Advanced Materials Research Vols. 154-155

Abstract: Laser forming is a new flexible sheet metal forming process. By means of the theory of orthogonal experimental design method, design of experiment and optimization were carried out on thin aluminum-lithium alloy AA2090 sheet metal laser forming under the condition of water-cooling. And through the calculation and analysis of the experiments, the effect of the four process parameters related to the energy of laser beam on bending angle under the condition of water-cooling were ranked in order of laser power, number of scan, scan speed and beam diameter. Furthermore, the optimum process parameters were obtained, and experiment verifications were carried out.

Abstract: The dimension accuracy and the too life are the major issues of the machining of hard-to-cut materials. To fulfill the requirements of accuracy and tool life needs not only well planning of cutting path but also the proper cutting conditions of cutters. The vibration and deflection of cutters caused by poor selection of cutting conditions can be predicted using models of cutting force and tool deflection. In this paper, a cutting force model considering the effect of tool helical angle and a cantilever beam model of tool deflection were proposed for the high speed machining of hard-to-cut material SKD11. The shearing force, the plowing forces, and the helical angle of cutters are considered in the elemental force model. The material of workpiece, SKD11, studied in this paper is commonly used for the die and mold industries. The cutting constants of the proposed force model are determined via the cutting experiments carried out on a high speed machining center. A dynamometer and a high frequency data acquisition system were used to measure the x-, y-, and z-direction cutting forces. The obtained cutting constants were used to predict the cutting forces and compared with the results obtained from the cutting experiment of verification using cutters with different helical angles. The theoretical and the experimental cutting forces in the x-, y-, and z- direction are in good agreement using flat cutters with 30 and 45 degrees of helical angle. The dimension deviations of the cut surface in the cutting experiment case of tool deflection were measured using a touch probe and an infrared receiver installed on the machining center. The measured average dimension deviation, 0.163mm, is close to the predicted tool deflection, 0.153mm, using the proposed cantilever beam model. The comparisons of the cutting forces and the average of the cut surface dimension deviation are in good agreement and verify the proposed cutting force and the tool deflection models are feasible and useful.

Abstract: The corrosion behavior of the nitrocarburized JIS SKD61 and DH31S hot work steels has been investigated. The as received JIS SKD61 and DH31S steel was quenched and tempered to obtain the tempered martensitic microstructure. The nitrocarburizing treatment was conducted in a 570°C salt bath for 40, 80, and 120 minutes, respectively. Treated specimens were characterized by means of microstructural analysis, microhardness measurements, X-ray diffraction analysis, glow discharge spectrometer analysis and electrochemical tests in a 3.5wt% NaCl aerated solution. The thickness of compound layer of nitrocarburized specimens was about 1-3μm, and the microhardness is in the range between 790 – 820 HV0.05. The compound layer of the nitrided specimen was consisted of ε-phase (Fe2-3N) and the γ’-phase (Fe4N). The highest corrosion potential (Ecorr) in this study reached to -0.3 V for NC-S80 and NC-H80 specimen, it’s about 1.5 times higher than that of ferrite substrate. There is no evident difference on corrosion current density (Icorr) with prolonging nitrocarburizing treatment for both steels. Nevertheless, the corrosion properties were improved by nitrocarburizing process.

Abstract: Surface modification of 40Cr steel by high current pulsed electron beam has been investigated . The pulsed times of HCPEB was changed from 1 to 25 to prepare different specimens. Surface microstructures and section microstructures after HCPEB irradiation were detected by using metallurgical microscope, SEM and X-ray diffractometer. It is shown that crater defects were found on the surface after the irradiation of HCPEB and the density of craters will decrease with increasing pulses times. When treated by 27Kev accelerating voltage, with increasing pulse times, the particles located in surface layer were obviously refined .The surface roughness, hardness, wear properties and corrosion resistance were analyzed after irradiation of HCPEB. The wear resistance and corrosion resistance were obviously enhanced after 10 pulses treatment.

Abstract: Sedimentation bulk density and rheology of TBA-based hydroxyapatite suspensions have been investigated in terms of solid loading and types of additives (gelators, gelators/dispersant, gelators/dispersant/surfactant).

Abstract: A ductile iron coated with metal-matrix pastes containing hard phase TiC and CrxCy was laser alloyed by an Nd: YAG laser and a CO2 laser. The microstructure, composition and wear resistance were analyzed by scanning electron microscopy (SEM), incorporating energy dispersive spectrum (EDS), X-ray diffraction analysis (XRD) and friction wear tester respectively. Results revealed that the alloyed area was composed by alloyed zone and heat affected zone. The microstructure of the alloyed layer was significantly influenced by the laser beam kind. Finer grains and fewer cementites were contained in the alloyed layer produced by Nd: YAG laser. Friction and wear experiments showed that the alloyed layer had better tribology properties.

Abstract: Based on the functional features of SIEMENS840D, a plan to realize the machining technology with cycloidal rotary indexing compound locus is provided. The machining principle with cycloidal rotary indexing compound locus method is stated at first, in which technological requirements for numerical control system are determined. Then, in combination with the functional features of SIEMENS840D, the overall structure of numerical control program produced with cycloidal rotary indexing compound locus, as well as the detailed parts of the program are proposed. Finally, the feasibility of the plan is verified with a machining example.

Abstract: This paper describes a new method of die surface modification by ordinary Electrical Discharge Machining (EDM) tool. First, the principle of this method is studied. Secondly, the technology and characteristics of the die steel coating are discussed in detail based on lots of experiments, and the results show that the die steel characteristics are improved evidently by using EDM. At last, the technology is applied to the punch die initially, and it can be drawn that the life of the coated punch die is improved evidently compared with the non-coated punch die through the punching test.

Abstract: Thermal residual stress in diamond film deposited onto Mo substrate was simulated and analyzed comprehensively by using the finite element method on condition that the substrate’s plasticity was considered. The contour plots of the stresses were described. Moreover, the effect of the film’s thickness on thermal residual stress was investigated. The results show that every stress component in the film has the remarkable stress concentration at the intersection of the interface and the side of the film. The location of maximum tensile principal stress in the film is at the upward face or side face of the film or the interface. The magnitude of maximum tensile principal stress increases when the film becomes thicker. These conclusions are useful to the proper choice of the film’s thickness and the effective control of the stresses during preparation of diamond film.

Abstract: Intermetallic compounds layer will be formed at the interfaces between alloy layer and matrix in the diffusion process of hot dip aluminized steel, which is beneficial to enhance the binding ability of alloy layer with matrix. However, when the thickness of intermetallic compounds exceeds the certain value, the vast extending force of interfacial void will cause the crack of intermetallic compounds and greatly weaken the spall resistance of aluminized layer. Therefore it is very important for the applications of hot dip aluminized steel to research and control the formation of intermetallic compounds at the interfaces. According to the characteristics of diffusion process of hot dip aluminized steel, the growing model of intermetallic compounds were established in the paper. The computed results were in accord with the experimental value. It can provide reference to the choice of the diffusion parameters of hot dip aluminized steel.