14. Incorrect picking methodology
Picking is the highest
labour activity in the warehouse and consequently gets a lot of focus on
optimising it by both the Warehouse system developers and the materials
handling equipment manufacturers. Failing
to select the best picking methodologies for your particular business needs
will see you missing out on what can be relatively easily won productivity
gains.
There are three basic
picking methodologies and a nearly endless variety of variations depending on
the technology, equipment and layout employed in your warehouse. The three basic picking methods are:
1.
Discrete picking
a.
Picking one order in its entirety before moving onto
the next order. This is the standard
picking method employed by all order processing systems.
b.
Most suited to intermediate to large sized
orders comprising multiple pallets or cartons of stock (including large re-pack
orders).
2.
Multi-order picking
a.
Picking several orders at once in one pass
through the warehouse. If you have ever grabbed
pick slips for a dozen single line orders and sorted them into correct travel
sequence then you have performed a multi-order pick.
b.
The key to multi-order picking is to create a
batch of orders that can be picked by one person onto one trolley. Each order is assigned a carton number. The picks are sorted into travel path
sequence regardless of the order number.
Each pick is taken from the shelf and placed into the carton number
associated with each order.
c.
Multi-order picking functionality is normally
only provided by a WMS, but provided you have a modern system with some
flexibility in data access, it is quite possible to create a paper based
multi-order pick. (Contact us for more details)
d.
Suited to small order sizes where the entire
order will fit into one or two boxes.
3.
Batch pick and assembly (also called
consolidated picking)
a.
Performing a single pick for the sum of the quantities
required for each item in a batch of orders.
This allows a single pass through the warehouse to pick an entire wave of
orders. The stock is staged in an
assembly area and needs a subsequent pick process to assemble the individual
orders.
b.
Most suited to picking from slow to access areas
where discrete picking would be very slow.
This can be used as an entire picking strategy but be wary of the fact
that the assembly process is effectively double handling and the selection of
items from a large batch pick can be slow.
c.
The slow assembly process can be facilitated by
locating the items in the assembly area so that they can be found quickly. This functionality is not common, but not
difficult to code if required, and manual workarounds can also be devised to
speed the selection process.
Some common variations and combinations
are:
·
Discrete pick the fast zone batch pick the slow
zone or bulk areas
o
In this method the majority of the order picks
are done for a single order from the fast pick area and a second batch pick for
the order wave collects the stock from the slow zone and stages it in an area
of the fast pick zone. The order picker then collects what he needs from this
staging area to complete the order and thus avoids the travel time through the
slow zone.
·
Multi-order pick the fast zone and batch pick
the slow zone
o
Similar to the above but more suited to small
order picking. As above but the picker
completes multiple orders in one pass through the fast zone.
·
Zone picking (discrete or multi-order or batch)
o
For very large orders or where stock requires
different storage conditions grouped into location zones (such as temperature
control, security, dangerous goods, special racking). The order is broken up into zones and picked
separately in each zone (often by different operators). The picks from each zone are usually then
brought together on the dock for consolidation for shipping purposes.
Further adding to the options available are
various technology and materials handling equipment assisted methods. Here is a quick summary.
·
Goods to the man systems
o
These are a means to eliminate picker travel and
speed up picking. They can be used for
discrete or multi-order picking depending on their level of sophistication.
o
Vertical or horizontal carousels keep the
operator in position and move the shelves to present the goods required for
picking. These systems require their own
control systems that interact with the WMS to manage the picking and put-away
processes.
·
Conveyor based zone picking
o
This methodology is the province of the large
distribution centre. A conveyor moves
totes for orders through each zone of the warehouse so that a picker can be
restricted to picking from a limited range of items into the tote. The tote is directed to each zone where a
pick is required and ends up at a despatch station for freight labelling and
staging.
o
This method also works for carton picks but in
this case the picker picks and labels cartons on to the conveyor which directs
the cartons from each zone to sortation lanes where the cartons are palletised
for each order.
o
Some of the picking may be automated picking
systems such as the A
Frame high speed picker or AS/RS systems picking pallets and delivering
them directly to the dock with AGVs.
·
Wireless terminal assisted picking
o
Warehouse management systems provide the
opportunity to manage the information normally presented on a paper pick slip
with in any way you could possibly imagine.
An RF terminal can drive discrete, multi-order or batch picking and
present the information to the picker via a screen or via voice and even vision
based systems
o
Screen and barcode scanning is the most
common. All products and warehouse
locations are barcoded to build accuracy into the pick process. The RF terminal could be fixed to a trolley
or forklift, or hand held. There are
also wearable units that allow the user constant use of both hands and
eliminate the need to pick up and put down a scanner.
o
Voice directed picking has been implemented
widely and is highly efficient because the picker does not have to stop to read
a screen or scan a barcode. Accuracy is
built into the process with verbal confirmations of check digits and quantities
picked.
·
Pick To Light systems (PTL)
o
Pick to light is a static racking based system
usually built into carton live storage (roller racks) that uses a small
electronic display at each pick face to indicate how many items to pick. The operator presses a button to confirm the
pick. This is suited to high volume
discrete picking (several hundred units per hour) of small items into repack
cartons or totes. PTL is often one of
the zones in a large distribution centre but can also a be stand-alone
installation.
What picking method should you use? This is a very good question and it will
depend on your business profile - what sort of inventory you carry and what
your order size, quantity and frequency are.
Once this is known then it is a matter of costing the various options to
find a suitable return on investment.
The important point to realise is that you may be missing out on
increasing both your productivity, service level and accuracy by not taking
advantage of what the best picking methods have to offer your business.
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