The quest for the last µ

In the unusually complex process of grinding, the shape and specification of grinding wheels only exercise a small influence on the overall process. However, since they are immediately responsible for the quality and shape of the workpiece, they do play quite an important role. In contrast to the actual grinding machines, workpieces and a whole range of other invariable parameters, grinding wheels are in many respects variable, making them the “dynamic component” in every application. WTG therefore concentrates its research and development on this dynamic component and frequently concludes through its new product design efforts that there will never be a universal grinding wheel.

Due to profitability considerations, not every variable can be examined to the last detail in the actual practice. For this reason, simplified assumptions (e.g. the machine is an ideally invariable system without a trace of consideration for disturbance potential) and expanded tolerance limits are used. Although this may be understandable for manufacturing, it certainly limits the potential for advances in engineering.

Often, the design of new grinding wheels is a matter of getting the last µ. Command of scientific skills (mathematics, chemistry, physics, metallurgy, etc.) combined with laboratory technology and experience is only one prerequisite. The other prerequisites require the freedom from economic constraints and the courage to travel down unknown paths over longer periods of time, both of which are only possible removed from the production process. This is the means by which the WINTERTHUR GROUP designs and manufactures products that are not based solely on assumptions, but rather on exact findings. Of course, all products are subject to tests under realistic conditions prior to their availability on the market. Several of these tests are fundamental, i.e. they include factors that are relevant for every grinding process, such as the detection of wear or the influence of aggressive substances. Grinding tests that address the needs of a complete grinding system (machinery, workpiece, grinding wheel, operator, etc.) particular to a certain type of grinding are usually performed on site under the regular manufacturing conditions to incorporate the many influential variables. Especially if new materials, processing techniques or machinery pose increased demands, the cooperation between the operator and grinding-wheel manufacturer and the mutual input of expertise gained from experience is the ideal formula for success. Thanks to its extensive research and development department, the WINTERTHUR TECHNOLOGY GROUP is well-equipped to react quickly and in a targeted manner to specific customer requirements. Furthermore, WINTERTHUR’s engineering painstakingly and constantly researches topics that are of relevance to grinding, giving particular attention to the abrasive grain and its interaction with the bond and the workpiece. Some of WTG’s current projects include:

Materials:

• PCD/PCBN plates for hard or finish turning
• Nickel-based material alloys (and their alternatives) for the turbine manufacturing industry
• Highly-complex modern cermet materials
• Tungsten-carbide micro drills

Components:

• Mirrors and glass for solar power installations
• Components for wind power systems
• Crankshafts for internal combustion engines
• Cermet composite materials

Grinding wheel raw materials:

• Hybrid bonding systems
• Use of safe, environmentally neutral substances
• Use of new, more highly effective grit

Combination breeds success
Combination wheels comprised of several grinding coatings are constantly conquering new areas, In particular, grinding tools for the machining of polycrystalline materials, such as PCD and CBN, will be increasingly configured with both rough and finish grinding coatings, because it drastically cuts machining time, since only a single set-up is required. The work piece quality is also better. Especially suitable are composites of synthetic resin bonds for rough grinding and vitrified bonds for finish grinding.

L75
L75 is the new high-performance bond for peripheral cutting of indexable inserts out of cermet or tungsten carbide. WENDT’s engineers assumed that many materials from which indexable inserts are manufactured are sensitive to the high temperatures and strong normal forces that occur in the course of grinding. Common standard bonds are limited in their ability to handle this problem. The new L75 grinding wheel bond is completely different. Thanks to its special material, the grinding wheel has a much higher capacity to absorb and dissipate heat to the flange and subsequently the machine.

Moreover, another engineering feat par excellence is the combination of a gentler grinding behaviour with an outstanding tool life. The new design is the fruit of close collaboration with the Institute of Machining of the University of Dortmund under the direction of Prof. Dr.-Ing. Dr.h.c. Weinert, where ultrafine-grained tungsten carbides and cermets were machined with the new bond. Especially cermets are extremely sensitive to temperature. The L75’s grit, coating and the bond itself were all optimised, leading to significant improvements. Reputable tool manufacturers are currently using the new products for the peripheral cutting of indexable inserts and the initial results are superb in terms of longevity and cutting performance. Especially the quality of the insert edges – always a very critical criterion – is outstanding. The grinding wheels, commonly available in 250 to 400 mm outside diameters and various widths, consist of rings manufactured from the new high-temperature synthetic resin, which are bonded to prefabricated steel hubs with pressure and heat. They are ideal for use with the WENDT WAM and WAC series of peripheral cutting machines as well as those of other manufacturers. The new synthetic resin bond furnishes excellent grit bonding for exceptional wear resistance.

Compared to conventional standard grinding wheels, the wheels manufactured with the new L75 bond have a 20% longer wheel life. Still another advantage is the bond’s reliability, i.e. the grinding performance and wheel life are always the same. The grinding process runs very smoothly and, which is indispensable to all production operations - remains stable.