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SPECIAL REPORT I MATERIAL COATINGS
for rough-grinding, down to 1-2 microns for superfinishing/ honing. Meister Abrasives has also made improvements in its mixing and wheel processing techniques for improved product homogeneity and consistency. These improvements are said to provide Meister Abrasives with a 50% greater range of options for fine tuning vitrified diamond wheel products to best meet any specific process requirements.
Grinding HVOF components productively: Requires a rigid, well maintained CNC grinding system with automated rotary dressing
company’s vitrified diamond wheel is automatically dressed during various stages of the process. By using different dressing parameters, the same wheel can be used for both roughing and finishing. Automatic dressing at specific intervals also results in exceptionally consistent surface finishes and geometries from part to part. “Establishing the right dressing parameters is critical for any grinding application but especially to develop productive and cost-effective HVOF grinding processes for our customers,” Batson explains. “The ability to standardise on a single Meister vitrified diamond abrasive specification for our wheels has allowed us to become very proficient at using the dress cycles to alter the cutting characteristics of the wheel as required.”
Between the wheels Several years’ research and development has resulted in substantial improvements in the performance and durability of Meister Abrasives’ vitrified diamond grinding wheel product range. “We offer our customers much more than a ‘one bond fits
all’ solution to their grinding problems,” continues Batson. “Our developments have added several new bonding matrices, including the proprietary High Performance Bonding (HPB) technology and we have also added a number of advanced diamond grains. This results in a greater choice to meet the specific requirements of customer applications. The selection of the diamond crystal shape with the most suited toughness, friability, and heat resistance together with the appropriate vitrified bonding gives Meister its technology advantage.” The breadth and number of grit size choices has also been expanded. Grit sizes range from FEPA 427 microns
Dressed to thrill A rotary system is always recommended as being the most efficient way of dressing vitrified products, which is usually possible in one operation. Dressing is actually a combination of two processes, truing and sharpening. Truing is the procedure used to ensure that the wheel, once it has been installed on the spindle, is optimally round, it may also refer to the methods used to create shapes on grinding wheel surfaces. Sharpening involves removing bonding material from between the abrasive grains to expose them so that they are ready to cut. For vitrified-bonded wheels these two processes occur simultaneously. Meister Abrasives generally recommends a metal bond rotary dresser to condition the wheel, although it is also developing its hybrid diamond dressing (hDD) technology to address the requirements of this and many other demanding applications. Among the variables manipulated to impart appropriate stage- specific wheel conditions are: wheel speed; dresser speed; direction of rotation of dresser and wheel at point of contact (unidirectional or counter-directional dressing); speed ratio of dresser to wheel, traverse speed and the overlap ratio. Unlike resin bonded diamond wheels, the vitrified diamond
wheels can be effectively and efficiently rotary dressed on the machine, so the need to have separate machines or wheels for roughing and finishing is avoided. Vitrified bond diamond wheels have a porous structure with strong chemical bond ‘posts’ that give maximum utilisation of the diamond grain rather than relying on a mechanical process to hold the diamond in place such as with a resin bonded diamond wheel. Dressing the vitrified diamond wheel correctly ensures new cutting edges are exposed consistently. This makes it possible to control the cutting behaviour of the wheel with the dressing process and therefore achieve the desired results on the part. For example, typical applications use a unidirectional dressing cycle to ‘open up’ the wheel, exposing more diamond for aggressive cutting during the roughing stage. Later in the process this can be switched to counter-directional dressing to ‘close down’ the wheel and smooth it out for finish grinding. The Meister Abrasives vitrified diamond wheel chosen for
this application has provided the ability for customers to develop complete unattended HVOF grinding processes that result in increased productivity together with high levels of
geometry and surface finish consistency. ❙
www.meister-abrasives.co.uk
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