金刚石表面的膜层沉积处理及其感应钎焊的研究

将热丝化学气相沉积(HFCVD)处理的金刚石作为磨料感应钎焊制作金刚石工具。HFCVD处理试验中,混合气为H2和CH4(体积流量比为100∶1.5),炉内压力为2.0kPa,700℃下处理45min后,在金刚石表面沉积了一层非晶碳膜。感应钎焊HFCVD处理的金刚石显示,出露部分的金刚石棱边能保持良好的锋利性;浸没在钎料层下面的金刚石表面形成了有均匀孔隙且形状不规则的铬碳化合物,液态钎料充填这些化合物孔隙之间,能够增强钎料对金刚石的把持强度。3种金刚石磨料感应钎焊制作的金刚石磨盘的高效重负荷石材磨削试验显示,HFCVD处理的金刚石的整体破碎率和脱落率最低。     

钎焊气氛对金刚石钎焊性能的影响

主要利用Cu-10Sn-5Ti钎料粉末,在空气、Ar气保护和真空气氛下分别对金刚石进行钎焊试验,通过扫描电子显微镜观测金刚石钎焊形貌、X射线衍射仪分析界面生成物成分、激光拉曼光谱仪检测金刚石石墨化程度、磨损试验分析金刚石破损形式等手段,考察研究不同钎焊气氛对金刚石钎焊性能的影响。试验结果表明,在空气中钎焊时,钎料粉末出现了一定的氧化,生成的氧化膜阻碍了界面反应的充分进行,对钎焊性能有一定的影响,金刚石也出现了较严重的热损伤,磨削过程中出现了少数部分颗粒脱落的情况;而在Ar气保护和真空钎焊时,钎料充分润湿和铺展,实现了对金刚石的高强度把持,金刚石石墨化程度很小,金刚石主要经历了完整、小块破碎、大块破损、磨平等正常磨损形式,金刚石利用率高。     

钎焊气氛对金刚石磨耗特性的影响

采用NiCr合金钎料,通过Ar气保护和真空钎焊的方法制备了钎焊金刚石耐磨性试件,并研究了钎焊气氛对金刚石磨耗特性的影响。结果表明：在试验条件完全相同的情况下,不同的钎焊气氛导致金刚石磨耗特性不同,即经真空钎焊金刚石的磨耗特性表现为破碎方式,而经Ar气保护炉中钎焊金刚石的磨耗特性初始表现为磨耗平台方式,其后随着磨耗平台面积的增大,金刚石出现破碎。最后采用Ar气保护和真空钎焊方式制作了金刚石套料钻并进行了钻削试验,由于磨耗特性的不同,Ar气保护炉中钎焊套料钻较真空钎焊套料钻具有更长的使用寿命。     

On the grindability of low-carbon steel under dry, cryogenic and neat oil environments with monolayer brazed cBN and alumina wheels

Grinding of low-carbon steel often exhibits severe wheel loading due to the formation of long chips and high adhering tendency of the work material with the grits. Conventional composite-type alumina wheels are commercially utilised for grinding low-carbon steel. However, the actual nature of grit wear cannot be truly understood in a composite wheel. The truing and dressing conditions also have some influences on the wear mechanism. Therefore, in order to explore the wear pattern on a single layer of grits, monolayer brazed cBN, white and grey Al₂O₃ wheels were used in the present study. The grindability of AISI 1020 steel was evaluated under dry, liquid nitrogen and neat oil environments. The surface profile of the workpiece after being ground in each environmental condition was traced with a surface profilometer to reveal the mechanism of grit wear. The post-grinding conditions of the wheels were observed using scanning electron microscopy. The cBN wheel was found to outperform the alumina wheels in terms of grinding forces and grit wear. The wear of the cBN wheel was remarkably arrested with the application of neat oil. On the other hand, large-scale adhesion and breakage of grits in white alumina wheel were observed under cryogenic environment. In fact, the beneficial role of liquid nitrogen could not be realised in reducing grinding forces and grit wear with all the three types of wheel. A lubricating agent like neat oil appeared to be more suitable than cryogenic cooling when grinding low-carbon steel.     

钎焊金刚石薄壁小孔钻研制

以Ni-Cr合金为钎料,分别用真空加热和高频感应加热两种方式进行了金刚石磨粒与0Cr18Ni9不锈钢基体的钎焊,制作了基体外径为3 mm的薄壁小孔钻头。进行了半钢化玻璃钻削试验,用扫描电子显微镜观察钻削试验前后钻头的微观形貌。结果表明:两种钎焊工艺皆实现了金刚石磨粒的高强度连接;加热源不同及金刚石磨料出露高度差异性是影响钻头磨损方式的主要因素;为确保钻头的寿命和高效,磨粒出露高度应控制在其自身高度的50%-60%之间。     

Investigation and development of a molding process for the production of micro-hairs

Cubic boron nitride (cBN) is a unique synthetic material on account of its high hardness, high wear resistance, excellent cutting edge stability and relative chemical inertness compared to diamond. The introduction of monolayer electroplated cBN wheels replaced the complex pre-grinding wheel preparation work (truing and dressing) of composite cBN wheels and thereby extensively facilitating the application in high-efficiency deep grinding, creep feed grinding, etc. The present work has aimed at developing a precisely controlled brazing technique suitable for bonding the cBN grits to a steel substrate in monolayer form with higher bond strength, larger grit protrusion and more uniform grit distribution compared to that in the currently used galvanically bonded wheels. Experimental investigation have clearly demonstrated the potential of the newly developed brazed wheels under varying grinding conditions for processing materials like bearing steel. Improved capability of these wheels over galvanically bonded wheels could be better recognised during dry grinding at high material removal rate and for large stock removal when galvanically bonded wheels were found to suffer from severe wheel loading in grinding bearing steel and from unusual increase in grinding forces due to grit pullout. Creation of wider inter-grit spaces with strong bonding and uniform grit spacing happened to be the essence of the present brazed cBN wheel.     

Ni—Cr合金Ar气保护炉中钎焊金刚石砂轮的研究

用活性行钎料钎焊单层金刚石砂轮与传统电镀砂轮相比具有磨锋利，寿命长等优异性能。利用Ar气谷护炉中钎焊的方法，用Ni-Cr合金粉末做钎料，迁当控制钎焊温度，保温时间和冷却速度，实现了金融石与钢基体的牢固连接，利用扫描电镜和X射线能谱，结合X射线衍射结构分析，发现在钎焊过程中Ni-Cr合金中的Cr元素分离出在金刚石界面形成富Cr层并与金刚石表面的C元素反应生成Cr3C2和Cr7C3，这是实现合金与金刚石有较高结合强度的主要因素，重负荷磨削实验表明金刚石为正磨损，没有整颗金刚石脱落。     

Study on diamond vacuum brazed with Cu-based filler metal containing Cr

To reduce the thermal damage to the diamond and production cost, Cu-Sn-Ni-Cr and Cu-Sn-Cr were used to braze the diamond. SEM, EDS, and XRD were used to analyze the morphology of the diamond and the microstructure of the interface and the brazing alloy. Graphitization of the brazed diamond was tested by laser Raman, and the static compressive strength and toughness index of the diamond abrasive were measured. The results show that it realizes chemical metallurgical bonding between the diamond and either of these two filler metals, while Cu-Sn-Ni-Cr shows better wettability to the diamond. The brazed diamond has complete morphology and smoothing surface, there is almost no graphite in the diamond, but the static compressive strength and TI decrease slightly. On the surface of the diamond, it generates continuous laminar (Cr, Fe)₇C₃. The bonding strength between the diamond and the filler metal can meet the need of grinding. During the solidification process of the brazing alloy, dendrite α-Cu precipitates out firstly; then there is peritectic transformation and eutectoid transformation to form dendrite α-Cu, Cu_6.5Sn, Cu₉NiSn₃, and eutectoid α-Cu.     

Some remarks on the chemical wear of diamond and cubic BN during turning and grinding

Previous experiments using simple grinding wheels consisting of a single layer of cubic boron nitride (CBN) or diamond grits on an electroplated rod have shown that the production of wear flats on the grits leads to an increasing grinding force which eventually results in the destruction of the nib. In one of the present experiments, similar worn areas are observed on the grits in a conventional type grinding wheel. The wear of the flats appears to be similar in type to that observed on the flanks of turning tools fabricated from single crystals of diamond and CBN. Experiments with such turning tools show wide variations in the rates of wear between diamond and CBN and between different difficult metal workpieces. These and previous results imply that the flats are formed by an attritious wear process conditioned by the chemical constitution of the tool, workpiece and environment. Further consideration of these various points should lead to the enhanced performance of diamond and CBN grinding wheels.     

干式磨抛用钎焊金刚石磨抛盘制备与试验

为解决传统树脂砂轮片干式磨抛高强度钢存在的磨抛效率低、火花大、粉尘多、安全性低等问题,分析了利用钎焊金刚石技术的优势制备新型磨抛盘的可行性,并提出了解决对策。结合新型金刚石磨料排布工艺,利用Ni-Cr合金焊料,真空钎焊制备了钎焊金刚石磨抛盘。对AH36船用高强度钢进行了干式磨抛对比试验。试验表明:与传统树脂砂轮片相比,钎焊金刚石磨抛盘磨削效率提高40%左右,磨削寿命是前者的12倍以上;磨屑平均体型较大且种类多,无熔融状磨屑存在,磨粒表面基本无磨屑粘附,证明了新型磨抛盘干式磨削时可有效控制磨削温度。     

ON CUMULATIVE DEPTH OF TOUCH-DRESSING OF SINGLE LAYER BRAZED cBN WHEELS WITH REGULAR GRIT DISTRIBUTION PATTERN

The present work deals with a single layer brazed type cBN grinding wheels, which have been developed in-house. Grits were actively brazed on the working surface of the wheels in a regularly distributed pattern so that it could perform grinding without loading. In general, such a wheel produces substantially high transverse roughness. This happens because of its low active grain density. A touch-dressing technique, developed in-house, has been successfully applied on these brazed wheels so that most of the grits did participate and the average roughness could be brought down to an acceptable magnitude. This work investigated the co-relation between the grit size and cumulative depth of dressing required to achieve an acceptable magnitude of transverse roughness. It was found that the required cumulative depth of dressing was dependent on the size of cBN grits. This paper also shows the effect of gradual touch-dressing on improvement of roughness of the surface ground by such new class of recently developed wheels. Experiments were conducted with microcrystalline cBN grits of three different sizes.     

ON CUMULATIVE DEPTH OF TOUCH-DRESSING OF SINGLE LAYER BRAZED cBN WHEELS WITH REGULAR GRIT DISTRIBUTION PATTERN

The present work deals with a single layer brazed type cBN grinding wheels, which have been developed in-house. Grits were actively brazed on the working surface of the wheels in a regularly distributed pattern so that it could perform grinding without loading. In general, such a wheel produces substantially high transverse roughness. This happens because of its low active grain density. A touch-dressing technique, developed in-house, has been successfully applied on these brazed wheels so that most of the grits did participate and the average roughness could be brought down to an acceptable magnitude. This work investigated the co-relation between the grit size and cumulative depth of dressing required to achieve an acceptable magnitude of transverse roughness. It was found that the required cumulative depth of dressing was dependent on the size of cBN grits. This paper also shows the effect of gradual touch-dressing on improvement of roughness of the surface ground by such new class of recently developed wheels. Experiments were conducted with microcrystalline cBN grits of three different sizes.     

钎焊单层金刚石砂轮关键问题的研究

概述了用活性钎料将金刚石磨料钎焊到钢基体表面制作单层金刚石砂轮，比传统的单层电镀金刚石钞轮具有明显的工艺优势。分析指出了钎焊工艺用现存的关键问题，即如何实现金刚石磨料与合金钎料层高的结合强度，钎料层厚度的均匀性和金刚石磨料的有序排布。给出了可行的解决方案，即利用Ag-Cu-Cr或Ni-Cr等活性钎料与金刚石界面化学反应生成的Cr7C3和Cr23C7，实现钎料层与金刚石间的高强度结合；通过化地貌优化，优化出磨粒排布方式，然后按优化的结果排布磨料。     

Ni-Cr合金真空钎焊金刚石界面微结构分析

钎焊单层超硬磨料砂轮极高的结合强度和接近理想的锋利形貌 ,使它在生产应用中显示出传统砂轮无法比拟的优异性能。这种新型超硬磨料砂轮以其卓越的磨削性能必将逐步取代传统单层电镀砂轮。本文在真空炉中用钎焊的方法 ,用Ni Cr合金钎料 ,适当控制钎焊温度、保温时间和冷却速度 ,实现了金刚石与钢基体的高强度连接。并用深腐蚀的方法处理钎焊后的试样 ,用扫描电镜、X 射线能谱仪 ,结合X 射线衍射结构分析 ,对金刚石与钎料界面微区结构进行了分析。结果表明 :在钎焊过程中 ,钎料会在金刚石界面形成富铬层并与金刚石表面的C元素反应生成Cr7C3 和Cr3 C2 ,其中Cr7C3 呈笋状生长 ,Cr3 C2 呈片状生长。Ni Cr合金与金刚石的冶金结合 ,是实现金刚石和钢基体有高结合强度的主要因素。最后通过磨削对比实验确证了金刚石与钎料有较高的结合强度     

两种钎焊金刚石工具微观结构的对比分析

分别利用真空电阻炉中钎焊和氩气保护下高频感应钎焊制作单层钎焊金刚石工具,借助SEM、EDS和XRD等分析了两种工具的微观结构。结果表明：电阻炉中钎焊的金刚石一钎料界面上有两层结构,内层产物是Cr3C2,外层产物是Cr7C3;高频钎焊的金刚石一钎料界面上仅有单层产物Cr3C2。这两种工艺制作出来的工具,其界面结构虽有差别,但都存在化学冶金结合,足以保证金刚石和钎料层之间具有较高的结合强度。     

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.     

Preparation mechanism and grinding performance of single-layer self-lubrication brazed CBN abrasive wheels

In order to fabricate single-layer self-lubrication brazed cubic boron nitride (CBN) abrasive wheels, brazing experiments of graphite particles and AISI 1045 steel were carried out using Ag–Cu–Ti filler alloy. Optical microscope, scanning electron microscope, energy-dispersive spectroscopy, and X-ray diffraction were employed to characterize the microstructure and phase constitution of the brazing interface between graphite particles and Ag–Cu–Ti alloy. The formation mechanism was discussed. The results show that TiC resultants are formed via the diffusion behavior of Ti atoms and C atoms towards the joining interface. The chemical resultants of TiC have the granular shape at the early stage. Then, they grow across the joining interface between the graphite particle and Ag–Cu–Ti alloy. Finally, the continuous lamellar TiC compounds come into being around the graphite particle. Chemical joining of graphite particles and Ag–Cu–Ti filler alloy is accordingly realized. A comparative experiment displayed that the single-layer self-lubrication brazed CBN abrasive wheel has better performance than the conventional brazed counterpart.     

金刚石孔钻连续炉钎焊工艺研究

通过在连续炉钎焊炉中对金刚石进行钎焊试验,并用所制得的金刚石孔钻进行钻削试验,得到了批量生产金刚石孔钻的可行钎焊工艺。利用扫描电镜比较了金刚石磨粒分别在真空钎焊和网带炉钎焊后的不同形貌,建立了孔钻的有限元模型,并模拟计算出孔钻在钎焊炉中的热循环曲线。对比热电偶实测结果,验证了有限元模型的准确性,对比分析了真空钎焊工艺和连续网带炉钎焊工艺的异同及其对孔钻使用寿命的影响。     

金属结合剂金刚石砂轮的研究进展

介绍了用不同方式制造的金属结合剂金刚石砂轮的工艺特点及其应用 ,着重分析了单层高温钎焊金刚石砂轮的工艺优势、存在的问题及发展前景     

Effect of nanosized alumina fillers on manufacturing of UV light-curable-resin bond abrasive tool

As one of the rapid prototyping technologies, ultraviolet-curable resin (UV-resin) curing was recently introduced into the manufacturing of resin bond abrasive tools. This research was conducted to evaluate the influence of nanosized alumina filler on the manufacturing of UV-resin bond diamond grinding wheel, and comparatively study the machining performance of filler-loaded and filler-unloaded tools. The UV-resin and diamond abrasive grains were prepared with nanosized alumina filler in a proportion of 0, 2.5, 5.0, 7.5, and 10 wt%. The cure depth, hardness, and tensile strength of the cured mixture was studied, and the interfacial bond between the diamond grain and cured resin matrix was investigated as well. Two UV-resin bond diamond grinding wheels were fabricated to examine the influence of filler loading on wear performance of the tools. Experimental results based on ceramic workpieces showed that the introduction of alumina filler improved not only the material properties of cured resin matrix but also led to a significant improvement on the abrasive machining performance of grinding wheel.