Cutting Through the Challenges
Brian Sandalow, Associate Editor
Click here to see this story as it appears in the September/October 2017 issue of Metal Casting Design & Purchasing
The Columbiana, Alabama, lost foam casting facility that’s currently owned by AFS Corporate Member American Axle & Manufacturing was handed a difficult challenge in 2015. They had to produce a chainroll, and one that was incredibly complex.
It was a test, and one the facility ultimately passed.
This ductile iron casting for agricultural producer 360 Yield Center (Morton, Illinois) works in pairs and utilizes complex intermeshing tooth and blade geometries to precisely crimp and cut corn-stalk residue into the desired final size during harvesting. The numerous crimp sites exposed for microbial breakdown help accelerate decomposition and nitrogen release into the soil, which improves the next year’s crop.
The chainroll is meant to help create the right conditions for healthy emergence, healthy soil and healthy yields. It does this by cutting stalks precisely, crimping and scoring stalks to expose the interiors to microbes, and sizing them for faster decomposition and microbial breakdown. The units themselves are built to create specific lacerations in each stalk. The rolls have both cutting and chaining flutes that work to pull out the cut, bringing a chainlike pattern that leaves areas exposed for microbes to enter. And the hardened surfaces get sharper with more acres, bringing a durability that’s similar to standard rolls.
The lost-foam tooling was designed to produce multiple part configurations and part numbers with a single tool by utilizing interchangeable inserts to facilitate a family of chainrolls to fit a variety of corn head models.
Obviously, it’s a complicated product, and to produce it correctly meant dealing with many unique challenges. It meant figuring out how to handle difficult geometries and challenging tooling. To succeed, the project required a strong working relationship with the customer that needed to be trusting and consistent.
“If I were to give some advice, it would be to develop that customer relationship with that common understanding,” said Jim Gilchrist, process engineering manager, AAM Columbiana. “If you just throw that design over the wall and you just work on it by yourself and you present them with a sample submission, at some point in the future you’re probably doomed to failure without that extra interaction with something of this magnitude.”
Starting the Process
In the summer of 2015, AAM Columbiana began working on how it would cast this product.
By the time the design got to AAM Columbiana, 360 Yield Center already had worked through design and prototyping. The product had been prototyped in printed sand, which resulted in a casting that looked somewhat similar to what was wanted, but in reality was not quite what was desired. The first time AAM Columbiana saw anything, the plans just had the teeth area in it, which at first glance was daunting.
This part was designed to work with the rolls already made, which intrigued AAM Columbiana.
The team figured if this product took off and did as well as 360 was saying it could, it might be a higher volume part than AAM Columbiana was expecting. And it could be an aftermarket part that farmers would choose over the current design.
Fortunately, when AAM Columbiana was awarded the project, the basic design was in place. Now it had to tell the customer what was needed to make it in lost foam, to make it toolable, and to be able to cast it.
The first thing AAM Columbiana did when it received the original models was to look at how the product would be cast in lost foam.
Figuring out where they were going to split the foam was one challenge. This part was considerably different than the current stock rolls the metalcaster makes, and posed multiple challenges with the teeth and internal parts that are inside the part.
At least knowing the part had to be cast via lost foam provided some clarity, because without it, there would have been difficulties assembling a core.
“We knew our final design was going to be difficult to cast,” said Phil Russell, buyer, 360. “Due to the geometry, lost foam was the only option. (AAM Columbiana) was brought in early to provide guidance and direction on what would be possible and also to help with the tolerances that would be able to be met.”
With lost foam an automatic choice, AAM Columbiana set out to tackle this challenge.
Though the facility was ready and eager, many challenges were ahead. The biggest one was the teeth at the end of the roll, which are round with intervals.
The teeth are all backdrafted, plus they come out to a little tiny point, which doesn’t make them favorable for casting. AAM Columbiana was heavily concerned about carbides and other similar issues. The team had to figure out if it could even create a tool to make those little teeth.
The teeth also have a small cup under the backside. The facility made prototypes using a cut foam process where had it had foams and patterns machined out of billet and used for test castings just to prove they could cast the product. Everybody involved was pleased with the resulting accuracy of the model, and that was what pushed the design and program into production.
AAM Columbiana contacted three outside vendors about the project. Only one of them, a tooling shop in Michigan, responded with a quote after seeing the complexity and difficulty of the task at hand.
Gilchrist and the rest of the AAM Columbiana team can look back on this project with pride. They built a complex product that is good for everybody’s business, and they did it via good foundry practices.
It wouldn’t have been accomplished if not for how well their facility worked with the customer’s engineers, the team said. The employees from 360 were open to what AAM Columbiana had to say and were interested. They visited numerous times to understand the process and were clearly engaged.
Gilchrist praised 360 for being at the foundry at crucial moments of the project, something that helped it succeed.
“In fact, they were on site when the tool was delivered and when the first patterns were manufactured and delivered to the foundry,” Gilchrist said. “They actually helped us prepare the first mold. They were really excited about that.”
The customer was also understanding of how difficult and complex the project was.
“That was a stipulation from the start that we would have to develop an acceptance criteria for these features because they were so delicate. You could imagine a piece of foam with a little featherish tooth out there,” Gilchrist said. “You can just touch it and knock the edge off of it. We told them up front ‘Hey, we’re going to have to say you can have so many teeth with a defect in it’ or something along those lines so that we would be able to make a part with an acceptable scrap amount.
“They were very open to that and understanding.”
For Gilchrist, that’s the lesson he would teach other foundries about this kind of project.
“From a perspective of having to go back and relaunch this there’s always lessons to be learned. I would say probably the biggest thing I learned was that I actually liked the customer involvement in not only the part design but our process design,” Gilchrist said. “The process design for this part from the casting perspective had as much to do to make or break the project than the part design from the customer’s side of things. Having them onboard with the recognition that they knew this was a difficult project was key.
“They knew that this has never been done before. They knew this was the first time for everybody just to have that pulling in the same direction with a common goal to get this done knowing they might have to make accommodations for something. The level of cooperation has to be there.”