The order processing strategy you choose for your warehouse or distribution center can have a significant impact on your overall productivity. So, what’s the difference between wave-based and waveless processing?
Those familiar with wave-based order processing often wonder how a waveless process can have higher productivity than one that’s wave-based. Read on for side-by-side comparisons that apply each strategy to a single picking operation, either manual or automated.
In a wave-based picking process, a picker receives a list of items to pick from their zone at the beginning of each wave. The picker starts picking from the beginning of the pick zone, then moves to pick along the entirety of the zone, fully completing that batch/wave at the end of the zone. The picker returns back to the beginning of the zone, receives their next picking list, and begins the next wave.
A waveless picking process begins much in the same way as wave-based. The picker receives a list of items to pick and starts at the beginning of their zone. However, as the picker completes each pick, the Warehouse Execution System (WES) checks to see if the next pick on the list is still the best one, then dynamically directs the picker to the location of whatever is truly the best next pick — it could be part of an order that was activated long ago or a fraction of a second ago. This cycle of adapting to always-changing information continues as the picker continues moving along his/her pick loop for as many times as the picker needs to go around the pick loop.
Though they start the same, wave-based and waveless scenarios have very different end points and results. The wave-based picker will travel around their loop to complete the assigned pick list. However, the waveless picker will pick all those items, as well items for newly placed or recently prioritized orders. In the same travelled distance, the waveless picker will pick more items than the wave-based picker.
If a wave-based process requires five waves to complete the day’s orders, the pickers will need to walk their pick loops five times. In a waveless process, that same day’s orders may only have the pickers to go around the loop only four times. If both groups of pickers complete the same amount of work, but the waveless picker does it with fewer steps, waveless is more productive in two ways: time savings and distance avoidance.
The approximate percentage decrease in walked distance per order in a waveless system can be calculated with the following formula:
Note: simulation modeling of both approaches (waveless and wave-based) for a given set of operational conditions is required to validate the above statements and quantify the benefits.
Automated picking comparison
A typical automated storage and retrieval (ASRS) system includes a rack/staging system, multishuttle at each level for horizontal shifts, a lift for vertical moves, and at least one goods-to-person (GTP) workstation. In this configuration, the multishuttle typically has unused throughput capacity, while the lift is always working at full capacity.
To overcome this disparity, the Dematic Multishuttle lift is designed to carry two totes at once. Even when the lift is at 100% utilization (zero work starvation), the productivity of the lift is higher when the lift can extract two loads from one level, versus traveling to two levels for two loads.
When a wave-based process is applied to an ASRS such as Dematic Multishuttle, it’s common for productivity to decline as jobs are completed in a batch. After all, there are more opportunities to pick up two loads per level at the beginning of a batch, when the batch is at its largest. This phenomenon is called a wave tail, as productivity drops in tandem with batch size. If wave tails happen often, inefficiency proliferates.
A waveless process eliminates wave tails. Because the batch of current work dynamically receives new jobs as previously assigned jobs are being completed, the batch size remains at an optimally large size with many opportunities for two-load lifts. In ASRS applications, a waveless process is also a tail-less process.
Beyond productivity… additional benefits of waveless
In addition to higher productivity, waveless order processing offers the following benefits over wave-based processing:
- Elimination of wave transitions
- Elimination of wave tails
- Reduced dwell time of orders at sorter chutes
- Higher throughput capacities (when resources are more productive, their capacity increases)
- Elimination or reduction of wave buffers
- Better ROI
- Higher throughput capacities can result in lower initial investments
- Higher productivity can result in lower ongoing operational costs
- Shorter cycle times (no wait between wave completion and packing)
- Flexibility to prioritize either productivity or cycle time as needed
- Better exception handling (the impact of the exception only affects that order, not the entire batch). Waveless processing does not eliminate exceptions but makes their impact less critical. An exception only impacts the order with the exception rather than the whole batch, as often happens in wave-based systems. It is not unusual to see elimination of “wave cleaning teams” upon conversion from wave-based to waveless processing; not because exceptions are eliminated but because they have a lower impact on the operation.
- Real-time re-allocation of inventory: The real-time nature of waveless processing allows the re-allocation of inventory already in process from low to high priority demand.
Making the switch
For many warehouses and distribution centers, the shift from a wave-based system to a waveless operation can be achieved through software optimization alone — without major equipment changes, if any at all.
To your pickers, there is little to no difference in how they receive their work orders. To you, what now feels like swimming upstream will become more like sailing in the breeze.