Key Engineering Materials Vol. 667

Abstract: Basing on the milling experiment of carbon fiber reinforced plastics (CFRP), the machining surface qualities of different edge shape and coated tools are researched contrastively. The results show that: when the CFRP is milled by general right-hand edge milling cutter, due to the small tool rake angle, bad tool sharpness, and carbon fibers of upper and lower surface are both subjected to upswept cutting force, the burrs appear at the upper surface of workpiece. But there is no burr at the lower surface. When the CFRP is milled by interlaced edge or herringbone edge diamond coated milling cutter, which are designed to left-hand and right-hand interlace, the carbon fiber of workpiece’s upper and lower surface are subjected to downward and upswept cutting force respectively. There is no burr at the upper and lower surface of workpiece. Compared with interlaced edge diamond coated milling cutter, herringbone edge diamond coated milling cutter is more suitable for finish machining of CFRP.

Abstract: Silicon carbide particles reinforced aluminum matrix composite (abbreviated as SiCp/Al) offers excellent performance such as high specific strength and stiffness, which make it widely used in aerospace, automobile and other fields, but it is hard to be manufactured. An aluminum matrix composite reinforced with 45% volume fraction of 5μm silicon carbide particles in an A12 aluminum matrix was experimental studied by ultrasonic vibration-assisted scratch (UVAS) and traditional scratch. Cutting forces and surface topography were measured by Kistler dynamometer and SEM. The experimental results showed that the cutting forces fluctuated obviously and the axial force was larger than the tangential force during both UVAS process and traditional scratch process. Average cutting forces of UVAS process were less than those of traditional scratch process. At the same time, small chips of SiC and high surface quality were observed in the scratch surface of UVAS. These indicate that ultrasonic vibration-assisted method plays an important and effective role in reducing cutting forces and improving surface quality.

Abstract: Cr, Ni, Mo, V exist in materials of high, medium and low pressure turbine rotor. Its composition contains higher carbon content, so leads to poor hardenability. Shear characteristics of martensite phase transformation is caused by a large number of micro defects inside crystal of microstructure in rotor during the service status. Martensite phase transformation is by strengthening because of plastic deformation in cutting process. Mechanical properties and phase transformation plasticity in cutting process show that rotor is hard machining material. Plastic deformation aggravates tool wear, and leads to an increased cutting force; hard points of uneven material internal organization lead to fluctuation of cutting force, and induced cutting chatter. During the course of machining critical or ultra-supercritical rotor, boring bar becomes a flexible system surrounded by rotating stirred vortex cutting fluid inside and outside it. BTA processing system is in a complicated hydraulic-solid coupling environment. Whether or not BTA deep hole boring processing system is stable, the essence is converted into estimating dynamic stability of BTA boring bar coupled fluid--solid with multi-physics environment. The system will be triggered cutting chatter, fluid flutter and self-excited vibration combination. This paper establishes nonlinear mathematical physics model on BTA deep hole processing system. The perturbation equation and Lyapunov function of BTA system are obtained, through introducing the stable Rumjantsev part variables analysis theory. Based on stability characteristic under the significance of Lyapunov, the constraint condition undisturbed stability is gotten and the global bifurcation analysis is finished. Hyperbolic periodic orbit and heteroclinic connection are found throughout the entire phase space of Hamiltonian system. The bifurcation condition on quadratic heteroclinic is acquired, by analyzing intersection relationship between hyperbolic stable manifold and its unstable manifold of Poincare mapping. The intersection critical conditions are shown on hyperbolic fixed stable manifold and its unstable manifold, by using computer numerical simulation to draw 3-D surface relationship among resonant frequency, cutting fluids flow velocity and the radius of free surface. The result could provide a reference on multi-machining parameters optimization for BTA deep hole boring process practical production.

Abstract: The scanning process of fused deposition modeling is realizing the fill of certain region, Therefore, reasonable scanning path planning directly affects the forming efficiency and the precision of the work piece. The method of Hilbert curve fractal scanning path which basing on the characteristics of both partition and parallel scanning is put forward basing on the analysis of the existing scanning mode. Application of improved curve filling method for complex curved surface forming planning, according to the characteristics of the Hilbert curve and Hamilton circuit, combined with the characteristics of the scanned level scan path trajectory planning, generate a continuous and comprehensive function value which the weight minimum scanning track under the premise of ensuring the quality of scanning. In order to avoid the generation of island type trajectory, setting a decimal for each loop can easily distinguish between each circuit, finally obtains the scan trajectory. The method can be used to generate scanning track continuous greatly reducing the spray head start and stop times and improves the processing efficiency of the whole, not only to meet the accuracy requirements and can generate non scanning path interference but also high forming efficiency.

Abstract: Metallic glasses have a variety of excellent properties compared with the majority of conventional crystalline alloys, and have a broad application prospects in the military, aerospace and sports equipment. Cutting, as an efficient and high-precision machining process, is expected to be an important processing method for metallic glasses. Currently, investigation on cutting metallic glasses is in a nascent stage. Although the machining precision of several tens of nanometers has been achieved, its cutting mechanism remains unclear. In this paper, a molecular dynamics simulation of orthogonal nanometric cutting of metallic glass Cu50Zr50 was carried out.The material deformation, cutting force, and workpiece temperature distribution were studied at microscopic scale. It is found that the deformation accumulation first occurred on the tool rake face. Then with the cutting progressing, materials underwent stable plastic deformation in the shear zone. Analysis on cutting force shows that in the initial material deformation process the cutting force increases rapidly until the cutting process is stabilized, , and then it is reduced to a stable value. Finally, the temperature change of the workpiece during cutting was calculated, and the result shows that the maximum temperature reaches the glass transition temperature. Further, the radial distribution function analysis of workpiece was used to confirm the occurrence of the glass transition.

Abstract: Light scattering of the upper polymer have a great influence on welding quality. Light scattering of high density polyethylene (HDPE) and low density polyethylene (LDPE) are assessed by constructing experiment and numerical computation method. Firstly, the beam quality of semiconductor laser is analyzed, power flux distribution of the laser beam in a defocused plane is measured by knife edge method; Afterwards, the power flux distributions of the laser beam after passing through HDPE/LDPE are measured by line scanning method; Lastly, with the combination of the mathematical model which is used to calculate scattering coefficient and standard deviation of scattering, scattering related parameters and the laser power flux distribution at the welding interface are obtained by writing a program in MATLAB. The results show that the light scattering coefficient of high density polyethylene is up to 0.988, the light scattering coefficient of low density polyethylene is 0.92; Higher crystalline polyethylene leads to more obvious light scattering; the laser beam power flux distribution at the weld interface affected by scattering is determined, which lays a solid foundation on numerical simulation in laser transmission welding.

Abstract: To understand the thermal effects on material removal at atomic level, molecular dynamics (MD) simulation and optimization method are performed with the aid of Morse, EAM and Tersoff potential. The heat distribution is showed in 3D images under various parameters. The simulation results reveal that the heat distribution is roughly concentric around the tool edge and a steep temperature gradient is observed between diamond tool and chip. During material removal process, there is a narrow region with high temperature in shear zone where most of heat generated due to plastic deformation of workpiece material, the high temperature extends from here to chip, diamond tool and workpiece, but the highest temperature lies in chip. Compared with low speed, a higher temperature region below the tool edge implied a larger shear stress is built up in a local region and a rougher machined surface is generated at high cutting speed.

Abstract: Molecular dynamics (MD) simulations of nanomachining of monocrystalline silicon were performed with the aid of Tersoff potential. The effects of machining conditions on the nature of heat distribution and corresponding phase transformation during nanomachining were investigated. It is clearly demonstrated that heat distribution shows a roughly concentric shape around the shear zone. A steep temperature gradient is observed in diamond tool and the highest temperature lies in chip. Stress distribution presents dual annular shapes, the highest compressive stress and tensile stress lay in shear zone and machined surface, respectively. Phase transformation mainly occurred in chips, shear zone and machined surface. Additionally, atoms in the machined surface are transformed from diamond cubic structure (Si-I) to β-tin structure (Si-II) and bct5-Si.

Abstract: To solve the problem of low efficient, big noise and vibration during cutting of the high strength high temperature thin-walled steel tubes, explore and research a new kind of blade with special ingredients for the working band, unique design for the overall blade structure, and process optimization. The investigations are done to obtain the basic cutting performance through the elaborate and literal formula, to ensure the blade to work smoothly, heat dissipation fast, and noise reduction considerable by using discontinuous and uneven distribution of working band and setting cooling--heat dissipation gaps and heat dissipation holes. Ten steps of saw blade manufacturing process are created——alloying of copper, tin and rare metals - water atomization - special ball milling - ingredients and mixture - whole sintering - gap laser cutting for cooling and heat dissipation-laser cooling hole-thermal gap and heat dissipation hole - calibration and stress relief - quality inspection. Eventually the actual saw blade performances are got: high efficiency, smooth cutting, low noise and long service life. Experimental study and production practice show that this kind of cutting piece has obvious advantages relative to the resin, which is a effective tool for cutting high strength high temperature thin-walled steel pipe.

Abstract: Usually, generating parts with complex surfaces, especially three-dimensional (3D) curved-surface blades, involves difficult designing, complicated manufacturing processes, and low production efficiency. In this study, by integrating 3D curved-surface modeling and the rapid prototyping functions of the pro/E software platform with computer-aided design, layered manufacturing, and material curing technologies, an improved process was realized. The once-challenging fabrication of irregular curved-surface blades was transformed into a simple technique of making planes. By selectively curing the raw material, as demonstrated in this study, complex surfaces can be manufactured rapidly, thus shortening research and development stages of new products, reducing costs, and endowing manufacturers with an improved capacity to research and develop products with greater competence and accuracy .