Warehouse Management

How you pick orders determines your overall warehouse efficiency. It's easy to understand why: warehouses typically source goods in bulk (think pallets) but fulfill orders by disaggregating the bulk packs. As a result there are many more pick transactions than putaway transactions in your warehouse. Therefore an efficient picking process has a big impact on your on-time order fulfillment and overall warehouse budget.

In this post, I will put some of my thoughts about the popular pick strategies in a warehouse such as order picking, cluster picking, pick and pass, etc. I will also discuss which ones are more appropriate for your warehouse (or more importantly which pick strategies are not).

A picking strategy consists of the following three policies:

Pick Method: How do you group the tasks for execution?

• Order Pick: All tasks for an order are grouped and assigned to the operator. Order pick implies one or more pass of the pick zone for each individual order. Order pick is ideal for those orders with pick volume that exceeds the equipment capacity. Order pick implies one or more pass of the pick zone for each inividual order.  Therefore order pick involves higher travel time. However since each order is picked individually, the time to sort items for an order and time to consolidate order with other picks is less. Since order pick ensures that an individual order is picked entirely, it ensures that a given order is fulfilled quickest. It is a preferred pick method for emergency orders or other "hot" orders. 

• Wave: No grouping of tasks is done. The most optimum task among a pool of eligible tasks is dispatched to the operator. Wave pick is ideal for picking those items that are shippable units with their shipping label and hence do not need packing into another LPN. This method is ideally suited for case and pallet picks. Wave pick results in the least travel time. However wave picks may require additional work if consolidation with other order lines and palletization is needed.
  

• Bulk: When a small number of items are ordered by a large number of orders, it's possible to improve the picking efficiency by bulking the multiple pick tasks for an item and locator combination into a single task. The pick execution occurs by performing a single pick load for the bulk task and performing the drop operation for each individual order. Consider bulk picking those items that occur in a significant proportion of orders in a wave.

• Carton Pick: This means that a group of lines in an order are cartonized and a suitable container is identified for them to pick. The carton is also assigned an LPN and the LPN label is assigned to the piking operator at the start of picking. Some warehouses actually pick the lines into a final shipping carton and eliminate an intermediate packing step. However don't go looking for Carton Pick in Oracle WMS. You wont find it. Instead look for "Pick by Label" in Oracle WMS task menu.

• Other Grouping Criteria: While the above grouping criteria are common, Warehouses can adopt any other flexible grouping options e.g. Delivery or Delivery and Zone (Sub-Inventory). Oracle WMS allows the use of pick slip grouping rule to perform this type of groping and the use of "Discrete Pick" to actually execute the picks.
  

Cluster Size: Cluster size indicates how many groupings of tasks are being picked simultaneously.

If cluster size is 1 and grouping criteria is "Order", you are essentially performing picking of one order at a time. However if cluster size is 2 and grouping criteria is "Order", picks are being performed for two orders at a time. All tasks for these 2 orders are grouped and executed as a single group by one or more operators (see pick options). In Oracle this is commonly referred to as Cluster Pick. Some warehouses also refer to it as a batch pick. Because cluster pick allows more than one order to be picked simultaneously in a single pass of the warehouse, it often results in significantly less travel time. Therefore cluster pick is often recommended when a warehouse has to fulfill a large number of smaller orders and each order has a pick volume that is significantly below pick equipment capacity.

Pick Options: A given order may be split across zones for picking. The picking process across zones may occur in one of two ways:

• Parallel Pick in Zones (Zone Pick): Parallel pick involves picking the order in parallel in multiple zones. The picks from multiple zones are consolidated in staging area.

• Sequential Pick across Zones (Pick and Pass): Order and Cluster pick can be performed in a pick and pass mode. This involves picking for the same order sequentially across multiple zones.

Here is a comparison of these two options:

How should you go about selecting an optimum pick strategy?

The answer is that there is no one optimum picking strategy. Depending upon items, type of demand, frequency of items in order, storage and equipment used, different stratgies might be better for each situation. More on this topic in my next post.