Let’s talk about the basic process of warehouse picking. Picking is the selection of items that are in storage so that they can be prepared for shipment. Here is an overview of this fundamental process.
Another great reference by Ed Frazelle for an overview of warehousing processes and analysis is here. But today we’re just going to cover Picking.
Warehouse Picking, also called “selecting,” is the process of identifying and removing a product for storage so that it can be prepared for shipment.
It is usually the most labor-intensive function in a warehouse. A good rule of thumb is that 55% of a warehouse’s labor goes into picking alone (Bartholdi). This can change–for example in a reverse-logistics center–but regardless of the site it is very labor intensive.
Picking has different types that are identified by the unit of measure (UOM) picked and/or by the order sortation method. For example, here are some common order-sortation methods of picking:
- Batch picking
- Zone picking
Units of measure often include pallets, cases, inner-packs, or eaches. Eaches–or pieces– are individual items that may be very small, like a gift card, or very large, like the mast of a boom-lift.
Picking systems include broad categories of person-to-goods or goods-to-person. Person-to-goods refers to systems where the employee moves to the location of the pick. Goods-to-person describes systems that bring the pick items to the employee for removal from the location and processing.
How Picking Works
Before picking, a downstream customer places demand with the warehouse. The warehouse identifies the components of each order. These are referred to as “order-lines” and contain the item and quantity ordered.
The warehouse then matches each order component to a product in the warehouse and identifies its location. Then the warehouse system transmits this information to an employee, who goes to the location and retrieves the item. The employee checks that the item is correct and then moves the item to the next processing step, which may be some sort of value added service (VAS), packing, or movement to the outbound dock for shipping. This continues until it completes the planned demand for the day or shift.
This is a generic description of the order and pick process. Each of the steps described above is usually automated. The order analysis and identification of product in the warehouse is called “allocation”, where product is matched up to the orders to fill. “Waving” is the grouping and transmission of instructions for items to pick and their locations (“picks” or “pick-lines” or “pick tasks” or the “pick sheet”) to employees.
The retrieval step is the selection and picking itself. The employee travels to the picking location, also called a “pick-facing.” The employee physically removes the item, checks that it is the correct item, records the action, and moves on to the next pick.
Order Consolidation and Sortation
Earlier we mentioned “batch picking” and “cluster picking.” What are those?
When a customer orders from a warehouse, all the things on the order may not be physically together in the warehouse. This means that to complete the order the picker would have to walk (or drive) all over the warehouse. That is inefficient, because travel takes a lot of time and time costs money.
To deal with this low efficiency, operations tries to reduce the distance the picker is traveling. This means they will often have pickers work only in a certain part of the warehouse and picking items for sets of orders that are in that area, or pick many full orders at once. This means the picker will have less distance between picks than he did picking full single orders. But it creates a new problem, which is how to separate different orders and how to consolidate the orders that were picked by multiple pickers.
This is where sortation comes in. This is the process of separating unlike orders. Then the product for each order must be consolidated together. The approach to picking requires a corresponding sortation and consolidation approach. They cannot be considered separately.
Orders may be sorted at the time of picking or downstream at other sortation stations.
Examples of picking/sortation concepts include:
- Order picking – picking a single order to completion
- Batch picking – picking many items to a container for sortation and consolidation into complete orders later
- Cluster picking – picking to individual orders’ containers on a pick cart, which may be complete or passed elsewhere in the warehouse for completion.
Why Picking Is Labor-Intensive
Picking is labor intensive because it handles the most units the longest distances in the warehouse. Receiving might handle whole pallets or cases into a putaway location. Shipping teams stack packed boxes or pallets into a truck. But for every pallet that came in, a picker might make two, five, 10, or 50 visits to the location before the stock is depleted. So picking less-than-case quantities like eaches means very many trips to the location and a lot of handling, which is very expensive.
There is a lot to understand about warehouse picking. There is a wide variety of storage media, inventory strategies, equipment, and technology options available to optimize picking. And managing picking is something of an art form. While picking is well-understood, good execution of picking is complex. We’ll explore those aspects of picking in other posts.