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Manajemen Persediaan Bab 11-12. Persediaan Stok barang yang dimiliki untuk memenuhi kebutuhan masa depan Manajemen persediaan menjawab dua pertanyaan.

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Presentasi berjudul: "Manajemen Persediaan Bab 11-12. Persediaan Stok barang yang dimiliki untuk memenuhi kebutuhan masa depan Manajemen persediaan menjawab dua pertanyaan."— Transcript presentasi:

1 Manajemen Persediaan Bab 11-12

2 Persediaan Stok barang yang dimiliki untuk memenuhi kebutuhan masa depan Manajemen persediaan menjawab dua pertanyaan Berapa banyak pesanan waktu pemesanan

3 Tipe Persediaan Bahan baku Bagian yang dibeli dan persediaan Tenaga Kerja Produk dalam proses bagian komponen modal kerja Alat, mesin, dan peralatan

4 Alasan menggunakan inventori Memenuhi permintaan tak terduga permintaan musiman atau siklus yang smooth Memenuhi variasi permintaan pelanggan Mengambil keuntungan dari diskon harga Melindung nilai terhadap kenaikan harga kuantitas diskon

5 Dua bentuk permintaan Dependent Dependent Item yang digunakan untuk menghasilkan produk akhir Independent Independent Item yang diminta oleh pelanggan eksternal

6 Inventory Costs Carrying Cost Biaya pengadaan item dalam persediaan Ordering Cost Biaya pengisian persediaan kekurangan Shortage Cost Kerugian sementara atau permanen dari penjualan ketika permintaan tidak dapat dipenuhi

7 Inventory Control Systems Sistem kontinyu ( fixed -order - kuantitas ) Jumlah konstan diorder ketika persediaan menurun ke level yang telah ditentukan Sistem periodik ( - periode waktu yang tetap ) Pesanan ditempatkan untuk jumlah variabel setelah berlalunya waktu yang tetap

8 ABC Classification System Volume permintaan dan nilai barang bervariasi Mengklasifikasikan persediaan menjadi 3 kategori, biasanya atas dasar nilai dolar untuk perusahaan PERCENTAGEPERCENTAGE CLASSOF UNITSOF DOLLARS A B3015 C

9 ABC Classification 1$ PARTUNIT COSTANNUAL USAGE Example 10.1

10 ABC Classification Example $ PARTUNIT COSTANNUAL USAGE TOTAL% OF TOTAL% OF TOTAL PARTVALUEVALUEQUANTITY% CUMMULATIVE 9$30, , , , , , , , , , $85,400

11 ABC Classification Example $ PARTUNIT COSTANNUAL USAGE TOTAL% OF TOTAL% OF TOTAL PARTVALUEVALUEQUANTITY% CUMMULATIVE 9$30, , , , , , , , , , $85,400 A B C

12 ABC Classification Example $ PARTUNIT COSTANNUAL USAGE TOTAL% OF TOTAL% OF TOTAL PARTVALUEVALUEQUANTITY% CUMMULATIVE 9$30, , , , , , , , , , $85,400 A B C % OF TOTAL CLASSITEMSVALUEQUANTITY A9, 8, B1, 4, C6, 5, 10,

13 ABC Classification – – – – – 0 0 – |||||| % of Quantity % of Value A B C

14 Asumsi dasar model EOQ Permintaan diketahui dengan pasti dan konstan dari waktu ke waktu Tidak ada kekurangan yang diperbolehkan Lead time untuk menerima perintah konstan Jumlah pesanan diterima sekaligus

15 The Inventory Order Cycle Demand rate Time Lead time Order placed Order receipt Inventory Level Reorder point, R Order quantity, Q 0 Figure 10.1

16 EOQ Cost Model C o - cost of placing orderD - annual demand C c - annual per-unit carrying costQ - order quantity Annual ordering cost = CoDCoDQQCoDCoDQQQ Annual carrying cost = CcQCcQ22CcQCcQ222 Total cost = + CoDCoDQQCoDCoDQQQ CcQCcQ22CcQCcQ222

17 EOQ Cost Model C o - cost of placing orderD - annual demand C c - annual per-unit carrying costQ - order quantity Annual ordering cost = CoDCoDQQCoDCoDQQQ Annual carrying cost = CcQCcQ22CcQCcQ222 Total cost = + CoDCoDQQCoDCoDQQQ CcQCcQ22CcQCcQ222 TC = + CoDQCoDQ CcQ2CcQ2 = + CoDQ2CoDQ2 Cc2Cc2  TC  Q 0 = + C0DQ2C0DQ2 Cc2Cc2 Q opt = 2CoDCc2CoDCc Deriving Q opt Proving equality of costs at optimal point = CoDQCoDQ CcQ2CcQ2 Q 2 = 2CoDCc2CoDCc Q opt = 2CoDCc2CoDCc

18 EOQ Example C c = $0.75 per yardC o = $150D = 10,000 yards Q opt = 2CoD2CoDCcCc2CoD2CoDCcCc 2(150)(10,000)(0.75) Q opt = 2,000 yards TC min = + CoDCoDQQCoDCoDQQQ CcQCcQ22CcQCcQ222 (150)(10,000)2,000(0.75)(2,000)2 TC min = $750 + $750 = $1,500 Orders per year =D/Q opt =10,000/2,000 =5 orders/year Order cycle time =311 days/(D/Q opt ) =311/5 =62.2 store days Example 10.2

19 EOQ with Noninstantaneous Receipt Q(1-d/p) Inventorylevel (1-d/p) Q2 Time 0 Maximum inventory level Average Figure 10.3

20 EOQ with Noninstantaneous Receipt Q(1-d/p) Inventorylevel (1-d/p) Q2 Time 0 Order receipt period BeginorderreceiptEndorderreceipt Maximum inventory level Average Figure 10.3

21 EOQ with Noninstantaneous Receipt p = production rated = demand rate Maximum inventory level =Q - d =Q 1 - Qpdp Average inventory level = 1 - Q2 dp TC = dp CoDCoDQQCoDCoDQQQ CcQCcQ22CcQCcQ222 Q opt = 2C o D C c 1 - dp

22 Production Quantity C c = $0.75 per yardC o = $150D = 10,000 yards d = 10,000/311 = 32.2 yards per dayp = 150 yards per day Q opt = = = 2,256.8 yards 2C o D C c 1 - dp 2(150)(10,000) TC = = $1,329 dp CoDCoDQQCoDCoDQQQ CcQCcQ22CcQCcQ222 Production run = = = days per order Qp2, Example 10.3

23 Production Quantity C c = $0.75 per yardC o = $150D = 10,000 yards d = 10,000/311 = 32.2 yards per dayp = 150 yards per day Q opt = = = 2,256.8 yards 2C o D C c 1 - dp 2(150)(10,000) TC = = $1,329 dp CoDCoDQQCoDCoDQQQ CcQCcQ22CcQCcQ222 Production run = = = days per order Qp 2, Number of production runs = = = 4.43 runs/year DQDQ 10,000 2,256.8 Maximum inventory level =Q 1 - = 2, =1,772 yards dpdp Example 10.3

24 Quantity Discounts Price per unit decreases as order quantity increases Price per unit decreases as order quantity increases TC = + + PD CoDCoDQQCoDCoDQQQ CcQCcQ22CcQCcQ222 where P = per unit price of the item D = annual demand

25 Quantity Discounts Price per unit decreases as order quantity increases Price per unit decreases as order quantity increases TC = + + PD CoDCoDQQCoDCoDQQQ CcQCcQ22CcQCcQ222 where P = per unit price of the item D = annual demand ORDER SIZEPRICE $ ( d 1 ) ( d 2 )

26 Quantity Discount Model Figure 10.4 Q opt Carrying cost Ordering cost Inventory cost ($) Q( d 1 ) = 100 Q( d 2 ) = 200 TC ( d 2 = $6 ) TC ( d 1 = $8 ) TC = ($10 )

27 Quantity Discount Model Figure 10.4 Q opt Carrying cost Ordering cost Inventory cost ($) Q( d 1 ) = 100 Q( d 2 ) = 200 TC ( d 2 = $6 ) TC ( d 1 = $8 ) TC = ($10 )

28 Quantity Discount QUANTITYPRICE $1, , C o =$2,500 C c =$190 per computer D =200 Q opt = = = 72.5 PCs 2CoD2CoDCcCc2CoD2CoDCcCc2(2500)(200)190 TC = + + PD = $233,784 C o D Q opt C c Q opt 2 For Q = 72.5 TC = + + PD = $194,105 CoDCoDQQCoDCoDQQQ CcQCcQ22CcQCcQ222 For Q = 90 Example 10.4

29 When to Order Reorder Point is the level of inventory at which a new order is placed R = dL where d = demand rate per period L = lead time

30 Reorder Point Example Demand = 10,000 yards/year Store open 311 days/year Daily demand = 10,000 / 311 = yards/day Lead time = L = 10 days R = dL = (32.154)(10) = yards Example 10.5

31 Safety Stocks Safety stock Safety stock buffer added to on hand inventory during lead time buffer added to on hand inventory during lead time Stockout Stockout an inventory shortage an inventory shortage Service level Service level probability that the inventory available during lead time will meet demand probability that the inventory available during lead time will meet demand

32 Variable Demand with a Reorder Point Figure 10.5 Reorder point, R Q Time Inventory level 0

33 Variable Demand with a Reorder Point Figure 10.5 Reorder point, R Q LT Time LT Inventory level 0

34 Reorder Point with a Safety Stock Figure 10.6 Reorder point, R Q LT Time LT Inventory level 0 Safety Stock

35 Reorder Point With Variable Demand R = dL + z  d L where d=average daily demand L=lead time  d =the standard deviation of daily demand z=number of standard deviations corresponding to the service level probability z  d L=safety stock

36 Reorder Point for a Service Level Probability of meeting demand during lead time = service level Probability of a stockout R Safety stock dL Demand z  d L Figure 10.7

37 Reorder Point for Variable Demand The carpet store wants a reorder point with a 95% service level and a 5% stockout probability d= 30 yards per day L= 10 days  d = 5 yards per day For a 95% service level, z = 1.65 R= dL + z  d L = 30(10) + (1.65)(5)( 10) = yards Safety stock= z  d L = (1.65)(5)( 10) = 26.1 yards Example 10.6

38 Order Quantity for a Periodic Inventory System Q = d(t b + L) + z  d t b + L - I where d= average demand rate t b = the fixed time between orders L= lead time  d = standard deviation of demand z  d t b + L= safety stock z  d t b + L= safety stock I= inventory level

39 Fixed-Period Model with Variable Demand d= 6 bottles per day  d = 1.2 bottles t b = 60 days L= 5 days I= 8 bottles z= 1.65 (for a 95% service level) Q= d(t b + L) + z  d t b + L - I = (6)(60 + 5) + (1.65)(1.2) = bottles


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