Simplifying the Daily Grind

Advanced software tools and data analytics help streamline grinding processes

Eñaut Arrizabalaga, senior commissioning engineer at Danobat Group, probably speaks for all top machine builders when he says the company’s human machine interface (HMI) is designed to free the operator from needing any specialized CNC programming knowledge. Advanced software also eases, and sometimes entirely automates, other grinding challenges.

Danobat, which has its United States headquarters in Rolling Meadows, Illinois, offers a wide range of grinders and hard turning machines, all using the company’s DoGrind+ HMI. In addition to the machine interface, customers can use the “offline version to create part programs and export them to the machine easily,” Arrizabalaga explained.

One notable module makes eccentric outer diameter/inner diameter (OD/ID) grinding a snap. This “forms module” includes predefined shapes such as P3G and CAPTO, and operators can import a profile defined by a CSV file, which Arrizabalaga said can be in either polar or Cartesian mode. The latter defines points in X and Y; while in the polar mode, each point defines an angle and a radius. Or, “you can define a few parameters like the diameter or radius and so on, and it automatically creates the shape. Once the form is created, the programmed shape can be visualized in the software,” Arrizabalaga said.

For example, many mold and die applications require the generation of complex profiles developed through formulas, polynomials or other strategies that the machine software must simplify for the user. Danobat provides an interactive graphical environment to create and edit these profiles, as well as “visual guarantees” to ensure the trajectories that the machine will execute are the desired ones. The Danobat software also includes “geometric and grinding process parameters to reduce the final form errors,” added Arrizabalaga. “Once you create the first part, you can use different acceleration velocities for each area of the grinding to improve the final shape and the grinding process of the eccentric part.”

Thus, a CNC programmer isn’t needed to create difficult forms. As an example, Arrizabalaga cited engine assemblies produced by a major American aerospace engine manufacturer. “Several components of these engines have non-round, eccentric areas,” he said, noting that one of the most complex is a scalloped surface on the compressor stator that DoGrind+ makes easy.

In hydraulic applications, Arrizabalaga continued, “it is often common to encounter challenges beyond very tight dimensional and geometric tolerances. In countless applications, the matching of different parts becomes a fundamental requirement for the proper functioning of the final solution, and that is where applying match grinding strategies adds value.”

Danobat’s software includes traceability functions that track the dimensions obtained in grinding “Type-A” parts and then performs subsequent grinding operations on “Type-B” parts with optimal dimensions for a perfect match. “The software greatly facilitates the processes, keeping full control of the correlation of the parts and, if necessary, transmitting output and qualitative data to the company’s production control systems,” he added.

Danobat’s HMI also features a module to create and edit a wheel dressing profile. “It’s similar to a turning profile, and we use this profile editor in our machines that have turning capability,” explained Arrizabalaga. “We can use the same segments of the model to create the path where the turning tool will cut the part, or the dresser will dress the wheel.”

That’s a natural marriage, because it’s often the case that a manufacturer would want to finish grind a profile that has been turned. One such example, cited Arrizabalaga, are vertical grinding machines with turning capability in which the user wants to dress the wheels to grind specific areas on bearings.

As with the forms module, the profile editor requires no special programming or trigonometric knowledge. “The operator can easily edit the profile following the part drawing, and he can see the profile while editing to ensure the programming is correct,” Arrizabalaga said.

Previous versions required operators to define start and end points for each segment, and the angle, often requiring mathematical calculations. Now the software can automatically calculate any intersections and the related angles. The operator can also simply import a profile defined by a DXF or similar files.

Silicon carbide (SiC) chip manufacturing is coming back to the U.S. in a big way, subsidized by billions of dollars in government funding. And several key players are looking to Miamisburg, Ohio-based United Grinding North America Inc. for clever solutions to some of the field’s tricky problems.

Doug Emerson, a United Grinding regional sales manager for its cylindrical grinders, explained that long before silicon is sliced, cut and etched into tiny integrated circuits, the raw material is grown in a quartz crucible. What comes out is an ingot measuring about two to three feet (0.6-0.9 m) in length and 12 inches (305 mm) in diameter, with a dome at each end comparable to the shape of a rugby ball.

The ingot is chemically pure, but highly anisotropic. In other words, the structural and electronic properties of the crystal vary significantly depending on their orientation. And you can’t predict the orientation of the crystal plane beforehand. That’s where the fun starts.

Historically, the useless dome ends would be cut off with a diamond saw, noted Phil Wiss, regional sales manager for United Grinding’s profile grinding division. “That’s about a three hour process. And a good diamond saw costs in the range of $2 million.”

The ingot is then cut into 4-inch (101.6-mm) thick segments. In the next step, each segment is X-rayed and calculations are made to determine the lay of the crystal plane. That data is used to figure out how to shim each part so that a simple surface grinder can be used to flatten the end such that it’s in line with the crystal plane. That’s another time-consuming, and risky, process, Wiss observed. “An operator would have to write down the data from the X-ray, and then hand type that into the control. A decimal point is everything here … there’s a lot of opportunity for error.”

Wiss claims United Grinding offers better solutions for almost all these challenges. Take the process of cutting off the 2" (50.8 mm) dome at the end of each ingot. One of the company’s creep feed grinders would tackle that two to three hour job in 15 minutes, according to Wiss.

And rather than trying to achieve the correct part alignment with shims, based on off-line X-ray data, United Grinding has integrated X-rays into its five-axis Blohm Profimat MC and Mägerle MFP 30 machines. On either model, the X-ray and associated software automatically determine the orientation of the crystal plane, and then the machine uses multi-axis interpolation of the worktable such that it grinds parallel to the plane. “We’re taking all the troublesome calculations and data entry out of the operators hands,” Wiss said.

The application calls for diamond wheels, Wiss said, adding that United Grinding is open to using anything from resin bond to vitrified or plated.

“We’ve even used some segmented abrasives. Most of our grinding is using the periphery, but we do have a customer that prefers a swirl pattern on their part, so we grind with the side of the grinding wheel. We have all the capabilities and develop the process around customer preferences.” For example, the Mägerle MFP 30 would include a wheel changer to enable the application of multiple abrasives on the same part, if desired.

Once the segment is flat on each end, it typically goes into a cylindrical grinder. United Grinding’s Studer brand offers a sophisticated solution here.

“We integrate an X-ray into one of the tool positions in the wheel head, which rotates on the B-axis,” Emerson explained. “The wheel head swings around to position the X-ray relative the part, and then the machine’s C-axis workhead aligns the part to where the crystal structure is best suited to deliver the desired chip performance.”

These parts often require a flat on the OD, which Studer would create using an OD wheel and its out-of-round grinding software, Emerson added. To grind a notch, which is another frequent requirement, Studer would use a horizontal wheel mounted in a third position in the wheel head.

The transition to electric vehicles (EVs) is also boosting the demand for grinding, due to changing noise issues. “When you drive an electric vehicle you suddenly hear sounds from the transmission and elsewhere that you never heard before because your gas-powered engine would have drowned them out,” Emerson explained. “Our Canadian distributor said a sound from the back of his Tesla was driving him crazy, because he couldn’t figure out the source. It turned out to be two coins rubbing together that his kids had left in a cupholder.”

To address such issues, automakers are tightening tolerances. And transmission surfaces that used to be turned now must be ground.

One example: An input gear with a face, plus two IDs and an OD that must meet the H6 tolerance, all with a surface finish of 0.8 µm. Such an application would require something like a multiple wheel-head Studer S33, Emerson explained. But for simpler OD-only projects in the EV space, Studer has introduced the S36. By limiting configurations and the related engineering, the S36 is packaged to satisfy automotive suppliers that focus on cost per piece.

One of ANCA Ltd.’s latest contributions to tight tolerance grinding is a patented technique called Motor Temperature Control (MTC). Grinding generates heat, and heat causes spindle growth. Likewise, any changes in temperature, owing to downtime or changing from one operation to another, would cause enough variation in spindle size to affect part size. MTC controls the temperature by varying the current to the motor, while maintaining the required torque and speed for grinding operations.

MTC avoids the cost and complexity of a separate liquid chiller system, yet keeps the spindle to within 0.5° C, virtually eliminating spindle growth and achieving grinding accuracies within a few microns, according to the company.

The system also achieves a steady state within five minutes, eliminating the need for a lengthy warm-up cycle at the start of a shift. MTC is built into the motor spindle drive firmware and requires just a few pieces of reliable hardware, such as an electronic choke, so it’s essentially maintenance free. ANCA has added MTC technology to three models requiring the utmost precision, including its CPX pinch-peel grinder, GCX skiving cutter grinder and MX7 Ultra tool grinder.

Applications Engineer David Goolsby reported running batches of 75 tools or more in the ANCA CPX with a diameter variation under two microns. The machine also delivers a better surface finish with a D91 grit wheel than some machines manage with a finer grit D64 wheel, he said, attributing the improvement to the inherent vibration dampening of the pinch-peel process and the machine’s unique steady rest.

“It’s a simple design, without a lot of moving parts that can cause issues,” Goolsby said. “And it’s extremely stout and bolted right into the foundation of the machine’s polymer concrete base, rather than being free floating and on a moving apparatus like competing machines. There is very little opportunity for vibration to enter the process.”

As for the GCX, the push toward EVs is driving the need for skiving cutters with tolerances under 0.0001" (0.0025 mm). “I’ve even seen prints with plus or minus one micron,” Goolsby said.

Lower interest rates typically leads to increased homebuilding, and therefore greater consumption of woodcutting tools. United Grinding is focusing more in this area with software improvements that ease production of carbide blades and brazed-polycrystalline-diamond (PCD) tools, said Simon Manns, vice president for tool grinding (Walter and EWAG brands).

Regarding the blades used for crown moldings and the like, Manns said grinding them efficiently requires “autoloading them into a holder straight up and down and aligned with the center of the workhead. But if they’re going into a cutter body that gives them a rake angle, you have to account for this and grind a profile that’s different from the profile you’ll actually cut in the molding.” For example, cutting a quarter round profile might require a blade with an oval edge.

“Our software really helps,” Manns asserted. “You import the desired DXF part profile, or program the profile. Then plug in the rake and clearance figures for the intended cutter body. The software automatically makes the necessary adjustments,” he said, noting an operator can easily program the robot to load each set of blanks to the same consistent centerline position, even mixing different batches in one setup.

Walter’s Tool Studio software has been expanded to cover almost all PCD tool types, Manns said, greatly easing the task of programing machines that both erode and grind, such as the Helitronic Power Diamond. “Pretty much every grinding operation that’s in Tool Studio can now be switched to erosion.”

It’s particularly helpful for solid round tools such as compression routers with brazed PCD inserts, Manns explained. “You can simulate the whole tool and show the PCD in a different color from the rest of the material [typically carbide]. So you can make sure your program won’t grind into the PCD, while also ensuring you erode through the PCD and into the carbide to create a smooth transition.”

The software also includes suggested erosion parameters for different materials and desired surface finishes, making it possible for a typical tool grinding operator to expand into PCD tooling without specialized expertise.

So far we’ve covered solutions that combine OD and ID grinding, grinding and turning, and even grinding and erosion. In none of these examples did the different operations occur simultaneously, but that’s yet another feature Danobat has introduced in response to customer demand, according to Arrizabalaga. The company offers machines with wheel heads on independent slides, the CNC supports simultaneous grinding on two channels, and DoGrind+ gives the operator an intuitive means to program such a sequence, he said.

This practice is common in lathes, of course, usually using the subspindle to machine the end of the part that had just been clamped in the main spindle (while the main spindle moves onto the next part). You can do the same in grinding, though Arrizabalaga said it’s more common to use one spindle to grind the ID of a part while using another spindle to grind the OD.

Another common application, one in which both spindles might be simultaneously used on the same workpiece, is in grinding “big bearings where you have plenty of space for the two spindles to approach. Such simultaneous grinding can save a lot of time,” Arrizabalaga said.

The software makes it easy to program which operations can occur simultaneously and which cannot, Arrizabalaga said, taking care of interference concerns, dressing cycles and so forth. Plus, the HMI makes it possible to incorporate input from third-party systems such as wheel balancers or acoustic sensors on the main screen, so the operator has everything in one window.

Software may not have entirely taken over the world yet. But it’s certainly helping to make grinding easier.

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