Advanced Materials Research Vol. 497

Abstract: A new approach for the precise grinding of crankshaft pin is presented. In which, noncircular following strategy is investigated based on the motion model consists of horizontal feeding axis, additional lifting axis for wheel frame, and the active rotary axis for workpiece. The straight line relationship of wheel center, pin center and grinding point is ensured by the synchronism between standard arc interpolation motion of wheel frame and eccentric circular motion of pin section. Comparing with traditional tangential point tracing scheme, both constant grinding line-speed and simple control algorithm are fulfilled simultaneously. The negative effect of perpendicular deviation introduced by lifting axis is kinematically analyzed as well as the dynamic response error of servo system, and solving methods are carried out accordingly. By computer simulation and experimental test, the reported noncircular following strategy emerges good characteristics in the manufacturing of crankshaft, such as a strong adaptability for wheel wearing, simple motion control and high roundness precision.

Abstract: Problems with gear shaft formed by cross wedge rolling (CWR), such as slip, disorder of tooth, material deficiency at two sides of the gear, have restricted the application of this craft to form gear shafts. In this paper, numerical simulation on the process of gear shaft formed by cross wedge rolling was carried out with the help of solidworks and deform 3d. Compared with the standard profile, there is margin on the profile of the gear shaft for further process. It’s proved that the traditional methods to make a gear shaft can be replaced by CWR. From curves of force in three directions, it is easy to conclude that radical force and tangential force are the main forces which are exerted on the dies and vary similarly in all stages.

Abstract: As a search algorithm for optimization based on the mechanics of natural selection and genetics, Genetic Algorithm (GA) has been widely used for solving optimization problems in various fields. According to the present manufacture situation of Austempered Ductile Iron (ADI), three samples with different quenching temperature were prepared and their mechanical properties were tested. The ceramic cutter CC6050 were used in the precise dry cutting experiment and 2205 profilometer was used to measure the surface roughness of the workpieces. The predictive models of the surface roughness during the dry finishing process were established based on Genetic Algorithm, then the results were compared with those gotten by multiple regressions, and the relationship between the surface roughness and the quenching temperature was analyzed. the cutting speed and the feed rate has greater impact on the surface roughness among the three cutting parameters, and the obtained surface roughness was larger as the quenching temperature increased.

Abstract: The purpose of this study is to acquire design method of machine tools with higher dynamic stiffness and consequently higher chatter stability. This study focuses on stiffness of main structures and friction damping in guide of a machine tool, because stiffness and friction damping are considered to have major influence on the dynamic stiffness. A special testing machine with variable stiffness and friction was developed to clarify effects of the stiffness of main structures and the friction in guide on the dynamic stiffness and therefore the chatter stability. The stiffness of main structures and the friction in guide were changed experimentally, and it was clarified that the optimal friction force exists at every stiffness condition, and that higher stiffness does not always lead to higher stability.

Abstract: CVD diamond coated inserts with different coating thickness are fabricated using hot filament chemical vapor deposition (HFCVD) method. Scanning electron microscope (SEM) and Raman spectroscopy are introduced to characterize the diamond films. The cutting performance of as-fabricated CVD diamond coated inserts is evaluated in dry turning aluminum alloy. The uncoated WC-Co tool is also adopted in the cutting tests for the sake of comparability. The testing results show that diamond coated tools exhibit much better cutting performance. Coating thickness affects the characteristics of diamond coated cutting tools, the thicker of coating, the more adhesive chips, but the better delamination resistant. The uncoated WC-Co tool suffers adhesive wear for the built-up edge (BUE) breaking.

Abstract: The working performance of the spindle system is the most important factor to embody the overall performance of the machine tool. To ensure the advanced capabilities, besides the high-precision manufacturing technologies, it is mainly depending on the bearing module and the forces on the spindle. In this paper, a new strategy of the vertical spindle supporting system is presented to meet the high stiffness requirement for the aerostatic bearing. Based on the computational fluid dynamics and finite volume method, a fluid dynamic model and structure model of the large diameter incorporate radial-thrust aerostatic bearing is developed and simulated to find out the pressure distribution laws of the spindle supporting system. The grid subdivision in the direction of film thickness is paid more attentions when establishing the grid of the whole gas film. Simulation results show that this special structure of bearing module can supply enough load capacity and stiffness for the machine tool. The results also indicate that the static characteristics of the bearing are improved as the supply pressure increases and as the supply orifice diameter decreases.

Abstract: Two kinds of vitrified bonds, bond L (low temperature bond) and bond G (high strength bond), were blended by ball-milling in producing diamond wheels. Proper Sintering techniques were employed by analyzing properties of the wheel through DSC testing and fracture strength. The wheels were applied in machining PDC in comparison with similar product on market. It showed that the blended bond reached its highest fracture strength when bond L amount was about 20wt~24wt%; combination of this two kinds of vitrified bonds would improve the wheel’s comprehensive properties by raising its fracture strength to 89MPa when bond L takes up 22wt%; service life of wheels prepared by this blended bond was 30~50% longer than similar market product and efficiency improved by more than 20%.

Abstract: In order to process heterotype hole of workpiece precisely, an open abrasive flow polish machine is designed, and the optimization design of machine frame is done for low cost. Firstly, basing on the parameters designed with traditional ways, three-dimensional force model is set up with the soft of SolidWorks. Secondly, the statics and modal analysis for machine body have been done in Finite element methods (FEM), and then the optimization analysis of machine frame has been done. At last, the model of rebuild machine frame has been built. Result shows that the deformation angle value of machine frame increased from 0.72′ to 1.001′, the natural frequency of the machine decreased from 75.549 Hz to 62.262 Hz, the weight of machine decreased by 74.178 Kg after optimization. It meets the strength, stiffness and angel stiffness requirement of machine, reduces the weight and cost of machine.

Abstract: Powder metallurgy (PM) nickel-based superalloy is regarded as one of the most important aerospace industry materials, which has been widely used in advanced turbo-engines. This work presents an orthogonal design experiments to study the cutting force and cutting temperature variations in the face milling of PM nickel-based superalloy with PVD coated carbide tools. Experimental results show that with the increase of feed rate and depth of cut, there is a growing tendency in cutting force, with the increase of cutting speed, cutting force decreases. Among the cutting parameters, feed rate has the greatest influence on cutting force, especially when cutting speed exceeds 60m/min. With the increase of all the cutting parameters, cutting temperature increases. However the cutting temperature increases slightly as the increasing of feed rate. Tool failure mechanisms in face milling of PM nickel-based superalloy are analyzed. It is shown that the breakage and spalling on the cutting edge are the most dominate failure mechanisms, which dominates the deterioration and final failure of the coated carbide tools.

Abstract: The dynamic characteristics of a hydrostatic and hydrodynamic journal bearing with two arrays of eight holes have been investigated theoretically by the three-dimensional Computational Fluid Dynamics (CFD) models with respect to equilibrium position. The various dynamic coefficients for design parameters, such as orifice diameter, length to diameter ratio, eccentricity ratio, supply pressure, and rotational speed, are analyzed systematically under the action of displacement disturbance and velocity disturbance which are considered by the User Definition Function (UDF) programs. Results show that the dynamic coefficients greatly affected by design parameters. The cross stiffness coefficients increase rapidly more than direct stiffness with an increase of length to diameter ratio and rotational speed. Conversely, the direct stiffness coefficients are larger than cross stiffness with an increase of supply pressure and eccentricity ratio. It indicates that the journal bearing with two arrays of eight holes is suitable for their applications to small diameter grinding spindle by the means of optimizing the operating parameters and the structural parameters in order to obtain a better dynamic characteristic.