The Woodstock LucasVarity Div. of Kelsey-Hayes (Woodstock, Ontario) is basically a large machining operation for turning out brake components—disk brake rotors, brake drums, and hubs—for customers including Ford, Chrysler, GM, Isuzu, and Mazda. It's largely turning high volumes of brake components from gray cast iron.
During the plant's history, there has been an array of manufacturing equipment utilized. Among the latest technology are nine cells consisting of vertical turning machines built by Hessapp, a German machine tool manufacturer, sourced through Turmatic Systems Inc. (St. Louis, MO), a company of Thyssen Production Systems. Each cell consists of a 400 DVH single-spindle machine and a 400 DVT two-spindle machine; the machines are connected by a belt conveyor. The conveyor is adjustable for the various workpiece configurations (e.g., hubs are high and narrow while brake disks are wide and flat) with a quick-adjustment feature.
|Here are rough blanks entering the first machine ...|
Typical brake disk machining in the cell often takes place in three chuckings. The first and second operations are performed on the twin-spindle 400 DVT. The DVT features a traveling spindle. It picks up the workpiece from an incoming conveyor, positions it above the turret, then the bottom of the workpiece is machined. Next, the traveling spindle transfers the workpiece to an upward-facing stationary spindle, positioning it for the top of the workpiece to be machined. When these two operations are complete, the part is unloaded by a gripper mounted on the tooling and transferred to the self-loading and unloading DVH 400 for the final chucking and finishing operation.
Achieving High Quality
Typical quality-related specs include: repeatabilities of 0.000098 in. (2.5 microns); standard C-axis positioning accuracy of ±3 arc seconds; and feedrates programmable in 0.00004-in. (1-micron) increments.
"Tolerances are getting tighter by the week to the point where they're difficult to measure," says John Bond, engineering manager at the facility. "It's not a question of being able to produce to these tolerances, it's more a question of being able to measure what you've produced. But at the end of the day, you've got to produce what the customer requires."
Bond refers to a program Woodstock is currently engaged in with one of its major customers: to achieve the tightest tolerances ever achieved on a brake rotor. "We're the pilot plant on this program because others thought the tolerances were impossible to turn. We can achieve these tolerances, and this will give LucasVarity a significant edge on our competition."
While he is unwilling to say just how tight the tolerances are, he does reveal, "We can turn tolerances with the CNC Hessapps that you can't achieve with grinding."
"About half the product line is now done on the Hessapps," Bond says. That's no small amount. "Our volumes run about 9- to 10-million parts per year," he explains, adding, "The thinking here is that the Hessapps are the technology for the future."
Making the Choice
|...the first chucking...|
|...is followed by the second, wherein the bottom is machined...|
|...then the second machine receives the part for finish machining...|
The selection of the Hessapp verticals—based on an understanding that the selection would have an effect on what would be used for some time to come—wasn't made lightly. Jim Findlay, manager of the Advanced Manufacturing and Engineering Group at the facility, explains that two years were spent assessing capital equipment for their requirements. "The group, with some plant operating personnel involvement, reviewed more than a dozen different equipment manufacturers. At the end of a very thorough, intensive investigation, Hessapp came out clearly on top."
A large part of the reason why the machines were selected relates to the fundamentals of the equipment. First up, by being verticals, the footprint is small. Chip disposal is not a problem. For automatic loading, there is the benefit of gravity. Bond adds, "But most significant is vertical turning's remarkable spindle accuracy, which gives us excellent control of our tolerances and this provides us some advantages others simply cannot meet.
With regard to the specific machines, Bond says, "We have a 50-hp [35-kW] spindle in these machines, and we can machine a rotor just over 6 in. [150 mm], and then, in a very short time, we're able to changeover and machine a rotor much larger, close to 14 in. [350 mm]."
But what about the brand? The Hessapp nameplate isn't widely known in North America. Bond points out that the name is well known in Europe, "where vertical turning is well accepted and where Hessapp has a large customer base, including Volkswagen, Mercedes, BMW, Fiat, Opel and others. So there was no technology risk at all."
What's more, the companies worked closely together to assure that (1) the equipment was up and running quickly and (2) that the equipment was kept in operation.
A Demanding Task
|...where the parts end up like this, with some additional drilling and tapping to be done.|
About the first, Findlay recalls, "In 1997, Woodstock undertook seven major product launches simultaneously. These were rotors and hubs for various customers. New machines and lines had to be installed and proved out. Equipment had to be debugged. Parts had to be run and tested to customer spec. And each of these launches was `job one' and had a firm deadline. A single new launch is tough enough, but committing to seven was really sticking our neck out." The machines began arriving from Germany. "We just put them on the floor, arranged them in cells, started them up, and began making parts. In the end, we hit every launch on time, on target, and that's something we're very proud of."
With regard to keeping the machines up and running: "We've an arrangement with Turmatic Systems," Bond says, "for a supply of Hessapp spare parts to be on the shelf in Michigan"—in a service base they've established in Brighton—"dedicated to the needs of LucasVarity, which is the largest Hessapp user in North America, with some 55 to 60 machines."