Diamond/CBN Abrasive Wheels with Adaptive Abrasive Composite Technologyfor Ultra-High Capacity and Precision Finishing Machining of Hard-to-Machine Materials<br />Mr. N. Ignatov<br />Mr. Y. Pashchenko<br />Aignesco Abrasive Systems Co.<br />Canada<br />
The traditional response to the challenges of the cutting zone is the determination to maximize the bond stability under highly unstable conditions.<br />The alternative may be the development of adaptive, self-organizing abrasive composites.<br />Anew criterion for the behaviour of polymer-bonded abrasive composites – the adaptive capacity:<br />Where, α – the index of adaptive capacity of the composite based on polymeric bond,<br />Е1, Е2 – elastic modulus for less rigid and more rigid states of the composite,<br /> – transition period.<br />ΔЕ = Е2 – Е1,<br />Δτ<br />Fig.1 The change of elastic modulus of the adaptive (1) and traditional (2) composites under variable intensity of ultrasound impact on the sample.<br />In the adaptive composites the growth of the contact forces causes its reversible structural transformation into a more rigid state. <br />Fig. 2 Spectral density of vibrations generated in the cutting area by the traditional (1) and adaptive (2) composites while grinding the hard alloy.<br />The application of the adaptive composites results in significant narrowing of the width of the density of spectral distribution for the vibrations generated during the grinding process.<br />
Two compositions of the traditional composites and three adaptive composites with different proportions of the components were tested.<br />Table 1<br />1,2 – olygoamidoimide + silicon carbide<br />3,4 – hybrid epoxy-siloxane + modified clay<br />5,6,7 – adaptive composite<br />Δ<br />Fig. 3 The correlation of halfwidth of spectral density 50of vibrations in the cutting area by the adaptive and traditional composites with elastic modulus (a) and the adaptive capacity of the composites (b)<br />1…7 – order of specimens according to Table 1<br />
The mentioned composites demonstrated comparable results on G ratio and surface roughness.<br />The significant difference appeared in 2 indicators, namely:<br /><ul><li> the bearing face of the machined workpieces,
the operational time for polishing to the final roughness Rа2,2 nm</li></ul>Fig. 4 The relation of the polishing time till Rа 2,2 nm (а) and the bearing surface (b) of the monocrystalline sapphire samples <br />at the halfwidth of spectral density of vibrations 50, generated during grinding with different composites.<br />Δ<br />The adaptive capacity has a direct impact on the spectrum of vibrations generated in the process of grinding. In turn, it determines the bandwidth of the energy exchange channels between the abrasive composite and the workpiece.<br />
The surface formed by grinding may be compared not only by the geometrical parameters of roughness. It is complemented by the characteristic of a surface microrelief defined in the process of its deformation.<br />The surface of the hard alloy formed by the adaptive composite demonstrates a qualitatively different behaviour.<br />b<br />Fig.5 Spectral density of indenter vibrations by scanning the hard alloy surface machined with traditional (a) and adaptive (b) composites<br />1,2 (b) – consecutive scanning on one track<br />a<br />Fig.5 Spectral density of indenter vibrations by scanning the hard alloy surface machined with traditional (a) and adaptive (b) composites<br />1,2,3 (a) – consecutive scanning on one track<br />The adaptive abrasive composites pave the way to the formation of another large class of surface structures which behaviour does not fit the traditional view.<br />Being stochastic by the geometry, they are able to self-organizing.<br />Such surfaces acquire an unusual property that could be named the “fractal capacity”.<br />The tool creates a hierarchy of structural “spare positions”.<br />The data prove that the architecture of the surface grinded by the traditional composite is formed by a large number of independent overlapping systems of roughness.<br />These systems tend to evolve independently under external influence.<br />
Under more intensive deforming influence, the ensemble of surface microroughnesses formed by the adaptive composite organizes and reproduces itself on a new scale level.<br />These structural differences in the surfaces with the equal Ra machined with adaptive and traditional composite essentially effects the wear resistance of the workpieces.<br />The effect of the self-organization of the surface layer of the workpieces is truly evident not only with single samples, but with the groups of aggregated components in the integrated mechanisms.<br />Fig.7. Wear of bearings aggregated in one mechanism up to failure:<br />а – rolling paths machined with the traditional composite<br />b – rolling paths machined with the adaptive composite<br />For the groups of 6 bearings with the rolling paths formed by the adaptive composite the time to failure in overload was 25-40% longer in comparison with the products machined by the traditional analogue.<br />The aggregate of 6 bearings was still able to operate at the total wear much greater than it was for the same group machined with the traditional composite. <br />Fig. 6. The wear of hard alloy cutter on back surface for steel,<br />1- cutter machined by an adaptive abrasive wheel, <br />2- machined by a traditional grinding wheel. <br />
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