What picking is and why it matters
Picking is the removal of goods from their locations to fill an order or a transfer. It is the process in which the warehouse delivers, or fails to deliver, what was sold. A picking error reaches the customer as the wrong product, an incomplete quantity or the wrong lot, and it returns as a customer return.
For that reason, picking is measured with two indicators: productivity, in lines or units per hour, and accuracy, the share of lines picked without errors. A method that improves one at the expense of the other is rarely the right choice.
Discrete picking (by order)
One picker takes a complete order, visits the locations it lists and delivers it to packing. It is the easiest method to train and supervise, and the one with the lowest risk of mixing items from different orders.
Its limitation is travel: the picker visits every zone of the warehouse for each order, even when the next order includes products from the same locations. It works well with few orders per day or with orders that have many lines.
Zone picking
The warehouse is divided into zones, and each picker works in one zone. An order with products from several zones is split, each picker takes their part, and the parts are consolidated at the end, in packing.
Zone picking reduces aisle congestion and allows each person to know their zone well. In exchange, it requires a point where the parts of each order are consolidated, and a zone with a heavier workload than the others becomes the bottleneck.
Batch picking
One picker fills several orders in a single route, with a cart divided into compartments, one per order. If three orders include the same product, the picker takes the total quantity at one stop and separates it on the cart.
Batch picking reduces travel when orders have few lines and share products, as in e-commerce. The risk is in the separation: an item placed in another order's compartment is an error that only scan validation detects in time.
Wave picking
Orders are grouped into waves that are released together, for example according to each carrier's cutoff time. Within a wave, orders can be picked by order, by zone or in batches.
Wave picking coordinates picking with truck departures and helps plan how many people are needed at each time. It requires more planning: criteria to build the waves, release times and a rule for urgent orders that arrive between waves.
Comparison
| Criterion | Discrete | Zone | Batch | Wave |
|---|---|---|---|---|
| Travel per order | The longest | Short, within the zone | Shared among orders | Depends on the method in the wave |
| Risk of mixing orders | Low | Medium, when the parts are consolidated | High without validation | Depends on the method in the wave |
| Consolidation point | No | Yes | On the cart | Usually yes |
| Prior planning | Minimal | Defining the zones | Grouping orders | Release criteria and times |
| Suited to | Orders with many lines | Large warehouses or distinct zones | Many orders with few lines | Defined carrier cutoff times |
What every method requires
- Coded locations and stock recorded by location.
- Allocation by the system: the location and lot that fill each line, with FEFO for products with an expiration date.
- Scan validation of the location and the product at each pick.
- Pick faces with a minimum and a maximum and replenishment from reserve stock, so the picker does not find the location empty.
- Shortage records with approval, so that no shortage disappears without a decision.
How Chainlink WMS picks
Chainlink allocates stock by FEFO or FIFO and guides the picker on the handheld, in route order, with location, product, lot and quantity. Each pick is confirmed with a scan. An outbound document can be split by zone so several pickers work at the same time, and each pick list has a lead and can have helpers. See guided picking.