The setup requirements of WMS can be extensive. The characteristics of each item and location must be maintained either at the detail level or by grouping similar items and locations into categories. An example of item characteristics at the detail level would include exact dimensions and weight of each item in each unit of measure the item is stocked (cases, pallets, etc) as well as information such as whether it can be mixed with other items in a location, whether it is rackable, maximum stack height, maximum quantity per location, hazard classifications, finished goods or raw material, fast versus slow mover, etc. Although some operations will need to set up each item this way, most operations will benefit by creating groups of similar products.
System decides exactly which location to pick from, replenish from/to, and put away to, and in what sequence these events should occur (WMS is all about “directed” movement). Specific logic is assigned to the various combinations of item/order/quantity/location information that will occur.
Some of the logics used in determining actual locations and sequences are:
- Location Sequence: Define a flow through your warehouse and assign a sequence number to each location. In order picking this is used to 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 the 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 the term random location is a little misleading. Random locations generally refer to areas where products are not stored in designated fixed locations. Some additional logic is required to determine exact locations.
- First-in-first-out (FIFO): Directs picking from the oldest inventory first.
- Last-in-first-out (LIFO): Opposite of FIFO. Companies selling perishable goods use LIFO for their overseas customers (because of longer in-transit times) and FIFO for their domestic customers.
- Quantity or Unit-of-measure: Direct picking from different locations of the same item based upon the quantity or unit-of-measured ordered. For example, pick quantities less than 25 units would pick directly from the primary picking location while quantities greater than 25 would pick from reserve storage locations.
- Fewest Locations: This logic is used primarily for productivity. Pick-from-fewest logic will use quantity information to determine least number of locations needed to pick the entire pick quantity. Put-to-fewest logic will attempt to direct putaway to the fewest number of locations needed to stock the entire quantity. While this logic sounds great from a productivity standpoint, it generally results in very poor space utilization. The pick-from-fewest logic will leave small quantities of an item scattered all over your warehouse, and the put-to-fewest logic will ignore small and partially used locations.
- 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 predetermine specific locations are required to put away to or pick from. An application for reserved locations would be cross docking, where certain quantities of an inbound shipment which are specified be moved to specific outbound staging locations or directly to an awaiting outbound trailer.
- Nearest Location: Also called proximity picking/put away, this logic looks to the closest available location to that of the previous put away or pick. Look at the setup and test this type of logic to verify that it is picking the shortest route and not the actual nearest location. Since the shortest distance between two points is a straight line, this logic may pick a location 30 feet away (thinking it’s closest) that requires the worker to travel 200 feet up and down aisles to get to it while there was another available location 50 feet away in the same aisle (50 is longer than 30).
- 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. Create additional moves to consolidate like product stored in multiple locations.
- 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 one may chose to use pick-to-clear logic within first-in-first-out logic when there are multiple locations with the same receipt date. He may change the logic based upon current workload. During busy periods he may chose logic that optimizes productivity while during slower periods you switch to logic that optimizes space utilization.
