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sequence your picks to flow through the warehouse, in put away the logic would look for the first location in the sequence in which the product would fit.
Zone Logic. By breaking down your storage locations into zones you can direct picking, put away, or replenishment to or from specific areas of your warehouse. Since zone logic only designates an area, you will need to combine this with some other type of logic to determine exact location within the zone.
Fixed Location. Logic uses predetermined fixed locations per item in picking, put away, and replenishment. Fixed locations are most often used as the primary picking location in piece pick and case-pick operations, however, they can also be used for secondary storage.
Random Location. Since computers cannot be truly random (nor would you want them to be) the term random location is a little misleading. Random locations generally refer to areas where products are not stored in designated fixed locations. Like zone logic, you will need some additional logic to determine exact locations.
First-in-first-out (FIFO). Directs picking from the oldest inventory first. Last-in-first-out (LIFO). Opposite of FIFO. I didn't think there were any real applications for this logic until a visitor to my site sent an email describing their operation that distributes perishable goods domestically and overseas. They use LIFO for their overseas customers (because of longer in-transit times) and FIFO for their domestic customers.
Pick-to-clear. Logic directs picking to the locations with the smallest quantities on hand. This logic is great for space utilization.
Reserved Locations. This is used when you want to predetermine specific locations to put away to or pick from. An application for reserved locations would be cross-docking, where you may specify certain quantities of an inbound shipment be moved to specific outbound staging locations or directly to an awaiting outbound trailer.
Maximize Cube. Cube logic is found in most WMS systems however it is seldom used. Cube logic basically uses unit dimensions to calculate cube (cubic inches per unit) and then compares this to the cube capacity of the location to determine how much will fit. Now if the units are capable of being stacked into the location in a manner that fills every cubic inch of space in the location, cube logic will work. Since this rarely happens in the real world, cube logic tends to be impractical.
Consolidate. Looks to see if there is already a location with the same product stored in it with available capacity. May also create additional moves to consolidate like product stored in multiple locations.
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Lot Sequence. Used for picking or replenishment, this will use the lot number or lot date to determine locations to pick from or replenish from.
It’s very common to combine multiple logic methods to determine the best location. For example you may chose to use pick-to-clear logic within first-in-first-out logic when there are multiple locations with the same receipt date. You also may change the logic based upon current workload. During busy periods you may chose logic that optimizes productivity while during slower periods you switch to logic that optimizes space utilization.
Other Functionality/Considerations
Wave Picking/Batch Picking/Zone Picking. Support for various picking methods varies from one system to another. In high-volume fulfillment operations, picking logic can be a critical factor in WMS selection. See my article on Order Picking for more info on these methods.
Task Interleaving. Task interleaving describes functionality that mixes dissimilar tasks such as picking and put away to obtain maximum productivity. Used primarily in
full-pallet-load operations, task interleaving will direct a lift truck operator to put away a pallet on his/her way to the next pick. In large warehouses this can greatly reduce travel time, not only increasing productivity, but also reducing wear on the lift trucks and saving on energy costs by reducing lift truck fuel consumption. Task interleaving is also used with cycle counting programs to coordinate a cycle count with a picking or put away task.
Integration with Automated Material Handling Equipment. If you are planning on using automated material handling equipment such as carousels, ASRS units, AGNS, pick-to-light systems, or separation systems, you’ll want to consider this during the software selection process. Since these types of automation are very expensive and are usually a core component of your warehouse, you may find that the equipment will drive the selection of the WMS. As with automated data collection, you should be working closely with the equipment manufacturers during the software selection process.
Advanced Shipment Notifications (ASN). If your vendors are capable of sending advanced shipment notifications (preferably electronically) and attaching compliance labels to the shipments you will want to make sure that the WMS can use this to automate your receiving process. In addition, if you have requirements to provide ASNs for customers, you will also want to verify this functionality.
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Yard Management. Yard management describes the function of managing the contents (inventory) of trailers parked outside the warehouse, or the empty trailers themselves. Yard management is generally associated with cross docking operations and may include the management of both inbound and outbound trailers.
Labor Tracking/Capacity Planning. Some WMS systems provide functionality related to labor reporting and capacity planning. Anyone that has worked in manufacturing should be familiar with this type of logic. Basically, you set up standard labor hours and machine (usually lift trucks) hours per task and set the available labor and machine hours per shift. The WMS system will use this info to determine capacity and load. Manufacturing has been using capacity planning for decades with mixed results. The need to factor in efficiency and utilization to determine rated capacity is an example of the shortcomings of this process. Not that I’m necessarily against capacity planning in warehousing, I just think most operations don’t really need it and can avoid the disappointment of trying to make it work. I am, however, a big advocate of labor tracking for individual productivity measurement. Most WMS maintain enough data to create productivity reporting. Since productivity is measured differently from one operation to another you can assume you will have to do some minor modifications here (usually in the form of custom reporting).
Integration with existing accounting/ERP systems. Unless the WMS vendor has already created a specific interface with your accounting/ERP system (such as those provided by an approved business partner) you can expect to spend some significant programming dollars here. While we are all hoping that integration issues will be magically resolved someday by a standardized interface, we isn’t there yet. Ideally you’ll want an integrator that has already integrated the WMS you chose with the business software you are using. Since this is not always possible you at least want an integrator that is very familiar with one of the systems.
WMS + everything else = ? As I mentioned at the beginning of this article, a lot of other modules are being added to WMS packages. These would include full financials, light manufacturing, transportation management, purchasing, and sales order management. I don’t see this as a unilateral move of WMS from an add-on module to a core system, but rather an optional approach that has applications in specific industries such as 3PLs. Using ERP systems as a point of reference, it is unlikely that this add-on functionality will match the functionality of best-of-breed applications available separately. If warehousing/distribution is your core business function and you don’t want to have to deal with the integration issues of incorporating separate financials, order processing, etc. you may find these WMS based business systems are a good fit.
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Implementation Tips
Outside of the standard “don’t underestimate”, “thoroughly test”, “train, train, train” implementation tips that apply to any business software installation ,it’s important to emphasize that WMS are very data dependent and restrictive by design. That is, you need to have all of the various data elements in place for the system to function properly. And, when they are in place, you must operate within the set parameters.
When implementing a WMS, you are adding an additional layer of technology onto your system. And with each layer of technology there is additional overhead and additional sources of potential problems. Now don’t take this as a condemnation of Warehouse Management Systems. Coming from a warehousing background I definitely appreciate the functionality WMS have to offer, and, in many warehouses, this functionality is essential to their ability to serve their customers and remain competitive. It’s just important to note that every solution has its downsides and having a good understanding of the potential implications will allow managers to make better decisions related to the levels of technology that best suits their unique environment.
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