ABRASIVES
Meister’s 3D Abrasives Technology combines grits as small as 10 µm in a matrix with pores as big as 500 µm, enabling a tiny wheel on a quill (left) to grind the internal bore of this fuel injector nozzle without defl ection, for a 7× improvement in cylindricity and taper.
a master at producing wheels for diffi cult ID grinding opera- tions like fuel injector nozzle bores. That’s a tough application because the tolerance is tight and the bore is long relative to the diameter. That forces you to grind with a tiny wheel on a long quill, an inherently unstable confi guration, making it very diffi cult to avoid tapering. Meister’s Vice President and General Manager, Bruce Northrup, explains that the three “go to” options are prob- lematic: “You could dress more aggressively to produce a sharper wheel, but that would probably result in a rougher surface fi nish, so you’d end up slowing the grind. Or you could use a softer wheel to get a better fi nish and taper, but the wheel would break down more rapidly. Or you could use a very fi ne mesh abrasive wheel. You’d get the desired fi nish and form, but fi ne grit wheels with conventional bonding have not been able to handle the advanced nozzle materials at full production rates without burning or loading.”
10 µm Grains in a 500 µm Matrix Meister’s solution is a new vitrifi ed product called 3D Abrasives Technology that incorporates diamond or CBN grits in the “most open, self-sharpening bonding matrices ever created.” Before 3D, Meister says, a grinding wheel manufacturer had to reduce a wheel’s porosity (its open- ness) when they used smaller grain sizes. So fi ner fi nishing wheels were necessarily less porous. With 3D, Meister can bond grains as small as 10 µm in a matrix with pores as large as 500 µm.
The goal, explains Northrup, is to “minimize the interac- tion of the bond” (as opposed to the abrasive) “with the workpiece. The less the bond rubs the workpiece, the less heat you’re generating and the less force you’re generat- ing, which in turn means less defl ection of the quill.” At the same time, Meister says they’ve fi gured out how to retain the exposed grains in the bond so the wheel stays sharp longer than you might expect. To prove the benefi ts of their new technology Meister
did controlled tests comparing their standard vitrifi ed CBN ID wheel (a state-of-the-art industry benchmark) with a 3D wheel of identical CBN type, grit size, concentration, wheel hardness, and shank. They used the same machine and grinding process, including dressing parameters. The parts ground with the 3D wheel were seven times better in taper accuracy (0.22 µm vs. 1.44 µm) and seven times better in cylindricity (0.11 µm vs. 0.74 µm ), with nearly identical surface fi nishes.
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AdvancedManufacturing.org | November 2016
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