Even a glimpse at John Deere's tractors and combines will quickly drive away any doubt about the growing use of plastics in agricultural equipment. Over the past decade, the company has converted a wide variety of styling and functional components from sheet metal to plastics—reducing secondary operations, complexity, weight, and cost in the process. "Virtually every plastic and composite manufacturing process is utilized in producing our harvester components," says Greg McCunn, a supply management engineer at John Deere Harvester Works.
At this year's Structural Plastics Parts Competition, John Deere's 8000 Series Tractor won awards for a new plastic hood assembly whose cosmetic surfaces and underlying structural frame are all made from engineering thermoplastics.
And he's not kidding. Deere has made styling and appearance parts—both interior and exterior—with sheet molding compound (SMC), reaction injection molding (RIM), resin transfer molding (RTM), injection molding, thermoforming, and rotational molding. Wear-resistant and functional parts have been injection molded, extruded from ultra-high-molecular-weight polyethylene, cold formed, blow molded, overmolded, and cast in urethane.
Among its latest forays into plastics, Deere has taken a leading role in using plastics based on sustainable feedstocks, adopted modern twin-sheet thermoforming as a way to replace stamped metal parts, come up with some award-winning rotomolded components, and made use of an innovative RTM process. Here's a closer look at all four developments:
Tofu tractors. Just when you thought your coffee cup would be the last place for soy products to turn up unexpectedly, Deere has come up with two new soybean-based composites. These "HarvestForm" materials consist of a polyurethane RIM system developed in conjunction with Bayer Corp. (Pittsburgh) and an SMC concocted with the help of Ashland Specialty Chemicals (Columbus, OH). Starting this year, all combines built at John Deere Harvester Works will sport body panels made from one of these soy-based materials, McCunn reports. Such widespread use adds up to more than a hill of beans. According to McCunn, the RIM panels alone will consume about 225,000 lbs of soybeans this year.
Deere has started to incorporate renewable resources into its products. This year, many of the company's combines will sport soybean-based RIM body panels - including the harvester's rear wall and access door.
Adopting the soy-based materials shouldn't be too tough for Deere since both of them offer identical mechanical and physical properties to the conventional materials they replace. "That was our initial stipulation," McCunn says. "We had to be able to pick a standard or a soybean material out of the bin and have them mold the same, look the same, and perform the same." Deere initially had exclusive rights to the two materials, but this year they became available for other users. "Part of our commitment to using renewable resources is that we really want everyone to use them," McCunn says.
New sheets. Deere has used thermoforming before, but only recently did the company adopt the twin-sheet variety as a way to make a folding grain tank cover for some of its combines. Created as a way to comply with European safety regulations, the tank cover had some tough strength and packaging requirements. According to McCunn, each of the cover's 3 × 1.5m panels needs enough rigidity to keep from sagging into the grain tank, to stand up to the weight of a farmer walking on top of it, and to support the edge of the grain pile when open. "The covers also had to fit within a narrow design envelope," McCunn says, explaining that the tank had no room to add a "structural bow" and that European regulations limit the overall height of combines, further restricting the space for the cover.
This elaborate tractor roof integrates dozens of air conditioning, lighting, audio and mounting components into a single rotomolded part.
To come up with a strong cover that keeps a low profile, Deere engineers created two panels of acrylic/ABS sheet that overlap with a built-in locking feature. Twin-sheet thermoforming allowed them to include an insert-molded steel tube—between the two sheets—to further boost strength. "This reinforced, twin-sheet structure provided a higher stiffness-to-weight ratio than steel doors could," McCunn says. Twin-sheet thermoforming also offered a couple of additional benefits: Laminated sheet is easily color matched to John Deere green, eliminating the need for any topcoat. Thermoforming allowed the use of a single tool to make both the right and left panels. "Interchangeable tooling inserts make the molded part a 'right' or a 'left'," says McCunn.
What goes around. Rotationally molded parts have also been on the upswing. McCunn notes that rotomolded parts started appearing on harvesters in the early 1990's, as a replacement for formed, painted sheet metal. And he calls the 1993 conversion of corn harvester row points, decks, and fenders from metal to linear-low-density polyethylene (LLDPE), "the most successful example of rotomolding in the agricultural industry." Since then, myriad shield and cover components have gone into rotomolding—including end shields for corn and grain platforms, clutch shields, a tailings elevator cover shield, and chopper drive covers. According to McCunn, applications like these hinged on rotomolded LLDPE's ability to offer good cosmetics, corrosion and dent resistance, and relatively low cost tools. Today, the company's experience with rotomolded parts has gone even further. "Now we've started to move them into more structural applications," McCunn says.
One key to VEC Technology Corp.'s low-pressure composite technology is its "Floating Mold," which works on the principle that fluids are non-compressible in pressure ranges used in the closed-molding process. To make these liquid-filled molds, the company forms two composite laminate skins from a master model. These skins form the molding cavity and also attach to two open-top pressure vessels, which are filled with liquid to create the finished tool. The chief advantage, other than a low initial tooling cost, is flexibility: When part designs change, the tooling can keep pace with a simple switch of the composite skins.
A recent grain bin extension cover, for example, uses a rotomolded LLDPE to hold steel components in place. "The corners hold the steel side extension in place and carry some indirect load from the grain pile," McCunn says. Deere engineers selected rotomolding for this job primarily because it produces a double-walled hollow part that pairs good structural capabilities with complex geometries.
In non-structural jobs, rotomolding's ability to make hollow parts serves another purpose: Sometimes Deere molds a single hollow part and then cuts it in half to make two finished parts. "It's like getting two parts for the price of one," McCunn says. "Often the hollow part construction of rotomolding makes the conversion from metal to plastic possible."
Closed-mold composites, too. Deere has lastly begun to experiment with "Virtual Engineered Composites" (VEC), a proprietary RTM process from VEC Technology Corp. (Greenville, PA). "VEC lends itself very well to low-volume, large structural parts with a simple geometry," McCunn says, citing 600 to 800 parts per year as the sweet spot for this closed molding process. The company has used VEC in limited production runs of a newly designed rear wall and access door on a low-volume model of its STS Combine.
Noting that VEC uses tooling made from steel-supported polyester, McCunn says Deere's interest in this alternative to hand lay-up and RIM primarily comes down to the low tooling cost. He reports that the two-cavity family mold cost approximately one quarter the prices of new RIM nickel shell tooling. "The part prices were also much lower than hand lay-up prototypes," he says.
Aside from tooling cost, the process has environmental implications, too. McCunn says it has low styrene emissions and also supports the use of natural fiber reinforcements. Though the process usually relies on glass mat reinforcements, Deere was able to use natural fiber flax mat instead—in keeping with the push into materials based on renewable resources.