Enhanced CNC lathe capability by addition of a grinding spindle

CNC grinding machines are widely used to obtain a good surface finish and tight tolerances. However, these machines are expensive, therefore manufacturers are considering adding a grinding spindle, interchangeable with a boring bar, to a turning lathe. To facilitate this, complex software is required because the programmer must control the whole surface of the grinding wheel not just the tool or cutter tip, as in turning or milling. This paper presents a general algorithm to simplify the grinding programme. The programmer will use this algorithm to create a subroutine suitable for the machine. The subroutine may then be used for all grinding operations. The programmer will need only to describe the contour of each workpiece, as for a CNC lathe program, in a separate small program. The algorithm has been applied to a hollow spindle lathe equipped with Sinumeric 840 C numerical control, and several gun barrels were turned and ground using the proposed approach. Satisfactory results were obtained.     

Comparative analysis of performance of cubic boron nitride and microcrystalline alumina tools in profile grinding of form cutters

A comparative analysis of performance of cubic boron nitride, microcrystalline alumina, and white fused alumina wheels has been carried out in profile grinding of long-length HSS profile broach under production conditions. In a particular case, where grinding is accompanied by impact loading and the wheel has to be frequently dressed to provide precise profiling, the vitrified cubic boron nitride wheel has demonstrated an essentially better performance in terms of removal rate, minimum time for dressing cycles, and overall labor input in shaping a working profile of the broach.     

Influence of dressing parameters on grinding performance of CBN/ Seeded Gel hybrid wheels in cylindrical grinding

Wide use of vitrified bond CBN grinding wheels in today's production grinding is due to their higher grinding efficiency and longer wheel life compared to other types of CBN wheels or conventional wheels. Trueing and dressing, however, strongly affect these advantages, since superabrasive wheels usually act dull after a dressing operation and require an initial break-in period. In this study, a rotary trueing and dressing process was investigated for vitrified bond CBN/ Seeded Gel wheels to determine optimum parameters required to eliminate the initial break-in period and to grind at steady-state right after dressing. This paper describes the effects and importance of dressing factors on wheel grinding performance. A limiting factor for useful wheel life between dresses is also suggested.     

高强度铸铁基cBN砂轮修整实验研究

消失模铸造制备的奥-贝球墨铸铁基cBN砂轮具有胎体强度高、胎体对磨粒把持力大等优点,但也存在着铸造砂轮毛坯尺寸精度不高、磨削层修整余量大、修整较为困难等不足之处.本文针对铸造铸铁基大粒度cBN砂轮毛坯,分别进行机械修整、电解修整和电解-机械-电解复合修整试验,探究不同修整方式下的最优工艺参数和修整效率,以及修整后磨粒的破碎和出刃情况.研究结果表明:采用Si C修整轮修整,当转速比为+0.3时修整效率最高,但修整效率随着时间的增加逐渐减小,修整至120 min才能够达到砂轮的目标精度;采用电解修整,砂轮在最优工艺参数下修整30 min后将产生钝化,电解修整难以继续进行;采用电解-机械-电解复合修整,不仅其修整效率比机械修整有所提高,而且砂轮表面磨粒破碎较少,磨粒出刃高度较大.     

Nano finish grinding of brittle materials using electrolytic in-process dressing (ELID) technique

Recent developments in grinding have opened up new avenues for finishing of hard and brittle materials with nano-surface finish, high tolerance and accuracy. Grinding with superabrasive wheels is an excellent way to produce ultraprecision surface finish. However, superabrasive diamond grits need higher bonding strength while grinding, which metal-bonded grinding wheels can offer. Truing and dressing of the wheels are major problems and they tend to glaze because of wheel loading. When grinding with superabrasive wheels, wheel loading can be avoided by dressing periodically to obtain continuous grinding. Electrolytic inprocess dressing (ELID) is the most suitable process for dressing metal-bonded grinding wheels during the grinding process. Nano-surface finish can be achieved only when chip removal is done at the atomic level. Recent developments of ductile mode machining of hard and brittle materials show that plastically deformed chip removal minimizes the subsurface damage of the workpiece. When chip deformation takes place in the ductile regime, a defect-free nano-surface is possible and it completely eliminates the polishing process. ELID is one of the processes used for atomic level metal removal and nano-surface finish. However, no proper and detailed studies have been carried out to clarify the fundamental characteristics for making this process a robust one. Consequently, an attempt has been made in this study to understand the fundamental characteristics of ELID grinding and their influence on surface finish.     

圆柱齿轮磨齿机的选型

对圆柱齿轮磨齿机中的蜗杆砂轮磨齿机和成型磨磨齿机的磨削原理及应用场合作了介绍,从用户的角度对机床选型、对机床供应商的要求作了分析,指出国内磨齿机机床厂家,应联合夹具专业厂商、磨料生产厂商组成强大的综合服务队伍,对于争夺日趋激烈的磨齿机市场具有现实意义.     

On theoretical substantiation of the choice of effective grain profile shape in modeling of diamond layer in dressing tools. Part 1. Electroplating

The paper gives theoretical substantiation of the phenomenon of a circular shape of a scratch cross-section averaged over a set of cuts produced by far-from-round tips of diamond grains of electroplated dressing tools that work on the abrasive material of grinding wheels. This cross-sectional shape is identified as an effective shape of the grain that produces the scratch. Information on the scratch parameters and their relationship with the diamond grain size in the tool is needed for calculating individual and total cross-sections of cuts, dressing forces, and surface roughness of workpieces upon grinding with abrasive wheels dressed by a diamond roll.     

激光修整金刚石砂轮研究进展

金刚石砂轮在磨削领域起着举足轻重的作用.对于失效金刚石砂轮的止损,合理地选择金刚石砂轮修整方法成为一大难题.激光修整技术集光、电、热、机械等多种方法于一体,能有效实现金刚石砂轮的修整,受到国内外学者的广泛关注.综合阐述了激光修整金刚石砂轮的基本原理,分析了激光修整技术研究现状,并展望了未来激光修整金刚石砂轮的发展前景.     

Impact of dressing infeed on SiC wheel for grinding Ti-6Al-4V

Present experimental investigation is directed toward the optimization of dressing infeed for silicon carbide (SiC) wheel to be employed for grinding difficult-to-machine super alloy Ti-6Al-4V. Grinding wheels are dressed using separate, however, identical 0.75 carat single point diamond dressers at 5, 10, 15, 20 and 25 µm infeed values. Differently dressed wheels are consequently, applied for grinding Ti-6Al-4V under different infeed values of 5, 10 and 15 µm. All the operations have been performed at a constant velocity of 1810 m/min. The performances of the differently dressed SiC wheels are evaluated based on the variations of grinding force components, average surface roughness values, grinding ratio, chip forms and based on the analyses of the micrographs of wheel topologies and also of the ground surfaces, obtained using scanning electron microscope. Following the performance evaluation, the optimized dressing infeed has been found to be 20 µm for the operation range considered herein.     

Optimization of dressing infeed of alumina wheel for grinding Ti-6Al-4V

In the present experiment study, dressing infeed values of 5, 10, 15, 20, and 25?µm are conceived on alumina wheel using 0.75 carat identical diamond dressers. The surface topologies of the dressed wheels are observed under scanning electron microscope. Differently dressed wheels are subsequently, employed for up-grinding Ti-6Al-4V in dry environment for 20 passes while the grinding infeed is kept constant at 10?µm during each pass. The grinding ratio is evaluated and the typical surface roughness parameters are measured using a mechanical type stylus. Tangential and normal force components are accurately measured with the help of dynamometer while the quality of ground substrate is observed under high resolution microscope. The performances of the differently dressed wheels are evaluated and subsequently, the dressing parameters are optimized based on the results obtained herein.     

Simulation of cylindrical plunge grinding based on the behaviour of cutting edge wear

In cylindrical plunge grinding, a series of workpieces are ground successively without intermediate dressing of the wheel. Through the grinding, the wheel characteristic is continuously changed by the wear, fracture and new exposure of abrasive grains, having a profound effect on the grains on wheel surfaces in the cylindrical grinding process are developed to make it possible to describe the time dependent results of grinding and to establish the grinding operation standards capable of estimating grinding wheel performance and selecting grinding conditions, in which many parameters in actual grinding operations are considered. This simulation system can display its results in graphical form including the time dependent results and the effects of various parameters as well as optimization capabilities. This simulation has the same effects as many grinding experiments, and capable of selecting the optimum grinding wheels and conditions.     

Topographic error analysis of a gear plunge shaving cutter finished by a cone grinding wheel

Abstract

Gear shaving is one of the most efficient and economical ways to finish gears roughed by hobbing or shaping. The theoretical pitch surface of a gear plunge‐shaving cutter is a hyperboloid with hollow tooth form. The tooth profile of a plunge shaving cutter is usually ground by a cone grinding wheel. In this paper, we propose a mathematical model to calculate the topographical error of the tooth surface of a ground plunge‐shaving cutter compared with the theoretical tooth surface that is conjugated with the work gear. The proposed mathematical model can be used to calculate the profile data of the cone grinding wheel and the corresponding machine setup at a predetermined operating pitch cylinder. The topographic error sensitivities of the plunge‐shaving cutter due to varied operating pitch cylinder, helix angle, and grind wheel data are discussed based on the proposed mathematical model. This paper provides approximate guidance for choosing the proper operation cylinder, the helix angle, and the geometrical data of the cone grinding wheel for the finishing or resharpening of the plunge shaving cutter.     

The specific cost of grinding R6M5F3 steel with various dressing methods and electric discharge actions on Kubonit wheel working surface

A comparative study of grinding R6M5F3 steel with metal-bonded Kubonit wheels in various dressing methods and with electric discharge action on the wheel working surface is carried out based on the minimum specific cost criterion. The electric discharge dressing method has been found to provide a reduction in specific grinding cost by one order of magnitude in comparison to an abrasive method. Electric discharge actions on the wheel working surface in the course of grinding result in a higher specific machining cost; therefore, it is advisable to perform grinding with periodic in-process electric discharge dressing.     

Superabrasive grinding wheels in the machine tool system: Restrictions by the rigidity criterion

The paper provides some findings of the investigation aimed at determining the required values of the rigidity index of superabrasive grinding wheels as one of the machine tool elements in the course of machining. Standard grinding wheels are shown to have a certain rigidity margin; critical values of this parameter are discussed.     

Grinding of Toroidal and Cylindrical Surfaces on SiC Using Diamond Grinding Wheels

This paper presents the methods and experimental results for grinding toroidal and cylindrical surfaces made of silicon carbide using diamond grinding wheels and an inexpensive CNC machining center. The mirrors were successfully obtained by automatic grinding operations with good shape accuracy, mirror surface finish, and low roughness heights. The time consumed in the process is very short. Industrial manufacture of lenses usually involves three operations — grinding without dressing, lapping, and polishing. In the laboratory studies, however, mirrors and lenses have been manufactured only with grinding process, because of 100% ductile-mode material removal in grinding with dressing. These processes were individually evaluated for surface roughness and surface integrity using surface roughness testers and a scanning electron microscope.     

The measurement and analysis of micro bonding force for electroplated CBN grinding wheels based on response surface methodology

The superabrasive (e.g. CBN or diamond) grain dislodgement occurrence on the wheel surface due to insufficient bonding force is the major failure phenomena in the grinding process with electroplated grinding tools. This failure leads to the abrupt increase of load on the immediate grains, accelerating more grain dislodgement on wheel surface. Ultimately, the aggregated grain dislodgement causes the workpiece profile accuracy degradation and catastrophic wheel sharpness loss. Therefore, the provision of sufficient and uniform micro bonding force all through the wheel surface is the critical task in electroplated superabrasive grinding wheel design. Considering the complexity in the micro bonding force enabling factors, e.g. the grain shape, dimensional size, spatial orientation, and bond layer thickness, it is vital to establish the quantitative and comprehensive relationship between these factors with the micro bonding force for optimal electroplated grinding wheel design. In this paper, an inclined micro-thread turning test is developed to measure the single grain micro bonding force. In addition, the finite element model of single CBN grain bonding force is established and validated to simulate the grain dislodgement. Finally, the response surface methodology (RSM) is applied to build the comprehensive correlation of the bonding force with its dimensional size, spatial orientation, and bond layer thickness. Therefore, the optimal bonding condition through regressed prediction model is identified to provide the quantitative basis for the electroplated CBN grinding wheels design, which indicates that the bonding force can be predicted for specific wheel manufacturing parameters and improved by related variable adjustment.     

纳米结构陶瓷涂层的外圆磨削力以及磨削表面精度的实验研究

使用功率计监测磨削加工的能量消耗，探讨了纳米结构陶瓷涂层的外圆磨削过程；对纳米陶瓷涂层和传统陶瓷涂层在磨削力和磨削表面精度方面进行了比较．磨削实验使用了外圆磨床和陶瓷结合剂金刚石砂轮．通过测量主轴功率获得切向磨削力，讨论了加工参数，如切深、进给率以及砂轮粒度对切向磨削力的影响．还对磨削后的涂层表面用粗糙度仪和扫描电镜进行了评估，揭示了表面粗糙度与加工参数的关系．     

Highly Efficient Grinding of Ceramic Parts by Electrolytic In-Process Dressing (ELID) Grinding

In the manfacture of structural ceramic components, it has been well documented that the grinding costs can be as high as 90% of the total cost. Grinding costs of ceramics can be reduced by maximizing the material removal rates (MRR). A novel grinding technology that incorporates in-process dressing of metal bonded superabrasive wheels, known as Electrolytic In-Process Dressing (ELID) has been developed (1) which can significantly increase the MRR. This technique uses a metal bonded grinding wheel that is electrolytically dressed, during the grinding process, for continuous protrudent abrasive from superabrasi ve wheels. The principle of ELID grinding technology will be discussed in this paper as will its application for rough grinding. The effects of various parameters such as wheel bond type and type of power supply on the ELID grinding mechanism will also be addressed in this paper.     

THE SIGNIFICANCE OF CONTINUOUS DRESSING IN PRECISION GRINDING OF HARD AND BRITTLE MATERIALS

The precision grinding of hard cemented carbides and brittle ceramics using diamond wheels with continuous electrochemical dressing is considered. A novel grinding apparatus, the electrochemical dressing Miskolc (ECDM), was developed and used. Higher grinding efficiency was observed as compared to grinding using mechanically dressed wheels.     

Structural design of a carbon fiber-reinforced polymer wheel for ultra-high speed grinding

Ultra-high speed grinding (UHSG) is receiving considerable attention owing to its ability to achieve high machining accuracy and productivity. The materials and design of the grinding wheels play a significant role in this technology. Wheels with steel bodies are currently widely used, but have deficiencies such as a large mass loading imposing on the spindle, along with high power consumption, large stress and deformation, and limited practical grinding wheel speed. Wheel bodies made of carbon fiber-reinforced polymer (CFRP) show promise for use in UHSG because of the low density and high specific strength of this material. The main aim of this paper is to carry out a structural design of a CFRP grinding wheel for UHSG. Comparisons of stress and deformation, dynamic characteristics, thermal deformation, and power consumption between steel and CFRP wheel bodies reveal the superior performance characteristics of CFRP. The design of the laminate structure of the CFRP is then optimized, considering various laminate processes. The abrasive layers are designed with regard to the number and thickness of segments. Finally, a CFRP wheel for UHSG is developed based on the design proposal.