Home Failure Analysis Warehouse Load Collapse and Distribution Damage

Warehouse Load Collapse and Distribution Damage

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Achievements and Results

  • Significant reduction in warehouse damage
  • Significant reduction in customer complaints
  • New stacking method implemented

The Problem

The client was packaging a food product in polymer pouches that were then packed into corrugated cases. The product provided zero internal support to the overall package. The product bags were of varying size and weight, but all were between 6 oz. and 16 oz. label weight, and were packed 12 bags per corrugated case. There were no partitions or internal corrugated supports, and the corrugated cases were provided by several suppliers. The packed cases were automatically palletized at the manufacturing plant, and then loaded onto a truck for shipment to an off-site warehouse. At the warehouse, the palletized loads were stacked "2-high" in an unconditioned area awaiting distribution to customer warehouses, which occurred by truck and/or rail carriers. All loads were handled by fork-lift trucks, and shipments occurred on pallets or slip-sheets.

The client experienced a dramatic increase in warehouse load failure and customer complaints about damaged cases. Pallet stacks began toppling over in the warehouse, apparently due to insufficient case strength. Customer returns due to damaged cases also increased significantly. The client had not changed anything in their process, and the packaging material specifications had not changed. The increase in load collapse in the warehouse also did not appear to be related to any weather or humidity changes. The warehouse manger demanded that the packaging materials be improved and/or redesigned to eliminate the problems.

The initial evaluation revealed that while the load toppling and customer damage complaints appeared to be random, there were several important observations that could be made early on.

- There was one corrugated supplier whose cases had a much higher incidence of failure than the other suppliers.

- The mathematical analysis of the stacking strength of the loads indicated that a 2-high pallet stack was safe, but that a 3-high stack was marginal or unacceptable.

-  The failure of the bottom tier cases on the bottom pallets was the main (but not the only) cause for the overall failure of the stack, and this case failure appeared to occur in approximately the same location on the cases.

-  There was a higher incidence of failure during the humid summer months, but there was also significant failure that occurred when and where dry conditions existed.

It was agreed that solving the problems that existed in the manufacturer's warehouse would likely reduce or eliminate the problems experienced by their customers, so the initial focus would be on the manufacturing process and things that could be controlled by the company.

 

The Solution

The first step was to do a complete examination of the packaging and warehousing process, to determine possible causes for the damage that was occurring. This included an analysis of the corrugation being supplied by the case manufacturers, since there was little or no incoming quality inspections on the corrugated cardboard boxes. 

In addition, a controlled stack test was initiated to verify the mathematical calculations for inherent load stack strength under ideal conditions, and also under more adverse / humid conditions. Then a complete examination of the warehousing and handling process was completed. This process provided the necessary information to identify exactly what was occurring and when, and help guide the client to a successful resolution of the problems.

This project produced a number of interesting findings, all of which played a part in the overall increase in damage being experienced by the client .

It was found that the supplier whose cases had a higher incidence of damage had maintenance issues on their corrugator. Even though this supplier was using liner and medium materials that usually exceeded the required specifications, it was determined that cases were being produced that had small linear voids in the adhesive between the linerboard and the corrugating medium ("finger lines"), and in some cases large areas where the liner was not adhered to the medium. In cases with load-bearing contents, this defect was not always as critical; but in these product cases the defects resulted in cases that could not support the loads they were designed for. The other corrugated suppliers had little or no incidence of these defects.

The manufacturing plant had begun using slip-sheets on the palletized loads, since some customers refused to accept loads on wooden pallets. These slip-sheets were placed onto the pallet automatically, and then the cases were stacked onto the slip-sheeted pallet by the palletizing robot. The slip-sheets were made of a very heavy solid fiber material that was extremely stiff. There was a "tongue" that extended out past the load which allowed a fork truck to clamp onto the slip-sheet. This tongue was supposed to be scored so that it bent up and out of the way during warehousing and shipping. It was discovered that this tongue was not always scored sufficiently, and / or the sheet was not always positioned properly. When the fork truck operator placed loads in the warehouse, they frequently butted them together tightly. This resulted in the bottom cases getting creased by the slip-sheet from the adjoining pallet, producing failure in precisely the same place over and over again. This creasing was hidden by the stretch-wrap holding the load together, so it was not seen until a load collapsed or a customer complained. Modifying the slip-sheet slightly, and changing the spacing between stacked loads in the warehouse, resulted in a significant reduction in this particular damage and failure.

Stack tests confirmed that even under ideal conditions, the stacked loads could not withstand 3-high stacking, even in dry conditions. To reduce warehousing costs, the warehouse had begun stacking 2 pallets high, with a third pallet bridging two stacks of 2 pallets. They concluded that this was only 2-high stacking, as each pallet stack was only supporting half of the third pallet above, in their opinion. It was shown that this was an incorrect assumption, and once this practice was eliminated there was a noticeable reduction in stacking damage.

It was found that on occasion, careless fork truck operators would "bump" a palletized load when backing out of a bay, or while operating in a trailer. The stretch-wrap holding the load hid any damage that might occur. However, this bumping by the fork truck produced dents in the corrugated cases at a very consistent height and location, often resulting in repeated case failure in precisely the same location. Educating the fork truck operators to the consequences of their actions helped to greatly reduce this particular damage.

Other items found to contribute to the overall damage rate, while not as significant as the above items, still were easily fixed and helped the overall effort to reduce damages. These included:

-  A production line with a case coder that was too close to the cases as they passed by, resulting in crushing of the cases at the code location. The coder was adjusted, and ultimately replaced by a non-contact coder.

-  Conveyor guide rails that were too tight, resulting in creasing of some cases when jams occurred. Adjusting the rails eliminated the creasing, and also reduced the incidence of jams.

 

Benefits Realized

The client could have incurred a substantial increase in packaging material costs by strengthening the case materials, and probably would not have solved the damage problems they experienced. 

By carefully examining the overall situation, and analyzing and addressing all the contributing factors, the client experienced a significant reduction in warehouse damage and customer complaints, without incurring additional packaging material costs. The reduction in damage and customer return costs, more than offset the increase in warehousing costs incurred by changing the stacking method of their pallets.

 

To see the resume of the expert associated with this case study, see the link below.

Resume of LKU Packaging Development, Product Innovation Expert Consultant Resume

 

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