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Order picking in most distribution centers represents the largest area of cost – often 50 percent or more of labor costs – and has become increasing complex for many companies in recent years.

A recent article on the Material Handling Institute web site by Norman Saenz offers a basic but common sense framework for designing your order picking systems right. (See also SCDigest column “The Do’s and Don’ts of a designing a World Class Facility”)

Saenz offers a seven-step framework:

• Activity Profiling: Defining the product movement in terms of lines ordered per product; in other words, the number of times you travel to a location to pick an item. Based on this criterion, products are classified as: fast (A); medium (B); slow (C); or dead (D) moving items. Key is not only analyzing unit volume but also cubic movement and profile by unit of measure (eaches, cases, pallets, etc.)
  
  
• Picking Equipment/Technology: After activity profiling analysis, consider the appropriate storage mode and technology support for each picking area. Typical technologies used for each, case and pallet picking are shown below:

• Slotting Strategy: Effective slottingcan increase throughput, improve labor utilization, reduce injuries, improve cube utilization, and reduce product damage. “The art of effective slotting is assigning the fast-moving items to the most ergonomic levels, while balancing the volume across many aisles to reduce order and labor congestion…The slotting assignment must be reviewed for its effectiveness monthly and/or as the activity of products fluctuates with seasonality.
  
  ”An important component of slotting is calculating the number of facings or locations required for each product. This requirement is determined by considering the desired days on hand for each product. The days-on-hand value is multiplied by the quantity ordered per day to calculate the pick location inventory. This value is divided by the capacity of the assigned location type to calculate the number of facings required.”
  
  
• Replenishing Forward Pick: Effective replenishment of forward pick slots is key to order picking productivity, and often the biggest operational challenge. Replenishment strategies range from “visual” (operators/supervisors see a location is running low) to a variety of WMS-generated replenishment tasks. Storage modes, material handling equipment decisions, WMS capabilities and warehouse design must all come together to achieve efficient replenishment.
  
  
• Layout/Pick Zone Design: The basic choices for picking area design are U-shaped and straight-through. Picking and replenishment lanes/paths should generally be kept separate to avoid congestion. “ The development of pick zones within the active picking area is crucial to the productivity of the picking operation. A common philosophy is "items that are shipped together are also stored and picked together." Other pick zone philosophies include storing by a product's physical characteristics or specific product category. A newer philosophy introduced as a result of growing e-commerce business is creating pick zones by business type or order size. The driving factors behind selecting a philosophy include volume-balancing, labor congestion, pick travel distances, routing, and order consolidation. Layout planning is closely knitted to the development of picking methods. The development of pick zones within the active picking area is crucial to the productivity of the picking operation. A common philosophy is "items that are shipped together are also stored and picked together." Other pick zone philosophies include storing by a product's physical characteristics or specific product category. A newer philosophy introduced as a result of growing e-commerce business is creating pick zones by business type or order size. The driving factors behind selecting a philosophy include volume-balancing, labor congestion, pick travel distances, routing, and order consolidation.”
  
  
• Picking Methods: Picking methods are defined in terms of: (a) pickers per order - the number of pickers that work on a single order at one time; (b) lines per pick - the number of orders a single item is picked for at one time; and (c) periods per shift - the frequency of order scheduling during one shift.

The most common pick methods are illustrated in the following table:

• Material Handling: The warehouse layout and material handling equipment design and selection are of course closely intertwined, and much usually be developed using an iterative process.

What would you add to this framework for order picking system design? Let us know your thoughts.