03_Perencanaan Agregat

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Perencanaan AgregatPerencanaan dan Pengendalian Produksi

Pendahuluan(1)

Tujuan Aggregate planning (AP) adalah membangkitkan (generate) top level production plans Basis AP adalah hasil ramalan dan target produksi. Target produksi ditentukan oleh top level business plan yang memperhatikan kapasitas & kapabilitas perusahaan Analisis dilakukan dalam kelompok produk (product family) dengan unit agregat Melibatkan pemilihan strategi manufaktur Peran AP adalah sebagai interface antara perusahaan/sistem manufaktur dan pasar produknya.

Pendahuluan(2)

Company top level plans

W h o le s a le r

Aggregate Planning

R e t a ile r F a c to ry

End consum er

Aggregate Planning Strategies(1)

1) 2) 3)

Capacity options Demand options Mixed strategies

Capacity options: Mengubah-ubah tingkat inventory (level production) Mengubah-ubah ukuran tenaga kerja: hiring/lay off (chase strategy) Mengubah-ubah production rate: over time/under time Menggunakan part time workers

Aggregate Planning Strategies(2)

Demand options Mempengaruhi demand: advertensi, promosi, personal selling, discount, diskriminasi harga Backordering Pure strategy Bila yang diubah-ubah hanya satu variabel Mixed strategy Melibatkan pengubahan beberapa variabel, misalnya bila pure strategy tidak feasible

Controllable (decision) variable

Inventory Production rate Manpower Kapasitas: over time/recruitment/layoff (tenaga kerja/work force) Subcontract

Methods

Trial and Error (Charting/graphical methods) Pure strategy Mixed strategy Mathematical (optimal) approach: Linear Programming Model Transportation Model Management Coefficient Approach atau empirical approach Simulation

Relevant cost

Hiring/layoff cost Overtime/under time cost Inventory carrying cost Subcontracting incremental cost Part time labor cost Backorder cost Stock out cost

CONTOH : Perencanaan Aggregat dengan Trial and ErrorDiketahui demand selama 8 kuartal ke depan (hasil ramalan lihat slide berikutnya) Ongkos produksi : Regular time (Cr): 10 (US$/unit) Over time (Co): 30 (US$/unit) Ongkos kenaikan tingkat produksi (Ch) : 100 US$/unit (hiring cost) Ongkos penurunan tingkat produksi (Cl): 150 US$/unit (lay-off cost) Ongkos inventory (Ci): 50 US$/kuartal Incremental cost for subcontracting (Cs): 80 US$/unit

Forecasted Demand per kuartal

Kuartal 1 2 3 4 5 6 7 8 Total

Demand (unit) 220 170 400 600 380 200 130 300 2400

DEMAND PER KUARTAL(UNIT) 800

600

400

200

0 1 2 3 4 5 6 7 8

Alternatif penyusunan Perencanaan Aggregat

1. Level strategy Production rate = average demand

1. Chase strategy Production rate = demand

1. Subcontract strategy Production rate dipilih konstant Kekurangannya dipenuhi dengan subkontrak

1. Mixed strategy

Alternatif 1 : Level StrategyProduction level = average demandKu artal D and em In itial (u it) n In toy (unit) ven (a) (b) 22 0 20 7 17 0 30 5 40 0 40 8 60 0 30 8 38 0 8 0 20 0 0 13 0 10 0 30 0 20 7 Prod uction rate (unit) En d In ventory Prod uction Regu lar Overtim e Inventoy (unit) Cost (US$) Cost (US$ ) (c) (d) (e)= c+ )-a (f)= d *Ci (g)= *Cr+ (b+ d (b+ )/2 (b c*Co) 2 00 10 0 30 5 1 .5 0 5 0 5 0 .0 0 2 00 10 0 40 8 2 .7 0 0 5 5 0 .0 0 2 00 10 0 30 8 2 .5 0 1 0 5 0 .0 0 2 00 10 0 80 1 .5 0 1 0 5 0 .0 0 2 00 10 0 0 2 0 .0 0 5 0 .0 0 2 00 10 0 10 0 2 0 .5 0 5 0 .0 0 2 00 10 0 20 7 9 5 .2 0 5 0 .0 0 2 00 10 0 20 7 1 .5 0 3 0 5 0 .0 0 9 .5 0 6 0 4 .0 0 0 0 Total cost 16 0 3 .5 0

1 2 3 4 5 6 7 8

*)

Initial inventory: 270

Alternatif 2: Chase Strategy (Production= demand)Kuartal Dem and Production (unit) Sub (unit) Regular Overtim Kontrak e (a) (b) (c) (d) 1 220 200 2 170 170 3 400 200 100 100 4 600 200 100 300 5 380 200 100 80 6 200 200 7 130 130 8 300 200 100 Total Changing Hiring Lay-off Production Production Production cost cost cost (unit) (unit) (US$) (US$) (US$) (e e (e)= c) (f ) = ) (g)= ax(0,f)*Ch (h)= in(0,f)|*Cl (i)= (b+ m |m (b*Cr+ c*Co) 200 0 2.000 170 -30 4.500 1.700 300 130 13.000 5.000 300 0 5.000 300 0 5.000 200 -100 15.000 2.000 130 -70 10.500 1.300 300 170 17.000 5.000 30.000 30.000 27.000 Total costt t -1

Subcontract cost (US$) (j)= (d)*Cs 8.000 24.000 6.400 38.400 125.400

Alternatif 3: Subcontract StrategyProduction level = constant regular (200) dan kekurangan kapasitas di subcontract Kuarta Demand l 1 2 3 4 5 (unit) (a) 220 170 400 600 380 Production (unit) Regular (b) 200 200 200 200 200 200 400 180 Subcontrac Production Subcontract t (unit) (c) 20 cost (US$) cost (US$)

(d)=(b*Cr) (e)=(d)*Cs 2.000 2.000 2.000 2.000 2.000 16.000 32.000 14.400 1.600 -

Alternatif 4: Mixed StrategyKuartal Sub Total Changing End Subcon- Inventory Dem and Production (unit) Kontrak Production Production inventory Hiring cost Lay-off Production tract cost cost (unit) Regular Overtim (unit) e (unit) (unit) (unit) (US$) cost (US$) cost (US$) (US$) (US$) (a) (b) (c) (d) (e)= c) (b+ (f) (g) (h)= ax(0,f) (i)= in(0,f)| (j)= m |m (b*Cr+ (k)= (d)*Cs (l) *Ch *Cl + c*Co) 270 220 0 0 50 8.000 170 200 200 200 80 20.000 2.000 6.500 400 200 100 20 300 100 0 10.000 5.000 1.600 6.000 600 200 100 300 300 0 0 5.000 24.000 380 200 100 80 300 0 0 5.000 6.400 200 200 200 -100 0 15.000 2.000 130 200 200 0 70 2.000 300 200 30 200 0 0 30.000 15.000 2.000 23.000 2.400 34.400 Total cost 20.500 122.900

0 1 2 3 4 5 6 7 8

Linear Programming

Min Z = r Pt + h At + f Rt + v Ot + c I tt =1 t =1 t =1 t =1 t =1

k

k

k

k

k

Subject to

Pt mt ; t = 1, 2, ..., k Ot nt ; t = 1, 2, ..., k I t = I t 1 + Pt + Ot Dt ; t = 1, 2, ..., k

P, O = jml unit yang diproduksi pada RT dan OT A, R = jml unit kenaikan dan penurunan r, v = ongkos produksi per unit RT dan OT c = ongkos simpan per unit D = ramalan demand I = jml unit inventory m, n = kapasitas RT dan OT

At Pt - Pt 1 ; t = 1, 2, ..., k

Rt Pt 1 - Pt ; t = 1, 2, ..., k At , Rt , I t , Pt , Ot 0

Transportation Model(1)

Perioda 1 2 3 4

RT 700 800 900 500

Supply capacity OT Subcontract 250 500 250 500 250 500 250 500

Demand 500 800 1700 900

Inventory awal: 100 unit Inventory akhir yang diinginkan: 150 unit Ongkos RT: $100/unit Ongkos OT: $125/unit Ongkos SC: $150/unit Ongkos simpan: $20/unit/perioda

Transportation Model (2)Sumber Inv entory awal RT OT SC RT OT SC RT OT SC RT OT SC Demand Perioda penjualan 2 3 Unused Capacity Available Capacity 100 700 250 500 800 250 500 900 250 500 500 250 500 6000

Perioda Produksi 1

1

4

2

3

4

500

800

1700

1050

Transportation Model (3)

Perioda Produksi 1

2

3

4

Sumber Inventory RT OT SC RT OT SC RT OT SC RT OT SC Demand Unallocated

Perioda penjualan Unused Available 1 2 3 4 Capacity Capacity 0 0 50 50 0 100 200 700 500 250 500 500 800 800 250 500 500 900 900 250 250 500 500 500 500 500 250 250 250 500 250 500 800 1.700 1.050 1.950 6.000 0 0 0

Transportation Model (4)

Sumber Periode Inventory Regular 1 Over time

10

12

15

Transportation Model (5)

Aggregat Planning Periode A. Production Planning Demand (unit) Produksi (unit) a. Regular b. Overtime Subkontrak (unit)

Management Coefficient Model(1)

Bowman Model (sumber Bedworth halaman 133-137) Work-force Wt = jumlah tenaga kerja pada periode t Ft = jumlah demand hasil ramalan pada periode t I* = tingkat inventory yang diinginkan It-1 = tingkat inventory pada periode t-1 f = fungsi

Wt = f(Ft, I*, It-1 , Wt-1 ) Contoh :

Wt = 0 +1Wt 1 +2 ( I * I t 1 ) +3 Ft

= koefisien manajemen (Ditentukan dari data empirik)

Management Coefficient Model(2)

Production levelPt = tingkat produksi pada periode t Pt = g(Wt, I*, It-1, Ft, Ft+1, Ft+2,)

Pt = 0 + 1Wt + 2 ( I * I t 1 ) + {[1 /(i + 1)]Ft +1}Contoh :

2

= koefisien manajemen

i =0

Contoh data empirik (Bedworth, page 128) 1 +i F i= 0 2

1

t+ i

t 1 2 3 4 5 6 7

Ft 20 0 20 1 20 4 30 0 20 5 20 0 10 6

It-1 3 0 4 8 6 0 2 7 5 0 4 9 6 5

W t 2 7 2 5 2 8 2 8 2 8 2 5 2 2

Management Coefficient Model(3)

Contoh coefisient management (detail ada di buku Bedworth halaman 134-135)

Wt = 1,49 + 0,503Wt 1 0,02( I * I t 1 ) + 0,49 Ft = 0,9322Pt = 63,2 + 9,62Wt + 1,32( I * I t 1 ) + 0,095 {[1 /(i + 1)]Ft +1}2

= 0,9757

i =0

LatihanDiberikan data peramalan dan produksi sebagai berikut : (Fogarty, page 74)

Jan Feb Mar Apr May Jun Deman 40 40 40 32 d Required safetystock (unit) = 5 32

Jul

Aug Sep Okt Nov Dec

Holding cost (US$/unit/month) = 300 Hiring cost (US$/worker) = 50 Layoff cost (US$/worker) = 100 Labor cost (US$/worker/month)= 480 Overtimecost ((US$/hour/worker) = 18 Production rate (units/month/worker)=8 Workday per month = 21 Current work force (workers)=5

32 48 48 48 60 60 60 Tugas : a. Buat perencanaan agregat (+ biayanya) jika digunakan chase strategy. b. Buat perencanaan agregat (+ biayanya) jika digunakan level production strategy. c. Komponen biaya apa perlu mendapat perhatian utama? Apa saran Anda untuk mengatasinya?