Aggregate And Master Scheduling

AGGREGATE PLANNING AND MASTER SCHEDULING Hubungan pada perencanaan aggregate: Pasar dan permintaan

Riset dan Teknologi

Keputusan produk

Proses perencanaan dan keputusan kapasitas

Permintaan peramalan, order

Tenaga Kerja Bahan Baku

Aggregate Plan for Production

Persediaan

Kapasitas eksternal / subkontrak

MPS dan MRP

Rencana Kerja Detail Aggregate Plan: Month J F No Of 40 25 motors MPS: Month AC Motors 5 hp 25 hp DC Motors 20 hp WR motors 10 hp

M 55

A 30

M 30

J 50

J 30

A 60

S 40

M

A

M

J

J

A

S

J

F

15 20

25

30 25

15

15

30 15

20

30

10 20

-

-

-

-

-

-

10

10

-

5

-

-

15

15

5

-

20

10

Some Decision Variables and Costs in Aggregate Planning:

1. 2. 3. 4. 5. 6.

Decision Variables Varying size of work force Using overtime or accepting idle time Varying inventory level Accepting back orders Subcontracting work to others Changing the use of existing Capacity

1. 2. 3. 4. 5.

Associated Costs Hiring, training & layoff costs Wage premiums & nonproductive time costs Carrying & storage costs Stockout costs of lost orders Higher labor & material costs

6. Delayed response & higher fixed costs

Metode Untuk Perencanaan Agregat 1. Metode Strategy

Grafik(Trial

and

Error):

Pure

Strategy,

Mixed

a. Menentukan permintaan tiap periode b. Menentukan kapasitas untuk waktu regular, overtime dan subkontrak tiap periode c. Menentukan biaya tenaga kerja, pemecatan dan rekruitmen serta biaya inventori d. Mempertimbangkan kebijakan perusahaan e. Mengembangkan rencana-rencana alternative dan evaluasi biaya totalnya Contoh 1: Bulan Januari Februari Maret April Mei Juni Jumlah

Ekspektasi permintaan 900 700 800 1200 1500 1100 6200

Hari Produksi 22 18 21 21 22 20 124

Permintaa n per hari 41 39 38 57 68 55 298

Tingkat produksi untuk memenuhi permintaan rata-rata = Total ekspektasi permintaan = 6200 = 50 unit / hari Hari Produksi 124 List Beberapa Alternatif: Misal: a. Menyiapkan tenaga kerja cadangan b. Produksi dengan laju yang konstan dan sisanya di subkontakkan c. Kombinasi kerja lembur dan subkontrak Contoh 2: Diketahui Informasi biaya sebagai berikut: Biaya penyimpanan persediaan Biaya Subkontrak per unit Tingkat Gaji rata-rata Gaji lembur Jam Tenaga Kerja utk produksi/unit Biaya untuk meningkatkan produksi Biaya utk mengurangi tingkat produksi

$ 5/unit/bulan $ 10 $ 5/jam ($ 40 / hari) $7/jam (diatas 8 jam) 1,6 jam/unit $ 10 / unit $ 15 / unit

Rencana 1 (level production): Asumsi: produksi per hari 50 unit Konstan Tenaga Kerja, Tidak ada overtime – idletime, tidak ada subkontrak dan stok (inventori awal = 0; inventori akhir = 0) Bulan

Produksi

Januari Februari Maret April Mei Juni Jumlah

1100 900 1050 1050 1100 1000

Peramala n 900 700 800 1200 1500 1100

Perubahan Inventori + 200 + 200 + 250 - 150 - 400 - 100

Biaya: Inventori 1850 unit x $ 5 / unit Tenaga Kerja Reguler *10 TK x $40/hr x 124 hr (*1,6 jam / unit → 8 jam kerja = 5 unit untuk produksi 50 unit / hr → 10 TK) Biaya lain

Inventori Akhir 200 400 650 500 100 0 1850

= =

$ 9.250 $ 49.600

=

$0 $ 58.850

Rencana 2 (chase demand): Produksi 38 unit sendiri, sisanya: subkontrak TK yang dibutuhkan

38 = 7,6 (7pekerja full time; 1 pekerja part time) 5

Selama periode produksi dihasilkan = 38 unit/hr x 124 hr = 4712 unit

Sisa→ sub kontrak = 6200 – 4712 = 1488 unit Biaya TK Reguler : 7,6 TK x $ 40/hr x 124 hr Sub KOntrak : 1488 unit x $ 10/unit

= $ 37.696 = $ 14.880

$ 52.576 2. Metode Pendekatan Matematika (menggunakan Linear Programming atau metode2 Transportasi) Contoh 1: Sebuah perusahaan ban memiliki data yang berhubungan dengan produksi, permintaan, kapasitas dan biaya di pabriknya

Permintaan Kapasitas - Reguler - Overtime - Subkontrak Inventori awal Biaya Reguler Overtime Sub kontrak Inventori

$ $ $ $

40 50 70 2/

Maret 800 700 50 150 100

Periode April 1000

Mei 750

700 50 150

700 50 130

Periode 2 550

3 750

400 50 200

450 50 200

/ ban / ban / ban ban / bulan

Solusi: dengan metode transportasi!! Contoh 2: Diketahui data sbb:

Forecast Kapasitas - Reguler - Overtime - Subkontrak Inventori awal Biaya Reguler Time Overtime Sub kontrak Inventori

$ $ $ $

50 65 80 1/

1 450 300 50 200 50 / unit / unit / unit unit / periode

Alokasikan kapasitas produksi untuk dpt memenuhi permintaan pada biaya yg minimum!!

Contoh : Perencanaan Aggregat 1. RAP-X-PRESS adl sebuah perusahaan jasa paket barang (antarjemput). Manajer produksi / manajer operasional bertanggung jawab utk menentukan jumlah personil yg dibutuhkan setiap kuartalnya untuk setiap kategori karyawan, seperti pada gambar.

Misal :

Rata-rata gaji $ 5000 per kuartal Cost of shortage (lost sales) $ 6000 Cost of using overtime $ 8000

Bagaimana struktur biaya pada perusahaan ini bila: a. Menggunakan strategi “level production”( karyawan tetap 40) b. Menggunakan strategi “chase demand” dengan 30 karyawan? 40 karyawan? 2. Precision Products makes a variety of complex, highly engineered wastewater pump. Sales forecast for individual models have been aggregated and are given, along with other important data as follow: Demand forecasts for each quarters of the year are 400, 600, 300, and 100, with this pattern repeating itself in the future as far as can be foreseen. Current workforce : 30 Each worker can produce : 10 unit/quarter atau sktr 1 unit/week Inventory cost : $ 100/unit/quarter Shortage cost : $ 130/unit/quarter Hiring/Layoff cost : $1000/worker Idle worker : $ 1500/ quarter Overtime : $ 150 each Find the best aggregate plan if all demand must be met! Level Production: Demand, # 400

600

300

100

Production, # Inventory, # Inventory cost =($100x#) Shortage, #

350

350

350

350

0 0

0 0

0 0

0 0

50

Shortage cost =(130x#) Overtime, # Overtime cost =($150x#) Idle worker Idle cost =($1500xIW) Hire-Layoff Hire-Layoff cost =($1000xHI) TOTAL

6.500

50+250= 300 39.000

30050=250 32.000

250250=0 0

50 7.500

50 7.500

50 7.500

50 7.500

14.000

46.500

40.000

7.500

TOTA L

78.00 0 30.00 0

108.0 00

Chase Demand with Overtime & Idletime: Demand, # 400 600 300 Production, # Inventory, # Inventory cost =($100x#) Shortage, # Shortage cost =(130x#) Overtime, # Overtime cost =($150x#) Idle worker

Idle cost =($1500xIW) Hire-Layoff Hire-Layoff cost =($1000xHI) TOTAL

100

400

600

300

100

0 0

0 0

0 0

0 0

0 0

0 0

0 0

0 0

400300=100 15.000

600300=300 45.000

300300=0 0

0 0 300100=200 200/10= 20 30.000

15.000

45.000

30.000

TOTA L

60.00 0

30.00 0

90.00 0

Mixed Strategy: In this case, a better strategy than any other strategy considered thus far is to permanently hire another 10 workers, which results in one-time charge of $10.000. Then, 400 units of level production are run for 3 periods and 200 units in last period to match the annual demand of 1400 units. Demand, #

400

600

300

100

Production, # Inventory, # Inventory cost =($100x#) Shortage, #

400

400

400

200

0 0

0 0

0 0

0 0

0

600400=200

100200+100 =0

0

26.000

300400 + 200=10 0 13.000

Shortage cost =(130x#)

0

TOTA L

39.00 0

Overtime, # Overtime cost =($150x#) Idle worker Idle cost =($1500xIW) Hire-Layoff Hire-Layoff cost =($1000xHI) TOTAL

20 30.000

26.000

13.000

30.00 0

30.000

69.00 0

MASTER SCHEDULE FOR PUMPS Lead time : 0 Time Fence : 0 On hand : 64 Time Fence : 8 Period 1. Forecast 2. Customer Order(commit ted) 3. Projected on-hand inventory 4. MPS 5. ATP (uncommitte d)

Lot Size

: 70

Demand

Safety Stock : 0 1 30 33

2 30 20

3 30 10

4 30 4

5 40 2

Planning 6 40

7 40

8 40

MASTER SCHEDULE FOR PUMPS Lead time : 0 Time Fence : 0 On hand : 64 Time Fence : 8 Period 1. Forecast 2. Customer Order(commit ted) 3. Projected on-hand inventory 4. MPS 5. ATP (uncommitte d)

Lot Size

: 70

Demand

Safety Stock : 0 1 30 33

2 30 20

3 30 10

31

1

-29

4 30 4

5 40 2

Planning 6 40

MASTER SCHEDULE FOR PUMPS

7 40

8 40

Lead time : 0 Time Fence : 0 On hand : 64 Time Fence : 8 Period 1. Forecast 2. Customer Order(commit ted) 3. Projected on-hand inventory 4. MPS 5. ATP (uncommitte d)

Lot Size

: 70

Demand

Safety Stock : 0

Planning

1 30 33

2 30 20

3 30 10

4 30 4

5 40 2

6 40

7 40

8 40

31

1

41

11

41

1

31

61

70

70

70

70

MASTER SCHEDULE FOR PUMPS Lead time : 0 Time Fence : 0 On hand : 64 Time Fence : 8 Period 1. Forecast 2. Customer Order(commit ted) 3. Projected on-hand inventory 4. MPS 5. ATP (uncommitte d)

Lot Size

: 70

Demand

Safety Stock : 0

Planning

1 30 33

2 30 20

3 30 10

4 30 4

5 40 2

6 40

7 40

8 40

31

1

41

11

41

1

31

61

70 70

70 70

11

70 56

70 68