Experimental Research on the Ground Surface Quality of Creep Feed Ultrasonic Grinding Ceramics (Al_2O_3)

In order to grind the ceramic blade surface with the Numerical Control contour evolution ultrasonic grinding method using the simple shape grinding wheel, primary comparative experiments of creep feed grinding with and without ultrasonic vibration were carried out to grind Al2O3 ceramics so as to implore the effects of different process parameters on the machined surface quality. It can be concluded that when the direction of ultrasonic vibration is parallel to the direction of creep feed, the value of the surface roughness will be decreased; otherwise the surface quality will become worse. With the ultrasonic grinding method, the slower feed-rate, the smaller grinding depth, the higher grinding speed and the compound feed grinding method should be applied in order to improve the surface quality. The creep feed grinding meehanisms with and without ultrasonic vibration were analyzed theoretically from the experimental results. With the selected grinding parameters resulted from the experiments, the feasibility experiment of ultrasonic grinding ceramic blade surface was cartied out.

Unsteady-state Grinding Technology (III) Studies on the Surface Quality

In conventional grinding theory, the chief removed mode of ceramic coprocessor by diamond tools was brittle removal. In order to perform the plastic removal or ductility processing of engineering ceramics the high degree of accuracy and high rigidity grinner must be using micro grain size diamond grinding wheel to direct the processing of micron below rank depth to prevent form the occurring of the brittle processing zone. This will resulted in the high expense of grinding. The expense of grinding could even reach the 80% of the total manufacture cost of the ceramic part. Ultra-precision grinding for advanced ceramics has been achieved by the unsteady-state grinding technique. In this paper, we mainly deals with observing and analyzing the surface quality of the silicon nitride ground by pink fused alumina wheel in different grinding parameters. To optimize the grinding parameters in the process of the unsteady-state grinding, the experiments of X-ray diffraction, energy spectrum analysis, SEM observation and roughness measurement were performed. The results show that: 1. In the process of unsteady state grinding, high line speed (rotational speed) of the grind wheel can improve the roughness of the silicon nitride apparently. It was also evident that the larger the grain mesh size, the better the surface quality. 2. There exists an optimum combination of grinding conditions such as grinding wheel speed, rotational speed of the workpiece, feed rate between the grinding wheel and the workpiece, grinding times and cutting coolant. The surface quality of the silicon nitride can be up to the standard of mirror finishing. 3. By analyzing the finished surface with X-ray diffraction and energy spectrum, the existence of some new phases including titanium and alumina was proved. 4. By utilizing the unsteady state grinding technique, the surface roughness of Ra ≤ 0.030 μm can be achieved by grinding the silicon nitride with the pink fused alumina wheel in low cost. Based on the unsteady-state grinding technique, this paper put forward a new processing method which by utilizing aluminum oxide grinding wheel to perform burnishing process and impudent the low surface roughness processing of engineering ceramic, the Ra is about 0.01 μm. Furthermore, the working efficiency of this method is high, and the process cost is low, so it is a prospective processing method.

Surface Finish Evaluation of AISI P100 Steel after Grinding with MQL Technique with Different Flow Rates

Grinding operation is a finishing process often employed when high precision and narrow geometric tolerances are required.These requirements can be achieved only if cutting conditions are properly selected,especially the cooling-lubrication technique.In general,grinding is performed in presence of cutting fluid,however,due to the environmental impacts and costs of the conventional coolant delivery technique(flow rates from 4 L/min to 300 L/min),alternative cooling-lubrication techniques have been developed on restriction of the coolants use.Among the several techniques,MQL(minimum quantity of lubricant)technique has received special attention from machining users because of its advantages in terms of surface quality of workpiece and drastic reduction in use of coolant.In this context,this paper evaluated the performance of the MQL technique as compared to the flood coolant in peripheral surface grinding of AISI P100(VP100)steel with conventional aluminum oxide grinding wheel in relation to the surface roughness(Ra and Rz).Input parameters tested were equivalent chip thickness(0.09μm,0.18μm and 0.27μm)and flow rate of the cutting fluid(60 mL/h,150 mL/h and 240 mL/h)of the MQL system.Results showed that the grinding with MQL technique provided lower surface roughness values compared to conventional flood cooling,especially when machining under the intermediary cutting conditions.Also,with exception of heq of 0.09 m,the MQL technique resulted in lower values of Rz parameter as compared to the conventional coolant technique,regardless of the flow rate tested.

Prediction of undeformed chip thickness distribution and surface roughness in ultrasonic vibration grinding of inner hole of bearings

Ultrasonic vibration grinding differs from traditional grinding in terms of its material removal mechanism.The randomness of grain-workpiece interaction in ultrasonic vibration grinding can produce variable chips and impact the surface roughness of workpiece.However,previous studies used iterative method to calculate the unformed chip thickness(UCT),which has low computational efficiency.In this study,a symbolic difference method is proposed to calculate the UCT.The UCT distributions are obtained to describe the stochastic interaction characteristics of ultrasonic grinding process.Meanwhile,the UCT distribution characteristics under different machining parameters are analyzed.Then,a surface roughness prediction model is established based on the UCT distribution.Finally,the correctness of the model is verified by experiments.This study provides a quick and accurate method for predicting surface roughness in longitudinal ultrasonic vibration grinding.

Experimental Evaluation on Grinding Texture on Flank Face in Chamfer Milling of Stainless Steel

The surface quality of chamfer milling of stainless steel is closed related to the products of 3 C(Computer, Communication and Consumer electronics), where a cutter is a major part to achieve that. Targeting a high-quality cutter,an experimental evaluation is carried out on the influence of grinding texture of cutter flank face on surface quality.The mathematic models of chamfer cutter are established, and they are validated by a numerical simulation. Also the grinding data are generated by the models and tested by a grinding simulation for safety reasons. Then, a set of chamfer cutting tools are machined in a five-axis CNC grinding machine, and consist of five angles between the cutting edge and the grinding texture on the 1 st flank faces, i.e., 0°, 15°, 30°, 45° and 60°. Furthermore, the machined cutting tools are tested in a series of milling experiments of chamfer hole of stainless steel, where cutting forces and surface morphologies are measured and observed. The results show that the best state of both surface quality and cutting force is archived by the tool with 45° grinding texture, which can provide a support for manufacturing of cutting tool used in chamfer milling.

Study on the Ground Surface Quality of Cr_2O_3 Coatings

The ground surface quality of Cr 2O 3 coatings is investigated in this paper. The influence of some typical grinding parameters on ground surface integrity is discussed in detail. It is found that the ground surface roughness increases with the increase of depth-of-cut. The surface finish is improved as the increase of grinding speed, but too high grinding speed may result in serious vibration of the system. The increase of workpiece speed causes deterioration of surface finish and produces big grinding noise. Experiments on plateau treatment after the rough ground surface were also carried out. The surface profile of the ground surface after plateau treatment becomes much smoother than the former rough surface. Some sharp peaks on the ground surface may be effectively removed by the plateau treatment, which produces a reasonable surface profile and can stand much more load. Surface observations and analyses show that plastic deformation and micro-cracks occur on the ground surface. The material removal process is primarily a serious of localized surface fractures accompanied by multi-plastic deformations. Much more plastic deformation and micro-cracks emerge on the ground surface when the depth-of-cut increases. The increase of workpiece speed may produce more surface micro-cracks, but the relative increase of grinding speed is beneficial to ground surface quality.

Grinding force and surface quality in creep feed profile grinding of turbine blade root of nickel-based superalloy with microcrystalline alumina abrasive wheels

Creep feed profile grinding of the fir-tree blade root forms of single crystal nickel-based superalloy was conducted using microcrystalline alumina abrasive wheels in the present study. The grinding force and the surface quality in terms of surface topography, subsurface microstructure,microhardness and residual stress obtained under different grinding conditions were evaluated comparatively. Experimental results indicated that the grinding force was influenced significantly by the competing predominance between the grinding parameters and the cross-sectional root workpiece profile. In addition, the root workpiece surface, including the root peak and valley regions, was produced with the large difference in surface quality due to the nonuniform grinding loads along the root workpiece profile in normal section. Detailed results showed that the surface roughness, subsurface plastic deformation and work hardening level of the root valley region were higher by up to25%, 20% and 7% in average than those obtained in the root peak region, respectively, in the current investigation. Finally, the superior parameters were recommended in the creep feed profile grinding of the fir-tree blade root forms. This study is helpful to provide industry guidance to optimize the machining process for the high-valued parts with complicated profiles.

An investigation on machined surface quality and tool wear during creep feed grinding of powder metallurgy nickel-based superalloy FGH96 with alumina abrasive wheels

In this study,the machined surface quality of powder metallurgy nickel-based superalloy FGH96(similar to Rene88DT)and the grinding characteristics of brown alumina(BA)and microcrystalline alumina(MA)abrasive wheels were comparatively analyzed during creep feed grinding.The infuences of the grinding parameters(abrasive wheel speed,workpiece infeed speed,and depth of cut)on the grinding force,grinding temperature,surface roughness,surface morphology,tool wear,and grinding ratio were analyzed comprehensively.The experimental results showed that there was no significant difference in terms of the machined surface quality and grinding characteristics of FGH96 during grinding with the two types of abrasive wheels.This was mainly because the grinding advantages of the MA wheel were weakened for the difficult-to-cut FGH96 material.Moreover,both the BA and MA abrasive wheeIs exhibited severe tool wear in the form of wheel clogging and workpiece material adhesion.Finally,an analytical model for prediction of the grinding ratio was established by combining the tool wear volume,grinding force,and grinding length.The acceptable errors between the predicted and experimental grinding ratios(ranging from 0.6 to 1.8)were 7.56%and 6.31%for the BA and MA abrasive wheels,respectively.This model can be used to evaluate quantitatively the grinding performance of an alumina abrasive wheel,and is therefore helpful for optimizing the grinding parameters in the creep feed grinding process.

Subsurface damage and bending strength analysis for ultra-thin and flexible silicon chips

Subsurface damage(SSD) is an unavoidable problem in the precision mechanical grinding for preparing ultra-thin and flexible silicon chips. At present, there are relatively few studies on the relationship between SSD and the bending strength of ultra-thin chips under different grinding parameters. In this study, SSD including amorphization and dislocation is observed using a transmission electron microscope. Theoretical predictions of the SSD depth induced by different processing parameters are in good agreement with experimental data. The main reasons for SSD depth increase include the increase of grit size, the acceleration of feed rate, and the slowdown of wheel rotation speed. Three-point bending test is adopted to measure the bending strength of ultra-thin chips processed by different grinding conditions. The results show that increasing wheel rotation speed and decreasing grit size and feed rate will improve the bending strength of chips, due to the reduction of SSD depth. Wet etching and chemical mechanical polishing(CMP) are applied respectively to remove the SSD induced by grinding, and both contribute to providing a higher bending strength, but in comparison, CMP works better due to a smooth surface profile. This research aims to provide some guidance for optimizing the grinding process and fabricating ultra-thin chips with higher bending strength.

Grain erosion wear properties and grinding performance of porous aggregated cubic boron nitride abrasive wheels

Cubic boron nitride(cBN)superabrasive grinding wheels exhibit unique advantages in the grinding of difficult-to-cut materials with high strength and toughness,such as titanium alloys and superalloys.However,grinding with multilayered metallic cBN superabrasive wheels faces problems in terms of grain wear resistance,the chip storage capability of the working layers and the stability and controllability of the dressing process.Therefore,in this work,novel metallic cBN superabrasive wheels with aggregated cBN(AcBN)grains and open pore structures were fabricated to improve machining efficiency and surface quality.Prior to the grinding trials,the airborne abrasive blasting process was conducted and the abrasive blasting parameters were optimized in view of wear properties of cBN grains and metallic matrix materials.Subsequently,the comparative experiments were performed and then the variations in grinding force and force ratio,grinding temperature,tool wear morphology and ground surface quality of the multilayered AcBN grinding wheels were investigated during machining Ti-6Al-4V alloys.In consideration of the variations of grain erosion wear volume and material removal rate per unit of pure metallic matrix materials as the abrasive blasting parameters changes,the optimal abrasive blasting parameters were identified as the SiC abrasive mesh size of 60#and the abrasive blasting distance and time of 60 mm and 15 s,respectively.The as-developed AcBN grains exhibited better fracture toughness and impact resistance than monocrystalline cBN(McBN)grains because of the existence of metal-bonded materials amongst multiple cBN particles that decreased crack propagation inside whole grains.The metallic porous AcBN wheels had lower grinding forces and temperature and better ground surface quality than vitrified McBN wheels due to the constant layer-by-layer exposure of cBN particles in the working layer of AcBN wheels.

复合纳米自润滑金刚石砂轮磨削SiC陶瓷的试验研究

提出一种复合纳米自润滑金刚石砂轮的制备方法,并对制备的砂轮进行SiC陶瓷的磨削试验,分析砂轮表面不同质量分数的复合纳米颗粒对磨削性能的影响。使用MoS2、TiO2纳米颗粒作为自润滑砂轮基底的填充材料,采用复合纳米自润滑金刚石砂轮和传统金刚石砂轮进行磨削对比试验,研究复合纳米自润滑金刚石砂轮的润滑机制。研究结果表明,复合纳米自润滑金刚石砂轮自释放的纳米颗粒有效地参与了磨削区间的润滑,砂轮的法相力、切向力降低,提升了工件表面质量。在磨削深度为2~8μm内,复合纳米自润滑金刚石砂轮的具体表现为法向磨削力降低18.6%~38.7%、切向磨削力降低11.2%~28.6%,工件表面粗糙度降低13.9%~41.5%。根据本试验所得数据,当砂轮表面复合纳米颗粒质量分数为8%时,润滑性能和工件表面质量最佳。

机器人磨抛复杂曲面加工轨迹对表面质量的影响研究

为了探究不同加工轨迹及其排布对工件磨抛加工表面质量的影响,本文进行了机器人磨抛轨迹对工件表面质量影响规律的研究。基于Preston去除方程和Hertz接触理论建立了砂带磨抛加工材料去除深度模型,分析了表面残留纹理的生成机理。以曲面航空发动机叶片为试验样件,利用自行搭建的机器人磨抛系统,分别使用等距轨迹、摆线轨迹进行加工试验,分析材料去除效果及表面纹理情况。试验结果表明,采用传统直线加工的等距轨迹于搭接处产生条带状纹理;摆线因其多方向性的加工动作,均化了表面纹理,提高了加工表面一致性。

碳化硅陶瓷的激光改性磨削

为了实现碳化硅陶瓷的高精加工,激光辐照被引入磨削加工中。本文以碳化硅陶瓷为研究对象,采用激光改性磨削工艺,利用激光辐照对碳化硅陶瓷进行改性处理,进而对碳化硅陶瓷进行磨削试验。与普通磨削进行比较,研究了碳化硅陶瓷试样的磨削力、表面粗糙度、表面形貌和亚表面损伤。实验结果表明,与普通磨削相比,激光改性磨削可以有效降低法向磨削力、切向磨削力、表面粗糙度,最大下降幅度分别为33.91%、37.31%和33.14%。激光改性磨削促使SiC陶瓷在磨削过程中以塑性去除为主,磨削表面规则且光滑;工件亚表面微裂纹较少,亚表面损伤深度小;实现了大磨削深度的塑性去除,提高了SiC陶瓷的磨削质量。

轴承内圆轴向超声高速磨削理论建模与试验研究

目的以GCr15材料的6309型轴承内圆为研究对象,探究高转速超声磨削过程中超声辅助振动对磨粒运动轨迹、磨削后表面粗糙度、圆度以及微观形貌的影响规律。方法基于超声内圆磨削磨粒切削轨迹及超声振幅与砂轮转速对轨迹影响的理论仿真,构建磨削去除量与磨削表面粗糙度的理论模型,通过对轴承内圆进行超声磨削试验,研究高转速(16000~22000 r/min)下各工艺参数对内圆表面质量的影响并验证理论粗糙度评价模型。结果超声振幅的增大使磨粒与内圆接触轨迹变长,但随砂轮转速的提高,磨粒切削轨迹的密集程度也有所下降。振幅和砂轮转速的增大可使切削去除量增大、粗糙度降低,铬刚玉粒度100#陶瓷结合剂砂轮磨削GCr15轴承内圆后,其表面质量更有优势,单因素下表面质量变化趋势与理论分析结果相一致。结论在相同磨削参数下,1.5μm振幅超声磨削可使内圆圆度降至0.92μm,粗糙度降至130.5 nm,与传统磨削相比,粗糙度最高减小了41.5%,圆度最高减小了52.6%。在高转速下,各因素按砂轮对磨削后表面质量的影响由大到小的顺序依次为砂轮转速、超声振幅、进给速度,当磨粒线速度超过41.8 m/s、进给速度超过600 mm/min、振幅超过1.5μm时,表面质量呈下降趋势。

磨削工艺参数对硬质合金刀具磨制损伤的影响

硬质合金刀具被广泛应用于航空航天、汽车、冶金等高端制造领域。硬质合金刀具的生产通常采用金刚石砂轮磨削加工,因此,砂轮的磨削工艺参数对刀具的成品质量有重要影响。本试验通过改变砂轮的线速度及进给速度加工硬质合金麻花钻,加工完成后,采用超景深显微镜、白光干涉仪和扫描电镜对钻头的磨削表面以及亚表面进行检测,分析砂轮进给速度及线速度对加工损伤的影响。结果表明:砂轮进给速度和线速度越大,锯齿量越大;当线速度与进给速度较小时,钻头的主切削刃易出现微崩刃现象;砂轮进给速度越大,钻头后刀面表面粗糙度越大;砂轮线速度越大,钻头后刀面表面粗糙度越小;钻头后刀面处的亚表面最大损伤深度随线速度的增大而减小;当线速度30m/s、进给速度160mm/min时,钻头的磨削损伤最小。

基于曲面响应法的短电弧磨削蜂窝环工艺研究

蜂窝密封结构是当代航空发动机的先进高效密封结构,传统加工难以满足加工质量的要求,需要采用短电弧加工技术加工此类零部件。为获得最优的加工参数,以重铸层厚度和微观形貌为指标,分析电流及电压波形、表面能谱、工件表面和截面形貌,并进行响应曲面分析。结果表明:对重铸层厚度和加工时间影响的显著性为:进给速度>工件转速>电极转速,重铸层厚度随进给速度增加而增加,随工件和电极转速增加而减小,且表面质量有相同的趋势。多目标优化获得最佳参数为:工件转速5.863 r/min,电极转速287.114 r/min,进给速度0.087 mm/min。因此,适当降低进给速度,提高工件和电极转速,可减少微裂纹、冲蚀凹坑和熔滴颗粒等现象,提高工件表面质量,降低重铸层厚度。

五轴数控工具磨床制程能力与过程能力的定量评价研究

为考察五轴数控工具磨床的制程能力,选用两种不同品牌的五轴数控工具磨床加工硬质合金球头立铣刀,测量了立铣刀球头的曲率、刀具球头与圆柱部分衔接处的刃口崩边大小和砂轮磨痕间距来定量评价磨床加工复杂刀具的能力(即制程能力);通过过程能力指数C_(p),从刀具跳动、刀刃直径、球头半径R和球头曲率等四个参数评价磨床的过程能力。

超声振动下建筑结构钢磨削划痕尺寸表面质量分析

超声辅助磨削方法是在传统磨削加工方法上加入超声振动的新磨削技,可以显著改善加工性能。以结构钢作为结构钢,设置不同划痕深度下普通超声振动划痕测试。研究结果表明,超声振动磨削划痕期间形成很大振幅,划痕深度明显提高。超声振幅提高会在系统中获得更大输入能量,提升了材料去除率。金刚石压头振动冲击时,位于划痕底部与两侧区域产生持续裂纹缺陷。随着振幅增加,在断续冲击过程中形成了更长划痕。提高划入深度,达到了相对稳定划入深度,表现为脆性去除特点。

自动化研磨技术在机械抛光精加工中的实践

随着我国现代工业化水平的不断提高,自动化研磨技术在机械抛光精加工领域的应用成为工业制造业发展的重要趋势。自动化研磨技术是一种结合信息化、智能化与自动化控制的新型工艺,融合了磨削过程控制、表面质量检测与机器人设计等多项技术内容,在机械抛光精加工过程中主要应用于表面抛光、精密研磨以及工艺优化等领域,推动了机械制造系统的进一步优化升级,实现了对机械设备的高效精细加工。基于此,简要概述自动化研磨技术的内涵,分析机械抛光精加工中的自动化研磨技术,提出自动化研磨技术在机械抛光精加工中的实践应用,以推进工业制造产业的智能化和精细化发展。

Machining Characteristics in Cryogenic Grinding of SiCp/Al Composites

In this study, liquid nitrogen was applied to grind SiCp/Al composites with high volume fraction and large SiC particle at different levels of cutting conditions, and the effects of grinding depth and speed on grinding force, surface morphology, and surface roughness were investigated. At the same time, the effect of cryogenic cooling was also compared with that of conventional wet grinding. The experimental results indicated that cryogenic cooling is effective in enhancing supporting function of Al matrix to the SiC particles and improving surface quality. Additionally, the brittle fracture of SiC particles was suppressed and some ductile streaks on SiC particle could be observed.