Papers by Author: Wei Xia

Abstract: To investigate surface stress distribution of rectangle piston ring, method of increment loading based on energy variational principle is used to ascertain contact state and solve elastic contact problems by iteration. Calculation results show that the central section of the first sealing surface is subjected to lower stress while two sides higher stress. The theoretical analysis and experimental results indicate that appearance of stress peak on surface is related to movement direction of piston ring. Relatively critical wear regions of piston ring are consistent with finite element analysis results. Wear width of both sides is 0.2mm more or less. The section of maximal stress appears at position near ring groove of the first sealing area.

Abstract: In this paper, a new analytical method of laser clad geometric simulation was developed. The effects of laser process parameters such as laser power, scanning speed, and powder feed rate on estimating clad geometry were investigated in this approach. A series of cladding was prepared by 1 kW diode pumping solid-state laser, to characterize the cross-section image of the clad by optical microscope. The clad profile was fitted by pitch arc and line in AutoCAD, with results displaying the arc-like upper profile of the clad. The theoretical results are discussed and compared with experimental data. The simulation based on the mass conservation is capable of predicting the clad width and depth with reasonable accuracy at medium powder feed rate.

Abstract: . An analytical model is developed for the prediction of residual stresses in burnishing. The model is simplified as a concentrated force pressing on elastic-plastic half-space using the solution to the Boussinesq-Flament problem. The treated material admits the elastic-plastic properties with hardening using a power law constitutive relation. Trial computation using Johnson-Cook model on AISI 1042 steel is presented and the results are verified with the experimental results given by Bouzid’s previous work. The residual stresses in the feed direction show the same trend with the experimental results while some differences still exist near the surface because of the concentrated normal force assumption and such stresses increase with the increase of burnishing force, decrease with the increase of depth and turn to zero beyond the plastic deformation boundary.

Abstract: The quality of the green and the shaping efficiency are affected by the mold structure during the course of powder injection molding (PIM). Based on the numerical simulation, the mathematic model for the optimal design of the gating and runner system in PIM mould is constructed. The method is testified by the Moldflow software and the experiment. From the result, it is suggested that the clamp force and the shape cycle are clearly decreased, the green is densified and the samples’ density error of the green is decreased after the optimal design of the mold structure. Furthermore, the number of trial mold is reduced and the shape efficiency is improved.

Abstract: In this paper, based on the CAE technology for MIM and fractional factorial design method, the simulation for the filling process was executed in different process conditions by the Moldflow software. And then it was realized that the extent of the effects of the single factor and pairwise interaction between the process parameters on quality of green parts were forecasted. According to that, the relationships of pressure, velocity and time and their optimal combination were researched by the experiments using a FC-80 plastic-Injection-Moulding machine. The experimental results suggested that the pressure, velocity and time have a obvious pairwise interaction which can have more effect on the product than single factor. It was shown that there was a good consistency between the numerical simulation and experiment. The CAE technique and the experiments are combined to optimize the process conditions and improve the part quality automatically by using smaller number of experiments.

Abstract: This paper gives the details of High Speed Milling experiments with AISI 52100 steel (HRC52) by using coated carbide end mills. Cutting force and Surface roughness data are presented. The effects of cutting speeds (1000-8000rpm), widths of cut (0.05-0.4mm) and cutting conditions (dry cutting and dry cutting with air coolant) are investigated. The results show that in high speed milling of hardened steels, when cutting speed surpasses a critical value, cutting forces decrease as cutting speed increasing; and the increasing of widths of cut causes the increase of cutting forces approximately linearly; surface roughness does not experience obvious increase or decrease and has a minimum in a specific condition; the machining results of dry cutting with air.

Abstract: A coupled thermo-mechanical model of plane-strain orthogonal metal cutting including burr formation is presented using the commercial finite element code. A simulation procedure based on Normalized Cockroft-Latham damage criterion is proposed for the purpose of better understanding the burr formation mechanism and obtaining a quantitative analysis of burrs at exit. The cutting process is simulated from the transient initial chip formation state to the steady-state of cutting, and then to tool exit transient chip flow, by incrementally advancing the cutting tool. The effects of cutting condition on the non-steady-state chip flow while tool exit can be investigated using the developed finite element model.

Abstract: Burnishing, an ultra-precision superficial plastic deformation process, is used increasingly as a surface enhancement finishing treatment after machining operations not only to give a mirror-like and work-hardened surface but also to impose favorable compressive residual stress in it. To analyze the feasibility of turning-burnishing hybrid process, the Taguchi’s L27(313) orthogonal array method with the analysis of variance (ANOVA) were used to analyze the influence of the initial turning process on surface integrity of roller burnished AISI 1045 steel such as surface roughness, surface microhardness. three turning parameters, namely the cutting feed, cutting depth and cutting speed, three burnishing parameters, namely the burnishing feed, burnishing depth and burnishing speed were selected as the experimental factors in Taguchi’s design of experiments to determine which one has the dominant influence and how it works on burnishing effects, namely the surface roughness and surface microhardness, the interactions between cutting feed, burnishing feed and burnishing depth were considered. The experimental results agreed well with the theoretical analysis and the conclusion is cutting feed has dominant influence on burnished surface integrity.

Abstract: Microstructure of machined copper chips at very low velocity was characterized by transmission electron microscopy. The structure of the machined chip produced by reasonable combinations of machining parameters is virtually entirely occupied by isolated equiaxed submicron grains of 100~300nm in size with high-angle boundaries. A finite element model was developed to study large plastic deformation in plain orthogonal machining copper. The numerical results show most of the grain refinement associated with the formation of ultra-fine grained chip may be attributed to the large shear strain imposed in the deformation zone. It is feasible to take machining process as a method of preparing ultra-fine grained materials. But the optimal design of the machining process requires a precise and quantitative understanding of the mechanics of deformation-induced subgrain microstructure.

Abstract: 2D finite element model with the same material for backup to minimize the burr size was developed to investigate mechanism of burr formation and burr minimization. The flowstress of the workpiece and backup material are taken as a function of strain, strain-rate and temperature. Temperature-dependent material properties are also considered. The Cockroft-Latham damage criterion has been adopted to simulate ductile fracture. The crack initiation and propagation is simulated by deleting the mesh element. The result shows putting a backup material behind the edge of the workpiece is an effective way to minimize the burr size. The effects of cutting condition, temperature and different backup material properties on the burr formation and burr size can be investigated using the developed finite element model. This model could be useful in the search for optimal tool geometry and cutting condition for burr minimization and for the modeling of a burr formation mechanism.