Lecture 4 supply chain planning

SUPPLY CHAIN MANAGEMENTSUPPLY CHAIN MANAGEMENT
Lecture 4:Lecture 4:
AGGREGATE PLANNING IN A SUPPLY CHAIN
HUMAYUN AKHTARHUMAYUN AKHTAR

© 2007 Pearson Education8-2
Outline
 Role of aggregate planning in a supply
chain
 The aggregate planning problem
 Aggregate planning strategies
 Implementing aggregate planning in
practice

Role of Aggregate Planning
in a Supply Chain
 Capacity has a cost, lead times are greater than
zero
 Aggregate planning:
process by which a company determines levels of
capacity, production, subcontracting, inventory,
stockouts, and pricing over a specified time horizon
goal is to maximize profit
decisions made at a product family (not SKU) level
time frame of 3 to 18 months
how can a firm best use the facilities it has?

Role of Aggregate Planning
in a Supply Chain
 Specify operational parameters over the time
horizon:
production rate
workforce
overtime
machine capacity level
subcontracting
backlog
inventory on hand
 All supply chain stages should work together on an
aggregate plan that will optimize supply chain
performance

The Aggregate Planning Problem
 Given the demand forecast for each period in the
planning horizon, determine the production level,
inventory level, and the capacity level for each period
that maximizes the firm’s (supply chain’s) profit over the
planning horizon
 Specify the planning horizon (typically 3-18 months)
 Specify the duration of each period
 Specify key information required to develop an aggregate
plan

Information Needed for an Aggregate Plan
 Demand forecast in each period
 Production costs
 labor costs, regular time ($/hr) and overtime ($/hr)
 subcontracting costs ($/hr or $/unit)
 cost of changing capacity: hiring or layoff ($/worker) and cost of adding
or reducing machine capacity ($/machine)
 Labor/machine hours required per unit
 Inventory holding cost ($/unit/period)
 Stockout or backlog cost ($/unit/period)
 Constraints: limits on overtime, layoffs, capital available,
stockouts and backlogs

Outputs of Aggregate Plan
 Production quantity from regular time, overtime, and
subcontracted time: used to determine number of workers
and supplier purchase levels
 Inventory held: used to determine how much warehouse
space and working capital is needed
 Backlog/stockout quantity: used to determine what
customer service levels will be
 Machine capacity increase/decrease: used to determine if
new production equipment needs to be purchased
 A poor aggregate plan can result in lost sales, lost profits,
excess inventory, or excess capacity

Aggregate Planning Strategies
 Trade-off between capacity, inventory,Trade-off between capacity, inventory,
backlog/lost salesbacklog/lost sales
 Chase strategyChase strategy – using capacity as the lever– using capacity as the lever
 Time flexibility from workforce or capacityTime flexibility from workforce or capacity
strategystrategy – using utilization as the lever– using utilization as the lever
 Level strategyLevel strategy – using inventory as the lever– using inventory as the lever
 Mixed strategyMixed strategy – a combination of one or more– a combination of one or more
of the first three strategiesof the first three strategies

Chase Strategy
 Production rate is synchronized with demand by varying
machine capacity or hiring and laying off workers as the
demand rate varies
 However, in practice, it is often difficult to vary capacity
and workforce on short notice
 Expensive if cost of varying capacity is high
 Negative effect on workforce morale
 Results in low levels of inventory
 Should be used when inventory holding costs are high and
costs of changing capacity are low

Time Flexibility Strategy
 Can be used if there is excess machine capacity
 Workforce is kept stable, but the number of hours
worked is varied over time to synchronize production and
demand
 Can use overtime or a flexible work schedule
 Requires flexible workforce, but avoids morale problems
of the chase strategy
 Low levels of inventory, lower utilization
 Should be used when inventory holding costs are high and
capacity is relatively inexpensive

Level Strategy
 Maintain stable machine capacity and workforce levels with a
constant output rate
 Shortages and surpluses result in fluctuations in inventory
levels over time
 Inventories that are built up in anticipation of future demand
or backlogs are carried over from high to low demand periods
 Better for worker morale
 Large inventories and backlogs may accumulate
 Should be used when inventory holding and backlog costs are
relatively low

Aggregate Planning at
Red Tomato Tools
Month Demand Forecast
January 1,600
February 3,000
March 3,200
April 3,800
May 2,200
June 2,200

Fundamental Tradeoffs in Aggregate
Planning
 Capacity (regular time, overtime, subcontract)Capacity (regular time, overtime, subcontract)
 InventoryInventory
 Backlog / lost salesBacklog / lost sales
Basic Strategies
 Chase strategy
 Time flexibility from workforce or capacity
 Level strategy

Aggregate Planning
Item Cost
Materials $10/unit
Inventory holding cost $2/unit/month
Marginal cost of a stockout $5/unit/month
Hiring and training costs $300/worker
Layoff cost $500/worker
Labor hours required 4/unit
Regular time cost $4/hour
Over time cost $6/hour
Cost of subcontracting $30/unit

Increased Demand Fluctuation
Month Demand Forecast
January 1,000
February 3,000
March 3,800
April 4,800
May 2,000
June 1,400

Aggregate Planning in Practice
 Think beyond the enterprise to the entire
supply chain
 Make plans flexible because forecasts are
always wrong
 Rerun the aggregate plan as new information
emerges
 Use aggregate planning as capacity
utilization increases

Lecture 4 supply chain planning

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