Today's Distribution Centres - Are You Picking the Right Orders?

By Enabliser Derek

Productivity and accuracy in fulfilment are two constant challenges in today’s distribution centres (DC). Knowing if you are picking the right order or, more importantly, picking the order in the right way becomes an important determinant in the overall productivity of your operations.

This paper outlines the approach to defining order types and describes various pick process options available to the warehouse manager using AccellosOne WMS.

If you are fortunate, you will have one basic order type that can be processed by a standard pick methodology. However, most distribution operations will end up picking single line, one each orders for direct to consumer; multi-line, variable quantity orders for replenishments and large orders for the mega on-line retailers. In these situations, it is essential to understand the various order types in your operations in an effort to match the best pick process to the order.

This paper outlines the approach to defining order types and describes various pick process options available to the warehouse manager using AccellosOne WMS. While the processes described are standard functionality in AccellosOne WMS, the focus is limited to medium volume, non-mechanized operations that want to do a better job of improving pick labour productivity with minimal capital investment.

If you are like most companies, you have multiple customers ordering in different quantities and with different service level requirements. To help optimize the use of labour and space in the DC, the first step to efficient planning is to define your order profiles. This is done by reviewing order history and assessing and identifying patterns around order size and product movement.

For example, a sporting goods supplier assessed their orders and determined the distribution in Table 1:

With this knowledge of their order types they were able to build specific pick processes around each order type to improve pick labour productivity while exceeding customer service levels.

If you do have different order types but are picking each order the same way, you are sitting on a gold mine of opportunity to improve labour productivity and throughput. For example, picking a single line, one each order typical in e-commerce fulfilment is significantly different than picking a larger multi-line, multi-item order. There are different handling characteristics, packaging needs, and labelling requirements. With the right systems and processes in place you should be able to take advantage of applying the correct pick process to the correct order type.

Pick Design Considerations

Keep these objectives in mind as you develop your overall picking strategy:

  • Keep pickers picking…not waiting…Keep a queue of orders and/or products available to the picker. This requires an effective replenishment strategy if you are using a forward pick/reserve storage layout.
  • Keep pickers picking…and not doing non-pick tasks…Do not bog pickers down with other tasks such as carton erection and taping, labelling, wrapping, adding dunnage, etc. Pickers are typically your most skilled warehouse resource.
  • Minimize product touches…Ideally, it is best to design your pick process so that there is sufficient accuracy at the time of picking to eliminate the need for subsequent checking and repacking. Each unit of product is touched only by the pickers’ hands before the carton is sealed and transported to an outbound truck.
  • Minimize travel…Pick from both sides of the aisle from properly sized pick modules. Unused space between pick modules and pick lanes can unnecessarily lengthen a pick path. Segregate slow movers from fast moving SKUs to avoid repetitive, unproductive travel past them when not needed. Consider picking very slow moving SKUs from reserve storage rather than forward pick bins. Seek opportunities to batch pick many smaller orders in one trip. Pick all one-line, single-piece orders together since no sorting is necessary to break them down into a discrete order level.

Alternative Pick Methods
There are two basic pick methodologies – Process Based Picking and Layout Based Picking. Process Based Picking focuses on how the order is picked while layout based picking focuses on how the pick area is organized and operational flow.

  • Discrete Picking. Discrete picking, or one operator picking one order at a time, is the most common pick process due to process simplicity and control. Picking one order at a time is typically easier to control and manage. There is only one carton or tote to pick which minimizes the potential of the picked item being placed into the wrong carton. For larger multi-line type orders, this might be a good pick process. But for single line, single item orders, this process results in lower operator productivity. In a discrete pick, the operator is directed to each bin in sequence, and told the product, packsize, and quantity to pick. You pick the required product and scan its barcode label. You are then provided the carton number in which to pack the product. You place the items into this carton and scan the label for that carton. Finally, you enter the quantity of product you picked. You are then directed to the next pick, and the process is repeated until you have picked and packedthe complete order.
  • Wave/Cluster Picking. An extension of discrete picking is cluster or wave picking. With Wave Picking, multiple orders are grouped into small groups or waves. An order picker will pick all orders within the wave in one pass using a consolidated pick list. Usually the picker will use a multi-tiered picking cart maintaining a separate tote or carton on the cart for each order. Wave sizes usually run from 4 to 12 orders per wave depending on the average picks per order in that specific operation. In operations with low picks per order, Wave Picking can greatly reduce travel time by allowing the picker to make additional picks while in the same area. In high volume operations, Wave Picking is often used in conjunction with zone picking and automated material handling equipment. In order to get maximum productivity in wave pick operations, orders must be accumulated in the system until there are enough similar picks to create the waves. This delay in processing may not be acceptable in same day shipping operations.

To help maintain labour productivity and order integrity, wave picking requires more analysis in the type of handling cart used in the pick process. For example, an operator picking a wave with 4 orders would require a pick cart or pallet setup to stage 4 cartons or totes that are easily accessible to the operator. This planning is simple if you are working with 4 small cartons, however if the boxes are larger or you have more orders in the wave, the planning and cart design becomes more complex. Additionally, pick cart design will have an impact on space requirements or availability. When picking one discrete order to a carton, aisle width is not a major consideration. However, when wave picking multiple orders, pick carts will require more manoeuvring space and typically largest pick path aisles.

The wave pick process is the same as the discrete pick. The operator is directed to each bin in sequence, and told the product, packsize and quantity to pick. You pick the required product, and scan its barcode label. You are then told the carton number into which to pack the product. You place the items into this carton, and scan the label for that carton. Finally, you enter the quantity of product you picked. You are then directed to the next pick which could be another pick for the same item to a different order in your wave, and the process is repeated, until you have picked and packed all orders in your wave. The primary benefit of wave picking is reduced travel time associated per order. For example picking four orders on one pick tour (in a wave) would reduce the average travel time associated to each order by up to 75%. Factoring in the ability to pick the same item for multiple orders while at the location will reduce associated average travel time per order even more.

  • Batch Picking. Batch picking allows the picker to collect all the products required in a wave (a group of orders) before packing them into cartons. For each pick, you are guided to the pick bin, and told the product and quantity to pick, but not the cartons into which to pack the items. Instead, you place the products in aggregate onto a pallet, cart, or into totes and bring them to a sorting area where you then segregate them into cartons for the appropriate orders.

This method of picking is particularly well suited to a warehouse layout that is not conducive to bringing cartons through aisles of pick bins. It is also an efficient way to pick a large number of orders (each with a few lines), as it lets you split the picking and packing functions between two people. When planning a Batch Pick process, consideration must be given to pack station space and configuration.

At the pack station, the pack operators will be breaking down the batch of inventory into discrete orders (this is often referred to as a secondary pick) so there should be adequate space and equipment to support the inventory and handling. Similar to Wave Picking, the primary benefit of batch picking is reduced travel time associated per order. However, process benefits should also factor in the increased space and labour required to perform the secondary pick process at the pack stations. Pick labour versus pack labour is the balance to measure when Batch Picking.

Process Based Pick Methods

  • Zone Picking. Zone Picking is the order picking version of the assembly line. In Zone Picking, the picking area is broken up into individual pick zones. Order pickers are assigned a specific zone, and only pick items within that zone. This method divides up aisles of bins so that individual pickers only work in a specified number of aisles. In Zone Picking it’s important to balance the number of picks from zone to zone to maintain a consistent flow.

Zones are usually sized to accommodate enough picks for one or two order pickers. Creating fast pick areas close to the conveyor is essential in achieving high productivity in zone picking. Zone Picking is most effective in large operations with high total numbers of SKUs, high total numbers of orders, and low to moderate picks per order. Separate zones also provide for specialization of picking techniques such as having automated material handling systems in one zone and manual handling in the next.

Depending on the layout and setup, Zone Picking can be done sequentially or simultaneously.

  • Sequential Zone Pick (Pick and Pass). With Sequential Zone Pick, one picker picks all the products in one area of the warehouse (a zone). Orders are moved from one zone to the next as the picking from the previous zone is completed (also known as “pick-and-pass”). To improve throughput, conveyor systems can used to move orders from zone to zone or, in a more manual process, the picker hands off the rest of the wave to the next picker in another area of the warehouse.

  • Simultaneous Zone Pick (Pick and Merge). With Simultaneous Zone Pick, pickers in different areas (zones) of the warehouse work on the same order at the same time. The cartons are then consolidated and/or re-packed downstream when zones have been completed. Simultaneous Zone Picking can prevent the problem of slowdowns in picking because of hold-ups in a particular area or due to a bottle neck in the packing.

The goal of zone picking is to create greater speed in the picking process. Zone picking also allows specialization based on skill level. For example, fork truck operators can be assigned to a zone that exclusively houses large items that must be picked with a lift. Zone picking also has a potential positive effect on employee morale by having pickers take pride and ownership in their area and can result in less operator fatigue and the end of shifts due to reduced travel distances.

  • Replenishment Picking. Replenishment Picking combines the concepts of Batch Picking and the Reserve Storage/Forward Picking best practice. Reserve Storage/Forward Pick is the practice of segregating the warehouse into a storage (Reserve Storage) area and a picking (Forward Pick) area. This approach tends to optimize overall space utilization and pick labour productivity. Space utilization is improved by storing product in bulk (pallets or cases) in dense storage locations. Pick labour productivity is improved by keeping pickers working in smaller forward pick zones that typically hold smaller inventory volumes (days on hand vs. months on hand) with the inventory, eaches, or cases, in more easily accessible and ergonomically friendly locations referred to as “golden” or “strike” zones. When using this approach it is common practice to setup a replenishment strategy to move inventory from the (reserve) storage locations into the forward pick locations. The timing of the replenishment activity is driven by a predetermined reorder point and the amount of inventory to replenish is typically driven by a pre-determined inventory level set at the forward pick location. The same basic storage and picking principles apply when using Replenishment Picking – Forward Pick with minor variation to reorder point and quantity. With Replenishment Picking, a dedicated forward pick zone is setup to allow operators to work in a smaller area and the inventory is replenished from bulk reserve storage locations. However, replenishment quantity and timing is driven by the projected number of orders over a given time frame (typically a day). Once a group of orders for the day is created, the orders are replenished, in batch, to the forward pick area. At the end of the day, the forward pick area is picked clean and ready for the next pick cycle.

Another form of Replenishment Picking is replenishing to a pack station rather than a dedicated forward pick zone. In this process, all inventory for a group of orders is replenished in batch from reserve storage locations and deposited at a pack station. At the pack station, the inventory is picked to specific orders for shipment processing as outlined in the Batch Picking process.

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