Post on 23-Dec-2015
The Warehouse Design and Control Problem
Based on Rouwenhorst et. al.
EJOR, Vol. 122
pgs 515-533, 2000
Topics already covered
• The roles of the Warehouse in contemporary distribution networks– Buffer
– Consolidation
– Value Adding Processing
Topics already covered (cont.)
• Warehouses processes and the associated material flow
Receiving Shipping
Reserve Storageand
Pallet Picking
CasePicking
BrokenCase
Picking
Accumulation, Sortation & Packing
Cross-docking
Directputawayto reserve
Directputawayto primary
Replenishment Replenishment
Topics already covered (cont.)
• Major warehouse equipment, its functionality, and justification– Containers & Unitizing Equipment
– Storage and Retrieval Equipment• Unit Load
• Small Load
– Conveyors
– Warehouse docks and dock-related equipment
– Automatic Identification and Communication Equipment
Major decisions underlying the Warehouse deployment and operations
• Configuration issues– Organization of the material flow
• Unit Loads
• Establishment of a forward area– items to be included in the forward area
– sizing of the forward area
• zoning, batching, sortation and consolidation schemes
– Equipment selection and its sizing• storage modes
• order picking and material handling equipment
• Warehouse management system and automatic identification and communication equipment
– Layout
– Personnel skills and sizing
Major decisions underlying the Warehouse deployment and operations
• Policies– Receiving policies
• Assigning trucks to docks
– Storage policies• Assigning received material to storage locations
– Replenishment policies– Order processing policies
• order batching policies
• zoning policies
• picker routing
– Sortation and consolidation policies– Shipping policies
Decision / Performance Criteria
Responsiveness
Quality
CostInvestment +OperationalSpace/Equipment/Labor
Product qualityOrder accuracy
Order flow timethroughputfill ratevolume flexibility/storage capacitymix flexibility
=> Multi-criteria Optimization Problem!
Warehouse types/missions and Competitive Strategies
• Factory warehouse: Interfaces production with wholesalers– small number of large orders daily– advance info about order composition
=> focus on cost and order accuracy
(responsiveness depends heavily on production schedules)
• Retail Distribution warehouse: Serves a number of captive retail units– advance info about order composition– carton and item picking from a forward area– more orders per shift than consolidation/shipping lanes
=> focus on cost, accuracy and fill rate
(responsiveness depends heavily on truck routing schedules)
Remark: If the retail units are not captive, then responsiveness becomes a crucial issue!
Warehouse types/missions and Competitive Strategies
• Catalog Retailer: A warehouse filling orders from catalog sales– a large number of small (frequently single-line) orders– item and, sometimes, carton picking– daily composition of orders usually unknown– only statistical information available
=> focus on cost and response time
• Support of Manufacturing operations: A stock room providing raw material and/or work-in-process to manufacturing operations– many small orders– only statistical information available about order composition– stringent time requirements (e.g., response in 30 min)
=> focus on response time but also accuracy and cost
Addressing the problem complexity:Hierarchical Decomposition
• Strategic-level decisions: they have the longer-lasting impact on the operation of the warehouse, and involve major investment– process flow design
– equipment selection
• Tactical-level decisions: medium-term decisions which might still involve significant investment– sizing of the facility areas and its equipment
– layout
– resolution of organizational issues like the storage and replenishment schemes, and batch sizing
• Operational-level decisions: Decisions and policies related to the real-time operation of the facility– assignment and control problems of people and equipment
Strategic-Level Concerns (Rouwenhorst et.al.)
Receiving Storing Orderpicking Shipping
Resources
Processes
OrganizationSeparatereserve area?
Batching?
Differenttypes ofstorage?
Types ofstorage
Storageunit
Types ofsorting eq.
Receiving Storing Orderpicking Shipping
Resources
Processes
Organization
Tactical-level concerns(Rouwenhorst et. al.)
Forward andreserve area
Storageconcept
Pick zones
Batch size
Numberof docks
Tech. zones Numberof docks
LayoutStoring and Picking eq. capacity
Peripheral eq. and workforce capacity
Operational-level concerns(Rouwenhorst et. al.)
Receiving Storing Orderpicking Shipping
Resources
Processes
Organization DockAssignment
Replenish-ment Policy
Storageplan
DockAssignment
Batchformation
Picking taskAssignment
Routing
Dwell point
Chute Assignment
Workforce Assignment
General Remarks• The decomposition is ad-hoc: no theoretical justification
• Top-down approach: Higher-level decisions constitute constraints for lower-level decision making: – However, they must be revised if the lower-level problems become infeasible
• Most existing quantitative analysis addresses tactical and operational issues
• Strategic level issues hard to formally model and analyze due to– underlying problem complexity– elusive / intangible nature of some of the considered criteria (e.g., flexibility).– Typically, one seeks to narrow down the design alternatives to a few
configurations that tend to minimize (annualized investment and operational) costs, while meeting some technical and performance-related constraints
Course roadmap• Familiarize ourselves with the formal theory and key analytical results
addressing some of the problems identified in the above taxonomy.– Storage configuration and storage policies– the forward/reserve problem– order-picking: batching, zoning, and routing– Pallet-building– Warehouse layout– Configuring and controlling automated storage and retrieval equipment– Cross-docking
• Address the synthesis/design problem through project assignments• Rouwenhorst et. al.: a good starting point for tracing literature on a
particular problem.
But first of all...
• Warehouse profiling:Retrieving and evaluating the problem data.
• In general,– project inception– data acquisition– functional specification– technical specification– selection of means and equipment– layout– selection of planning and control policies