Key Engineering Materials Vols. 375-376

Abstract: Many thin-walled aero-parts have complex structure, and high machining accuracy is required. But because of their poor rigidity, it is easy to bring machining deformation caused by the existence of the clamping residual stress, and influences machining accuracy of workpiece. At the present time it is a focal point how to reduce the deformation the machined surface. Present studies mainly focus on the influences of clamping points, clamping order and clamping force on residual stresses. It is few studied for clamping schemes how to influence the residual stresses and the fatigue resistance of the machined parts. To reflect the relationship between clamping schemes and residual stresses and fatigue resistance, finite element models with different clamping schemes were built and the clamping process was simulated. A conclusion is obtained that it is advisable to adopt even and symmetry distributed clamps and multi-point clamps to reduce the workpiece distortion of aero-multi-frame components due to the clamping. This study conclusion has been validated by the actual production.

Abstract: The models for three-dimensional velocity and hydrodynamic pressure of abrasive fluid in contact zone between wheel and workpiece on abrasive jet finishing with wheel as restraint were presented based on Navier-Stokes equation and continuous formulae. The emulational results shown that the hydrodynamic pressure was proportion to grinding wheel velocity, and inverse proportion to the minimum gap between wheel and workpiece and the maximum pressure was generated just in the minimum clearance region in which higher fluid pressure gradient occur. It can also be concluded the pressure distribution was uniform in the direction of width of wheel except at the edge of wheel because of the side-leakage. The velocity in the x direction was dominant and the side-leakage in the y direction existed. The velocity in the z direction was smaller than the others because of the assumption of laminar flow. The smaller the gap distance is, the larger the velocity in the x direction. The magnitude of the velocity is also proportional to the surface velocity of the wheel.

Abstract: The physical simulation of high-speed cutting (HSC) is a hot research in cutting field. Dynamic physical simulation is the key technical difficulty of physical simulation. It can afford the machining process parameters quickly and efficiently, such as cutting stress, cutting temperature, tool wear etc., which have important academic and practical value. The cutting theoretical mathematical model based on the elastic-plastic mechanics and tribology was built up. The two-dimensional / three-dimensional (2D/3D) HSC dynamic physics simulation models were built up by the finite element method. The stress, thermal distribution and tool load etc. during the high speed machining (HSM) was obtained. These parameters provided key technical basis for the establishment and optimization of HSM parameters. They can save much machining experiments cost and improve the processing efficiency.

Abstract: Based on the theoretic analysis and experiments on milling the carbon structural 45 steel with the flat rake milling insert and the waved-edge milling insert with complex 3D grooves which is developed by HarBin University of Science and Technology, we have studied on the impact disrepair mathematic model and groove optimization. On the basis of the milling force mathematic model and force density function of the waved-edge milling insert with complex 3D grooves the author built, we have the finite element analysis and blurry synthetical judgement of the 3D stress field, and forecast that the anti-impact disrepair capability of the waved-edge milling insert is choiceness. We find out the difference of the impact disrepair invalidation types between different grooves milling inserts by the experiments. Based on the plentiful and systemic impact disrepair experiments, as the emphasis in this paper, we build the impact disrepair life cumulating distribution function mathematic model by the mathematics statistic method and have contrast analysis of the impact disrepair average lives between the two types of milling inserts, and prove that the anti-impact disrepair capability of the waved-edge milling insert is choiceness. All these studies provide the theoretic and experimental basis for solving the cutter disrepair which is the key problem in the automatization production and groove optimization.

Abstract: In this paper, the impact pressure of abrasives acting on the polished materials was deduced by Field Theory and the model of surface roughness for polishing super hard materials with Abrasive Water Jet (AWJ) was established. The model indicates that the surface roughness increases linearly with an increase in the maximum depth of abrasives indenting into materials and that the relationship between the surface roughness and polishing parameters including water pressure, abrasive pressure, the impact angle, the hardness of the polished material, the elastic distortion of abrasive, abrasive size, abrasive density, nozzle diameter and standoff.

Abstract: A burr formation process in micro-cutting of Al7075-T7451 was analyzed. Three stages of burr formation including steady-state cutting stage, pivoting stage, and burr formation stage are investigated. And the effects of uncut chip thickness, cutting speed and tool edge radius on the burr formation are studied. The simulation results show that the generation of negative shear zone is one of the prime reasons for burr formation. Uncut chip thickness has a significant effect on burr height; however, the cutting speed effect is minor. Unlike in conventional cutting, in micro-cutting the effect of tool edge radius on the burr geometry can no longer be neglected.

Abstract: In order to solve the difficulty of polishing process at present. Polishing posture was analyzed at the contact spot of polishing cutter with work piece in this paper, and how to layout the polishing path and its built method were discussed emphatically, carried out simulation analysis with Mastercam software, and proposed suitable building method of path according to different region using different polishing method. Finally, it is proved that an ideal effect would be achieved.

Abstract: The generation and distribution of workpiece surface and sub-surface residual stress were predicted through the dynamic finite element simulation of the grinding ceramic process. The base of the simulation is that the thermo elastic-plastic finite element theory and the coupling of grinding forces and temperature were adopted. The results obtained from X-ray diffraction measurement compared well with the values calculated from theory. The correlation between grinding parameters and the ceramic residual stresses was investigated. The research results show that the normal grinding force is the primary factor responsible for the generation of residual stress in grinding ceramic. The mechanical effect of the grains is to affect the magnitude, the depth of penetration and the gradient of the residual stresses.

Abstract: Complex parts are the main object for CNC machining. The 3-TPS hybrid machine tool can achieve 3-axis, 4-axis, 5-axis, vertical and horizontal machining. The analysis of nonlinear error of the 3-TPS hybrid machine tool on 5-axis machining and the reduction the error by self-adaptation linearization are introduced in the paper. The obtained formula for nonlinear error can be used in different situations and estimate three-dimensional cutter evelope forming error.

Abstract: Abrasive jet finishing process is a novel process whose objective is to remove surface defect layer and to diminish roughness and ripple after grinding. Experiments were performed with plane grinderM7120 and workpiece material 45# steel which was ground with the surface roughness values of Ra =0.2-0.6 μm . The machined surface morphology was studied using SEM and the microcosmic geometry parameters were measured with MICROMESVRE2 instrument. In this paper, with the fractal dimension, Ra , Rq and the supporting rate curve, the surfaces of grinding machining and abrasive jet finishing machining were researched. The result indicated that the machined surfaces changed from continuous parallel micro-groove and plough to randomly distributed discontinuous micro-pit could be observed with the increase of machining circles and surface roughness was obviously improved. Furthermore, the isotropy surface and uniformity veins both parallel and perpendicular machining direction were attained by abrasive jet precision finishing with grinding wheel as restraint. The supporting rate curve of the surface profile can be increased. This is favorable for the wearable capability of the workpiece.