Smart approach to dressing process

An all too common attitude is 'If it isn’t broken, why should I fix it?' Paul Batson, sales and marketing diretor of Meister Abrasives suggests that if that is your strategy, maybe you should reconsider: "The truth is simple, one of the most effective things you can do to improve the quality and productivity of your grinding processes is to methodically assess and fine tune the process you are using to dress your grinding wheels.”

When Meister engineers are called out to help solve a customer’s grinding problem, most of the changes they make to the grinding process involve dressing. Batson continues: "We often show customers how to make their vitrified bonded CBN or diamond grinding wheel sharper for more aggressive cutting or duller for a smoother surface finish, simply by adjusting the dressing variables." 

The company believes manufacturers who take advantage of these tips can improve productivity by reducing cycle time and making fewer wheel changes, save money with better wheel life, and improve part quality with better finishes and tighter tolerances.

Achieving these improvements may be as simple as changing the speed or direction of rotation of your dressing tool. Rotary dressing tools often do not have to rotate at a fixed speed or direction relative to the grinding wheel. In fact, varying the speed/direction of rotary dressing gives you the flexibility needed to optimise your wheel for either aggressive roughing or smooth surface finish applications. 

While adjusting the dressing process, it is worth considering whether or not the dressing tool selected is best suited to the application. Meister’s hDD (hybrid Diamond Dresser) technology, for example, can often reduce total grinding costs while improving grinding wheel performance. Meister has invested heavily in R&D to produce a range of stationary and rotary dressing specifications that can improve its customers grinding process whether using vitrified CBN, diamond, ceramic or conventional abrasives wheels. The dressing family consists of engineered bonds and specifications to ensure consistent wear and freeness of cut during the dressing process to produce a stable and controllable grinding process.  

A recent application of a Meister hDD rotary dresser on an internal bore-grinding application with vitrified CBN provided significant process improvements. The customer was looking to improve cutting ability and longevity of the grinding wheel, and produce a more stable process. In this case, the original metal-bonded dressing tool was believed to be dulling the wheel too much, resulting in unsatisfactory results. 

Grinding a rocker arm made from En 31 100Cr6 case/through hardening steel on a Meccanica Nova grinding machine using a neat oil coolant, the component required 0.2mm stock removal from the radius. The dresser was replaced with a hybrid-bond hDD dressing tool of the same design. Although the dressing interval increased from 80 to 200 components the surface finish improved from 1.46 to 1.38 micron Rz, and the number of components per grinding wheel increased from 17,000 to 36,000.

Similar wheel life improvements were achieved using a Meister hDD dresser on a dry-grinding application on a Felsomat machine using vitrified CBN wheels. Producing syncro cone gears, the customer was looking to improve cutting ability and longevity of the CBN grinding wheel. Using a plated diamond dressing disk the customer was achieving a skip-dress of 10 workpieces. The dresser was replaced with a hybrid-bond hDD dressing tool. The process more stable and the grinding wheel acted sharper and more open, allowing more efficient stock removal. The result was faster grinding cycles, an increase in skip dress to 20 workpieces, and the hDD steel base can be reused.

Addressing dressing forces

Excessive forces generated during dressing cycles can have a negative impact on the grinding process. Meister Abrasives recently completed a comparison of two different processes for dressing a 400mm diameter CBN wheel used to plunge grind a critical automotive steering component with a tightly finished and close-tolerance cylindrical wear surface.

The test compared dressing forces generated by the user’s standard metal-bonded diamond dresser and those generated by full-radius Meister cDD dresser. Meister says its cDD (CVD-tipped Diamond Dresser) technology produces rotary dressing tools that hold their profiles better and their sharpness longer. The dressing tools rely on a novel structure in which high-quality CVD diamond inserts are strategically embedded within Meister’s hDD porous hybrid-bond diamond matrix. Users need not choose a dressing tool that is optimised either for truing or for sharpening; cDD dressing tools excel at both.

Meister Abrasives says that over the entire dressing cycle the cDD dresser generated 30% less force on the wheel. This resulted in a sharper and uniform wheel surface. Benefits included a sharper wheel, longer intervals between dresses, closer dimensional tolerances, lower grinding forces, and improved cycle time and surface finish.

Paul Batson concludes: "Of course, the benefits you achieve from improving your dressing results depend on the goals you have established for your grinding process. But one thing is sure, the ones that are most critical can be improved, and often substantially.”