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Advanced Grinding for Sharper Tools, Sharper Production

Bruce Morey
By Bruce Morey Senior Technical Editor, SME Media
Rollomatic’s GrindSmart 529XW producing an end mill. At IMTS 2016, the company demonstrated over 20 hours of lights-out operation that produced 60 end mills to predetermined specifications.

Advanced tool grinding technology, more capable and precise than ever, has meant new ground-breaking cutting tools, such as a variable geometry designs. Just as importantly, other machine tool providers need to offer automation and advanced in-process sensing to make proven tool grinding operations even more efficient. With the introduction of extremely hard tooling materials, tool grinding suppliers are even looking at offering alternative means of creating tools, such as lasers and EDM.

“Our customers demand exact precision,” stated Bjorn Schwarzenbach of Rollomatic (Mundelein, IL), a supplier of tool grinding and laser cutting equipment. These demands are the same for customers owning a couple of machines for special tooling, to those that own a hundred machines used in round-the-clock production,  according to Schwarzenbach, and durability is also a given. “Some of our customers have had our 600 series grinders for over 20 years, producing tools with the same precision,” he said.

Precision remains key. For example, the company’s GrindSmart 529XS guarantees holding concentricity and runout accuracy to less than 2 µm (0.00008″). According to Schwarzenbach, maintaining the quality of the environment is critical to accuracy. “We know that holding the temperature inside the machine for any of our models is important for the grinding process of each tool,” he said.

No less important than precision is cost-effective, no-fuss operation. “Everyone wants a perfect tool with faster cycle time. No one wants to stand by the machine for 20 hours and create 60 end mills and make sure they are perfect,” stated Schwarzenbach. “They can’t afford to put in 80 tool blanks to only get 60 good tools.” This means that Rollomatic has added equipment like in-process measurement of tool-runout in the GrindSmart series that allows for in-process compensation. “The runout is measured as the tool is ground so that the tool can adjust itself, particularly the work end,” he explained.

Setting up a production run is another focus. Rollomatic makes a point in offering its VirtualGrind Pro software, a specialized CAM package for tool grinding offered standard with the company’s GrindSmart machines. Rollomatic set up a demonstration of lights-out manufacturing at IMTS 2016 using one of its GrindSmart 529XW machines. Over 20 hours of untended operation, the system produced sixty ¾” (19.05 mm) four-flute end mills with a primary width specification of 0.004″ (0.102 mm) and a radial relief angle of 0.5°. According to measurements taken, maximum outer diameter variation was 0.004″ and maximum runout in any of the tools was 0.000018″ (0.00046 mm). “We gave the tools out so that potential users could take them home and see how they work,” he said.

Rollomatic provides its VirtualGrind Pro software for off-line programming and tooling setup.

Beyond the tool grinding operation itself, Rollomatic also recognizes that most machinery today exists, or will exist, in an information ecosystem. Later in 2017, the company plans to introduce the RConnect software for collecting data to analyze and measure tool production for its tool grinding machines. According to the company, the software provides a floor production manager and overview of each machine grinding state, giving insight into the hours out of production and hours in production for each machine. That shows the manufacturer the shifts in a machine’s production based on tooling needs. It will also provide raw data for an overall equipment effectiveness (OEE) or Total Effective Equipment Performance (TEEP) calculation.

“We believe that the key to tool grinding today is achieving or obtaining OEE,” agreed Russell Riddiford, president of ANCA Inc. (Wixom, MI). “To do this, you first need a reliable and robust machine for the application,” such as tool grinding, he said. Accuracy through quality components of the machine are important, according to Riddiford.

For example, ANCA uses cylindrical linear motors for precise motion control. With traditional flatbed linear motors the magnets are laid out horizontally. However, on ANCA’s cylindrical LinX Linear Motors the magnets are “rolled up” into a shaft rather than being laid out onto a flat bed. As the magnetic force is cylindrical there are no downward forces on the linear rails or problems with cogging. Some of the benefits ANCA claims over flatbed linear motors or ballscrews include: no loss of preload or rigidity, smoother axis motion, reduced reversal errors with no backlash, and higher acceleration and rapid traverse rates (up to 50 m/min). The LinX motion control is featured on the FX Linear and MX Linear range (and Y axis) of CNC tool grinders.

Riddiford also points to an important fact—improving efficiency in tool manufacturing today probably means concentrating on processes outside of grinding. Physics and a century of innovation means the grinding process itself is not necessarily ripe for improvement, especially in accuracy. “The big difference is getting to the point of making a cutting tool,” he explained. “Once you start grinding, the cycle time is pretty much the same.” That is where automating the setup processes are important.

Measurement in process is also key. ANCA uses laser gages fitted inside the machines and feeds data to its own controllers for precise in-process compensation. Like others, ANCA also provides a tool grinding specific CAM programming tool it calls ToolRoom to improve setup time, maximize efficiency in grinding, and avoid in-process issues like collisions.

ANCA’s Edge hybrid tooling manufacturing machine, which both erodes PCD tools and grinds carbide and HSS tools, delivers the best of both worlds.

Diversity and Flexibility

Getting the most out of any particular machine means making it capable of producing the widest possible range of tools. In January, 2017, ANCA introduced its TX7 Spindle Speed increaser to broaden the range of its grinders. “Cutting small features on cutting tools, such as pockets or small gashes, typically requires a small-diameter grinding wheel, usually smaller than ½” [12.7 mm] or so,” he explained. PCD typically also needs a higher rpm, up to 42,000. But the normal spindle speed for an 8 or 10″ [203 or 254 mm] wheel is 3000 and most of ANCA’s machines topped out at 10,000 rpm. Available as an accessory to the TX7 or TXcell, the Spindle Speed Increaser can spin wheels at speeds up to 42,000 rpm, catering to very small diameter grinding wheels. “This gets you the most out of your tool grinding investment without a second machine or a second option. No need for a second machine to run a dedicated small D grinding wheel,” explained Riddiford. All of ANCA’s machines are now MTConnect-compliant.

The manufacturers making tools are diverse in their needs; some produce thousands of cutting tools, others small batches of three or five at a time. While automation is important, so is addressing the wide needs of this diverse market, according to Markus Stolmar, vice president for tool and measurement at United Grinding (Miamisburg, OH). For the small-batch manufacturers—a significant segment of the market—reducing setup time is vital. “There are a lot of setups in that type of operation,” Stolmar said.

He believes that off-line programming with simulation is the key to both reducing setup time and eliminating collisions while enhance productivity. This includes a 3D model of the machine, workholding, wheels, and tool blanks. “Using software to plan the setup is very important. Our users want to create a program off line, where the machine and the tooling can be simulated so that when it is time to set up at the machine, that time is short.”

United Grinding is a collection of different grinding brands, with its Walter and EWAG supplied machines especially targeting making cutting tools. Like other suppliers interviewed, each United Grinding brand supplies its own software planning package. “You can look at the machine moving, you can look at the part afterwards, you have collision detection so that you know how far out you clamp your part to avoid that,” he said. The Walter brand provides a software package called Helitronic Tool Studio, with easy-to-use features like wizards that tap into an existing knowledge database. EWAG supplies a software package built on software supplied by NumRoto, with additional unique features added.

Grinding Wheel Advances

While grinding is a proven technology, and the physics are well understood, advances in grinding wheel technology are providing even better tool quality and economics. A number of people interviewed for this article viewed advances in grinding wheel technology as important, especially the ability to drive grinding wheels harder with less edge degradation than was evident in the past.

“Primarily what our customers are looking for from us as a supplier of grinding wheels is what I call the ‘whole package’,” explained Alfredo Barragan, corporate applications engineer for Norton Saint-Gobain Abrasives (Worcester, MA). “They are looking for higher grinding efficiency, higher productivity, better cycle times, and tighter tolerances.”

As an example of advances in this area, Barragan pointed to the company’s Norton Paradigm grinding wheels for round tool production. To understand the Norton Paradigm technology, it is important to understand two popular types of super abrasive grinding wheel bond systems: vitrified versus metal. Vitrified bonded wheels are rigid and porous but brittle, whereas metal bonded wheels are tough and dense, which is important for holding form and keeping the wheel sharp. According to Barragan, the Norton Paradigm technology offers the toughness of a metal bonded wheel with the truing and porosity properties of a vitrified bond wheel.

The company notes that the Norton Paradigm wheels are especially targeting grinding on carbide round tools and periphery grinding on carbide and cermet inserts. “High porosity brings better coolant to the grinding zone, better chip clearance, lower cutting energies with highest quality part edges and finishes, and therefore less spindle load,” explained Barragan. “That means better cutting and lower power usage. Better bonding means longer cutting without having to dress the wheel. In superabrasives, the biggest gain in grinding is in the bond system, not necessarily in the abrasive.” Because of the improved bonding, Norton Paradigm wheels boast up to 46% porosity with a 2:1 diamond to bond ratio. “A typical product has about 20–25% porosity for comparison,” said Barragan.

ANCA uses laser gages fitted inside its grinding machines and feeds data to its own controllers for precise in-process compensation.

Future in Using Light

Grinding is an old technology, proven in its abilities as new grinding wheels and software setups add to its capabilities. Stolmar from United Grinding points out that edge preparation after a primary grinding operation is one area where new technology like laser machining is showing promise. “Today, edge preparation is undefined with drag finishing using media like walnut shells or brushes,” he explained. “Using laser allows you to remove along that cutting edge precisely the correct amount of material. Laser will be an augmentation to standard old-fashioned grinding.” EWAG offers two laser machines for cutting tools, the Laser Line Ultra and Laser Line Precision, which are advertised as especially useful in hard cutting materials such as carbide, CBN, ceramic, PCD, CVD-D and MCD.

Rollomatic also offer its Lasersmart 500 for cutting ultra hard tooling materials like PCD, CVD, MD and natural diamond. It, too, is advertised for cutting-edge generation as well as chip-breaker machining and laser marking. The company makes a point that the surface finish from laser finishing is far superior to other means such as EDM or traditional grinding.

ANCA delivers the best of both with its Edge hybrid tooling manufacturing machine, which both erodes PCD tools and grinds carbide and HSS tools. “The Edge is widely used in aerospace; Boeing and Airbus are working hard on these exotic composite materials,” said Riddiford from ANCA.

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