Manufacturers are relying more and more on tote boxes, platforms, trays, racking and palletized containers made from plastics and their numerous derivatives to safeguard parts during handling and shipping functions.
These new plastic devices are typically reusable, yet, unlike metal containers, usually offer lower initial costs, shorter lead times, are lighter in weight and require less maintenance costs. Compared to consumable containers, such as cardboard, plastic units eliminate long-term repetitive investments, breakdown and disposal costs. They are also impervious to cutting fluids and lubricants and better able to protect parts from collisions. And, plastic containers provide economic opportunities to modify designs to meet a specific application challenge.
Merely substituting a plastic container for metal or cardboard would make the job simple, according to Greg Hancock, vice president and general manager of ThermoFlex LLC, Morrison, Tenn.- based thermoforming specialists. However, in most cases, it’s not that easy.
“The number of plastic material options, the different manufacturing processes and the applications themselves,” says Hancock, “present myriad design, engineering and process challenges that require unique and innovative solutions. Load capacities, strengths, stacking capability, handling options, environmental hazards, economics and ergonomics, as well as part configuration and protection, are integral elements of the tool design, the material and the process selection. Those are the elements we’ve recently incorporated into a new pallet tray concept designed to protect heavy metal components.”
In particular, one application Hancock refers to was for an automotive supplier that finishes gears and other drivetrain components. The supplier had already switched to vacuum-formed trays made from high-density polyethylene (HDPE) for handling inprocess gears. However, there was a problem with the sharp edges of the parts in that, when placed in the trays, the pieces were gouging the
relatively soft tray surface and creating plastic shavings that could contaminate the parts. This problem was compounded by the fact that the vacuum-forming process does not typically hold tight tolerances, thus parts could move substantially and make further contact with the surface and create additional slivers.
That’s when ThermoFlex engineers proposed a dual-faceted solution, combining the economy and size capabilities of the vacuum-forming process to produce trays with molded thermoplastic urethane (TPU) inserts as nests for the parts. The trays are formed to ¼-inch material thickness, measure approximately 45 inches x 48 inches x 3 inches high and are designed to hold just one layer of gears—stowing 36 parts in total.
The trays use a 180-degree stackand- nest design that allows the trays to be securely stacked when filled with parts. Then, by reorienting the trays 180 degrees to each other, the design provides partial nesting to save space for storing and transporting empty containers.
One unique feature of ThermoFlex’s new system is working with its sister company, PolyFlex Products (Livonia, Mich.), manufacturers of thermoplastic injection, low-pressure foam urethane, cast solid elastomers and thermoset components. Another feature is using the TPU material and the injection molding process to fabricate the inserts, establishing the surface toughness and resilience required to withstand multiple contacts with sharp edges and producing ‘nests’ of tighter size tolerances that restrict movement of the parts. The inserts are formed to a ½-inch thickness, providing a strong and stable stowage space.
The molded inserts are attached to the bottom of the tray by an expanding plug or anchor attached to the insert. The bottom of each tray is drilled with 36 holes through which the plug end of an insert is pushed. Once through, the anchor expands to prevent its withdrawal and hold it snugly to the tray. The interior bottom of the tray also features a formed projection that each insert fits over to aid in its positioning.
According to Hancock, the twomaterial, two-process tray and dunnage units are proving to be successful in many applications other than the gear manufacturing project. “The largest parts of these handling systems, the tray,” he explains, “are made from HDPE, which is about one-third the cost of TPU, just in material. As a result, we’ve been able to keep the costs contained while improving the performance of these containers, the quality of the output and the productivity of the operations. Working with PolyFlex, with their range of options and resources, allows us to deliver optimum solutions instead of promoting just one process or material.”