a margin for error
@sed #hen timing of orders is the issue
&afet lead time is not just an inflated lead time
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Pegging
Pegging provides a lin? bet#een demand
(order releases$ customer orders$ etc!) and
the gross requirements for partsPegging records include the specific part
numbers associated #ith a gross requirement
Pegging information can trac? the impact of a
problem (e!g! material shortage) bac? to theorder(s) it #ill affect
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Planning Aori7on
*otal amount of time included in MRP
calculations
5onger planning hori7on increasescomputational requirements
&horter planning hori7on ma result in less
effective plans if significant future demand is not
visible%t a minimum$ should cover the cumulative lead
time for all finished goods items
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&cheduled Receipts vs!
Planned -rder Releases &cheduled receipts represent an actual commitment
(purchase order$ production order$ etc!)
Planned orders are onl the current plan and can be
changed more easil &cheduled receipts for production orders alread have
component materials assigned&cheduled receipts do not impact gross requirements
Planned order releases do not have component materialsassignedPlanned order releases do impact gross requirements
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@sing the MRP &stem
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MRP Planner *as?s
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E9ception Codes
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+ottom@p Replanning
@sing pegging data to guide efforts to solve
material shortages
Pegging data allo#s the planner to ta?eaction onl #hen actual customer orders are
impacted
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MRP &stem -utputPart number and description MRP sstem data
MRP planning data
E9ception messages
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MRP &stem 'namics
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Principles
Effective use of an MRP sstem allo#s development of a
for#ardloo?ing approach to managing material flo#s!
*he MRP sstem provides a coordinated set of lin?ed
product relationships$ #hich permits decentrali7ed decisionma?ing for individual part numbers!
%ll decisions made to solve problems must be implemented
#ithin the sstem$ and transactions must be processed to
reflect the resultant changes! Effective use of e9ception messages allo#s attention to be
focused on the vital fe# rather than the trivial man!
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Bui7 " Chapter 6
Material Requirements Planning (MRP) ta?es place in the front
end sstems of the manufacturing planning and control sstem
(*rue:8alse)
,n a Material Requirements Planning (MRP) sstem$ #hat does
timephasing of gross requirements mean
8ront scheduling logic starts each step of the process as late as
possible (*rue:8alse)
% lotforlot order polic generates orders for a fi9ed quantit$
independent of actual requirements (*rue:8alse) Processing all Material Requirements Planning (MRP) records in
a single computer run is called DDDDDDDDDDD
&afet lead time involves inflating lead times to ensure stoc?
availabilit (*rue:8alse)