One very popular Warehouse Design option is Shuttle Racks. Shuttle racks can generate a very high level of pallet storage in a relatively small footprint when compared to alternative concepts. The racks visually look like Drive In racks. The shuttle racks are supplied with an extra rail upon which remote-controlled shuttles transfer pallets into / out of the racks.
An Example Remote Controller
The shuttle racks are usually operated using a Reach Truck (subject to the heights of the racks – low level installations could be serviced using a forklift truck). The Reach Truck locates or retrieves pallets from the rack front position (this helps reduce damage). The shuttle operates in either a Putaway or Retrieval mode and is controlled remotely by the truck driver. The shuttles are fitted with a sensor to allow for the positioning of pallets close to the rack end, or another pallet. Generally, one shuttle is usually operated by one driver, but not always.
Shuttle racks can be used as the main storage and picking area if full pallets only are processed through the warehouse. The shuttle racks can also be used to provide bulk storage for pallet picked items and replenishment stock for a picking area. Slow moving palletised items should be stored in a separate area of the warehouse. Case pick operations should also be separate.
Not only do Shuttle racks provide an efficient use of space, they can allow for very efficient operations. A poorly designed system can result in low storage utilisation and inefficient operations. This blog will help you understand at a high level the Solution Design process and some of the factors to be considered.
Section 1 – The product
One of the first things to consider is the product to be stored, and if it is suitable to be stored shuttle racks. Are the pallets of a good quality (slave pallets can be used), and is the load stable with no overhang?
We will also need to know if products are picked in a FIFO (first in First Out) or FEFO (First Expiry First Out) basis, and if batch codes can be mixed.
Section 2 Data Analysis
Any warehouse design whatever the storage concept will require a high level of data analysis. The investment required for a storage system such as shuttle racks is considerable, and this stage should not be overlooked, or the complexity underestimated.
Data Analysis Inbound - Receipt
The first phase of the analysis is to review the receiving data. We need to understand how many loads are received each day, what time the loads are processed and ready to be put away, and how many pallets of each SKU are received.
Data Analysis Outbound - Retrieval
Following on from analysing the receiving data we can then review the retrieval data. We would need to analyse the retrieval data, by time for each SKU. Each time the operator needs to retrieve a new SKU from a new channel the shuttle car will need to be relocated from the previous channel.
Data Analysis Storage Requirement
The data analysis phase is required to determine
the number of lanes required
the depth of lanes – possibly with more than 1 depth considered – factoring in travel times for the shuttles in the racks
the height of the lanes
if certain SKU’s should be stored outside the shuttle rack area
I use a model created in an Excel spreadsheet to quickly perform this analysis.
Alternative Storage Concepts
Shuttle racks should not be considered in isolation. The overall cost of the racks and shuttles are expensive compared to some of the following alternatives.
The other alternatives to be considered will include
Adjustable Pallet Racking (APR) - single deep – is cheaper to install, each pallet is individually accessible, high levels of utilisation. The storage area footprint required will be considerably more than a shuttle rack solution, with increased travel distances. However, APR could provide additional space in the height for an extra 1 or 2 pallets levels.
Note : the inclusion of the shuttle rails requires approximately 250mm of additional space per level.
Double deep racks. This rack is like APR, but 2 pallets deep. This solution provides increased storage capacity over single deep APR with a reduced storage footprint. There will be a reduction in task rates as put away and retrieval of pallets to the 2nd pallet position takes longer. Travel distances may reduce with a smaller operating area. The rack utilisation for double deep will be lower than APR.
Drive in racks can also be provide a dense storage. They are generally used in lower level buildings and provide less accessibility to product.
Automation should also be considered for large scale projects. This will require a far greater level of investment, but the overall system should be more efficient.
Section 3 Warehouse AutoCAD Layout Design
If we have got this far and concluded that Shuttle racks are a viable option, we should now create concept AutoCAD layouts and supporting resource models. At this stage we can consider the
Position of building columns
Picking area if feeding from a bulk shuttle rack area
Task rates and volumes for each scenario considered
At this stage we should also consider future volume growth and SKU range growth. The design should allow for the addition of extra bays of racking if required at a later stage.
Alternative Concept: Pick Tunnel with Shuttle Racks above
Shuttle racks can also be positioned above pick tunnels. In the example below 4 levels of shuttle racks have been positioned above a gravity fed pick area. This provides a highly visual replenishment process and allows for segregation of pickers and replenishment trucks. The space above is also utilised for reserve storage of the picking lines.
Example Warehouse Design
This warehouse has capacity for 14,000 pallets in a footprint of 65,000 sq. ft, or (6,000 sq. m). The equivalent storage area assuming an APR single deep layout would require 115,000 sq. ft plus additional marshalling space.
This operation has central service aisle used for Putaway and Retrieval. The retrieval is for full pallets picked and marshalled ready for despatch on the gravity roller area feeding despatch.
Section 4 Other Considerations
To conclude the process, we must consider:
The functionality of the WMS
Map out the processes and assess if the WMS supports the allocation and retrieval of pallets based on the rules required by the operation.
The shuttles have an operational time of up to 10 hours. Additional time will need to be factored into the operational plan to allow for battery changing. There will also be times that shuttles may need to be retrieved from racks in the event of a flat battery, a blockage, or some other reason.
Training of staff
Staff will need additional training to make best use of the shuttles and Warehouse Management System.
During periods of high inventory levels then some level of housekeeping may be required. This could include clearing low utilised lanes and moving pallets to another area of the warehouse.
Designing a fit for purpose Shuttle Rack operation and layout is not a straightforward process. We are looking to maximise the utilisation of the space available and to provide efficient operations. A large installation of shuttle racks will require a significant investment.
Please do not hesitate to ask for advice. Of course, I would be very happy to provide a quotation to complete the work if required.