Professional profiles: General Industry Coverage

Grinding a complex cutting tool can be, well, complex. And defining what makes a cutting tool complex can be challenging too.

“A complex cutting tool is generally defined by the tool profile and its tolerances,” said Paul Ehrlich, senior applications engineer for grinding machine builder United Grinding North America Inc., Miamisburg, Ohio. “You really need to take both of those parameters into consideration, because you might have a wide open geometry with a tolerance of two or three thousandths, and that’s not a big deal, but an odd shape, even with a looser tolerance, would be complex.”

The Walter Helitronic Vision grinding machine produces rotationally symmetrical tools and parts with complex geometries. Image courtesy United Grinding North America.

Bill Freese, president of grinding machine builder Rush Machinery Inc., Rushville, N.Y., concurred, adding that multifunction tools, which may feature geometries intended to serve multiple purposes, are also complex.

Toolmaker and machine tool builder Star Cutter Co., Farmington Hills, Mich., expands the definition of complex to encompass anything outside of its normal range, noted Paul Schulte, manager of advanced technology.

“We view ‘complex’ as a tool with more than one diameter or a tolerance that is tighter than our off-the-shelf products,” he explained. “Our customers serve the automotive industry, which covers a range of tooling, so anything outside of that would definitely be complex.”

Software Solutions

While some disagree about what is the most important factor when grinding tools with complex forms, software always plays a big part in the discussion.

“You must ensure that whatever you see in the software is what comes out of the machine,” said Frank Holubeck, president of Reinecker Grinders, Pompano Beach, Fla., which sells grinding machines from German builder Ulmer Werkzeugschleiftechnik GmbH & Co. KG. “We urge our customers to spend time designing tools and running 3D simulations in NUMROTO software so blanks aren’t wasted. Carbide is expensive, so we want to make sure we are right on the screen, our machine is set up properly and the wheels are dressed properly. It’s not a time for trial and error.”

“The machine tool is not going to be the problem,” added United Grinding’s Ehrlich. “All toolmakers have 5- or 6-axis machines that can interpolate the most complex geometry you can think of. The real questions are, does the software possess the ability to process that kind of geometry, and can you produce the tools consistently?”

Radiac says its STARTEC XP-P abrasive reduces cycle times when grinding the flutes of round tools through effective profile retention, minimized tool deflection and reduced machine load. Image courtesy Radiac Abrasives.

United Grinding’s tool grinding machines utilize proprietary grinding software, which imports CAD drawings and feeds toolpaths to the machine. According to the company, what sets its software apart is specially developed correction software called FTC (Form Tool Compensation), which feeds data from the company’s Helicheck CNC measuring machines into the grinding machine’s CNC.

“If there are any deviances in the tool profile beyond a certain, predetermined tolerance, the Helicheck will correct the shape of the profile, and FTC will send that corrected shape to the grinder,” he explained. “A CNC grinder can usually be accurate to ±10µm; if we are checking regularly, we not only can account for variables like wheel wear, we can reduce that tolerance to ±3µm.”

In addition, whereas tool design and production were previously treated as separate processes, customer demands for high repeatability has led to the grinding process becoming more integrated with the design process, said Jason Walter, plant manager for the machine tool operations at Star Cutter. “We want to create an accurate simulation, and then we want to take that simulation and bring it to the shop floor as quickly as we can. The goal is keeping control over the process from beginning to end, without having to hand off the job from one point in the process to another.”

Wheel Be Back

Grinding wheels, of course, are a key part of making complex tools. “Obviously, you want a grinding wheel that is going to have good form-holding qualities, good mrr and be well balanced with excellent axial and radial runout.” said John Guenther, business unit manager–cutting tools for Radiac Abrasives, Oswego, Ill. “That means the tool you’re making plays a part. A small-diameter tool will be more vulnerable to pressure from the grinding wheel, so you won’t be able to really push the wheel the way you might on a large tool. Larger tools are a bit more forgiving, so you can shoot for a higher mrr.”

Wheel selection, added Rush’s Freese, also involves the tool geometry and determining the proper grit size, core material and bond.

“When you’re working with complex profiles, the grinding wheel itself becomes critical,” he said. “You are trying to hold a lot of tolerances in a lot of areas, and the more complicated the geometry, the more those come into play. We supply the machines for dressing and truing the wheels to do the job, because more complex geometries can require a more complex shape on the wheel itself.