AGGREGATE PLANNING

Proses peramalan  informasi jumlah produk Buat rencana produksi : upaya menjabarkan hasil peramalan menjadi rencana produksi yang layak untuk dilakukan. Salah satu metode  AGGREGATE PLANNING AGGREGATE PLANNING Concerned with determining the quantity and timing of production for the intermediate future  3-8 months To determine the best way to meet forecasted demand by adjusting production rates, labor levels, inventory levels, overtime work, subcontracting rates  minimizing cost Use a logical overall unit for measuring sales and output  not individual unit product

Individual product Aggregate product Examples: Individual product Aggregate product - Red car Green car unit car Blue car Keripik tempe pedas Keripik tempe manis bungkus keripik tempe/gr Keripik tempe asin Keuntungan penggunaan satuan agregat : Kemudahan dalam pengolahan data Ketelitian hasil yang diharapkan Kemudahan memahami mekanisme sistem produksi yang terjadi dalam implementasi rencana.

Several question need to be answered before applying aggregate planning Should inventories be used to absorb changes in demand during the planning period? Should changes be accommodated by varying the size of the workforce? Should part timers be used, or should overtime and idle time adsorb fluctuation? Should subcontractors be used on fluctuating orders so stable workforce can be maintained? Should prices or other factors be changed to influence demand?

Capacity options (Production Strategy) Changing inventory levels Increase inventory during periods of low demand to meet high demand in the future periods Varying workforce size by hiring or lay offs Hire or lay off production workers to match production rates Varying production rates through overtime and idle time Keeping constant workforce while varying hours may be possible Subcontracting Subcontracting work during peak demand periods Using part-time workers Use part time workers  service sector TO ANSWER FLUCTUATION DEMAND

Pure Mixing Options Level Strategy Equal amount produced each period Steady employment Vary inventory to meet variations in demand Inventory costs or the expense of a shortage Service – constant but poor utilization: Too large - poor utilises workforce Too small – lose some demand to competitor

Chase Demand Production identical to demand for the period Vary the work-force Overtime or hiring and laying (high costs) No inventory cost, no shortage cost Service – overtime, split shifts, overlapping shifts, call-in workers, part- time

PERENCANAAN AGREGAT DENGAN METODE GRAFIS Melihat gambaran permintaan kumulatif dan rata-rata permintaan kumulatif. Tahap-tahap : Gambarkan histogram permintaan dan tentukan kecepatan produksi (Pt) rata-rata yang diperlukan untuk memenuhi permintaan. 2. Gambarkan grafik permintaan kumulatif terhadap waktu serta grafik permintaan rata-rata kumulatif terhadap waktu. Identifikasikan periode tempat terjadinya kekurangan (back order) dan periode-periode adanya kelebihan (inventory) 3. Tentukan strategi yang akan digunakan untuk menanggulangi kelebihan dan kekurangan barang tersebut.

4. Hitung ongkos yang ditimbulkan oleh setiap strategi dan pilih ongkos terkecil. DATA PERMINTAAN UNTUK 8 PERIODE MENDATANG : Persediaan Awal : I t - 1 = 0 Back Order = Rp. 100,-/unit/bl Ongkos sub kontrak = Rp. 800/Unit. Ongkos untuk menaikkan produksi = Rp. 1.000,-/Unit Ongkos simpan / penundaan = Rp. 50,-/Unit/periode Ongkos untuk menurunkan produksi = Rp. 1.500,-/Unit Rencanakan kecepatan produksi (Pt) selama 8 periode yad t 1 2 3 4 5 6 7 8 Dt (Unit) 220 170 400 600 380 200 130 300

Solusi : 1. Histogram Demand dan Pt. Dt Pt = 300 t

Plot demand kumulatif vs t dan Demand rata-rata kumulatif vs t. 1 2 3 4 5 6 7 8 dt 220 170 400 600 380 200 130 300 Demand Kumulatif 390 790 1390 1770 1970 2100 2400 Demand rata-rata kumulatif 900 1200 1500 1800

back order. Dt. Produksi rata-. rata kumulatif. demand kumulatif back order Dt Produksi rata- rata kumulatif demand kumulatif inventory t

Ongkos kenaikan produksi (Rp) Ongkos penurunan produksi (Rp) ∑ Cost STRATEGI YANG DIGUNAKAN: a. Tenaga kerja diasumsikan sama dengan pola permintaan - ongkos merekrut (menaikan produksi) - ongkos memberhentikan (menurunkan produksi) b. Inventory, menyediakan persediaan pada awal periode yang mungkin  ongkos persediaan. c. sub kontrak, memberikan sebagian produksi pada pihak luar  ongkos sub kontrak. 4. Perhitungan ongkos dari setiap strategi 4.1. Perencanaan tenaga kerja  Rumus dasar : Pt = Dt – It-1 + It t dt Pt Ongkos kenaikan produksi (Rp) Ongkos penurunan produksi (Rp) ∑ Cost 1 2 3 4 5 6 7 8 220 170 400 600 380 200 130 300 - 230.000 200.000 170.000 75.000 330.000 270.000 105.000 1.440.000

4.2. Mengadakan persediaan, tingkat produksi KONSTAN Permintaan (Dt) Tingkat Produksi (Pt ) Persedian yang timbul (It ) Penyesuaian dengan perse -diaan awal Ongkos total 220 170 400 600 380 200 130 300 80 210 110 -190 -270 -170 350 480 100 270 17.500 24.000 19.000 4.000 5.000 13.500 96.500

4.3. Sub kontrak Bulan Permintaan Tingkat Produksi Besarmya sub kontrak Ongkos total 1 2 3 4 5 6 7 8 220 170 400 600 380 200 130 300 90 40 270 470 250 70 72.000 32.000 216.000 376.000 200.000 56.000 136.000 1.108.000

Kapasitas jam kerja lembur OT PERENCANAAN AGREGAT DENGAN MODEL TRANPORTASI (LAND) Contoh : Permintaan selama 4 periode serta sumber daya yang dimilikinya selama 4 periode tersebut, sbb : t Permintaan Jam kerja biasa RT Kapasitas jam kerja lembur OT Sub kontrak SK 1 2 3 4 500 800 1700 900 700 250

Diketahui pula bahwa pada periode 1 sudah terdapat persediaan awal sebesar 100 unit dan pada akhir periode 4 diinginkan adanya persediaan sebesar 150 unit. Ongkos produksi pada jam kerja biasa (reguler time) Rp. 100/unit, pada jam kerja lembur (over time) Rp. 125/unit, ongkos untuk mengadakan sub kontrak Rp. 150/unit dan untuk menyimpan produk di kenakan ongkos Rp. 20,-/unit/periode.

Persediaan RT OT SK Sumber Periode Kap. Tak terpakai Kap. Total 1 2 3 4 Persediaan 100 20 40 60 - RT 400 120 300 140 160 700 OT 125 145 165 185 250 SK 150 500 800 900 Permintaan 1700 1050 6000

Contoh soal : Sun Valley ski company, which produces the famous sun ski, has a production cost of $ 60 per pair during regular time and $ 70 per pair on overtime. The firm’s production capacity and forecast demand as shown below : Period (quarter) : Forecast demand : 900 500 200 1900 units Beginning inventory is 200 pair, and stock is carried at a cost of $ 5 per pair-quarter. Demand is to be met without any hiring, layoff, subcontracting, or back orders. Unused regular time has a cost of $ 20/pair 1 2 3 4

Supply, units for Periode unused Total available First quarter Second quarter Third quarter fourth Initial inventory 200 5 10 15 - 1 Regular 60 700 65 70 75 Overtime 80 85 300 2 500 3 100 4 Forecast demand 900 1900 4200

Contoh Michigan manufacturing produces a product which has a 6-month demand cycle, as shown. Each unit requires 10 worker-hour to be produces, at a labor cost of $ 6 per hour regular rate (or $ 9 per hour over time). The total cost per unit is estimated at $200, but unit can be subcontracted at a cost $208 per unit. There are currently 20 workers employed in the subject department, and hiring and training cost costs for additional workers are $300 per person, where as layoff cost are $400 per person. Company policy is to retain a safety stock equal to 20 % of the monthly forecast,

Jan Feb March April May June Lanjutan Contoh : and each months safety stock becomes the beginning inventory for the next month. There are currently 50 units in stock carried at a cost of $2 per unit-month stock outs have been assigned a cost of $20 per unit-month. Jan Feb March April May June Forecast demand Work days Worker hr at 8/day 300 22 176 500 19 152 400 21 168 100 200 20 160

Three agregate plans are proposed : Plan 1 : vary the work-force size to accommodate demand Plan 2 : Maintain a constant work force of 20 and use overtime and idle time to meet demand. Plan 3 : Maintain a constant work force of 20 and build inventory on incur a stockout cost The firm must begin January with the 50 unit inventory on hand

Month Forecast demand Cumulative demand SS 20 % Beginning Inventory Production requirement ( Forecast + SS - beginning inv) Jan Feb March April May June 300 500 400 100 200 800 1.200 1.300 1.500 1.800 60 80 20 40 50 310 540 380 220 320

JANUARY FEBRUARY MARCH APRIL MAY JUNE TOTAL COST 1 2 3 4 5 6 7 8 Production required Production hours reguired (1x10) Hours available per worker at 8/day Number of workers Required (2 : 3) Number of workers hired Hiring cost (5 x $ 300) Number of worker laid off Lay off cost (7 x $ 400) 310 3.100 176 18 - $800 540 5.400 152 36 $5.400 380 3.800 168 23 13 $5.200 40 400 20 $8.000 220 2.200 10 $3.000 320 3.200 160 $2.100 $10.500 $14.000 $24.500 dfdfsdfssfsfsf

5 6 7 8 12 3 4 Production hours reguired (1x10) JANUARY FEBRUARY MARCH APRIL MAY JUNE TOTAL COST 12 3 4 5 6 7 8 Production required Production hours reguired (1x10) Hours available per worker at 8/day Total hour available (3 x 20) Number of over time hours required (2-4) OT premium* (5 x $ 9) Number idle time Hours (4-2) IT cost (7 x $ 6) 310 3.100 176 3.520 - 420 $2.520 540 5.400 152 3.040 2.360 $21.240 380 3800 168 3.360 440 $3.960 40 400 2.960 $17760 220 2.200 1.320 $7920 320 3.200 160 $25.200 $28.200 $53.400

Cumulative production reguired JANUARY FEBRUARY MARCH APRIL MAY JUNE TOTAL COST 12 3 4 5 6 7 8 9 Production required Cumulative production reguired Total hours available at 20 worker Unit produced (3:10) Cumulative production Unit short (2 - 5) Stortage cost (6 x $ 20) Excess units (5-2) Inventory cost (8 x $2) 310 (176x20) 3.520 352 - 42 $ 84 540 850 3.040 304 656 194 $3880 380 1.230 3.360 336 922 238 $4760 40 1.270 1.328 58 $116 220 1.490 1.680 190 $380 320 1.810 3.200 2.000 $8.640 $960 $9.600