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Best Practices for Warehouse Picking System - Selecting The Right Method and Technologies

Posted: October 23, 2008 by Ly Phan

Best Practices for Warehouse Picking System - Selecting The Right Method and Technologies

In our previous chapter on Best Practices for Picking, we revealed the secret to great picking efficiency is imperative to minimize walk time and product handling by your picking staff. Each unnecessary footstep taken by a picker reduces optimal efficiency, as do multiple touches of items. The simplest and easiest way to avoid these situations is to locate a product by warehouse picking system.

 

OK, while this shouldn't be hard to understand, what picking system and which technologies increase the chances of picking efficiently?

 

There are 3 main types of picking systems, piece picking, caseload picking, and pallet picking. Some warehouses will be able to use just one, while others will find their greatest efficiency and performance levels by using two or more in combination. Next, we'll discuss which picking methods work best for each picking system. Finally, we'll look at a wide variety of technology and equipment choices, weighing their pros and cons for each picking system and method.

 

Picking Systems

Piece Picking

In piece picking, you pick individual items and put them into shipping containers (usually cartons or boxes). You often find this method in warehouses housing lots and lots of SKUs. When you have large quantities of items to pick (think in terms of thousands or tens of thousands of SKUs), piece picking is typically what you will use.

 

Your classic mail order house or parts distributor stores their inventory in fixed locations on static shelving or racks. Pickers fill one order at a time. It is a basic system that works well in warehouses that fulfill a smaller number of orders per day. As volume grows, however, the system can begin to fall apart due to excessive picker travel time and aisle congestion.

Tip: Accurate inventory-by-location data is a prerequisite to efficient, successful picking so make sure your staff continually updates your Warehouse Management System (WMS).

 

Case Picking

Case picking works for operations that aren't filling orders with open box picks. A warehouse using case picking usually has fewer product SKUs from which it fills its orders as well as higher picks per SKU. You'll see a lot of pallet jacks or pump trucks in these operations as well as motorized pallet trucks to retrieve cases stored in racks.

 

Pallet Picking

If you're shipping pallets out, then you're using some form of pallet picking. You've also got a lot of choices as far as storage configurations and equipment and the lift trucks/motors your pickers will use to retrieve pallet loads.

 

Picking Methods

There are five common picking methods: basic picking, batch picking, multi-order picking, zone picking, and wave picking.

Basic (Fixed Location) Picking

This is the most common picking method, regardless of whether you are piece case or pallet picking. Inventory remains in a fixed location, with orders filled one at a time. In piece picking, the product rests in bins or sits on static shelving or pallet racks. In case-pick and pallet pick warehouses, the product is stored in pallet racks or sits on the floor. The piece picker, usually pushing a cart up and down aisles, fills one order at a time.

 

As mentioned previously, you should have the fastest moving SKUs positioned as close as possible to the start of the pick routes. The picking document should be synchronized with the pick location of the items listed on it. (Refer to your WMS user manual on how to do this). Case and pallet picking are similar, although done with equipment such as a hand, motorized pallet jack, or a lift truck.

 

Batch Picking

When batch picking, you combine individual order picks into small groups. You use a consolidated pick list and place items for different orders into separate totes or different shelves on a picking cart. You need a lot of SKU accuracy in your WMS to effectively consolidate orders. If your orders usually call for a few picks each, batch picking can help reduce those unnecessary extra footsteps.

 

One of batch picking's chief drawbacks, though, is that you have to wait for orders to pile up so you can aggregate them into one path for the picker. Delivery promises to customers may make this delay unacceptably long. Batch picking generally doesn't work for case picking due to the physical dimensions of cases and it has no application in pallet picking because you're usually picking a single pallet per trip.

TIP: If you're going to do batch picking, you need some Quality Assurance (verification) procedures to prevent order mixing.

 

Zone Picking

If your operation has lots of SKUs, lots of orders per day, but a relatively low pick-to-order ratio, zone picking could work. Think of it as an assembly line, where the entire picking team is contributing to the success of each individual order. Individual team members are responsible for an area or zone and only pick items located within it. Items are usually moved along from zone to zone on a conveyor. Zone picking works well for piece picking but the physical dimensions of cases, again, restrict its use in case picking. Zone picking doesn't really apply in pallet picking operations, other than delivering individual pallets to staging areas close to the shipping docks.

TIP: The lowest common denominator rule applies here. You're only as fast as your slowest picker, with zone picking throughput limited by whoever is slowest or by the capacity of your busiest pick zone.

 

Wave Picking

If your operation has lots of SKUs as well as higher then average pick-to-order ratios, wave picking (a combination of zone and batch picking) might work well for you. Rather than taking a sequential approach to picking, all zones complete their picks simultaneously. After the pickers are finished retrieving the items, they are sorted into individual orders.

 

Picking Equipment and Technology Options: Your Shopping List

Selecting the right equipment for your picking system will help enhance your warehouse operational metrics.

By selecting appropriate equipment and technologies that fit and complement your operational profile, you can improve the operational metrics? accuracy, productivity and cycle time? that we discussed in the previous Best Practices chapter. You'll also accrue other benefits, such as reducing product damage and improving space utilization.

TIP: Technology isn't a panacea but it can help you address employment issues, such as rising labor cost, and the decreasing availability of workers, that could seriously affect your operation in the future.

Here are some of the options you have to increase automation use in your facility:

 

Automatic picking machines

The use of fully automated picking machines is generally restricted to operations combining high volume with high accuracy requirements.

 

Automatic storage and retrieval systems

An expensive, high-volume retrieval system of rows of racking used in both putaway and picking. Storage density can be very high but they are expensive to install and can limit your operational flexibility as market conditions change. Probably better suited to case and pallet picking operations than piece picking.

 

Automated conveyor and sortation systems

Automated conveyor systems and sortation systems are commonly found in high-volume piece pick operations as well as some variations (zone picking, for example) of case pick and pallet pick operations.

 

Bar code scanners

About as proven a technology as you can find in the modern warehouse, bar code scanning increases accuracy and works best when time-to-pick is longer. If your operation requires high-volume piece picking, scanning bar codes can slow productivity. In contrast, it is very useful when picking by the caseload or pallet.

 

Carton flow rack

Similar to static shelving, except that the shelves are angled downwards, enabling gravity feed of totes, bins or totes to the pick face. Flow racks are very useful for helping pickers fill many orders from the same SKU. Depending on the size of the racks, they can be used in both case pick and pallet pick operations.

 

Carousels

Well-suited to piece picking, you've probably noticed horizontal carousels in your local dry cleaners, as you waited for shirts or blouses to appear from around the corner. A series of hanging racks that hold storage bins of various sizes, these systems help warehouses fill high volumes of orders. While you can also find vertically oriented carousels in laboratories and specialty manufacturing operations, they are rarely used in regular order picking operations.

 

Lift trucks

Lift trucks (in all of their versions) are a common sight in case pick operations. Their use in pallet pick operations depends upon how and where pallets are stored. Depending on your storage design, you may have to use standard lift trucks, reach trucks, swing mast or turret trucks.

 

Pallet racking

Pallet racking is a prerequisite for any case pick or pallet pick operation. Which type you choose (from the standard back-to-back single pallet design to drive-thru racking) depends on many issues. How many pallets per SKU and per pick do you expect to have? How dense is your warehouse layout? How many orders will you be filling daily? How much racking can you afford to install?

 

Paper

Not exactly a technology, unless you consider how leading edge it was when first invented in China during the early 2nd century, if you use paper in your facility, remember a few simple rules. Design your forms so they are easy to read. Make sure the printing is legible by keeping a sufficient inventory of printing supplies on-site so that pickers can read what they are supposed to pick. Failing to do this increases the chances of inaccurate picking.

 

Pick-to-light

Often integrated into carousels, pick-to-light systems consist of lights and LED displays for each pick location, using software to light the next pick task and display the quantity to pick. You will usually see very high accuracy rates, as the light displays can be integrated into cartons and totes into which picked items are placed. These systems are good for high pick-per-SKU shipments. Because the lights can be easily moved, they also adapt well to warehouses in which SKU location changes due to merchandise seasonality.

 

Radio frequency (RFID)

Thanks to Wal-Mart, RFID applications in distribution are getting a lot of media coverage. Some interesting case pick applications involve combining voice recognition to direct the picker, followed by RFID sensors that identify cartons as they are placed on a pallet, and then confirm picking accuracy (the correct cases and quantities).

 

Static shelving

Most commonly found in piece pick operations, this is best suited for low-volume small parts operations. If you're just starting out, look around and you can probably find lots of used equipment.

 

Voice and speech recognition

Many industry experts anoint this as the biggest technological innovation since the 1970s. To clarify, voice recognition is capturing the voice to identify the speaker. Speech recognition captures the voice for the purpose of identifying and confirming what the speaker has said. You don't have to search very hard in the supply chain industry trade media to find case studies of companies that have reaped great returns from voice or speech recognition technology using systems from vendors such as VoCollect, Lucasware, CTG, and Voxware. While increasingly popular for inventory and receiving, it has tremendous picking applications, regardless of whether you are picking by the piece, case, or pallet.

 

Voice-directed picking can have a huge impact on increasing productivity and accuracy. One of the main catalysts to the dramatic growth in voice technology adoption in recent years is that WMS vendors have increasingly supported voice integration. Voice has now become a standard feature with most WMS offerings.

TIP: When pickers have to recite long sequences of alphanumeric characters (think serial numbers and UPC codes), speech recognition is less reliable than RFID and barcode scanning.

 

Warehouse Management Systems (WMS)

As mentioned earlier, Warehouse Management Systems are a huge productivity booster for picking. Properly used, they are the glue that helps you organize all of your data so that picking is fast and accurate and efficient.

TIP: It is garbage in/garbage out so keep your WMS filled with real-time and accurate inventory data. Properly program your system so that pick sheets or lists have the items in the same order the picker will find them in the warehouse.

 

Some General Rules for Equipment Selection

There is an inverse relationship between automation and operational flexibility. Little automation maximizes flexibility. If you are fortunate to operate in a low wage area where labor costs are still manageable, you may not even have to justify automation projects. The more you are married to physical equipment, the less nimble you can be in growing your business. To rigid finance people, this might be enough to kill new technology acquisition projects. They might also balk at the fact that ROI calculations used to justify the expense of new equipment must be based on future projections.

 

It is a leap of faith for everyone and, sometimes, finance people have trouble pushing off the ground. Their perspective also changes depending on whether they have the luxury of working for a private company whose payback timelines are usually much longer than the quarterly "earnings-per-share" slavery of publicly traded companies. A listed company simply doesn't have the same patience for large capital projects to pay off.

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