Ag Iron Conversion Cuts Weight by 30%
For years, the company discussed with Dotson Iron Castings, Mankato, Minn., the possibility of converting the welded product to an assembly of metal castings. With the design materials and inventory up in smoke, the ice storm made it the perfect time to take the talks to the next level. It took several years and an act of God, but Dotson finally won the job to reverse engineer the metal castings from the existing weldment and fulfill the customer’s needs.
One thing was certain. After the storm wiped out the inventory and design plans for the welded Agri-Speed Hitch, there was no choice but to continue making the product. Not only did the customer have pending orders, but the hitch had been saving lives for years.
Farmers often find themselves in dangerous situations when they exit their cab and walk behind a multi-ton tractor to make a hookup. Prior to the development of the automatic Agri-Speed Hitch, many workers were crushed by wayward pieces of farm equipment.The solution was a hitch that enables automatic hookup and disconnect of farm equipment without requiring the operator to leave the cab of his or her tractor. When the male end of the hitch is backed into the female end, it automatically snaps into place. To unhook the hitch, the operator pulls a chord, also from inside the cab of the farm vehicle. Converting to castings would not change the function or performance of the life-saving hitch.
“In terms of performance, the casting is similar to the weldment,” said Chris Witt, sales account manager for Dotson. “In terms of appearance, it’s quite a lot different. You don’t just take a weldment and make a casting the same. That’s not the efficient way to make a conversion. You need to unlock the benefits of the shapes and pockets that a [metalcasting facility] can do and a weld shop cannot.”
What a Metalcaster Can Do
The designers of the new cast metal Agri-Speed Hitch had only the versions of the welded hitch to work with. They wanted to retain all the good things about the weldment—its function—while improving its appearance and weight.
"We wanted something more consistent than the weldment,” the customer said. “We wanted something that looked more professional. We have a huge freight bill, because we ship [the hitches], and with freight going up, we wanted a lighter part, as well.”
The 70-lb. (31.75-kg), 11-piece assembly measures 30 x 24 x 8 in. (76.2 x 60.96 x 20.32 cm). To survive the rough conditions through which many ag users put it, four of the five ductile iron castings were austempered, a process by which the ductile iron is isothermally heat treated, quenching in molten salt, to produce ausferrite, a very strong, highly wear resistant casting structure. According to a spokesperson for the agricultural manufacturer, the material properties of the hitch have been elevated, and they have approximately three times more wear life than the steel parts. The austempering was performed as an insurance policy that yielded benefits worth the cost.
Dotson produces the Agri-Speed Hitch in the horizontal green sand molding process on its automatic lines. With the help of Enterprise Pattern, Jordan, Minn., and austempering firm, Applied Process Westshore, Oshkosh, Wis., the company was able to offer its customer the first completed hitch just eight weeks after the job was commissioned. It now runs the castings in its regular production schedule, per the customer’s orders.
Working with the pattern maker and the customer to limit weight, Dotson was able to design a new part that offers a more efficient use of metal than its predecessor. The redesign resulted in a 30% weight reduction, which was achieved both because the casting incorporates undercuts where the weldment did not, and because iron weighs less per cubic inch than steel. Cross sectional sizes of the castings have been optimized to eliminate the need for expensive alloys. The castings were closer to the minimum metal configuration that was required for the operation of the hitch than was the weldment. In other words, the design was nearer to the net shape with no machined features necessary. The weight reduction has contributed to lower shipping costs for the customer.
According to Witt, the simplest aspect of the conversion process is making a casting that looks like the weldment. Taking a part that had been welded together and designing it for castability is necessary. The challenging but most rewarding aspect of conversions is making use of the casting process’ benefits to optimize the configuration and shape.
Thickness had to be altered in order to improve the feeding and solidification of the molten alloy to the mold, as the rate of solidification in castings is highly affected by the volume of the sections. If the thicknesses had not been changed, the castings may have been produced with a variety of defects, including shrink. Thick section sizes also require special alloys of chrome or molybdenum for thorough austempering. Reducing section sizes in unnecessary places eliminated the need for an expensive alloy.
The aesthetics of the piece also were improved. According to the customer (who previously had produced the steel weldment in-house), the casting looks more professional, as “unnecessary corners were rounded off,” and the company was able to cast its name and address directly onto the piece.
The new hitch was designed to be interchangeable with the old weldment; however, it is also more versatile. The newer version is compatible with farm equipment that has both wide and narrow tongues. It is slightly larger than its predecessor, making it appropriate for larger wagons, but it is light enough to work on more delicate machinery, such as equipment used in nurseries.
Because of the ability of the casting process to produce the component quickly and in high volumes, Dotson believes the customer should be able to market the product to a wider range of customers than it had previously targeted. But for the time being, the agricultural manufacturer is simply enjoying the hitch’s improved look and lower shipping costs.
“Whenever something bad happens, you can find good things that come out of it,” the customer said. “And this was a good thing that came out of the fire.” METAL