The old "Unit Load Principle"

One of the original principles of materials handling system design is the Unit Load Principle; handle as large a load as possible to reduce the total number of moves. For years, this principle guided the development and application of pallet load handling. Today, it’s hard to imagine a time when standardized pallets were not an integral part of any storage and handling system.

However, as “just-in-time” began to dominate our thinking we pulled back from the pallet load as the only option. For many products, a full pallet represented several weeks of supply, and good inventory management dictated that we get better at handling small quantities through manufacturing and distribution processes.

So, maybe the full pallet, almost synonymous with “unit load,” is too limiting a definition.

For starters, a half-pallet can still be a unit load. It often represents a quantity that is a better “unit” for production, replenishment and filling orders. A production run might still be multiple half-pallets, but the smaller load can eliminate much individual case handling.

Other handling units deserve similar scrutiny. How many units should be packed in a case? Presumably, it should be a quantity that is, or could be, a common ordering increment. The beverage industry traditionally offered 6-packs and full cases of 24.  But, the full case was just a little more than consumers could comfortably handle. How many case handling moves did they eliminate when they introduced the intermediate sized 12-pack?

Years ago, we developed an approach toward unit load design for manufacturing processes whose capacity matched the number of pieces that were loaded in a rack, or fixture for a machine cycle so that partial loads were eliminated.

Frequently, the “unit load” is determined by a container that is easy to move, or carry. Totes and orderpicking carts are good examples. We should choose batch sizes that match their capacities.

For products whose flow can be measured in multiple pallets/day, double stacking them for transport and storage saves both handling moves and space.

When inventories of a single product reach the 100-plus pallet level, they might be left on trailers and pallets transferred at the dock to fill outbound orders. The key is to put only one SKU in the trailer, and bring it to the dock only once. The warehouse gets significantly smaller. And, the handling distance for the fastest moving products is reduced to a simple cross-dock move.

In a project involving the movement of automobiles through several steps of cleaning and re-conditioning with storage in-between, the handling unit might be determined by the number of drivers that fit in a shuttle van. Consequently, storage lanes for the cars should be in those increments.

Similarly, good engineering principles and analysis apply to the selection of the capacity of a shuttle bus serving remote rental car and parking lots at the airport.
How fast do the customers arrive, and how long is it reasonable to ask them to wait?

Unit load theory is not limited to the classic pallet dimensions. There are many different definitions and configurations. The question is; what are the right “unit loads” for your operation?

ABOUT THE AUTHOR

James M. Apple, Jr. is a Director in The Progress Group. Prior to co-founding The Progress Group in 1991, he was a Partner with Coopers & Lybrand's SysteCon division. During 1992-1995 he served as a Senior Systems Advisor with Vanderlande Industries, a major conveyor and systems provider in Europe.

Jim is an internationally recognized thought leader in the area of facility design and integrated distribution systems. His contributions to the improvement of distribution practices have been recognized by his receipt of the prestigious Reed-Apple Award, which is given for lifetime contributions to the advancement of the material handling profession. Jim has also received the Institute of Industrial Engineers' Facilities Planning and Design Award. He has written numerous articles and handbook chapters on warehousing and logistics operations and is a popular speaker on logistics seminar and conference programs.

Prior to SysteCon, Jim worked as an Industrial Engineer with IBM, was Supervisor of Facilities Planning for the Oldsmobile Division of General Motors and was Executive Vice President for an automotive aftermarket parts supplier. He holds B.S. and M.S. degrees in Industrial and Systems Engineering from the Georgia Institute of Technology.