Material Requirement Planning. Independent and Dependent Demand Independent Demand A B(4) C(2) D(2)E(1) D(3) F(2) Dependent Demand Independent demand

Material Requirement Planning

Independent and Dependent Demand

Independent Demand

A

B(4) C(2)

D(2) E(1) D(3) F(2)

Dependent Demand

Independent demand is uncertain. Dependent demand is certain.

Dependant Demand Dependent demand: Demand for items that

are subassemblies or component parts to be used in production of finished goods.

Once the independent demand is known, the dependent demand can be determined.

物料需求計劃(Material Requirements Planning)

The MRP’s objective is to determine what components are needed to meet the master production schedule and,based on lead time, to calculate the periods when thecomponents must available.

•What to order•How much to order•When to order•When to schedule delivery

MRP in American Industry

1960 - IBM

1971 - 150 MRP systems in use

1972 - The American Production and Inventory Control Society (APICS) launched its MRP Crusade to publicize and promote MRP

1982 - 8000 MRP Systems in use

1984 - 16 companies sold $400 million in MRP software

1989 - $1.2 billion worth of MRP software was sold to American Industry


Investment in MRP

1191000

795000

0 200000 400000 600000 800000 1000000 1200000 1400000

Standard Deviation

Mean

LaForge and Sturr 1986



MRP

MPS

BOM

InventoryRecords

工令

請購單


•Bill of Material Structure

1. 彙總式 (Summarized Parts List)

2. 多階式 (Multilevel Bill)

3. 單階式 (Single-Level Bill)

4. 規劃料表 (Planning Bill)


•彙總式 (Summarized Parts List)

料號名稱數量欄位

B 1

C 1

D 3

E 2

F 1

G 1

項目 A

E(1) F(1)

B(1)

D(1) E(1) G(1)

C(1) D(2)

A

Product Tree


•多階式 (Multilevel Bill)

F

J K (2)

G(2)

B(2) C

M (2) N

D

X

P

J K (2)

G

L M N(2) O

Y


•單階式 (Single-Level Bill)

B(2) C D

X

L M N(2) O

Y

F G(2)

B

M (2) N

D

P G

L

J K (2)

G


•規劃料表 (Planning Bill) - Used to simplify forecasting (MPS, MRP)

Common parts L egs Sides Tops

Table

Leg A40%

Leg B35%

Leg C25%

Side A55%

Side B30%

Side C15%

Top A45%

Top B30%

Top C25%

100%


用途表 (Where-Used Report)

•與 BOM 相關表格

溯源報表 (Pegging Report)

Where-used reports give the same information as a BOM, butthe where-used report gives the parents for a component whereas the BOM gives the components for a parent.

A pegging report is similar to where-used report. However, the pegging report shows only those parents for which there is an existing requirement.


•溯源報表 (Pegging Report)

WeekItemNumber

1 2 3 4 5

C 50 125 25 50 150

A 50 25 25 50 50

B 100 100

Pegged Requirements

Source of Requirements

C

C D

B

A


•Uses for Bill of Material

•Product Information•Engineering Change Control•Service Parts•Planning•Order Entry•Manufacturing•Costing


•MRP Process

Exploding andOffsetting

Gross and NetRequirements

Releasing Orders


•Exploding and Offsetting

Exploding the requirements: This is a process of multiplying the requirements by the usage quantity and recording the appropriate requirements throughout the product tree.

Offsetting: This is the process of placing the exploded requirements in their proper periods based on lead time.

Output Planned Orders

Note: Lead time is the period from when an order is placed until the part is available for use.


•Exploding and Offsetting - Example

D(L T=1) E(L T=1)

B(L T=2) C(L T=1)

A(L T=1)

WeekPartNumber

1 2 3 4 5

A Planned Order ReceiptPlanned Order Release 50

50

B Planned Order ReceiptPlanned Order Release 50

50

C Planned Order ReceiptPlanned Order Release 50

50

D Planned Order ReceiptPlanned Order Release 50

50

E Planned Order ReceiptPlanned Order Release 50

50

Planned Order


•Gross and Net Requirement

Often inventory is available and must be included when calculating quantities to be produced.

Planned OrderInventory Information


•Gross and Net Requirement - ExampleWeekPart

Number1 2 3 4 5

A Gross RequirementProjected Available 20Net RequirementPlanned Order ReceiptPlanned Order Release

20 20 20 20

30

5003030

B Gross RequirementProjected Available 10Net RequirementPlanned Order ReceiptPlanned Order Release

10 10

20

103002020

C Gross RequirementProjected AvailableNet RequirementPlanned Order ReceiptPlanned Order Release

0

30

3003030

D Gross RequirementProjected AvailableNet RequirementPlanned Order ReceiptPlanned Order Release

0

20

2002020

E Gross RequirementProjected AvailableNet RequirementPlanned Order ReceiptPlanned Order Release

0

20

2002020


•Released Orders

Since the objective of the MRP is to have material available when it is needed and not before, orders for material should not be released until the planned order release date arrive. Thus an order is notnormally released until the planned order is in the current week.

Before a manufacturing order is released, component availability mustbe checked.

When the authorization to purchase or manufacture is released, the planned order receipt is canceled, and a scheduled receipt is created in its place.


•Released Order - Scheduled Receipt

The scheduled receipts row shows the quantities ordered and when theyare expected to be completed and available.

WeekPartNumber

1 2 3 4 5

D Gross RequirementScheduled ReceiptsProjected AvailableNet RequirementPlanned Order ReceiptPlanned Order Release

0

202000

E Gross RequirementScheduled ReceiptsProjected AvailableNet RequirementPlanned Order ReceiptPlanned Order Release

0

202000

Note: Net Requirement = Gross Requirement - Scheduled Receipts - Available Inventory


•Released Order - Closed Out

When the goods are received into inventory and available for use, the order is closed out, and the scheduled receipt disappears to become part of the on-hand inventory.

U.S. Manufacturing Inventory Turns

55.5

66.5

77.5

88.5

9

1940 1950 1960 1970 1980 1990 2000Year

Inven

tory T

urns

Note: Inventory turns are defined as gross annual sales divided by average on-hand inventory


10%

90%

Booz, Allen, and Hamilton, from a 1980 survey of over 1100 firms

Be able to recoup theinvestment in an MRP

system within two years

Trouble with MRP (1)


9%

31%60%

ABC&D

1982 APICS Survey of 679 APICS members

Class A: with fully implemented, effective systemsClass B: Have fully implemented, but less than fully effective systemClass C: Have partially implemented, modestly effective systems.Class D: Have marginal systems providing little benefit to the company

Trouble with MRP (2)


•“MRP is a $100 billion mistake”

•“90 percent of MRP users are unhappy”

•“MRP perpetuates such plant inefficiencies as high inventories”


The Cause of Most MRP System Failures

•Lack of top management commitment.

•Lack of education of those who use the system.

•An unrealistic master production schedule.

•Inaccurate data, including bills of material and inventory records

APICS Literature (Latham, 1981)


An MRP system is capacity-insensitive, and properly so, as its function is to determine what materials and componentswill be needed and when, in order to execute a given masterproduction schedule. There can be only one correct answer to that, and it cannot therefore vary depending on what capacity does or does not exist.

Orlicky 1975


Fundamental Wrong with MRP

MRP

Flawed Model

)f( numberpart timelead

Note: Lead times are not affected by the status of the plant


The Solutions ?

Fixed Lead TimePlant has finite

Capacity

Release jobs too late•Destroy the desired coordination of parts at assembly•Finished products to come out too late

Inflate the MRP lead times

•More work into the plant•Increase the flow time


MRP II HierarchyDemandForecast

AggregatePlanning

ResourcePlanning

MPSRough-Cut

Capacity Planning

MRP

Job Pool

JobRelease

JobDispatching

Capacity RequirementPlanning

BOM

InventoryStatus

RoutingData

Long-RangePlanning

Intermediate-RangePlanning

Short-TermPlanning

Capacity Requirement Planning(產能需求規劃 )

Capacity Requirement Planning

The capacity requirements plan (CRP) occurs at the level of the material requirements plan. Planned orders from the MRP and open shop orders (scheduled receipts) are converted into demand for time in each work center in each time period. This process takes into consideration the lead times for operations and offsets the operations at work centers accordingly. In considering open shop orders, it accounts for work already done on a shop order.

CRP

Planned Order Releases

Open Orders

Routing Data Capacity and lead Timefor Process Centers

Shop Calendar

Work Center Load Report


•Open Order

An open order file appears as a scheduled receipt on thematerial requirements plan. It is a released order for aquantity of a part to be manufactured and completed on a specific date

•Planned Order Releases

Planned orders are determined by the computer’s MRP logicbased upon the gross requirements for a particular part.

Terms Definition


Routing File

A routing is the path that work follows from work center to workcenter as it is completed. It should exist for every component manufactured and contain the following information:

•Operations to be performed•Sequence of operations•Work centers to be used•Possible alternate work centers•Tooling needed at each operation•Standard times: setup times and run times per piece


Part Name: Gear Shaft Part Number: SG123Drawing Number: D123X

Operation Work S/U Time Run Time/Piece No. Center (Standard Hours) (Standard Hours) Operation

10 12 1.50 0.2 Turn Shaft 20 14 0.50 0.25 Mill Slot 30 17 0.30 0.05 Drill Hole 40 03 0.45 0.10 Grind 50 Stores Inventory Routing Data


Work Center FileA work center is composed of a number of machines or workers capableof doing the same work.The machinery will normally be similar so there are no differences in thekind of work the machines can do or the capacity of each. A work center file contains information on the capacity and move, wait,and queue times associated with the center.

Move time: the move time is the time normally taken to move material from one work station to another.Wait time: the wait time is the time a job is at a work center after completion and before being moved.Queue time: the queue time is the time a job waits at a work center before being handled.Lead time is the sum of queue, setup, run, wait, and move times.


WorkCenter

QueueTime

WaitTime

MoveTime

AvailableTime

Utilization Efficiency

12 4 1 1 24 100% 100%14 3 1 1 24 100% 100%17 5 1 1 24 100% 100%03 8 1 1 24 100% 100%

Work Center FileAvailable time : The available time is the number of hours as work center can be used.Utilization : The percentage of time that the work center is active compared to the available time is called work center utilization. It can be determined from historical records or by a work sampling study. Efficiency : The workers might be working at a faster or slower pace than the standard pace, causing the efficiency of the work center.


Ex: A work center has the following open orders and planned orders for week 20. Calculate the total standard time required (load) on this work center in week 20. Order 222 is already in progress, and there are 100 remaining to run.

OrderQuantity

SetupTime

RunTime

Released Orders

Planned Orders

222333

100150

01.5

0.20.2

444555

200300

32.5

0.250.15


Week 20 21 22 23 24 TotalReleased

Load51.5 45 30 30 25 181.5

PlannedLoad

100.5 120 100 90 100 510.5

Total Load 152 165 130 120 125 692Rated

Capacity140 140 140 140 140 700

Over/UnderCapacity

-12 -25 10 20 15 8

Work Center Load Report


Documents

Material Requirement Planning. Independent and Dependent Demand Independent Demand A B(4) C(2) D(2)E(1) D(3) F(2) Dependent Demand Independent demand