Casting an Achievement in Design, Coordination

Click here to see this article as it appears in Modern Casting.

By Brian Sandalow

When a complicated casting for a major company is designed, it’s not a one-person job. Multiple teams, crews and departments are involved. Each has specific roles they need to fill with their respective areas of expertise, which helps even more when challenges and hiccups arise.

What happened when John Deere Waterloo Works built the drive housing casting for the 9RX 4-Track shows the importance of that teamwork.

The engineering and casting sides of the company communicated frequently, exchanged ideas and worked together to create a component that helped John Deere jump into a new market segment—four-track tractors.

“In order for this to be a success it took a lot of collaboration between a lot of different groups within Deere,” said staff engineer Jeff Lubben. “Machining people, our foundry, our analysis group, design. In order to make this a success on the assembly line and for our customers it took a lot of work from a lot of different folks.”

The drive housing carries the gear train and supports the whole tractor and undercarriage for the track system. It also limits the articulation of the undercarriage and transfers the torque from the axle to the shaft, enclosing all the gear train.

Engineers at Deere determined a single large casting would achieve better gear alignment. The tractor has large spur gears, one of which is over 27 in. in diameter, and the gears were aligned so that the critical bearing bores and shaft features were machined in one operation.

The designers also wanted to incorporate a self-contained lubrication system for the axle within the housing to avoid any external routing oil lines. The oil was designed to route through the housing via a patented system.
Each tractor has four of these castings—one in the left front, right rear, right front and left rear.

Casting it, opposed to other processes, was an obvious fit.

“Obviously, you could make a stamped and welded part look nice but there’s only so much you can do with a cut and fold piece of steel,” said Pete Murfey, senior engineer. “Weight savings was a big goal, so we were able to manage where we put the weight in the part, focusing on just adding iron where we needed it and taking it out where we could. The casting gave us the ability to put all the features exactly where we wanted them.”

The component was eventually cast in ductile iron via the green sand process, but getting there took teamwork.

Starting From Sketch
In September 2010, Lubben went to work on a simple piece of paper, sketching concepts that were startlingly similar to what eventually was produced.

One of the goals of the casting was for it to be relatively low mass. It also was intended to minimize the number of leak paths and share common geometry with Deere’s wheel tractors.

Before the work could bear fruit, teamwork was needed.

A lot of teamwork.

“It was from, literally, a sketch on an 8 1/2 x 11 sheet of paper when we started collaborating,” said Anthony Childers, foundry pattern development engineer, John Deere. “That’s about the right time to get a foundry involved. We’re very proud of that collaboration.”

That collaboration was an important one for John Deere. One of the market leaders in farming machinery, Deere was looking to break into a new market segment with a four-track tractor.

This wasn’t an insignificant project.

“The four-track capability is something that’s growing in popularity on the market, and Deere decided it was high time we got in the market,” Murfey said. “Being able to spread out the load across four large track footprints rather than tires or two tracks is a big improvement in the field. The biggest advantage I think it offers is the ability to turn a tight corner without pushing up a large berm of dirt that you get with a two-track tractor.”

To deliver what was needed, Deere needed to design and implement a large casting.

The casting was designed to fit Deere’s new green sand molding line at its Waterloo, Iowa, casting facility.

“Even though we worked very closely with engineering to size the part, they had certain vehicle requirements to meet. So the part ended up being larger than we’d ever anticipated,” Childers said.

“It is very challenging to keep the flasks clean enough and very challenging to mold the part. Yet we’ve been very successful in doing this.”

To complicate things, the line was being installed while the casting was being designed and engineered.

“We actually had to give this thing a haircut in two out of three directions to get it to fit in our new bigger mold line, which was already too small for this part as we initially designed it,” Murfey said. “We took an inch off the arms and three inches off the top to be able to get it to fit in the flask.”

The casting ended up being a slightly shallower mold than what had been anticipated, which created a situation where the engineering team had to modify the component about 75% of the way through the design process.

“We made it up in the cover design so it didn’t adversely impact us and didn’t set the program back. It was just a little bit of a struggle,” Childers said.

Early durability tractor builds used air-set molding in the metalcasting facility prototype shop. Deere was also able to pare eight weeks from the product development time of each build via 3D printing. 

“We worked on a once or twice weekly basis with engineering as the design was being developed because we had a core manufacturing strategy that we were pursuing and we asked for a myriad of changes in the casting design to accommodate that,” Childers said. “Plus we asked them to make changes in the casting design for directional solidification and for the flow of stresses through the casting. We made some design suggestions that made the casting stronger and stiffer.”

After the first durability build, Deere asked for a reduction in mass.

“With a tractor you want it heavy enough to be able to put all the power to the ground but not any heavier than that,” Murfey said. “Any extra weight you’re carrying beyond what you need is just creating extra soil compaction and hindering the ability of the crop to grow.”

Ultimately, Deere trimmed 211 pounds out of the casting while still meeting all of the finite element analysis and functional requirements of the part.

The Finished Product
Eight cores are needed for each casting, and they are automatically gantry-set at two stations on the line.

The castings are 100% machined at GMT Corporation, Waverly, Iowa, and delivered to Deere’s plant in Waterloo, Iowa, where internal components are assembled. Then they are sent to tractor cab and assembly operations in Waterloo for the tractor builds.

The 9RX 4-Track hit the market in February and has brought what Deere wanted.

It offers less soil compaction, a better turning radius, no skidding and other benefits. The 9RX is a very effective puller, with its four large axles and undercarriages transferring power from the engine to the ground.

“The component carries the gear train and it supports the whole tractor, the undercarriage for the track system,” Lubben said. “It limits the articulation of the undercarriage and basically supports the tractor, transfers the torque from the axle to the shaft and encloses all the gear train. It’s one of the largest parts we pour at our facility.”