Controlling the Process

Using Siemens' CNC technology on advanced machine tools helps Forest City Gear remain an industry leader worldwide.

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Gear manufacturers have always embraced the latest technologies, constantly fine-tuning their operations to eliminate glitches and optimize efficiencies. This has become even more important in recent years, with an economy still struggling toward recovery and competition from around the world becoming increasingly aggressive. In response smart companies streamline their production processes, explore new markets, and invest in the most cutting-edge technologies to be found. When it comes to gear manufacturing equipment, that would include controls from the Siemens CNC group

Changing Times
First a little background. Roscoe, Illinois, is home to many more gear companies than your average town of 10,000 people, but the reason is obvious. During the peak of the machine tool boom in nearby Rockford it was critical to have these important components made locally. Over the years that market has changed, and so have the gear companies here, each taking its expertise in other directions to offset the decline in local machine tool building.

Forest City Gear took a different track to remain competitive. “We decided long ago to do two things,” according to Fred Young, CEO. “First, to make the very best fine and medium coarse pitch gears in the world, and to do so by using the best machines, people, and quality assessment practices possible. Second, and just as important, we became committed to reinvesting our company’s profits in newer and better machinery, based on the global standards and the ongoing technical advancements made by machine tool builders around the world.” Figure 1

This precision gear and spline maker performs nearly every aspect of production in-house, including blanking, turning, hobbing, shaping, milling, gear grinding with form wheels and generating grinding, thread grinding, broaching, honing, straightening, laser marking, magnetic particle inspection, metal-etching, CMM, hardness testing, and final surface inspection. Forest City Gear continues to subcontract heat treating and plating. The blanking department, though relatively new, has been expanded several times to keep pace with increasing production. The company boasts nearly every leading brand of gear-making machine tool on the world market, Young says. “We really do put our money where our mouth is, to use that old expression. In a typical year we invest between 25 and 40 percent of our gross sales back into better gear machines and metrology.”

Sophisticated Solutions
Among the most advanced gear-making machines in this shop are four Gleason shapers and two Samputensili grinders (form and generating style), plus a Hoefler gear grinder. All these machines have something in common. At the heart of any machine tool, of course, is the CNC that drives it, controls the motion, and detects and integrates all the cutting parameters, feeding back that information to the computer logic of the control to ensure the part being made is as close as possible to the programmed specifications. Meanwhile, the ergonomic or operator-to-machine interaction must always be considered, because a control that’s too difficult to learn and use will result in substantial and costly delays in production. While Forest City Gear has a healthy mix of longtime and newer employees who all bring a variety of computer knowledge and machining skills to the job, this company has consistently sought the most advanced equipment on the market as part of its “Excellence Without Exception” motto and its practical desire to stay ahead of the competition in the global gear market.

The control on these machines is the Sinumerik 840D from Siemens, with specialized gear software. “The extensive gear software developments available are quite remarkable,” Young says. “Most have been a cooperative venture between a machine builder, the CNC builder, and folks like us. The result has been software that’s specific to hobbing, shaping, gear grinding, and thread grinding.”

He also notes features of the Siemens CNC that have yielded positive impacts on production, including “sophisticated executive software for all machine movements and the fast program reading that allow us to cut and grind much faster, with more options such as reverse direction, segment cutting, and combined operations when compared to other controls we see.” Figure 2

Typically the CNC is used for all axis, rotary, and spindle movements, and the machine operators particularly appreciate the multiple standard cycles for cutting with degressive feeds, increasing speeds plus special cycles for gear tooth removal and reversing directions to improve finish or reduce cutter wear.

As is the case with many gear manufacturers, Forest City Gear cuts a wide variety of standard and exotic materials in the production of its gears and splines. These include titanium, Inconel, 4340, 300M, Vascomax 250 and 300, Nitralloy 135M, 9310, 4150, 4140, 8620, aluminum bronze, 13-8, 15-5, 17-4, 316 and 440 stainless, Hastelloy, Ferrium and numerous thermoplastics. The shop can carbide rehob to 60-62 RC, and gear grind at all hardnesses.

Rave Reviews
Kevin Chatfield, a longtime Forest City Gear employee with 20 years’ CNC machine experience, works with the Samputensili grinders and says “I’ve used all the brands of controls we have here, and for many jobs no other control can do what the Siemens 840D can do. One example would be the internal, external, and form grinding I do on the Samputensili machine. If the other controls could perform these operations at all, which is doubtful, it would be a very slow process.” Figure 3

Mark Cunningham, a 12-year veteran of CNC, runs the Gleason machines and notes the controls are very user-friendly. “The screens are easy to program and modify, then you get a clear picture of what’s happening at every step in the cycle. The precision is so good we sometimes need to ‘lie’ to the program to get what we want from the machine.”

Brian Turnbull—a newcomer to Forest City Gear but a longtime machinist—had worked with a competing brand to Siemens CNC and was initially hesitant. “Then, as soon as I saw the easy layout and how quickly it could be set up and put into action with no trouble navigating at all, I was convinced that Siemens was simply a better control.”

Young makes one last point about the CNCs on these machines. “These machine tools produce our most complex parts, including helical splines and internal gears that most other shops simply cannot or will not make,” he says. “The cycle and program read times on the Siemens controls are critical to our production work, plus these are the most expensive machines in the shop, so their run-time cost is the highest. Most of our jobs, though not all, are short runs on very expensive materials. If the machine takes too long to complete the first part or has repeat rejects we lose money, it’s that simple. I’m proud to say that neither our operators nor our production supervisors allow that to happen. And the controls on the machines are a big reason why we stay so successful in achieving that accuracy and consistently good part production at Forest City Gear.” Figure 4

Conclusion
The company has remained among the leaders in the market for high-precision gears owing to this strategy of buying the best machines, hiring the best gear-makers available, and verifying the output of this 100-person shop by using the power of the industry’s leading quality lab, which occupies a cleanroom-level environment in the middle of the factory.

“We do checking of our gears and splines at various test stations located throughout the shop, but the final proof resides in our quality lab,” Young says. “Our equipment is so sophisticated, even our competitors often bring us their work to have it checked. It’s one of the things that’s led to our current customer base of about 400 companies, about 20 percent of whom are other gear companies or gear producers themselves.

“Most of the best gear-making machines in the world use Siemens CNC, and I’ve seen a lot of them in my time,” he says with a laugh.