Guang Qi Cai

Model and Simulation of Slurry Velocity and Hydrodynamic Pressure in Abrasive Jet Finishing with Grinding Wheel as Restraint

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.

Study on the friction coefficient in grinding

Abstract The friction between the abrasive grains and workpiece is a crutial factor determining the main grinding output. Few studies have been carried out investigating the values of the friction coefficient in grinding, due to the difficulty of direct measurement. In this paper, a mathematical model of the friction coefficient in grinding has been established with the aid of a new grinding parameter C ge . Heavy grinding with different wheels and also single-grit grinding tests have been conducted for various work materials. The friction coefficients under different grinding conditions have been obtained using the model and the experimental results. The effects of grinding speed, wheel and work material on the friction coefficient have been discussed.

Application of Lubrication Theory to Near-Dry Green Grinding – Feasibility Analysis

This paper describes an investigation about the grinding fluid optimization supply based on lubrication theory. The models for three-dimensional hydrodynamic flow pressure in contact zone between wheel and work are presented based on Navier-Stokes equation and continuous formulae. It is well known that hydrodynamic fluid pressure generates due to this fluid flux, and that it affects overall grinding resistance and machining accuracy. Moreover, conventional methods of delivering grinding fluid, i.e. flood delivery via a shoe or jet delivery tangential to the wheel via a nozzle, have been proved that they can not fully penetrate this boundary layer and thus, the majority of the cutting fluid is deflected away from the grinding zone. Therefore, in this paper, a new delivery method of grinding fluid, the minimum quantity lubricant (MQL)-near-dry green grinding is presented and analyzed for it not only reduces hydrodynamic lift force but also reduces grinding fluid cost to achieve green manufacturing. Experiments have been carried out to validate the performance of the MQL supply compared with conventional flood cooling. The experimental results have shown that the theoretical model is in agreement with experimental results and the model can well forecast hydrodynamic pressure distribution at contact zone between and workpiece and the MQL supply in grinding is feasible. Experiments have also been carried out to evaluate the performance of the MQL technology compared with conventional flood cooling. Experimental data indicate that the proposed method does not negatively affect to the surface integrity and the process validity has been verified.

A study on the kinematics and dynamics of a 3-DOF parallel machine tool

Abstract A new kind of 3-DOF parallel machine tool has been developed to apply in billet snag grinding by Northeastern University, China. It has the advantages of simple structure, higher stiffness, higher ratio of force-to-weight, larger working space, simple kinematics equations, no motion coupling and no singular pose. This robot can be used for grinding, milling, polishing and other machining process with suitable tools. In this paper, its structure and degree of freedom, the workspace, the kinematics and accuracy analysis, the static and dynastic analysis, the simple robot and its parameters are introduced.

Study on Dynamic Strength Model of Contact Layer in Quick-Point Grinding

Ultra-high grinding speed and point contact are the salient natures of Quick-point grinding. Based on the damage dynamics theory, there are impact damages with a lot of micro-cracks and micro-defects and adiabatic shearing caused by ultra-high strain rate in the contact layer in such grinding manner. The micro-damages are relation to the strain rate and the materials properties, and increase with raise of strain rate. Because of the weakening effect of strain rate, the dynamic strength of the contact layer in Quick-point grinding is decreased and the grinding performance of ductile and brittle materials is also changed. The dynamic strength model of the contact layer in Quick-point grinding was built in this paper, and the weakening effects of strain rate caused by impact micro-damages on the dynamic strength of the layer and the materials removal mechanism in grinding layer were analyzed through the study on the theory and the experiments.

Material Removal Model and Experimental Verification for Abrasive Jet Precision Finishing with Wheel as Restraint

The material removal rate (MRR) model was investigated in abrasive jet precision finishing (AJPF) with wheel as restraint. When abrasive wore and workpiece surface micro-protrusion removed, the size ratio for characteristic particle size to minimum film thickness gradually diminishing, the abrasive machining from two-body lapping to three-body polishing transition in AJPF with grinding wheel as restraint. In the study, the material removal rate model was established according to machining mechanisms and machining modes from two-body to three-body process transition condition, and active number of particles in grinding zone were calculated and simulated. Experiments were performed in the plane grinder for material removal mechanism and academic models verification. It can be observed from experimental results that the surface morphology change dramatically to a grooved or micro-machined surface with all the grooves aligned in the sliding direction in two-body lapping mode. On the other hand, the surface is very different, consists of a random machining pits with very little sign of any directionality to the deformation in the three-body machining mode. Furthermore, the material removal rate model was found to give a good description of the experimental results.

Groove, Chip and Force Formation in Single Grain High-Speed Grinding

Abstract. High-speed single-grain grinding tests were carried out for 45 steel, 20Cr alloy. The grooves’ morphology and area removal ratio, chip morphology, grinding force ratio, and specific grinding force are studied. The area removal rate η increases with the grinding section area increasing. The plowing decreases with the grinding section area and grinding speed increase. Surface integrity can be improved under high speed and deep grinding.

Development and Study of a New Kind of 3-DOF Tripod

Abstract A novel 3-DOF parallel machine tool based on a tripod mechanism has been developed and studied. The main aspects of its structure, kinematics, workspace, parameter design, error analysis and force analysis are introduced. Through theoretical analyses and operation tests, it shows some distinctive advantages, such as high ratio of force-to-weight, simple structure and simple kinematic equations, large workspace with no kinematic coupling and no singularity configuration. The unique performance of the tripod machine tool provides a high potential and a very good prospect for its practical implementation in manufacturing industry.

An Evaluation on Surface Topography Finished by Abrasive Jet with Grinding Wheel as Restraint

Surface microcosmic topography finished by abrasive jet with grinding wheel as restraint was analyzed and evaluated. Generating mechanism of surface morphology finished by abrasive jet with grinding wheel as restraint was investigated and surface topographical characteristics were also evaluated with cross correlation of random process. Experiments were performed with plane grinder M7120 and workpiece material 45# steel which was ground with the surface roughness values of Ra=0.20.6m. The machined surface morphology was studied using SEM and microscope and the microcosmic geometry parameters were measured with TALYSURF5 instrument. The experimental results shown that the machined surface change from continuous and parallel micro-groove and plough to randomly discontinuous micro-pit can be observed with machining circles increasing and surface roughness was obviously improved. Furthermore, The finished surface has little comparability compared to grinding machining surface.The isotropy surface and uniformity veins both parallel and perpendicular machining direction were attained by abrasive jet precision finishing with grinding wheel as restraint.

A Micro Milling Model Considering Metal Phases and Minimum Chip Thickness

In this paper, a micro milling model is brought forward. The influences of different metal phases and the minimum chip thickness are considered in the model. The cutting forces and the surface generation in the micro milling process are predicted. Through the experiment validation, the results correlate to the model very well.