Papers by Author: Sheng Dun Zhao

Abstract: In this study, ZL104 aluminum alloy supplied in cold rolled state was introduced in recrystallization and partial melting (RAP) process to fabricate semi-solid billets. During the RAP process, samples cut from cold rolled ZL104 aluminum plate were heated to different semi-solid temperatures, and the effects of isothermal treatment parameters on the microstructures of semi-solid billets were investigated. Results showed that, with the increase of isothermal holding temperature and time, both the average grain size and the shape factor were increased. Namely, the shape of solid grain was more and more spherical, but the size of solid grain was larger and larger, which may be not suitable for semi-solid forming. The size of liquid droplets was increased while the number of liquid droplets was decreased with increasing the isothermal holding temperature and time. Microstructural coarsening of solid grain were attributed to coalescence and Ostwald ripening mechanisms, however, the latter one played a more and more important role with the increase of isothermal holding time and temperature. Additionally, The optimal isothermal holding temperature and time are 570 °C and 5 min, respectively, and the coarsening rate constant is 1357.2 μm³/s at 570 °C.

Abstract: Tension stretching process is an important link in production of aluminum alloy thick-plate. Exploring the change of load in tension stretching process is important for the structure designing and key component checking of large-scale tension stretcher. In this paper, the changing law of stretching force in the tension stretching process of aluminum alloy 6063 thick-plate has been investigated by numerical simulation method, and the influence of initial thickness of plate and friction condition in clamping area was analyzed. The results indicated that the initial thickness has a notable influence but friction condition has a little influence on stretching load; and the stretching force increases at first and then decreases slightly, and then it is tending toward stability; and the larger the values of thickness and friction, the more stable the stretching force in the process.

Abstract: With the accuracy improvement of twin-screw compressor rotor machining, higher requirement of crew rotor grinded equipment and grinding process is put forward. Based the theory of screw grinding and CNC forming grinding wheel dress technology, the relationship between machine working parameters, CNC grinding wheel dressing parameters and screw rotor grinded process parameters are investigated, and the relationship between CNC grinding wheel dressing parameters and the screw rotor grinded process parameters is established, and its formulas are presented to describe the distances between grinding wheel axis and screw rotor axis. Through these formulas, the CNC wheel dressing program could be designed easily, the performance and efficiency of machine would be improved, and especially the machining quality of screw rotor would be enhanced and becomes more stability.

Abstract: This paper firstly introduces the principle and characteristic of traditional extrusion tapping of internal thread, elaborates the material flow law during tapping process. Then puts forward a novel process of vibration-assisted extrusion tapping of internal thread, explains the effect mechanism of vibration during extrusion tapping of internal thread. Finally, with the finite element method (FEM), the simplified model of extrusion tapping are built, and the simulation of thread forming process of traditional extrusion tapping of internal thread are conducted, furthermore, the characteristic and influencing law of different vibration parameters (include vibration frequency, amplitude and direction) of vibration-assisted extrusion tapping of internal thread are studied, and some practical results are obtained. The simulation results show that applying vibration to extrusion tapping of internal thread can reduce tapping torque and improve thread forming quality, the reasonable selection of vibration parameters are very crucial to this novel process.

Abstract: In order to solve the narrow range and control difficulties of the excited frequency in metal bar cropping with variable frequency vibration, the structure of the eccentric block in cropping machine was improved on in the paper and a new structure model of changing the integral eccentric block into one of main eccentric block and some small adjustable eccentric blocks, was also proposed. The key parameters of the cropping machine in the action of two different types of eccentric blocks were analyzed theoretically in detail. At the same time, the corresponding amplitude frequency characteristics of the cropping machine were also obtained. The cropping experimental results of 45 steel bar show that the cross-section quality and the cropping time are improved remarkably in the action of one main eccentric block and four adjustable eccentric blocks, comparing with the cropping results in the action of the whole eccentric block.

Abstract: This paper introduces the principle and characteristic of extrusion tapping of internal thread, presents the simplified mechanical model of extrusion tapping firstly. Then generalizes the key technology of extrusion tapping and their influencing law on tapping torque and thread forming quality, such as extrusion tap type, lead hole diameter, tapping speed and friction. Finally, numerical analysis on the key technology of extrusion tapping are conducted based on DEFORM-3D, the results show that the effect of lead hole diameter and friction on tapping torque are obvious, the effect of extrusion tap type and tapping speed on tapping torque are next and this effect degree is related to the stress-strain relation of workpiece material under different strain-rate closely. These researches will contribute to the right selection of workpiece material, extrusion tap type, lead hole diameter, tapping speed and lubrication of extrusion tapping of internal thread in practical manufacture.

Abstract: Based on the description of 20MN fast forging press hydraulic system, the paper analyzed the possibility of energy conservation which the accumulator made in the fast forging machine system. When accumulator was used in fast forging machine, then analyzed the calculation results, and the energy conservation program of fast forging machine energy accumulator was evaluated briefly. The test system was set up on 20MN fast forging machine, and the paper researched the application of accumulator in fast forging press hydraulic system on absorbing hydraulic shock and eliminating pressure pulsation.

Abstract: Extrusion tapping is a novel and important processing method of internal thread, carrying out research on the thread forming process can contribute to a better application of this process in more industrial situation. The principle of extrusion tapping of internal thread is introduced in this paper firstly, and then the simplified finite element model of extrusion tapping and the thread forming simulation is conducted. Next, the thread forming process and metal plastic flow law during extrusion tapping of internal thread are analyzed based on the simulation. Finally, the revised formulas for calculating extrusion deformation area and volume are presented and comparison are made with the referenced formulas, the results show that the revised formulas can express the practical extrusion deformation area and volume more correctly. Furthermore, the similar law between the revised extrusion deformation volume and extrusion force obtained from simulation are proved effectively.

Abstract: According to the analysis of friction distribution on radial direction in the precision forging spur gear, the reason that the tooth corner was difficult to fill is revealed. Changing the motion mode of the floating die will change the friction condition between billet and floating die, as well as the filling situation of tooth corner. Finally, the scheme was further validated by DEFORM-3D, and the results show that the validity of floating die to tooth corner filling.

Abstract: Thixoforming of steel is a potential forming technology, which can realize near-net-shape forming process with good quality in one forming step. In this paper, thixoforming process was used to replace the conventional hot forging process to form the auto claw-pole. The finite element code Forge2008Ó was used to simulate the auto claw-pole thixoforming process. The impact of three main process parameters such as initial billet temperature, punch speed and die temperature on the forming process were investigated. The reasonable process parameters for the auto claw-pole thixoforming were obtained: initial billet temperature 1430~1440°C, punch speed 100~200mm/s and die temperature 300~400°C.