金属基金刚石圆弧砂轮电火花修整的廓形仿真与实验研究

根据金属基金刚石圆弧砂轮修整的需要,研制了杯型修整电极式电火花修整装置,并介绍了装置的结构特点。分析了修整电极与砂轮尺寸对砂轮修整圆弧廓形的影响,根据修整电极与砂轮的尺寸推导出圆弧廓形的表达式,并利用Matlab进行了仿真计算。结果表明:修整宽度为10mm的砂轮时,圆弧半径理论误差在0.02mm以内。通过研制的杯型修整电极式电火花修整装置进行了电火花修整实验,修整后的砂轮实际廓形与仿真廓形误差小于3μm。     

放电参数对电火花修整金刚石砂轮效率的影响

利用电火花工艺对金刚石砂轮进行修整具有明显的技术优势。为了提高其修整效率,探究电气参数对砂轮修整效率的影响,采用控制变量法设计了试验流程,在专用数控机床上利用电火花工艺对金刚石砂轮进行修整。在测量砂轮的修整量时,由于砂轮去除量微小,分别计量砂轮的去除厚度和去除质量,两种方法互相印证,说明结果的正确性。试验结果表明:在一定范围内提高脉冲电源的输出功率,可以提高其修整效率,在一定范围内增加脉冲间隔,反而会提高砂轮修整效率。分析结果可以为提高电火花修整金刚砂轮的效率提供参考。     

电火花加工表面形貌的分形研究

利用分形理论,采用一种新的分形维数计算方法,得出电火花加工表面的二维分形维数。研究了电火花表面的磨损分形行为,从而为预测和提高模具寿命提供了依据。     

金刚石砂轮修整新技术的研究

通过一系列试验，研究了适用于MK9025数控光学曲线磨床上金刚石砂轮修整的3种新技术：激光修整法、气中电火花放电修整法、激光辅助机械修整法，实验结果表明3种金刚石砂轮修整技术都是可行的，是很有前途的新技术。     

不同介质中电火花修整金属基金刚石砂轮的研究

用电火花方法修整金属基金刚石砂轮时,不同的放电介质对修整过程有不同的影响,考虑到电火花在线修整金刚石砂轮对加工介质的特殊要求,文章比较和研究了压缩空气、水雾气、雾状乳化油3种放电介质对修整过程的影响.试验中用VH-1000三维数字显微镜对修整后的砂轮形貌进行了分析,同时比较了修整效率,用表面粗糙度仪测量了不同放电介质修整后的金刚石砂轮磨削工件后的表面粗糙度.试验结果表明:压缩空气为介质的修整速度最慢,表面质量最差;雾状乳化油为介质的修整效率及效果最好;水雾气为介质的修整效率与效果接近雾状乳化油.     

电火花修锐对金属结合剂CBN砂轮表面形貌的影响

采用电火花修锐方法对青铜结合剂锯齿形CBN砂轮在平面磨床上进行修锐实验,对修锐前后的砂轮表面形貌进行观测,修锐后砂轮的有效磨粒数、磨粒凸出高度明显增加,修锐时间以4~6h为宜;采用修锐后的砂轮对材料2T8/SK5进行了锯齿磨削加工实验,经测量,锯齿角度轮廓精度有较大提高。电火花修锐方法适合于金属基CBN砂轮的修锐。     

表面放电辅助金刚石砂轮复合修整的可行性研究

针对金刚石砂轮修整困难的问题,提出了基于表面放电辅助的金刚石砂轮的复合修整法,并通过测量放电时的表面温度对该方法的可行性进行了研究,最后基于研究结果进一步提出了改进方案.     

Special wire guide for on-machine wire electrical discharge dressing of metal bonded grinding wheels

To improve accuracy in wire electrical discharge dressing (WEDD), special attention should be given to wire vibration. In this work, the use of a specially designed wire guide is proposed, which is responsible for both ensuring the stability of the wire and improving the efficiency of dielectric delivery to the dressing zone. For carrying out experiments with metal bonded diamond grinding wheels, a WEDD-device was designed, manufactured and integrated into a grinding machine. High erosion material removal rates and dressing accuracy were achieved, thus demonstrating the feasibility and efficient performance of this in situ dressing process.     

Mechanisms in the generation of grinding wheel topography by dressing

For the process of dressing vitrified bonded grinding wheels with diamond tools it has been unknown how the wheel topography is generated. Moreover, the influence of the kinematical dressing parameters on the wheel wear behavior has not been quantified. In the course of this article the grinding wheel was dealt with as a porous ceramic composite. In FEM simulations common dressing forces and usual dressing tool geometries were applied. The results were verified by dressing tests and grinding wheel scratch tests which show the wheel wear mechanisms. The common practice of decreasing the grinding wheel surface roughness by a finishing dressing stroke has to be reconsidered, because previous dressing strokes with higher depths of cut can weaken the grinding wheel structure and lead to an unsteady phase with high grinding wheel wear after dressing.     

In-process wire electrical discharge dressing (IWEDD) of metal bonded diamond wheels

Electrical discharge dressing has been established as alternative for conditioning metal bonded diamond wheels, which will be exploited to develop in-process wire electrical discharge dressing (IWEDD). The main requirements for its successful implementation are first presented in this work. Small depth of dressing cuts was found to be feasible and high material removal rates were achieved without damaging diamonds. Dulled grains are finally removed by mechanical contact with the work piece. It was found that grinding forces can be kept constant over time while non-productive time is reduced, showing that IWEDD is a suitable conditioning method with great potential for future industrial applications.     

An experimental investigation of dry-electrical discharge assisted truing and dressing of metal bonded diamond wheel

Metal-bonded diamond wheels have superior qualities such as high bond strength, long wheel life, wear-resistant ability and high grinding efficiency. But it is very difficult to true and dress diamond wheel because of its highest hardness. Traditional mechanical truing does not guarantee truing accuracy of diamond wheel because of single diamond dresser wears out very quickly. To reduce wear of diamond dresser and hence guarantee a desired wheel surface, a novel truing and dressing method, namely, dry electrical discharge (dry-ECD) assisted truing and dressing, is proposed and tested to achieve good dressing quality and efficiency. Because the diamond wheel is mounted on the MK9025 optical profile grinder, dielectric liquid is forbidden. The new dry-ECD dressing/truing method basically eliminates the use of dielectric liquid. Therefore, it is free from the serious problem of electrolytic corrosion caused by electrolytic current flowing through water encountered in conventional ECD. The FE analysis of temperature distribution in dry-ECD assisted truing and dressing diamond wheel using ANSYS is performed in this study. Temperature field simulation helps to select optimized parameters under certain conditions. Energy dispersive X-ray (EDAX) analysis was used to measure the composition of diamond wheel before and after dry-ECD assisted truing and dressing. Further, hard alloy grinding experimental results proves that a little variation in material composition of diamond wheel after dry-ECD assisted truing and dressing does not influence grinding result. A series of experiments of dry-ECD assisted truing and dressing of metal bonded diamond wheel are conducted to investigate truing efficiency, truing accuracy, dresser wear, dressed wheel profiles and three-dimensional truing/dressing forces in comparison with those of the conventional single diamond methods. Experimental results show that the new dry-ECD assisted truing and dressing technique offers a number of advantages over the conventional single-tip diamond dressing and truing method. Furthermore, mechanism of the dry-ECD assisted truing and dressing is investigated through the careful analysis of the properties of chips.     

砂轮表面形貌仿真方法研究

砂轮表面形貌对磨削加工过程和已加工表面质量有着极大影响,但由于砂轮表面磨粒分布的随机性,描述砂轮表面形貌非常困难。通过对砂轮表面进行采样和数据处理,运用统计学理论和Johnson变换方法获得了非正态分布砂轮表面形貌的数学描述方程,在此基础上对砂轮表面形貌进行仿真。选用伯明翰14参数集的部分参数作为评价标准,对测量的砂轮表面形貌和仿真形貌进行比较,结果显示:二者具有很好的一致性,6个参数的平均相对误差仅为2.97%。结果充分证明了该仿真方法的正确性。      

Influence of different grinding wheel and dressing roller specifications on grinding wheel wear

A targeted adjustment of the dressing results and the methodological influence of the dressing process on the non-stationary wear of a grinding wheel after dressing increases the productivity and the reproducibility of grinding processes. Despite the great economic importance of grinding processes with vitrified corundum grinding wheels and the great relevance of the dressing process for the application behavior of these grinding wheels, quantitative models are missing for the purposeful design of the dressing process. In previous studies, a dressing model was successfully developed which predicts the dressing force in the dressing process as well as the workpiece roughness and the grinding wheel wear behavior in a grinding process for a specific grinding wheel and form roller specification. However, a transferability of this model to other grinding wheel and form roller specifications is not possible because the influence of the grain size and the hardness of the grinding wheel as well as the dressing tool topography on the grinding wheel wear and thus on parameters of the dressing model are not known. The objective of this work was to extend the model to additional grinding wheel and form roller specifications to ensure a broad applicability of the model.     

Electrical discharge dressing and its influence on metal bonded diamond wheels

Although EDM is a thermal removal process, when it is applied for dressing diamond grinding wheels, usually little or no thermal damage is caused to the diamonds. In this work, a better explanation for this fact is provided. A thermo-electrical model is used to calculate the temperature distribution inside diamonds showing that even for high discharge energies small amount of graphitization occur. Here, the exceptional properties of diamond contribute to minimize thermal damages. Still, a concentration of discharges can occur around the diamonds and thus lead to thermal damages. However, this phenomenon is more evident for large diamonds.     

Study on micro-topographical removals of diamond grain and metal bond in dry electro-contact discharge dressing of coarse diamond grinding wheel

A coarse diamond grinding wheel is able to perform smooth surface grinding with high and rigid grain protrusion, but it is very difficult to dress it. Hence, the dry electro-contact discharge (ECD) is proposed to dress #46 diamond grinding wheel for dry grinding of carbide alloy. The objective is to understand micro-topographical removals of diamond grain and metal bond for self-optimizing dressing. First, the pulse power and direct-current (DC) power were employed to perform dry ECD dressing in contrast to mechanical dressing; then the micro-topographies of diamond grains and metal bond were recognized and extracted from measured wheel surface, respectively; finally, the relationship between impulse discharge parameters and micro-topographical removals was investigated with regard to grain cutting parameters, dry grinding temperature and ground surface. It is shown that the dry ECD dressing along with spark discharge removal may enhance the dressing efficiency by about 10 times and dressing ratio by about 34 times against the mechanical dressing along with cutting removal. It averagely increases grain protrusion height by 12% and grain top angle by 23%, leading to a decrease 37% in grinding temperature and a decrease 46% in surface roughness. Compared with the DC-25V power along with arc discharges, the Pulse-25V power removes the metal bond at 0.241 mm³/min by utilizing discharge energy by 73% and diamond grain at 0.013 mm³/min through surface graphitization, respectively, leading to high and uniform grain protrusion. It is confirmed that the impulse discharge parameters are likely to control the microscopic grain protrusion topography for efficient dressing according to their relations to the micro-removal of metal bond.     

Study of electrical discharge grinding using metal matrix composite electrodes

An investigation was made into the combined technologies of electrical discharge machining and grinding (EDMG). A metal matrix (Cu/SiC_p) electrode with a rotating device was made and employed to study the EDMG technology. It was found that 3–7 times the normal electrical discharge machining (EDM) material removal rate (MRR) could be achieved in EDMG under suitable conditions of electrode rotating speed, SiC_p particle size and current. This novel achievement is attributed to the fact that, under appropriate conditions, the hump-shaped melted material created by the EDM mechanism is vulnerable to attack by the grinding mechanism during the EDMG operation, greatly increasing the removal rate. Conversely, under inappropriate conditions, in which hump-shaped material solidifies prior to the non-conductive ceramic particle grinding, the above function becomes negligible and results in much lower MRR.