Aarrowcast Wins Casting of the Year
The winning 842-lb. John Deere oil pan is a complex component that combined a steel fabricated oil pan, frame casting and two steel brackets into one casting for reduced weight.
Shannon Wetzel, Senior Editor
(Click here to see the story as it appears in May's Modern Casting.)
Aarrowcast Engineering manager Jim Olson called the John Deere oil pan project the most complex, biggest job the ductile iron casting facility has ever handled. But the hard work put into the casting paid off in more than a successful delivery. “This part took us out of our comfort zone, and as a result, we’ve changed our entire system to work with our customer up front to ensure success at launch,” Olson said.
Even with OEM and casting supplier collaboration, the 842-lb. ductile iron oil pan casting for a John Deere 9-liter engine took several iterations and a couple of years to perfect in production. But Olson said that without close communication with first the John Deere design engineer and, later, the John Deere Casting Center of Excellence (CCOE), ultimately, the converted casting might not have been delivered. Through active participation in the design and development process, Aarrowcast was able to produce quality cast oil pans that reduced weight by 77 lbs. to meet stricter emission requirements while providing the necessary strength and oil capacity to accommodate a higher horsepower engine. Because of those efforts, Aarrowcast, Shawano, Wis., has earned the 2014 AFS/Metal Casting Design & Purchasing Casting of the Year award for its John Deere 9-liter engine oil pan.
John Deere wanted to cut weight in two of its large tractor engines to meet higher emissions requirements coming in Europe, and converting a stamped steel oil pan and frame casting to a single ductile iron casting was one way to shave off some pounds. At the same time, it was raising the engine output (by about 60 horsepower in the 9-liter engine), which imparted additional forces on the oil pan that not only holds oil but also connects the front of the tractor to its rear under the engine.
When John Deere connected with Aarrowcast to make the part, it was clear what the part needed to accomplish, but not how it would. One of the stickiest criteria to meet was maintaining the capacity for the necessary volume of oil.
“Because they wanted to reduce weight, we ran into a lot of space restrictions,” Olson said. “We worked to stretch the available capacity up into the corners and moved bosses to provide more space.”
Aarrowcast used temporary tooling to test out a final design iteration, but successfully pouring samples on the temporary tool material proved difficult. A quality test casting was finally poured after 10 failed attempts. Testing at John Deere revealed the wall thicknesses in the design weren’t sufficient for the application. More changes to the design were needed.
“There was a lot to learn in this casting process,” said Jack Smith, Aarrowcast vice president of operations. “It is not your everyday casting, and the methods we have applied to the part were new for us.”
After adjusting the design for thicker walls, Aarrowcast produced successful test samples using a semi-permanent tool. The key to pouring good castings was adjusting gating practices for low velocity flow of molten metal at the gates. Aarrowcast uses pressurized gating for in-mold ductile iron treatment. Simulations of typical gating practice showed flow at the gates for the oil pan to be at a rate of 70 in./second. Aarrowcast engineers slowed the flow to 25 in./second by stepping the gates for lower pressure.
Depending on the engine, the oil pan castings require up to 13 cores, all of which are manually set into the mold by Aarrowcast technicians. To ease coresetting, Aarrowcast adjusted the core locks and used seats for chaplets to facilitate core placement. But plant supervisor Mark Burmeister said training also was integral to achieving tight tolerances. “It takes a skilled hand to put the mold together,” he said.
After the oil pan had been in production for a few months, Aarrowcast was discouraged by ongoing issues that resulted in too many scrapped castings and too much rework. The casting facility contacted John Deere’s CCOE for help. Jim McKee, manager of John Deere’s CCOE, stepped in to assist in resolving the issues.
McKee worked to draft a critical acceptance criteria document for the oil pan casting using finite element analysis data as a guide. This document outlined where various imperfections could or could not be found on the casting, according to the application requirements. “We knew where high stresses were and where defects absolutely could not occur for salvage filling surface defects in the casting,” McKee said. Aarrowcast worked with the CCOE and John Deere Product Engineering to define the acceptance criteria that ultimately helped achieve higher throughputs.
“This part has to be ultra clean because it has to meet engine criteria,” Smith said. “But in some cases, we were putting too much work into the part than was needed in finishing.”
Additionally, the machining strategy was later adjusted to put all the machining locators on the drag side of the mold where all the cores are set. Previously the locators were on both sides of the parting line and caused excessive part-to-part variation through machining.
Now the part runs smoothly through Aarrowcast’s operations and machining processes, and both customer and suppliers are pleased with the results.
“Aarrowcast is happy with the business, and we are happy with their part of the business,” McKee said. “And now the machine shop is happy because they get consistency from part to part.”
The lessons learned from the collaboration on this project have not been lost on the metalcasting facility. Throughout development and into production, engineers from John Deere and Aarrowcast met face to face and electronically to work through several iterations with a goal of achieving sound metalcasting practices to meet the application’s requirements.
“We probably would not be in production if that level of effort was not put in up front,” Smith said.
Olson can’t imagine not establishing similar collaboration on future new projects. “Put it this way, if our customer doesn’t hold a design review with us, we’re holding it with them,” he said.