PIECE PICKING: WHICH METHOD IS BEST?

OPSdesign White Paper:PIECE PICKING: WHICH METHOD IS BEST?PIECE PICKING:WHICH METHOD IS BEST?By Robert Muller OPSdesign Consulting, a trademark of Operations Design, Inc. 2007This white paper shall lay out a 10 step plan for evaluating the multitude ofalternatives available in designing a piece picking system.www.OPSdesign.com

OPSdesign White Paper:PIECE PICKING: WHICH METHOD IS BEST?Variations of PickingArea of ConcernPiece picking is one of the most labor intensive processes within a distribution center and as such, it is amajor area of concern for operations professionals. As a result, operations professionals are often askedthis question “Which piece picking method is best?”For the purposes of this paper, piece picking is defined as any order selection process that requires theproduct (units) picked to be individually handled and/or placed into an outer carton, tote, or other containerbefore shipping.In comparison to full-case or pallet picking operations, piece picking typically has lower unit volume, lowerrevenue, and higher labor costs. The higher labor costs are accrued due to the need to open vendorcartons, pick SKUs less densely, erect/pack/seal shipping cartons, and apply carton labels while picking lessvolume per item than full case or pallet picks. The movement towards just-in-time supply chains and theproliferation of direct-to-consumer catalog/internet fulfillment operations is driving a change in order profiles.Smaller orders (those with fewer line and piece counts) are being received more often in many industriesand market channels.To design or re-design a picking operation, one needs to develop a cost versus benefit analysis to includethe systems to be considered. In order to fully analyze the nearly innumerable alternatives available, onecan follow a 10 step plan to narrow down to the feasible options as illustrated below:Step 1: Selection of Possible Storage/Picking ModulesMine available historicaloperational data, apply designyear projections, and profileitem inventory, movement, &unique characteristics todetermine the alternative pickmodules available (cubicvelocity by SKU).In an over-pack pickingsystem high density drawers,bin shelving, carton flow rack,vertical lift modules, andcarousels may be among thecandidate infrastructure to beconsidered.Systemic support and overallcapital budget constraintsmay eliminate some of themore mechanizedalternatives.The matrix at right providessome high-level rules ofthumb for pick moduleselection.www.OPSdesign.com

OPSdesign White Paper:PIECE PICKING: WHICH METHOD IS BEST?Step 2: Mode of Order TransportationThere are two common options inselecting the method used totransport the order to and fromeach pick location:1.2.Pick toCartA combination or hybrid of the pickto cart/pick to conveyor option iscommonly used, in which, fast pickitems would be picked to conveyorand slow picks would utilize a cart.Conveyor could be used totransport orders to and from eachcart pick zone. The picker mayload the cart at the beginning thezone and unload to cartons ortotes to conveyor at the end of thezone.Benefits“Draw Backs” Noconveyorcost Highlyflexible Multiplepickers perzone, ifrequired Low pickrate due totypicallylong travelpaths Low number ofitems High volumeitems Large numberof very smallitems (i.e.jewelry) High pickrate due tosmall pickzones Typicallyonly onepicker perzone ConveyorcostBenefits“Draw Backs”PaperPickingCommonlyUsedOperations Smalloperationswith littlesystemicsupportRadioFrequencyPicking All typesofoperationsPick toLight Low # ofitems withhighvolumesVoicePicking Large # ofitemsspreadacross alarge areaPick to cartPick to conveyorA decision is typically made basedon the overall size of the piecepicking area (travel requirement).SKU velocity, pick density, andrelated considerations often definethe appropriate method.Commonly UsedOperations Large numberof items withlow movementper item Full case andpiece picksoperations withlittle systemsupport to splitout the ordersPick toConveyorStep 3: Selection of Picking TechnologyOperations with a large number ofpicks in a small area benefit themost from pick to light technology,while operations with picks spreadacross a large pick area (manypick facings) are better suited foreither RF or voice picking.The benefits of voice versus RF isthat voice is “hands free”, thepicker never has to put down (orholster) an RF device (scan gun)to either pick or open cartons. In avoice system, picking time can bereduced by the picker listening tothe voice directive while travelingto the next location instead ofstopping to read the RF device.The RF device, however, has theability to capture detailed iteminformation, typically a productionbatch or serial number, quickly byscanning item barcode labels.Voice may be more cumbersomein these applications.www.OPSdesign.com Low technologycost Low risk High accuracy Paperless Ability to captureitem specificinformation (i.e.serial numbers) High accuracy High pick rate “Hands Free” Medium pick rate Medium to Highaccuracy “Hands Free” Low pickrate Low pickaccuracy Long ordercycle time Low pickrate (oftenthe sameas paperpicking) Highhardwarecosts Medium tohigh capitalcosts forsystems &headsets

OPSdesign White Paper:PIECE PICKING: WHICH METHOD IS BEST?Step 4: Order BatchingOrder batch picking is the process of grouping orders together to create a larger pick order, which reducesthe overall pick lines in an operation versus a discrete order pick (picking of one order at a time). Sincemultiple orders are being picked into one container, in most cases this will result in the requirement for anorder sortation station, an area designed to split the pick order into the individual customer orders (discreteorders). If the order batch contains all single unit orders or all orders of the same item, the batch willtypically not require a separate sortation station, the items are allocated to a specific order at the time ofpacking or manifesting. Hardware costs based on number of users, not locations Hardware costs basedon number of users, not locations Hardware costs based on number of users, not locations Hardware costsbased on number of users, not locationsTypes of Order BatchesDescriptionBatch ByOrderCommonalityBatch ByPick ZoneBatch BySingle LineOrdersBatch BySingle UnitOrdersProcess ofgroupingorderstogethercontainingsimilar itemsProcess ofsplittingorders bypick zone,then groupingwithin thatzoneProcess ofgroupingsingle lineorders of thesame SKUtogetherProcess ofgroupingsingle unitorderstogetherCommonlyUsedOperations All types Operationswith multiplepick zones Internet &catalogfulfillmentoperations Internet &catalogfulfillmentoperationsBenefits“Draw Backs” Reduces the picking laborrequirement by reducinghits Reduces congestion onpick line conveyor Systemic supportof advancedbatching logic Requires a batchsortation area Reduces congestion onpick line conveyor No need to pass totesbetween zones Could be used inconjuction withcommonality batching Reduces congestion onpick line conveyor No need to pass totesbetween zones No need for a batchsortation area Reduces congestion onpick line conveyor No need to pass totesbetween zones No need for a batchsortation area Systemic supportof simplebatching logic Requires a batchsortation & ordermerging area Systemic supportof simplebatching logic Systemic supportof assigningorders at packing Systemic supportof simplebatching logic Systemic supportof assigningorders at packingStep 5: Batch Sortation TechnologiesMuch like the picking technologies, batch sortation can be performed utilizing paper, RF, voice, or a put-tolight system (which is a reverse of a pick-to-light system). Since a piece pick batch sortation is typically in acondensed area, usually consisting of sections of carton flow rack or shelving, the methods that are mostcommonly used and are the most effective are RF and put-to-light. Put-to-light is more expensive, but theproductivity rates are considerably higher, 100-150 lines/hr for RF versus 200-over 250 lines/hr for put-tolight (broad industry estimates).Step 6: Cluster PickingCluster picking is a methodology of picking into multiple order containers at one time. The containers couldeither be either totes containing order batches, discrete order shippers, or discrete order totes. There aretwo main piece picking systems that benefit from the use of cluster picking:1. Pick to cart operations, in which, a cart would be loaded with multiple totes or shippers and thepicker will make one pass through the pick zone and sort to the pick containers, thereby avoidingunproductive travel.www.OPSdesign.com

OPSdesign White Paper:PIECE PICKING: WHICH METHOD IS BEST?2. Vertical lift modules (VLM) or carousel operations utilizing the independent zone picking technique,the picker would setup the pick container batch, this would initiate the mechanized pick modules,and the items would be sorted to the proper pick container. This technique is used to optimize theVLM & carousel pods by limiting the number of machine cycles.Step 7: Cluster Picking Sortation TechnologiesThe same options and reasoning that applied to batch sortation applies here. The same task is beingperformed on a smaller level, typically sorting into two to four pick containers. The most common clusterpicking system contains a put-to-light cart, whereas the picker utilizes RF or voice picking technology.Step 8: Select a Picking ContainerPick into aTotePick Directlyto a ShipperCommonly UsedOperations Batch picking 100% inspectionrequired Special packagingrequirementsBenefits Discrete order picking Allows for anadditional check onorders Allows for thepotential to batchorders Reduces overallhandling of the orderby eliminating thepacking requirement“Draw Backs” Requires additional handlingat packing No secondary order check May result in additionalcartons being shipped due toimperfect cartonizingPick to tote operations typically utilize order batching & sorting techniques that reduce the picking laborgreater than the additional labor required for packaging and sorting.Pick to shipper operations are executed in one of three ways1. Picker erects the cartons at time of picking. Requires the replenishment of cartons to multiple areas.2. Cartons are erected and transported to the pickers via separate conveyance system (i.e. monorail).Requires added capital equipment expenditure.3. Cartons are erected and inducted directly into the system with the contents pre-allocated. Requiresextensive systems support.Step 9: Multiple Pick Zone Order Routing MethodologyPick to tote operations with orderbatching lends itself to theindependent zone pick method, aprocess in which segments of eachorder are picked independently invarious zones and directed to aconsolidation area where theelements of the order are combinedto the shipper (batch sortation area).Pick to shipper or discrete order pickto tote operations are typically mosteffective in either a pick and pass orzone routed system. This routingmethod will reduce the overallnumber of totes or cartons in thesystem. A zone routed systemalthough more complex and costly,will significantly improve productivityand work flow especially inoperations in which an orderrequires picks from multiple zones.Unlike a pick and pass system, zonerouted totes or shippers are onlytouchedby those people in zoneswww.OPSdesign.comwhere product needs to be picked.All touches are productive as aresult.NoneCommonlyUsedOperations Independentzone picking,order ismerged later.Benefits“Draw Backs” No orderaccumulationper zonerequired Ordermerge areais required. Everypickerneeds totouch anorder untilcomplete Cost ofcontrolsanddivertingequipmentPick &Pass Pick toconveyoroperations Low capitalinvestmentZoneRouting Larger pickto conveyoroperations Highproductivity