Papers by Author: Jian Li Song

Abstract: Synchronized hydraulic bulging forming technology on three-layer-metal tubes was studied. The possibility of three-layer-metal tubes formed by hydraulic bulging method was discussed and proved by elastic-plastic theory. The calculation formulas about the bulging pressure, the residual contact stress and the relationship between them were derived and the main process parameters were analyzed. Finite element analysis was carried out on bulging forming process using MSC. Marc. Practical bulging forming experiments were conducted and well compounded three-layer-metal tubes with tight interfaces were obtained. Through the comparison of the results of theoretical analysis, numerical simulation and practical experiments, proper parameters for the bulging process were obtained and the theoretical analysis was verified and proved.

Abstract: Laser cladding forming (LCF) is one of the new developed advanced manufacturing technologies. It integrates the advantages of rapid prototyping manufacturing and laser cladding surface modification, and three dimensional near-net-shape metal components can be directly manufactured without dies. Due to the dramatic heating and cooling characteristics of laser cladding forming process, the cladding layers is liable to crack, which greatly impedes the further and wider application of this technology. In this paper, numerical simulation on the three-dimensional transient temperature field and stress field of powder-delivery LCF has been carried out with parametric programming methods. The temperature field, temperature gradient and cooling rate of the laser cladding layer have been obtained. The influences of laser power and scanning speed on the temperature gradient and cooling rate of the cladding layers, especially the cooling rate of solid-liquid interface of the melt pool have been studied, which is tightly correlated with the cracking generation of the deposited layers. According to the simulation, process parameters were optimized to minimize the cracking possibility; LCF experiments have also been conducted to verify the simulation results.

Abstract: Cold rolling precision forming process of spline is one of the high-efficiency, precision and non-chip forming advanced manufacturing technologies. It has the characteristics such as high forming efficiency, energy-saving, low material consumption and better forming properties of components. The process and principle of involute spline cold rolling precision forming was analyzed. A measuring and testing system for the force and energy parameters in the forming process was set up, and the real-time variation curves of the torque moment of the spindle and the radial feeding force were obtained. Also, the influencing rules of process parameters on the maximum radial feeding force and spindle torque were investigated. Finally, Precision forming experiments of involute spline cold rolling were carried out with optimized parameters. Precision measuring and hardness testing of the tooth outline section shows that the components obtained by the experiments were free of defects. Compared with the spline components obtained from conventional cutting process, the hardness and wear ability was greatly improved, which is suitable for the requirement of application.

Abstract: Laser rapid forming is a kind of new developed technology combining laser surface modification and rapid prototyping technology. It provides a powerful tool for the manufacturing and repairing of metal components. Laser rapid forming repairing experiments of 45 and 2Cr12 steel have been carried out with 316L stainless steel powder. Microstructure and properties of the repaired components are analyzed and tested with optical microscopy (OM), scanning electron microscopy (SEM) and electronic tensile experimental machine etc. Repaired components of different materials have been metallurgically bonded with the deposited layers, with fine microstructure, better mechanical properties and free of defects.

Abstract: The influence of process parameters on isothermal precision forging of a screw propeller is studied by means of FEM (Finite Element Method) simulation. The even degree of deformation, distributions of the flow line and effective strain within the billet and the forging load are analyzed. Notable difference of the effective strain is existed between the blades and the wheel hub of the screw propeller. Large deformation of the blade has been obtained, which is favorable for the blade strength. The material flow and the distribution of deformation can be adjusted by changing the process parameters and the forming quality can be improved. Both the forming temperature and punch speed have large influence on the forming load but less influence on the distribution of deformation. The result of simulation shows that the precision forging of screw propellers can be formed with the isothermal precision forging satisfactorily.

Abstract: Laser cladding rapid manufacturing technology is a kind of new developed advanced manufacturing technology integrating the advantages of rapid prototyping manufacturing and laser cladding surface modification. Due to the complex thermo-physical and metallurgical factors in the deposition process, the cladding layer is liable to crack, which seriously impedes the industrial application of this technology. Experiments of laser cladding rapid manufacturing 316L stainless steel were carried out. The cracking behavior and phenomena has been observed, cracking mechanism of 316L stainless steel was investigated by means of microstructure characterization and phase analysis with optical microscopy (OM), X-Ray diffraction (XRD), scan electronic microscopy (SEM) and phase diagram analysis. Factors influencing the cracking susceptibility has also been studied. Results show that the cracks of 316L stainless steel were hot solidification cracks caused by the high residual stress and separating of the liquid films among dendrites. Through the optimization of process parameters, adding protective atmosphere, etc. cracking sensitivity has been effectively reduced and crack free 316L stainless steel components have been obtained.

Abstract: Preparation of semi-solid microstructure with less liquid content of 7A09 aluminum alloy industrial extrusion billets is studied in this paper. In the treatment, melting-stirring and predeformation of the alloy billets are not required. The influences of different heating temperatures and insulation time on the microstructure evolution are studied and the obtained microstructure is observed and analyzed by optical microscopy. The results indicate that a fine microstructure can be obtained with the proposed process and the processing parameters can be controlled over a wide range. The liquid content can be controlled within a certain range.

Abstract: Numerical simulation and test forming of the isothermal precision forging of an impeller was carried out. The forming processes were simulated with DEFORM-3D to obtain the forming characteristics and metal flow pattern. It indicated that the impeller can be forged by the method of isothermal-forging, and the deforming process can be divided into 3 stages. The forming of blades was depended on the extrusion of materials. During the forming, uneven deformation was existed in the billet, especially in the field of the blade root. The forging load was increased rapidly during the later stage of the forming process, and the maximum forging load was about 2961kN. According to the simulations, the die structure and the billet dimension were determined, the forging die was designed and manufactured, and the precision forgings of the impeller were produced successfully. Both of the simulation and the test forming indicated that the impeller forging could be performed with the assembled structure die and the isothermal extruding forming style satisfactorily. The ideal parameters to produce the precision forgings of the impeller are: a forging temperature of 450°C and a punch speed of 1mm/s. Under these conditions, the forgings of the impeller can be produced with full blades, smooth outer surface and good flow line, which can meet the requirements of the precision forging of impellers.

Abstract: Preparation of semi-solid microstructure of 7075 aluminum alloy industrial extrusion billets was studied in this paper. A new semi-solid microstructure preparation process is proposed. In the treatment, melting-stirring and predeformation of the alloy billets are not required. An ideal microstructure and higher dimensional precision of the billet can be obtained only with a direct heating and insulation method. The influences of different heating temperatures and insulation time on the microstructure evolution were studied with orthogonal testing methods. The obtained microstructure was observed and analyzed by optical microscopy, and the formation mechanism of the semi-solid microstructure is further discussed. The results indicate that a fine microstructure can be obtained with the proposed process and the processing parameters can be controlled over a wide range. Also, the grain microstructure obtained by the present process is better than that of the SIMA. For 7075 aluminum alloy billets, perfect fine equiaxial grains can be obtained under a heating temperature of 620°C and a holding time of about 25 minutes. The average grain size is around 80μm.

Abstract: The forming process of spline cold rolling was analyzed. The unit average pressure, contact area and rolling force in the cold rolling precision forming process were analyzed and solved. The mechanical and mathematical model has been set up on the basis of the analysis. The numerical simulation of spline cold rolling process was carried out. The results obtained by comparison of theoretical analysis, numerical simulation and experiment provide a theoretical basis for the study and application of spline cold rolling process.