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Boost Grinding MRR With Engineered Abrasive Grains

UNITED GRINDING North America has long partnered with Norton and its parent company, Saint-Gobain, to help manufacturers achieve the highest grinding productivity possible with development of advanced abrasives. Now, the company has pushed the state of the grinding art even further at its Northborough, Massachusetts-based Higgins Grinding Technology Center (HGTC) with what is known as nano-scale ceramic grain technology. In addition to being exceptionally hard and durable, these grains also allow manufacturers in challenging industries such as aerospace to achieve significantly higher material removal rates (MRR) in the toughest of materials.

Known as Norton Targa, the new engineered ceramic grains begin as alumina nanoparticles, which are transformed into abrasive grains through seeded-gel (SG) sintering technology. The resulting crystallites can be engineered for controlled, sub-micron fracturing that produces cutting points that number in the thousands. A pre-sinter extrusion process further refined the design of the grains, which now resemble blunt needles or filaments with low packing density.

Typical grains and their blocky geometry make packing more grains onto a wheel’s surface difficult. But instead of the roughly 50% packing density found with normal grains, Targa grains can reach densities that approach 30%, which not only produces more cutting points but increases the permeability and porosity of the wheel surface, boosting the efficacy of coolant. Furthermore, the long shape of the Targa grains gives them the chipmaking ability of bigger grains, reducing the cutting energy required and enabling greater MRR.

For the highest level of productivity, particularly for applications involving superalloys common to the aerospace industry, Targa grains are blended with other abrasives. Given that these premium ceramic abrasives have a premium price tag, Norton | Saint-Gobain have studied how blending engineered abrasive grains can perform at different ratios of SG grains to conventional grains. The results of the test, which were performed on Inconel 718 sample workpieces, were as expected: productivity rises as more Targa grains are added to the blend, and the highest productivity, lowest cycle time and greatest MRR were achieved with 100% engineered ceramic grain wheels.

Increasing the concentration of Targa grains did not have a significant effect in wheel wear or surface quality, but it did increase the power required for dressing and create significant cutting energies, which can add risk to processes involving materials sensitive to thermal effects. For fully optimal grinding, manufacturers can adjust the ratio of engineered abrasives and conventional abrasives until the perfect balance of performance and price is achieved.

New and innovative engineered abrasives have significant impact on not only the grinding process itself, but also on grinding machine performance – and vice versa. Companies like Norton | Saint-Gobain design new wheels with today’s high-quality, high-rigidity grinders in mind. A creepfeed grinding machine used in research and product development, for instance, must provide wide application flexibility, effectively run different wheel formulations with overhead, continuous or non-continuous dressing and provide sufficient static and dynamic stiffness at a range of grinding power settings. According to Norton | Saint-Gobain, it would be problematic if they tuned a new abrasive product to work well on a particular machine that, for instance, had a low dynamic stiffness. Then, if that product ran on a machine with higher stiffness or a different dynamic response, it would perform very differently.

To learn more about the potential of Norton Targa grains and the potential of working with cutting-edge grinding wheel technology, see “Blending Engineered Abrasives Improves Grinding Wheels” by Dr. K. Philip Varghese and Mark J. Martin of Norton | Saint-Gobain Abrasives in Aerospace Manufacturing and Design.

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