piece picking-which method is best

7/21/2019 Piece Picking-which Method is Best

1/8

OPSdesign White Paper:PIECE PICKING: WHICH METHOD IS BEST?

www.OPSdesign.com

PIECE PICKING:WHICH METHOD IS BEST?

By Robert Muller OPSdesign Consulting, a trademark of Operations Design, Inc. 2007

This white paper shall lay out a 10 step plan for evaluating the multitude ofalternatives available in designing a piece picking system.


2/8


www.OPSdesign.com

Variations of Picking

Area 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 Modules

Mine 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.


3/8


www.OPSdesign.com

Step 2: Mode of Order Transportation

Commonly UsedOperations

Benefits Draw Backs

Pick toCart

Large numberof items with

low movementper item Full case andpiece picksoperations withlittle systemsupport to splitout the orders

Noconveyor

cost Highlyflexible

Multiplepickers perzone, ifrequired

Low pickrate due to

typicallylong travelpaths

Pick toConveyor

Low number ofitems

High volumeitems

Large numberof very small

items (i.e. jewelry)

High pickrate due tosmall pickzones

Typicallyonly onepicker perzone

Conveyorcost

Step 3: Selection of Picking Technology

CommonlyUsed

Operations

Benefits Draw Backs

PaperPicking Smalloperationswith littlesystemicsupport

Low technologycost Low risk

Low pickrate Low pick

accuracy Long order

cycle timeRadio

FrequencyPicking

All typesofoperations

High accuracy Paperless Ability to captureitem specificinformation (i.e.serial numbers)

Low pickrate (oftenthe sameas paperpicking)

Pick toLight

Low # ofitems withhigh

volumes

High accuracy High pick rate Hands Free

Highhardwarecosts

VoicePicking

Large # ofitemsspreadacross alarge area

Medium pick rate Medium to Highaccuracy

Hands Free

Medium tohigh capitalcosts forsystems &headsets

There are two common options inselecting the method used totransport the order to and fromeach pick location:

1. Pick to cart2. Pick to conveyor

A decision is typically made basedon the overall size of the piecepicking area (travel requirement).SKU velocity, pick density, andrelated considerations often definethe appropriate method.

A 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.

Operations 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.


4/8


www.OPSdesign.com

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 locations

Types of Order BatchesDescription Commonly

UsedOperations

Benefits Draw Backs

Batch ByOrder

Commonality

Process ofgroupingorderstogethercontainingsimilar items

All types Reduces the picking laborrequirement by reducinghits

Reduces congestion onpick line conveyor

Systemic supportof advancedbatching logic

Requires a batchsortation area

Batch ByPick Zone

Process ofsplittingorders bypick zone,then groupingwithin thatzone

Operationswith multiplepick zones


No need to pass totesbetween zones

Could be used inconjuction withcommonality batching

Systemic supportof simplebatching logic

Requires a batchsortation & ordermerging area

Batch BySingle Line

Orders

Process ofgroupingsingle lineorders of thesame SKUtogether

Internet &catalogfulfillmentoperations



No need for a batchsortation area


Systemic supportof assigningorders at packing

Batch BySingle Unit

Orders

Process ofgroupingsingle unitorderstogether

Internet &catalogfulfillmentoperations



No need for a batchsortation area


Systemic supportof assigningorders at packing

Step 5: Batch Sortation TechnologiesMuch like the picking technologies, batch sortation can be performed utilizing paper, RF, voice, or a put-to-light 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-to-light (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.


5/8


www.OPSdesign.com

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 Container

Commonly UsedOperations

Benefits Draw Backs

Pick into aTote

Batch picking 100% inspectionrequired

Special packagingrequirements

Allows for anadditional check onorders

Allows for thepotential to batchorders

Requires additional handlingat packing

Pick Directlyto a Shipper

Discrete order picking Reduces overallhandling of the orderby eliminating thepacking requirement

No secondary order check May result in additional

cartons being shipped due toimperfect cartonizing

Step 9: Multiple Pick Zone Order Routing Methodology

CommonlyUsed

Operations

Benefits Draw Backs

None Independentzone picking,order ismerged later.

No orderaccumulationper zonerequired

Ordermerge areais required.

Pick &Pass

Pick toconveyor

operations

Low capitalinvestment

Everypicker

needs totouch anorder untilcomplete

ZoneRouting

Larger pickto conveyoroperations

Highproductivity

Cost ofcontrolsanddivertingequipment

Pick 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. Requires

extensive systems support.

Pick 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 onlytouched by those people in zoneswhere product needs to be picked.All touches are productive as aresult.


6/8


www.OPSdesign.com

Step 10: Order Consolidation MethodologyThere are several methods with which to consolidate an order before shipping. If your operation is shippingonly parcel orders, this might not apply if each carton is shipped independently of each other and nophysical consolidation is necessary. For operations that must keep order integrity at the shipping dock, thecommon techniques are as follows:

1. Consolidate the order before packing occurs when either pre-picking orders before all items areavailable or discrete order picking to a tote with a 100% order check or to reduce outbound cartons.

a. Manual sortation on conveyors human sortation system, a person is assigned the task ofsorting the totes to gravity conveyor lanes typically directed by RF scan

b. Automated sortation on conveyors requiring controls and divertsc. Tote mini-load system AS/RS (Automated Storage & Retrieval System) stores all totes

until order is complete then releases entire order to packing in a slug or train.2. Sortation is commonly required after packing, typically for LTL or TL shipments.

a. Manual sortation on conveyors human sortation system, a person is assigned the task ofsorting the totes to gravity conveyor lanes typically directed by RF scan

b. Automated sortation on conveyors requiring controls and diverts

ConclusionOnce the options available for your operation are narrowed down a cost versus benefit analysis must beperformed for each remaining alternative. Some questions that need to be answered are:

1. What is the projected labor cost?2. Does the alternative meet the projected throughput requirements?3. What are the initial capital costs?4. Are there any on-going costs & expenses?5. How much space does this system consume?6. Does it meet order accuracy goals requirements?7. Does the alternative meet the required packaging standards and that of your customers?8. Is the system flexible and scalable?9. What are the risks associated with deploying such a system?

The chart on the page which follows, depicts 100 different combinations of infrastructure,systems, and methods for piece picking which may be considered.


7/8


www.OPSdesign.com

About the Author


8/8


www.OPSdesign.com

ABOUT THE AUTHOR:

Robert Muller is an Engineer - Consultant with OPSdesign Consulting, an independent (Category A, Tier1) supply chain consulting organization specializing in the design of warehousing, distribution, and fulfillmentoperations.

Muller has engineered and managed projects in a variety of industries and market channels includingautomotive, food, electronics, pharmaceuticals, media, construction materials, government, retail, consumerproducts, internet, & apparel.

Muller has a bachelors of science in Industrial Engineering from Rutgers University. He is currently anactive member in APICS The Association for Operations Management and the Warehouse EngineeringResearch Council (WERC).

Contact:[email protected] Ext. 1051-866-OPS-DESIGN

piece picking-which method is best

Documents