In the last Warehouse Performance article we discussed how achieving high performance in picking operations depends on many factors. Adoption of technology per se does not automatically deliver performance gains if the processes used are not operationally appropriate. In this part we look at where and why some of the standard picking methodologies are used.
First let us consider single order picking – the oldest and simplest method of picking. Historically, a paper docket was made out with the customer’s order and given to a warehouseman to go and find the goods, usually based on memory and experience. The goods would then be brought to the customer counter or waiting delivery van. Technology has updated the process somewhat but this is still a very common method of picking. The question is, why?
Well, one factor will be warehouse size as some of the alternative methods (see below) need space to be done properly. But it would also seem to be a picking methodology that suits an operation with lower order volumes and fewer personnel. For that reason you would think any operation doing more than a moderate volume would have dispensed with such a seemingly inefficient handling process. But this is not so. In fact many quite large operations still pick in exactly this way.
The reason is that it’s simple and self-contained. It’s also accurate and less error-prone because pickers handle only one order at a time, and it can offer more flexibility for urgent or unusual orders. It can also be surprisingly efficient, for example where a product range is concentrated in a small area to reduce picking ‘travel time’. And if combined with a subsequent packing process performed by the same operative it can achieve consistent accuracy.
There are downsides of course and these will be more apparent in larger scale operation. For high volume products it means intensive pick face visits, potentially causing congestion as well as frequent replenishments requiring additional handling operations. And where order volumes require high staff numbers there is always a question of whether to deploy them on picking only, or spread across all despatch activity which usually includes, for single order picks, a separate pack operation.
Some issues associated with single order picking are dealt with by the (no less traditional) method known as ‘bulk pick’ or ‘bulk pick and sort’. In this method the stock required to meet many orders (selected by a range of criteria) is picked in bulk, mostly full or part pallet quantities. This stock is then ‘sorted’ in one of two ways: either ‘by order’ where each order is made up in turn from the assembled picked products; or ‘by product’ where each product is distributed in turn to assemble several orders.
So it’s easy to see how space is essential to this method. If there’s a significant order volume you’ll need space for several pallets of product, plus extra room for staff to assemble orders. However it obviously works well for picking orders which have many products in common. This reduces pick face issues by picking product from backup storage. For the same reason it may reduce picker numbers, and by using skilled sortation staff instead, all orders can be checked to ensure despatch accuracy.
As for disadvantages, space aside, this method is in effect ‘double handling’. An extra process is included which is not needed with single order picking. Many would argue this should be unnecessary, and considering some other picking methodologies we will discuss in future, this is true.
From the view of a warehouse management system (WMS) however, both these methodologies are established practices. It would be alarming if any WMS worthy of the name did not offer the facilities, with full real time options, to control these processes in a simple, accurate manner.