Talking about pick lines and their impact on distribution performance, most operators think primarily about picking efficiency. While of utmost importance, pick lines affect every labor activity in the warehouse.
When only thinking about picking efficiency, the goal is to minimize travel time as it represents about half of a selector’s work hours. However, reducing the travel distance to a minimum will penalize the other labor functions in the DC. Here are some of the implications:
The driver of pick slot size is the velocity of the item it holds – this slot opening will dictate the size of pallets in reserve for that item.
- This has direct repercussions on the frequency of fork moves for both putaway and replenishment tasks. Smaller slots translate into more pallets to handle for a given amount of inventory. In the case of slow moving product where the pick slot does not hold a pallet (e.g., case flow racks or handstack positions), replenishment labor will become even more intensive if trying to fit an item which is too fast for that opening.
- In turn, this will affect receiving labor from a fingerprinting point of view where inbound pallets have to be broken down to fit in that slot. Again, smaller slots mean more time spent on the dock (ideally, the goal is to have vendors configure pallets that matches your needs, but this is not always as easy as it sounds – ask purchasing!)
Therefore, focusing solely on reducing the travel distance might provide the best picking productivity but these gains will become insignificant because of the penalties imposed on receiving, putaway and replenishment. Moreover, aisle congestion issues and ergonomics cannot be neglected as they are also related to workers’ efficiency.
Design decisions will be driven by SKU variety, product velocity and order profiles and will ultimately dictate a pick line’s length. Other components involved in the design of a pick line are the type of equipment used, single vs. multiple zones and the merging of orders (when applicable), and batching or grouping of orders, just to name a few.
In the end, pick lines affect distribution performance on many levels. They have to balance the efficient use of space – which is the capital cost component of the equation – and optimal overall productivity – which is the operating cost aspect.