At the largest factory for the world's leading agricultural equipment suppler, building a team to re-develop manufacturing processes hiked throughput on gray cast iron parts. John Deere Waterloo Works in Waterloo, IA forged a close working partnership between manufacturing engineers, a machine tool builder, and tool supplier Sandvik Coromant. The team members were charged with making best use of new machining centers to reduce cycle time and hike productivity. "A large part of our productivity improvements came from new milling technology from Sandvik," explains Kallin Kurtz, project manager for cast iron redevelopment.
The coordinated approach to reprocessing and modern milling tools eliminated excess manufacturing steps on a precision transmission cover. The productivity improvements yielded reductions in cycle time and cost improvements. A broader Productivity Improvement Program is also pursuing plant-wide savings in other operations.
John Deere Waterloo Works produces the large tractors that have come to symbolize John Deere around the world. In one manufacturing location at the plant, the company builds drivetrain components for Series 7000, 8000, and 9000 agricultural tractors. Deere is in the middle of a complete redevelopment effort in Waterloo. One initiative targeted for improvement is the time-intensive manufacturing of the transmission manifold and its mating cover.
Kallin Kurtz, right, project manager for cast iron development at
John Deere Waterloo Works examines a transmission cover with
Sanvik Coromant representative Curt Brown. A team of John Deere
and Sandvik Coromant experts instituted productivity improvements
that boosted transmission cover productivity 34%.
"We are deploying newer technologies in machines and tooling to maximize our flexibility, competitiveness, and utilization, " says Mr. Kurtz. "We purchased new machines, we also had to become more innovative in our tooling and processes."
The transmission cover was previously manufactured on purpose-built machines using ISO-standard square shoulder mills and other vintage tools. Each part also required multiple processing steps with lots of manual material handling and inspection.
"There are tremendous efforts to reduce the amount of non-value-added work that our wage workforce is doing," says Mr. Kurtz, "and we tried to focus on reducing total cost through tooling."
Flat And Accurate
The transmission cover is approximately 37 in. long by 50 in. per side. The part is first rough-milled to a 0.2 in. depth of cut over the full surface and then finish-milled within 0.006 in. flatness. The same rough and finish cuts are repeated on the other side. "This part is very touchy because of the mating parts and the hydraulic valves driven out of the transmission cover," observes Mr. Kurtz.
Improving transmission cover throughput without compromising tolerances required a new approach to tooling and machine tool suppliers. Sandvik Coromant representative Curt Brown listened to their redevelopment goals and total cost focus.
"I met with engineering to get a list of the tools, not knowing the exact machining centers," he recalls. Deere Waterloo Works ultimately selected a Mori Seiki MH-633 horizontal machining center and sought to introduce the new machine and its new tooling simultaneously.
The process redevelopment effort called upon the tool and machine suppliers to recommend improvements. I set the expectations at the front end of the project, and if they had improvements on those expectations, they offered alternate suggestions." Mr. Kurtz explains.
A 3 in. diameter CoroMill 290 with six Sandvik Coromant Grade 3020
carbide inserts enabled John Deere to use their new horizontal machining
center to full capability. Roughing cuts ran about twice as fast as
old-technology cutters on previous machines.
Mr. Brown noted, "One of the main cycle-time drivers was the milling of the top and bottom of the part. To achieve the desired cycle time reduction, we had to maximize material removal rates." Based on experience and trying to specify standard rather than special tools, Mr. Brown suggested the CoroMill̉ 290 facemill with new screw-down carbide inserts for roughing and screw down silicon nitride inserts with one CBN wiper insert for finishing.
The abrasive gray iron used by John Deere must initially penetrate even harder scale. "Because of this, we stayed with carbide for rough milling and ceramic for finish milling," states Mr. Kurtz. Compared with carbide cutting inserts, the heat- and wear-resistant ceramic inserts promised longer productive life at higher cutting speeds for finishing. Tooling costs typically account for just 3 to 4% of overall machining costs, longer life pays productivity dividends in more parts between tool changes. Sandvik Coromant Grade CC6090 is a pure silicon nitride ceramic optimized for high cutting speeds in gray cast iron.
Maximize The Machine
While the old process used silicon nitride inserts, the 6 in. diameter ISO-style
milling cutters would be unable to exploit the full power of the new machining centers. The CoroMill 290 concept cutter is precision machined from hardened steel to minimize runout and withstand heavy cutting loads. In addition, screw-down inserts are more
accurate and stable than traditional clamp-in designs. Self-locating, screw-mounted inserts with carbide shims locate edges precisely and protect the cutter body. Mr. Brown explains, "The combination gives you better repeatability with no presetting, and more flexibility in cutter choices."
A 3 in. diameter CoroMill 290 with 10 Sandvik Coromant Grade 6090 silicon nitride inserts fit the new machine work envelope. The new tool also made it possible to use the new machine to full capacity, and Sandvik Coromant specialists suggested preliminary machining data. Mr. Brown recalls, "We provided them with speed and feed recommendations for the tooling based on earlier success making different parts on the same type machine." Roughing cuts ran at 1280 SFM with about a .014" chip load a load much heavier than in the previous processes.
Combination Milling
Finishing cuts called for an innovative combination milling approach. To achieve a fine finish at higher milling speeds, another CoroMill 290 cutter mixed six silicon nitride inserts with a single CB50 cubic boron nitride (CBN) insert. Extended 0.0005" in. beyond the silicon nitride inserts, the CBN edge presents a wiper geometry with an
extended face continuing after the cutting nose radius. The leading edge removes metal and produces a surface roughened by peaks and grooves. The extended face remains in contact with the work to wipe down or burnish away the peaks. The effect is a finish twice as smooth at the same surface speed or equally smooth at twice the surface speed. John Deere and Sandvik Coromant engineers ran finishing cuts at 3,500 sfpm, again, about twice as fast as the old process. Feed was 0.006 in. per revolution. "We're maxing-out the machine RPM and feed rates on some of these cuts," notes Mr. Brown. The parts emerged from the finish cut with a mirror finish. "We achieved better flatness and better finish," observes Mr. Kurtz.
To achieve a fine finish at higher milling speeds, another CoroMill 290
cutter mixed six silicon nitride inserts with a single CB50 cubic boron
nitride (CBN) insert. The effect is a finish twice as smooth at the same
surface speed or equally smooth at twice the surface speed.
Better Tools, Better Process
The two-step process enabled John Deere Waterloo Works to cut cycle time on the transmission cover by 34%, exceeding the original expectations.
Sandvik Coromant teams also provided training for John Deere operators and the machine tool builder. Cutting tool training teaches users milling theory and how to approach the part. It addresses tool maintenance and how to identify tool wear.
The successful partnership on the transmission cover led to a broader Productivity Improvement Program. Sandvik Coromant applications specialists routinely team with manufacturers on several hundred Productivity Improvement Programs a year. Experience shows that partnerships boost throughput 20% on average and trim up to $500,000 a year in machining and maintenance, repair, and operating costs. The program at the John Deere Waterloo Works is aimed initially at axle housings and will extend to all components in the cast iron operations. Mr. Brown explains, "We're trying to anticipate what Deere will need one, five, 10 years from now. In doing so, we can help the company reduce costs and improve cycle time in their manufacturing processes. The idea is to listen to them and work together to achieve their goals."
Mr. Kurtz concludes, "We're moving towards a lean manufacturing environment and sticking to our three main goals - maximum flexibility, maximum asset utilization, maximum cost effectiveness." |