Better layout = higher throughput
To squeeze more throughput out of your warehouse, consider these factors when designing or reconfiguring a facility.
By Maida Napolitano -- Logistics Management, 5/1/2003
Want to speed product flows through your warehouse? If you're looking for one place to focus your efforts, then zero in on maximizing throughput by improving your facility layout.
Although many companies today choose to make those gains through implementing technologies like a warehouse management system (WMS) or radio frequency (RF) equipment, changing a facility's layout can offer just as many opportunities to speed up operations. A better warehouse design, in fact, can create a beneficial "domino effect" of reduced cycle times, lower labor costs, less damaged merchandise, lower inventory levels, and more satisfied customers.
What follows are some recommendations on how to use the layout and design of receiving and shipping docks, storage areas, and order-processing areas to speed products through warehouses and distribution centers. As you think about these suggestions, keep an open mind—a facility's initial plans or existing layout should not necessarily be set in stone. There are many quick fixes as well as long-term recommendations that you can apply to both existing warehouses and new facilities.
Rev Up Shipping and Receiving
Fast-flow environments such as cross docking and Just-in-Time operations make it imperative that docks be designed for speed. Failure to plan for all of a facility's shipping and receiving needs can severely compromise throughput.
To maximize throughput in the dock area, deepen the dock itself. At first glance, this seems to contradict the standard rule of minimizing travel distances from docks to storage. But in a fast-flow environment, most activity will be concentrated in the dock area and won't enter reserved storage. This is especially evident in cross-docking operations, where product enters the receiving dock, is sorted and/or consolidated with other parts of an order, then is transported directly to shipping. For these types of operations, docks that are 60 to 70 feet deep are rapidly becoming the norm. In existing facilities, however, storage racks may have to be removed to make room for this kind of dock operation.
Next, bring shipping and receiving closer together. Locating the shipping and receiving doors adjacent or close to each other promotes faster cross-docking and provides more flexibility in dock usage. In addition, less overall space may be required. Take your cue from "pure" cross-dock facilities, which have dock doors on both sides of very narrow rectangular buildings to facilitate the movement of unit loads from receiving into shipping.
Free up dock doors to expedite product moving in and out of the facility. If you are still dedicating a door to a compactor, consider moving it elsewhere to leave the door free for receiving or shipping. If designing a new facility, use a simple simulation program to test whether or not you have provided for an adequate number of doors. When you build, install knock-out panels and pits for more doors and dock levelers to accommodate future expansion.
Take a good look at the dimensions of your own and your suppliers' tractor-trailers to make sure doors are wide enough to handle them. The newer 102-inch-wide trailers often have low-profile truck tires that position the trailer floor 36 or even 30 inches off the ground. Doors that are 108 inches wide will allow sufficient room for a 102-inch trailer to back up to the dock with some margin for error. In addition, doors should be at least 10 feet high to allow full access to a trailer's interior. An inadequately-sized dock door could force you to de-palletize and hand-stack shipments if fully loaded pallet jacks and lift trucks can't fit through them.
Consider installing conveyors to load/unload and sort products. If you have a substantial volume of floor-loaded receipts that must be sorted and palletized, a sortation system on the receiving dock can make a difference. Unloading floor-loaded trailers can be a nightmare for throughput, but with these systems, trailers can be unloaded so much faster that you may need fewer dock doors.
Make Storage More Efficient
Laying out the storage area for increased throughput frequently means giving up storage space. Thus, before you can design for faster product flow, you'll need to reduce items in storage to free up space. Start by examining inventory profiles and removing obsolete stock. Consider transferring slow movers to satellite facilities where they can be cross docked into your warehouse only when needed. Use off-site storage at peak times to avoid placing additional stock in areas where they could obstruct movement. To facilitate cross docking, identify the highest-volume items with the most predictable demand. These are the easiest to cross dock without entering storage.
Once you've identified the fast-moving items, then it's appropriate to examine layout considerations for your storage space. To start, lay out racks perpendicular to thedocks. (See Figure 1.) Parallel runs would lengthen the path of storage and retrieval. With perpendicular runs, lift trucks can move directly from the docks into the storage aisles to store or retrieve pallets.
In laying out storage areas, make sure to add cross aisles and avoid dead-end aisles. In adding aisles, any loss in storage locations should bring about a gain in throughput. This becomes especially significant when you pick from the storage area. Pick paths decrease when there is quicker access between aisles. In addition, it is faster to maneuver around a corner of an aisle than it is to make a U-turn at a dead end.
Use push-back and gravity-flow racks to move products more quickly. For vertical storage that's two to five pallets deep, push-back racks improve throughput by automatically indexing pallets to the front facing without relying on a reach mechanism. Costs can range from $90 to $175 per pallet position, depending on how deep you want to go. They are not recommended, however, for First-In/First-Out (FIFO) applications. Gravity-flow pallet racks can be used for the same purpose, especially when storage areas double as pick locations, but they will require front and rear access aisles. Costs range from about $100 to $350 per pallet position depending on lane depth, but they can go deeper than push-back racks. Depths for both types of equipment are limited by the available headroom for the slope required to make these dynamic storage locations work efficiently.
Keep in mind that product slotting is both an operations and a layout issue. A very basic but smart strategy is to slot fast-moving products in the lowest, most accessible locations closest to the dock, and position slow- moving items up high and in the back. As a precaution, verify that these rules have been programmed into your warehouse management system, and periodically update storage locations based on changes in product movement patterns.
The order-processing area is where product, equipment, labor, and operating systems come together to accomplish the facility's primary mission. It's critical, therefore, that the picking layout be designed for speed and efficiency.
First, consider widening aisles in high-traffic areas. Wherever the most popular items are located, that's where you'll generate the most traffic and are most likely to experience congestion. Widening high-traffic aisles can solve that problem by allowing the passage of multiple vehicles. The downside is that widening aisles will, of course, reduce storage space.
Another option is to place or relocate inventory to better support picking and replenishment. To maximize throughput, keep replenishment items close to the pick facing. You can also place pallet racks behind the case-flow racks so pick locations can be replenished without having to wait for a lift truck to deliver a load. (See Figure 2.)
An approach worth considering is to adopt different pick methods for different types of orders. One catalogue company, for example, recognized that it had a large number of single-line orders for certain products. To speed handling and shipping, the company created separate pick-and-pack workstations for those orders, complete with gravity-flow racks, scissor lifts, and easy access to take-away conveyors, instead of forcing them through their regular picking process.
Depending on the types of products you handle, you might consider using different pick modules and picking equipment. Picking fast movers from pallet-flow racks to conveyors, as shown in Figure 3, can result in full-case pick rates of up to 400 cases per person per hour. Slow movers can be picked with trucks from another area and merged with orders later. For piece picking, install multiple carousels for one picker to eliminate waiting time for indexing an item to that picker. When picking from floor locations in the storage area with a pallet jack, have workers pick from gravity-flow racks to minimize waits for replenishment. To further boost productivity, pick two pallets at a time with a double pallet jack.
If your picking operation is manual, think about automating the pick process. When manual operations can't meet throughput requirements and labor costs are high, automation may be more economical. Calculate the total operating costs to justify the purchase and installation of automated order-picking devices such as mini-loads and A-frames. (For more on automating picking and other warehouse operations, see "Should you build an island of automation?" in the April 2003 issue of Logistics Management. )
Finally, keep ergonomics in mind. Keep totes and packing material within easy reach, and fit the task to the picker instead of making the picker adapt to an inadequately designed pick area. Keep fast movers in slots where the picker won't have to reach or bend. Attaching the pick conveyor to the case-flow rack also eliminates the need for the picker to twist to place pieces into pick totes.
A Last Word
If you undertake a comprehensive review of the design of an existing or a planned facility, you're likely to uncover more gaps and opportunities for improvement than we could cover here. These can often be fixed with a combination of experience, creativity, and common sense.
Keep in mind that any layout that's designed for maximum throughput may result in the loss of storage space. But with better inventory controls and the adoption of efficient logistics practices, the resulting gains in productivity will be sure to add value to your warehouse.
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