Improving grinding fluid delivery using pneumatic barrier and compound nozzle

Grinding fluid is commonly applied to control grinding defects caused by high grinding zone temperature. Delivery of fluid to the grinding zone is obstructed by the formation of a stiff air layer around the grinding wheel. This results in huge wastage of grinding fluid. In the present paper, results of using a pneumatic barrier and a compound nozzle are discussed with respect to delivering fluid deep into the grinding zone. Grinding fluid passing through the grinding wheel contact zone is measured under different modes of fluid delivery using a flood cooling, or a compound, nozzle, with or without the application of a pneumatic barrier. It is found that the system using a pneumatic barrier with flood cooling nozzle, and that employing a compound nozzle perform better than the flood cooling nozzle. A compound nozzle along with a pneumatic barrier renders substantially less wastage of grinding fluid even at a low flow rate of grinding fluid. Above a fluid discharge of 475 ml/min, the compound nozzle alone shows effective penetration of grinding fluid through the grinding zone. Reduction of grinding force, specific energy and roughness of ground surface are obtained after using compound nozzle fluid delivery system. Compound nozzle may be used instead of flood cooling nozzle as it improves grinding performance even using 52.5 % less discharge of grinding fluid.     

Superfinishing and grind-strengthening with elastic bonding system

This paper presents with a new grinding strategy for a surface superfinishing and a grind-strengthening of the surface layer of steels in a single grinding step. To grind-strengthen a surface layer both abrasive material removal and a plastic deformation are needed. This combination together with an appropriate grinding wheel design offers the possibility to ensure high precision surfaces with a consistent quality finish that meets the highest standards. This kind of grinding process could be applied to bearings, for example. During the run-in period, the initial contact surfaces change until they stabilize to a running-in condition and have a new surface topography. Grinding with the new process strategy leads to benefits because a grind-strengthened surface layer eliminates initial wear and abrasion within the system, reduces surface finish roughness, extends fatigue strength, and reduces risk of part failure during operation.     

An investigation on wear mechanism of resin-bonded diamond wheel in Elliptical Ultrasonic Assisted Grinding (EUAG) of monocrystal sapphire

An investigation is carried out to analyze and quantify the wear mechanisms of resin-bonded diamond wheel in Elliptical Ultrasonic Assisted Grinding (EUAG) of monocrystal sapphire. The EUAG is a new grinding method proposed by the present authors in which an elliptical ultrasonic vibration is imposed on the workpiece by using an elliptical ultrasonic vibrator. In this paper, a series of grinding experiments under the presence/absence of ultrasonic vibration assistance are performed. The grinding forces and work-surface roughness are measured, and the wheel surface is examined too. The experimental results indicate that during grinding, the steady process region performed in EUAG is longer than that in Conventional Grinding (CG) by 20%, meaning that the grinding wheel has a longer sharp cutting period in EUAG. It is validated that the main wear mechanisms in EUAG is micro-fracture and cleavage of abrasive grains, which has a positive effect on the better grinding performance, such as lower grinding forces, force ratio F_n/F_t, wheel loading, and smoother work-surface. This study demonstrates that the improved grinding performance of diamond wheel can be realized by using EUAG method.     

An investigation on surface grinding using graphite as lubricant

Grinding requires high specific energy and the consequent development of high temperature impairs workpiece quality by inducing tensile residual stress, burn, micro cracks etc. Control of grinding temperature is achieved by providing effective cooling and lubrication. Conventional flood cooling is often ineffective due to the relative inaccessibility of the fluid to the actual grinding zone, film boiling etc. Further these fluids are also a source of health hazards. Minimization and possibly the elimination of fluid coolants by substituting their functions by some other means is of current research interest. This paper deals with an investigation on using graphite as a lubricating medium to reduce the heat generated at the grinding zone. An experimental set-up has been developed for this and a detailed comparison has been done with dry and coolant flooded grinding in terms of forces, specific energy, temperature and surface finish. Results show that grinding force, energy and temperature are reduced and resultant surface finish depends on workpiece material.     

A fundamental study on the mechanism of electrolytic in-process dressing (ELID) grinding

Demands for high quality surface finish, dimensional and form accuracy are required for optical surfaces and it is very difficult to achieve these using conventional grinding methods. Electrolytic in-process dressing (ELID) grinding is one new and efficient method that uses a metal-bonded diamond grinding wheel in order to achieve a mirror surface finish especially on hard and brittle materials. However, studies reported so for have not explained the fundamental mechanism of ELID grinding and so it has been studied here by conducting experiments to establish optimal grinding parameters to obtain better surface finish under various in-process dressing conditions. In this research the results show that the cutting forces are unstable throughout the grinding process due to the breakage of an insulating layer formed on the surface of the grinding wheel; however, a smoother surface can be obtained using a high dressing current duty ratio at the cost of high tool wear. ELID grinding is efficient for feed rates of less than 400 mm/min, and surface cracks are observed when it exceeds this limit.     

导弹天线罩CNC修磨机床用户界面设计与应用

导弹天线罩CNC修磨机床属于大型薄壁复杂三维曲面硬脆材料磨床,用于半精加工后的导弹天线罩内廓形修磨加工,保证天线罩电厚度指标达到设计要求。根据修磨机床的使用要求,遵循用户界面的设计原则和思想,设计了导弹天线罩CNC修磨机床用户界面。按不同模块的需求用Visual Basic和VisualC 混合编程,组成人机界面窗口。在屏幕上显示出天线罩测量加工的状态信息、修磨机床的各轴坐标、运行中的数控G代码文件等,并于内部封装了对其他系统模块的调用。在实际的天线罩修磨加工中通过了检验。     

Fine finishing of gears with high shape accuracy

Besides high demands on surface integrity machining of gears aims on very low surface roughness and high shape accuracy. These properties will have positive impacts on the lifetime of gears. In this context the challenges of profile grinding of cylindrical gears by using elastic bonded grinding wheels are addressed. For this new gear fine finishing approach, the very high potential of the process is revealed by analyzing the influence of the grinding wheel specification and the machining parameters on surface finish. Results show that gears with high shape accuracy and very good surface finish with almost optical quality can be achieved.     

Fuzzy pattern recognition of AE signals for grinding burn

Grinding burn is a common phenomenon of thermal damage that has been one of the main constraints in grinding difficult-to-machine materials. Grinding burn damages materials and degrades properties, by causing tensile residual stresses or microfractures in the workpiece surface. Numerous methods have been proposed to identify grinding burn. However, the main problems of current methods are their sensitivity and robustness. This paper describes a new method of grinding burn identification with highly sensitive acoustic emission (AE) techniques. The wavelet packet transform is used to extract features from AE signals and fuzzy pattern recognition is employed for optimising features and identifying the grinding status. Experimental results show that the accuracy of grinding burn recognition is satisfactory.     

新型多孔金属结合剂金刚石磨盘研制与磨削实验研究

针对引入孔隙结构后,多孔金属结合剂超硬磨具耐用度降低的问题,提出利用超硬磨料钎焊技术改善胎体对金刚石磨料的把持力,以提高工具寿命,并成功研制出一种新型多孔金属结合剂金刚石磨盘。测试分析了新型磨盘的节块性能,并通过磨削花岗岩安溪红635试验,对新型磨盘的磨削效果进行评价。实验结果表明:新型磨盘节块强度在100MPa左右,孔隙率为60%,孔隙在节块内部分布均匀,且金属结合剂与金刚石表面发生了牢固的化学冶金结合;磨削石材的表面粗糙度Ra0.77~1.59μm,磨盘的磨削比达到760。     

New tool concept for grinding a plateau-like surface for tribological applications

One of the most important factors for energy efficiency is the reduction of friction in machine elements. The grinding process is often the final machining process in machining hardened steel parts and the resulting surface finish influences the tribological behavior. The combination of grinding with a honing process can generate a plateau-like surface to reduce friction and create an oil reservoir to decrease abrasive wear and improve the fluid film stability. Additional processes like laser machining, micro milling or etching are able to generate micro dimples to improve the reduction of friction. Today, grinding processes are limited to machine plateau-like surfaces. Within this paper, a new tool concept will be presented, composed of a grinding tool with two different grain sizes and a metallic bonding. The use of small abrasive grains generates a smooth surface with low roughness values. A few additional larger grains induce stochastic scratches and create the plateau-like surface. Grinding experiments are conducted to analyze the effect of feed rate, feed angle and ratio between small and large grains on the resulting surface.     

镀镍金刚石在硬质合金精密磨削中的性能

为研究镀镍金刚石砂轮在硬质合金精密磨削时的磨削性能,用裸料金刚石砂轮同其进行对比磨削实验,分析二者在磨削功率、磨削比、磨削表面粗糙度以及砂轮表面形貌等方面的差异。研究结果表明:在磨削参数相同的情况下,镀镍金刚石砂轮在磨削时消耗的功率比裸料金刚石砂轮大,但是相对稳定;镀镍金刚石砂轮的体积磨削比要高于裸料金刚石砂轮的体积;在粗糙度方面,镀镍金刚石砂轮优于裸料金刚石砂轮,但是其黏屑较多,砂轮有堵塞现象。      

Influence of oil mist parameters on minimum quantity lubrication – MQL grinding process

Promising alternatives to conventional dry and fluid coolant applications are minimum quantity lubricant (MQL) or near dry grinding. Despite several researches, there have been a few investigations about the influence of MQL parameters on the process results, such as oil flow rate, air pressure, MQL nozzle position and distance from the wheel–workpiece contact zone. The current study aims to show through experiment and modeling, the effects of the above parameters on grinding performance such as grinding forces and surface roughness. The results show that the setting location of the nozzle is an important factor regarding the effective application of MQL oil mist. It has been shown that optimal grinding results can be obtained when the MQL nozzle is positioned angularly toward the wheel (at approximately 10–20° to the workpiece surface). In addition, it is found that the efficient transportation of oil droplets to the contact zone requires higher mass flow rate of the oil mist towards the grains flat area and longer deposition distance of an oil droplet. Applying the new setup, considerable reduction in the grinding forces and surface roughness has been achieved.     

The effect of ELID grinding on the flexural strength of silicon nitride

Advanced structural ceramics, such as silicon nitride-based materials, are of significant interest due to their excellent physical and mechanical properties. However the cost of grinding these ceramics, an integral part of their fabrication, is very high and can result in surface and subsurface damage to the material. These defects can significantly reduce the strength and reliability of the finished component and are sensitive to grinding parameters. In this investigation, the effect of finish electrolytic in-process dressing (ELID) grinding on the flexural strength of silicon nitride specimens were studied. Kyocera's silicon nitride SN 235, in the form of Modulus of Rupture (MOR) specimens, were ground using the application of ELID grinding with a # 6000 grit sized cast iron bonded diamond (CIB-D) grinding wheel. A significant improvement in the strength of the Si₃N₄ specimens was noted when finish ELID grinding was performed. This was the result of ductile regime grinding using the application of finish ELID grinding. Another method to improve the flexural strength of silicon nitride specimens will also be addressed in this paper.     

Dressing and truing of hybrid bonded CBN grinding tools using a short-pulsed fibre laser

This paper presents the results of an investigation into the dressing and truing of hybrid bonded (metal-vitrified) CBN grinding wheels using a short-pulsed fibre laser. Truing of complex contours on CBN grinding tools with sharp edges (edge radii of less than 20 μm) could be successfully applied, whereas other dressing methods have been neither technically nor economically successful. Sharpening by laser can provide the same wheel surface topography which is conventionally produced by SiC and/or Al₂O₃ sharpening tools. Grinding characteristics and long-term performance of the laser-profiled tools are discussed.     

Influence of dressing feed on the performance of laser dressed Al2O3 wheel in wet grinding

The influence of dressing feed on the performance of a laser dressed Al₂O₃ wheel in surface grinding under wet, plunge grinding conditions is discussed. The performance of a grinding wheel dressed with different feed rates was evaluated by means of several grinding parameters such as grinding forces, wheel wear against work material removed (G-ratio), worksurface finish and its integrity. The performance of a laser dressed wheel was compared with that of a diamond dressed wheel. Analysis of the results clearly indicated the satisfactory performance of the laser dressed Al₂O₃ wheel in wet grinding, especially when dressed with a feed of 0.35 mm/rev and with an intensity of 4.0 × 10¹⁰W/m2. Further, this particular analysis suggests the selection of smaller feed rates for dressing grinding wheels with a laser in order to modify the wheel surface topography considerably, so as to produce effective grinding results with laser dressed grinding wheels.     

微晶刚玉砂轮磨削钛合金TC17磨削力研究

针对航空发动机常用材料钛合金TC17,采用白刚玉砂轮与微晶刚玉砂轮开展磨削试验,研究微晶刚玉砂轮对工件表面质量和磨削力大小的影响规律。试验结果表明:微晶刚玉砂轮磨削后工件表面质量更好,表面粗糙度值降低0.14 μm,磨削力降低10%左右。针对微晶刚玉砂轮进行磨削参数对磨削力影响规律的单因素试验,从磨削力角度分析微晶刚玉砂轮磨削钛合金的合理工艺参数。综合磨削力与加工效率因素,确定磨削钛合金TC17的合理参数为:砂轮线速度v_s=27 m/s、磨削深度a_p=0.01 mm、工件进给速度v_w=12 m/min;对磨削力试验数据进行多元线性回归分析,建立了法向磨削力和切向磨削力的回归模型。      

GCr15钢的ELID磨削性能实验研究

为了探讨GCr15钢的ELID（Electrolytic In-process Dressing）磨削性能，在基于大量实验的基础上，对GCr15钢采用ELID磨削时磨削力的变化规律进行了详细分析，并将磨削力、磨削表面粗糙度与普通磨削进行了比较。结果表明，采用铸铁结合剂CBN砂轮进行ELID磨削时磨削力几乎不随时间的变化而变化，而采用白刚玉砂轮进行磨削时的磨削力随时间的变化不断增大，在线电解修整使CBN砂轮在磨削过程中始终保持良好的磨削性能，有利于节省砂轮修整时间，提高加工效率。在ELID磨削中，采用微细砂轮进行磨削可以获得很低的表面粗糙度，实现对GCr15钢的超精密镜面磨削。     

数控快速点磨削技术的绿色特性分析

分析了数控快速点磨削(Quick-point Grinding)超高速、薄超硬磨料砂轮、点接触和连续轨迹数控成型的技术特征，以及数控快速点磨削工艺的加工性能。快速点磨削主要工艺特点是磨削力和磨削温度低、磨削比大、表面完整性和加工精度好。基于绿色制造理论，通过对快速点磨削技术的磨削机理及绿色特性的分析，提出了实现干式绿色快速点磨削的主要研究内容及方向，并结合该项新技术的发展现状，讨论了开展面向绿色制造的快速点磨削技术的理论与应用研究的重要意义。     

A study of the convection heat transfer coefficients of grinding fluids

By using hydrodynamic and thermal modelling, the variation of the convection heat transfer coefficient (CHTC) of the process fluids within the grinding zone has been investigated. Experimental measurements of CHTC for different grinding fluids have been undertaken and show that the CHTC depends on the grinding wheel speed and the fluid film thickness within the contact zone. The film thickness is determined by grinding wheel speed, porosity, grain size, fluid type, flow rate and nozzle size. The CHTC values are compared for a wide range of grinding regimes, including high efficiency deep grinding (HEDG), creep feed and finish grinding.     

A new two-dimensional ultrasonic assisted grinding (2D-UAG) method and its fundamental performance in monocrystal silicon machining

A new two-dimensional (i.e., elliptical) ultrasonic assisted grinding (UAG) technique is proposed to achieve high material removal rate and high surface quality in the machining of hard and brittle materials such as monocrystal silicon. In this method, the workpiece attached on an elliptical ultrasonic vibrator is ground with a resin bond diamond grinding wheel under the presence of elliptical ultrasonic vibration. The elliptical ultrasonic vibrator is produced by bonding a piezoelectric ceramic device (PZT) on a metal elastic body (stainless steel, SUS304) and its detailed structure/dimensions are determined by FEM (finite element method) analysis. When two alternating current voltages with a phase difference are applied to the PZT at the same frequency that is close to the resonant frequency of the longitudinal mode and bending mode of vibrator, two ultrasonic vibrations are generated simultaneously, and the synthesis of the vibrations results in an elliptical motion on the end face of the vibrator. If the phase difference is set at 0° or 180°, two kinds of one-dimensional ultrasonic vibrations, i.e., axial or vertical vibrations, can be obtained. Grinding experiments are carried out involving monocrystal silicon to confirm the performance of the proposed elliptical UAG. In addition, grinding experiments under the presence of the axial and vertical ultrasonic vibrations and the absence of ultrasonic vibrations, i.e., conventional grinding, are also carried out for comparison. The obtained results show that: (1) compared with conventional grinding, the axial ultrasonic vibration results in greatest improvement in the work surface quality and a slight reduction in the grinding forces; (2) under the vertical ultrasonic vibration, the grinding forces are decreased significantly but the surface roughness is increased slightly; (3) elliptical ultrasonic vibration leads to the significant reduction of both the surface roughness and grinding forces. These indicate that the high efficiency and high-quality grinding of monocrystal silicon can be performed with the proposed two-dimensional ultrasonic assisted grinding technique.