Rui Tao Peng

DEM Simulation and Experimental Investigation of Silicon Carbide on Pre-Stressed Machining

In this paper, the technology of pre-stressed machining suitable for ceramic materials was presented. Using the cluster method, the discrete element method (DEM) model of SiC ceramic was established to simulate the crack’s initiation and propagation in cutting processes with different pre-stress value. The scratching tests were carried out to confirm the validity of simulation. Both the DEM simulation and the experimental investigation showed that: with the increasing of pre-stress, the number of radial cracks reduced and the transverse cracks replaced the radial cracks to some extent, and also caused the material removal in the form of smaller fragments. Using pre-stressed machining can decrease the machining damage and improve the surface quality, and further prove that using DEM to simulate the machining process of ceramic materials was feasible.

Simulation of Tool Wear in Prestressed Cutting Superalloys

In high speed machining superalloys processes, tool wear is strongly influenced by the cutting temperature and contact stresses. Finite element analysis of machining can be used as a supplementary to the physical experiment, this paper provides investigations in 2D and 3D finite element modeling and simulation of prestressed cutting for GH4169 superalloy, a tool wear model for the specified tool and workpiece pair is developed based on the Usuis wear model, furthermore, tool temperature, wear rate and nodal displacement on the face of tool in prestressed cutting of superalloy is analyzed under various prestress condition and cutting parameters, and Python language is adopted to modify the Abaqus code used to allow tool wear calculation and tool geometry updating. The results of the simulation indicate that the tool wear rate increases with the increase of cutting time, and the influence of the prestress to tool wear in prestressed cutting process of shaft part is unremarkable.

DEM Simulation of Ceramic Tool Abrasion in Machining Superalloy

The discrete element method (DEM) model which describes the friction and abrasion behavior of the interface between Sialon ceramic tool and superalloy chip in machining were established, effects of cutting speed and depth of cut on tool abrasion were numerically investigated. The abrasion behaviors of the Sialon ceramic tool mainly appear in terms of abrasive wear, fatigue wear, adhesion wear and diffusion wear. The DEM simulation results show that, within a certain range, the higher cutting speed effectively results in the slighter wear of Sialon ceramic tools, meanwhile the deeper depth of cut leads to more serious tool wear. It is further validated that discrete element method is feasible to simulate the tool wear behavior.

3D Finite Element Analysis of Prestressed Cutting

In order to reveal the adjustment principle of prestressed cutting on the residual stress of hardened bearing steel GCr15, a three-dimensional thermal elastic-viscoplastic finite element model was developed using an Arbitrary Lagrangian Eulerian (ALE) formulation. Several key simulation techniques including the material constitutive model, constitutive damage law and contact with friction were discussed, simulation of chip formation during prestressed cutting was successfully conducted. At the prestresses of 0 MPa, 341 MPa and 568 MPa, distributions of residual stress on machined surface were simulated and experimentally verified. The results indicated that residual compressive stress on machined surface were achieved and actively adjusted by utilizing the prestressed cutting method; meanwhile, within the elastic limit of bearing steel material, the higher applied prestress leads to the more prominent compressive residual stress in the surface layer and subsequently the higher fatigue resistance of the part.

Structure Noise Performance Analysis and Optimization Research on a Low-Floor Gearbox

With the rail vehicle industry development and increasing request to the riding comfort, to reduce the structure vibration and noise caused by the gearbox is increasingly valued. Multibody dynamics method is proved to be very effective to structure optimization for noise control in gearbox design process. This paper aims to find an optimization way for the gearbox structure to increase the structure noise performance. Initially gear shafts and the casing were discretized using the finite element method, subsequently the multi-flexible body of low floor gearbox was established in the SIMPACK which considering the time-varying mesh stiffness and backlash, bearings were modelled via radial, axial and rotational stiffness elements, then the multi-flexible body dynamic response were analyzed and the structure noise was predicted. Finally, optimization schemes, in terms of gear modification and structure improvement, were proposed to improve the structure noise performance.

Experimental Study on Prestressed Cutting of Alloy Ring Parts

In order to solve the poor cutting performance for the titanium alloy and the serious residual tensile stress distribution on the machined surface in cutting titanium alloy, the utilization of prestressed cutting method is proposed to actively control the residual stress distribution status on the machined surface in machining process. Titanium alloy ring parts were pre-stretched at different condition by a lathe-specific pretension device respectively. By the cutting experimental, the cutting force ,chip formation and surface integrity indexes are compared and studied. The results show that in suitable compressive residual stress on machined surface are achieved by utilizing the prestressed cutting method ,meanwhile procedures of residual stress adjustment after machining could be omitted. Furthermore, the magnitude of compressive residual stress could be actively controlled by adjusting the magnitude of prestressed force in certain extent. And uniform saw-tooth chip are generated in prestressed cutting, meanwhile there’s no significant increment of cutting force. Prestressed cutting method could generate good surface integrity.

Optimal Design Analysis of the Thickness of Shrink-Fit Holder

A calculation scheme to gain the relationship between the thickness of shrink-fit holder and thermodynamic properties. Based on the theoretical analysis of fitting molder between shrink-fit holder and tool, then the thermodynamic properties of the shrink-fit holder and cutting tool such as contact pressure, equivalent stress and deformation are analyzed at different thickness of shrink-fit holder in static, under cutting force and inducting heating by using the finite element software ANSYS. The results show that the total contact pressure and maximum equivalent stress increased and the minimum thermal displacement difference decreased with the increase of holder thickness. Under the action of cutting force, the contact stress on the tool holder no longer uniformed and the maximum contact stress significantly increased, cutting tool also deformed. Finally a method to determine the reasonable holder thickness is given and it has a practical guiding significance for the design and selection of the shrink-fit tool holder.

Dynamic Characteristics Analysis and Structural Topology Optimization of the Plane Grinder

The dynamic characteristic is one of the important indicators which determine the performance of a machine tool, in this paper, the finite element model of a plane grinder is established with consideration of the behavior of joint, the static dynamic characteristics of machine tools are analyzed to reveal the vibration weak link, the column structure is topology optimized and redesigned based on the variable density degradation method. Static and dynamic characteristics of the original and new column are compared, and the dynamic characteristics of the machine tool before and after modification are discussed. The results indicate that the static and dynamic characteristics of the plane grinder are all improved after optimization.

Prediction of Chip Morphology and Cutting Force during Prestressed Cutting of TC4

Chip morphology plays a predominant role in determining machinability and tool wear during the machining of titanium alloys. Chip formation process in prestressed cutting of titanium alloy TC4 was numerically explored via the finite element method. Crack initiation during the chip segmentation was realized by using a ductile fracture criterion which based on the strain energy. Effect of prestress on cutting force and chip formation as well as Mises stress distributions were revealed. The results indicate that chips show the similar characteristic of continuous and regular serrated shape, which is not affected by prestress. Initial stress distribution of workpiece was changed by prestress, which correspondingly leads to the alteration of stress distribution in the subsurface layer. The generated cutting force curves share the same average amplitude and analogous rhythm, which correspond to the chip forming process respectively.

Residual Stresses in Prestressed Turning of Nickel-Based Superalloy

Aiming to get appropriate residual compressive stress distribution on machined surface just in the machining process, the technique of prestressed cutting is applied for nickel-based superalloy shafts. This article studies theoretically and experimentally the effect of prestress on the residual stress in the machined surface layer. Prestressed turning tests under the conditions of different prestress, cutting speed, depth of cut and feed rate were carried out, residual stresses were determined via an X-ray diffraction technique. Theoretical result demonstrates that higher prestress leads to more prominent residual compressive stress and validated by experiments, meanwhile measured residual stress profiles indicate that lower cutting speed and lower feed rate lead to more remarkable compressive stress state, contrarily depth of cut shows relatively indistinctive effect.