Study On Preparation Mechanism And Properties Of Laser Brazed Single-Layer Coated CBN Grinding Wheel With AgCuTiZr Brazing Alloy

As the foundation supporting the development of high-end precisionequipment,tool technology determines the level of equipments to a certain large extent.With the development of manufacturing industry,the requirements of machining precision of mechanical parts are increasingly improved,and the status of the grinding process becomes more and more prominent in the efficient precision machining.Higher standard requirements are proposed for the material compounds of grinding tools and their manufacturing technology.The new grinding wheel preparation technology with high strength and low wear rate becomes one of the key points to realize efficient grinding.Some defects can usually be found on the cBN wheel manufactured with the traditional technologies such as bonding,electroplating and common heat source brazing process.Poor performance is exposed due to low bonding strength between abrasive particles and matrix,large thermal deformation of the matrix,which seriously restricts the machining efficiency and the lifespan of grinding wheels.And a few certain security issues would be occurred in the employment of these types of tools.Based on the above problems in the preparation and manufacturing of cBN grinding wheel and the demands of rapid,efficient and green development of manufacturing industry,active Zr modified AgCuTi brazing alloy had been applied to conduct the preparation and processability research of new brazing cBN grinding wheel with the remarkable advantages such as convenient operation,high efficiency and low pollution of laser brazing technology in this paper.Some brief jobs were completed as following:1)Study on the modification effects of component in brazing alloy.The active element Zr was introduced into the brazing alloys for connecting cBN abrasive particles.Based on the theoretical analysis of thermodynamic compatibility of Ag-Cu-Ti-Zr multicomponent components,AgCu₂₈-4.5Ti and AgCu₂₈-4.5Ti-4Zr active brazing alloys were prepared by mechanical alloying.The experimental results indicated that the active element Zr is beneficial to refine the particles.The formation of hard-brittle Cu-Ti compounds was decreased and the melting range of brazing alloys was compacted.And the gradient distribution of elements in the transition zone between brazed layer and matrix was improved.Prepared AgCu₂₈-4.5Ti-4Zr brazing alloy presents good performances of wettability and high bonding strength.2)Study on optimization of laser brazing parameters.The parameters,such as laser current,pulse width,frequency,scanning speed and defocuing amount,were optimized by single-factor tests.The parameters of laser power and scanning speed were proved to be the most important factors that affect the quality of brazed layer.The finite element simulation results of the laser brazing temperature field shown that the increment of the brazing temperature would be gradually enlarged when the power reaches a certain value,and the changing of scanning speed has significant influence on the brazing temperature only when it is at a low value.The thermal cycle curve of a single node with different laser power and scanning speed shows that the temperature has a significant difference between the initial node and the final node under the action of laser.A relatively stable temperature field can be obtained by adjusting appropriate brazing parameters.Based on the results of a single factor test and finite element simulation,an orthogonal test was designed to further analyze and obtain the optimized laser parameters finally.3)Study on wettability of brazing alloy.The theoretical model of brazing alloy’s wettability was established.The relationship between the value of wetting angle and the spreading radius as well the wetting height of the brazed alloys is derived.The wetting angle of AgCu₂₈-4.5Ti and AgCu₂₈-4.5Ti-4Zr active brazing alloy were measured,and the wetting angle was solved according to the theoretical model by measuring the width and height of brazed layer simultaneously.The applicability of the model is proved according to the consistency between the calculated and the measured results.The quantitative evaluation of the brazed alloy wetting to the matrix in brazing process can be realized with the established model.4)Study on cBN connection mechanism with AgCu₂₈-4.5Ti-4Zr active brazing alloy.The analysis of brazed cBN interface shows that Zr B₂,Ti B,Ti B₂,Ti N and other compounds are formed at the interface between the abrasive particles and the brazed alloy to form the inner structure,and the new intermetallic compound such as Ag Zr₂,Cu₁₀Zr₇ formed the outer layer structure.The brittle crushing or micro crack propagation of cBN abrasive particles are mainly occurred during the friction and wear tests,and the brazed layer provides a large holding force for cBN particles.5)Study on the performance of laser brazed cBN grinding wheel.With optimized technological parameters,a new brazed cBN grinding wheel is developed with mechanical alloyed brazing alloy.Morphology of laser brazed cBN samples were quantitatively evaluated in the aspects of distribution concentration,transverse uniformity and longitudinal equalization of abrasive particles.The technical feasibility was verified.It is shown according to the analysis results of wear status after grinding test that the abrasive particles have gone through the stages of complete angularity,abrasion wear and slight wear.It is implied that the reliable connection between cBN particles and 45-steel matrix is realized.