3D-Technology

3D Technology in CBN – a new dimension of internal grinding?

Reduced bore diameters on workpieces, materials which are difficult to machine as well as increasingly tighter tolerances in the precision machining of bores call for new concepts in terms of the design of abrasive tools. The well-known great features of vitrified bonded CBN abrasive tools, the optimised CBN crystal types, hardness and porosity, as well as the complementary dressing technology are starting to be stretched to their limits here.

The combination of a new innovative production procedure as the basis for designing the required structures, as well as a new conceptual approach when it comes to designing the structure, make big advancements for a small bore.

Generally speaking, the 3D technology provides a highly porous tool concept, which optimises the following factors in terms of the previously unknown variability:

  • Pore volume up to 60%
  • Pore radius distribution –  5 - 10 x larger than the abrasive grain
  • Wear resistance –  at least the same value as the current standard
  • Use of very fine CBN grit sizes with a simultaneously high material removal rate

In practice, the current state of the art technology results in a significant reduction to grinding forces and thus deflection of the internal grinding quills, which allows considerable improvement to the geometries on the workpiece. Nevertheless, at the same time, no compromises must be made where wear resistance is concerned.

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3D-Technology

3D CBN grinding wheel

3D-Technology

3D CBN structure 3.2x zoom

HPB-Technology

As a specialist in vitrified CBN and diamond wheels, Meister Abrasives present as a new tool concept its innovative HPB (High-Performance Bond) technology which can offer the user major benefits in terms of cost and quality.

The newly developed generation of abrasive tools optimises both productivity (cycle times, dressing intervals, machine downtime etc.) and component quality (geometric requirements, damage to the workpiece boundary layer etc.).

Meister devoted particular attention to a number of factors when developing the new HPB technology:

  • Getting the right CBN grit properties
  • Ensuring (wear) strength over the crystal morphology
  • Obtaining cutting ability over the crystal morphology in conjunction with targeted pretreatment

Optimising grit retention forces:

  • Ensuring the strength of the bond bridges with the right composition and heat treatment of the vitrified bond
  • Interfacial bonding of the CBN grit by optimising the wetting of the grit during manufacture and controlled chemical reaction/compatibility

The results: 

  • Improved wear resistance and stability of form
  • Increased pore volume
  • Improved coolant supply and chip discharge

With the help of its HPB technology and by selectively optimising these individual factors, Meister Abrasives have succeeded in increasing the variability of the whole system and enhancing the cutting ability and wear resistance of the tool.

The relative weighting of these factors can be individually adjusted in order to address a specific shaping requirement. The principle is shown by way of example in the following chart.

If we assume average cutting ability, pore volume and grit retention forces for a standard composition, then as well as the general improvement in all three parameters, with the HPB principle the benefits can be weighted more strongly either in favour of the grit retention forces and hence wear resistance, or alternatively of the pore volume and hence cooler abrading.

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HPB-Technology

HPB bond structure REM image

HPB-Technology

HPB bond triangle

HPC-Technology

The increasing requirements for bore grinding applications using dressable CBN abrasive tools have required yet another step towards an even more optimised bond. As a market leader in the field of vitrified CBN wheels, Meister Abrasives is enlarging its range of high-performance tools to meet these demands.

The already successful HPB (High-Performance Bond) systems must be developed further to meet the needs of customers seeking to achieve ever-higher stock-removal rates for very small bores while optimising surface quality at the same time.

Under the designation HPC for High-Performance Cutting, the company has succeeded in enhancing still further the benefits of the Meister high-performance tools, especially in fine abrasive grit sizes from 500-1500 mesh.

The result – stock-removal rates which compare favourably with far coarser grits, combined with much finer surface qualities, while the greatly increased dressing intervals give an added boost to cost-effectiveness.

For very small abrasive grit sizes therefore, this new development in bond technology offers unequalled:

  • Pore volumes
  • Reductions in cutting forces
  • Stock-removal rates
  • Improvements in component geometry
  • Dressing intervals

The company's technological approach is based on the use of strength-enhancing synthetic raw materials which improve the bond's toughness and the grit retention forces.

Although aimed primarily at applications using very fine CBN grits, the technology is also basically suitable for coarser grit sizes.

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HPC-Technology

HPC Bond; highly porous structure SEM image

cDD-Technology

The cDD technology with its reinforced edges allows path-controlled dressing of very complex shapes to very close tolerances. These properties combined with the option of multiple re-contouring contribute to a significant reduction in overall process costs.

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cDD-Technology

rotating cDD dresser

cDD-Technology

stationary cDD dresser

cDD-Technology

SEM picture cDD

vDD-Technology

If a CBN (internal) abrasive tool is needed for very low abrasive pressures, then the surface structure must be dressed accordingly. The creation of an open structure, optimum grit projection and outstanding stock-removal properties is determined largely by its system partner, the dressing tool.

It is here where we find the ideal application for vitrified dressing tools. Following decades of experience in the development of vitrified bond systems, Meister has created an optimum range of vitrified vDD tools ("vitrified Diamond Dressers") specifically for dressing purposes.

The bonds which can be used for vitrified diamond tools consist mainly of a group of metal oxides, similar to the CBN-capable bond systems. However the characteristic poor affinity of the diamond with the oxidic ceramic bonds means that the conditions for adequate wetting by the bond/glass melt are much more complex.

For the purpose of vDD technology therefore, grit adhesion has been optimised with a thoughtful selection of synthetic metal oxides and the introduction of a low-temperature consolidation process to the point where the diamond crystal qualities that are needed for successful dressing processes can be wetted and bonded.

The wear resistance of modern vitrified dressing tools allows the precision shaping of abrasive wheel geometries provided there is a straight line contact between the two systems.

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vDD-Technology

vDD dresser on a UVA machine

structure vDD dresser

hDD-Technology

Hybrid technology (hybrid Diamond Dresser) makes it possible to synthesise a unique structure within the active dressing tool rim. The porous base matrix achieves a free-cutting structure which enhances the abrasive wheel's stock-removal capability in dressing operations.

A dressing tool based on hybrid technology also exhibits exceptional wear resistance. This is achieved by a selected combination of metal and ceramic properties in the matrix of the dressing coating.

Today, hDD tools are used in large-scale production processes both as dressing cups on small turbines and as dressing discs with internal or external diamond rims up to 420 mm in diameter, or as stationary dressers.

System characteristics

  • No ancillary times / only small ancillary times for resharpening the dressing tool
  • Significantly improved geometry of the ground components
  • Better surface quality of the workpiece due to optimum cutting ability of the grinding tool
  • No running-in period after dressing
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hDD-Technology

REM hDD in 427µm grit size

hDD-Technology

Closeups hDD and metal bond

hDD-Technology

hDD double disc dresser

hDD-Technology

hDD dressing cup

hDD-Technology

hDD stationary dresser

Vit-Technology conventional

The vitrified bond for conventional abrasive tools is the oldest matrix used for bonded abrasives. Since the early 1960's Meister has developed all of the bonds which it uses for complete process control in-house.

The introduction of the vitrified sintered corundum tools counts as a major technological advance. Even on older-generation machines, these tools provide huge reductions in process costs.

The key to the success of this bond system which has become so essential to high-productivity serial processes, is in the outstanding abrasive properties of these largely porous structures, its outstanding receptiveness to contouring and dressing, and the high stock-removal volumes which its good wear properties can achieve.

The structure of a vitrified abrasive wheel can be classically characterised in a ternary system by the following elements:

  • the abrasive (or its chemical and physical properties)
  • the bond
  • the resulting microstructure

The available grades of corundum, silicon carbide and sintered corundum crystals offer a wide range of cutting properties and are selected for specific applications.

Most vitrified bonds are made from frits, feldspar, kaolin and different clays. 

Their chemical and physical properties are determined ultimately by the combination of raw materials, the grit sizes that are used and the firing cycle, i.e. vitrification.

The microstructure is a function of the relative proportions of abrasive grits and their specific mix of type and size, bond content and residual pore volume, and is an essential precondition for an efficient tool.

The toolmaker's know-how consists of his judicious choice of individual components and the very closely controlled production process.

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Vit-Technology CBN and Diamond

Vit-CBN abrasive tools have been used successfully for around 25 years and with a steadily growing share of the market. The key to the success of this by now most important bond system for CBN is in the outstanding abrasive properties of these largely porous structures, its controlled receptiveness to contouring and dressing and the high stock-removal volumes which its good wear properties can achieve.

Meister has developed all of the ceramic bond systems for CBN and diamond in-house since the 1980's, a long tradition that will ensure its further development and worldwide technological leadership going forward.

The structure of the vitrified abrasive wheel can be classically characterised in a ternary system by the following elements:

  • the abrasive (or its chemical and physical properties)
  • the bond
  • the resulting microstructure

The available grades of CBN crystals offer a wide range of cutting properties and are selected for specific applications.

Vitrified bonds are usually made from frits, feldspar, kaolin and different clays. The vitrified bonds mostly contain the following cations: Al3+, Fe 3+,Ti4+, Ca2+, Mg2+, K+ and Na+ and less commonly, Li+. Modern bond systems are lead-free for health and applications reasons.

Their chemical and physical properties are determined ultimately by the combination of raw materials, the grit sizes that are used and the firing cycle, i.e. vitrification.

The microstructure is a function of the relative proportions of the abrasive grits (usually with a secondary grit in the case of CBN/diamond), bond content and residual pore volume, and is an essential precondition for an efficient tool.

The HPB bond and HPC technology are current further developments of vitrified bonding technology.

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