planeacion de requerimientos de los materiales

7/29/2019 Planeacion de Requerimientos de Los Materiales

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The McGraw -Hill Companies, Inc., 2004

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Materials Requirements

Planning


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OBJECTIVES

Material Requirements Planning (MRP)

MRP Logic and Product Structure Trees

Time Fences

MRP Example

MRP II and Lot Sizing


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Material Requirements Planning

Defined Materials requirements planning (MRP) is a

means for determining the number of parts,components, and materials needed to producea product

MRP provides time scheduling informationspecifying when each of the materials, parts,and components should be ordered orproduced

Dependent demand drives MRP

MRP is a software system


4/26The McGraw -Hill Companies, Inc., 2004

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Example of MRP Logic and Product

Structure TreeGiven theproduct structure tree for A and the lead time anddemand information below, provide a materials requirements

plan that defines the number of units of each component andwhen they will be needed

Given theproduct structure tree for A and the lead time and

demand information below, provide a materials requirements

plan that defines the number of units of each component and

when they will be needed

B(4)

E(1)D(2)

C(2)

F(2)D(3)

A

Product Structure Tree for Assembly A Lead Times

A 1 dayB 2 daysC 1 dayD 3 daysE 4 days

F 1 day

Total Unit DemandDay 10 50 A

Day 8 20 B (Spares)Day 6 15 D (Spares)



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First, the number of units of A are scheduled

backwards to allow for their lead time. So, in the

materials requirement plan below, we have to place

an order for 50 units of A on the 9

th

day to receivethem on day 10.

First, the number of units of A are scheduled

backwards to allow for their lead time. So, in thematerials requirement plan below, we have to place

an order for 50 units of A on the 9th day to receive

them on day 10.

LT = 1 day

Day: 1 2 3 4 5 6 7 8 9 10

A Required 50

Order Placement 50


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Finally, repeating the process for all components, we have the

final materials requirements plan:

Finally, repeating the process for all components, we have the

final materials requirements plan:

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Day: 1 2 3 4 5 6 7 8 9 10A Required 50

LT=1 Order Placement 50

B Required 20 200

LT=2 Order Placement 20 200

C Required 100

LT=1 Order Placement 100

D Required 55 400 300

LT=3 Order Placement 55 400 300

E Required 20 200

LT=4 Order Placement 20 200

F Required 200LT=1 Order Placement 200

B(4)

E(1)D(2)

C(2)

F(2)D(3)

A

40 + 15 spares

Part D: Day 6


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Master Production Schedule (MPS)

Time-phased plan specifyinghow many and

when the firm plans to build each end item

Aggregate Plan(Product Groups)

Aggregate Plan(Product Groups)

MPS(Specific End Items)

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Types of Time Fences

Frozen

No schedule changes allowed within this window

Moderately Firm

Specific changes allowed within product groups as

long as parts are available

Flexible

Significant variation allowed as long as overall

capacity requirements remain at the same levels

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Exhibit 15.5Exhibit 15.5Example of Time Fences

8 15 26

Weeks

Frozen

Moderately

Firm Flexible

Firm Customer Orders

Forecast and available

capacity

Capacity

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Material Requirements Planning System

Based on a master production schedule, amaterial requirements planning system:

Creates schedules identifying the specific partsand materials required to produce end items

Determines exact unit numbers needed

Determines the dates when orders for those

materials should be released, based on leadtimes

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From Exhibit 15.6From Exhibit 15.6

Firm ordersfrom known

customers

Forecastsof demand

from randomcustomers

Aggregateproduct

plan

Bill ofmaterial

file

Engineeringdesign

changes

Inventoryrecord file

Inventorytransactions

Master production

Schedule (MPS)

Primary reportsSecondary reports

Planned order schedule for

inventory and productioncontrol

Exception reportsPlanning reports

Reports for performancecontrol

Material

planning(MRP

computerprogram)

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The McGraw -Hil l Companies, Inc., 2004

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Bill of Materials (BOM) File

A Complete Product Description Materials

Parts Components

Production sequence Modular BOM

Subassemblies Super BOM

Fractional options

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Inventory Records File

Each inventory item carried as a separate file

Status according to time buckets

Pegging

Identify each parent item that created demand

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Primary MRP Reports

Planned orders to be released at a future time

Order release notices to execute the planned

orders Changes in due dates of open orders due to

rescheduling

Cancellations or suspensions of open orders due

to cancellation or suspension of orders on the

master production schedule Inventory status data

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Secondary MRP Reports

Planning reports, for example, forecasting

inventory requirements over a period of time Performance reports used to determine

agreement between actual and programmed

usage and costs

Exception reports used to point out serious

discrepancies, such as late or overdue orders

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Additional MRP Scheduling Terminology

Gross Requirements

Scheduled receipts

Projected available balance

Net requirements

Planned order receipt

Planned order release

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MRP Example

A(2) B(1)

D(5)C(2)

X

C(3)

Item On-Hand Lead Time (Weeks)

X 50 2

A 75 3B 25 1

C 10 2

D 20 2

Requirements include 95 units (80 firm orders and 15 forecast) of X

in week 10

Requirements include 95 units (80 firm orders and 15 forecast) of X

in week 10

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A(2)

X

Day: 1 2 3 4 5 6 7 8 9 10

X Gross requirements 95

LT=2 Scheduled receipts

Proj. avail. balance 50 50 50 50 50 50 50 50 50 50

On- Net requirements 45

hand Planned order receipt 45

50 Planner order release 45

A Gross requirements 90


Proj. avail. balance 75 75 75 75 75 75 75 75

On- Net requirements 15hand Planned order receipt 15


B Gross requirements 45





C Gross requirements 45 40


Proj. avail. balance 10 10 10 10 10

On- Net requirements 35 40hand Planned order receipt 35 40

10 Planner order release 35 40

D Gross requirements 100


Proj. avail. balance 20 20 20 20 20 20 20




It takes

2 As foreach X

It takes

2 As foreach X

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Day: 1 2 3 4 5 6 7 8 9 10




























B(1)A(2)

X

It takes

1 B for

each X

It takes

1 B foreach X

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Day: 1 2 3 4 5 6 7 8 9 10




























A(2) B(1)

X

C(3)

It takes 3

Cs foreach A

It takes 3

Cs for

each A

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A(2) B(1)

C(2)

X

C(3)

Day: 1 2 3 4 5 6 7 8 9 10




























It takes 2

Cs foreach B

It takes 2

Cs for

each B

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A(2) B(1)

D(5)C(2)

X

C(3)

Day: 1 2 3 4 5 6 7 8 9 10




























It takes 5

Ds foreach B

It takes 5

Ds for

each B

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Closed Loop MRP

Production PlanningMaster Production SchedulingMaterial Requirements PlanningCapacity Requirements Planning

Realistic?No

Feedback

Execute:Capacity PlansMaterial Plans

Yes

Feedback

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Manufacturing Resource Planning

(MRP II)

Goal: Plan and monitor all resources of a

manufacturing firm (closed loop):

manufacturing

marketing

finance

engineering Simulate the manufacturing system

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Lot Sizing in MRP Programs

Lot-for-lot (L4L)

Economic order quantity (EOQ) Least total cost (LTC)

Least unit cost (LUC) Which one to use?

The one that is least costly!

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