Advanced Materials Research Vols. 154-155

Abstract: Thermal errors of motorized spindle are of great importance to affect final machining precision of CNC machine tool. Thermal characteristics simulation analysis of motorized spindle is realized by ANSYS; thermal errors test measurement is completed based on 5-point method; and prediction models of thermal errors are constructed by multiple linear regression (MLR) method, Back Propagation (BP) neural network method and Radial Basis Function (RBF) neural network method respectively. The results of simulation and experiments illustrate that simulation results can represent thermal characteristics of motorized spindle, whose degree of confidence mainly depending on setting of thermal load and boundary conditions properly or not; RBF neural network model has highest prediction precision for thermal errors of motorized spindle based on test data.

Abstract: TiO2 has been loaded on cordierite porous ceramic to prepare the SCR catalyst carrier by using both APCVD and sol-gel method. The physical properties, SEM and SEM-EDX of the TiO2-cordierite carrier have been analyzed. The results showed that TiO2 loaded by APCVD method were of graininess shape and accumulated evenly. The loading rate of TiO2 and the specific area of carrier sample were increased 114% and 21% respectively when using APCVD method. In the results of sol-gel method, the maximal difference of Ti content was 66.92%, while the result of APCVD method was 18.89%. It demonstrated that TiO2 was uniformly attached with the cordierite ceramic by using APCVD method. That would ensure the active ingredients well loaded on the TiO2-cordierite carrier in the next process.

Abstract: In recent years, hydropiercing technique has been used widely. In this work, its special type of hydropiercing-bend is simulated using Rice and Tracey ductile criterion based on VUMAT of ABAQUS/Explicit and verified by experiments. Hydropiercing-bend processes with different slope angles of chamfer are discussed to predict the ultimate quality. It is shown that the angle of chamfer should be less than 70º for this kind of material and technical condition in order to make the slug attached with the tube blank.

Abstract: In recent, the development of new die materials is one of the important topics in the field of die research. In this paper, effects of nano-ZrO2 addition on the microstructure and mechanical properties of Ti(C,N)-based cermets were studied. The newly developed Ti(C,N)-based cermet die materials with different contents of nano-ZrO2 of 0~25wt% were prepared by hot pressing technique under vacuum atmosphere at 1450°C for 30min. Moreover, the microstructure of this Ti(C,N)-based cermet die materials was observed by environmental scanning electron microscope. It indicates that the comprehensive mechanical properties can reach the optimum when the weight percent of the nano-ZrO2 is 10%. The corresponding flexural strength and fracture toughness is 967 MPa and 13.62 MPa•m1/2, respectively which is approximately 65% and 110% higher than that of the cermet without nano-ZrO2 addition. It suggests that the addition of nano-ZrO2 can improve the mechanical properties especially the fracture toughness and flexural strength of Ti(C,N)-based cermet die materials.

Abstract: The induction heating of the billets is a critical step in the thixoforming process. To improve the quality of thixoforming, the induction heating strategy should be investigated. In this study, by using an induction heating system of 50 kHz, multi-step reheating schemes were adopted to reheat the nondendritic A356 alloy to the temperature between the solidus and liquidus line. To obtain uniform temperature distribution and fine globular microstructure, the effects of the reheating parameters, such as reheating time, reheating temperature, holding time and holding temperature, were investigated. Then the analysis of the final temperature difference and the optical microstructure of the reheated billets were conducted, the results showed that two-step reheating process is suitable for A356 alloy with the size of 45 mm × 25 mm, and the suitable time for the final holding process is 2 min.

Abstract: Currently, most of electroless nickel phosphorus plating on magnesium alloys has following disadvantages. First, it has been suffering from corrosion issues caused by acidic electroless bath. Second, in order to increase the strength of Ni-P coatings to the Mg substrate, the pretreatments for electroless Ni-P employ hydrofluoric acid (HF) and hexavalent chromium (Cr6+) which can cause pollution and health problems . In this paper, we developed HF-free and alkaline electroless Ni-P deposition process on AZ91D magnesium alloy which avoids the use of SO42- and Cl- ions in the electroless plating bath, thus leading to good adhesion and corrosion resistance of electroless Ni-P coating on magnesium alloy. XRD, SEM, EDS techniques were used to study the structure, morphology, and chemical compositions of the conversion coating and Ni-P coating, respectively. Polarization measurements indicated that the corrosion rate of Ni-P coated Mg was six times lower than that of bare Mg. Electrochemical impedance spectroscopy (EIS) also showed that the Ni-P coating could effectively protect Mg alloy from corrosion.

Abstract: This paper focuses on the simulations of nanometric grinding process on face centered cubic structure (FCC) single metal crystals (Cu, Ni) using Molecular dynamics. In order to analyze the plastic deformation of sample metals in nanometric grinding processes, we propose an approach using techniques of central symmetry parameters and neighbor changing ratios. The simulation results show that besides the normal dislocation defects, weak slipping defects locating on {111} crystal planes are found under the surface layer. In addition, the distribution of the neighbor changing ratio indicates that the nano grinding processes will likely cause the global plastic deformation in the surface layer.

Abstract: The experiments on ultraprecision turning of SiC reinforced aluminium composites have been done by using polycrystalloid diamond (PCD) tool with the three-dimensional cutting forces measured with a Kistler dynamometer, the quality of the machined surfaces was examined under Atom Force Microscope (AFM) and Scanning Electron Microscope (SEM) and the roughness of the machined surfaces was measured with roughometer of Talysurf-6. The experimental results show that the quality of the machined surfaces of SiC reinforced aluminium composites is predominantly controlled by the deformation mechanisms of SiC reinforcements, and the quality of the machined surfaces is better when reinforcements deform in the form of direct cutoff than in the form of pullout. The higher the volume fraction of SiC reinforcements, the worse the quality of the machined surfaces and the greater the amplitude of vibration and the average value of the cutting forces. On the same condition of volume fraction and cutting, the quality of the machined surfaces of SiC whiskers reinforced aluminium matrix composites is better than that of SiC particles reinforced aluminium matrix composites.

Abstract: This study is to develop a tool system, which is formed by a series of procedures, modifications, and assemblies, and to learn how processing characteristics are affected and what various processing parameters are. According to the cutting tool compressibility and clamping devices of rigidity and flexibility, three distinct combinations are as follows, that is (1) rigid clamping devices with hard cutting tools, (2) flexibile clamping devices with hard cutting tools, and (3) rigid clamping devices with soft cutting tools. The first are generally cutting processes, while the second are polishing processes and the third produce milling wipe or grinding and polishing compound processes. The cutting part is quite different and may cause different accuracy and removing rate. The mixture processes, such as turn-burnishing, milling-burnishing and grind-polishing, are existed. If certain flexible clamping devices with hard cutting tools are formed, the most suited to this process will be practical benefits. Considering the flexible cutting tools of clamping devices are less systematically designed, this study would mainly focus on the establishment of a systematic design, and actual cutting to explore its applications. In order to take into account the characteristics of flexibility and reduction of the retardation when connected, meanwhile, to meet not only the fixture complexity and availability (being easy) to manufacturing, but also to fit the strength and processing requirements, the systematic design is to create a tool system. After some cutting experiments have been conducted, the results proved that different degrees of flexibility on the workpiece surface would lead to different degrees of accuracy.

Abstract: A new ZrO2 nano-composite ceramic tool and die material was prepared with vacuum hot pressing technique. The effects of sintering parameters on the nano-composite ceramic tool and die materials were studied. The results indicated that the mechanical properties of ZrO2 nano-composite ceramic tool and die material with the additions of TiB2 and Al2O3 are higher than that of the pure ZrO2 ceramic material. Sintering at 1100 for 120min could improve the density and mechanical properties of ZrO2 nano-composite ceramic material. The flexural strength, fracture toughness and hardness with the optimum sintering parameters can reach 878MPa, 9.54MPa•m1/2 and 13.48GPa, respectively, obviously higher than that with non-optimum sintering parameters.