chapter 3 network planning 1. three hierarchical steps network design – number, locations and size...
TRANSCRIPT
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Chapter 3
Network Planning
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Three Hierarchical Steps• Network design
– Number, locations and size of manufacturing plants and warehouses– Assignment of retail outlets to warehouses– Major sourcing decisions – Typical planning horizon is a few years.
• Inventory positioning: – Identifying stocking points – Selecting facilities that will produce to stock and thus keep inventory– Facilities that will produce to order and hence keep no inventory– Related to the inventory management strategies
• Resource allocation: – Determine whether production and packaging of different products is
done at the right facility– What should be the plants’ sourcing strategies? – How much capacity each plant should have to meet seasonal
demand?
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3.2 Network Design
• Physical configuration and infrastructure of the supply chain.
• A strategic decision with long-lasting effects on the firm.
• Decisions relating to plant and warehouse location as well as distribution and sourcing
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Key Strategic Decisions
• Number of facilities.• Location of each facility.• Size of each facility.• Allocating space for products.• Sourcing requirements.• Determining distribution strategies
Objective: Design or reconfigure the logistics network in order to minimize annual system-wide cost subject to a variety of service level requirements
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Data Collection & Aggregation• Locations of customers, retailers, existing warehouses and distribution
centers, manufacturing facilities, and suppliers.• All products, including volumes, and special transport modes (e.g.,
refrigerated).• Annual demand for each product by customer location.• Transportation rates by mode.• Warehousing costs, including labor, inventory carrying charges, and fixed
operating costs.• Shipment sizes and frequencies for customer delivery.• Order processing costs.• Customer service requirements and goals.• Production and sourcing costs and capacities
Customer Zones & Product Groups
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Transportation RatesRates linear with distance but not volume
InternalTL - Zone-to-zone costs provides cost per
mile per truckload between any two zones.
LTL – Class, Exception & Commodity RatesMileage estimation
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Warehouse Costs• Handling costs
– Labor and utility costs– Proportional to annual flow through the warehouse.
• Fixed costs– All cost components not proportional to the amount of
flow – Typically proportional to warehouse size (capacity) but in a
nonlinear way. • Storage costs
– Inventory holding costs– Proportional to average positive inventory levels.
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Warehouse Capacity• Estimation of actual space required• Average inventory level =
Annual flow through warehouse/Inventory turnover ratio• Space requirement for item = 2*Average Inventory Level• Multiply by factor to account for
– access and handling – aisles, – picking, sorting and processing facilities– AGVs
• Typical factor value = 3
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Potential Locations
• Geographical and infrastructure conditions.• Natural resources and labor availability.• Local industry and tax regulations.• Public interest.
• Not many will qualify based on all the above conditions
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Service Level Requirements
• Specify a maximum distance between each customer and the warehouse serving it
• Proportion of customers whose distance to their assigned warehouse is no more than a given distance – 95% of customers be situated within 200 miles of
the warehouses serving them – Appropriate for rural or isolated areas
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Future Demand
• Strategic decisions have to be valid for 3-5 years
• Consider scenario approach and net present values to factor in expected future demand over planning horizon
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$-
$10
$20
$30
$40
$50
$60
$70
$80
$90
0 2 4 6 8 10
Number of Warehouses
Co
st (
mil
lio
ns
$)
Total Cost
Transportation Cost
Fixed Cost
Inventory Cost
Number of Warehouses
Optimal Number
of Warehouses
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Sexy Example• Single product• Two plants p1 and p2
– Plant p2 has an annual capacity of 60,000 units.
• The two plants have the same production costs.• There are two warehouses w1 and w2 with identical
warehouse handling costs.• There are three markets areas c1,c2 and c3 with
demands of 50,000, 100,000 and 50,000, respectively.
Unit Distribution Costs
Facility warehouse
p1 p2 c1 c2 c3
w1 0 4 3 4 5
w2 5 2 2 1 2
Two heuristics and an optimization technique:1. Choose the cheapest warehouse to source demand2. Choose the warehouse where the total delivery
costs to and from the warehouse are the lowest3. LP
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Heuristic #1:Choose the Cheapest Warehouse to Source Demand
D = 50,000
D = 100,000
D = 50,000
Cap = 60,000
$5 x 140,000
$2 x 60,000
$2 x 50,000
$1 x 100,000
$2 x 50,000
Total Costs = $1,120,000
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Heuristic #2:Choose the warehouse where the total delivery costs to and from the warehouse are the lowest
[Consider inbound and outbound distribution costs]
D = 50,000
D = 100,000
D = 50,000
Cap = 60,000
$4
$5
$2
$3
$4$5
$2
$1
$2
$0
P1 to WH1 $3P1 to WH2 $7P2 to WH1 $7P2 to WH 2 $4
P1 to WH1 $4P1 to WH2 $6P2 to WH1 $8P2 to WH 2 $3
P1 to WH1 $5P1 to WH2 $7P2 to WH1 $9P2 to WH 2 $4
Market #1 is served by WH1, Markets 2 and 3are served by WH2
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D = 50,000
D = 100,000
D = 50,000
Cap = 60,000
Cap = 200,000
$5 x 90,000
$2 x 60,000
$3 x 50,000
$1 x 100,000
$2 x 50,000
$0 x 50,000
P1 to WH1 $3P1 to WH2 $7P2 to WH1 $7P2 to WH 2 $4
P1 to WH1 $4P1 to WH2 $6P2 to WH1 $8P2 to WH 2 $3
P1 to WH1 $5P1 to WH2 $7P2 to WH1 $9P2 to WH 2 $4
Total Cost = $920,000
Heuristic #2:Choose the warehouse where the total delivery costs to and from the warehouse are the lowest[Consider inbound and outbound distribution costs]
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The Optimization Model
The problem described earlier can be framed as the following linear programming problem.Let
• x(p1,w1), x(p1,w2), x(p2,w1) and x(p2,w2) be the flows from the plants to the warehouses.
• x(w1,c1), x(w1,c2), x(w1,c3) be the flows from the warehouse w1 to customer zones c1, c2 and c3.
• x(w2,c1), x(w2,c2), x(w2,c3) be the flows from warehouse w2 to customer zones c1, c2 and c3
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The Optimization ModelThe problem we want to solve is: min 0x(p1,w1) + 5x(p1,w2) + 4x(p2,w1) + 2x(p2,w2) + 3x(w1,c1) + 4x(w1,c2) + 5x(w1,c3) + 2x(w2,c1) + 2x(w2,c3)
subject to the following constraints: x(p2,w1) + x(p2,w2) 60000 x(p1,w1) + x(p2,w1) = x(w1,c1) + x(w1,c2) + x(w1,c3) x(p1,w2) + x(p2,w2) = x(w2,c1) + x(w2,c2) + x(w2,c3) x(w1,c1) + x(w2,c1) = 50000 x(w1,c2) + x(w2,c2) = 100000 x(w1,c3) + x(w2,c3) = 50000
all flows greater than or equal to zero.
Optimal SolutionFacility
warehousep1 p2 c1 c2 c3
w1 140,000 0 50,000 40,000 0*
w2 0 60,000 0 60,000 50,000*
Total cost for the optimal strategy is $740,000*Your text has the w2c3 and w1c3 numbers reversed
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DSS for Network Design• Flexibility to incorporate a large set of preexisting network
characteristics • Other Factors:
– Customer-specific service level requirements.– Existing warehouses kept open– Expansion of existing warehouses.– Specific flow patterns maintained – Warehouse-to-warehouse flow possible– Production and Bill of materials details may be important
• Robustness – Relative quality of the solution independent of specific environment,
data variability or specific settings
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Inventory Positioning and Logistics Coordination
• Multi-facility supply chain that belongs to a single firm• Manage inventory so as to reduce system wide cost• Consider the interaction of the various facilities and the
impact of this interaction on the inventory policy of each facility
• Ways to manage:– Wait for specific orders to arrive before starting to manufacture them
[make-to-order facility]– Otherwise, decide on where to keep safety stock? – Which facilities should produce to stock and which should produce to
order?
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Single Product, Single Facility Periodic Review Inventory Model
• Assume -– SI: amount of time between when an order is placed until
the facility receives a shipment (Incoming Service Time)– S: Committed Service Time made by the facility to its own
customers.– T: Processing Time at the facility.–
• Net Lead Time = SI + T - S• Safety stock at the facility:
STSI
STSIzh
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2-Stage System
Reducing committed service time from facility 2 to facility 1 impacts required inventory at both facilities Inventory at facility 1 is reduced Inventory at facility 2 is increased
Overall objective is to choose: the committed service time at each facility the location and amount of inventory minimize total or system wide safety stock cost.
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ElecComp Case• Large contract manufacturer of circuit boards and other high
tech parts. • About 27,000 high value products with short life cycles• Fierce competition => Low customer promise times <
Manufacturing Lead Times• High inventory of SKUs based on long-term forecasts =>
Classic PUSH STRATEGY– High shortages– Huge risk
• PULL STRATEGY not feasible because of long lead times
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New Supply Chain Strategy• OBJECTIVES:
– Reduce inventory and financial risks– Provide customers with competitive response times.
• ACHIEVE THE FOLLOWING:– Determining the optimal location of inventory across the various stages – Calculating the optimal quantity of safety stock for each component at each
stage• Hybrid strategy of Push and Pull
– Push Stages produce to stock where the company keeps safety stock– Pull stages keep no stock at all.
• Challenge:– Identify the location where the strategy switched from Push-based to Pull-
based– Identify the Push-Pull boundary
• Benefits:– For same lead times, safety stock reduced by 40 to 60%– Company could cut lead times to customers by 50% and still reduce safety
stocks by 30%
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Notations Used
FIGURE 3-11: How to read the diagrams
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Trade-Offs• If Montgomery facility reduces committed lead time to 13
days– assembly facility does not need any inventory of finished goods– Any customer order will trigger an order for parts 2 and 3.
• Part 2 will be available immediately, since it is held in inventory• Part 3 will be available in 15 days
– 13 days committed response time by the manufacturing facility– 2 days transportation lead time.
– Another 15 days to process the order at the assembly facility– Order is delivered within the committed service time.
• Assembly facility produces to order, i.e., a Pull based strategy• Montgomery facility keeps inventory and hence is managed
with a Push or Make-to-Stock strategy.
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Current Safety Stock Location
FIGURE 3-12: Current safety stock location
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Optimized Safety Stock Location
FIGURE 3-13: Optimized safety stock
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Current Safety Stock with Lesser Lead Time
FIGURE 3-14: Optimized safety stock with reduced lead time
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Supply Chain with More Complex Product Structure
FIGURE 3-15: Current supply chain
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Optimized Supply Chain with More Complex Product Structure
FIGURE 3-16: Optimized supply chain
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Key Points• Identifying the Push-Pull boundary• Taking advantage of the risk pooling concept
– Demand for components used by a number of finished products has smaller variability and uncertainty than that of the finished goods.
• Replacing traditional supply chain strategies that are typically referred to as sequential, or local, optimization by a globally optimized supply chain strategy.
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Local vs. Global Optimization
FIGURE 3-17: Trade-off between quoted lead time and safety stock
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Global Optimization
• For the same lead time, cost is reduced significantly
• For the same cost, lead time is reduced significantly
• Trade-off curve has jumps in various places– Represents situations in which the location of the
Push-Pull boundary changes – Significant cost savings are achieved.
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Problems with Local Optimization
• Prevalent strategy for many companies:– try to keep as much inventory close to the customers – hold some inventory at every location – hold as much raw material as possible.
• This typically yields leads to:– Low inventory turns– Inconsistent service levels across locations and products,
and– The need to expedite shipments, with resulting increased
transportation costs
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Integrating Inventory Positioning and Network Design
• Consider a two-tier supply chain– Items shipped from manufacturing facilities to primary
warehouses – From there, they are shipped to secondary warehouses
and finally to retail outlets • How to optimally position inventory in the supply
chain? – Should every SKU be positioned both at the primary and
secondary warehouses?, OR – Some SKU be positioned only at the primary while others
only at the secondary?
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Integrating Inventory Positioning and Network Design
FIGURE 3-18: Sample plot of each SKU by volume and demand
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Three Different Product Categories
• High variability - low volume products• Low variability - high volume products, and• Low variability - low volume products.
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Supply Chain Strategy Different for the Different Categories
• High variability low volume products – Inventory risk the main challenge for– Position them mainly at the primary warehouses
• demand from many retail outlets can be aggregated reducing inventory costs.
• Low variability high volume products – Position close to the retail outlets at the secondary
warehouses– Ship fully loaded tracks as close as possible to the
customers reducing transportation costs.• Low variability low volume products
– Require more analysis since other characteristics are important, such as profit margins, etc.