MECHANICAL-ELECTRIC COUPLING DYNAMICAL CHARACTERISTICS OF AN ULTRA-HIGH SPEED GRINDING MOTORIZED SPINDLE SYSTEM

On the basis of the traditional mechanical model of a grinding wheel rotor and the mechanical-electric coupling model with ideal sinusoidal supply, taking high-frequency converting current of inverter power switches into further consideration, a modified mechanical-electric coupling model is created. The created model consists of an inverter, a motorized spindle, a grinding wheel and grinding loads. Some typical non-stationary processes of the grinding system with two different supplies, including the starting, the speed rising and the break in grinding loads, are compared by making use of the created model. One supply is an ideal sinusoidal voltage source, the other is an inverter. The theoretical analysis of the high-order harmonic is also compared with the experimental result. The material strategy of suppressing high-order harmonic mechanical-electric coupling vibration by optimizing inverter operating parameters is proposed.

Development and Prospectives of Ultra-High-Speed Grinding Technology

Ultra-high-speed grinding(UHSG)is a significant and powerful machining method in view of the enhanced productivity and precision demands.Previous researches regarding formation mechanisms and crucial technologies are comprehensively and thoroughly summarized to highlight state-of-art technology of UHSG.On the basis of the interdependence between process and machine innovations,theoretically,grinding mechanisms in strain hardening,strain rate strengthening,thermal softening,size effect and process characteristics need more in-depth studies to clarify the dominance of UHSG.Technically,CFRP wheel integrating with the brazed bonding has a prominent advantage in bonding strength and grit′s configuration over vitrified bonding,which would be superior in UHSG.Furthermore,external high pressure cooling combining with inner jet cooling methods,accompanied by scraper plates to alleviate the effect of air boundary,are crucial and practical measures for realizing effective cooling in UHSG.Grinding processes,especially those being related to grinding parameters and precise in-process measuring approaches,are also prerequisite for fitting and investigation of UHSG.

Simulation and Experimental Analysis of Super High-Speed Grinding of Ductile Material

This study aims to reduce the work-affected layer of the machined surface by carrying out the grinding at the speed over static pr o pagation speed of plastic wave of ductile materials and also aims to clarify suc h super high-speed machining mechanism.This paper reports on the result obtain ed through the molecular dynamics simulations and experiments on the super-spee d grinding below and beyond static propagation speed of aluminum.From the simul ation results,it is verified that the plastic deformation is reduced when the m a chining speed exceeds the material static propagation speed of plastic wave and its mechanism is completely different from that of the ordinary grinding process .Experimental results also show the improvement of the surface integrity when t he machining speed exceeds the material static propagation speed of plastic wave .

Development of CAD/CAM system and profile measuring device for CNC grinding machine to obtain an optimal grinding speed

Cam mechanics is one of the most popular devices for generating irregular motions and is widely used in automatic equipment,such as textile machines,internal combustion engines,and other automatic devices.In order to obtain a positive motion from the follower using a rotating cam,its shape should be correctly designed and manufactured.The development of an adequate CAD/CAM system for a cam profile CNC grinding machine is necessary to manufacture high-precision cams.The purpose of this study is the development of a CAD/CAM system and profile measuring device for a CNC grinding machine to obtain an optimal grinding speed with a constant surface roughness.Three types of disk cams were manufactured using the proposed algorithm and procedures to verify effectiveness of the developed CAD/CAM system.

Dechlorination of pentachlorophenol by grinding at low rotation speed in short time

In order to apply grinding method for degradation of pentachlorophenol(PCP) to an industrial scale,the proportion of different materials[CaO,SiO_2 and CO(NH_2)_2]and the size of grinding balls were examined.For saving energy and increasing dechlorination efficiency,the rotation speed and grinding time were maintained at relatively low values.At a mass ratio of grinding balls to materials(40:1),PCP was added into a big steel jar(300 ml) with other materials to grind at 300 r ·min^(-1)for 5 h.The results indicated that when PCP was mixed with CaO and SiO_2in a molar ratio of 1:60:60,the best dechlorination of 58.4%was achieved.CO(NH_2)_2 could not be used as hydrogen donor in the dehalogenation by mechanochemical reaction,since it restrained the dechlorination process.The size of grinding balls has significant effect on the reaction.The experiment with 5 mm steel balls indicates that the weight is too light to provide appropriate energy for the reaction,while steel balls of 10 and 15 mm could give better dechlorination reaction.It indicates that dechlorination depends on the mass of balls and fill rate.

Characterization and Analysis of Inconel 718 Alloy Ground at Different Speeds

Inconel 718(IN718)alloy is widely applied to fabricate high temperature resistant or corrosion resistant parts due to its excellent mechanical performance.However,the machining of IN718 alloy is difficult as it may cause serious tool wear and poor surface quality(SQ)of the workpiece.In this work,grinding experiments on IN718 alloy at different speeds were conducted by using a CBN grinding wheel.The relationship between grinding speed,SQ and subsurface damage(SSD)was well studied.With increasing grinding speed,surface roughness decreased,and SQ was greatly improved.Meanwhile,the microhardness of the grinding surface declined as the grinding speed increased.The SSD depth was almost unchanged when the grinding speed was lower than 15 m/s,then it decreased with higher grinding speeds.It was attributed to the mechanical-thermal synergistic effect in the grinding process.The results indicated that increasing grinding speed can effectively improve the SQ and reduce the SSD of IN718 alloy.The conclusion in the work may also provide insight into processing other hard-to-machining materials.

Investigation of Creep Feed Grinding Parameters and Heat treatment Effects on the Nickel-base Superalloys

The Nickel base Superalloys are the most famous complicated and useable of Superalloys to make hot zone components of the gas turbines. The complicated dimensional tolerances, specially at the root of the blade show importance of grinding processes at the production of blades root. The prediction of the effect of machining parameters on the soundness of component surface strengthening for reaching to a suitable surface finishing and avoiding from crack formation at the work part during machining operation often is not easy and feasible so needs to more industrial investigation. This research is about frame 5 blade designed by GE and made from Superalloy IN738LC has been investigated. The formation of a plastically deformed and heat affected zone during grinding of Superalloy IN738LC with a high depth of cut but slow work speed (creep feed grinding) was investigated. Parameters such as work speed, depth of cut and radial dressing speed have been considered as variables and their effects have been studied. During experimental performed, the voltage and current of motor measured and power and special energy calculated. Some samples heat-treated (of the 1176°C for 1 hr under neutral argon gas and cooling rate of 15°C /min up to 537°C and then air cooling) to study grains recrystallization. Other samples have been created from the roots of blades and then coated by Nickel to measure boundary layer micro-hardness. The results show that increasing work speed leads to increasing the use power. Increasing the depth of cut, by increasing material removal rate, and the radial dressing speed, by decreasing power, lead to decreasing special energy. The temperature created by grinding lead to decreasing plastic deformation and boundary layer formation. When the radial dressing speed changes from 1 to 0.6 u,m/rev and other parameters are kept unchanged the roughness of surface increases and the special energy decreases. Sufficient dressing is very essential in limiting the width of the molten zone to few micrometers. As a result, it was found that local melting at contact spots to be a rather common mechanism during grinding of superalloys, lead to so-called white layers which can easily be observed on metallographic cross sections.

Theoretical Study on Non-transmission High Efficient Parallel Camber Grinding Machine

Be directed against the development trend of modern CNC grinding machine towards high precision and high efficiency, some general weaknesses of existing camber grinding machine are analyzed in detail. In order to develop new type CNC camber grinding machine that can grind complex die, and genuinely achieved accurate feed and high efficient grinding, a new type camber grinding machine is put forward, called non-transmission virtual-shaft CNC camber grinding machine. Its feed system is a parallel mechanism that is directly driven by linear step motor. Therefore, traditional transmission types, such as the ball lead-screw mechanisms, the gears, the hydraulic transmission system, etc. are cancelled, and the feed system of new type CNC camber grinding machine can truly possess non-creep, good accuracy retentiveness a wide range of feed-speed change, high kinematical accuracy and positioning precision, etc. In order to realize that the cutting motion is provided with high grinding speed, step-less speed variation, high rotational accuracy, good dynamic performance, and non-transmission, the driving technology of hollow rotor motor is applied to drive the spindle of new type grinding machine,thus leading to the elimination of the transmission parts of cutting motion. The principle structure model of new type camber grinding machine is advanced. The selection, control gist and driving circuit line of the linear step motor are expounded. The main technology characteristics and application advantages of non-transmission virtual-shaft CNC camber grinding machine are introduced.

Separate critical condition for ultrasonic vibration assisted grinding

Separate characteristic of the tangential ultrasonic vibration assisted grinding (TUAG) machining is analyzed based on TUAG process, and a critical speed formula is given to correctly set the machining parameters to insure the separate characteristics of TUAG process. The critical speed is not only related to the ultrasonic vibration amplitude and frequency, but also to the grinding wheel velocity and the cutting point space, and the grinding force can be decreased during the TUAG process with separability. Grinding force experiments are conducted, and the experimental results are in good agreement with the theoretical results.

Controllable and high-throughput preparation of microdroplet using an ultra-high speed rotating packed bed

Microdroplets and their dispersion,with a large specific surface area and a short diffusion distance,have been applied in various unit operations and reaction processes.However,it is still a challenge to control the size and size distribution of microdroplets,especially for high-throughput generation.In this work,a novel ultra-high speed rotating packed bed(UHS-RPB)was invented,in which rotating foam packing with a speed of 4000-12000 r·min^(-1) provides microfluidic channels to disperse liquid into microdroplets with high throughput.Then generated microdroplets can be directly dispersed into a continuous falling film for obtaining a mixture of microdroplet dispersion.In this UHS-RPB,the effects of rotational speed,liquid initial velocity,liquid viscosity,liquid surface tension and packing pore size on the average size(d_(32))and size distribution of microdroplets were systematically investigated.Results showed that the UHS-RPB could produce microdroplets with a d_(32) of 25-63μm at a liquid flow rate of 1025 L·h^(-1),and the size distribution of the microdroplets accords well with Rosin-Rammler distribution model.In addi-tion,a correlation was established for the prediction of d_(32),and the predicted d_(32) was in good agreement with the experimental data with a deviation within±15%.These results demonstrated that UHS-RPB could be a promising candidate for controllable preparation of uniform microdroplets.

Applications of High-Efficiency Abrasive Process with CBN Grinding Wheel

High-efficiency abrasive process with CBN grinding wheel is one of the important techniques of advanced manufacture. Combined with raw and finishing machining, it can attain high material removal rate like turning, milling and planning. The difficult-to-grinding materials can also be ground by means of this method with high performance. In the present paper, development status and latest progresses on high-efficiency abrasive machining technologies with CBN grinding wheel relate to high speed and super-high speed grinding, quick point-grinding, high efficiency deep-cut grinding, creep feed deep grinding, heavy-duty snagging and abrasive belt grinding were summarized. The efficiency and parameters range of these abrasive machining processes were compared. The key technologies of high efficiency abrasive machining, including grinding wheel, spindle and bearing, grinder, coolant supplying, installation and orientation of wheel and workpiece and safety defended, as well as intelligent monitor and NC grinding were investigated. It is concluded that high efficiency abrasive machining is a promising technology in the future.

德钢4号高炉烟气自循环制粉系统设计

对四川德胜集团钒钛有限公司应用不带脱水装置的烟气自循环制粉工艺进行了介绍和总结,该制粉工艺的烟气炉采用全烧高炉煤气、中速磨煤机制粉、一级大布袋收粉,磨制的烟煤挥发分为25%,在稳定生产期间系统末端氧含量控制在12%以内,粉尘排放浓度<10 mg/Nm^(3)。生产实践表明:不带脱水装置全烧高炉煤气的烟气自循环制粉工艺安全可靠,满足生产要求。

风电轴承大尺寸钢球光球加工技术

针对国内现有风电轴承大尺寸钢球光球机加工精度低,加工效率低的问题,对钢球在光球机动、静磨盘沟道内的运动规律、受力特点和磨削机理进行分析,光球时钢球受到的磨削力与动、静磨盘沟道深度比有关,并基于ADAMS仿真得到最佳动、静磨盘沟道深度比为7∶3,去两极和环带、成形、走圆工序最佳动磨盘转速分别为90,120,90 r/min。样机试验结果表明,改进后光球机的光球效率提高了30%,球形误差至少提高了0.2 mm,表面粗糙度Ra值至少减小了0.03 mm。

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。

CFRP砂轮高速外圆磨削稳定性分析

为分析不同影响因素对CFRP砂轮高速外圆磨削稳定性的影响,采用铁木辛柯梁理论对具有阶梯特征的工件进行动力学分析,结合锤击试验测得砂轮动态特性,对高速磨削过程中的砂轮-工件两自由度系统进行了磨削稳定性分析。在对阶梯工件进行动力学分析的过程中,发现阶梯特征对于动态特性的影响较小,误差小于2%。在稳定性分析中发现,不同的砂轮转速和不同的工件磨削位置均会影响磨削稳定性。磨削位置越靠近工件中心,工件刚度越弱,磨削稳定性降低易诱发颤振;而在靠近顶尖支撑的位置,由于工件刚度增强,该位置的磨削稳定性将同时受到工件和砂轮的动力学性能的影响。通过磨削试验验证了分析方法的有效性,试验结果表明,工件磨削位置的刚度差异将会影响加工表面质量,由磨削失稳导致的粗糙度增幅可达51.6%。

体育器材SAE1008低碳钢高速磨削砂轮工艺优化

利用CBN砂轮高速磨削处理技术,对体育器材用SAE1008钢开展单因素测试,对比了不同磨削工艺下表层残余应力变化特征,并分析了相关影响因素。研究结果表明:当砂轮线速度到达60m/s时,获得了较大切向力,残余压应力相对其它工艺条件明显减小。当砂轮进给速增大后,形成线性降低的残余压应力,获得了更大比磨削能和更小残余压应力。位于(0.5~0.6)mm/min范围内呈现拉应力状态,应力作用造成的层深介于(100~150)μm,形成了更高磨削温度。230/270砂轮相对其它砂轮在磨削阶段形成更小表面残余应力,沿深度方向也产生了残余拉应力。该研究为设计减小残余拉应力以及改善钢材工件表面组织结构完整性的高速磨削技术提供了一定的参考价值。

Thermal and mechanical behavior of casting copper alloy wheel during wheel and belt continuous casting process

To investigate the thermal and mechanical behavior of casting wheel,a two-dimensional thermoelastic-plastic finite element model was used to predict the temperature,stress and distortion distribution of the casting wheel during the wheel and belt continuous casting process.The effects of grinding thickness and casting speed on the thermal and mechanical behaviors of the center of the hot face of the casting wheel were discussed in detail.In each rotation,the casting wheel passes through four different spray zones.The results show that the temperature distribution of the casting wheel in different spray zones is similar,the temperature of the hot face is the highest and the temperature reaches the peak in the spray zoneⅢ.The stress and distortion depend on the temperature distribution,and the maximum stress and distortion of the hot face are 358.2 MPa and 1.82 mm,respectively.The temperature at the center of the hot face decreases with increasing grinding thickness and increases with increasing casting speed.

High speed laser cladding as a new approach to prepare ultra-high temperature ceramic coatings

Ultra-high temperature ceramic(UHTC)coatings are used to protect the hot-end components of hypervelocity aerocrafts from thermal ablation.This study provides a new approach to fabricate UHTC coatings with high speed laser cladding(HSLC)technology,and places more emphasis on investigating the formation mechanism,phase compositions,and mechanical properties of HSLC-UHTC coatings.Results show that a well-bonded interface between the coating and the tantalum alloy substrate can be formed.The coating is mainly composed of(Zr,Ta)C ceramic solid solution phase with a content of higher than 90% by volume and Ta(W)metal solid solution phase.At a relatively high powder feeding rate,the ZrC ceramic phase appears in the coating while a dense ZrC UHTC top layer with a thickness of up to~50μm is successfully fabricated.As for the mechanical properties of the HSLC coatings,the fracture toughness of the coating decreases with the increase of powder feeding rate.The increase of carbide solid solution phase can significantly improve the high temperature microhardness(552.7±1.8 HV0.5@1000℃).The innovative design of HSLC ZrC-based coatings on refractory alloys accomplishes continuous transitions on microstructure and properties from the substrate to the UHTC top layer,which is a very promising candidate scheme for thermal protection coating.

高速机械粉磨对油基钻屑灰渣活性的影响

对油基钻屑灰渣进行了高速机械粉磨处理,研究了粉磨时间(0~7 min)对灰渣粒径分布和比表面积的影响,分析了掺灰渣胶砂试件的力学性能,并进行了XRD、SEM、FTIR微观分析。结果表明:与未粉磨处理的灰渣相比,粉磨3 min灰渣的粒径分布范围缩小至1.220~40.100μm,D50降低了60.9%,比表面积增大了27.6%;与其他粉磨时间的灰渣相比,用粉磨3 min的灰渣等质量取代30%水泥所制备的胶砂试件的28 d抗压强度最高,28 d抗折强度也较高;适宜的粉磨时间能够促进灰渣中的活性Si O2、Al2O3等与水泥水化产物Ca(OH)2发生二次水化反应,生成C-S-H凝胶和AFt,提高胶砂结构的密实度。

基于五轴平台的枞树型轮槽铣刀加工工艺分析

轮槽成型铣刀是加工汽轮机轮毂槽的重要工具,其结构复杂且加工困难。为提高加工效率和精度,以某型高速钢轮槽铣刀为例,提出基于五轴平台的加工工艺方法。使用UG软件基于五轴车铣复合机床规划粗加工刀具路径,并采用专用后置处理器生成数控加工程序,通过虚拟机床进行仿真验证;采用NUMROTO软件规划精加工路径,获得磨削NC代码并进行虚拟加工验证;进行实际切削验证,通过DOOSAN PUMA SMX2600ST车铣复合加工中心对刀具进行粗加工后,在SAACKE UWIF五轴工具磨床上完成刀具的精加工。实验结果证明,该工艺方法不仅能保证产品质量符合工艺设计要求,而且制造效率提高了20%。