生产运作管理Chapter 14

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Independent vs. Dependent Demand
Independent Demand (Demand not related to other items or the final end-product)
Dependent Demand (Derived demand items for component parts, subassemblies, raw materials, etc.)
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Dependent Demand
Effective use of dependent demand inventory models requires the following
Master production schedule Specifications or bill of material Inventory availability Purchase orders outstanding Lead times
Top level is 0; next level is 1 etc.
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MRP Requirements
Computer system Mainly discrete products Accurate bill-of-material Accurate inventory status Stable lead times
© 1984-1994 T/Maker Co.
12 major ambulance designs
18,000 different inventory items 6,000 manufactured parts 12,000 purchased parts
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Collins Industries
Gross Requirements for Spinach Quiche Week Amount 7 8 9 100 200 150 10 11 12 60 13 75 14 15 100 16 and so on
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Bill-of-Material
List of components & quantities needed to make product Provides product structure (tree)
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MRP Benefits
Better response to customer orders Faster response to market changes Improved labor & equipment utilization Reduced inventory levels without reduced customer service Better inventory planning & scheduling
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The cutaway of one ambulance interior
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Work cell- Metal fabrication shop
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Installing the Wiring(15 miles)
Established in terms of specific products
Must be followed for a reasonable length of time The MPS is quite often fixed or frozen in the near term part of the plan
No
Realistic??
Yes
Execute Capacity Plans Execute Material Plans
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Material Requirements Planning (MRP)
Manufacturing computer information system Determines quantity & timing of dependent demand items
Parents: Items above given level Children: Items below given level
Shows low-level coding
Item is coded at the lowest level at which it occurs BOMs are processed one level at a time
Amount on hand
Stable demand
Safety stock Tim e
Dependent Demand
“Lumpy” demand
Time
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Amount on hand
Time
Time
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The Planning Process
Aggregate Production Plan Master Production Schedule Material Requirements Plan Capacity Requirements Plan
January 1,500
February 1,200
2
3
4
5
6
7
8
100 500
100 500 300
100 450
100 450 100
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MPS Examples
Table 14.1
For Nancy’s Specialty Foods
Gross Requirements for Crabmeat Quiche Week Amount 6 50 7 8 100 9 47 10 60 11 12 110 13 75 14 and so on
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Structure of the MRP System
Figure 14.5
Data Files BOM Master production schedule Output Reports
MRP by period report
MRP by date report
1
Gross Requirements Scheduled Receipts Available Net Requirements Planned Order Receipts Planned Order Releases
2 20
3 30
4 25
5 15 8 7 7
2 5 25
2333337 Nhomakorabea© 1995 Corel Corp.
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Materials arriving overnight
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Dependent Demand
The demand for one item is related to the demand for another item Given a quantity for the end item, the demand for all parts and components can be calculated In general, used whenever a schedule can be established for an item MRP is the common technique
Forecast & Booked Forecast & Booked Customer Orders Customer Orders EOQ & ROP
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Calculated Calculated
MRP
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Independent Demand
Dependent vs. Independent Demand
IBM AS400 + MAPICS DB
Reduced inventory by more than 30% in just 2 years
Four Key Tasks
Material plan must meet both the requirements of the master schedule and the capabilities of the production facility Plan must be executed as designed Reducing inventory investment through effective “timephased” deliveries, consignments, and constant review of purchase methods Maintenance of record integrity, accuracy
OPERATIONS MANAGEMENT
Chapter 14 Material Requirements Planning (MRP)
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Collins Industries
Largest manufacturer of ambulances in the world International competitor
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Dependent vs. Independent Demand
Item Demand Demand Source Source Material Material Type Method of Method of Estimating Estimating Demand Demand Planning Planning Method Method Materials With Independent Demand Company Customers Company Customers Finished Goods Finished Goods Materials With Dependent Demand Parent Items Parent Items WIP & Raw Materials Materials
A rolling schedule
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Derived from aggregate plan
Figure 14.2
Months Aggregate Production Plan (shows the total quantity of amplifiers) Weeks Master Production Schedule (shows the specific type and quantity of amplifier to be produced 240 watt amplifier 150 watt amplifier 75 watt amplifier 1
Lead times
(Item master file) Planned order report
Inventory data Material requirement planning programs (computer and software)
Purchase advice
Exception reports Order early or late or not needed Order quantity too small or too large
Purchasing data
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Master Production Schedule
A statement of what is to be produced, not a forecast of demand Derived from aggregate plan