Konsep Dasar Persediaan Outline: 1. What is Inventory? 2. Key Factors in Inventory Management Decision 3. Financial Inventory Performances 4. 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.
Kinerja: Siklus Aliran Material Input other (6) wait time (5) move time (4) queue time (3) setup time (2) run time (1) Output Cycle Time (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.
Contoh Inventory Stok material Cadangan kapasitas Contoh:
II. Key Factors in Inventory Management Decision Key Factors in Inventory Management Decision: 1. Inventory management objectives 2. Flow of material 3. Pola supply dan demand 4. Inventory functions 5. 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 material terdiri dari: 1. Raw materials 2. Work-in-process (WIP) 3. Finished goods 4. Distribution inventories 5. Maintenance, repair, operational supplies (MRO s)
Contoh: Berdasarkan aliran material Industri Komputer Persediaan (Inventory). Aliran Material Raw Mat'l WIP Fin. Goods
Contoh: Berdasarkan Kuantitas & Nilai Industri Otomotif Persediaan (Inventory) A Aliran Material Kuantitas & Nilai C B Raw Mat'l WIP Fin. Goods A Items B Items C Items
Contoh: Berdasarkan Jenis Permintaan Persediaan (Inventory) Aliran Material Kuantitas & Nilai Jenis Permintaan Independent Raw Mat'l WIP Fin. Goods Item A Item B Item C Independent Dependent Dependent
Contoh: MROs Persediaan (Inventory) Aliran Material Kuantitas & Nilai Jenis Permintaan Lain-lain Raw Mat'l WIP Fin. Goods Item A Item B Item C Independent Dependent Mainten. Repair Operating
2.3. Pola Supply & Demand 1. Inventory tidak diperlukan, bila supply bisa memenuhi demand. 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 dapat didekati, bila produksi dapat dilakukan dengan line-flow system. 3. Kondisi keseimbangan antara produksi dengan demand sulit dicapai, 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 inventory 2. Fluctuation inventory (safety stock) 3. Lot size inventory 4. Transportation inventory 5. Hedge inventory 6. 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, losts sales, 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 unit S = $30 i = 0.20 c = $15 Q = 600 unit. Jadi: 1. Annual ordering cost = A/Q x S = 10000/600 x $30= $500 2. Annual carrying cost = Q/2 x c x i = 600/2 x $15 x 0.20 = $900 3. Total annual cost = $500 + $900 = $ 1,400.
III. Financial Inventory Performances 1. Inventory turnover = Annual CGS/Average Inventory $ Contoh: Bila Annual CGS 1 juta $, dan Average 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 Analysis Divides on-hand inventory into 3 classes A 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 ABC % Annual $ Usage 100 Class % $ Vol % Items 80 60 40 20 0 0 20 40 60 80 100 % of Inventory Items
Classifying Items as ABC % Annual $ Usage 100 80 60 40 20 0 A Class % $ Vol % Items A 80 15 0 20 40 60 80 100 % of Inventory Items
Classifying Items as ABC % 100 Annual $ Usage 80 60 40 20 0 A B Class % $ Vol % Items A 80 15 B 15 30 0 20 40 60 80 100 % of Inventory Items
% Annual $ Usage 100 80 60 40 20 0 A Classifying Items as ABC B Class % $ Vol % Items A 80 15 B 15 30 C 5 55 0 20 40 60 80 100 % of Inventory Items C
Contoh: ABC Classification You re a buyer for Auto Palace. Classify the following items as A, B, or C. Stock # Annual Volume (Units) Unit Cost 206 26,000 $ 36 105 200 600 019 2,000 55 144 20,000 4 207 7,000 10 Note: Example is for illustration only; too few items.
ABC Classification Solution Stock # Vol. Cost $ Vol. % ABC 206 26,000 $ 36 105 200 600 019 2,000 55 144 20,000 4 207 7,000 10 Total
ABC Classification Solution Stock # Vol. Cost $ Vol. % ABC 206 26,000 $ 36 $936,000 105 200 600 019 2,000 55 144 20,000 4 207 7,000 10 Total 26,000 x 36
ABC Classification Solution Stock # Vol. Cost $ Vol. % ABC 206 26,000 $ 36 $936,000 105 200 600 120,000 019 2,000 55 110,000 144 20,000 4 80,000 207 7,000 10 70,000 Total 1,316,000
ABC Classification Solution Stock # Vol. Cost $ Vol. % ABC 206 26,000 $ 36 $936,000 71.1 105 200 600 120,000 019 2,000 55 110,000 144 20,000 4 80,000 936,000 1,316,000 207 7,000 10 70,000 Total 1,316,000
ABC Classification Solution Stock # Vol. Cost $ Vol. % ABC 206 26,000 $ 36 $936,000 71.1 105 200 600 120,000 9.1 019 2,000 55 110,000 8.4 144 20,000 4 80,000 6.1 207 7,000 10 70,000 5.3 Total 1,316,000 100.0
ABC Classification Solution Stock # Vol. Cost $ Vol. % ABC 206 26,000 $ 36 $936,000 71.1 A 105 200 600 120,000 9.1 A 019 2,000 55 110,000 8.4 144 20,000 4 80,000 6.1 207 7,000 10 70,000 5.3 Total 1,316,000 100.0
ABC Classification Solution Stock # Vol. Cost $ Vol. % ABC 206 26,000 $ 36 $936,000 71.1 A 105 200 600 120,000 9.1 A 019 2,000 55 110,000 8.4 B 144 20,000 4 80,000 6.1 B 207 7,000 10 70,000 5.3 Total 1,316,000 100.0
ABC Classification Solution Stock # Vol. Cost $ Vol. % ABC 206 26,000 $ 36 $936,000 71.1 A 105 200 600 120,000 9.1 A 019 2,000 55 110,000 8.4 B 144 20,000 4 80,000 6.1 B 207 7,000 10 70,000 5.3 C Total 1,316,000 100.0