Picking Strategies Ecommerce Warehouses

A Comparison of Picking Strategies
Order Base Picking | Cluster Picking | Batch Picking

Deciding proper picking strategy is an essential process of e-commerce warehousing that most of the operational costs occur in this process. More efficient picking process will end up dramatic cost savings. That’s why an advanced warehouse management system (WMS) creates a higher return on investment through the efficient management of picking processes. A warehouse management system should have the flexibility to apply different picking strategies based on the requirements of the warehouse, product type or order structure.

A sample study to define the best picking method in an e-commerce warehouse


Order picking is one of the main activities within the warehouse. 60% of the operational costs in a distribution center is picking cost, when compared to shipping, storage and receiving stages. Picking process has a direct impact on customer service level. This makes order picking one of the vital logistics processes.

Below picture shows the complexity of an average e-commerce warehouse. The complexity is not only finding the right product but also picking productively. In this article, 3 different picking scenarios and their effects on productivity and costs are analyzed.

 

e-commerce warehouse management software Picking Methods

 

We simulated 3 different scenarios along with some assumptions. As a result, above table shows the total time that is needed to complete picking process for each method. As you can see, cluster picking and batch picking have a tremendous effect on productivity. The definition of the models and methods are discussed in the further sections of the paper.

 

Sample Warehouse Model


The sample warehouse is defined as a retail and e-commerce warehouse. In this sample study, we use mezzanine locations, staging areas and sorting locations (Pigeon holes). The objective is to show the effect of picking strategy on labor productivity.

Warehouse Management Software

Scenario

  • There are 1000 orders to be shipped. Each order has 4 products.
  • There are totally 4000 products to be picked.

Warehouse layout

  • The sample warehouse layout has 240 bins (Locations) and 5 aisles.(How to design a simple warehouse layout?)
  • The picking process starts from the staging area and finishes at the staging area.
  • Trolleys are used to execute picking tasks.
  • There are 2 packing stations.
  • There are unlimited picking trolleys.
  • There is 1 sorting/consolidation station which has 250 bins.

Order Based Picking


Order based picking is the most common order-picking method, products are stored in fixed locations(bins). An order picker picks one order at a time following a trip up and down each aisle until the entire order is picked. The order picker usually uses trolleys, empty pallets or picking carts.

Inventory Management Software - Order Picking

Use Cases

  • Picker gets a trolley from the staging area.
  • Picker uses his mobile device to pick the next order.
  • Picker is directed by WMS to the item’s location to pick the items.
  • Picker picks the item and puts it into the trolley.The user continues until the entire order is picked.
  • Picker leaves the trolley to the staging area.

Standard-Times and Distances

  • Average Picking Time: Average picking time of a product from a bin  is 5 seconds
  • Walking Speed: A picker walks 3.28 feet in 1 second(1 meter/second)
  • Average setup time: The required time to start order picking (setting the trolley) is 20 seconds

Assumptions

  • Each order is picked separately. A picker starts from the staging area and visits all the product locations and returns back to the staging area. Each order has 4 products.
  • Average distance to pick an order is 196.8 feet. The picker walks 60 seconds (3.28 feet / second) for each order.
  • Setup time for an order is 20 seconds (Picker prepares the empty trolley for the next trip and drops the picked trolley)

Results

Total time to pick 1000 orders = (#Orders * Setup time) + (#Orders * Average distance to pick an order) + (#Order Line * Operation time to pick a product)

Total time to pick 1000 orders = (1000 * 20) +(1000*196.8) + (4000 * 5) = 100.000 seconds

Cluster Picking


Cluster picking is the process of picking products into multiple order containers (totes) at one time. In our scenario, the picking carts have 12 totes. The picker starts his trip to pick 12 orders (48 products) into 12 totes.

Use CaseInventory Management System - Cluster Picking

  • Picker gets a trolley from the staging area.
  • Picker uses his mobile device to pick the next cluster.
  • Picker is directed by the WMS to the item’s location to pick the items.
  • Picker picks the item and puts it into trolley’s suggested bin. Picker continues the operation until entire orders are picked.
  • Picker leaves the trolley to the staging area.

Standard-Times and Distances

Average Picking Time: Average picking time of a product from a bin and putting the item into the bin is 6 seconds.

Walking Speed: A picker walks 3.28 feet in 1 second (3.28 feet /second).

Average setup time: The required time to start order picking (getting the trolley, preparing the totes) is 120 seconds

Cluster size: The number of orders that are picked together in a cluster is 12.

Total clusters: The total number of clusters to pick 1000 orders is 83.

Average walking time: The picker walks 190 seconds through all the aisles up and down to pick for 12 orders in a cluster 48 items.

Assumptions

  • 12 orders are picked together on each trip. A picker starts from the staging area and visits all the product locations and returns back to staging area. Each order has 4 products.
  • In order to pick 48 products, the picker visits 22 locations. (Assumed that there are similar products within 12 orders.)
  • Average distance to complete a cluster is 623.2 feet. The picker walks 190 seconds (3.28 feet / second) for each cluster.
  • Setup time for a trip (12 orders) is 120 seconds. (Picker prepares the empty trolley for the next trip and drops the picked trolley)

Results

  • Total time to pick a cluster which includes 12 orders = (Trolley setup time) + Average walking time for 12 orders in a cluster) + (#Order Lines * Operation time to pick a product)
  • Total time to execute a cluster which includes 12 orders = (120) +(190) + (48 * 6) = 598 seconds
  • Total time to pick 1000 orders= #Clusters * Total time to execute a cluster
  • Total time to pick 1000 orders= 550 * 83 = 49.833 seconds

 

Batch Picking


Batch picking is the picking method that combines multiple orders into one picking trip. After the picking process, items are sorted/consolidated by order. Batch picking increases throughput and operational efficiency. Batch picking improves picking efficiency by consolidating pick quantities and minimizing the walking distances.

Use Case

  • Picker gets a trolley from the staging area.Warehouse Management System - Batch Picking
  • Picker uses his mobile device to get next batch to be picked.
  • Picker is directed by WMS to the item’s location to pick the items.
  • Picker picks the item and puts it into the trolley.The user continues the operation until the entire batch is picked.
  • Picker moves the trolley to the sorting station.
  • Picker gets an item from the trolley.
  • Picker is directed by the WMS to the sorter bin.
  • The picker puts the item into the sorter bin and continues till all the items are put into bins.

Standard-Times and Distances

  • Average Picking Time: Average picking time of a product from a bin is 5 seconds.
  • Walking Speed: A picker walks 3.28 feet in 1 second(3.28 feet/second).
  • Average setup time: The required time to start order picking (getting the trolley, preparing the totes) is 120 seconds.
  • Average picking time: The operation time to pick a product from the bin is 5 seconds.
  • Average time sort an item:  The operation time to sort a  product in the put-wall station is 1.5 seconds.
  • Batch size: The number of orders that are picked together in a batch is 250 Orders.
  • Total batches: The total number of batches to pick 1000 orders is 4 batches.
  • Average walking time: Picker walks through all the aisles up and down for 250 orders in a cluster

Assumptions

  • 250 orders are picked together in each trip. A picker starts from the staging area and visits all the product locations and moves the trolley to the sorting station.
  • In order to complete picking of a batch, the picker visits 45 locations. (Assuming that there are similar products within 250 orders.)
  • Average distance to complete a batch is 190 meters. The picker walks 190 seconds (3.28 feet/ second) for each batch.
  • Setup time for a trip is 120 seconds (Picker prepares the empty trolley for the next trip and leaves the picked trolley)

Results

  • Total time to pick a batch which includes 250 orders = (Trolley setup time) + Average walking time for 250 orders in a batch) + (#Order Line * Operation time to pick a product)
  • Total time to execute a cluster which includes 12 orders = (120) +(190) + (1000 * 5) = 5310 seconds
  • Total time to pick 1000 orders= #Batch * Total time to execute a batch
  • Total time to pick 1000 orders=5310 * 4 = 21.240 seconds
  • Total time to sort a batch (250 orders/1000 items)= (Setup time for a batch) + (#Order Line * Operation time to sort a product)
  • Total time to sort a batch (250 orders/1000 items)= 120 + 1000*1.5 = 6030 seconds
  • Total time to sort 4 batches= 4 * 6030 = 24.120 seconds
  • Total time to complete all orders=21.240 + 24.120 = 45.360

 

Conclusion


Picking is the most essential process in warehousing that most of the operational costs occur in this process. More efficient picking process will end up dramatic cost savings. That’s why a warehouse management system creates a higher return on investment through more efficient management of picking processes. A warehouse management system should have the flexibility to apply different picking strategies based on the requirements of the warehouse, product type, order structure etc.

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