De Jin Hu

Electrical Discharge Grinding of Polycrystalline Diamond

This paper presents the tests of electrical discharge grinding (EDG) of polycrystalline diamond (PCD) on electrical discharge machine tool with high speed rotating device. The effects of wheel speed, open circuit voltage, peak current, pulse on time, and pulse off time of EDG on the material removal rate (MRR), wheel wear rate (WWR) and surface roughness (SR) are investigated respectively. The tests indicate that it is possible to shape PCD blank with EDG. The wheel speed makes the MRR increase dramatically. The higher the open circuit voltage, the larger is the MRR. The effect of peak current on the MRR, WWR and the SR is similar with that of open circuit voltage. However, the influence of the peak current is much larger than that of the open circuit voltage. Moreover, the peak current should be smaller than 32A. There is a best ratio between the pulse on time and pulse off time. If a ratio is larger or smaller than that value, there may be adverse effect on the SR and the MRR. Large pulse on time makes the MRR increase and the WWR decrease. However, all the parameters investigated have little influence on the SR of PCD. The SR is determined mainly by the grain size of PCD.

Fractal Characteristic and Wear Prediction of Surface Micro-Topography of Laser-Textured Roller

To investigate the effect of micro-topography on the wear properties of the cold roller, rough surface was characterized with fractal geometry, and the profile of laser-textured surface was measured based on the analysis of surface profile self-similarity, feasibility of fractal characterization of the surface was studied with power law method. Results show that Isotropic surfaces tend to be fractal and surfaces processed under definite technological conditions can be characterized with fractal geometry. On this basis, effects of surface fractal parameters on the wear rate of the roller were analyzed with fractal geometry model for wear prediction. Condition of achieving optimal fractal dimension was presented and the expression of the optimal fractal dimension was derived for the minimum normalized wear rate. It shows that normalized wear rate is mainly determined by fractal dimension besides the material properties and an optimal fractal dimension existed for the engineering surface is affected by the plastic index, normalized true contact area and scale coefficient. The results will provide bases for the studies of friction and lubrication of the textured steel sheet and guidance for the actual processing.

Real-Time Measurement and Compensation for Wheel Wear in Curve Grinding Based on Image Processing Method

This paper deals with an application to automatic compensation of grinding wheel wear by an image processing based real-time measurement method in dry curve grinding. An online image measurement system was schemed out and its principle was introduced in detail. Real time image of workpiece and grinding wheel is grabbed by CCD camera during grinding process. For the purpose of increasing the measurement precision, a new sub-pixel level accuracy edge detection approach combining Zernike moments operator with Sobel operator is proposed for locating the edge of the machined workpiece, which has advantages of fast processing speed and high edge locating accuracy. The wear amount of the grinding wheel is calculated by the image processing software, and is compensated automatically by NC controller. Finally, this method is applied to a new type CNC curve grinding machine MD9040. The experimental results show that the measurement and compensation method proposed in this paper is effective, and the contour error of the workpiece with real-time compensation is less than the feeding resolution for a compensation of 2μm.

Monitoring and Compensation of Thermal Error of Profile Grinding Spindle

Spindle thermal deformation is the main error source of many precision profile grinders. In this paper, the relationship between spindle temperature and either radial or axial thermal deformation is studied based on experiments. The placement and amount of temperature sensors are optimized. Then a kind of thermal error modeling method based on support vector machine is presented and applied in the modeling of thermal error of profile grinding. The result shows the model is robust and the on-line accurate prediction of grinding thermal error is realized based on monitoring of temperature rise of spindle. Finally, the error compensation strategy is discussed for further application of thermal error modeling.

Dynamic Monitoring and Intelligent Dressing of Diamond Wheel for Precision Curve Grinding

This paper deals with an application for achieving precision curve grinding by automatic dressing and compensation of diamond wheel wear through non-contact measuring method. A realtime vision measurement combined with vibration analysis method for the wear of a grinding wheel is presented. The wear condition is evaluated by analyzing the topography changes of the wheel surface and the vibration signals in the grinding process. A kind of PC-based integrated control system with dynamic monitoring and automatic dressing function is investigated, and the control algorithm is also proposed. The benefits of the proposed methods are confirmed by the grinding experiments. Dynamic monitoring of the wheel facilitates determining the optimum dressing amount and interval. A much higher abrasive machining precision and efficiency are attained by the real-time error measurement and compensation arrangement.

Research on NC Point-Grinding of the Curve Based on Normal Tracing

This paper presents a new technology, which is the normal tracing, for NC point-grinding of the curve. The development of the technology is based on the simultaneous three-axis machining. By controlling the superposition between the rotary surface of the grinding wheel and the normal vector of the curve, point contact between them is realized. So grinding just like turning, the abrasive machining of the complex curve is easy to be realized. The main advantage of the technology is the fact that it can not only reduce the deformation of the grinding wheel and simplify the NC programming, but also improve surface quality and profile accuracy. This paper builds the mathematic model of the normal tracing by analyzing the geometric property and the kinematic relationship between the wheel and the work piece. Then the control algorithm of the normal tracing is given and used in a new-type digital curve grinder successfully, MD9040 developed by ourselves.

Quantitative Analysis and Evaluation of Valve Core Spherical Surface Grinding Texture

High hardness surface coating sphere components are widely used in metal sealing ball valves. The spherical surface grinding texture influences the valve’s tribological performances such as friction, lubrication and wear of interacting surfaces. It can be used to develop the index of grinding parameter optimization. In this paper, based on the discussion of sphere generating grinding methods, the surface grinding texture is quantitatively analyzed. The space trajectory of abrasive particles during sphere grinding is studied. The trajectory mathematical models are built based on two kinds of sphere grinding manners and are verified by comparing the theoretical results against experimental measurements. The influence of grinding parameters on the texture is analyzed. Texture density are defined to quantitatively describe the surface texture. The relationship between grinding texture and ball valve performance is finally discussed. The conclusions can help to optimize the spherical surface grinding process.

Mathematical Modelling the Process of Cup Wheel Precision Grinding of Rotating Concave Paraboloid

A novel principle of cup wheel grinding of rotating concave quadric surface was proposed. The mathematical model of machining process was established to prove the feasibility of precision grinding of rotating concave paraboloid based on the introduced principle. The conditions of non-interference grinding of concave paraboloid were mathematically derived. The processing range and its influence factors were discussed. The trajectory equation of abrasive particle was concluded. Finally, the math expressions of numerical controlled parameters was put forward in the process of grinding of the concave paraboloid.

Experimental Study on the Laser Rapid Forming Repairing of 45 Steel and 2Cr12 Components

Laser rapid forming is a kind of new developed technology combining laser surface modification and rapid prototyping technology. It provides a powerful tool for the manufacturing and repairing of metal components. Laser rapid forming repairing experiments of 45 and 2Cr12 steel have been carried out with 316L stainless steel powder. Microstructure and properties of the repaired components are analyzed and tested with optical microscopy (OM), scanning electron microscopy (SEM) and electronic tensile experimental machine etc. Repaired components of different materials have been metallurgically bonded with the deposited layers, with fine microstructure, better mechanical properties and free of defects.

Online Wear Evaluation of Grinding Wheel in Machining WC-Co Coating

This paper presented a new technique, which was the online wear evaluation of wheel in grinding WC-Co coating by using wavelet packet decomposition. Based on the measurement method, theory of online wear evaluation of wheel was introduced. The selection principle of characteristic signals was brought up, and the grinding acceleration signal was the best choice among many characteristic signals. The time domain signal analysis method of wavelet packet decomposition was analyzed. Lastly, experiments on the wear of wheel were performed, and experimental results showed the validity of the method.