Papers by Author: Feng Qi Han

Abstract: Fe₂O₃、CaO have been added into the combustion system of manual SHS welding as slagging elements and the effects of their addition have been studied. Results showed that the combustion velocity and the adiabatic combustion temperature both became lower as the amount of the additives increased. The additives have dropped the density and the solidification temperature of the slag, which accelerated the separation of the slag and gas from the weld pool. (0.2~2.0) g of Fe₂O₃ and (0.2~1.2) g of CaO have been added into the rod. Experiments showed that the appropriate added amounts of Fe₂O₃ and CaO for each combustion weld rod were 1.2g and 0.6g respectively. The weld slag was honeycomb, brittle and easy to be removed from the weld metal. Analysis of the microstructure and composition showed that the matrix of the weld slag was glass, with some ceramics distrabuting on it. The ceramics had high content of Al₂O₃, which was created in the combustion reaction. The matrix of the weld alloy was α-Cu solid solution, on which a second phase with high content of Fe precipitated. There were no non-metallic inclusions in the weld metal ultimately. The weld joint had favorable mechanical performance, which tensile strength reached 400MPa, that fulfil the requirement of emergency welding.

Abstract: Service life of tap is shorter when low frequency torsional vibration tapping is used to tap on superalloy GH4169. The analysis of experimental data show that excessive repeated cutting times and high friction speed result in rapid wear of tap. In order to avoid above unfavorable factors, step type vibration tapping is proposed, which has larger cutting angle, such as 90°, and lower spindle speed. It was proved by experiments on superalloy GH4169 that service life of tap of step type vibration tapping is about twice of that of common low frequency torsional vibration tapping .

Abstract: In order to provide references for the application of low frequency torsional vibration tapping, three typical difficult to cut materials 30CrMnSi, GH4169 and TC4 were selected to carry out experiments. Experiment results show that net cutting angle L_T and backoff angle L_G have great influence on tapping torque, and the process parameters should be selected reasonably according to material characteristics and combining with tapping efficiency. Larger L_G and smaller L_T should be selected for materials with small elastic modulus such as TC4. Smaller L_G and larger L_T can be selected for materials similar to 30CrMnSi. For materials similar to GH4169, parameters should be selected between that of TC4 and 30CrMnSi.

Abstract: Vibrator is the key part of vibration tapping machine. In this paper, a kind of oblique cam type mechanical vibrator was designed. The vibrator has the advantages of simple structure and easy manufacturing, and the output amplitude of the vibrator can be adjusted by changing the inclination angle of oblique cam. It is verified by experiments that the process is successful when the oblique cam type vibrator is used to machine big thread holes, and compared with common continuous tapping, the torque of vibration tapping decreases significantly.

Abstract: Low frequency torsional vibration tapping is an effective method to solve the problem of tapping in difficult to cut materials. Tapping parameters affect tapping torque and service life of tap, and cutting angle is the key parameter. Experiments were conducted to study the lubrication mechanism and the influence of cutting angle on lubrication effect. Experimental results indicate that the separate type boundary lubrication mode greatly enhances the lubrication effect of cutting fluid and the lubrication effect decreases with the increase of cutting angle. To obtain good technological effect, the smaller cutting angle should be selected.

Abstract: Manual SHS welding is a new method of emergency welding based on SHS reaction. The large amount of Al2O3 created in the reaction restricts the welding performance seriously. In this paper, CaO and MgO were added as slagging elements to improve the characters of the slag, and the effects of their addition have been studied. Results showed that the combustion velocity of the rod decreased when the content of CaO and MgO increased. The rods with 0.2g MgO and 1.2g or 1.5g CaO were easy to control, which combustion velocities were about 12mm•s-1. No obvious changing rule was found for the density of the slag when the content of additives changed. But the densities of slag were all lower than that of metal Fe and Cu. Viscosity calculation showed that the viscosity value of slag increased when the temperature drop. The additive CaO and MgO reduced the slag viscosity. The viscosity value of the slag with 1.5g CaO and 0.2g MgO added was about 0.9 Pa•s at 1450°C and was lower than 0.7 Pa•s at 1500°C. Welding experiments showed the fluidity and the detachability of the slag were improved. Phase composition and microstructure analysis showed that the slag had multi-phases and its matrix was glass. The tensile strength of the joints was above 350MPa, which meets the requirement of mechanical properties for emergency welding. SEM micrograph showed there were slag inclusion in the fracture of welded joint, which was one of the reasons restricting the mechanical performance of the weld joint.

Abstract: Early breakage of tap often occurs when tapping on difficult-to-cut materials with the method of low frequency torsional vibration tapping, which decreases the technological effect and restricts its application. The effect of impact load on tap breakage in vibration tapping was analyzed, and the stress state in tap teeth was simulated by FEM, on this basis, it is concluded that too large tensile stress in tap teeth is the main cause of early breakage of tap. To reduce the tensile stress and enhance the shock resistance of tap teeth, the tap should be ground to minor negative rake angle. Experiments showed that the failure mode of grinded taps changed to wear, and thereby the service life of tap was prolonged significantly.

Abstract: The mechanism of prolonging service life of tap in low frequency vibration tapping was studied from two aspects of the reduction of wear and the insensitivity of the passivation of tap. Repeated cutting and separate type boundary lubrication improved the contact and lubrication status on rear face of tap. On the one hand, it greatly reduced the wear of rear face the tap, on the other hand, it markedly decreased the passivation sensitivity of tap to blunt radius and flank wear. With the interaction of two factors mentioned above, the service of life was prolonged greatly by low frequency vibration tapping.

Abstract: Stepping tapping is a new tapping mode for Nickel-based superalloy GH4169. Longer life of tap and higher machining efficiency can be obtained. But chipping of tap is very prevalent. In this paper, the mechanism of chipping in step tapping is investigated. Based on the wavelet analysis of the signals of tapping torque, the load applied to the tap in every stage of the period of motion is studied. It is found that chipping is prone to occur at the moment when the rotating direction of tap shifts from forward to backward, which is caused by the too large and rapidly changed tensile stress on cutting edge. The excessive wear of cutting edge results in the too large tensile stress. To reduce the wear, the backward rotating angle of tap should be selected to be smaller than 100°.