Storage Systems

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- Temasek Polytechnic, School of Business
- Diploma in Logistics & Operation Management
- Year 2's Students
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Drive In Drive Through
Monday, December 31, 2007 @ 12:04 AM
Drive In Rack

A drive in rack gives a tunnel effect where the lift truck drives in through the storage rack. The lift truck operator drives into the rack and places the unit load in the innermost position, filling all positions until the rack is full. Since only the outermost loads are easily accessible for picking, last in, first out inventory rotation results. Primarily, this type of storage mode is used in distribution centre for medium to fast moving items that have nonstackable products and where FIFO, lot control, and expiration date are not required.

For instance, if all that is being stored is one model or one lot number of microwaves and selectivity is not needed, then this may be a candidate for a drive in rack. The grocery industry or manufacturing storage and distribution is a good example where this type rack is utilized, especially in freezer storage for which maximum space utilization is needed. In the industry, push back racks and pallet flow racks are being used as alternative to drive in and drive through racks.

Advantages:
- This storage method limits wasted aisle space and greatly improves the use of the storage space.
- It is ideally suited to operations that maintain a large quantity of a relatively low number of SKUs.

Disadvantages:

- The reduction of lift truck travel speed needed for safe navigation within the confines of the rack construction.
- The honeycombing losses because no more than one SKU should be housed in a lane.
As a result, drive-in rack is best used for slow to medium velocity SKUs with 20 or more pallets on-hand.
- Results in LIFO inventory rotation
- Limits selectivity because loads must be removed vertically on each level before the next layer is accessible.

As was the case with block stacking, loads should be retrieved with a LIFO discipline and with a retrieval discipline to free up each lane as quickly as possible.

For the drive-in-rack, the number of unit loads deep per storage lane is varied to place building columns within the flue space of the back-to-back drive-in rack rows. The drive-in rack storage lanes are best designed between building columns. This feature means that the building columns are not in the drive-in rack storage positions or lanes. In all drive-in rack down-aisle designs, structural members require fire sprinklers and lift truck mast and overhead guard clearances.

Most drive-in racks are designed with the fork-opening side of the pallet board facing the aisle. This arrangement has the maximum number of faces per aisle and provides excellent unit-load stability in the rack position. If possible, in a carton-handling (pick) operation, the rack has the 48-in (stringer) dimension or side of the pallet board facing the aisle.

To make deposits and withdrawals in a drive-in rack storage concept, a lift truck enters the floor-level storage lane from aisle A, deposits or withdraws a unit load, and backs out the storage lane into the same aisle A. because of this operational characteristic, a drive-in rack can handle a medium volume and has a LIFO product rotation.

Drive Through Rack

Drive-Through Racks allow a lift truck to enter the rack from either side to pick up or pull out pallets. Loads are supported by rails attached to upright frames, and lift trucks are driven between uprights to reach pallets. This is done because pallets can slide backwards on a continuous rail. It's open at both ends, allowing first-in, first-out storage.
Drive-Through Racks offer the ability to store a large amount of similar loads in a smaller area. Selectivity is sacrificed, but storage density is enhanced since many pallets are stored and are available through a single pallet position.

With no back bracing, drive-through rack is designed as a stand-alone rack row with a lift truck aisle on both sides. This means that it is not designed with back-to-back rows. This arrangement handles a medium volume, and the product rotation is LIFO or FIFO.

With LIFO product rotation, the lift truck enters the storage lane from aisle A, deposits or retrieves the unit load, and backs out of the storage lane into aisle A.

With FIFO product rotation, the lift truck enters the storage lane into aisle A, deposits the unit load in the unit-load position, and backs out (from the storage lane) into aisle A without a unit load from the storage lane. An alternative procedure in FIFO product rotation is to exit from the storage lane by driving without a unit load through the storage lane from aisle B, retrieves the unit load, and backs out of the storage lane into aisle B.

Drive-through rack has medium storage density and poor unit-load accessibility. The dimension of the pallet load position has the same characteristics as that of drive-in racks.