Key Engineering Materials Vols. 315-316

Abstract: Cutting temperature has direct effects on tool wear and tool life, as well as machining accuracy and machining quality. Titanium alloys, however, are generally machined at lower cutting speeds with cemented carbide tools due to its low thermal conductivity and high chemical reactivity with cutting tool materials. This paper deals with cutting temperature in high-speed milling of a near alpha titanium alloy. The measuring principle of cutting temperature by the workpiece-constantan thermocouple method was illustrated and the physical meaning of the electromotive force (EMF) signals was described in the paper. The effects of cutting parameters and wear status on cutting temperature were studied, and the temperature distribution along the cutting edge was investigated.

Abstract: Simulation on velocity field of gas-liquid flow in the abrasive water jet nozzle was studied by the computed fluid dynamics (CFD) software, The complex velocity field of the flow in the abrasive water jet nozzle can be obtained by means of simulation. The study on the effect of the nozzle inner cone angle on the velocity field shows that the cone angle affects the whirlpool’s intension and position of the whirlpool in the nozzle of abrasive water jet (AWJ), and it also affects velocity ‘s magnitude and distribution of the velocity on the cone surface.

Abstract: An effect of nano-scale TiN grains on the mechanical properties and microstructure of Si3N4 based ceramic tool materials is investigated at the different sintering temperature. Compared to monolithic Si3N4 ceramic tool materials, the sintering temperature is decreased and mechanical properties is enhanced when only one percent of nano-scale TiN in term of mass is added into the Si3N4 matrix. The optimum mechanical properties are achieved when Si3N4/TiN nanocomposites tool materials were sintered at the sintering conditions of 1650
, 30MPa and holding time of 40min. The flexural strength, fracture toughness and hardness are 1018.2MPa, 8.62MPa⋅m1/2 and 14.58GPa respectively. SEM micrographs indicate that microstructure is composed of the elongated and equiaxed β-Si3N4 grains, and some nano-scale TiN grains are enveloped into matrix grains.

Abstract: High-energy femtosecond laser pulses were utilized to ablate single-crystalline silicon wafer. Collateral damage areas around the ablation zone can be observed in microscope. The morphology in such areas changes gradually. The microscopic morphology and nanomechanical properties of the pre-polished back surface were measured by AFM and Hysitron TriboIndenter respectively. The topography and roughness in the ablated, metamorphic and unaffected zone are almost equal. Yet the elastic ratio and hardness on the back surface vary gradually with indent positions, which coincide with the gradual morphological changes in the metamorphic zone on the front surface. Such regular changes in nanomechanical properties, to some extent, reflect the distribution of collateral damages near the ablated zone on the back surface. And they also testify the occurrence of the ill effects that go against micromachining during high-energy femtosecond laser irradiation.

Abstract: High speed and high quality precision are essential requirements of NC lathes in modern industry. Since the heat generated from headstock system is a major factor causing machining inaccuracy, in this work, the thermal 3D model of the headstock system is built and its thermal characteristics are investigated using FEM. From the comparison of the numerical results with the experiment results, it is found that the FEM predicted well the thermal characteristics of the headstock system and the model is reliable to further optimum design of the headstock system.

Abstract: Smooth kinematic profiles are very important for high speed curve machining. During parametric interpolation, simple adaptive feedrate with confined contour error may cause acceleration and jerk to fluctuate acutely. To avoid the undesirable influence, an interpolation algorithm for parametric curves with smooth kinematic profiles is presented. The interpolator consists of three parts, look-ahead module, feedrate planning module and interpolation module. In look-ahead module, a pre-interpolator is designed to produce the required feedrate profile considering chord error. By feedrate planning, a smooth feedrate profile with confined acceleration and jerk is schemed based on bell-shape ACC/DEC profile by feedrate profile matching and feedrate profile synthesis. Then the parametric curve can be interpolated with the planned feedrate in interpolation module. Simulation results have been also provided to illustrate that the proposed interpolator can generate smooth kinematic profiles required for the high tracking accuracy at high speed with confined chord error, acceleration and jerk, and can be used for high speed and precision curve machining.

Abstract: Many thin-walled structure components widely used in aero industries not only have complex structure and large size, but also need high machining accuracy. However, because of their poor rigidity, it is easy to bring machining deformation caused by the existence of the initial residual stresses, the fixing stresses, cutting forces and cutting heat. The difficulty in ensuring their machining accuracy becomes a big problem, so that how to effectively predict and control the machining deformation has become an important subject in the development and production of our national defense weapons. This paper established a 3-D Finite element model with consideration of milling forces, clamping forces and initial residual stress field. By using this model, machining deformation of thin-walled frame shape workpieces has been computed. The simulated results are compared with experimental data, and the correctness of the simulation is verified. The study is helpful to the prediction and the control of machining deformation for thin-walled parts.

Abstract: A algorithm of interference free tool path generation for 5-axis NC machining with flat end cutter is presented. The approach includes: To obtain cutter location points from cutter contact points; interference pretreatment by convex box of NURBS surfaces and reducing check area; interference detection and tool-position correction based on mesh model while the interference problem is substituted with the relationship between tool and triangles. The algorithm is speed and reliable.

Abstract: An experimental study was carried out to investigate the process in surface grinding of two kinds of typical granite with a brazed diamond wheel. The horizontal and vertical forces were measured to obtain the data for the tangential and vertical force components as well as specific energy. Micrograph observations on tool surface and granite surface were coupled to check the prevailing mechanisms for material removal. Although the red granite is more difficult to machine than the black granite, according to factory records, the normal and tangential force components and specific energy for red granite were lower than that for black one, which might be attributed to the high height protrusion of brazed tool and the more ductile flow occurred in the grinding arc of black granite compared to the red one.

Abstract: Nano ceramics possesses excellent mechanical property and physical characteristics in contrast to conventional engineering ceramics, so it has tremendous application prospect. Adopting ultrasonic composite processing we describe the influences of grinding speed, grinding depth, wheel granularity and no-spark grinding times on the surface roughness of nano ZrO2 ceramics. By means of SEM and AFM the surface character and critical ductile grinding depth of nano ZrO2 ceramics in the condition of conventional and ultrasonic grinding are also discussed. At last, the residual stress of surface and crystalline phase transformation under the condition of conventional grinding and ultrasonic vibration grinding were analyzed by X-ray diffraction. The research indicated that ultrasonic vibration grinding could obtain nano finished surface with high efficiency. The residual stress of nano ZrO2 ceramics surface is determined much by different grinding styles.