Zone picking in a warehouse.

In modern distribution warehouses, it’s generally understood that order picking is the costliest workflow taking place.  As order volumes in nearly every industry continue to rise, picking efficiency is at the forefront of efforts to improve overall distribution center performance.  In this article, we’ll take a look at one method that distribution centers can employ to tackle these concerns – Warehouse Zone Picking. 

Warehouse Picking Overview

To better understand zone picking as an organizational tool, let’s first take a look at the full battery of most common warehouse picking process conventions.  We’ll break down three overlapping topics: order sequence, personnel organization, and pick routing.  

Order Sequence
  1. Single Order Picking – the most basic pick scheme, single order picking involves an employee receiving a single order ticket, traveling to pull all of the items on that single order one SKU at a time, and then delivering that order forward.  Multiple orders are picked consecutively.     
  2. Batch Order Picking – for the purpose of cutting travel redundancy, batch order picking involves an employee collecting a number of orders at once, traveling to pull all of the items across these multiple orders one SKU at a time, and then delivering the multiple completed orders forward altogether.  Multiple orders are picked concurrently
  3. Cluster Order Picking – another take on how to cut travel time, cluster order picking is similar to batch order picking, but instead of completing one SKU at a time, it completes multiple SKUs at one time.  Where batch order picking completes a group of orders line by line without consideration for any nearby items further down the list, cluster picking completes a group of orders by picking multiple SKUs located in one area before moving onto the next area.    
Personnel Organization
  1. Open Warehouse Scheme – in short, any picking staff member is required to travel to any location in the warehouse to pull items.  This is not so much describing that the SKUs are organized poorly by their velocity, though that is a topic for later discussion, but instead that employees are individually responsible for completing a full order no matter where in the building each item may reside. 
  2. Zone Picking Scheme – in contrast to an open warehouse scheme, a zone picking scheme limits picking personnel to small areas of the overall warehouse.  These employees are responsible for picking only the items on an order that reside within their zone, and multiple employees are then used to pull from multiple zones to complete an order.  The basic benefit to zone picking over an open warehouse is to limit employee travel.   
Pick Routing
  1. Pick-And-Pass Routing – this routing sees a picker pull items from their zone and place into a container, and then this container is passed to the next zone for the next picker to fill with their items, and so on.  This can be employed in either single order or batch order sequences.   
  2. Wave Routing – this routing method sees zones pick their items simultaneously, and then each zone sends their partial order container forward to a centralized sorting and packing station.  The sort station then separates out order portions from each zone, consolidates into singular orders, and delivers each completed order forward.    

There are multiple ways to combine the above order sequence, personnel organization, and pick routing approaches.  You can certainly have zone-batch or zone-wave picking, and even an advanced hybrid along the lines of zone-cluster-wave (where multiple zones are concurrently pulling multiple groups of SKUs across multiple orders into a series of containers sent up to a sort station to parse out).  Some combinations are clearly more complex than others.  We’ll leave the pros and cons of combination solutions for another article, and continue now to describe the general advantages of zone picking no matter which ultimate strategy is used.   

Employee Empowerment

Thanks to high-profile, high volume, distribution companies, fulfillment centers tend to be viewed negatively when it comes to employee care.  For this exact reason, we start our discussion of zone warehouse picking methods on this note, to show the human-centric positives that can come from properly implemented zone picking systems.   

The lowest-hanging fruit offered by zone picking is the potential to place workers in small portions of the overall warehouse, greatly reducing the distance they would otherwise travel during their shift.  Assigning an employee into a concise work area can reallocate time from traveling to active picking, cutting the stress rushing between picks, resulting in lower fatigue at the end of the day.   

Next, zone picking allows us to lay out our warehouse according to pick velocity, and then reorganize stock positions as needed to eliminate personnel congestion in high-velocity SKU areas.  Less congestion in a small space cuts down on waiting for others to get out of the way, and the sense of frustration that comes from falling behind on picks as a result.   

With a modest look towards the future of warehouse employee conditions, zone picking also offers a very beneficial long-term prospect:  staff specialization.  Your warehouse might include hazardous materials, special-handle products, SKUs requiring certified equipment operators to handle, or advanced pick technologies, all of which pave the way for employee training, specialized knowledge, and skill development over time.  Assigning a picker to a particular zone begins this process – they can own their space, be responsible for its performance, and be engaged for feedback on how to optimize their work.  Further development can push the employee into specialized work as both an incentive to advance, as well as a reward for excellent performance.  Any amount of specialization in this vein can boost morale, increase job engagement, and this reinforces employee wellbeing.   

Customer Service

Building on the employee benefits above, zone picking methodologies also translate into quantifiable customer benefits as well.  Engaged, motivated employees are more likely to be accurate, timely, and self-checking in their work, which can reflect on the distribution center in fewer order returns, fewer order complaints, more repeat business, and even opportunities for expanded sales.   

Zone picking sets the groundwork for optimizing pick travel and order pick time.  One of the results of these benefits is a faster time to order completion, which is of special interest to wholesale distributors serving counter clients.  From order placement to order completion, a counter customer is happier with faster times overall.  When used in combination distribution and service businesses, pulling parts to complete a fabricated assembly completes this work even faster, offering customer satisfaction as well as a clear competitive advantage.   

Carrying zone picking advantages in counter sale distribution centers further, let’s look at the case of an order picker also serving as the counter sales agent interacting with the customer.  Laying out zones where the most common SKUs are positioned closer to the counter, and with common accessories slotted in close proximity, creates a passive reminder for the sales agent to see, consider, and offer the customer additional items that might be of value on their order.  For example, a sales agent may pull a particular plumbing fitting order for a counter customer, and seeing the nearby strategically placed consumables, gaskets, and hardware, can offer those to the customer straight away.  The customer may or may not accept the offer, but at the least, they are left with the impression that the agent is knowledgeable and contentious in their field.

Operational Efficiency

Let’s turn now to hard operational metrics.  First up is raw operational efficiency.   

A non-optimized warehouse is usually laid out with high velocity SKUs up front, and low velocity SKUs farther away.  In this scheme, you’ll often end up with a bottleneck in the high velocity area.  High traffic and small spaces result in physical congestion and slow pick completion.  Further, the low velocity SKUs are a far distance away, taking more travel time overall.   

Applying zone picking to this scheme immediately improves pick efficiency in two ways.  Distributing SKUs out across distinct areas of the warehouse helps with the congestion issues straight away – more pickers can be sent to separate areas to pull items where they won’t be jammed into small spaces together.  Next, assigning pickers to portions of the warehouse reduces their individual travel distances, and allows for concurrent picking to occur across a single order or batch of orders.     

Our second suggestion towards improving raw operational efficiency is the introduction of technological tools designed to work symbiotically with zone picking schemes.   

Zone definition is partially a mathematical challenge, and software solutions are often a key component to designing a highly efficient new warehouse scheme.  Typically, you would engage an experienced material handling consultant to assess your operation, and to employ advanced software tools to help specify ideal zone areas, zone quantity, picker quantity, picker travel routes and distances, etc., for your specific warehouse.  Solving for metrics such as picking productivity, picking utilization, order ship time, and picking accuracy can all benefit from zone picking optimization using a material handling resource and their toolkit.   

Once zones and picking practices are defined, additional technology can be leveraged in an integrated material handling system to further improve efficiency.  Modern distribution centers today are introducing robotic and autonomous tools to this end.  A few examples: 

Robotic pick carts can be coupled with zone picking schemes in that the cart can move pick-and-pass order containers from zone to zone, reducing the time that a human must travel to transport containers.  The robotic cart can meet pickers at drop stations – the picker pulls parts at the same time that the robot is driving into their zone, the two rendezvous at a common drop station, and then the robot continues onto the next zone while the picker proceeds to their next order.   

Wave picking by zones can be benefited by the use of time-saving technology as well.  Sorting robots, mechanical conveyors, and auto-slotting bin racks can be positioned downstream of zone-wave picking schemes to cut final packing time and assure accuracy.  Automated warehouse picking systems can even be installed to remove employees entirely from dealing with high velocity, easy to handle SKUs. 

With all of the above techniques, overall distribution metrics such as total labor cost, net operating cost, order lead time, back order rate, and perfect order rate can all be bolstered.   

All of this begins with implementing a zone-based organizational scheme across your warehouse, and then over time, optimizing this scheme to fit your individual needs.  Zone optimizing is almost always an ongoing process, adjusting as market trends, material availability, workforce, and customer demands naturally evolve.  Whether you choose to tackle this process internally, or to utilize a trusted material handling systems resource externally, the benefits that come from dedicated zone picking solutions are worth investigating further.   


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