Advanced Materials Research Vols. 154-155

Abstract: Mold filling process in horizontal centrifugal casting was analyzed in this paper. The effects of rotation speed on flow pattern were studied. Results show that the flow pattern changes greatly with increasing rotation speed and the first thread interval shows significant differences within each group. It is found that inappropriate rotation speed results in liquid drop during filling process, leading to casting defects.

Abstract: Adiabatic shear banding during high speed machining is important to understand material removal mechanisms. This paper investigates the microstructure of adiabatic shear bands (ASBs) in the serrated chips produced during the high speed machining of AISI 1045 hardened steel. Optical microscope, scanning electronic microscope(SEM) and transmission electronic microscope(TEM) were used to explore the microstructural characteristics. It was found that there are two types of adiabatic shear bands. One is the deformed adiabatic shear band composed of a significantly deformed structure generated in a range of low cutting speeds, and the other is the transformed adiabatic shear band composed of very small equiaxed grains generated under high cutting speeds. The results indicated that the deformed band has a tempered martensite structure that formed through large plastic deformation and the transformed band has experienced a dynamic recrystallization process.

Abstract: It has been proved that the initial gap has obvious influence on nugget formation, but little works focused on the effect of initial gap on the tensile strength of resistance spot welded (RSW) joints. In this paper, a 3D FE model was built for solving this question. The results show that, even though there are some fluctuations of weld diameter and tensile strength of RSW joints with initial gap, the tensile strength and weld diameter of welded joints with initial gap are still larger than that of welded joints without gap, which confirm that the influence of initial gap on tensile shear strength is little significant. The computation results agree well with experiment.

Abstract: The residual stress in cold ring rolling could cause great error to parts quality. Due to the complicated formation of residual stress, it's difficult to calculate theoretically. In present study, measurement method is generally used. According to the shape of ring, cutting method is the best method for measuring residual stress. There were 6 stages in cold rolling deep groove ball bearing race. Electric wire discharge machine was used to cut the rings after rolling in each stage. The radius of rings would change after cutting. According to the derived analytic calculation theory of residual stress, the residual stress could be calculated in different rolling stage. The residual stresses were in the range of 110-200MPa. Compared the measurement results from finite element simulation results, the greatest difference was 20%, which was in accepted rang. Through calculation results of six stages in cold ring rolling, it could found that the residual stress increased with the increase of deformation, the straightening stage was benefit to decrease residual stress.

Abstract: A new non-sinusoidal oscillation waveform which is shown by waveform distortional rate was advanced. The amplitude, oscillation frequency, waveform distortional rate and casting velocity were established for a computer model of the continuous casting process. The range of waveform distortional rate was ascertained. The choosing method of amplitude and oscillation frequency was given. These offered a theory basis to the application of the advanced technique. Industrial scale experiments showed the new type waveform is effective on improving the quality of continuous casting slab and reducing breakout.

Abstract: In order to solve the difficult problem in analyzing the shaping law of numerical control electrochemical machining (NC-ECM) with ball-end cathode, the process simulation based on the finite element method (FEM) is used in this paper. First, the two-dimensional analysis model of the electric field in NC-ECM with ball-end tool-electrode built by use of ANSYS software was solved, and the current density distribution and the machined surface shape on the workpiece were obtained. Then, the experiments based on the simulation parameters were carried out, and the cutting depth values were measured. Finally, the accuracy of the simulation was verified by the comparison between the calculated values and the actual values. The experiments showed that the simulation method meets the accuracy of the engineering calculations in NC-ECM.

Abstract: In order to improve the flatness of cold rolled strips, the accurate knowledge of actuator performance in flatness control is required. As the basis of flatness control, efficiencies of flatness actuators provide a quantitative description to the law of flatness control. In this paper, a 1250 single stand 6-H reversible UCM cold mill was taken as the object of this study, with efficiency factors of individual actuators analyzed for better flatness control. For the purpose of obtaining accurate efficiency factors matrixes of actuators, a self-learning determination model of actuator efficiency factors was established in accordance with the practical rolling processes. The actuator efficiency factors can be determined and improved continuously by the self-learning model with correlative measurement flatness data input. With this study, performance of actuators in flatness control of UCM cold rolling mill has been obtained, which provides a theoretical basis for better flatness control.

Abstract: Effect of the size and shape of cup shaped forgings with flange on forming capability of aluminum alloy was investigated. The numerical simulation was carried out on the extrusion forming process for each part using two-dimensional elastoplastic finite element method. The metal flow behavior was analyzed, and the forming defects were predicted. Meanwhile, the corresponding experimental researches were conducted. The results show that the forming defects like folding or crack appear in each aluminum alloy forging. The size and shape of cup shaped parts have a great influence on the type and size of forming defects. Good agreement is found between the numerical results and experimental work. The results present important references for technology analysis and mould design.

Abstract: A simulation model for the filling of a tubular cavity during water assisted injection molding is proposed. The polymer melt and water are assumed to be incompressible and to follow a Hele-Shaw fluid behavior. The finite element/finite difference/control volume methods are adopted for numerical simulation of the melt front, pressure at injection location variation, water thickness fraction and bulk temperature about a curved pipe, the simulation results have good agreement with the results presented in the former experiment. In comparison with the simulation result of gas-assisted injection molding, water assisted injection molding can give parts with thinner and more uniform walls and more rapid cooling.

Abstract: A simulation model for the filling of a tubular cavity during water assisted injection molding is proposed. The polymer melt and water are assumed to be incompressible and to follow a Hele-Shaw fluid behavior. The finite element/finite difference/control volume methods are adopted for numerical simulation of the melt front, pressure at injection location variation, water thickness fraction and bulk temperature about a curved pipe, the simulation results have good agreement with the results presented in the former experiment. In comparison with the simulation result of gas-assisted injection molding, water assisted injection molding can give parts with thinner and more uniform walls and more rapid cooling.