'Lean' boosts brake drum, hub production: Illinois firm relies on cells with VMCs and twin-spindle VTLs.

Established in 1960, Cherry Valley Tool & Machine has, grown into one of the country's leading manufacturers of cast iron and steel parts for heavy-duty trucks and agricultural and construction equipment. Specializing in medium- to high-volume production runs with just-in-time delivery and armed with several contracts requiring expanded capacity, Cherry Valley moved into a modern, 120,000 square-foot facility on 11 acres in Rockford, IL, last year.

Roger Ackerman, vice president and general manager of the company, took this move as an opportunity to purchase new machine tools and lay them out in a lean manufacturing concept to yield a high rate of production for meeting the delivery schedules for brake drums and hubs needed for Mack, Peterbilt, Kenworth, and many of the other 18-wheelers that keep our nation's commerce flowing.

The lean concept begins at the back of the building, where 3,500 drum and hub castings are delivered daily and arranged in palletized stacks that dwarf the bustling forklift trucks in the raw material staging area. From here, pallets of the 150-lb brake drum castings and 60-lb hub castings are shuttled to two lines of Doosan twin-spindle vertical turning machines.

The first line of four machines, as well as the first two machines in the second line, is dedicated to the drums. Two other twin-spindle vertical turning centers in the second line are coupled with Doosan REVO vertical machining centers to produce the hubs.

"We looked at several machines out in the marketplace that were similar in capabilities and work piece area," says Ackerman, "but in terms of the investment cost, the quality, and the service reputation, I felt that Doosan was heads and tails above the others. We also liked the idea of two independent spindles on each machine because, in our 'lean' concept, if one spindle should be down for any reason, such as a broken tool, the other spindle keeps on producing. Right from the beginning, Doosan engineers worked side-by-side with us to reconfigure the machines' capabilities to optimize the performance of the operations we needed to achieve maximum throughput of our drums and hubs."

Castings at the ready

Forklift drivers keep three skids of raw castings at the entrance to the lines at all times to eliminate lack of product supply. The Doosan model V740T vertical turning centers selected by Ackerman offer 29" turning diameter and 30" turning height per spindle. They feature hardened and ground box ways for long-lasting precision, as well as Hrc 55-hardened and ground turrets for excellent rigidity and accuracy. A reduction gear on the ballscrew provides more thrust when needed during heavy turning operations.

Each vertical turning center at Cherry Valley has its own hoisting crane for loading and unloading pans. The two spindles of each machine are loaded separately so that one is always is running while the other is being first unloaded and then loaded with a new casting. This optimizes in-the-cut uptime on the machine. Identical operations are performed on each spindle, using carbide and silicon nitride tooling and special Cherry Valley-designed work-holding fixtures that permit machining all sides of the part in a single setup. The top of the 12" high, 19" diameter brake drum is faced, top and bottom, and the ID and OD are turned, and the outside of the drum and the "squealer band" surface are turned.

As the drums come off the vertical turning centers via hoist crane, they continue down the line to manual drilling machines, one assigned to the output of each turning center. After locating holes are drilled, the drill operators clean each drum, perform quality inspection of the holes and diameters, and apply a rust preventive before swinging the drums onto waiting pallets.

At the two "hub cells," each containing a Doosan V420T vertical turning center and a Doosan REVO vertical machining center, a forklift is kept busy delivering a supply of raw hub castings and retrieving the finished hubs. The Doosan model REVO 4020 vertical machining center was chosen for its rugged, high-performance reputation. It has a highly rigid structure with a boxed column and single cast bed that provides stable precision. Its 10,000-rpm spindle achieves high speed milling, drilling and rigid tapping with high cutting accuracy.

Reaching nuclear speed

On the first spindle of the turning center, the hub is faced and bored. The part is then "flipped" and brought to the second spindle, locating the bores onto the spindle fixture. After finishing operations, the OD is turned, including a very demanding interrupted cut. "There are four fins that protrude from the part that are included in the turning operation," says Ackerman. "This interrupted cut is taken in stride by the Doosans, and they hold a tolerance of 0.0015" on those fins with spectacular consistency."

After turning, the hubs move on to the REVO machining centers, where they are fixtured for finishing. The first operation here is a ten-hole bolt pattern. "The REVO does this at what I call 'nuclear' speed," says Ackerman. "The holes are 1" in diameter and 2" deep. The machine drills each hole in less than four seconds. The material removal rate is fantastic."

Next, a smaller, six-hole bolt pattern is drilled, counter-sunk, and tapped. "This is where working with good tool engineers pays off," says Ackerman. "High-speed rigid tapping in cast iron can be difficult. Hardness can vary and abnormal amounts of casting sand can be present. The tool engineers work with us to determine the optimal feeds and speeds to keep up with the machines' capabilities for fast throughput."

Cycle time in the hub cells is less than three minutes for turning and machining each hub. As they come off the REVO, they are cleaned, inspected, and placed on pallets. The omnipresent forklifts shuttle the pallets to the shipping department, where they are banded and shrink wrapped to keep them from shifting during transit to the customers.

Quality is the issue

Quality control is paramount at Cherry Valley. There are five employees in the QC department, with two people assigned full time to the lean lines, double-checking the in-process verifications made by the operators. All the bores and fins of the hubs are verified 100 percent because of the close tolerances demanded. The outside diameters are checked one in four. The last hole in each bolt pattern is checked to verify the accuracy of the entire pattern. On the brake drum line, checking is 100 percent. Verification paperwork generated by the inspections for every part is conveyed to the QC department and serves as a statistical process control (SPC) report card, which is kept on permanent file.

Walking through the plant, a visitor gets a good look at the obvious productivity that has resulted from Cherry Valley Tool & Machine's lean concept that includes lean warehousing. At any one time, some 7,000 drum and hub castings in various stages of manufacture are stacked in a long line under the cavernous ceiling. Within 48 hours, all of these will be replaced by 7,000 more. The line stretches from the delivery door for raw castings at the back, across the lean rows of machines and cells, and up to the shipping door at the front. Eight tractor-trailer loads of castings are delivered every day, and eight tractor-trailer loads of finished drums and hubs are shipped every day.

Cherry Valley Tool & Machine may be successful in lean manufacturing, but they are far from lean in their prospects for their future. "We are considering new contracts that will call for additional lines and cells of Doosans," says Ackerman. "We've proven to ourselves that the line-and-cell configuration achieved here will serve as a blueprint for our continued growth and success." Doosan Machinery America Inc., www.rsleads.com/509tp-163