Key Engineering Materials Vol. 620

Abstract: Based on molecular dynamics method, the tensile process of single crystalline Cu nanorod and single crystalline Cu bulk were simulated at atomic scale. The motion of atoms, total energy of atom-strain curves and number of dislocation atom-strain curves during the tensile process were acquired. The results shown that surface effect has a significant effect on the tensile mechanical properties of single crystalline Cu nanorod. For single crystalline Cu nanorod, the energy of atoms in the edges and surface were higher than the energy of atoms inside the nanorod. Dislocations nucleation in the edges that with high energy and extend along the {111} crystal plane. The nanorods produce plastic deformation and shows excellent ductility under the "dislocation nucleation-energy rising and dislocation layers cross-slip" mechanism of the alternating cycle. For single crystalline Cu bulk, dislocation nucleation randomly and extend to the entire simulation model along the {111} crystal plane quickly. The single crystalline bulk Cu produce fracture under the "microscopic vacancy-microscopic hole-penetration of microscopic holes-fracture" mechanism.

Abstract: In order to improve the comprehensive mechanics performance of AZ91 magnesium alloy which is used as car's material, the La element was added in AZ91 magnesium alloy and specimens was prepared by powder metallurgy method. The influence of La on microstructure, hardness and compression performance of AZ91 a magnesium alloy specimen was studied using metallographic electronic microscope, hardness tester, universal tension and compression testing machine. The experimental results show that when amount of La's addition is 1.2%, its mechanical performance is best, hardness is 67.1 HV, compressive strength is 115.8 MPa, increased respectively by 20.0% and 29.5% compared the AZ91 magnesium alloy substrate, and the grain refinement effect of AZ91 magnesium alloy is the best at this time.

Abstract: In order to further improve the surface quality in LS-WEDM, a new procedure as Gas-liquid Combined Multiple Cut (the finishing is in gas) is presented and has carried on the contrast experiment to conventional WEDM multi cutting processing in the paper. the single factor and orthogonal experimental design method were used to study Effects of pulse duration, pulse interval, peak current, servo voltage and servo feed on roughness in finishing in gas, By range analysis, analysis of variance and the binary table the optimum level of the above five factors was found in consideration of the above five factors interaction. The paper provides basis for advanced study of finishing process of LS-WEDM.

Abstract: Laser-driven flyer micro forming process is a promising microforming technology with the advantage of high efficiency, low cost, high flexibility. A series of experiments are conducted to investigate forming ability of aluminum foil with the thickness of 50μm. The effect of forming temperature and laser energy on forming ability characterized by forming depth, forming accuracy and surface quality is quantitatively analyzed. It is found that forming depth observed through three dimensional topography increases with the enhancement of forming temperature and laser energy. By elevating the forming temperature, the preheated workpiece suffers more homogenous deformation, presenting better forming accuracy. However, a certain degree of deterioration of surface integrity at the forming temperature of 200°C can be attributed to the earlier appearance of micro cracks caused by excessive thinning even at low laser energy. Overall, it is concluded that the optimal forming temperature is appropriately 150°C as the forming depth and forming accuracy is improved with no deterioration of the surface integrity.

Abstract: The existing safety evaluation of high-speed milling cutter mainly based on ISO15641 standards, which by idling experiments, then analysis and determine centrifugal force conditions what cause permanent deformation and fracture destructive of cutter, this method cannot be forecast and control the dynamic evolution of the milling cutter's safety and reliability, when cutting load changed suddenly.This paper using the high speed milling cutter's failure criteria and safety margin model of cutting hardened steel, analysed and evaluated coupled thermal field distribution caused by hardened steel surface feature that changed frequently and cutter's impact, fatigue, strength, stiffness, safety margin which cuased by mutated shock load of cutter, then forecast safety and reliability of high-speed milling cutter, and proposed the control method of safety and reliability that could milled hardened steel in high speed.

Abstract: In some special fields such as precision optics, the part surface has strict requirements on the frequency domain errors, besides the conventional spatial domain errors such as surface roughness error. In light of the available works lacking of the frequency domain error analysis in ultra-precision flycutting, this paper therefore presents its frequency domain error analysis. A case study of KDP crystal flycutting is carried out to show its detailed processes, where the processing parameters, tool geometry, motion dynamic error of the machine guideway and tool-work vibration induced dynamic error are considered. A surface profile generation method is put forward. Two cases with different tool-work vibration frequencies are carried out. The spatial frequency spectrum is obtained based on the FFT analysis of the generated profile in the specified direction. After the in-depth analysis, the inherent correlation of the generated spatial frequency components with feed spatial frequency and machine dynamic errors induced spatial frequency under certain machining conditions are found, which is very meaningful for the frequency domain error prediction in the real application. The proposed analysis method can also be applied into other types of surface machining.

Abstract: The research of the simulation for high speed cutting is usually based on 2D modeling by now, and the 3D simulation is few. Because the cutting process is a 3D deformation of workpiece, it's badly in need of the research on 3D finite element simulation of cutting process for further reveal the mechanism of high speed cutting. The 3D simulation of inclined cutting of hardened 45 steel (45HRC) is carried out base on ABAQUS. The forming process of serrated chip is simulated by adopting the Johnson-cook material modeling and separation criterion of shear failure. The change of chip morphology, chip flow angle and deformation coefficient of width under different rake angle and cutting depth are analyzed. The results show that the segment degree of chip becomes larger with the decrease of rake angle and increase of cutting depth. The chip flow angle is not effected by rake angle and its value is approximately equal to tool cutting edge inclination angle, an it increases with the increase of cutting depth. The deformation coefficient of width increase with the decrease of rake angle and increase of cutting depth.

Abstract: Hydrostatic lubricated vertical guideway is commonly used as a form of rail head bearing lubrication in CNC vertical lathe lubricated bearing. In order to improve the cutting performance of CNC equipment during machining, we have studied the hydrostatic vertical guideway with inner slide during the process of ram feed moving in this paper. The single rectangular cavity flow equation and velocity equation are derived. Numerical simulation of taking limit working conditions that the cutting force is taken byis studied by the Finite Volume Method (FVM). The flow field and velocity distribution of X direction and Y direction of hydrostatic vertical guideway are obtained by using quantitative method and supplying oil with a single chamber, with the inlet flow of 0.52L/min, with the film thickness of 0.023mm and the depth of oil cavity of . The mathematical model by theoretical derivation and the flow state regularity in limit working conditions are verified and revealed. The results of study above in this paper provide valuable theoretical basis for hydrostatic guideway design in practical projects.

Abstract: Adopting coaxial and side blown protective gas to control plasma, many experiments of CO₂ laser deep penetration welding on the stainless steel are finished. Considering the protective gas effect of melten characteristics on laser welding,the experiments choose the gas species and composition to promote the collision and energy exchange of gas and plasma; The laminar flow state is holded by controlling the gas runoff, the angle and direction, increaseing the gas stiffness to prevent plasma punctured, and the plasma energy exchange range is close on the surface of the workpiece so that the energy of laser beam is less absorbed by plasma than the workpiece.The experiments indicate that shielding gas suppression are adverse factors on plasma to use alone Ar, He and N₂. Adopting He-Ar-N₂ and the ratio of 7:4:l as a protective gas when gas flow rate is about 30L/min, the deep and wide ratio is large,the deep penetration welding seam surfaces obtained are smooth,the defects aren't obvious;the protective effect is poor if the gas flow is too large or too small.

Abstract: Compared with conventional ingot, difficulties in melting and casting of large size ZALCu5MnA alloy is due to the increase of ingot size, which lead to a depth increase in smelting bath process, mixing melting liquid is also difficult, and chemical composition of molten pool is not uniform. this paper uses finite element method to analyze the temperature field and thermal stress field of large size ingot of alloy in solidification process, heat transfer model, radiation the boundary condition and latent heat of solidification processing are discussed meanwhile the microstructure of the casting parts surface and center are related researched.