Pallet Rack Evaluation: Storage and Retrieval Speed Improvements
How can you store and pick pallets faster?
Your rack system is your business, if you’re operating a warehouse or distribution center—or, it at least holds your business.
Pallet racks aren’t simply rows of storage shelves, and you shouldn’t treat them that way. Something so fundamental to a warehousing operation can and should be evaluated for improvement. One of the chief roles of a rack system is to allow efficient, quick access to stored products. How fast can you store things? How fast can you retrieve them?
Working faster: pallet rack throughput
Everyone understands conveyor throughput—the number of units a conveyor system can process in a given period of time, but racks also have a throughput metric: the number of pallets in stock; the speed at which they are put away, picked and removed. Warehouse management systems may not be configured to provide this measurement, which is impacted greatly by inventory turns and downstream processes.
- Are people waiting for pallets to be picked and moved to the next step in the process?
- Can putaway processes lag because you can’t get pallets received and stored in rack positions efficiently?
- When does your storage and retrieval process reduce the efficiency of your storage strategy?
Focus on what happens around the pallet rack—the people and systems stocking and picking from it. Who does this, and how, and using what materials? While this seems more like an issue with personnel and training, the rack itself plays a major role. Is it designed, specified, and laid out for optimum throughput?
Above: a drive-in rack system reduces transit time between storage positions, but also requires drivers to enter the rack structure to store or retrieve pallets. It’s important to consider the balance between storage density and accessibility when designing storage systems.
Rack types and throughput
Selective racks
Selective racks allow fast access to every pallet at all times. This tends to allow for relatively fast storage and retrieval, but has its drawbacks. Because the selective rack is by nature more spread out, transit times between storage positions can slow operation; forklift drivers spend time driving rather than picking pallets. For each or partial picks from pallets, the process is less efficient. Pickers must walk to storage positions, pick their product and transport it. They may even have to use a rolling ladder or mobile picker to access the target, which will slow the process considerably. Find ways to reduce or eliminate elevated each picks if possible.
Drive-in racks
Unlike selective systems, drive-in racks have relatively little travel time, although in a large warehouse with many picking positions, that can still be substantial. Drivers still must navigate between uprights to either pick or store a pallet, which takes deliberation. While transit time between positions is lower compared to selective systems, picking pallets is usually much slower due to the need to drive into deep rack bays. Because you must store one SKU per bay in drive-in, you may face a slowdown as you must pick levels of the rack from top to bottom and front to back. Drive-in racks are a strong storage system, but not a particularly fast-access system.
Pushback rack
Pushback offers a strong combination of selectivity and on-point access. Like selective rack, drivers can access a pallet at the front of the rack bay; like drive-in, it compounds the space by storing multiple pallets deep in the same position. This should reduce the space needed overall, meaning less transit time for drivers.
Pallet flow systems
Flow systems combine easy access for picking or replenishment because there is only one place to either store or remove a given pallet. Pallets enter the system on the infeed side and flow to the discharge side for picking. Drivers can get to each pallet relatively easy with relatively little driving due to high storage density. Because pallet flow is restricted to one SKU per lane, you will sacrifice some storage flexibility.
Read more: Selectivity vs. Storage Density: Choosing the Right Pallet Rack for Your Application
How are your people interacting with the racks?
The most important thing to understand is the way your people use the rack system—loading, unloading, picking and moving through the system should be known and standard processes. Comprehensive understanding of and adherence to these operational factors helps you ensure safer and more efficient operations. These standards can help you alleviate big problems later, so it’s important to know the factors, create processes and work to maintain those processes.
Process steps to know
- Loading & putaway: How are pallets being loaded into the rack? Are forklift drivers working safely and by your standards? If you’re using AGVs or other automated systems, what are the protocols? Is there a consistent replenishment strategy? For first-in, first-out systems, how are product slotting and inventory rotation being maintained in the loading process? Consider safety enhancements such as tilt indicators, tine guidance lasers and cameras to help reduce loading and product damage problems.
- Retrieval: If you’re dealing with bulk or reserve storage, how are your drivers accessing the pallets? What safety processes are in place while they operate in a forklift aisle? Are your aisles wide enough for an average-skill driver to use safely and in ways that reduce the chances for rack impacts?
- Manual picking: People routinely each-pick from rack systems. Are those processes reducing the speed of forklift operations, and vice-versa?
Search for process gaps that cause “waiting time.” Where do these gaps slow your storage strategy, and how can you improve them? Are drivers getting bogged down by your receiving process, always waiting on pallets or waiting on available storage slots? Is there congestion in some aisles, while others are less busy?
Drivers have the most important interactions with pallet rack systems
Driver mistakes can be costly, so it’s important to continuously train drivers on safety and utilization processes. Even your veteran drivers can improve their processes to work safer and more productively if you provide them a good framework for improvement. Poorly designed operational environments can contribute to driver mistakes and unsafe conduct, so it’s important to create the best possible work environment and continue to maintain it.
Read more: How to Safely and Effectively Load & Unload Tall Pallet Racks
“Walking around”: One of the best ways to gain understanding of the process is to observe it frequently and document what’s happening. You can also talk to your forklift drivers, order pickers and plant management about the process. Often, they will find issues you may otherwise miss.
Focus on areas where people and forklifts routinely work in the same space
Above: a worker pulls a pallet jack through a typical 12-foot forklift aisle, which means any forklift that needs that aisle must wait. For higher velocity areas, this can significantly impact storage or retrieval speed.
Aside from being a safety risk, these areas almost always slow down your ability to access that part of the rack system. If you’re hand-picking cartons from the base level of the rack, it’s not only an ergonomics issue, it slows forklift access. When workers are constantly present in an area, forklifts must operate with more caution. They must wait until the person on foot leaves or moves aside. A worker pulling a pallet jack down an aisle is by nature slower than a forklift.
Can you design specific each-pick areas and remove the rest from your system? Everyone will function faster and safer that way.
If you have 200 pallets on the floor, and are routinely accessing some of those pallets, could you consolidate them into more efficient areas where people always work, and forklifts never do? This could improve the speed of both processes.
You will always need some mixed-use areas, but they certainly shouldn’t take up the entire warehouse and should exist by design.
Read more:Â How to Add Carton Flow to Pallet Racks
How much activity is there around your rack system or specific areas of it?
How many pallets enter the system in a given period of time, and how many leave it? If you’re picking too many pallets too quickly in a selective rack system, you may have a case for higher density or dynamic racks that can reduce the time people spend on those activities.
Empty pallets also affect overall productivity, as most every operation has to spend time dealing with them. What is your strategy for removing and storing them?
Metrics you should know
- Hours per week worked, and number of work shifts
- Number of pallets stored in a given period (can be a day, a week, a month, depending on your business)
- Quantity of pallets removed over a that same period
- Each or carton picks made from pallets during that given period
Throughput analytics and space utilization analysis helps you make decisions that can help you improve storage processes, inventory management and space efficiency. These numbers do not necessarily need to be comprehensive, but should be accurate so that you can make informed decisions about your rack system.
To increase storage and retrieval speed, focus on the processes
You’ll improve faster and more sustainably by focusing on metrics, then process, then people.
Consider changing storage procedures so to free congested aisles of some traffic by moving higher-volume pallets to more accessible locations. You can add targeted manual picking areas that remove each picks from the same bays as pallet picks. You can revise receiving processes to organize pallets in ways that help drivers operate faster and with less confusion than before.
Start with observation and document your facts, then move to changing the fundamental storage, process and training steps that can improve throughput across the entire operation.
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Scott Stone is Cisco-Eagle's Vice President of Marketing with 35 years of experience in material handling, warehousing and industrial operations. His work is published in multiple industry journals an websites on a variety of warehousing topics. He writes about automation, warehousing, safety, manufacturing and other areas of concern for industrial operations and those who operate them.