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Matakuliah
Tahun
: J1186 - Analisis Kuantitatif Bisnis
: 2009/2010
ANALISIS PERSEDIAAN
Pertemuan 13
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Framework
•
•
•
•
Konsep Persediaan
Persediaan dengan Permintaan Pasti
Metode Persediaan Time Series
Asumsi Model EOQ
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Konsep Persediaan
• Stock of materials
• Stored capacity
• Types of inventory
– Raw material
– Work-in-progress
– Maintenance/repair/operating supply (MRO)
– Finished goods
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Fungsi Persediaan
• To “decouple” or separate various parts of the production
process
• To provide a stock of goods that will provide a “selection” for
customers
• To hedge against inflation and upward price changes
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Jenis Persediaan
•
•
•
•
Persediaan Bahan Mentah
Persediaan Barang dalam Proses (WIP)
Persediaan MRO (Pemeliharaan, Reparasi, dan Operasi)
Persediaan Barang Jadi
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Klasifikasi Persediaan
Inventory
Process
stage
Raw Material WIP
Finished Goods
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Number
& Value
Demand
Type
A Items
B Items
C Items
Independent
Dependent
Other
Maintenance
Dependent
Operating
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Model Persediaan
Permintaan Independent vs Permintaan Dependent
• Independent demand - demand for item is independent
of demand for any other item
– EOQ
• Dependent demand - demand for item is dependent
upon the demand for some other item
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Biaya Persediaan
• Holding costs - associated with holding or “carrying”
inventory over time
• Ordering costs - associated with costs of placing
order and receiving goods
• Setup costs - cost to prepare a machine or process
for manufacturing an order
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Model Economic Order Quantity (EOQ)
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Model EOQ – Jumlah pemesanan ekonomis??
Annual Cost
Order (Setup) Cost Curve
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Optimal
Order Quantity (Q*)
Order Quantity
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Basic EOQ Model
Asumsi :
Tingkat permintaan konstan dan diketahui secara pasti
Pemesanan dibuat dan diterima seketika itu juga sehingga tidak ada kekurangan yang
terjadi
Tidak ada shortage
Tidak ada diskon
Hanya mempertimbangkan biaya pemesanan dan biaya penyimpanan
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EOQ Model Equations
Optimal Order Quantity
Expected Number of Orders
Expected Time Between Orders
d =
D
Working Days / Year
ROP = d × L
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2 ×D ×S
H
D
=N =
Q*
= Q* =
=T =
Working Days / Year
N
D = Demand per year
S = Setup (order) cost per order
H = Holding (carrying) cost
d = Demand per day
L = Lead time in days
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EOQ Models
 Biaya order per tahun
D
Co
*
Q
 Biaya Simpan per tahun
Q*
Ch
2
Total biaya persediaan
D
Q*
Co  Ch
*
Q
2
Jumlah pemesanan optimal
Q 
*
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2Co D
Ch
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 Order Cycle Time
Q*
D
 Frekuensi Pemesanan
1
Q*
D
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Dimana :
D = permintaan per tahun
Q*= Jumlah item per pesanan optimal
Co = Biaya pemesanan per pesanan
Ch = biaya penyimpanan per unit per tahun
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