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PUTTING OUR BEST FOOT FORWARD
by Rick Hudson
At RL Hudson, we provide our customers
with far more than finished parts. As a value-added supplier, we also offer
design assistance. In fact, designing custom-molded rubber, plastic, and
polyurethane parts is one of the things we do best. Our in-house engineers
understand the needs of production, and they apply their considerable knowledge
of materials and processes to each new design. Most importantly, they think "beyond
the part." They know that each design impacts assembly, marketing, and usage.
Trying to anticipate ramifications is part of the job. Let me give you an
example.
One of our largest customers, Rubbermaid, recently approached us with a design project. They needed "foot pads" for their new "1957 Survivor XC" cooler, a higher-end specialty product being developed for the SUV market. Because the cooler itself was to have a slick polyethylene shell, the pads would help keep it from sliding around on other smooth surfaces (such as in the backs of sport utility vehicles). Rubbermaid’s question: How should the pads be made such that they do their job without adding significantly to the cooler’s cost?
ACCEPTING THE CHALLENGE Here’s how we approached the project. First, we took a close look at the design for the cooler itself. Their design called for four feet (one at each corner) to be molded as part of the exterior. Each foot would be 2 to 3 inches wide (depending on design needs) and a half-inch deep. The pads we were asked to design would need to fit over these feet snugly and permanently, so as not to slip off. Because coolers aren’t always handled gingerly, the pads also needed to resist tearing and scuffing.
We initially considered 3-inch wide by 5/8-inch deep lathe cut rings. One ring would be pressed on over each foot, with the built-in interference holding them in place. There would be a half-inch of material on each side of the foot, and about 1/8 of an inch below the bottom. The rings would be made of styrene butadiene (SBR). As you may know, SBR is used chiefly in the production of automobile tires, so we felt it could provide the resistance Rubbermaid required. SBR is also less expensive than many other materials.
With lathe cut rings, the feet would have been completely covered, but they would still have been visible from below through the openings in the rings. The sides of the rings would have been straight rather than contoured in any way. In order to help Rubbermaid market the product effectively, we felt something more streamlined was required.
FINDING THE ANSWERS Working with Rubbermaid’s designers, we began to explore other options. We needed something requiring less secondary labor, and something that looked as attractive as possible. Rubbermaid’s team had originally suggested molded rubber "cups" that would fit up over the feet, covering them on both the sides and bottom.
The chief drawback to this idea centered on how the cups would be attached. We could have suggested using liquid adhesive to secure each cup, but manual application of the adhesive would have been messy and invariably inconsistent. Automated application would have been cost-prohibitive. Use of pressure-sensitive adhesive was an option, but, again, variables would have been impossible to control. We also knew that, regardless of how it is applied, adhesive can lose its grip over time. We certainly didn’t want the cups to start falling off a year or two down the road.
What if we could "design out" the need for fixative? What if the cups could interface with the cooler more directly? What if a barb molded into each cup’s center could snap snugly into an opening molded in the bottom of each foot? If the cooler’s shell was to be blow molded, openings in the feet would be out of the question; there would be no way to form them. They could be drilled later, but that’s more secondary labor. As fate would have it, however, the chest was to be injection molded. Eureka! Injection molding would allow the control necessary to form the holes. We were halfway home.
We decided that assembly would be further facilitated if we hollowed out the insides of the barbs. Hollow interiors would mean the walls of the barbs could flex more easily as they went into the holes. (As an added benefit, this "hollow barb" design would also make the part easier to remove from the mold during production.) With the barbs inserted and the cups in place, expandable polyurethane foam used to insulate the chests would flow into the hollow barbs and solidify, securing the cups.
Now it was time to optimize appearance and functionality. As already noted, the cups would be solid on the bottom. Adding molded-in nubs would serve two functions. The cups would look more "cutting edge," which would please the marketing folks. The nubs would also provide extra grip, further reducing the cooler’s ability to do any unwanted sliding. That would please the consumers.
MEETING THE OBJECTIVES But as nice as the cup design was, one objective still wasn’t met: cost. The cups did not meet Rubbermaid’s target pricing. More streamlining was the answer. They suggested eliminating the cups’ side walls, thus reducing material usage and bringing the cost into range. With the walls gone, the cups became pads. Instead of relying on walls for stability, the periphery of these pads would be encapsulated by thin lips molded into the cooler’s shell.
In the end, the SBR pads we designed in collaboration with Rubbermaid fully met their form, function, and expense needs. I call that a success! But don’t take my word for it – see for yourself. The new "Survivor XC" coolers are arriving in stores soon. Don’t you need two or three?
And remember, those foot pads are just one example of the innovative design work we do each and every day here at RL Hudson. If we can help you design a new part – or modify an existing design – please do not hesitate to call us at 1-800-722-6766. We’ll be happy to help!
