Papers by Author: Lan Cai

Abstract: SiC particle reinforced Cu composite was fabricated by powder metallurgy and hot extrusion process. The friction behaviour of pure Cu, braze and composites was studied on a block-on-ring test. The blocks were slid against 40Cr steel rings under the lubrication of 232# machinery oil. It shows that the wear rate of pure Cu is about then times of the 5 vol.% Cu composite at a normal load of 300 N. The satisfied wear resistance prove the SiC is a promising reinforcement material for Cu matrix composite. However, the 20 vol.% SiC did not exhibit prospected wear resistance. The discussion of this phenomenon was conducted.

Abstract: The dynamic characteristics of the parallel mechanism depend strongly on the operating modes corresponding to different inverse solutions, but few of them have been involved with. In this paper, a new kind of 2-DOF parallel manipulator actuated horizontally by two parallel linear actuators is investigated. Firstly, the four inverse solutions of this manipulator are derived and analyzed; Secondly, the closed form inverse dynamic model is presented using the Lagrange approach based on the generalized system coordinates. An explicit formula of the equivalent moment of inertia, driving forces and consumed energy of the mechanism are investigated; Finally, the changes of equivalent moment of inertia, actuator force and energy consumption of the mechanism in different operating mode are analyzed through the dynamic numerical simulation. The results show that, for a given motion, the configuration and the operating modes have a significant influence on the equivalent moment of inertia and actuator force. The analysis provides necessary information for dynamic performance analysis and control of this parallel manipulator.

Abstract: Two 3-D finite element models of coated tool and uncoated tool were established using the finite element code DEFORM-2D based on the updated Lagrangian formula. And their machinability on high speed orthogonal machining was simulated and compared. The investigation results indicate that the coated tool has higher surface temperature and lower inside temperature compared with the uncoated tool. Moreover, the cutting forces of the model using coated tool are lower than that using uncoated tool.

Abstract: Based on premixed high pressure water jet cutting, five kinds of nozzle models were established, and the control equations and closed equtions of liquid-solid two-phase were given. The inside-outside liquid-solid two-phase flow characteristics of the nozzles were simulated by Hybrid Finite Analytic Method (HFAM). The results indicate that the taper-beeline nozzle has better convergence characteristic, good hydraulic characteristic and lower radical velocity, thus it is more suitable for premixed high pressure water jet cutting nozzle.

Abstract: To prevent or reduce the formation of burr efficiently in metal cutting, it is necessary to reveal the burr formation mechanism. A finite element model of cutting-direction burr formation in orthogonal machining was presented in this paper. The simulation of the burr formation process was conducted. Undeformed chip thickness, rake angle, rounded cutting edge radius and workpiece material were included in cutting conditions, whose influences on burr formation were investigated, according to the simulation results. By comparing the results of the simulation and the experiment, good consistency is achieved which proves that the finite element model of burr formation in this paper is significant and effective to predict burr formation.

Abstract: Regular arrays of micro-pillars and nano-grooves structures on the silicon wafer are fabricated by using soft lithography, and the three dimension morphology of textured surface is observed by using scanning electron microscopy (SEM) and atomic force microscope (AFM). The static water contact angles are measured by using contact angle meter to characterize the wettabilities of these surfaces. To investigate how the presence of topography and the variations of wettability affect the haemocompatibility of textured surface contacted with blood, different patterned surfaces are designed and fabricated, and blood platelet adhesion test is carried out on these surfaces. The adhesion and coagulation of platelets are inspected by scanning electron microscopy (SEM). Experimental data presented in this paper indicate that different surface roughness and wettability are the important factors for blood platelet adhesion. The amount of adsorbed blood platelet is low on textured surfaces, compared with that on the flat surface. Especially, there is no coagulation and activation on the surface with nanometer grooves. That is to say, the superhydrophobic surface is apt to decrease blood platelet adhesion. The study suggests that surface with suitable wettabililty and textured structures exhibits superior blood compatibility.

Abstract: In order to predict the geometry character of laser surface micro-texturing, the finite element analyzing software ANSYS is used to simulate temperature field and crater on the laser ablation. The influence and change regulation of laser intensity, laser pulse number and pulse duration in laser surface texturing are analyzed in detail. The simulation results conclude the best laser intensity in laser-pulse and materials interactions on certain conditions, and the best pulse duration in nanosecond laser micromachining. This research establishes the foundation for laser machining regular non-smooth surface in a rapid and effective way.

Abstract: The rapid market need of MEMS (Micro Electromechanical System) and metal microparts are increasing gradually. The plastic microforming has received more interests and applications in MEMS because it ensures high precision and manufacturing efficiency. However, it raises the higher demand on the microforming and plastic processing technology. Here we present one new process to micro-extrude microparts with laser-aided heating method. The new process is to selectively heat the workpiece with the laser radiation method to the suitable temperature that is between room temperature and recrystallization temperature, and to extrude the workpiece. This process is characterized by decreasing the influence of strain strengthening and lowering the resistance to deformation, and increasing the uniformity of material flow. The key elements of the approach concerning the warm micro-extrusion and temperature control, such as process parameters, laser heating system, micro-extrusion die structure, have been advanced. Furthermore, an important aspect of the research is that the developed system and theory of micro warm extrusion based on laser heating can be explored for further investigation and understanding of plastic microforming.

Abstract: Laser surface texturing (LST) technology that is firstly used in rollers, is a specialized surface engineering process capable of enhancing the surface material properties, wear resistance, fretting fatigue life and reducing friction. This practical technology of the LST process is based on a pulsating laser beam that, by material ablation, generates the optimum topographical surface. In order to exploit the full potential of the process, a great amount of research has explored from the material removal mechanics to the development of the LST process. This paper reports on the LST research involving the LST technology surveying process optimization, LST equipment and its industrial applications. The paper also highlights the forming theory describing the skin-pass process of transferring the textured roller’s surface structure onto the steel sheet, and the laser-matter interaction that occurs when and intense laser beam is tightly focused in the workpiece surface. It presents the influence of various factors affecting the textured workpiece performance together with the investigations into tribology of textured components. The paper also discusses these developments and some fundamental on future LST research.

Abstract: Fabricating surfaces with controlled micro-geometry may be an effective approach to improved tribological performance. In this paper, the effect of laser surface micro-mesh texturing on the tribological performance is investigated theoretically with numerical solution of EHL point contact. In the theoretical model, the Reynolds equation is used as the governing equation. Well controlled micro-mesh texturing is described in film thickness equation. By Full Multi-Grid (FMG) method, the solutions of film thickness profile and pressure distribution map are present over a wide range of texturing parameters. The influence of width, depth and orientation of mesh texturing on the friction coefficient is analyzed. Result shows that, the film thickness profile and pressure distribution are sensitive to the parameters of micro-mesh texturing. The curve result of friction coefficient under two load conditions indicated that the parameters of mesh are key factor for texturing design. Solutions demonstrate the ability of numerical simulation on the design and optimization of surface mesh texturing.