Perencanaan Agregat

Perencanaan 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.

Factory

Wholesaler

Retailer

End consumer

Aggregate Planning

Company top level plans

Pendahuluan(2)

Aggregate Planning Strategies(1)

1) Capacity options2) Demand options3) 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 Error

Diketahui 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

Demand (unit)

1 220

2 170

3 400

4 600

5 380

6 200

7 130

8 300

Total 2400

DEMAND PER KUARTAL

0

200

400

600

800

1 2 3 4 5 6 7 8

(UNIT)

Alternatif penyusunan Perencanaan Aggregat

1. Level strategy• Production rate = average demand

2. Chase strategy• Production rate = demand

3. Subcontract strategy• Production rate dipilih konstant• Kekurangannya dipenuhi dengan subkontrak

4. Mixed strategy

Alternatif 1 : Level Strategy

*) Initial inventory: 270

Production level = average demand

Kuartal Demand Initial End Inventory Production(unit) Inventoy (unit) Regular Overtime Inventoy (unit) Cost (US$) Cost (US$)(a) (b) (c) (d) (e)=(b+c+d)-a (f)=(b+d)/2*Ci (g)=(b*Cr+c*Co)

1 220 270 200 100 350 15.500 5.000 2 170 350 200 100 480 20.750 5.000 3 400 480 200 100 380 21.500 5.000 4 600 380 200 100 80 11.500 5.000 5 380 80 200 100 0 2.000 5.000 6 200 0 200 100 100 2.500 5.000 7 130 100 200 100 270 9.250 5.000 8 300 270 200 100 270 13.500 5.000

96.500 40.000 Total cost 136.500

Production rate (unit)

Alternatif 2: Chase Strategy (Production= demand)

Total Changing Hiring Lay-off Production SubcontractKuartal Demand Sub Production Production cost cost cost cost

(unit) Regular Overtime Kontrak (unit) (unit) (US$) (US$) (US$) (US$)(a) (b) (c) (d) (e)=(b+c) (g)=max(0,f)*Ch (h)=|min(0,f)|*Cl (i)=(b*Cr+c*Co) (j)=(d)*Cs

1 220 200 200 0 - - 2.000 - 2 170 170 170 -30 - 4.500 1.700 - 3 400 200 100 100 300 130 13.000 - 5.000 8.000 4 600 200 100 300 300 0 - - 5.000 24.000 5 380 200 100 80 300 0 - - 5.000 6.400 6 200 200 200 -100 - 15.000 2.000 - 7 130 130 130 -70 - 10.500 1.300 - 8 300 200 100 300 170 17.000 - 5.000 -

30.000 30.000 27.000 38.400 Total cost 125.400

Production (unit)

)e(e(f ) 1-tt

Alternatif 3: Subcontract Strategy

Production level = constant regular (200) dan kekurangan kapasitas di subcontract

Kuartal Demand Production (unit) Subcontract Production Subcontract

(unit) Regular (unit) cost (US$) cost (US$)

(a) (b) (c) (d)=(b*Cr) (e)=(d)*Cs

1 220 200 20 2.000 1.600

2 170 200 2.000 -

3 400 200 200 2.000 16.000

4 600 200 400 2.000 32.000

5 380 200 180 2.000 14.400

6 200 200 0 2.000 -

7 130 200 2.000 -

8 300 200 100 2.000 8.000

16.000 72.000

Sub total 88.000

Alternatif 4:Mixed Strategy

Sub Total Changing End Subcon- InventoryKuartal Demand Kontrak Production Production inventory Hiring cost Lay-off Production tract cost cost

(unit) Regular Overtime (unit) (unit) (unit) (unit) (US$) cost (US$) cost (US$) (US$) (US$)(a) (b) (c) (d) (e)=(b+c) (f) (g) (h)=max(0,f) (i)=|min(0,f)| (j)=(b*Cr+ (k)=(d)*Cs (l)

*Ch *Cl +c*Co)0 2701 220 0 0 50 - - - - 8.000 2 170 200 200 200 80 20.000 - 2.000 - 6.500 3 400 200 100 20 300 100 0 10.000 - 5.000 1.600 6.000 4 600 200 100 300 300 0 0 - - 5.000 24.000 - 5 380 200 100 80 300 0 0 - - 5.000 6.400 - 6 200 200 200 -100 0 - 15.000 2.000 - - 7 130 200 200 0 70 - - 2.000 - -

8 300 200 30 200 0 0 - - 2.000 2.400 -

30.000 15.000 23.000 34.400 20.500

Total cost 122.900

Production (unit)

Linear Programming

k

t

k

ttt

k

tt

k

tt

k

tt IcOvRfAhPrZ

1 1111

Min

ktmP tt ..., 2, ,1 ; Subject to

ktDOPII ttttt ..., 2, ,1 ;1

ktnO tt ..., 2, ,1 ;

ktPPA ttt ..., 2, ,1 ;- 1

ktPPR ttt ..., 2, ,1 ;-1

0 ,,,, ttttt OPIRA

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

Transportation Model(1)

RT OT Subcontract

1 700 250 500 500

2 800 250 500 800

3 900 250 500 1700

4 500 250 500 900

Supply capacityPerioda Demand

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)

Unused Available

Perioda 1 2 3 4 Capacity Capacity

Produksi Inventory awal 100

RT 700

OT 250

SC 500

RT 800

OT 250

SC 500

RT 900

OT 250

SC 500

RT 500

OT 250

SC 500

Demand 500 800 1700 1050 6000

4

SumberPerioda penjualan

1

2

3

Transportation Model (3)

Unused Available1 2 3 4 Capacity Capacity

Inventory 0 0 50 50 0 100

RT 500       200 700 OT -     - 250 SC -       500 500 RT - 800     - 800 OT - - 250 SC -     500 500 RT - - 900   - 900 OT - - 250   - 250 SC - - 500   500 500 RT - - - 500 - 500 OT - - - 250 - 250 SC - - - 250 250 500 Demand 500 800 1.700 1.050 1.950 6.000 Unallocated - 0 0 0

3

4

Perioda

ProduksiSumber

Perioda penjualan

1

2

Transportation Model (4)

Unused Available

0 20 40 6050 50 - 100

100 120 160 220450 250 700

125 145 165 185250 250

150 170 190 210500 500

190 100 120 140750 50 - 800

215 125 145 165250 - 250

240 150 170 190500 500

280 190 100 120900 - 900

305 215 125 145250 - 250

330 240 150 170250 250 500

370 280 190 100500 - 500

395 305 215 125250 - 250

420 330 240 150300 200 500

STOCKOUT 250 250 250 250- - - -

DEMAND 500 800 1.700 900 End-horizon Inventory

150

PeriodeSumber

Periode

Capacity (unit)1 2 3 4

SubCont

Regular

Over time

SubCont

2

3

4

Over time

SubCont

Regular

Over time

SubCont

Regular

Over time

Regular

1

Inventory

Transportation Model (5)

Aggregat PlanningPeriode 0

A. Production PlanningDemand (unit)Produksi (unit) a. Regular b. OvertimeSubkontrak (unit)Inventory (unit) 100 Backorder (unit)Stockout (unit)

B. Financial PlanningPenjualan (US$)Biaya (US$)1. Produksi a. Regular b. Overtime2. Subkontrak3. Inventory4. Backorder5. StockoutTotal Biaya (US$Proyeksi laba/rugi 104.000 155.000 351.250 134.500

46.000 85.000 158.750 135.500 - - - - - - - -

1.000 5.000 - 3.000 - - 37.500 45.000 - - 31.250 37.500

45.000 80.000 90.000 50.000

150.000 240.000 510.000 270.000

- - - - - - -

50 250 - 150 - - 250 300 - 250 250 250

450 800 900 500

500 800 1.700 900

1 2 3 4

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 : tttt FIIWW 31*

2110 )(

manajemenkoefisien (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,)

Contoh :

})]1/(1{[)( 1

2

01

*210

t

ittt FiIIWP

manajemenkoefisien

Contoh data empirik (Bedworth, page 128)

t Ft It-1 Wt Pt Pr,t Po,t I*-It-1

2

0 1

1

iitF

i

1 200 30 27 209 200 9 20 385 2 210 48 25 230 200 30 2 430 3 240 60 28 250 224 26 -10 473 4 300 27 28 270 224 46 23 491 5 250 50 28 270 224 46 0 403 6 200 49 25 200 200 0 1 330 7 160 65 22 175 175 0 -15 268 8 150 72 20 160 160 0 -22 240 9 100 95 18 120 120 0 -45 213

10 120 97 18 120 120 0 -47 266 11 160 55 18 120 120 0 -5 333 12 200 31 20 180 160 20 19 386 13 220 47 22 200 176 24 3 421 14 230 68 28 250 224 26 -18 476 15 260 77 30 270 240 30 -27 525 16 350 27 33 300 266 34 23 561 17 270 55 33 300 266 34 -5 451 18 230 65 30 240 240 0 -15 423 19 200 102 30 240 240 0 -52 390 20 280 100 22 176 176 0 -50 411 21 150 129 22 176 176 0 -79 301 22 170 134 22 176 176 0 -84 353 23 200 108 22 176 176 0 -58 411 24 250 70 22 176 176 0 -20 470 25 260 26 270

Management Coefficient Model(3)

tttt FIIWW 49,0)(02,0503,049,1 1*

1

})]1/(1{[095,0)(32,162,92,63 1

2

01

*

t

ittt FiIIWP

0,9322

0,9757

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

Latihan

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

Jan Feb Mar Apr May Jun Jul Aug Sep Okt Nov Dec

Demand 40 40 40 32 32 32 48 48 48 60 60 60

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

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?