Electrochemical oxidation analysis for dressing bronze-bonded diamond grinding wheels

Electrochemical dressing of fine-grained metal-bonded diamond grinding wheels enables to grind hard and brittle materials in the ductile mode. Optical surfaces can be manufactured by grinding, which reduces the need for subsequent, time-consuming polishing work. When using metal-bonded grinding wheels, the emerging oxides regulate the electrochemical dissolution. Bronze-bonded grinding wheels are more suitable for grinding cemented carbides and ceramics than iron-bonded grinding wheels, as it is easier to modify their chemical composition to suit a specific grinding task. They can also be sintered at lower temperatures, which reduces the risk of thermal damage to the diamond. In this paper, the dissolution and the oxidation of different bronze alloys are characterized for the electrochemical dressing process. The relevant evaluation criteria are the oxide layer thickness, the electrical behavior and the different emerging bronze alloy oxides. This work is funded by the German Research Association DFG within the Transregional Collaborative Research Center SFB/TR4 “Process Chains for the Replication of Complex Optical Elements”.     

Dressing process model for vitrified bonded grinding wheels

A holistic dressing process model for vitrified bonded grinding wheels was designed. It regards the dressing process as a tribological system subjected to a complex load collective. The intensive analysis of the input variables and their impact on the system function led to new knowledge about the acting mechanisms. The model enables a qualitative prognosis of the grinding wheel topography, the dressing forces and the thermal dressing process load.     

旋转金刚石修整工具修整超硬磨料砂轮的研究

本文对比研究了金刚石修整笔和旋转金刚石修整工具,在修整超硬磨料砂轮时修整力、工具磨损、修整效率等参数的变化规律,结果表明:超硬磨料砂轮的修整中,旋转金刚石修整工具修整力、修磨效率和磨损等几乎不随修整次数增加发生变化,其原因是修整工作是由整个圆周上金刚石分担,旋转型金刚石修整工具在修整过程中,具有挤压砂轮的作用,使被修整的金刚石砂轮表面具有较好锋利度.结果表明:在优化的修整工艺条件下,旋转金刚石工具可以实现对超硬磨料砂轮的精密修整.     

微细金属粉末对金属结合剂砂轮性能的影响

为研究微细粉末对金属结合剂砂轮性能的影响,将微细粉末和普通粉末按照设计的比例均匀混合,采用热压烧结的方法制成胎体试块,且在混合粉末中添加超硬磨料制成金属结合剂超硬材料砂轮,利用硬度计、抗折试验机、扫描电镜、切割试验机等设备,分别测试金属结合剂胎体硬度、抗折强度、断口形貌以及金属结合剂超硬材料砂轮切割性能。结果表明:微细粉末的添加有利于提高金属结合剂胎体的抗折强度,最高可以提升20%;另一方面,还可增加超硬材料砂轮的耐磨性,相同试验条件下测得半径磨损量降低了25.7%。      

金属结合剂金刚石多孔砂轮磨削温度的实验研究

制备了不同孔隙率的金属结合剂细粒度和微粉金刚石多孔砂轮并进行了不同材质石材的磨削性能实验.采用热电偶测温法,研究了不同孔隙率、不同磨粒粒度的金属结合剂金刚石多孔砂轮对两种不同工件材料的磨削温度特性.实验结果表明,不同孔隙率、不同磨粒粒度的金属结合剂金刚石砂轮的磨削温度均随着转速及切深的增加而增加;细粒度的金属结合剂金刚石砂轮随着孔隙率的增大,磨削温度降低;而微粉金属结合剂金刚石砂轮则表现出和细粒度金属结合剂金刚石砂轮不同的特性,即孔隙率达到一定值时,随着孑L隙率继续增大,磨削温度反而升高;同一孔隙率金属结合剂金刚石砂轮,细粒度金刚石砂轮的磨削温度要低于微粉金刚石砂轮的磨削温度.     

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.     

铸铁结合剂金刚石砂轮ELID磨削硬质合金的性能研究

硬质合金具有硬度高、强度好、耐腐蚀和耐磨损的特点,采用传统方法难以满足精密及超精密加工的技术要求.本文采用不同粒度的铸铁结合剂金刚石砂轮ELID镜面磨削硬质合金,得到了不同加工效率以及不同加工表面质量的硬质合金磨削效果,揭示了不同粒度砂轮其磨削性能变化的规律与作用.实验结果表明:在相同的进给量下,粗粒度砂轮的磨削效率较高,能更好地控制工件的尺寸精度.细粒度砂轮则磨削效率较低,但能获得优良的加工表面质量.砂轮表面的氧化膜在磨削过程中扮演非常重要的角色,磨粒的粒径与砂轮表面氧化膜厚度的比值大小决定了砂轮的磨削性能.氧化膜的形成又受到电解参数的影响,可以通过对电解参数的调节实现高效率高精度的ELID磨削.     

Finishing characteristics of brittle materials by ELID-lap grinding using metal-resin bonded wheels

ELID-lap grinding is a method of constant pressure grinding which utilizes an electrically conductive wheel and the electrolytic in-process dressing (ELID) method. This method has the advantage of using micro grain-wheels above #10 000 and also, through simple modification, can be used on existing lap machines. To find the characteristics of metal-resin bonded wheels developed for ELID-lap grinding, experiments on the grinding of brittle materials were performed using wheels with a variety of grain diameters. The wheels used in the experiments were #8000, #120 000 and #3 000 000 metal-resin bonded diamond wheels (#8000 MRB-D, #120 000 MRB-D and #3 000 000 MRB-D wheels). The workpieces were silicon and glass. The results of the experiments showed that stable grinding can be achieved with the #8000 to #3 000 000 MRB-D wheels. With the #3 000 000 MRB-D wheel, very smooth surface finishes were obtained for both silicon (PV 2.8 nm) and glass (PV 2.5 nm). Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM) observations indicated these surfaces to be very smooth in the order of several nanometers, obtained by mechanical removal using an ultrafine wheel.     

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.     

Surface grinding of space materials using specially formulated vitrified grinding wheels

The quantum leap that is expected in the reliability and safety of machined engineering components over the next 20 years, especially in the space industries, will require improvements in the quality of cutting tools if science-based manufacturing is the goal for manufacturing by 2020. Significant improvements have been made in the past 10 years by understanding the properties of vitrified bonding systems used to bond conventional and superabrasive materials in grinding tools. The nature of the bonding system is of paramount importance if next-generation cutting tools are to be used for aerospace materials, especially if they are dressed using laser beams. This paper was presented at the fourth International Surface Engineering Congress and Exposition held August 1–3, 2005 in St. Paul, MN.     

Machining of micro rotational parts by wire electrical discharge grinding

Micro rotational parts are used in several industrial sectors. Well-known applications are micro shafts of gears, ejector pins in forming tools, pin electrodes for micro electrical discharge drilling or micro stamping dies. Depending on the geometrical complexity of micro rotational parts different process variants of micro electrical discharge machining characterized by a rotating work piece can be used: wire electrical discharge grinding (WEDG) with fine wire electrodes, electrical discharge turning (EDT) with micro structured tool electrode, cylindrical electrical discharge grinding (CEDG) with micro profiled disk electrode. Characteristic to these process variants is the superimposed relative motion between the rotating electrodes and the feed. This relative motion can be varied in a wide circumferential velocity range to improve the material removal process. The paper gives an overview of kinematic and technological restrictions and requirements of the WEDG process influencing the process behavior with respect to the technological requirements of micromachining.     

超硬磨料砂轮超声振动修整新进展

硬脆材料精密高效的磨削水平取决于超硬砂轮的修整,随着硬脆材料的广泛使用,超硬磨料砂轮的修整技术也有了新的发展。本文简要叙述了目前一些修整方法的局限性并重点论述了超声波振动修整方法的修整机理以及不同的修整方式,并且对各种修整方式的特点和效果进行了分析。超声振动修整技术是一种高效的修整方法,修整后的砂轮获得了理想的砂轮形貌。其中,单激励椭圆超声振动修整技术是一种有效而低成本的新型修整方法,可以实现金刚石砂轮的高效修整。     

Dressing of vitrified bonded CBN tools for continuous generating grinding

Profile accuracy, high surface quality and compressive residual stress in the tooth root and flank are necessary for a high durability of heavy stressed gears. This article shows the advantages of vitrified bonded cubic boron nitride (CBN) tools in comparison to corundum tools relating producible compressive residual stress. In this context, especially the relationship between the dressing strategy for vitrified CBN tools and the workpiece surface and subsurface was investigated in detail.     

Temperatures and wear mechanisms in dressing of vitrified bonded grinding wheels

For the first time dressing temperatures were measured directly in the contact zone of grinding and diamond dressing tool. With average temperatures of 400 °C and maximum temperatures of 810 °C without cooling lubricant, the need to cool the dressing tool sufficiently is affirmed. For a diamond dressing tile and form rollers in contact with vitrified bonded corundum and CBN wheels, the main grit wear mechanisms were adhesions instead of breakage or high volumetric splintering. Extensive analyses proved that components of the grinding wheel bonding and abrasives were molten during the dressing process and solidified amorphously. This verifies high peak surface pressures and flash temperatures.     

Ultra precision grinding of spherical convex surfaces on combination brittle materials using resin and metal bond cup wheels

This paper reports on a parametric investigation on ultra precision grinding of combination materials of zirconia and silica. Rotational grinding was adopted for the generation of spherical convex surfaces using metal and resin bonded cup wheels. The wheels have grit sizes ranging from 4 to 20 μm. A simplified geometrical model was used to analyse the effects of wheel wear on ground dimensional accuracy. Besides, a new truing and dressing technique of the cup wheel using loose abrasives was introduced. This new truing and dressing technique enables the precision profile truing of cup wheels. With the well prepared cup wheel, high form accuracy (average PV 0.25 μm) with mirror/near-mirror surface finish for silica and zirconia was achieved.     

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。     

Wire electro discharge trueing and dressing of fine grinding wheels

In this paper fundamental investigations are presented regarding the capabilities of Wire-EDM for trueing and dressing of fine grained metal bonded diamond grinding wheels. These wheels are often used for precision grinding operations of hard and brittle mould materials like ceramics or cemented carbides. They are characterised by high profile constancies and wear resistances. Due to the electrical conductivity of the bond material, Wire-EDM offers an efficient and powerful alternative to conventional trueing and dressing. Achievable grit protrusion and possible thermal damage to smallest diamond grits are theoretically and experimentally examined. Additionally, machining strategies for high profile accuracy are presented.     

Dressing of metal-bonded superabrasive grinding wheels by means of mist-jetting electrical discharge technology

Preparation of superabrasive grinding wheel becomes one of the most important subjects on precise machining field at present. In this research, mist-jetting electrical discharge dressing (MEDD) technology was applied to dress metal-bonded superabrasive wheels. The author proposed a systematical study on the mechanism of selective removal of the bond of wheel. An experimental study has been carried out on a Die-Sinking Electrical Discharge Machine. The quality of wheels under different dressing electrical parameters was analyzed in terms of wheel profiles and wheel topographies. In addition, the performance of MEDD’ed wheel was evaluated by measuring grinding forces. Experimental results indicate favorable dressing quality can be obtained under suitable processing parameters, and MEDD is feasible for metal-bonded superabrasive grinding wheel.     

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.     

Internal mirror grinding with a metal/metal–resin bonded abrasive wheel

Precision internal cylindrical surfaces are increasingly utilized in industries where highly efficient methods to fabricate such surfaces are of great importance. Presently, several processes usually performed on different machines are used successively to achieve a mirror finish. In this paper, a novel method is presented to accomplish roughing and finishing processes on one machine, using super abrasive cast–iron–bond CBN (CIB–CBN) wheels and metal–resin–bond CBN (MRB–CBN) wheels. Two dressing methods, electrolytic interval dressing and electrolytic in-process dressing (ELID), are also developed for these wheels respectively. The CIB–CBN wheel is trued by an on-machine electrical discharge truer (EDT) and dressed at intervals with a pipe-shape electrode; the MRB–CBN wheel is dressed in process, in which no specific dressing electrode is utilized, instead the conductive workpiece acts as a dressing electrode. Precision grinding has been carried out on an ordinary grinder with an attachment for internal cylindrical grinding. Wheels of #325, #1200, #2000, and #4000 grit sizes have been applied in the process to obtain mirror surfaces.