Study On Performance Assessment And Preparation Process Of Bronze-bonded Diamond Grinding Wheel Matrix

The bronze-bonded diamond grinding wheels have a series of advantages, such as high bonding force and high wear resistance of matrix, high wheel profile accuracy, long life-span, withstanding heave loading, etc.. However, there are also some disadvantages like low efficiency and poor self-sharpness ability. So the bronze-bonded wheels are mainly used for the machining of nonmetallic hard-brittle materials, and the coarse grinding, semi-finishing grinding, deep grinding and form grinding of cemented carbide. The bronze-bonded matrix for supporting diamond grits is the determinant of wheels performance, and the matrix properties are determined by the matrix formula, powder materials mixing process and sintering parameters.The reasonable characterization and assessment of matrix performance, which is a very important aspect in both experimental studies and practical production, are mainly used for the guidance and improvement of tool performance. At present, mechanical properties tests (such as hardness, bending strength, impact toughness, etc.) are widely carried out to evaluate tools performance. However, this method has some limitations. To resolve the low stability of bronze-bonded wheels and give more reasonable performance assessment methods, the paper evaluated matrix performance by metallographic analysis, and optimized the preparation process of wheels production by combining with mechanical properties test.Based on the wheels matrix formula and preparation process of a company, several groups of bronze-bonded matrix samples were designed and sintered in four different process conditions. Using X-ray diffraction analysis, backscattered electron imaging technology, X-ray energy spectrum analysis and metallographic analysis, the microstructures of samples were analyzed; combining with the metallographic structure of samples, the sintering mechanism was analyzed; considering the properties requirement of metallic bonded materials of diamond grinding wheels, the merits and demerits of sample matrix microstructure were analyzed.The metallographic analysis results showed that the samples were composed by two phases (a phase:Sn dissolve into the gap of Cu crystal lattice, then the solid solution a phase was formed;δphase:Cu4iSnn,a solid solution based on a electron compound Cu31Sn8). The solid solution (a phase) was a plastic phase, which had white block morphology. The (α+δ) eutectoids were hard-brittle phases, which had steel-gray ribbon morphology with small white block phase distributed among them. In the sintering temperature range from 710℃to 740℃, the content of a solid solution first increased and then decreased. Besides, the size of a solid solution and the matrix porosity increased significantly under the fourth condition. The content of (α+δ) eutectoids were relatively high in the second and third conditions, and the change of porosity did not have a clear regularity.The samples'mechanical properties were also tested, including the density, Rockwell hardness, bending strength, and friction and wear properties. The test results were analyzed by considering the requirement of bonding materials properties and the mechanism of grinding process. The density of samples, which had a surge growth at the temperature of 740℃, decreased with the increase of sintering temperature. The Rockwell hardness of upper surface was bigger than that of lower surface. The macrohardness of samples did not have direct relationship with the content of hard-brittle phase of samples, but had a same change trend of density. The bending strength decreased with the increase of porosity. The content of hard-brittle phases and porosity were a major influence on the friction and wear property of samples, so the method of evaluating wear resistance of matrix with macrohardness test was unreasonable.The metallographic analysis and mechanical properties test results showed that the samples produced under the given conditions had drawbacks of unstable performance. In the practical production of wheels, the low accuracy of equipments and operational errors might result in waste products, so it was necessary to analyze the temperature distribution of sintering process. Weather the pressure of pre-press forming, the sintering temperature and sintering time were reasonable needed to be further studied with experiments. Using the software of CFDesign, this paper simulated the temperature distribution of furnace chamber with different heating rates, and the influence of opening furnace door on the temperature distribution of furnace chamber. The temperature change trend of samples and the temperature distribution of chamber in sintering process were also studied. Finally, a series of samples were produced by changing the pre-press forming pressure, sintering temperature, and sintering time. The technological process was optimized and improvement suggestions were given after metallographic analysis and mechanical properties tests.The temperature filed simulation results showed that:the temperature difference existed in the furnace chamber; the sintering time was short in four sintering processes, so the temperature of samples did not achieve the given sintering temperature after sintering finished; the temperature field distribution of samples existed temperature difference, which were widen with the increase of heating rates; the process of sending samples to furnace chamber after the furnace being heated to a given temperature was reasonable, which could improve the production efficiency of diamond tools but also result in high thermal stress in the samples.The process optimization results showed that:the pre-press forming pressure had significant influence on the products performance which was not taken into serious consideration; comparing to increasing sintering time, the increase of sintering temperature had greater influence on the metallographic structure of sample; the performance stability could be improved by increasing the pre-press forming pressure and decreasing the sintering time; when the pre-press forming pressure was set as 150MPa and the sintering time was set as 80 minutes, the mechanical properties kept relatively stable and the content of hard-brittle phase first increased and then decreased with the sintering temperature changing from 680℃to 710℃. When the sintering temperature was 720℃, the size of metallographic particle increased significantly and existed the overbuming phenomenon.