Aggregate Planning
(Perencanaan Agregat)
2
Dealing with the Problem Complexity through Decomposition
Aggregate Planning
Capacity and Aggregate Production Plans
SKU-level Production Plans
Manufacturing
and Procurement
lead times
Component Production lots and due dates
Part process
plans
(Plan. Hor.: 1 year, Time Unit: 1 month)
(Plan. Hor.: a few months, Time Unit: 1 week)
(Plan. Hor.: a few months, Time Unit: 1 week)
Shop floor-level Production Control
(Plan. Hor.: a day or a shift, Time Unit: real-time)Pendahuluan
•
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.
•
Resources
5
•
Total cost of a plan
•
Projected levels of inventory
Inventory
Output
Employment
Subcontracting
Backordering
Aggregate Planning Outputs
6
Aggregate Planning Strategies
•
Proactive
Alter demand to match capacity
•
Reactive
Alter capacity to match demand
•
Mixed
Some of each
•
Pricing
•
Promotion
•
Back orders
Demand Options
•
Hire and layoff workers
•
Overtime/slack time
•
Part-time workers
•
Inventories
•
Subcontracting
9
Aggregate Planning Strategies
•
Maintain a level workforce
•
Maintain a steady output rate
•
Match demand period by period
•
Use a combination of decision
variables
10
Basic Strategies
•
Level capacity strategy:
Maintaining a steady rate of regular-time output
while meeting variations in demand by a combination
of options.
•
Chase demand strategy:
Matching capacity to demand; the planned output for
a period is set at the expected demand for that
period.
Chase Approach
•
Advantages
Investment in inventory is low
Labor utilization in high
•
Disadvantages
The cost of adjusting output rates and/or workforce levels
Level Approach
•
Advantages
Stable output rates and workforce
•
Disadvantages
Greater inventory costs
13
1.
Determine demand for each period
2.
Determine capacities for each period
3.
Identify policies that are pertinent
4.
Determine units costs
5.
Develop alternative plans and costs
6.
Select the best plan that satisfies objectives. Otherwise
return to step 5.
Techniques for Aggregate Planning
14
Linear programming
: Methods for obtaining
optimal solutions to problems involving
allocation of scarce resources in terms of cost
minimization.
Simulation models
: Computerized models that
can be tested under different scenarios to
problems.
Summary of Planning Techniques
Technique
Solution
Characteristics
Graphical/charting Heuristic (trial
and error)
Intuitively appealing, easy to
understand; solution not
necessarily optimal.
Linear
programming
Optimizing
Computerized; linear assumptions
not always valid.
Simulation
Heuristic (trial
and error)
Computerized models can be
examined under a variety of
conditions.
17
Controllable
(
decision
)
variable
•
Inventory
•
Production rate
•
Manpower
•
Kapasitas:
over time
/
recruitment
/
layoff
(tenaga
kerja/
work force
)
•
Subcontract
18
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$/unit)
Over time (Co): 20 (US$/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
Kuartal
Demand
Kumulatif
D em and per kuartal
0
Forecasted Demand
per kuartal
Production
Adjusted
Ongkos
level
Inventory
*)inventory
1
220
300
80
350
17,500
2
170
300
210
480
24,000
3
400
300
110
380
19,000
21
Kuartal
Demand
Hiring
Layoff
Total
1
220
0
0
0
2
170
0
7,500
7,500
3
400
23,000
0
23,000
4
600
20,000
0
20,000
5
380
0
33,000
33,000
6
200
0
27,000
27,000
7
130
0
10,500
10,500
8
300
17,000
0
17,000
Total
138,000
3
400
130
270
21,600
4
600
130
470
37,600
5
380
130
250
20,000
6
200
130
70
5,600
7
130
130
0
0
8
300
130
170
13,600
Total
108,800
Kuartal
Demand
Subcontract
Subcontract Strategy
Regular Additional Overtime Inventory Overtime Changing Production units needed Production cost cost work force
1 220 200 20 50 30 30 1,500 1,000 0 2,500
2 170 200 -30 0 30 60 3,000 0 0 3,000
3 400 200 200 50 -150 -90 0 1,000 9,000 10,000
4 600 200 400 50 -350 -350 0 1,000 26,000 27,000
5 380 200 180 50 -130 -130 0 1,000 33,000 34,000
6 200 200 0 0 0 0 0 0 19,500 19,500
Mixed Strategy
Linear Programming
25
Inventory
awal: 100 unit
Inventory
akhir yang diinginkan: 150 unit
Ongkos RT: $100/unit
Perioda 1 2 3 4 Capacity CapacityProduksi Inventory awal 100
RT 700
Demand 500 800 1700 1050 6000
4
100 120 160 220
450
250 700
125 145 165 185
250
250
150 170 190 210
500
500
190 100 120 140
750
50 - 800
215 125 145 165
250
- 250
240 150 170 190
500
500
280 190 100 120
900
- 900
305 215 125 145
250
- 250
330 240 150 170
250
250 500
370 280 190 100
500
- 500
395 305 215 125
250
- 250
420 330 240 150
300
200 500
