Bio-mimetic surface structuring of coating for tribological applications

A novel multilayered coating was developed for applications associated with friction reduction and wear resistance improvement. The nano-engineered coating integrates a soft lubricating layer, consisting of MoS₂-PTFE, onto hard load-supporting layers, with controlled surface morphology (roughness and patterning) of cBN-TiN. The coating was synthesized by sequential procedures including electrostatic spray deposition of cBN particles with different average particle sizes, chemical vapor deposition of TiN, deposition of nano- and micro-sized MoS₂ dispersed in PTFE, and curing. The effect of cBN particle size (with different combinations of particle size) and deposition parameters (specifically electrical voltage) on the cBN-TiN surface morphology were studied experimentally and optimized. SEM characterization of the as-synthesized cBN-TiN coating shows surface features similar to that of colocasia esculenta, with alternating nano- and micro-sized domes and “pockets”; the MoS₂-PTFE top layer has MoS₂ particles retained in the pockets by a basket structure formed during PTFE curing. Tribological and scratch tests were carried out for the as-prepared cBN-TiN and cBN-TiN/MoS₂-PTFE multilayered coatings. Sliding test results demonstrate significantly lower friction coefficient for the multilayered coating, showing that the unique integration of soft lubricating layer and biomimetically structured hard layer can effectively improve tribological performance. It is suggested that lubrication at the frictional contacts was realized by continuous release of the lubricants, MoS₂ and PTFE, from the pockets.     

金刚石工具磨削石材摩擦磨损特性实验研究

使用电镀金刚石工具磨削石材,通过改变不同的实验参数,对金刚石工具的摩擦磨损特性进行研究。在MMW-1型立式万能摩擦磨损试验机上测试了工具在室温条件下干摩擦磨损性能,采用FA2004电子天平测量金刚石工具的磨损量,用VDM600体式电子显微镜对工具磨损表面进行微观形貌观察,用HV-1000显微硬度计测量石材的显微硬度。实验结果表明:金刚石工具的磨损量和摩擦系数都随着载荷的增加而增加,同时也随主轴转速增加而增加;另外,工具的磨损量和摩擦系数随着石材硬度的增加而增加。     

Injection molded spherical grinding tools: manufacture and application of a novel tool concept for micro grinding

Micro grinding offers the possibility of machining micro structures in hard and brittle materials producing small-scaled parts. Novel micro grinding systems and machines require miniaturized tools and spindles to meet the demands of small or desktop machines providing a small working space. This paper introduces a novel grinding module called ’GrindBall’, with highly integrated tool drive and bearing functions as well as a shaft-free, spherical grinding tool for micro machining applications in small-scaled machine tools. One of the challenges within the development of the GrindBall module is the manufacture of spherical grinding tools, which are not commercially available. A promising method to produce such grinding tools, the injection molding of micro particle filled polymers, is demonstrated in this paper. Injection molding and grinding experiments show that such spherical grinding tools meet the main requirements of this novel grinding technique and show significant material removal rates.     

Multicomponent nanostructured films for various tribological applications

Many engineering materials working under severe cutting, stamping, or bearing conditions including humid and corrosive environments, as well as temperature fluctuation require a combination of chemical, mechanical, and tribological properties. For load-bearing metallic implants, the combination of excellent mechanical and tribological properties with biocompatibility and bioactivity is also of great importance. Desired properties can be achieved in hard films based on carbides, borides and nitrides of transition metals by alloying with metallic (Al, Cr, Zr) or nonmetallic (O, P, Si, Ca) elements. The present work demonstrates the potential of self-propagating high-temperature synthesis (SHS), magnetron sputtering (MS), and ion implantation assisted MS of SHS-composite targets to produce multicomponent nanostructured films with enhanced combination of properties. Three groups of recently developed films for mechanical engineering and medicine are considered: hard tribological Ti–(Al, Cr)–(Si, B, C, N) films with enhanced thermal stability, corrosion and oxidation resistance; nanocomposite and multilayered TiCrBN/WSe_x films with improved lubrication; and multifunctional bioactive nanostructured (Ti, Ta)–(Ca, Zr)–(C, N, O, Si, P) films (MuBiNaFs).     

Structure-property relations in ZrCN coatings for tribological applications

ZrCN coatings were deposited by dc reactive magnetron sputtering with N₂ flows ranging from 2 to 10 sccm in order to investigate the influence of the nitrogen incorporation on structure and properties. Information about the chemical composition was obtained by glow discharge optical emission spectroscopy and Rutherford backscattering spectroscopy. The evolution of the crystal structure studied by X-ray diffraction revealed the formation of a face-centred cubic ZrCN phase for N₂ flows greater than 4 sccm. Additionally, the presence of an amorphous phase in the coatings deposited with the highest N₂ flows could be evidenced by Raman spectroscopy and X-ray photoelectron spectroscopy. This phase can act as a lubricant resulting in a low coefficient of friction as shown in the conducted ball-on-disc tests. Nanoindentation measurements showed that coatings deposited with a 6 sccm N₂ flow had the maximum hardness which also revealed the best performance in the conducted dry cutting tests.     

Toward a new tribological approach to predict cutting tool wear

This work aims at improving the numerical modelling of cutting tool wear in turning. The key improvement consists in identifying a fundamental wear model by means of a dedicated tribometer, able to simulate relevant tribological conditions encountered along the tool–workmaterial interface. Thanks to a design of experiments, the evolution of wear versus time can be assessed for various couples of contact pressure and sliding velocities (σ_n, V_s) leading to the identification of a new wear model. The latter is implemented in a numerical cutting model to locally simulate tool wear along the contact with regard to each local tribological loading.     

Hard CrCN/CrN multilayer coatings for tribological applications

Hard coatings were deposited using a cathodic arc evaporation method. The results of investigations of multilayer CrCN/CrN coatings are presented in this article. The microstructure and crystallinity of films have been investigated using X-ray diffraction (XRD). The composition was determined with energy dispersive spectroscopy (EDS). The adhesion of films was estimated on the basis of an analysis of scratch-test results. The hardness and tribological properties of films deposited on hardened and tempered HSS substrates were also investigated. The tribological tests were carried out in a pin-on-disc geometry. The influence of a normal load, sliding speed and a counterpart material on the friction coefficient and the specific wear rate of the coatings were studied. The counterparts were made of HSS and four types of wood: oak, beech, spruce and pine. The hardness and adhesion of multilayer CrCN/CrN coatings are respectively 25 GPa and 120 N.     

Nanolayer coatings for hard disk and demanding tribological applications

Coating properties and performance can be tailor-designed by proper control of nano structure andprocess conditions. This paper presents two examples: first, the synthesis and optimization of 1 nm thick nitrogenated carbon (CN_x) nano-layers as protective overcoats in extremely highdensity harddisksystems, and, second, the development of multilayer coatings for wear protection at elevated temperatures. Synthesis of these coatings was done by magnetron sputtering. These studies demonstrate that one canproduce atomically smooth 1 nmthickCN_xovercoatswith acceptable corrosionperformance. In addition, this paper shows that, with the proper choice of nanolayer thickness and process conditions, superhard coatings based on TiN/SiN_x and TiB₂/TiC multilayers with high thermal stability, low internal stress, and high wear resistance can be synthesized.     

Mirror surface grinding of ceramics using a three-axis precision cnc grinding machine

In this paper, the mirror surface grinding of ceramics, such as Si₃N₄ and Al₂O₃---TiC, was realized with average roughness less than 10 nanometers. For the grinding operation, a three-axis CNC grinding machine tool was designed and manufactured. The grinding machine is composed of an air spindle, a high damping resin concrete bed and a three-axis CNC controller with high resolution AC servo motors. The dynamic properties of the grinding machine, such as the natural frequencies and damping of the spindle, were experimentally measured to improve the ground surface quality. Also, the truing method to improve the straightness of the grinding wheel with 1 μm accuracy, was developed.     

Development of a micro diamond grinding tool by compound process

This study presents a novel micro-diamond tool which is 100 μm in diameter and that allows precise and micro-grinding during miniature die machining. A novel integrated process technology is proposed that combines “micro-EDM” with “precision composite electroforming” for fabricating micro-diamond tools. First, the metal substrate is cut down to 50 μm in diameter using WEDG, then, the micro-diamonds with 0–2 μm grain is “plated” on the surface of the substrate by composite electroforming, thereby becoming a multilayer micro-grinding tool. The thickness of the electroformed layer is controlled to within 25 μm. The nickel and diamond form the bonder and cutter, respectively. To generate good convection for the electroforming solution, a partition designed with an array of drilled holes is recommended and verified. Besides effectively decreasing the impact energy of the circulatory electroforming solution, the dispersion of the diamond grains and displacement of the nickel ions are noticeably improved. Experimental results indicate that good circularity of the diamond tool can be obtained by arranging the nickel spherules array on the anode. To allow the diamond grains to converge toward the cathode, so as to increase the opportunity of reposing on the substrate, a miniature funnel mold is designed. Then the distribution of the diamond grains on the substrate surface is improved. A micro-ZrO₂ ceramic ferrule is grinded to verify the proposed approach. The surface roughness of R_a = 0.085 μm is obtained. It is demonstrated that the micro-diamond grinding tool with various outer diameters is successfully developed in this study. The suggested approach, which depends on machining applications, can be applied during the final machining. Applications include dental drilling tools, precision optic dies, molds and tools, and biomedical instruments.     

Trenker公司推出生产大规格金刚石/CBN电镀砂轮的新概念设备

德国Trenker磨料磨具设备技术公司开发出了新系列电镀设备，实现了制造大规格，大型号的金刚石和立方氮化硼（CBN）外圆磨及仿形磨电镀砂轮，砂轮直径最大可达700mm，重量达300kg.     

Interactions of grinding tool and supplied fluid

This paper reviews the physical and chemical interactions between the rotating tool and the supplied fluid in grinding. The mechanisms of this tool-fluid interaction are the key for high performance grinding processes due to an efficient fluid supply resulting in a minimal thermomechanical impact on workpiece and tool. Reduced wear, increased surface finish, suitable subsurface properties of the machined material, increased material removal rates, and also energy efficiency can be achieved. In this context, the fluid supply towards the contact zone between tool and workpiece, the tool cleaning with high pressure cleaning nozzles as well as (tribo)-chemical phenomena between the abrasive layer and the supplied fluid are analysed and discussed. Finally, knowledge gaps are revealed which are indicating future research needs.     

Dynamic modeling of a novel workpiece table for active surface grinding control

In order to implement active control during surface grinding, a workpiece micro-positioning table utilizing a piezoelectric translator has been developed. The workpiece table has a working area of 100×100 mm and a nominal working range of 45 μm. The resolution of the workpiece table is less than 20 nm and the natural frequency is 579.2 Hz. The rigidity of the workpiece table under the open loop condition is approximately 17 N/μm. Under the closed loop condition, the rigidity is better than 400 N/μm. The design of the workpiece table is presented together with considerations to achieve the high dynamic characteristics, where the maximum acceleration is up to 33g (g is the acceleration of gravity). The dynamic models of the piezoelectric translator and the workpiece table have been established. Experimental testing has been carried out, verifying the performance of the workpiece table and the established dynamic models for the workpiece micro-positioning table.     

Micro grinding tool for manufacture of complex structures in brittle materials

This paper presents a novel micro shaft grinding tool with cylindrical tool tip diameter between 13 μm and 100 μm. The manufacturing of the tool itself is carried out on a prototype desktop machine. The shaping of the tool is accomplished by grinding the tool tip directly onto the cylindrical carbide tool shank. During tool grinding, the tool shank rotates in a micro spindle with air-lubricated bearings, leading to high concentricity and low run-out. The tool tip is electrically nickel plated with diamond grains. During first experimental tests of the tool, very low surface roughness values and sharp edges without burrs were achieved.     

SiC陶瓷非球面磨削工艺实验研究

为了研究磨削工艺参数对SiC材料磨削质量的影响规律,利用DMG铣磨加工中心做了SiC陶瓷平面磨削工艺实验,分析研究了包括主轴转速、磨削深度、进给速度在内的磨削工艺参数对工件表面粗糙度的影响。结果表明:工件表面粗糙度随着主轴转速的增加而减小,随着磨削深度和进给速度的增加而增加。在粗糙度工艺试验的基础上,以表面粗糙度最小为目标优选一组磨削工艺参数,进行了小口径SiC陶瓷非球面磨削实验,获得了较低的表面粗糙度值(0.5150μm)和较小的面形精度误差(4.668μm)。     

Experimental study on grinding force and grinding temperature of Aermet 100 steel in surface grinding

This paper investigates grinding force and grinding temperature of ultra-high strength steel Aermet 100 in conventional surface grinding using a single alumina wheel, a white alumina wheel and a cubic boron nitride wheel. First, mathematical models of grinding force and grinding temperature for three wheels were established. Then, the role of chip formation force and friction force in grinding force was investigated and thermal distribution in contact zone between workpiece and wheel was analyzed based on the mathematical model. The experimental result indicated that the minimum grinding force and the maximum grinding force ratio under the same grinding parameters can be achieved when using a CBN wheel and a single alumina wheel, respectively. When the phenomenon of large grinding force and high grinding temperature appeared, the workpiece material would adhere locally to the single alumina wheel. Grinding temperature was in a high state under the effect of two main aspects: poor thermal properties of grinding wheel and low coolant efficiency. The predicted value of grinding force and grinding temperature were compared with those experimentally obtained and the results show a reasonable agreement.     

金刚石车刀自动研磨装置图像处理系统的开发

本研究开发了能够应用于圆弧刃金刚石车刀自动研磨的图像处理系统,在使用基于形状的模板匹配的方法对车刀进行初始安装的基础上,进行了切削刃形状信息和位置信息的亚微米精度测量。测量结果表明:开发的图像处理系统实现了圆弧刃半径分别为1mm,0.5mm,0.2mm的金刚石车刀测量,能够在线获得自动研磨所需的形状信息和位置信息,在精度和效率上为自动研磨系统的开发提供了保证。     

A new in-feed centerless grinding technique using a surface grinder

This paper deals with the development of an alternative centerless grinding technique, i.e., in-feed centerless grinding based on a surface grinder. In this new method, a compact centerless grinding unit, composed of an ultrasonic elliptic-vibration shoe, a blade and their respective holders, is installed onto the worktable of a surface grinder, and the in-feed centerless grinding operation is performed as a rotating grinding wheel is fed in downward to the cylindrical workpiece held on the shoe and the blade. During grinding, the rotational speed of the workpiece is controlled by the ultrasonic elliptic-vibration of the shoe that is produced by bonding a piezoelectric ceramic device (PZT) on a metal elastic body (stainless steel, SUS304). A simulation method is proposed for clarifying the workpiece rounding process and predicting the workpiece roundness in this new centerless grinding, and the effects of process parameters such as the eccentric angle, the wheel feed rate, the stock removal and the workpiece rotational speed on the workpiece roundness were investigated by simulation followed by experimental confirmation. The obtained results indicate that: (1) the optimum eccentric angle is around 6°; (2) higher machining accuracy can be obtained under a lower grinding wheel feed rate, larger stock removal and faster workpiece rotational speed; (3) the workpiece roundness was improved from an initial value of 19.90 μm to a final one of 0.90 μm after grinding under the optimal grinding conditions.     

Mirror surface grinding for brittle materials with in-process electrolytic dressing

Use of a diamond wheel with superabrasive is required for mirror-like surface grinding of brittle materials. However, conventional dressing methods cannot apply to the diamond wheel with superabrasive. Recently, an electrolytic dressing method was developed for use with a cast iron-bonded diamond wheel and superabrasive. This technique can replace lapping and polishing. Using electrolytic dressing, surface roughness of the workpiece was improved significantly, and the grinding force was very low and the continuity of the grinding force was also improved. The purpose of this study was to achieve mirror-like surface grinding of ferrite with electrolytic dressing of a metal-bonded diamond wheel. For application of ultraprecision grinding for brittle material, superabrasive, air spindle, and in-process electrolytic dressings were used. Additionally, the effects of pick current and pulse width on ground surface were investigated, and suitable dressing conditions for ferrite were determined.     

Modeling and predicting of surface roughness for generating grinding gear

Gear surface has a significant effect on the load-carrying capacity and plays a crucial role for wear, friction and lubrication properties of the contact. However, most mathematical model of a generating gear grinding process trends to focus on grinding forces and temperature distribution in gear tooth. A new method for predicting gear surface roughness with the generating grinding process is developed in this paper. An algorithm for geometrical analysis of the grooves on the gear surface left by idea conic grains is given. To determine the final gear surface roughness produced by thousands of grinding wheel grains with randomly distributed protrusion heights, a search technique is proposed to systematically solve the gear surface roughness, which starts from the addendum circle along the involutes direction and ends at the dedendum circle. The numerical calculated results show that the surface of gear root part is smoother than that of gear top part.