Effect of porosity on the grinding performance of vitrified bond diamond wheels for grinding PCD blades

In this paper, the preparation of nano-AlN modified Na₂O–B₂O₃–SiO₂ vitrified bond diamond tools with various porosities is reported. The effects of porosity on the impact strength and grinding properties of the wheels for grinding PCD blades are also discussed. The results show that the porosity not only affects the impact strength of the wheels but also the grinding properties, such as the grinding efficiency, the self-dressing, the service life and the surface roughness of the work pieces. The optimum porosity for nano-AlN modified Na₂O–B₂O₃–SiO₂ vitrified bond diamond wheels for grinding PCD tools is approximately 40.5 vol%.     

微波烧结陶瓷结合剂金刚石砂轮研究

为了提高陶瓷结合剂金刚石砂轮的性能,采用微波烧结技术,通过一系列试验,分析了陶瓷结合剂金刚石砂轮的微波烧结温度、陶瓷结合剂含量和金刚石磨料粒度对其性能的影响。结果表明:微波烧结温度是影响陶瓷结合剂金刚石砂轮性能的最主要因素,远超其余二者;陶瓷结合剂金刚石砂轮试样的洛氏硬度和抗弯强度在740 ℃时达到极大值且气孔率较小,此时洛氏硬度为66 HRB,抗弯强度为76.5 MPa,气孔率为17.8%;由微观组织观察可知陶瓷结合剂金刚石砂轮在740 ℃时可以实现陶瓷结合剂对金刚石磨料的均匀包裹,并且气孔较少。     

Preparation of a novel vitrified bond CBN grinding wheel and study on the grinding performance

The vitrified bond CBN grinding wheels are characterized by high efficiency, high precision, and low environmental pollution. In recent years, the vitrified bond CBN grinding wheel has been widely used in manufacturing industries such as aerospace, automotive, and machine tools. In this study, a novel vitrified bond formulation containing nano SiO₂ and nano CeO₂ is selected to prepare the grinding wheel. The grinding experiments on 45# steel and YG20 alloy indicate that the grinding performance of the nano vitrified bond grinding wheel is significantly better than that of the conventional vitrified bond grinding wheel. The introduction of nano SiO₂ and nano CeO₂ greatly improves the machining performance of the vitrified bond CBN grinding wheel.     

Highly Porous Vitrified Bonded Abrasives by the Selective Extraction of Butyl Carbamate from Green Grinding Wheels with Supercritical CO2

Highly porous vitrified bonded grinding wheels were produced by selective extraction of butyl carbamate pore inducer using supercritical (sc) CO₂. Butyl carbamate was found to be an excellent pore inducer, as the extraction was fast and the desired pore structure was obtained. The investigation revealed that the extraction was controlled by the solubility of butyl carbamate in scCO₂ and the flow direction had a large effect on extraction times. The solubility of butyl carbamate determined from cloud point measurements was found to be high at moderate conditions. Grinding tests demonstrated that scCO₂ pore-induced wheels performed slightly better then conventionally produced wheels at the conditions investigated. The power required for grinding, wheel wear, and part quality were comparable with those of conventionally produced wheels at low metal removal rates. However, the extracted wheels outperformed the conventional wheel at high metal removal rates, indicating the scCO₂ processing produces a slightly superior product than that made by conventional means. Liquefaction of the pore inducer during extraction had a minor effect on the final properties of the wheel.     

陶瓷结合剂金刚石磨具用于陶瓷干磨的探索

对比了三种不同结合剂的金刚石磨边轮在陶瓷砖边棱干法磨削工序中的使用情况。实验表明,树脂结合剂磨具磨损快并易在陶瓷砖上产生黑痕,金属结合剂磨具易发生粘刀现象而且被磨陶瓷砖表面光洁度低,相比之下,在同样的工况条件下,陶瓷结合剂磨具既不产生黑痕,能得到较好的表面光洁度,又有较好的自锐性。说明陶瓷结合剂金刚石磨具比较适合于陶瓷砖干磨工序。     

Morphological evolution and grinding performance of vitrified bonded microcrystal alumina abrasive wheel dressed with a single-grit diamond

Dressing experiments under different conditions were carried out on a vitrified bonded microcrystal alumina abrasive wheel with a single-grit diamond dresser. The grinding performance of the as-dressed abrasive wheels was investigated. The dressing force, grinding force and the surface morphology of abrasive wheel and machined workpiece were studied to shed light on the relationship among the dressing processing vectors, morphology of abrasive wheel and the grinding performance. The results obtained show that the dressing forces increase with the increasing volume of the abrasive wheel material removed per unit time. The sensitive analysis reveals that the dressing feed speed take a greater effect than the single dressing depth on the dressing force. The self-sharpness of vitrified bonded microcrystal alumina abrasive wheel brings into some functions under certain dressing conditions, but a deep dressing depth would lead to an excessive abrasive self-sharpness, i.e. abrasive grits fall off and embed into the workpiece surface.     

A route to highly porous grinding wheels by selective extraction of pore inducers with dense carbon dioxide

A novel route for the production of highly porous vitrified grinding wheels was developed via selective extraction of pore inducers with dense CO₂. The extraction was performed with liquid and supercritical CO₂ (scCO₂) at temperatures ranging from 295 to 338 K, pressures from 8.8 to 27.6 MPa and flow rates of 3.4×10⁻⁵ and 7.5×10⁻⁵ kg s⁻¹ CO₂. The extraction rate was a strong function of temperature, flow rate, and flow direction, while unaffected by particle size of the pore inducer and pressure. The extraction had no detrimental effect on the green wheel’s microstructure. Grinding tests were performed on the CO₂ extracted pore induced wheels and results were compared to those from a conventionally manufactured pore induced grinding wheel. The extracted grinding wheels performed similarly to the conventional wheels. At high metal removal rates, the extracted wheels with large pore sizes outperformed the wheels with smaller particle sizes as well as the conventional wheel. This may be due to the larger pore sizes increasing lubrication at the surface and increasing the wheel strength.     

Investigation on preparation of composite vitrified bonding ultrafine diamond grinding wheel and machining of PcBN inserts

The grinding of polycrystalline cubic boron nitride (PcBN) is hard owing to its high hardness and superior wear-resistance capacity. Machining of PcBN tools via vitrified diamond grinding wheels with a size above 10 μm may lead to brittle fracture instead of a ductile machining because of the poor toughness of cubic boron nitride. A uniformly dispersed M0.5/1.5 diamond grinding wheel with a composite vitrified bonding was fabricated to improve the surface roughness of PcBN inserts. It is demonstrated that the preparation of composite vitrified bonding with various additions of vitrified bonding produced by the melting-quenching technique (VB-MQ) has little effect on the performance of vitrified bonding, such as bending strength, CTE and phase and achieves the uniform dispersion of M0.5/1.5 diamond as the addition of VB-MQ is no greater than 50%. Both the grinding ratios and the surface roughness of PcBN inserts are enhanced.     

Sintering,microstructure, and mechanical properties of vitrified bond diamond composite

The demand for high-performance grinding wheels is gradually increasing due to rapid industrial development. Vitrified bond diamond composite is a versatile material for grinding wheels used in the backside grinding step of Si wafer production. However, the properties of the vitrified bond diamond composite are controlled by the characteristics of the diamond particles, the vitrified bond, and pores and are very complicated. The main objective of this study was to investigate the effects of SiO₂–Na₂O–B₂O₃–Al₂O₃–Li₂O–K₂O–CaO–MgO–ZrO₂–TiO₂–Bi₂O₃ glass powder on the sintering, microstructure, and mechanical properties of the vitrified bond diamond composite. The elemental distributions of the composite were analyzed using electron probe micro-analysis (EPMA) to clarify the diffusion behaviors of various elements during sintering.The results showed that the relative density and transverse rupture strength of the composite sintered at 620 °C were 91.7% and 126 MPa, respectively. After sintering at 680 °C, the glass powder used in this study exhibited a superior forming ability without an additional pore foaming agent. The relative density and transverse rupture strength of the composite decreased to 48.2% and 49 MPa, respectively. Moreover, the low sintering temperature of this glass powder protected the diamond particles from graphitization during sintering, as determined by X-ray diffraction and Raman spectrum. Furthermore, the EPMA results indicate that Na diffused and segregated at the interface between the diamond particles and vitrified bond, contributing to the improved bonding. The diamond particles can remain effectively bonded by the vitrified bond even after fracture.     

Direct ink writing of hierarchical porous alumina-stabilized emulsions: Rheology and printability

Bio-inspired multi-scaled (hierarchical) porous structures have remarkable strength and stiffness-to-density properties. Direct ink writing (DIW) or robocasting, an additive manufacturing (or also commonly known as 3D printing) material extrusion technique is able to create near-net-shaped complex geometries. A new approach of combining DIW, colloidal particle-stabilized emulsion paste inks and partial densification to create tailored architectures of hierarchical porosity on three scales has been demonstrated. The printed and sintered ceramic lattice structures possess relatively high overall porosity of 78.7% (on average), comprising mainly (64.7%) open porosity. The effects of formulation (surfactant and oil concentrations, solids particle size, and mixing speed) on rheology and pore size and morphology have been investigated. The rheological properties (storage modulus, yield stress, and recovery of storage modulus) of the emulsions have been found to delineate the samples with good shape retention from those that slump. Additionally, the internal features of the sintered structures have been analyzed via X-ray tomography and scanning electron microscope. The role of emulsion stability on printability and the internal structure of the prints has been investigated.     

砂轮用聚酰亚胺胶粘剂的研究现状

聚酰亚胺树脂是一种耐高温、高强度的工程塑料,它可用于制造金刚石砂轮,使砂轮的耐热性得到改善。本文从耐高温性、可加工性、高粘结性、耐磨性等方面概述了聚酰亚胺作为金刚石砂轮结合剂的优越性,实践证明,聚酰亚胺胶粘剂具有优异的耐热和高温粘接性能,用其制造的金刚石砂轮耐磨性优于酚醛砂轮。     

工业陶瓷超声辅助加工技术研究

陶瓷材料具有耐高温、硬度高、绝缘性好的优良性能,在航空航天、军事医疗、电子信息等领域具有广泛的应用。旋转超声辅助加工的刀具磨损小、材料去除率高、加工精度高,在工业陶瓷精密加工领域取得了较好的运用。本文以常用的石英陶瓷和氮化硅陶瓷为加工对象,进行了表面磨削及钻孔试验研究,通过宏观形貌观察、测量表面粗糙度值、工件及刀具微观形貌分析,确定了PCD砂轮结合超声辅助磨削加工,可以得到较好的表面加工质量。开展了石英陶瓷凹槽面、平面及过渡面的磨削加工试验,取得了较好的表面形貌;利用不同类型的砂轮加工氮化硅陶瓷孔,从而确定高强度的金刚石磨头是加工硬性材料的最优砂轮。     

Effects of sintering in a high magnetic field on properties of vitrified bond and vitrified CBN composites

Vitrified bond CBN grinding wheels are being widely used due to their superior performance. Also, advantages of vitrified grinding wheels are high elastic modulus, stable chemical property, and low thermal expansion coefficient. Brittleness and low strength are key factors restricting the development of vitrified bond CBN grinding wheels. In this paper, the sintering in a high magnetic field was innovatively introduced into the manufacturing of vitrified bond CBN grinding wheels, and the effects of sintering in a high magnetic field on properties on vitrified bond and vitrified CBN composites were systematically investigated. Vitrified bond was characterized using three-point bending, scanning electron microscopy, X-ray diffraction. It was observed that microstructure of vitrified bond could be changed, grain orientation could be controlled and average grain size could be decreased in a high magnetic field, while vitrified bond strength could be simultaneously improved. High quality vitrified bond could be obtained by appropriately adjusting the strength and direction of high magnetic field. Results demonstrated that vitrified bond properties were improved when the magnetic field strength was 6?T. In order to highlight the high magnetic field effect on the vitrified CBN composites, the ordinary CBN abrasives and nickel plated CBN abrasives were used respectively. Microstructures, bending strengths of vitrified CBN composites were compared in different high magnetic fields. When the magnetic field strength was appropriate (less than 6?T), the binding characteristic of vitrified bond CBN composites with nickel plated CBN abrasives was greatly improved. The highest bending strength value of vitrified CBN composites was 79.5?MPa in 6?T high magnetic field.     

Modified gel casting technique to fabricate honeycomb structured vitrified-bonded ultrafine diamond grinding wheels

To avoid agglomeration of ultrafine diamond particles and to improve machining precision of silicon (Si) wafers, a combination of gel casting and pore-forming agent is introduced to fabricate vitrified-bonded ultrafine diamond grinding wheel with ultrahigh porosity (~75%), honeycomb structure, and homogeneous microstructure. Moreover, the as-prepared grinding wheel possesses uniformly distributed closed pores, which are highly desirable for chip removal, heat dissipation and extended service life. In addition, influences of sintering schedules on microstructure, porosity and bending strength of the as-prepared grinding wheel are systematically investigated. Because of the honeycomb structure, the as-fabricated grinding wheel renders superior self-sharpness, which is required for continuous grinding of Si wafers without dressing, and this subsequently enhances the working efficiency. Results reveal that the surface roughness and damaged layer of the ground Si wafers are approximately 5.0 nm and 0.21 μm, respectively. The current study provides a novel pathway for efficiently processing high-quality silicon wafers.     

Grinding of alumina ceramic with microtextured brazed diamond end grinding wheels

Brazed monolayer diamond grinding wheels have advantages of a high abrasive bonding strength, high protrusion, and a large chip disposal space. However, it is difficult to prepare ordered and fine-grained brazed diamond grinding wheels. This study presents a new method for grain-arranged, brazed diamond grinding wheels with microtextures with similar performance to ordered and fine-grained brazed diamond grinding wheels. First, coarse diamond grains (18/20 mesh) were orderly brazed to fabricate the end grinding wheels. Next, a series of microtextures were ablated on the diamond grains using a pulsed laser, and two types of textured end grinding wheels—TG-G (ablated microgrooves only) and TG-GH (ablated microgrooves and microholes)—were prepared. Then, an experiment involving the grinding of alumina ceramics was performed, and the grinding characteristics and grinding mechanism were analyzed. The results indicated that compared with untextured diamond end grinding wheels (TG), the textured diamond grinding wheels (TG-G and TG-GH) significantly reduced the grinding force and the roughness of the machined surface. The local stress concentration at the microtextures promoted the formation of microcracks in the diamond grains of TG-G and TG-GH, and the self-sharpness of the grinding wheel was significantly improved. The brittle fracture mode of ceramic materials in grinding included intergranular fracture and transgranular fracture. Ironing pressure action was a key material-removal mechanism. It had an important influence on the cutting force and plasticity characteristics of the TG machined surface. For the surfaces processed by TG-G and TG-GH, the effect of ironing was weakened, while shearing played a more important role. The TG-GH grinding wheel ablated with microgrooves and microholes was superior to the TG-G grinding wheel ablated with only microgrooves, with regard to the grinding force, roughness, and self-sharpening.     

Research on laser preparation and grinding performance of hydrophilic structured grinding wheels

In order to solve the problems of workpiece damage and grinding wheel clogging when grinding difficult-to-cut materials such as alumina ceramics, organisms with regular hexagonal structures distributed on the body surface and with strong hydrophilicity and high anti-wear functions were used as biomimetic objects for the first time, and the preparation process optimization, structure size design and grinding performance evaluation of hydrophilic structured bronze-bonded diamond grinding wheels were explored in this paper. The influence of the preparation process parameters on the micro-topography and the dimensional accuracy of the structure on the surface of the grinding wheel was revealed, and a new laser structuring process based on the coordinated control of focus position and scanning times was proposed, which could efficiently prepare regular hexagonal structures with a small wall inclination angle and a depth of several millimeters on the surface of the grinding wheel. It was the first to clarify the influence of sub-millimeter-scale structure size on the contact angle of grinding fluid droplet on the surface of the grinding wheel and the surface hydrophilicity of the grinding wheel. Compared with that of the non-structured grinding wheel, the hydrophilicity of the structured grinding wheel was significantly improved, and its surface hydrophilicity increased with the increase of the structure spacing and depth, but had little correlation with the structure side length. The grinding performance of hydrophilic structured grinding wheels and non-structured grinding wheels was evaluated under extreme working conditions. Under the condition of grinding depth of 50 μm, 100 μm and 200 μm, compared with that of the non-structured grinding wheel, the peak grinding temperature of the structured grinding wheel was reduced by 18.0%, 30.4% and 15.2%, respectively, and the surface damage depth of the alumina ceramic after grinding by the structured grinding wheel was reduced by 53.7%, 46.8% and 24.3%, respectively. The hydrophilic structured grinding wheel can enhance the storage and transportation capacity of grinding fluid/chips, effectively relieve the clogging and dullness of the grinding wheel, and significantly reduce the high temperature and damage of grinding. In the next step, we will try to apply this type of grinding wheel to form grinding, in order to provide a reliable solution for suppressing form grinding damage of difficult-to-cut materials.     

Fabrication of New Porous Metal-Bonded Grinding Wheels by Hip Method and Machining Electronic Ceramics

Grinding wheels with different abrasive grains and different bonding materials were fabricated using hot isostatic press (HIP) sintering. Poly-crystal diamond powder of #1000 mesh size, single-crystal diamond powder of #1000 mesh size, and synthetic single-crystal diamond abrasive grains of #325 mesh size were used as abrasive grains. Cast-iron, and two different particle sizes of iron powders were used for the bonding material. The grinding capacity of these grinding wheels as well as conventional grinding wheels was evaluated by constant-pressure-grinding method to grind Al₂O₃-TiC component ceramics, which are typical electronic ceramics used for magnetic memory devices. The hardness of the bonding materials, the adhesion strength between abrasive diamond grains and the bonding materials, and the porosity of sintered body strongly relate to the grinding capacity. The porous bonded grinding wheels showed higher grinding capacity than the conventional wheels. The HIP method enables to fabricate excellent porous metal-bonded grinding wheels.     

Enhancing ductile removal of Cf/SiC composites during abrasive belt grinding using low-hardness rubber contact wheels

C_f/SiC composites are used as advanced thermal protection and friction materials. However, machining these materials is difficult because of their hard, brittle, anisotropic, and heterogeneous characteristics. This study investigated the removal behavior and surface integrity of C_f/SiC composites during abrasive belt grinding using rubber contact wheels of various hardness. Additionally, detailed analysis was performed on their thermal-mechanical coupling characteristics, surface integrity (that is, surface roughness, surface micro morphology, and subsurface damages), and the grinding chips produced. Results revealed that with decreasing hardness of the contact wheel, the surface roughness in all directions, grinding force, and temperature decreased significantly. Moreover, the surface removal morphology of the C_f/SiC composites changed from macro-fracture to micro-fracture, and the subsurface morphology changed from SiC matrix cracking and carbon fibers pull-out to matrix plastic flow and fiber micro-fracture, respectively. Furthermore, strip chips with plastically squeezed and cut surfaces were visible in the grinding chips obtained under the 40-HA contact wheel. Therefore, the ductile removal behavior of the C_f/SiC composites was enhanced, and the surface quality in abrasive belt grinding with low-hardness contact wheels was markedly improved.     

Grinding characteristics of cBN-WC-10Co composites

In order to explore the grinding characteristics of cBN-WC-10Co composites, the grinding experiment with a resin bond diamond grinding wheel was carried out. The grinding forces, surface roughness, surface morphology and residual stress were investigated. It was found that the material removal mechanism of cBN-WC-10Co was the combination of the brittle fracture of cBN particles, ductile removal of Co phase, plastic deformation, grain dislodgement and grain crush of WC grains. The brittle removal model resulted in a lower specific grinding energy. The main contributor to the surface roughness was cBN particles. Some cBN particles over the surface of cBN-WC-10Co composites were fractured or pulled out and then formed cavities with different depths, this led to a rougher surface. The surface roughness was increased but the specific grinding energy decreased with an increase of the maximum undeformed chip thickness. A high-level residual compressive stress was induced at WC phase and it was increased with an increase of the depth of cut. The depth of cut has more significant influence on the grinding forces than the table speed or the wheel speed.     

Microstructural characteristics and mechanical properties of diamond grinding wheel brazed with modified Ni–Cr–W alloy using continuous tunnel furnace

A novel brazing technology using a continuous tunnel furnace with modified Ni–Cr–W filler alloy is presented to achieve brazed diamond grinding wheels with high efficiency and low thermal damage. Mechanical characterization confirms that the static pressure strength and impact toughness of the diamond brazed using the new brazing technology are 22.2% and 10.5% higher, respectively, than those of diamond brazed using conventional vacuum brazing technology, respectively. Raman spectroscopy reveals that the degree of graphitization of diamond brazed with the novel brazing technology is decreased. In addition, residual stress is reduced by 23% after brazing with new brazing technology. Scanning electron microscopy is used to observe interfacial microstructure of brazed diamond. The elemental distribution and phase composition of brazed joint are analyzed by energy dispersive spectroscopy and X-ray diffraction. The results demonstrate that metallurgical bonds are formed between diamond and modified alloy, endowing strong bonding force to diamond abrasives. Tungsten (W) can react with diamond and modified alloy to form W–C compounds and bonding phases. Besides, W combines with certain amount of Ni element to reduce graphitization degree, improve integrity and decrease residual stress of brazed diamond. Compared with commonly utilized vacuum brazed grinding wheel, grinding test indicates that service life of grinding wheel, prepared by new brazing technology, is improved. The machining efficiency is increased by 42.4% and the abrasive invalidation rate is reduced by 33.7%. In conclusion, the diamond grinding wheel, prepared by new brazing technology, exhibits superior performance.