Power and Wheel Wear for Grinding Nickel Alloy with Plated CBN Wheels

Electroplated CBN grinding wheels are manufactured with a single layer of abrasive grains. The grinding performance of these plated wheels changes significantly as the wheel wears down. The present investigation was undertaken to understand the transient grinding behavior with electroplated CBN wheels in order to provide a logical basis for process control. In this paper, particular attention is directed to the effect of wheel wear and operating parameters on grinding of a nickel alloy. Wheels were worn to various stages and then used to perform grinding tests under various grinding conditions to measure grinding forces and power and to produce ground specimens. Based on models for grinding with conventional aluminum oxide wheels, a power model for grinding of a nickel alloy with plated CBN wheels was established and validated. Microscopic observations of the ground specimens reveal that thermal damage in the form of a White Etch Layer (WEL) appears only when grinding with a worn wheel under conditions that lead to high temperatures.     

Burn threshold prediction for High Efficiency Deep Grinding

Burn threshold diagrams are useful for the prediction of thermally induced grinding damage and were originally developed to describe the conventional shallow cut grinding regime. With the development of new high stock removal grinding processes such as High Efficiency Deep Grinding (HEDG), the prevention of thermal damage to the workpiece is of particular concern. The principle of HEDG is based around the change in thermal characteristics of the grinding process at high Peclet numbers, whereby less heat is partitioned to the workpiece. Conventional burn threshold diagrams are valid for Peclet numbers below 50, well below the values expected in HEDG. This study presents a modified approach to the construction of burn threshold diagrams which takes account of the change in thermal partitioning with Peclet number. The approach has been validated through grinding trials over a range of specific material removal rates.     

An Investigation of Grinding with Electroplated CBN Wheels

Grinding of hardened bearing steel with electroplated CBN wheels was Investigated with particular attention to how the wear of the abrasive grains affects the wheel topography and grinding performance during the wheel ire. Power, surface roughness, and wheel topography data were obtained throughout the wheel life for internal cylindrical grinding. Dulling of CBN gratis by attrition was found to cause an increase in the grinding power, but the degree of dulling was restricted mainly by grain fracture and also by grain pullout. Grain fracture and pullout had a much smaller effect on the progressive increase in active grain density, which caused the surface roughness to progressively decrease. Wheel failure tended to occur by stripping of the abrasive layer when the radial wear reached about 70% - 60% of the grain dimension     

Factors Affecting Grinding Performance with Electroplated CBN Wheels

An experimental investigation was conducted to evaluate the effect of CBN crystal characteristics and plating thickness on the performance of electroplated CBN wheels. Wheels containing tougher CBN crystals generally exhibited less wear and a higher G-ratio, and also required less power. Furthermore, contrary to expectations, less wear and higher G-ratio were also obtained for wheels with a thinner layer of nickel plating despite an increased tendency for large-scale crystal loss. This would indicate that the overall wheel wear depends more on crystal exposure than on active grain density, which could facilitate chip removal and grinding fluid access. Extended grinding tests up to wheel failure ascertain the improved grinding performance with tougher crystals and thinner electroplated layers.     

陶瓷结合剂CBN砂轮磨损与磨削比的研究

通过对国产陶瓷结合剂CBN砂轮磨削45淬硬钢的试验,研究了磨削参数对CBN砂轮磨损与磨削比的影响规律,获得了磨削参数的最优水平,并建立磨损与磨削比的经验公式,探讨了冷却液流量对磨损与磨削比的影响规律。     

Three Dimensional Finite Element Simulation of Transient Heat Transfer in High Efficiency Deep Grinding

3D Finite Element simulations have been carried out to investigate transient heat transfer under high efficiency deep grinding (HEDG) conditions. The results have been compared to those obtained from 2D analytical models and experimental measurements. It has been found that the steady-state heat transfer condition can be readily obtained in HEDG after the maximum contact length is achieved and that side wall convective cooling has little effect on the grinding temperatures for thin steel plates. The temperature distribution on the workpiece across the grinding width in cylindrical grinding shows obvious slopes and film boiling of grinding fluid may occur at the trailing edge of grinding width. Good agreement has been found between the FE results and experimental observations. 3D FE simulation and 2D analytical modelling predict quite similar values for the maximum temperatures on the finished surface of the workpiece.     

高效深磨中温度的理论分析

本文提出了高效深磨的热模型。该热模型中，工件与砂轮的接触用圆弧面表述。发现接触角和Peclet数对磨削区温度有很强的影响。发现材料去除率高而且无磨削烧伤。新热模型对接触区温度很准确的预测。还发现高效深磨中比磨削能很低。而磨屑带走了大部分热。同时，在磨削液被阻碍进入磨削区后，工件的温度急剧上升。     

多元低合金贝氏体铸钢磨球的研究

针对常用磨球材质脆性大、耐磨性低、磨耗高的缺点，研制了多元低合金贝氏体铸钢磨球，它具有硬度高、硬度均匀性好和韧性高等特点，用于磨矿生产，磨耗接受高铬铸铁球，成本降低３０％～４０％，综合效益显著。     

Investigation of the heat partitioning in high efficiency deep grinding

The grinding heat partitioning in the high efficiency deep grinding (HEDG) process has been investigated. The ratios of heat partition to the different heat sinks, i.e. workpiece, chips, fluid and grits, have been calculated, based on both theoretical analysis and experimental data. The heat partitioning ratio to the grinding chips increases with the material removal rate and takes most of the grinding heat away from the grinding zone under HEDG conditions where very high material removal rates apply. The heat partition to workpiece decreases when increasing the material removal rate. Cooling fluid is especially important for the conditions of creep feed grinding when using low feed rates, with over 90% of heat convected away by the grinding fluid. Under HEDG conditions, only 5–10% of the grinding heat is taken away by the grinding fluid. Very high material removal rates can be achieved with good surface integrity, when using an optimised selection of process parameters.     

Development of Environmentally Friendly Fluid for CBN Grinding

Environmentally friendly water based fluids have been offered recently by many suppliers. On the other hand the G ratio values obtained for CBN grinding with water based coolants are much lower than with neat oil. This work presents a new water based grinding fluid formulation able to meet both the performance and environmental requirements for CBN grinding. The existence of a reaction between CBN grains and water is evaluated in grinding tests and also in a chemical reactor. The results show that the reaction between CBN grains and water is not significant when compared to the measured volumetric wheel wear in a grinding operation. Based on this fact, a new fluid concept consisting of a high concentration (up to 40%) of sulfonate vegetable oil in water is proposed and tested. In this way it was possible to combine high lubricity, better heat conductivity and good environmental properties in one fluid. The results show performance comparable to the obtained with neat oil.     

Surface Generation with Engineered Diamond Grinding Wheels: Insights from Simulation

Engineered wheels are a recent innovative development towards consistent and exceptional performance in fine grinding operations. Abrasive grains in an engineered wheel are positioned in a specific spatial pattern, as opposed to random locations in a conventional wheel. The present work relates to the formulation of a theoretical framework for the design of engineered wheels In terms of maximizing their performance with respect to their surface generation characteristics. Computer simulations Indicate that: (I) The distribution of abrasive protrusion height, rather than Its absolute maximum value, determines the roughness of the ground surface and controls the associated variability, and therefore by tailoring the distribution appropriately, the performance of the wheel can be improved significantly, (II) With an ordered arrangement of abrasive grains, the finish obtained is a strong function of the axial offset between adjacent rows of grains, but the best finish achieved thus is only on the order of that obtained with a conventional wheel, and (III) The effect of grain shape on the roughness of the ground surface is comparable to the Inherent process variability.     

Evaluation of Factors Controlling CBN Abrasive Selection for Vitrified Bonded Wheels

Grinding tests were made to investigate the impact of new CBN grains now becoming available through globalization. The study investigated the effect of grit size distribution and toughness in standard and newly developed vitrified bond systems. Tougher grits were found to require the development of stronger bonds to obtain economic benefit. The effect of observable and induced process variables was evaluated to determine minimum levels of wheel wear required for repeatability. It was found that micron levels of process variance significantly impacted wheel life.     

Thermal Analysis of Grinding

Thermal damage is one of the main limitations of the grinding process, so it is important to understand the factors which affect grinding temperatures. This paper presents an overview of analytical methods to calculate grinding temperatures and their effect on thermal damage. The general analytical approach consists of modeling the grinding zone as a heat source which moves along the workpiece surface. A critical factor for calculating grinding temperatures is the energy partition, which is the fraction of the grinding energy transported as heat to the workpiece at the grinding zone. For shallow cut grinding with conventional abrasive wheels, the energy partition is typically 60%-85%. However for creep-feed grinding with slow workspeeds and large depths of cut, the energy partition is only about 5%. Such low energy partitions are attributed to cooling by the fluid at the grinding zone. Heat conduction to the grains can also reduce the energy partition especially with CBN abrasives which have high thermal conductivity. For High Efficiency Deep Grinding (HEDG) using CBN wheels with large depths of cut and fast workspeeds, preheated material ahead of the grinding zone is removed together with the chips, thereby lowering the temperature on the finished surface. Analytical models have been developed which take all of these effects into account. Much more research is needed to better understand and quantify how grinding temperatures affect the surface integrity of the finished workpiece.     

立方氮化硼钎焊制备磨料砂轮的工艺及性能研究

利用Ag-Cu-Ti活性钎料在真空炉中钎焊,制备了单层钎焊CBN(立方氮化硼)磨料砂轮。实验结果表明,Ag-Cu-Ti合金钎料对立方氮化硼表现出良好的浸润性,并将立方氮化硼牢牢钎焊住。扫描电镜、X-射线能谱和X-射线衍射对界面微区组织的分析研究表明,钎焊过程中Ag-Cu-Ti合金钎料中的Ti向立方氮化硼磨粒界面富集,并与立方氮化硼磨料表面的N和B元素发生反应生成TiN和TiB2。     

陶瓷结合剂CBN砂轮磨削表面粗糙度的试验研究

本文通过一系列的试验，研究了陶瓷结合剂CBN砂轮磨削表面粗糙度的变化规律及其特点，建立了相应磨削表面粗糙度的经验公式。     

Profiled Superabrasive Grinding Wheels for the Machining of a Nickel Based Superalloy

Machining data are presented for small diameter, profiled (fir tree root form), single layer/electroplated CBN (B46, B76 and 91) and diamond (D46) grinding wheels, when cutting Udimet 720. Spindles operating at 60,000 and 90,000 rpm were employed, with a synthetic polyalphaolefine (PAO) oil based fluid in a down grinding mode on single sided specimens. Operating parameters were selected to reflect finishing conditions. Measured tool wear was lower for CBN grit as compared to diamond however workpiece roughness was lower with Ra approaching 0.75 μm when using D46 wheels. Higher rotational speed produced lower grinding wheel wear. No workpiece burning was observed irrespective of grit type at the conditions tested.     

镶块式CBN砂轮缓进给磨削钛合金

本文提出了一种将断续磨削的降温优势、CBN砂轮的耐磨特性以及缓磨本身的低温特性三者相结合的CBN砂轮断续缓磨技术。对整体CBN砂轮与断续CBN砂轮缓磨钛合金时的磨削性能进行了试验对比,并从微观上研究了CBN砂轮的磨损特征。实验结果表明,与整体CBN砂轮相比,断续CBN砂轮的极限切除负荷可提高80%以上。镶块式CBN砂轮在解决钛合金缓磨烧伤方面显示出可喜的前景。     

Development of Silica Polyvinyl Alcohol Wheels for Wet Mirror Grinding of Silicon Wafer

It is strongly desired to develop a cup grinding wheel which enables mirror finishing of a device wafer on the same machine after back grinding. Silica wheels have the capability of mirror finish in a dry condition but there remain serious problems in flatness and thermal damage to a dicing tape. A new silica wheel which can be used in a wet condition has been developed. The PVA (polyvinyl alcohol) was adopted as the bonding agent, by which the absorbent swell resulted in disturbance of water infiltration to the inside in cup grinding. A series of experiments show that mirror finishing will be achieved within 2 min. This could not be accomplished utilizing phenol wheels.