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Design Your Best Picking Layout

Balancing the costs of space/equipment, replenishment and picker time.

Every order picking operation represents a unique company solution to the question, "How can we best pick our orders to minimize costs and enhance shipping times?" This article will concentrate on how to tailor your equipment, space, replenishment needs and pick areas to exactly fit YOUR operational needs, YOUR unique product line, and YOUR order patterns and volumes.

STEP I

Obtain the data on your daily and weekly order volumes, product movement, and product cube. If this data is not available from your order processing system, you can physically measure key product sizes, and estimate movement for all key product groups. THIS IS THE SINGLE MOST IMPORTANT STEP IN A FACILITY REDESIGN. With these numbers, you will be able to calculate the very best solution to the question of "How best?"

STEP II - USE A COST CALCULATION SPREADSHEET (Example follows).

SPECIAL NOTE: You may request a copy of the Excel spreadsheet that I have developed to calculate the ideal equipment/personnel mix for operation. Use my Email listed on this site, and a free copy will be forwarded by Email.

  1. To understand how and why a specific pick layout should be chosen, we must look at the TOTALS of the costs of space, equipment, replenishment and pick travel.
  2. Calculate the cubic feet per pick to find the size of a piece (or pack or case), and multiply this number by the number of pieces in the average pick of this item. NOTE: The greater the cube of a pick, the more often it will have to be replenished into any given pick slot.
  3. Determine the average numbers of times per day that a picker physically passes an individual pick slot to pick an order. This number is extremely important - (also, calculate that the larger the pick slot, the more walking will be required, and this increases picking time.) This number need not be the same as the number of orders picked in the whole facility. (In a future article, we will discuss several strategies for GREATLY reducing the need to pass every pick slot with every order.)
  4. Find the average number of picks per item per day.
  5. Multiply the cubic feet per pick by this number and you have the cube per item per day, giving you a measure of the replenishment required.
  6. Finally, how many SKUs are in the slot where an individual item is located?

Now, you are ready to provide the weighting factors for determining your ideal layout.

INSERT - the spreadsheet

THE COST CALCULATION.

You will note that for every combination of storage device, product cube, movement and number of orders/day, a total cost calculation is listed on the spreadsheet. This cost is for one item for the entire year and includes the equipment amortization , space rental, replenishments, and pick walks past the slot. It must be emphasized that these numbers are approximate BUT also representative of the real world operations for which they were developed.

THE SHADED AREAS DENOTE THE LOWEST COST STORAGE OPTION FOR A PARTICULAR CUBE MOVEMENT OF AN INDIVIDUAL PRODUCT WITH A GIVEN NUMBER OF PICK TRIPS PAST THE SLOT.

GENERAL CONCLUSIONS:

  1. Larger picks work better in pallet slots, due to the need for fewer replenishments.
  2. Smaller items cost less to store in shelving.
  3. Flow rack does well with averaged size items with many pick trips past the slots.
  4. Pallet rack slots do well when then there are few pick trips required and the space is available.

 IMPORTANT NOTE: Anytime that you have a varying range of product cube and movement, you will save money by also using a matching range of storage racks and shelving.

IMPORTANT NOTE #2: Design your layout for expected demand TWO YEARS FROM NOW! Redoing your layout is expensive (and easily postponed). Too many companies are picking from slots that are too small and/or nearly empty. If you need more space or a mezzanine for additional pick area, get it NOW. It will be much less expensive in the long run.

FINAL NOTE ON PICKER TRAVEL TIME.

Orders/day is a measure of actual pick trips past a pick slot. There are several ways to reduce this number.

  1. Place all slow moving items in pick areas near (but not on), the main high mover pick aisles. Pickers will only need to go into these slow mover areas when they actually require a specific item. Also, this way, larger pick slots may be used, which will require less replenishment.
  2. Place all products that are often picked together on the same order, into a specific picking zone or department. Pickers will go into these departments only when required, and make as many picks in this department as possible.
  3. If you use pick conveyor, be sure that it diverts into departments ONLY when it is needed, and then make as many picks in that department as possible (see our next article on batch picking).

REAL WORLD EXAMPLES OF PICK AREA DESIGN.

EXAMPLE I: CATALOG DISTRIBUTOR OF DENTAL SUPPLIES

Walk times past orders was reduced by picking the slow and medium moving items into a tote on the conveyor from the far end of the pick aisles. If an aisle had no picks, it was bypassed. Medium movers were picked more frequently than slow movers, so they were located closer to the conveyor, minimizing walk time. The average slow mover was passed only 50 times a day versus 150 times per day in the previous layout. Since almost all orders have at least SOME high movers, they are passed 1000 times per day, and placed the closest to the conveyor at the end of the aisle.

As an aside, this facility has a serious jam-up at the end of the pick line almost every night. This jam has made it difficult to ship orders on time. The cause? - the need for 100% checking of every order, dropped haphazardly into cartons in the totes on the conveyor. If the orders had been batch picked, for instance16 at a time into shipping cartons, scanning or check keying every pick, this expensive and delay-causing check/repack operation could be ELIMINATED, saving at least, $150,000 annually, based on their current number of orders per day.

EXAMPLE II: DISTRIBUTOR OF PRINTER SUPPLIES

This operation was a good example of utilizing a conveyor with a divert ability, to bypass pick zones without picks in the order being processed. The order is started in a carton with an order ID label on its side. The divert system insures that the carton goes into all zones with designated picks. When all picks are completed, the carton is checked with an inline scale to insure that all picks were made (in addition to scanning each item as it was placed into the carton).

On the flip side, using short lengths of flow rack for high moving items and shelving for medium and slow movers, has meant that replenishment is a major problem, especially for larger and higher moving items such as laser printer cartridges. Since ample space was available in this facility, I recommended that full and 1/3 pallet rack slots should be used to a much greater extent than currently practiced.

Another issue with this system was the presence of a few extremely high moving items that appeared in 50% of all orders. If all of these high moving items had been put into one divert zone, orders would soon begin to back up on the conveyor. If placed into many zones, too much time in the system would be required to process these orders. The solution was simple - duplicate-slot these high volume items into several pick zones, always near the conveyor. When an order was diverted into that zone, the high movers were also picked in that zone. An extra benefit of this solution was that these high movers would require much less frequent replenishment secondary to their multiple slot placements

EXAMPLE III. EYEGLASS FRAME DISTRIBUTOR.

Eyeglass frames are small, but expensive. This was an ideal situation for batch picking from shelving. All the inventory for each item is kept in the pick slot or in the overhead shelving slot. Batches of 15 (or more) orders are picked in one picker trip with scanning of bar codes, verifying each item and package 100% of the time. Shipping labels and packing lists are printed before picking and guide the choice of the correct carton size based on numbers and previously calculated cube.

NOTE: In this case, the use of batch picking coupled with the small size of each shelf facing reduces pick trips to the point where pick travel is no longer a significant cost factor.

EXAMPLE IV: COSMETICS DISTRIBUTOR.

This unusual "paced" picking system is included in this discussion because it highlights a situation where a fully flow-racked picking system, coupled with a daily "micro adjustment" and a "pick- to-light" computerized picking system, could be appropriate

Orders are cubed by the computer, cartons are labeled and placed together on the start side of the conveyor. Pickers work on both sides of the conveyor, picking directly into the shipping carton as directed by the system. If an order is in danger of moving out of a picker's zone before all picks are completed, the conveyor will stop until the pick-to-light system notifies the conveyor that the order is completed.

The "micro-adjustment" mentioned earlier balances the sequence in which orders are picked to keep each picker's workload as equal as possible. The location of any given item is also changed as directed by this system. Significantly, these orders have been placed by sales representatives and concentrate many small cosmetic orders into fewer and larger distributor orders.

This final example shows quite dramatically how a system can be tailored to a company's highly individual demand pattern. This is the perfect picking solution for this unique fulfillment operation.

More on Warehouse layout

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