independent - dependent demand inventory sekolah tinggi manajemen ppm

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INDEPENDENT - DEPENDENT INDEPENDENT - DEPENDENT DEMAND INVENTORY DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

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Page 1: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

INDEPENDENT - INDEPENDENT - DEPENDENT DEMAND DEPENDENT DEMAND

INVENTORYINVENTORY

Sekolah Tinggi Manajemen PPM

Page 2: INDEPENDENT - DEPENDENT DEMAND INVENTORY 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

Page 3: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

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

Page 4: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

Schroeder/Operations ManagementSchroeder/Operations Management

A Water Tank Analogy for A Water Tank Analogy for InventoryInventory

Supply Rate

Inventory Level

Demand Rate

Inventory Level

Page 5: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

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

Page 6: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

Schroeder/Operations ManagementSchroeder/Operations Management

INDEPENDENTDEMAND

DEPENDENTDEMAND

Influenced By Market Condition Outside the Control OfOperations

Related to Demandfor Another Item, Not IndependentlyDetermined by theMarket

Page 7: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

Schroeder/Operations ManagementSchroeder/Operations Management

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

Page 8: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

Schroeder/Operations ManagementSchroeder/Operations Management

Total Cost of InventoryTotal Cost of Inventory

Page 9: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

Schroeder/Operations ManagementSchroeder/Operations Management

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.

Page 10: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

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)

Page 11: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

Schroeder/Operations ManagementSchroeder/Operations Management

Q SystemQ System

R = Reorder PointQ = Order QuantityL = Lead time

Page 12: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

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

Page 13: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

Schroeder/Operations ManagementSchroeder/Operations Management

P SystemP System

Page 14: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

Schroeder/Operations ManagementSchroeder/Operations Management

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.

Page 15: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

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)

Page 16: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

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%

Page 17: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

Schroeder/Operations ManagementSchroeder/Operations Management

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

Page 18: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

Schroeder/Operations ManagementSchroeder/Operations Management

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

Page 19: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

Schroeder/Operations ManagementSchroeder/Operations Management

BOM BOM (Table Example)(Table Example)

Top

Leg

Long Rail

Short Rail

Page 20: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

Schroeder/Operations ManagementSchroeder/Operations Management

BOM (Product Structure)BOM (Product Structure)

Short Rails(2)

Table(End Item)

Long Rails(2)

Legs(4)

Top(1)

Leg Assembly(1)

Page 21: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

Schroeder/Operations ManagementSchroeder/Operations Management

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

Page 22: INDEPENDENT - DEPENDENT DEMAND INVENTORY Sekolah Tinggi Manajemen PPM

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