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Efficient Pick Module Design
Design a Pick Module to Make Your Distribution Center More Efficient
By: Richard Gillespie
Your mission: Decrease labor costs, increase throughput rates and use the available floor space in your facility more efficiently. You also have to accommodate an increase in the number of SKUs (stock keeping units) and sales volume, all while giving your customers what they want accurately, efficiently, and as fast as possible. This mission is very possible by using a properly designed pick module in your distribution center. Designing an efficient pick module requires analyzing SKU information, assessing the building’s characteristics, identifying the proper picking technologies and methodologies, and complying with building codes; all while considering future growth demands.
First things first, so what is a pick module? Pick modules are made of shelving, pallet rack, pallet flow and carton flow rack to store inventory for picking and order fulfillment. These rack structures may be multi-level or single level. The available number of storage locations and SKUs stored in pick modules varies greatly from hundreds to thousands. It is common in large distribution centers to have entire pick modules or several multi-level pick modules with levels set up to handle certain types of product.
Equally as important as the design process of your pick module, is the design process of your facility. Before you can start to design an efficient pick module, there are several questions about your business that must be answered. The design process is a time to gather information such as: the level of service required; order accuracy expected; type of units picked (eaches, cases, pallets); order fulfillment methodology; lead time requirements; number of pickers needed; order picker requirements; number of pick modules needed; and productivity factors (travel time, technology aids, labor). The answers to these key questions provides vital information specific to each operation. This information must then be analyzed to provide the best solution for each facility’s picking needs.
Data and Velocity Analysis:
For optimal results in designing a pick module, a slotting analysis must be conducted to produce the most efficient pick place for each SKU. Slotting is the process of determining the most cost effective and ergonomically correct plan for storing inventory. Key considerations in finding an optimal slotting plan include understanding such considerations as the dimensions and weight of the products you are storing, the storage technologies, labor costs, space costs, and how often, and in what quantities, products are being picked/replenished.
A velocity analysis is performed to sort the SKUs based on the total number of items picked and the pick frequency (number of trips to a particular storage location to make a pick). This analysis not only helps with determining the type and number of storage locations, but also helps in determining the amount of replenishment storage needed. With this information, one can now determine the number of pick faces required per storage medium, which in turn sets boundaries on the pick module size. Keep in mind that in most cases, if not all, the ultimate results will require using a combination of picking mediums.
The distribution center building needs to be reviewed now that the number of pick faces (SKU locations) per storage/pick medium has been determined. Planning for a pick module must be done in regards to its location within your facility, compliance with local building and safety codes, and proper utilization of the space for your products. When choosing a location in your warehouse or distribution center for the pick module, consider its proximity to storage for ease of replenishment and the distance to the staging and shipping area to reduce travel times and increase throughput rates.
Building constraints and classifications must be considered prior to final pick module design. These important components guide the final design. The square footage and ceiling height of building are the two limiting factors in determining the total amount of storage. In many cases there is a lot of wasted space between the top of the pick module and the ceiling. Utilizing vertical space is efficient in applications where replenishment can be completed at a different time than picking. Building classification, along with type of fire suppression system and location of personal exit doors, determine the type of items that can be stored and the maximum egress (emergency exit path) that local and/or state codes will allow. The receiving and shipping dock locations help determine the optimal location for pick module(s), replenishment storage for pick module(s) and bulk storage.
Now that all contributing factors have been accounted for and analyzed, the actual pick module can be designed. The five components of designing a pick module that must be addressed are: Rack Structure; Picking Technology; Picking Methodology; Replenishment Strategy; and Transportation within the Facility.
Rack Structure. The two deciding factors for determining what type of storage medium(s) should be used are: unit type (split case, eaches or full cases) and velocity of picks. Determine what type of storage is best for the pick module: floor stack, selective pallet rack, shelving, carton flow, pallet flow.
The multi-level pick module structure can be supported by shelving, pallet rack, or constructed as a free standing mezzanine with independent storage elements. Shelving supported pick modules should only be considered when dealing with a very large number of SKUs of low volume. Pallet rack supported pick modules are the most common due to their diverse ability to accommodate different types of storage mediums (carton flow, pallet flow, static shelving, etc.). Pallet rack supported pick modules along with shelving supported modules are the least likely to require any additional floor footers due to the number of support columns. The final option is a mezzanine constructed pick module. These are the most accommodating for future and/or frequent modifications because the mezzanine structure is independent of the picking/storage mediums. Mezzanine constructed pick modules require less support columns because the picking/storage mediums are not integral to the mezzanine support structure. Because of the fewer support columns, the mezzanine constructed pick modules typically require modifications to the warehouse floor (footers) in order to support the weight of the structure and product.
Picking Technology. The use of picking technologies promotes order accuracy, resulting in customer satisfaction. Consider what can be incorporated into the pick module either now or in the future. Changing or modifying the picking technology requires few, if any, modifications to the pick module. Picking technologies currently in use are pick to paper, pick to light, pick to voice and RF picking.
Picking Methodology. Choosing the best picking methodology for each application is directly related to the slotting analysis that was performed prior to the start of pick module design. Slotting is the most critical aspect in any picking application. Maximum pick rates cannot be achieved without effective slotting, efficient slotting and continual evaluation of SKU slotting. A review of the picking methodologies needs to be completed in order to effectively slot the pick module(s). Picking methodologies include zone picking, fixed pick zone, flexible zoning and wave picking. It is critical to utilize golden zoning when slotting picking mediums to achieve the most efficient pick module layout.
Replenishment Strategy. A common mistake in designing for a picking operation, whether utilizing a pick module(s) or not, is not having enough storage in the picking medium per SKU to satisfy at least a shift’s worth of picking. In other words, if the picking medium is constantly empty because of its limited storage capacity, then picking efficiency and picking rates will decrease due to having to replenish the picking medium more frequently. Possible replenishment locations include: floor storage behind carton flow, static pallet rack above or behind carton flow, push back above or behind carton flow, and pallet flow behind carton flow.
Transportation within the Facility. The pick conveyor placement and conveyor flow must also be determined in the pick module design. The placement of the pick conveyor is typically in one of two locations – in front of the pick faces or down the center of the pick module. Pick conveyor that is placed in front of the pick faces is typically used for split case picking where there is a high number of SKUs per pick area and the picker is picking items to a tote or empty corrugated box. As the picker moves along the pick faces, the tote or corrugated box is pushed along the conveyor, therefore allowing minimal movement in picking the SKU to the order (tote or corrugated box). Pick conveyor that is placed down the center of the pick module is typically used for full case picking where the picks are high volume per SKU and the SKUs are spread out over a greater area.
The conveyor flow from the pick module is generally accomplished as either serpentine or direct flow. Serpentine flow is a single conveyor that starts on either the lower or top level of a pick module and snakes from level to level. Items picked from all levels will be on a single conveyor line. The serpentine flow method is able to handle low to medium volume of picks at a lower cost than the direct flow method. Direct flow, on the other hand, consists of multiple conveyors per pick module, where each level of the pick module has its own independent conveyor line. The direct flow method is ideal for high volume full case picking.
Ergonomics, Safety and Permitting:
All pick modules will require permits from the local municipality (city, county and/or state) to ensure that the pick modules are designed and installed per the governing building codes. Because each municipality has their own building codes and interprets the codes differently, it is suggested that an application review be conducted with the local building department prior to getting too far along into the layout and design process of the pick module. The three (3) items that garner the most attention from the permitting office are: structural analysis of pick module, egress and fire safety (sprinklers and emergency lighting). Structural and floor loading analysis will typically consist of detailed construction drawings showing connections details for all internal components. These drawings are usually accompanied with detailed engineering calculations. The most difficult aspect of the permitting process is trying to satisfy the fire safety requirement because it is the most scrutinized aspect of permitting. Areas that may need to be included in order to satisfy fire safety are: storage classification, sprinklers, egress and emergency exit lighting. Other requirements include ADA accessibility; this may be addressed as an exception, but do not count on it when designing a pick module. Compliance may require alterations to your pick module’s layout.
There are additional features that can be incorporated into the design of a pick module to improve picker ergonomics and/or morale, such as anti-fatigue matting, step bars to assist in picking from the top level, efficient slotting of picking mediums, convenience outlets for radios, fans to circulate air, automated trash handling system and empty pallet return lanes. Automated trash removal and pallet return lanes provide a method of removing empty corrugated boxes and pallets from the pick levels of the pick module and promote an uncluttered work environment that leads to picker efficiency and improved ergonomics. Task lighting is also helpful to those working in a pick module. Task lighting will typically require an additional electrical permit, which will also need to include emergency exit lighting. Special lighting may be necessary to achieve the highest efficiency from pickers. Task lighting is commonly used to assist workers in daily duties. If decking is used above the pick area, painting the underside white enhances the available light through better reflectivity.
Construction and Future Provisions:
After the design is agreed upon by all stakeholders, permits must be obtained from local municipalities before construction may begin on the pick module. This is most often the longest part of the pick module design process. Implementing a new pick module or redesigning a current pick module can take 3 to 6 months after the design is approved and permits are acquired. Being diligent in the design and construction of a pick module is extremely important for any future modifications or expansions that may take place. Planning for future expansion may seem presumptuous, but by leaving room for expansion your operation will be ahead of the competition. The physical expansion of the pick module can be challenging, so it is imperative when designing the pick module that velocity and slotting analyses are performed, future sales growth is forecasted and accounted for, and the pick module is designed to accommodate future expansion. The most common methods of expanding pick modules are to either add bays or add an additional level. In order to add an additional level, though, the support components need to be sized initially in order to handle the increase in component and product loading.
The benefits of a pick module are clear. Most managers can’t argue with the added value of a pick module that increases throughput rates, while decreasing labor costs. Designing an efficient pick module doesn’t happen overnight. Each part of the design process is extremely important, but take special care in gathering and analyzing the data. This is critical to designing the best pick module for each application.
Richard Gillespie is a Senior Project Engineer for Lakeland, FL-based TriFactor, a leading integrator of material handling systems. Richard holds a B.S. in Mechanical Engineering from the University of South Florida. He can be contacted at firstname.lastname@example.org or 863-577-2252.
Additional Resources: Critical Factors when Choosing an Order Picking System white paper in the TriFactor Learning Center.