Simulation based optimization of the NC-shape grinding process with toroid grinding wheels

For achieving high material removal rates while grinding free formed surfaces, shape grinding with toroid grinding wheels is favored. The material removal is carried out line by line. The contact area between grinding wheel and workpiece is therefore complex and varying. Without detailed knowledge about the contact area, which is influenced by many factors, the shape grinding process can only be performed sub-optimally. To improve this flexible production process and in order to ensure a suitable process strategy a simulation-tool is being developed. The simulation comprises a geometric-kinematic process simulation and a finite elements simulation. This paper presents basic parts of the investigation, modelling and simulation of the NC-shape grinding process with toroid grinding wheels.     

聚氨酯摩擦盘的磨削加工研究

聚氨酯橡胶是一种难切削加工非金属材料,材料软、弹性大且导热性较差,因此很难加工到要求的形状精度、尺寸精度及表面粗糙度。针对聚氨酯橡胶的这种加工性能,提出了聚氨酯摩擦盘的磨削加工工艺:先用成型法进行粗磨,再用成型法进行精磨和抛光。粗磨选用30#粒度的黑色碳化硅大气孔陶瓷结合剂砂轮,N级硬度,切削用量0.01mm,用电镀金刚石滚轮修整砂轮圆弧,成型磨削,可以保证聚氨酯摩擦盘的形状和位置精度(R=3.5-+00..1058,S/2=3±0.05mm);精磨选用具有抛光作用的120#白刚玉PVA砂轮,用电镀金刚石滚轮修整砂轮圆弧,精磨和抛光同时完成,可以保证聚氨酯摩擦盘的尺寸精度(ΦA=50±0.03mm)和表面粗糙度(Ra=0.4μm)。     

关于凸轮数控磨削加工的探讨

针对凸轮磨削的特殊性探讨了两轴联动数控凸轮磨床在磨削凸轮轮廓曲线时,砂轮中心的运动规律和被磨凸轮主轴变速规律的问题.并对提高凸轮磨削精度和表面质量所采用的"恒磨削率"及"恒磨削力"和"相对磨削线速度不变"的问题进行了理论上的探讨.     

精密电火花小孔磨削设备及工艺研究

论证了φ1mm以下精密小孔电火花高效磨削的可行性，介绍了此项工艺技术的特点和实际应用范围以及所能达到的技术指标。     

On the mechanics of the grinding process – Part I. Stochastic nature of the grinding process

Grinding of metals is a complex material removal operation involving cutting, ploughing, and rubbing depending on the extent of interaction between the abrasive grains and the workmaterial under the conditions of grinding. It is also a stochastic process in that a large number of abrasive grains of unknown geometry, whose geometry varies with time, participate in the process and remove material from the workpiece. Also, the number of grains passing through the grinding zone per unit time is extremely large. To address such a complex problem, it is necessary to analyze the mechanics of the grinding process using probability statistics, which is the subject of this investigation. Such an analysis is applicable to both form and finish grinding (FFG), such as surface grinding and stock removal grinding (SRG), such as cut-off operation. In this investigation, various parameters of the process including the number of abrasive grains in actual contact, the number of actual cutting grains per unit area for a given depth of wheel indentation, the minimum diameter of the contacting and cutting grains, and the volume of the chip removed per unit time were determined analytically and compared with the experimental results reported in the literature. Such an analysis enables the use of actual number of contacting and cutting grains in the grinding wheel for thermal and wheel wear analyses. It can also enable comparison of analytical work with the experimental results and contribute towards a better understanding of the grinding process. The analysis is applied to some typical cases of fine grinding and cut-off operations reported in the literature. It is found that out of a large number of grains on the surface of the wheel passing over the workpiece per second (˜million or more per second), only a very small fraction of the grains merely rub or plough into the workmaterial (3.8% for FFG and 18% for SRG) and even a smaller fraction (0.14% for FFG and 1.8% for SRG) of that participate in actual cutting, thus validating Hahn’s rubbing grain hypothesis.     

磨削加工仿真预报系统的研究现状及发展趋势

磨削加工作为大部分产品成形前的最后一道工序,直接影响产品的加工精度和表面质量。磨削加工的多参数输入、输出和磨削过程中输入、输出参数之间的非线性映射决定了计算机仿真技术在磨削加工中应用的重要性。概述了计算机仿真技术相关理论,基于国内外磨削加工及预报模型,包括磨削运动学、磨削力、磨削温度、磨削液等模型的研究现状,对国内外将计算机仿真技术与磨削加工预报模型理论相结合的磨削加工仿真预报系统的研究现状进行了阐述。着重叙述了国内学者在磨削加工仿真预报系统软件开发方面的研究工作,最后展望磨削加工仿真预报系统的研究发展趋势。     

烧结方式对金刚石微粉氧化、形貌和砂轮磨削性能的影响

研究了烧结前金刚石微粉以及经空气气氛烧结、氮气气氛烧结和陶瓷结合剂包裹空气气氛烧结的金刚石微粉形貌和氧含量,并以这些微粉为原料制备了陶瓷金刚石砂轮,研究了微粉状态对磨削性能的影响。结果表明:烧结方式对金刚石微粉氧含量和性能有较大影响。金刚石微粉在空气气氛中烧结后重量减少5.2%,总氧含量、表面氧含量和点氧含量分别为0.078%、4.84%和2.00%,均大幅度高于其他两种烧结方式。此外,由空气气氛、氮气气氛和陶瓷结合剂包裹烧结的金刚石微粉制备的砂轮的磨耗体积比只有用未经烧结金刚石微粉制备砂轮的59.6%、89.6%和67.6%。     

不同砂轮磨削牛密质骨的磨削力研究

本实验选取与人体骨组织生物力学性能相接近的牛长骨为研究对象,用不同种类的砂轮进行磨削,研究骨组织磨削特性。实验结果表明:长骨骨干不同方向的磨削力不同,截面磨削力最大,侧面磨削力次之,表面磨削力最小;骨组织磨削力随磨削深度和工件速度的增大而增大,随砂轮速度的增大而减小;采用金刚石砂轮磨削骨组织的磨削力比采用氧化铝砂轮磨削时的磨削力要小得多;骨组织的磨削力比在3~5之间。通过对骨组织磨削特性的研究,为磨削技术在骨外科手术中的应用提供一定的参考。     

Fabrication of grinding tool material by the SHS of Ni-Al/diamond/dilute

A mixture of Ni-Cr-P, Cu and B powder was used as a dilute for modifying the microstructure of the reacted product and easing the fast propagating rate and the high temperature in the self-propagating high-temperature synthesis (SHS) of Ni-Al matrix grinding tool material. The SHS process of the Ni-Al/diamond/dilute was examined and the microstructure of the reacted product was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The grinding performance of the tool was tested in the grinding of a synthetic single crystal of sapphire. The results showed that the dilute substantially reduced the propagating rate and the combustion temperature of Ni-Al SHS. Besides the dominating intermetallics NiAl and NiAl₃, Ni₄Al₃ was also identified in the reacted Ni-Al/diamond/dilute composite owing to the Ni rich environment. In the reacted composite there was a Cr-rich zone at the boundary of the diamond grit due to the formation of Cr₃C₂ between Cr and the diamond. In the grinding a lower wear rate and a better retention ability of diamond grits could be achieved for the grinding tool material that contained finer diamond grits.     

砂轮约束磨粒喷射精密光整加工工艺特性研究

研究了砂轮约束磨粒喷射精密光整加工工艺特性，分析了磨粒尺寸、磨料流体浓度、加工循环、砂轮速度、携带流体对加工表面质量的影响。利用平面磨床M7120对Q235A进行喷射加工实验，用TALYSURF轮廓仪测量加工后的微观几何参数值，用扫描电镜和金相显微镜观察表面微观形貌。实验结果表明，选用质量分数10％W7Al2O3微粉与防锈润滑液进行喷射加工20～30循环，不仅保持或获得高的表面肜状精度，而且又可高效的获得具有粗糙度Ra0．15～1．6μm的无缺陷加工表面，明显去除磨削加工过度塑性变形，减少表面层污染和磨削烧伤，实现高效、高精度、低粗糙度，并且磨削和抛光可以集成的表面精密光整加工新方法。     

A review of cutting fluid application in the grinding process

It is generally accepted that heat generation is the limiting factor in the grinding process due to the thermal damage associated with it. To combat this energy transfer, a cutting fluid is often applied to the operation. These cutting fluids remove or limit the amount of energy transferred to the workpiece through debris flushing, lubrication and the cooling effects of the liquid. There have been many new and exciting systems developed for cutting fluid application in the grinding process. This paper reviews some of the common as well as some of the more obscure cutting fluid systems that have been employed in recent years with an emphasis on creep-feed applications. The review also suggests possible avenues of future research in cutting fluid application for the grinding process.     

磨削深度对42CrMo钢磨削强化层的影响

研究了磨削深度对42CrMo钢强化层组织与硬度的影响。结果表明,在不同磨削深度条件下,强化层的马氏体粗细不均,表层显微硬度随磨削深度先增加后降低,完全强化层显微硬度在720～800 HV0.1之间,比基体硬度提高了2倍。随着磨削深度的增加,强化层厚度最小值也增加,在磨削深度为0.6 mm时强化层厚度可达1.8 mm。     

A local process model for simulation of robotic belt grinding

A local process model to estimate the material removal rate in robotic belt grinding is presented and applied to the process simulation system. It calculate the acting force by incorporating the local geometry information of the workpiece instead of the cutting depth parameter with only one certain value as in a global grinding model. The simulation accuracy can be improved to below 5% even for a non-uniform contact under stable cutting conditions.     

Characterization of the grinding process by acoustic emission

The properties of a ground surface can be estimated on-line during manufacturing based on the analysis of acoustic signals emitted by the grinding process. This possibility is demonstrated using an experimental system comprising an external grinding machine, a data acquisition unit and an artificial neural network. In the initial phase of system application, an empirical model of the grinding process is formed in the memory of the neural network by self-organized learning driven by empirical data consisting of the acoustic emission spectrum and a surface roughness correlation function. After learning, the system applies the model to estimate the correlation function of the surface profile from the input acoustic emission spectrum. For this purpose, non-parametric regression, based on the conditional average estimator, is utilized. Experiments were done on the grinding of hardened steel workpieces by a corundum wheel. During formation of the model, the surface profile and its correlation function were determined off-line, while in testing system performance the surface correlation function was estimated on-line from the acoustic emission spectrum. With respect to the estimation error, three characteristic periods of the process were observed corresponding to grinding with a newly dressed, slightly worn, and worn out wheel. The best estimation is obtained during grinding by a slightly worn wheel.     

Modeling of material removal rate in electric discharge grinding process

The mechanism of material removal in electric discharge grinding (EDG) is very complex due to interdependence of mechanical and thermal energies responsible for material removal. Therefore, on the basis of conceived process physics for material removal, an attempt has been made to predict the material removal rate (MRR). The proposed mathematical model is based on the fundamental principles of material removal in electric discharge machining (EDM) and conventional grinding processes. The inter-dependence of the thermal and mechanical phenomena has been realized by scanning electron microscopy (SEM) characterization of the samples machined at different processing conditions. The key input process parameters like pulse on time, pulse current, gap voltage, duty cycle, pulse off time, frequency, depth of cut, wheel speed and table speed are co-related with MRR for three distinct idealized processing conditions. The constant showing the extent of interdependence of two phenomena were evaluated by experimental data. The obtained expressions of MRR have been validated for processing conditions other than those used for obtaining constants. It was found that the discharge energy plays prominent role in material removal. The percentage difference in experimental findings and theoretical predictions was found to be less than 3%.     

光学材料的磨削损伤控制试验研究

基于K9玻璃不同的磨削工艺参数确定其磨削损伤层深度随工艺参数变化的规律,并通过工件磨削损伤层深度的动态检测研究其裂纹扩展规律。结果表明:工件磨削过程中的裂纹损伤是动态扩展过程。固定工艺参数下,裂纹稳态扩展,损伤层深度不变;采用损伤更小的工艺参数磨削,裂纹的扩展速度小于材料的去除速度,其损伤层深度逐渐减小,损伤的去除速度逐渐减慢直至二者间达到稳态平衡。同时,为了去除前道工序的损伤层,后道工序的材料去除量需达到前道工序损伤层深度的2～3倍。      

cBN砂轮在低速磨削中的应用

cBN砂轮在高速设备上使用非常广泛,但在老式低速磨床上采用cBN砂轮的非常少。我们在这方面做了大胆的尝试,就是在老式磨床上不做任何改进,直接更换相同直径的陶瓷cBN砂轮,通过更换皮带轮改变传动比,把砂轮速度从51.4 m/s提升到64.8 m/s,增大冷却液流量、压力,确定冷却液冲刷位置,改变切削的进给量,使cBN砂轮的一个修整频次内寿命大幅提升。最后证明陶瓷cBN砂轮在低速磨床中一样可以替代刚玉砂轮,并且不需要大的改造投资,可以获得非常好的综合经济效益。     

陶瓷零件精密成形磨削新工艺研究

本研究开发采用金刚石磨料砂轮精密成形磨削陶瓷材料新工艺,实现采用金刚石磨料砂轮精密(微米级)成形磨削复杂形状陶瓷零件.文章介绍了磨削工艺中采用的提高成形磨削砂轮工作形面精度保持性、金刚石磨料砂轮的高效精密成形修整、砂轮修锐等关键技术.采用的砂轮是1A1 305×20×127×10 MBD 150 B 100,其特别之处是采用了新型树脂结合剂,具有良好的高温强度性能,磨削速度为40 m/s,新的砂轮修正方法将金刚石砂轮修整过程分为修形、修磨和修锐几个阶段.采用切入式成形磨削,磨削余量约1 mm,磨削得到的陶瓷零件形面圆弧精度可达到:0.005 mm,齿距误差:0.0025 mm;此外还进行了磨削陶瓷轴承环试验,磨削后获得的陶瓷零件圆弧精度达0.005 mm,沟道形位精度:0.003 mm,尺寸分散度在微米级.采用本方法可以成形磨削几乎任意形面的陶瓷或其他适合金刚石磨料砂轮加工的材料零件.     

Correlating surface roughness and vibration on plunge cylindrical grinding of steel

Since the wear of a grinding wheel has a direct effect on the workpiece vibration and both have effect on the workpiece quality, the main goal of this work is to study the relation between the process vibration signals and the workpiece quality (mean roughness, circularity and burning) as the grinding wheel gets worn, in an attempt to use these signals to decide the exact moment to dress the wheel. In order to reach this goal, several experiments were carried out in a plunge cylindrical grinding operation of an AISI 52100 quenched and tempered steel, having as input variables the dressing overlap ratio, the spark out time and the workpiece velocity. The output variables were the workpiece surface roughness and circularity and also the process vibration during both, the cutting phase and the spark out phase of the grinding cycle. The main conclusions were: (1) it is possible to have good workpiece quality even with a vibration level much higher than that obtained with a recently dressed wheel; (2) vibration during cutting phase and at the end of complete spark out can be used to monitor the wheel condition at least when high dressing overlap ratio is used; and (3) the decrease in the spark out time makes the vibration at the end of spark out increase a lot, but does not cause such a damage in surface roughness. This fact makes the use of partial spark out feasible in some situations.     

On the mechanics of the grinding process, Part II—thermal analysis of fine grinding

Thermal analysis of fine grinding is conducted taking into consideration the stochastic nature of the distribution of abrasive grains and its role under fine grinding (dry) conditions to determine the grinding temperatures and the heat partition at the contacting interface. The analysis considers the grain–workpiece interactions at the local level and the wheel–workpiece interactions at the global level. The workpiece temperature in the grinding zone is taken as the sum of the background temperature due to distributed action of all the previous active grains operating in the grinding zone (global thermal analysis) and the localized temperature spikes experienced at the current abrasive grain tip–workpiece interfaces (local thermal analysis), similar to the work reported in the literature. Since the Peclet number, N_Pe, in the case of fine grinding is very high (a few hundred), the heat flow between the work and the contacting abrasive grains can be considered to be nearly one-dimensional. In this paper, we consider the interaction between an abrasive grain and the workpiece at the contact interface. Consequently, the heat source relative to the grain is stationary and relative to the workpiece is fast moving. The interface heat source on the grain side as well as on the workpiece side is equivalent to an infinitely large plane heat source (with the same heat liberation intensity as the circular disc heat source). However, it will be shown in the paper that the contacting times are different. For example, the abrasive grain contacts the heat source, as it moves over the interface, for a longer period of time (˜milliseconds) whereas the workpiece contacts the heat source for a shorter period of time (˜a few microseconds). The equivalent thermal model developed in the present investigation is simple and represents the process more realistically, especially the heat partition. The analytical results reported here are found to be in good agreement with both the analytical and experimental results reported in the literature by other researchers.