independent - dependent demand inventory sekolah tinggi manajemen ppm
TRANSCRIPT
INDEPENDENT - INDEPENDENT - DEPENDENT DEMAND DEPENDENT DEMAND
INVENTORYINVENTORY
Sekolah Tinggi Manajemen PPM
Schroeder/Operations ManagementSchroeder/Operations Management
OUTLINEOUTLINE
• Purpose of InventoriesPurpose of Inventories
• Inventory Cost StructuresInventory Cost Structures
• Independent versus Dependent DemandIndependent versus Dependent Demand
• Independent Demand: EOQ, Q-System, P-Independent Demand: EOQ, Q-System, P-SystemSystem
• Dependent Demand: MRPDependent Demand: MRP
Schroeder/Operations ManagementSchroeder/Operations Management
A MATERIAL-FLOW PROCESSA MATERIAL-FLOW PROCESS
Work inprocess
Work inprocess
Work inprocess
Finishedgoods
Work inprocess
Ven
dor
s Cu
stomer
Productive Process
Schroeder/Operations ManagementSchroeder/Operations Management
A Water Tank Analogy for A Water Tank Analogy for InventoryInventory
Supply Rate
Inventory Level
Demand Rate
Inventory Level
Schroeder/Operations ManagementSchroeder/Operations Management
REASONS TO CARRY REASONS TO CARRY INVENTORIESINVENTORIES
• To protect against uncertaintiesTo protect against uncertainties
• To allow economic production and To allow economic production and purchasepurchase
• To cover anticipated changes in To cover anticipated changes in demand or supplydemand or supply
• To provide for transitTo provide for transit
Schroeder/Operations ManagementSchroeder/Operations Management
INDEPENDENTDEMAND
DEPENDENTDEMAND
Influenced By Market Condition Outside the Control OfOperations
Related to Demandfor Another Item, Not IndependentlyDetermined by theMarket
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Inventory Cost StructuresInventory Cost Structures
• Item costItem cost
• Ordering (or setup) costOrdering (or setup) cost
• Carrying (or holding) cost:Carrying (or holding) cost:– Cost of capitalCost of capital– Cost of storageCost of storage– Cost of obsolescence, deterioration, and Cost of obsolescence, deterioration, and
lossloss
• Stock out costStock out cost
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Total Cost of InventoryTotal Cost of Inventory
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Economic Order Quantity (EOQ)Economic Order Quantity (EOQ)AssumptionsAssumptions
• Demand rate is constant, recurring, and Demand rate is constant, recurring, and known.known.
• Lead time is constant and known.Lead time is constant and known.• No stock outs allowed.No stock outs allowed.• Material is ordered or produced in a lot or Material is ordered or produced in a lot or
batch and the lot is received all at once.batch and the lot is received all at once.• Unit cost is constant (no quantity discounts).Unit cost is constant (no quantity discounts).• Carrying cost depends linearly on the Carrying cost depends linearly on the
average level of inventory.average level of inventory.• Ordering (setup) cost per order is fixed.Ordering (setup) cost per order is fixed.• The item is a single product.The item is a single product.
Schroeder/Operations ManagementSchroeder/Operations Management
Continuous Review Continuous Review SystemSystem
• Assumption of “constant demand” is Assumption of “constant demand” is relaxed.relaxed.
• Monitoring of “on hand” stock Monitoring of “on hand” stock position in a continuous systemposition in a continuous system
• Q systemQ system (another name for (another name for continuous review system)continuous review system)
Schroeder/Operations ManagementSchroeder/Operations Management
Q SystemQ System
R = Reorder PointQ = Order QuantityL = Lead time
Schroeder/Operations ManagementSchroeder/Operations Management
• All assumption of EOQ (except that All assumption of EOQ (except that demand is constant and “no demand is constant and “no stockout”) remains in effect.stockout”) remains in effect.
• Also known as Also known as “P System”“P System” or “Fixed- or “Fixed-order-Interval System”order-Interval System”
Periodic Review SystemPeriodic Review System
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P SystemP System
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Using P and Q System in Using P and Q System in PracticePractice
• Use P system when orders must be Use P system when orders must be placed at specified intervals.placed at specified intervals.
• Use P systems when multiple items Use P systems when multiple items are ordered from the same supplier are ordered from the same supplier (joint-replenishment).(joint-replenishment).
• Use P system for inexpensive items.Use P system for inexpensive items.
Schroeder/Operations ManagementSchroeder/Operations Management
ABC Inventory ManagementABC Inventory Management
• Based on “Pareto” concept (80/20 Based on “Pareto” concept (80/20 rule)rule)
• Classification of items as A, B, or CClassification of items as A, B, or C
• Example (See Table 15.4)Example (See Table 15.4)
Schroeder/Operations ManagementSchroeder/Operations Management
Annual Usage of Items by Dollar ValueAnnual Usage of Items by Dollar Value
Item
Annual Usage in
Units Unit Cost Dollar Usage
Percentage of Total Dollar Usage
1 5,000 1.50$ 7,500$ 2.9%2 1,500 8.00 12,000 4.7%3 10,000 10.50 105,000 41.2%4 6,000 2.00 12,000 4.7%5 7,500 0.50 3,750 1.5%6 6,000 13.60 81,600 32.0%7 5,000 0.75 3,750 1.5%8 4,500 1.25 5,625 2.2%9 7,000 2.50 17,500 6.9%10 3,000 2.00 6,000 2.4%
Total 254,725$ 100.0%
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ABC ChartABC Chart
0.0%
5.0%
10.0%
15.0%
20.0%
25.0%
30.0%
35.0%
40.0%
45.0%
3 6 9 2 4 1 10 8 5 7
Item No.
Pe
rce
nt
Usa
ge
0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
120.0%
Cu
mu
lati
ve %
Usa
ge
Percentage of Total Dollar Usage Cumulative Percentage
A B C
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Attribute MRP Order Point
Demand Dependent Independent
Order philosophy Requirements Replenishment
Forecast Based on master schedule Based on past demand
Control concept Control all items ABC
Objectives Meet manufacturing needs Meet customer needs
Lot sizing Discrete EOQ
Demand pattern Lumpy but predictable Random
Types of inventory Work in process and raw materials
Finished goods and spare parts
Attribute MRP Order Point
Demand Dependent Independent
Order philosophy Requirements Replenishment
Forecast Based on master schedule Based on past demand
Control concept Control all items ABC
Objectives Meet manufacturing needs Meet customer needs
Lot sizing Discrete EOQ
Demand pattern Lumpy but predictable Random
Types of inventory Work in process and raw materials
Finished goods and spare parts
MRP versus Order-Point MRP versus Order-Point SystemsSystems
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BOM BOM (Table Example)(Table Example)
Top
Leg
Long Rail
Short Rail
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BOM (Product Structure)BOM (Product Structure)
Short Rails(2)
Table(End Item)
Long Rails(2)
Legs(4)
Top(1)
Leg Assembly(1)
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MRP ElementsMRP Elements
• Bill of Materials (BOM)Bill of Materials (BOM)
• Master SchedulingMaster Scheduling
• Inventory RecordsInventory Records
• Capacity PlanningCapacity Planning
• PurchasingPurchasing
• Shop Floor ControlShop Floor Control
Schroeder/Operations ManagementSchroeder/Operations Management
Elements of Success in MRPElements of Success in MRP
• Implementation planningImplementation planning
• Adequate computer supportAdequate computer support
• Accurate dataAccurate data
• Management supportManagement support
• User knowledgeUser knowledge