Konsep Dasar Persediaan - Website Staff UIstaff.ui.ac.id/system/files/users/yadrifil.msc/material/pengepro-6-konsepdasar... · Penghitungan Biaya Persediaan 1. Biaya pemesanan per

Konsep Dasar Persediaan

Outline:1. What is Inventory?2. Key Factors in Inventory Management

Decision3. Financial Inventory Performances4. ABC Analysis.

Kuliah ke-6: Rabu, 22 Okt 2008

I. What is Inventory (Persediaan)?

• Inventories:

“…. are materials and supplies that a business carries either for sale or to provide inputs or supplies to the production process.”

• Inventory management:

“….is responsible for planning and controlling inventory from the raw material stage to the customer.”

• Since inventory either results from production or supports it, it cannot be managed separately, and therefore, must be coordinated.

(1). Waktu operasi (run time): Pekerjaan sedang dalam pengerjaan mesin. (2). Waktu persiapan (setup time): Pekerjaan pada stasiun kerja, dan stasiun kerja sedang

“dipersiapkan.“(3). Waktu antri (queue time): Pekerjaan antri sebelum diproses, menunggu pekerjaan yang

mendahuluinya.(4). Waktu pemindahan (move time): Waktu suatu pekerjaan berada dalam transit.(5). Waktu menunggu (wait time): Waktu pekerjaan menunggu untuk dipindahkan ke areal

kerja berikutnya.(6). Lain-lain (other): "Just-in-case" inventory.

– Siapkan jumlah pemasok kelas A yang lebih banyak– Lakukan kontrol fisik lebih ketat untuk item A – Lebih hati-hati meramalkan item A.

Kinerja: Siklus Aliran Material

other (6) waittime (5)

movetime (4)

queuetime (3)

setuptime (2)

runtime (1)Input

Cycle Time

Output

Contoh Inventory

• Stok material• Cadangan kapasitasContoh:

II. Key Factors in Inventory Management Decision

Key Factors in Inventory Management Decision:1. Inventory management objectives2. Flow of material3. Pola supply dan demand4. Inventory functions5. Inventory costs.

2.1. Tujuan Inventory Management

1) Maximum customer service:• Percentage of orders shipped on schedule• Percentage of line items shipped on schedule• Order-days out of stock• etc.

2) Minimum inventory investments

3) Low-cost plant operation:• Memungkinkan operasi berurutan dengan

production rate yang berbeda• Memungkinkan leveling production• Memungkinkan pembelian partai besar dengan order

cost rendah dan quantity discounts• etc.

2.2. Flow of material

Jenis inventory berdasarkan flow of materialterdiri dari:1. Raw materials2. Work-in-process (WIP)3. Finished goods4. Distribution inventories5. Maintenance, repair, operational

supplies (MRO’s)

Contoh: Berdasarkan aliran material

Persediaan(Inventory)

AliranMaterial

Raw Mat'lWIPFin. Goods

.

Industri Komputer

Contoh: Berdasarkan Kuantitas & Nilai

Persediaan(Inventory)

AliranMaterial

Kuantitas& Nilai

Raw Mat'lWIP

Fin. Goods

A ItemsB ItemsC Items

AA

BBCC

Industri Otomotif

Contoh: Berdasarkan Jenis Permintaan

Persediaan(Inventory)

AliranMaterial

JenisPermintaan

Kuantitas& Nilai

Raw Mat'lWIP

Fin. Goods

IndependentDependent

Item AItem BItem C

Independent

Dependent

Contoh: MROs

Persediaan

AliranMaterial

JenisPermintaan

Kuantitas& Nilai Lain-lain

Raw Mat'lWIP

Fin. Goods

IndependentDependent

Item AItem BItem C

Mainten.Repair

Operating

(Inventory)

2.3. Pola Supply & Demand

1. Inventory tidak diperlukan, bila supply bisa memenuhidemand. Kondisi yang diperlukan:• Demand yang stabil, predictable, dan konstan untuk

jangka panjang.• Production rate dibuat sama dengan demand rate

2. Kondisi keseimbangan antara supply dan demand dapatdidekati, bila produksi dapat dilakukan dengan line-flow system.

3. Kondisi keseimbangan antara produksi dengan demand sulitdicapai, karena:• Biasanya produksi dalam lot atau batch• Ada pemisahan antara areal mesin, perakitan dan welding• Pekerjaan bergerak dari satu workstation ke workstation

lainnya.

2.4. Inventory Functions

1. Anticipatipation inventory2. Fluctuation inventory (safety stock)3. Lot size inventory4. Transportation inventory5. Hedge inventory6. MROs inventory

2.5. Total Cost of Inventory

Inventory cost components

1. Item cost: price of item, incl. transportation cost, custom and duties, and insurance (landed costs)

2. Carrying cost: incl. capital costs, storage costs, risk costs (obsolescence, damage, pilferage, deterioration)

3. Ordering cost: incl. production control costs, setup and teardown costs, lost capacity cost, purchase order cost.

4. Stockout cost: could be backorder costs, lostssales, and possibly lost customers.

5. Capacity-associated costs: for changing output levels, may be needed costs for overtime, hiring, training, extra shifts, and layoffs.

Terminologi Biaya Persediaan

A = Pemakaian per tahun (unit)S = Biaya pemesanan ($ per pemesanan)i = rate biaya penyimpanan per tahun

(% atau desimal)c = Biaya per unit ($)Q = Kuantitas pemesanan (unit)

Penghitungan Biaya Persediaan

1. Biaya pemesanan per tahun (annual ordering cost) =Frekuensi pemesanan x Biaya per pemesanan= A/Q x S

2. Biaya penyimpanan per tahun (annual carrying cost)= Rata-rata persediaan x biaya penyimpanan

satu unit per tahun= Rata-rata persediaan x biaya per unit x

biaya penyimpanan= Q/2 x c x i

3. Biaya total per tahun = Biaya pemesanan per tahun + Biaya penyimpanan per tahun

= (A/Q x S) + (Q/2 x c x i)

Contoh penghitungan inventory costs

Annual demand 10,000 unit, ordering cost $30 per order, the carrying cost 20%, and the unit cost $15. Order quantity 600 unit.Maka:A = 10,000 unitS = $30i = 0.20c = $15Q = 600 unit.Jadi:1. Annual ordering cost = A/Q x S = 10000/600 x $30= $5002. Annual carrying cost = Q/2 x c x i = 600/2 x $15 x 0.20 = $9003. Total annual cost = $500 + $900 = $ 1,400.

III. Financial Inventory Performances

1. Inventory turnover = Annual CGS/Average Inventory $

Contoh: Bila Annual CGS 1 juta $, danAverage inventory = $ 500 ribu.Maka: Inventory turnover = 1 juta $/500 rb $ = 2.

2. Days of Supply = Inventory on hand/Average daily usage

Contoh: Perusahaan memiliki 9000 unit on hand, and annual usage = 48,000 unit. Ada 240 working days in the year.

Maka: Average daily usage = 48000/240 = 200 unit days of supply

IV. ABC AnalysisIV. ABC Analysis

• Divides on-hand inventory into 3 classesA class, B class, C class

• Basis is usually annual $ volume$ volume = Annual demand x Unit cost

• Policies based on ABC analysis– Develop class A suppliers more– Give tighter physical control of A items– Forecast A items more carefully

Classifying Items as ABCClassifying Items as ABC

020406080

100

0 20 40 60 80 1000

20406080

100

0 20 40 60 80 100% of Inventory Items% of Inventory Items

% Annual $ Usage% Annual $ UsageClass % $ Vol % Items

Classifying Items as ABCClassifying Items as ABC

020406080

100

0 20 40 60 80 1000

20406080

100

0 20 40 60 80 100% of Inventory Items% of Inventory Items

% Annual $ Usage% Annual $ Usage

AA

Class % $ Vol % ItemsA 80 15

Classifying Items as ABCClassifying Items as ABC

020406080

100

0 20 40 60 80 1000

20406080

100

0 20 40 60 80 100% of Inventory Items% of Inventory Items

% Annual $ Usage% Annual $ Usage

AA

BB

Class % $ Vol % ItemsA 80 15B 15 30

Classifying Items as ABCClassifying Items as ABC

020406080

100

0 20 40 60 80 1000

20406080

100

0 20 40 60 80 100% of Inventory Items% of Inventory Items

% Annual $ Usage% Annual $ Usage

AA

BB CC

Class % $ Vol % ItemsA 80 15B 15 30C 5 55

Contoh: ABC ClassificationContoh: ABC Classification

YouYou’’re a buyer for Auto Palace. Classify the re a buyer for Auto Palace. Classify the following items as A, B, or C.following items as A, B, or C.

Stock # Annual Volume (Units) Unit Cost206 26,000 $ 36105 200 600019 2,000 55144 20,000 4207 7,000 10

Note: Example is for illustration only; too few items.Note: Example is for illustration only; too few items.

ABC Classification SolutionABC Classification Solution

Stock # Vol. Cost $ Vol. % ABC206206 26,00026,000 $ 36$ 36105105 200200 600600019019 2,0002,000 5555144144 20,00020,000 44207207 7,0007,000 1010

TotalTotal

ABC Classification SolutionABC Classification Solution

Stock # Vol. Cost $ Vol. % ABC206206 26,00026,000 $ 36$ 36 $936,000$936,000105105 200200 600600019019 2,0002,000 5555144144 20,00020,000 44207207 7,0007,000 1010

TotalTotal

26,000 x 3626,000 x 36

ABC Classification SolutionABC Classification Solution

Stock # Vol. Cost $ Vol. % ABC206206 26,00026,000 $ 36$ 36 $936,000$936,000105105 200200 600600 120,000120,000019019 2,0002,000 5555 110,000110,000144144 20,00020,000 44 80,00080,000207207 7,0007,000 1010 70,00070,000

TotalTotal 1,316,0001,316,000

ABC Classification SolutionABC Classification Solution

Stock # Vol. Cost $ Vol. % ABC206206 26,00026,000 $ 36$ 36 $936,000$936,000 71.171.1105105 200200 600600 120,000120,000019019 2,0002,000 5555 110,000110,000144144 20,00020,000 44 80,00080,000207207 7,0007,000 1010 70,00070,000

TotalTotal 1,316,0001,316,000

936,0001,316,000936,000

1,316,000

ABC Classification SolutionABC Classification Solution

Stock # Vol. Cost $ Vol. % ABC206206 26,00026,000 $ 36$ 36 $936,000$936,000 71.171.1105105 200200 600600 120,000120,000 9.19.1019019 2,0002,000 5555 110,000110,000 8.48.4144144 20,00020,000 44 80,00080,000 6.16.1207207 7,0007,000 1010 70,00070,000 5.35.3

TotalTotal 1,316,0001,316,000 100.0100.0

ABC Classification SolutionABC Classification Solution

Stock # Vol. Cost $ Vol. % ABC206206 26,00026,000 $ 36$ 36 $936,000$936,000 71.171.1 AA105105 200200 600600 120,000120,000 9.19.1 AA019019 2,0002,000 5555 110,000110,000 8.48.4144144 20,00020,000 44 80,00080,000 6.16.1207207 7,0007,000 1010 70,00070,000 5.35.3

TotalTotal 1,316,0001,316,000 100.0100.0

ABC Classification SolutionABC Classification Solution

Stock # Vol. Cost $ Vol. % ABC206206 26,00026,000 $ 36$ 36 $936,000$936,000 71.171.1 AA105105 200200 600600 120,000120,000 9.19.1 AA019019 2,0002,000 5555 110,000110,000 8.48.4 BB144144 20,00020,000 44 80,00080,000 6.16.1 BB207207 7,0007,000 1010 70,00070,000 5.35.3

TotalTotal 1,316,0001,316,000 100.0100.0

ABC Classification SolutionABC Classification Solution

Stock # Vol. Cost $ Vol. % ABC206 26,000 $ 36 $936,000 71.1 A105 200 600 120,000 9.1 A019 2,000 55 110,000 8.4 B144 20,000 4 80,000 6.1 B207 7,000 10 70,000 5.3 C

Total 1,316,000 100.0