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Warehouse Wave Picking: What It Is And When You Should Use It

By Ruthie Bowles logiwa-blog-author | Tags: Warehouse Management

Wave picking is the answer to the age-old question: What do I do when I’m ready, but everyone around me is not?

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This is a big problem for warehouses, distribution centers, and production plants. When one step in the process encounters delays, there’s a domino effect that negatively impacts the rest of the operation. In one survey that asked foremen to rank the top 10 causes of unproductive activities, the majority reported that their work was most commonly held up by something or someone not being available on site

To supplement their results, the researchers also conducted onsite observations to find the biggest causes of unproductive activities. While they found the same sources of productivity loss as the survey respondents, the researchers’ rankings were different because they looked at which productivity lags had the highest cost impacts. 

Workers may recognize the issues, but may not be able to prioritize on the issues that are costing the most time and money. 

This has huge implications on a business’ viability. If you aren’t aware that certain actions (or lack of actions) are draining money, then you could quickly find your company operating at a loss. For instance, that same study found that trade interference cost more than 500 lost scheduled hours, but since these aren’t acutely obvious, the organization is blind to the loss. 

Oftentimes, workers on the ground intuitively understand that they’re getting paid a lot to stand around. Even if on-the-ground workers identify this as a waste of money, it isn’t communicated higher up. In fact, in some cases it’s dismissed as a side effect of the job. The problem is that incremental productivity losses add up to huge business risks. 

One way that companies address this issue is by using short interval scheduling (SIS), which in turn informs the warehouse picking methodology known as wave picking. 

What Is Short Interval Scheduling (SIS) and Why Does It Work So Well?

Short interval scheduling (SIS) is a scheduling tool that essentially narrows - or, ideally, eliminates - the gap between what’s actually happening on the ground and the information being delivered to leadership. 

Consider this: While a plan identifies what needs to happen, a schedule determines when it will happen. When schedules are large and complex, it’s difficult to notice a shift in timing for a particular activity until it’s too late. A shorter-term look at the schedule is more manageable. If a project must be completed within a month, then any problems may not be identified until the end of the month, resulting in delays. 

If a smaller piece of the project is supposed to be completed within a day, SIS can help the project manager identify scheduling issues in that same day, helping keep the project on track. When project managers use SIS as a scheduling tool, they can ensure their work plans and their work schedules are aligned. 

So, how does all of this apply to warehouse picking? Well, there are several warehouse order picking methodologies. The wave picking method is one of them, and it’s based on the same principles as short interval scheduling. 

How Does the Warehouse Wave Picking Methodology Work?

Wave picking creates intervals known as “waves” that align with variables like the order departure plan or the transportation plan. It’s an alternative to scheduling several workers per day and simply hoping to process the maximum number of orders. With wave picking, a warehouse can meet objectives like: “Getting X amount of orders out the door,” or “Ensuring transport trucks are used most efficiently.”

Some industry observers consider wave picking a variation of batch picking or zone picking, which makes sense when you consider how these other methodologies work. Batch picking involves a worker moving through the warehouse collecting goods for several orders at once, while zone picking involves workers dedicated to a specific section passing order totes from one zone to the next. With wave picking, orders are grouped and picked in batches, but at specific times of day.

Here’s how it works: 

  1. Worker receives a consolidated pick list. 
  2. Worker uses a multi-tote picking cart to manage the various items in a particular wave. 
  3. Worker picks approximately 4 to 12 orders (per wave)

Wave picking is useful for both low-pick and high-pick operations. For low-pick operations, wave picking reduces the number of trips workers take back and forth. For high-pick operations, warehouse managers couple wave picking with zone picking to run the most efficient workflow possible. 

There are some instances in which wave picking isn’t appropriate. In order for wave picking to be efficient, a wave can’t be initiated until there are enough similar picks or orders. Companies with same-day operations may not have the luxury of waiting for these conditions.

Designing Your Wave for Wave Picking

Wave picking is meant to get your orders picked, packed, and shipped in time to meet delivery promises to customers. There are a lot of variables that go into getting this right, and it would take an awful long time for warehouse managers to set this up manually. 

Fortunately, warehouse management system (WMS) software exists. When an influx of orders comes in and you need to get to work as quickly as possible, your WMS evaluates all sorts of variables including delivery times, transportation schedules, and labor schedules to break up the orders into waves. 

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There are different ways your warehouse management system can organize waves, such as:

  • Delivery Times: Your waves may be grouped based on “promised to customer” time. This method is normally used when the warehouse doesn’t use shipment numbers to sort outbound deliveries. 
  • Delivery Address: If your shipments are going to the same general area, you can group them together and send them out together. This not only optimizes your warehouse operation, it optimizes your transportation process as well. 
  • Shipment Number: If your main organizing criteria is shipment numbers, then you can easily organize your waves based on this factor. 
  • Shipment Number + Shipment Start Loading Time + Shipment End Loading Time: In this case, waves are grouped based on their shipment number in addition to the cut-off time for either start or end loading. You can then schedule backwards based on orders with the same or near-same cut off times. 

Once you have your waves, you can work through them sequentially to achieve the desired objective. 

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Choosing the Right Handling Cart Strategy

Even after you’ve decided to use a wave picking strategy and even after you have an idea of how you’ll organize your waves, there’s still some additional analysis to do. You’ll need to determine what kind of handling equipment you’ll give your workers. 

What do we mean by this?

Well, consider the variation in item size within waves. Your workers may be picking small, easily managed items or large, unwieldy packages. You may need to provide additional equipment like forklifts or couple your wave picking strategy with a zone picking layout so that waves with specific requirements are only assigned to specific workers. 

Additionally, you’ll need to think about things like aisle width to ensure your existing warehouse layout can accommodate the moving materials. 

What Are The Advantages of Wave Picking?

Compared to basic, discrete order picking, wave picking is a much more efficient effort. The overall operation, from picking to shipping, is optimized, thanks to a holistic undertaking. It also gives management a more accurate understanding of how resources are being used, how much time, money, and labor is being wasted, and where and why delays are occurring. 

Of course, wave picking doesn’t just identify areas of waste. It also helps managers identify the most productive functions and focus energy on figuring out what makes those activities more efficient than others, or what materials and training those areas have that the others don’t. As a result, managers can keep worker morale high by recognizing what’s going well and offering specific recommendations for improvement when delivering criticism. 

Finally, warehouses can understand fluctuations in demand due to sales pushes or marketing efforts. Rather than play it by ear, warehouse managers can record and identify patterns and come up with a structured, interval-based way of handling large influxes of orders.

What Are The Disadvantages of Wave Picking?

Because wave picking is a sequential process, workers have to complete one wave before the next can be started. While this is a good thing most of the time (because it keeps the process disciplined, efficient, and timely), it makes it difficult to accommodate exceptions or high-priority picks

There’s also an increased chance of errors since, depending on how you organized your waves, orders have to be sorted at the staging area. 

Another disadvantage of wave picking is the uneven length of time it takes to complete tasks. Workers may be left waiting for others to complete work, defeating the purpose of wave picking if operations become inefficient due to lags. 

Again, it’s about assessing whether wave picking is right for your operation. If it is, keep an eye out for any small issues. If it isn’t suited to your business, don’t force it. Remember that just because it’s a good solution, doesn’t mean it’s a good solution for you. 

Wave Picking for Reducing Warehouse Waste

Motion Waste

Consider the number of people who navigate your warehouse on a daily basis. Now think about the number of trips your workers take to find orders, pick them, and bring them to the staging area. When they take more trips than necessary - or even an inefficient route through the warehouse - it adds up to lost time, which means fewer orders filled that day. 

Wave picking reduces motion waste by finding an optimal route and optimal workflow based on the warehouse’s reality (e.g., availability of equipment, shipping schedules) and business needs (e.g., delivery promises to customers). 

Motion waste is also about a poor warehouse layout, so if you couple wave picking with zone picking, you can further reduce the amount of motion waste. 

Waiting Waste

This is perhaps the most frequently cited type of warehouse waste. A contractor can’t get to work because a site isn’t ready; a worker can’t operate a piece of machinery because it’s still in use elsewhere; equipment isn’t available even though a group of scheduled workers have arrived to operate it. Scheduled workers still need to be paid and there are no subsidies on rent due to unused time. Waiting costs money, but it’s not always tallied up and communicated to the higher-ups. 

Wave picking reduces waiting waste by scheduling work in tight intervals so there is less ambiguity about when workers should be working on something and when it should be completed.

How?

Well, consider some of the common causes of waiting waste:

  • Unscheduled downtime
  • Poor internal communication
  • Production bottlenecks
  • Long set-up times

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When a manager first hears about problems three months into a project (and only because a key milestone was missed) it’s hard to identify which instances of unscheduled downtime or poor internal communication caused the issue. But, when there’s a specific wave or interval meant to produce results, it’s easy to identify - and remedy - the problem.

Wave Picking Makes the Most of People, Process, and Technology

Wave picking removes the ambiguity from process improvement. By grouping work and using short interval scheduling techniques to time the work, issues are readily addressed. 

Of course, wave picking is not a band-aid solution that one can simply slap on their warehouse woes. Rather, warehouse managers must understand whether wave picking fits their unique requirements before applying it. Moreover, wave picking requires a warehouse management system to gather data and quickly configure waves aligned with the warehouse’s objectives, customer guarantees, and transportation schedules. 

Finally, warehouse managers must ensure their warehouse layout is properly designed to accommodate a wave picking operation. In this way, people, process, and technology align to create an efficient, cost-effective warehouse management operation. 

If you’re ready to bring advanced picking techniques into your warehouse, you’ll need an advanced WMS to go with it. Schedule your Logiwa demo today.

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Ruthie Bowles

Written by Ruthie Bowles

Ruthie is a content marketing consultant for Logiwa. Her specialties include small business development and inventory management.