Papers by Author: Qiu Lian Dai

Abstract: The new processing technique of vacuum evaporative pattern casting (V-EPC) process was explored to fabricate the cast-iron bonded cBN grinding wheels in this paper. The influences of pouring temperature, degree of vacuum, percentage and size of the cBN grits on the microstructures, distribution and thermal damage of cBN grits in the grinding layer, as well as the surface quality of the grinding layer were investigated. The experimental results revealed that thermal damage of the cBN grits and severe damage of nodulizer occurred when the pouring temperature was around 1480°C. The optimized pouring temperature for fabricate the austenite-bainite ductile cast-iron bonded cBN grinding wheels was about 1400°C. The appropriate degree of vacuum was 0.06Mpa. Too high or too low level of degree of vacuum would result in low surface quality of the grinding layer. The uniformity of the distribution of cBN grits in the metal matrix improved with the increase of the percentage and size of the cBN grits.

Abstract: The grinding temperatures were measured with half-cylindrical thermocouple which made by grinding method and measrued with foil thermocouple which made by rolling method respectively when grinding brittle granite with an Al₂O₃ wheel. Experimental results include average grinding zone temperatures and grains’ temperatures were analysed. The deviation of average grinding zone temperatures measured by them were within 6%. The foil thermocouples do not easily to lap due to the brittleness of the workpiece which usually makes the joint of thermocouples disconnected. But half-cylindrical thermocouples are more convenient to be prepared and be used than foil ones. However, the periodic “flash” impulses which reflect the grains’ temperature measured by half-cylindrical thermocouple were about 51% lower than the others. According to time constant, the thickness of the thermocouple less than 0.007mm is a necessary condition for measure the grains’ temperatures without distortion. The half-cylindrical thermocouple is too thick to have a momentary response time thus makes it out of the measurement accuracy range when it is used to measure the temperature of the grains. Therefore, foil thermocouple has an optimum thickness of 0.007mm is suitable for measuring the grains’ temperature while half-cylindrical thermocouple with average thickness less than 0.12mm is suitable for measuring the average grinding zone temperature.

Abstract: In this paper, a new type of aluminum bronze was used to substitute for the traditional tin bronze as the bonding matrix of the porous diamond wheel. Effects of hot pressing sintering temperature, the amount of Al and Fe on the mechanical properties of aluminum bronze based bond were studied by means of orthogonal test. A new kind of pore inducer with spherical shape was chosen. Effects of pore inducer size and processing parameters on the pore morphology and the mechanical properties of the porous metal bonds and diamond composites were studied. Experimental results revealed that the TRS of the new type porous aluminum bronze based bond and diamond composites increased by 119% and 258% respectively compared to the traditional porous tin bronze based bond and diamond composites. Also, stronger bonding between the metal bond and diamond grits was observed.

Abstract: The possibility of using the new processing technique of vacuum evaporative pattern casting (V-EPC) process to fabricate the Al-Si based bonded diamond grinding wheels was explored in this paper. Distribution of diamond grits in the diamond/EPS composite pattern and in the grinding layer of the cast of the grinding wheel were analyzed. Microstructures and mechanical properties of the metal bonds and diamond composites fabricated by V-EPC process were studied. It is confirmed that thermal damage of the diamond grits did not occur. Strong bonding between metal bond and diamond grits can be produced. However, the uniformity of the distribution of diamond grits in the metal matrix should be further improved. Also, further hardening on the metal bond is necessity by trying other kinds of aluminum alloys.

Abstract: In this paper, semi-solid metal (SSM) processing was first applied to fabricate Al-based matrix and diamond composites. A kind of Al-Cu alloy with an adequate solidification range was chosen. Samples of Al-Cu alloys were fabricated by rheocasting with different processing parameters. Specimens of Al-based matrix and diamond composites were fabricated by rheocasting and hot press sintering technology respectively. Microstructures, transverse rupture strength (TRS), hardness and wear resistance were studied. Experimental results revealed that the TRS of the Al-based matrix and diamond composites fabricated by rheocasting increased by 157% and 115% respectively compared to the ones fabricated by hot press sintering technology. The fracture surfaces of the rheocasting specimens exhibited ductile cup and cone behavior as well as strong bonding between the matrix and diamond grits.

Abstract: In this paper, metal-bonded diamond wheels of different sized abrasive grain with different porosity were fabricated. Grinding experiments with these wheels on three kinds of materials were carried out under different grinding conditions. Experimental results revealed that wheel with high porosity (38%) had smaller grinding forces and specific energy than the one with a medium porosity (24%) on grinding G603. However, on grinding harder materials like Red granite or ceramics of Al₂O₃, the wheel with 38% porosity had bigger grinding forces and specific energy than the wheel with 24% porosity. Both wheels exhibited good self-sharpening capability during the grinding process of G603 and Red granite, but on grinding ceramics of Al₂O₃ the wheel with 38% porosity displayed in dull state during the grinding process . With the same porosity, the grinding forces of the wheel with a grain size of 230/270 US mesh were lower than the one with a grain size of W10 when grinding Red granite and ceramics of Al₂O₃. However revising results were obtained on grinding G603.

Abstract: Effects of some alloying additives such as Cr, Co, Ni, Mn, Al on the microstructures, resulting fracture surfaces of bronze base bonds and diamond composites as well as the bonding between the metal bonds and diamond grits were studied. Experimental results revealed that under the hot pressing conditions sufficient alloying couldn’t develop as it does in the cast bronze. The degree of segregation varied with the melting point of the alloying elements. The metal with higher melting point led to a more serious segregation. Addition of strong carbide formation elements like Cr, Co could improve the bonding between the metal bonds and diamond grits and the retension of metal bond for diamond was enhanced in a way. However the addition of Al, Mn and Ni did not bring much improvement on the bonding between the metal bonds and the diamond grits.

Abstract: In this paper, two metal-bonded diamond wheels with different porosity were fabricated. The porosity of diamond wheel without additives of pore inducers is 7% and the wheel with pore inducers is 38%. Grinding experiments with these two grinding wheels on marbles were carried out under different grinding conditions. Experimental results revealed that highly porous grinding wheel has smaller grinding forces and better self-sharpening ability than the compact grinding wheel under the same grinding conditions.

Abstract: In this paper, three kinds of granite were lapped and polished by loose abrasives. Glossiness and surface roughness of the lapped and polished granites were measured and the surface morphologies were observed. The experimental results revealed that the readings of roughness were very discrete. High glossiness can be achieved only when the surface roughness is decreased to a certain level. The average surface roughness of the three kinds of granite after being finely polished can reach 0.02～0.04um. Further reducing of roughness has little effect on the glossiness because the existence of the defects, which prohibits the further increase of the glossiness.

Abstract: Effects of TiH2 on the mechanical properties and microstructures of Fe-based diamond composites as well as the performance of diamond segments in circular sawing of granites are presented in this paper. Experimental results reveal that the addition of 2%TiH2 into the Fe-based matrix leads to decreases in the mechanical properties of both matrix and diamond composites. The wear resistance of the saw-blade segments decreases by 7.3%. Microscope observations reveal that the specimen without TiH2 shows fewer pores and denser structures in the base matrix. The fracture surfaces of the bending test specimens exhibit ductile cup and cone behavior and strong bonding between the matrix and diamond. SEM micrographs indicate that there are much more pull-outs of diamond grits, much more serious wear of diamond particles and erosion of metal matrix on the worn surface of saw-blades segments with 2% TiH2 in the matrix.