Materi manajemen persediaan Manlog.pdf

3/3/2014

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Manajemen

persediaan

Minggu ke -4

Apa itu persediaan

Finished goods

Raw materials

Work-in-process (WIP)

Good in transits

Maintenance, repair, and operational supplies (MRO) Spareparts item that do not become part of the product

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Dimana adanya persediaan?

Materialsources

Inboundtransportation

Production Outboundtransportation

Finished goodswarehousing

Customers

Inventory

locations

Finished goods Shi

ppin

g

Inventoriesin-process

Rece

ivin

g

Productionmaterials

Ballou (2004) Prentice Hall, Inc.

Keputusan Utama pada Manajemen

Persediaan

Barang mana yang perlu di-stock?

Di mana barang mau disimpan? Terpusat

atau tersebar?

Berapa banyak tiap barang harus

disimpan?

Kapan suatu barang harus dipesan?

Berapa ukuran pesanan yang harus

dilakukan?Pujawan, Materi perkuliahan TI-ITS

3/3/2014

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Tujuan dari persediaan

Good inventory management is a careful balancing act between stock availability and the cost of holding inventory.

Service objectives- Setting stocking levels so that there is only a specified probability of

running out of stock

Cost objectives- Balancing conflicting costs to find the most economical replenishment

quantities and timing

Customer Service ,i.e., Stock Availability

Inventory Holding costs


Video

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Alasan perlunya persediaan

Improve customer service- Provides immediacy in product availability

Encourage production, purchase, and transportationeconomies

- Allows for long production runs- Takes advantage of price-quantity discounts- Allows for transport economies from larger

shipment sizes

Ballou 2004) Prentice Hall, Inc.

Alasan perlunya persediaan?

Act as a hedge against price changes- Allows purchasing to take place under most favorable price

terms

Protect against uncertainties in demand and lead times

- Provides a measure of safety to keep operations running when demand levels and lead times cannot be known for

sure

Act as a hedge against contingencies- Buffers against such events as strikes, fires, and disruptions

in supplyBallou 2004) Prentice Hall, Inc.

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Type dari persediaan

Pipeline- Inventories in transit

Speculative- Goods purchased in anticipation of price increases

Regular/Cyclical/Seasonal- Inventories held to meet normal operating needs

Safety- Extra stocks held in anticipation of demand and

lead time uncertainties

Obsolete/Dead Stock- Inventories that are of little or no value due to being out

of date, spoiled, damaged, etc


Philosofi dari persediaan

Pull- Draws inventory into the stocking location- Each stocking location is considered independent- Maximizes local control of inventories

Push- Allocates production to stocking locations based on

overall demand

- Encourages economies of scale in production Just-in-time

- Attempts to synchronize stock flows so as to just meet demand as it occurs

- Minimizes the need for inventory


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Philosofi dari persediaan

Supply-Driven- Supply quantities and timing are unknown- All supply must be accepted and processed- Inventories are controlled through demand

Aggregate Control- Classification of items:

Groups items according to their sales level based on the 80-20 principle

Allows different control policies for 3 or more broad product groups


Push vs Pull

Plant

Warehouse #1

Warehouse #2

Warehouse #3

A1

A2

A3

A = Allocation quantity to each warehouse

Q = Requested replenishment quantity

by each warehouse

Q1

Q2

Q3

Demand

forecast

Demand

forecast

Demand

forecast

PULL - Replenish inventory with

order sizes based on specific needs

of each warehouse

PUSH - Allocate supply to each

warehouse based on the forecast

for each warehouse


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Inventory Costs

Inventory holding costs

Order costs

Shortage / stockout costs

Pujawan, Materi perkuliahan TI-ITS

Biaya Simpan (holding costs)

Biaya persediaan per tahun ada pada kisaran 25% -

35% dari nilai barang yang disimpan.


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Biaya Pesan / Order Costs

On average about US$ 215 per purchase order

(basen on a survey in USA). It should be lower in

Indonesia.

This includes: labor costs, equipment costs, and

materials/consumables necessary for making an

order (like paper, catridge, etc)

The magnitude is affected by the complexity of

purchase.


Biaya Shortage / Stockout

Count be quite small or very large, depending on

the situation

Give examples where shortage cost is very large

Give some examples how would you assess

shortage costs for a consumer product!


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Pola biaya persediaanC

ost

Replenishment quantity

Stockout cost

Procurement cost

Total cost Minimum cost

reorder quantity


Ukuran Kinerja Sistem Persediaan

Inventory turnover ratio

Inventory days of supply

Service Level

Record accuracy


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Inventory Turnover Ratio

Inventory Turnover Ratio: Measures how many times or

how fast inventory is turn to the customers relative to those

kept in the warehouse.

Perhitungannya bisa didekati dengan rumus berikut:

nilai penjualan dalam setahun

Turnover ratio = ---------------------------------nilai persediaan

Semakin tinggi nilai turnover ratio semakin bagus bagi perusahaan


Contoh Benchmark Inventory Turnover

Ratio

INDUSTRY UPPER QUARTILE

MEDIAN LOWER QUARTILE

Electronics components and accessories

9.8 5.7 3.7

Electronics computers 9.4 5.3 3.5

Household audio & video equipment

6.2 3.4 2.3

Household electrical appliances

8.0 5.0 3.8

Industrial chemicals 10.3 6.6 4.4

Dairy products 34.4 19.3 9.2

Publishing and printing 9.8 2.4 1.3


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Inventory Days of Supply

Jumlah hari yang bisa dicover oleh rata-rata inventory. Dipengaruhi oleh lead time pengadaan, pola permintaan, harga, dan ketidakpastian supply.

Inventory days of supply bisa dihitung per item ataudiaggregasikan untuk semua item.

Rata-rata nilai inventory

Perhitungan IDS: ============================

Rata-rata pemakaian per hari


Example

Product Unit price Annual Sales

Average

Inventory

A1 2 1020 100

A2 15 800 180

B1 8 65 12

B2 30 180 25

B3 6 2500 195

What is inventory turnover ratio and inventory days of supply for

each item, each group (A and B) and the whole products. Working

days in one year is 250.


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Akurasi Catatan Persediaan

Bisa dihitung dengan mencari persentase catatan yang sama dengan jumlah fisiknya.

Salah satu cara untuk menaksir akurasi catatan persediaan adalah dengan Cycle counting. Cycle counting disebut juga sebagai stock opname atau physical counting. Intinya adalah melakukan pencocokan antara berapa yang ada di catatan dengan berapa yang ada di gudang.

Misalkan dari 1000 barang yang disampel ternyata 150 diantaranya ada deviasi antara catatan dan jumlah fisik maka akurasi catatan inventory adalah 850/1000 x 100% = 85%.


Customer Service Measures

Availability (stockout frequency, fill rate, perfect

order fulfillment)

Operational performance (speed, consistency,

recovery)


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Cost/Revenue trade-offs

Service level

cost

Inventory


Inventory Vs Service Level

Define service level = ( 1 probability of stockout

at the end of an order cycle)

Assume that demand follows a normal distribution

with mean M and standard deviation s

Lead time is consant = L

Develop a table showing the level of safety stock

needed to achieve different service level

What is the impact of increasing service level from

95% to 99% on safety stock level?


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Implications of Strategy on Inventory / Service

Level

Efficient:

Lower inventory, turnover ratio is very important to control

Easier to achieve high service level due to predictable demand

Responsive:

Higher inventory, product availability is critical

Difficult to eachive high service level due to uncertain demand

(and high service level maybe obtained through high costs)


Inventory Pooling

Pooling means that inventory serving different markets is located centrally in a certain location.

This is normally to reduce costs for items with uncertain demand and high carrying costs.

Example:

You manage two products to serve 5 market regions. Assume that demand for product A in each market region is normally distributed with mean 1000 and standard deviation 100. For product B, demand is normally distributed with mean 100 and standard deviation 70. Price for product A is Rp. 10.000 per unit, but for product B is Rp. 90.000 per unit. For both items, compare the total safety stock between centralized and decentralized policy.

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Vendor Managed Inventory (VMI)

VMI adalah model dimana pelanggan tidak lagi memesan, namun hanya memberikan informasi posisi inventory dan data permintaan. Vendor akan menentukan keputusan replenishment.

VMI tidak mengatur ownership dari inventory (VMI tidak sama dengan consignment).

Persyaratan:

Ada mekanisme sharing informasi secara cepat dan akurat dari buyer ke vendor

Vendor memiliki kemampuan untuk mengambil keputusan replenishment


Important in Managing Inventory

Information visibility

Collaboration

Consolidation

Data accuracy


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An Example of Consolidation

Sebuah perusahaan membeli oli dalam jumlah yang cukup besar

per bulan untuk kebutuhan mesin-mesinnya. Perusahaan memiliki 5

pabrik yang berlokasi di suatu wilayah. Pengadaan oli dilakukan

dengan cara sebagai berikut. Tiap ada kebutuhan, wakil dari

pabrik akan membuat dokumen permintaan pembelian yang

namanya purchase requisition (PR). PR akan diproses lebih lanjut

oleh buyer (di bagian pengadaan) menjadi purchase order

(dokumen pembelian yang akan dikirim ke supplier). Pengadaan

barang-barang (termasuk oli) untuk tiap pabrik dikerjakan oleh

buyer yang berbeda. Data dalam suatu bulan menunjukkan

bahwa PR oli dari tiap pabrik adalah seperti pada tabel

terlampir.Pujawan, Materi perkuliahan TI-ITS

Hari ke Pabrik 1 Pabrik 2 Pabrik 3 Pabrik 4 Pabrik 5

1 100 150

2

3

4 250

5 110 200

6

7 110

8 120

9 220

10 180

11 100

12

13

14 100

15

16 220 150

17

18 200

19

20 140

21

Berapa biaya pemrosesan

pengadaan yang terjadi

saat ini (satu PO rata-

rata biayanya Rp. 750

ribu)

Bila dikonsolidasi tiap

minggu, berapa

penghematannya? Apa

konsekuensi negatifnya?


Documents

Materi manajemen persediaan Manlog.pdf