感应钎焊温度对立方氮化硼砂轮磨削性能的影响

利用超高频感应钎焊在不同钎焊温度条件下制备立方氮化硼(CBN)砂轮,采用扫描电子电镜（SEM）和能量分散谱仪（EDS）对磨粒表面新生化合物进行观察与分析,并通过与电镀CBN砂轮进行比较,对感应钎焊CBN砂轮的磨削性能进行评价。结果表明：CBN磨粒界面新生化合物主要组成元素有N、B、Ti三种,活性元素Ti发生扩散并与N和B发生化合反应;当感应钎焊温度为940℃时,磨粒表面生成物致密覆盖在表面,且所制备的CBN钎焊砂轮的磨削力和磨削比能较小。在相同磨削用量下,对电镀CBN砂轮和感应钎焊CBN砂轮的磨损形式进行对比分析发现,电镀CBN砂轮的磨损形式为黏附磨损,钎焊CBN砂轮的磨损形式为破碎磨损。     

Effects of Abrasive Types on Grinding of Chopped Strand Mat Glass Fiber-Reinforced Polymer Composite Laminates

A grindability study of chopped strand mat glass fiber reinforced polymer laminates (CSM GFRP) has been carried out to evaluate the effects of abrasive types on grinding force ratio and area roughness at varying grinding parameters such as speed, feed and depth of cut. Performances of alumina (Al₂O₃) and cubic boron nitride (CBN) wheels were compared. Both wheels delivered the maximum grinding force ratios at low speed, high feed and low depth of cut. Alumina wheel produced smoother surface when grinding at low speed, low feed and high depth of cut. CBN wheel, on the other hand, gave smoother surface at high feed and low depth of cut conditions, regardless of speed. With CBN wheel, it is likely that a single grinding condition exists that maximizes grinding force ratio and minimizes area roughness. The findings indicate that CBN wheel exhibited higher grinding force ratio than alumina grinding wheel in general. CBN grinding wheel also outperformed alumina grinding wheel by producing smoother ground surface in most cases.     

Wear behavior and mechanism of single-layer brazed CBN abrasive wheels during creep-feed grinding cast nickel-based superalloy

Wear behavior and mechanism of single-layer brazed CBN abrasive wheels during creep-feed grinding nickel-based superalloy K424 was investigated. Grinding force and temperature acting on the abrasive wheels were measured. Optical microscopy and scanning electron microscopy were utilized to detect grain protrusion and wheel wear morphology. The normal distribution of the protrusion height of the brazed CBN grains on the wheel surface was determined. The results show that, though the grinding zone temperature is merely about 180°C during creep-feed grinding nickel-based superalloy, the grinding heat still has an important effect on the grain wear owing to the high temperature of the individual grain up to 500–600°C. Wear patterns of brazed wheels are composed of mild wear (attritious wear and grain micro-fracture) and severe wear (grain macro-fracture, erosion of the bonding layer). Strong joining of brazed CBN grains and Ag–Cu–Ti bonding layer improves significantly the resistance to grain pullout.     

Creep feed grinding of burn-resistant titanium (BuRTi) using superabrasive wheels

Following an introduction on the use of titanium alloys for aeroengine applications, results are presented on the creep feed grinding of a beta titanium alloy Ti-25V-15Cr-2Al-0.2C?wt.% (BuRTi) using vitrified bonded superabrasive wheels in a fractional factorial experimental design. Despite a general perception to the contrary, the range of titanium alloys in use is wide encompassing different alpha/near alpha, alpha/beta and beta designations, each with specific mechanical/physical properties. In terms of aeroengine use, there are seven or eight key alloys (or their equivalent) used globally with the trend for higher operating capability both in relation to temperature and stress level. In the experimental work, grinding forces were significantly lower with diamond; however, wheels employing CBN grits achieved the highest G-ratio (up to ~280) and lowest surface roughness (~0.73???m of Ra). This was accompanied by workpiece smearing and surface burn, which was evident in the majority of tests using CBN. Additionally, workpiece softening was observed within the first 15???m from the machined surface.     

High efficiency deep grinding with very high removal rates

High efficiency deep grinding (HEDG) achieves very high removal rates with moderate temperature rise. It is shown that key factors are high wheel speeds, large depths of cut and moderately high work speeds. High removal rates in HEDG are associated with very efficient grinding and very low specific energy compared to conventional grinding. Although HEDG-enabled machine tools are available, the wider adoption of HEDG requires confidence that high workpiece surface integrity is achievable and sustainable. HEDG is an aggressive machining process that requires a suitable machine tool and workpiece configuration. System requirements include a high-powered spindle drive motor also capable of high spindle speeds, a stiff machine structure, wear-resistant grinding wheels and high-capacity pressurized lubricant supply. This paper presents advances in the development of HEDG. Results of HEDG obtained using a newly designed and unique machine tool are presented to illustrate achievable removal rates. Specific grinding energies are shown together with grinding temperatures measured directly in the contact arc. An enhanced single-pole thermocouple technique is used to measure the actual contact temperatures in deep cutting for validation of predictions. New findings illustrate the performance of high-speed conventional wheels in HEDG compared with the performance of CBN wheels obtained from actual industrial tests.     

Effect of parameters on grinding forces and energy while grinding Al (A356)/SiC composites

Abstract

Grinding processes require a high energy input per unit volume of material removed, which is converted to heat at the grinding zone, resulting in increased force and wear. In the present study, the influence of grinding parameters like work speed and depth of cut on grinding forces and energy was studied. An attempt has been made to study the forces and energy involved while grinding aluminium alloy (A356)/silicon carbide (SiC) composite material with different grinding wheels. Experiments were carried out on a surface grinding machine. Three different types of wheels like SiC, cubic boron nitride (CBN) and diamond wheels were used. The grinding forces increased with increase in depth of cut and work speed. SiC exhibited high grinding force compared to the CBN wheel. In the case of the diamond wheel, it was even less. The specific grinding energy was highest for the diamond wheel followed by CBN and SiC wheels. The specific grinding energy decreased with increase in depth of cut and work speed.     

CBN砂轮在轴承套圈内圆磨削中的应用

CBN砂轮以其优异的性能在高效、高精度磨削中具有广阔的应用前景。文中以树脂结合剂CBN砂轮轴承圈内圆磨削为研究对象,采用金刚石滚轮修整器,研究选择合适的修整及磨削参数,使CBN砂轮的性能在轴承磨削中得到充分发挥。通过对修整前后砂轮表面形貌分析,揭示了修整参数对修锐效果的影响,并结合磨削后试件表面的精度获得了合适磨削参数,试验结果对CBN砂轮在轴承圈的大批量磨削中的广泛应用具有重要的指导意义。     

An experimental investigation of temperatures during conventional and CBN grinding

In many grinding applications, the material removal rate is constrained by the undesired thermal effects such as surface burn, tensile residual stresses, and micro-cracks on the ground parts. Thermal damage is a common productivity limitation factor for conventional grinding wheels largely employed in industry due to their convenient cost and known behavior. The development of superabrasive materials having high heat conduction coefficients allowed for higher material removal rates, pushing up the limits of productivity previously achieved with conventional wheels. This paper presents the results of a comparative investigation of maximum surface temperatures generated during the plunge grinding of 52100 steel using Al₂O₃ and CBN wheels. The experiments were conducted under wet as well as dry grinding conditions. The temperatures measured experimentally were compared to those determined analytically. A discussion relative to heat partition coefficients concludes this paper.     

The laser dressing of resin-bonded CBN wheels by a Q-switched Nd: YAG laser

Resin-bonded cubic boron nitride (CBN) grinding wheels are widely used in industry due to their good grinding ability. There is, therefore, a need to find a good method suitable for the dressing of these wheels. This paper presents a new method dressed by an acoustic-optic Q-switched Nd: YAG laser based on thermal interaction, which is unlike the conventional mechanical dressing methods based on force interaction. The mechanism of the selective removal of the bond was analysed. Experiments of a single pulse ablation on the resin bond and the CBN grains, and the laser dressing of resin-bonded CBN wheels with different dressing parameters have been carried out. The grinding force has been compared for the conventional mechanical dressed wheel and the laser dressed wheel. It is shown that the resin-bonded CBN grinding wheel is suitable for an acoustic-optic Q-switched Nd: YAG laser dressing with radial irradiation, which is better than a continuous wave (CW) laser dressing with radial irradiation and conventional mechanical dressing methods.     

Sensor elements made of conductive silicone rubber for passively compliant gripper

Grinding is regarded as a special multiple edge cutting process, in which the abrasive grains remove the workpiece material at the microlevel. The grain–workpiece interaction, which resembles the microcutting process, directly modifies the workpiece surface and dominates all the output measures of grinding process. Recently, a virtual single-layer cubic boron nitride (CBN) grinding wheel model is developed by simulating each wheel fabrication step, which makes the estimation of the single grain material removal mode possible in grinding. Therefore, the study of the grain–workpiece interaction through microcutting behavior on the abrasive grains becomes necessary for the quantitative investigation of grinding processes. In this paper, the influence of the grain orientation on the microcutting performance of CBN grains is studied through finite element method (FEM) simulation based on response surface methodology (RSM). The FEM simulation helps in both qualitative and quantitative understanding of microcutting process. And the RSM analysis is proved to be an effective tool for factorial analysis in this paper. The results indicate that the single grain microcutting force is sensitive to the grain wear condition and orientation status, and there exists preferable orientation condition for microcutting with abrasive grains to achieve minimum cutting force.     

超硬磨粒CBN砂轮的磨削性能

本研究的目的是评价三种砂轮在磨削高速工具钢时的磨削性能。采用ABWOOD平面磨床,在不同磨削条件下对材料去除率,比磨削能和磨削表面的热损伤进行了实验研究,同时借助专用装置采集了磨削过程中砂轮的动态磨损数据。研究结果表明,超硬磨粒CBN砂轮磨削M2高速钢时磨性能最佳,这种砂轮在硬铁族金属加工领域具有良好的应用前景。     

Force modeling and machining characteristics of the intermittent grinding wheels

In the surface grinding operations, the grinding fluid cannot be supplied sufficiently in the cutting zone. Temperature generated in the cutting zone increases rapidly and causes thermal damage such as burning on the surface of a workpiece. To reduce thermal damage, the intermittent grinding wheels, which have an excellent cooling effect, have been applied. This paper describes machining characteristics by using intermittent grinding wheels. The grinding force of the intermittent wheels has been simulated by the SIMULAB, which is a program for simulating dynamic systems. Using the intermittent grinding wheels, the characteristics of grinding force, temperature, surface roughness, and geometric error have been evaluated experimently.     

新型点磨削砂轮磨削参数对磨削温度影响研究

提出了一种带有粗磨区倾角θ的陶瓷结合剂CBN点磨削砂轮,这种新型砂轮具有磨除率高、加工精度好等优点。研究了磨削热产生与分配理论和红外测温原理。分别用不同θ角的砂轮在一系列磨削参数条件下磨削QT700材料的阶梯轴,用Thermovision A40M热像仪测量砂轮磨削工件时接触区的平均温度,得出了偏转角α、磨削深度ap、工件轴向进给速度vf和砂轮速度vs在磨削过程中对磨削温度的影响规律,并且比较了在同一组磨削参数下,三种不同θ角砂轮对磨削温度的影响情况。     

SEM observations of the sliding behavior of A12O3 and CBN against steel

Both aluminum oxide (A1₂O₃) and cubic boron nitride (CBN) are being used as the abrasive medium in grinding wheels. To compare the effectiveness of these abrasives, a study was made, using the scanning electron microscope (SEM), to observe the sliding behavior and surface damage resulting from single particles of polycrystalline A1₂O₃ and CBN sliding dry against hardened M-50 tool steel. These experiments were run in the chamber of the SEM, which permitted direct observation of the contact areas at high magnifications. Friction force was monitored and videotape recordings were made continuously during these tests. Significantly lower friction and smoother wear tracks were obtained with the CBN. The A1₂O₃ grit produced much sharper ridges and considerable microcracking on the ridges. These microcracks were formed perpendicular to the wear track. The wear tracks obtained in the SEM were compared with the surfaces produced by surface grinding hardened steel with both CBN and A1₂O₃ wheels. At high magnifications, marked similarities between the ground surfaces and the surfaces produced by the basic sliding tests were noted. It is suggested that because of the large number of microcracks formed during the grinding process with the A1₂O₃, the fatigue life of parts ground with an A1₂O₃ wheel would be shorter than those ground with CBN. Practical experience indicates that this is true.     

Tribological mechanism of carbon group nanofluids on grinding interface under minimum quantity lubrication based on molecular dynamic simulation

Carbon group nanofluids can further improve the friction-reducing and anti-wear properties of minimum quantity lubrication (MQL). However, the formation mechanism of lubrication films generated by carbon group nanofluids on MQL grinding interfaces is not fully revealed due to lack of sufficient evidence. Here, molecular dynamic simulations for the abrasive grain/workpiece interface were conducted under nanofluid MQL, MQL, and dry grinding conditions. Three kinds of carbon group nanoparticles, i.e., nanodiamond (ND), carbon nanotube (CNT), and graphene nanosheet (GN), were taken as representative specimens. The [BMIM]BF₄ ionic liquid was used as base fluid. The materials used as workpiece and abrasive grain were the single-crystal Ni–Fe–Cr series of Ni-based alloy and single-crystal cubic boron nitride (CBN), respectively. Tangential grinding force was used to evaluate the lubrication performance under the grinding conditions. The abrasive grain/workpiece contact states under the different grinding conditions were compared to reveal the formation mechanism of the lubrication film. Investigations showed the formation of a boundary lubrication film on the abrasive grain/workpiece interface under the MQL condition, with the ionic liquid molecules absorbing in the groove-like fractures on the grain wear’s flat face. The boundary lubrication film underwent a friction-reducing effect by reducing the abrasive grain/workpiece contact area. Under the nanofluid MQL condition, the carbon group nanoparticles further enhanced the tribological performance of the MQL technique that had benefited from their corresponding tribological behaviors on the abrasive grain/workpiece interface. The behaviors involved the rolling effect of ND, the rolling and sliding effects of CNT, and the interlayer shear effect of GN. Compared with the findings under the MQL condition, the tangential grinding forces could be further reduced by 8.5%, 12.0%, and 14.1% under the diamond, CNT, and graphene nanofluid MQL conditions, respectively.     

Development of abrasive cut-off wheel having side grooves

The abrasive cut-off wheel fails prematurely during the routine sectioning of workpiece, which may cause injury to the operator. One of the major reasons of premature failure is the improper mixing of the abrasive mixture. In order to provide strength to the wheel, it was reinforced by woven roving type glass fiber and the abrasive mixture was ball milled. Cutting zone temperature becomes high during the cutting operation, which may cause thermal damage to the workpiece and debonding of abrasive from the wheel. It is very difficult to supply the cutting fluid to the cutting zone in order to reduce the temperature. New types of abrasive cut-off wheels were developed, which have radial passages on their surfaces to supply the cutting fluid to the cutting zone. Performance of the wheels was compared and the mechanical strength of the wheel material was tested.     

MODELING OF DRESSING FORCES DURING ROTARY DIAMOND CUP DRESSING OF VITRIFIED CBN GRINDING WHEELS

This paper presents a mathematical model of dressing of vitrified CBN grinding wheels by a diamond cup dresser. It predicts the dressing forces during rotary diamond cup dressing of vitrified CBN grinding wheels. This model is based on the fracture of abrasive grits, the fracture of the bond and the contact forces between dresser and grinding wheel. It considers the kinematical influences and in particular speed ratio and overlap factor during the dressing process. A Weibull distribution is used to predict the probability of bond fracture and also the collision number between the diamond grits of a rotating dresser and the CBN grits. This model is validated by experimental results. The theoretical modeling values agree reasonably well with the experimental results. On the basis of this model the effect of different cup dressing parameters on dressing forces is theoretically discussed with the aim of establishing appropriate dressing process configurations. Furthermore the presented model provides a basis for further prediction of wheel topography and the grinding process.     

Mist-jetting electrical discharge dressing (MEDD) of nonmetal bond diamond grinding wheels using conductive coating

Diamond wheels are widely used in high-precision grinding of hard and brittle materials; unfortunately, they are difficult to true and dress. This paper addresses that problem in that it proposes an effective dressing technique—mist-jetting electrical discharge dressing (MEDD) of nonmetal bond diamond grinding wheels using conductive coating. A conductive phase is coated on the wheel surface to increase the conductivity of the nonmetal bond. Electrical discharge model was built to analyze feasibility and select optimized parameters of MEDD. Experiments were conducted to evaluate the dressing performance of MEDD in terms of surface morphology of the wheel surface, grinding force, and surface roughness of the workpiece. Experimental results show that abrasive grains on the wheel protrude are satisfied. The discharge parameters have an important influence on the dressing result. The grinding force and the surface roughness of the workpiece significantly reduced after dressing.     

The role of specific energy in micro-grinding of titanium alloy

This paper is concerned with understanding the role of specific energy in micro-grinding of conventional and additively manufactured Ti6Al4V. The effects of grinding and dressing parameters, cooling-lubrication conditions, and the directions of material build-up are studied. It is demonstrated that the minimum specific energy in single grain tests is independent of the material-fabrication method. The lowest measured specific energy obtained is 11.5 J/mm³ for both workpiece materials. The direction of material build-up influenced the process only when grinding with low aggressiveness, where 20% higher specific energy was observed. Similar specific energies were obtained for oil-lubricated and dry conditions, indicating that lubrication had minimal effect. The effects of the diamond concentration in the wheel and the dressing parameters were also investigated. Comparable specific energies were observed for wheels with C150 and C200 concentrations. The specific energy was found being predominantly influenced by dressing. Coarse dressing conditions produced 18% lower specific energy and, therefore, a more efficient micro-grinding process.     

超高速陶瓷结合剂CBN砂轮关键制备技术的研究

砂轮制备技术是实现超高速磨削的关键之一.本文介绍了超高速陶瓷结合剂砂轮的特点,综述了超高速陶瓷结合剂CBN砂轮的关键制备技术,分析了我国CBN磨料、砂轮结构、陶瓷结合剂、砂轮制备工艺等的研究现状,最后展望了超高速陶瓷CBN砂轮的研究及应用前景.