cBN Grains Research Articles

No-impact trajectory design and fabrication of surface structured CBN grinding wheel by laser cladding remelting method

The structured grinding wheels have a specially designed macro or microstructure on the surface, with a relatively low average grinding force and temperature in the cutting zone and more space for chips and coolant. Most traditional grinding wheel fabrication methods, such as electroplating, sintering, and brazing, have the problems of poor abrasive grain holding strength, random abrasive distribution, or thermal deformation of the substrate. To address this, laser cladding remelting technology is introduced to fabricate the structured CBN grinding wheel. A no-impact trajectory was designed on the substrate of the grinding wheel, which can reduce the fluid friction in the channel and increase the fluid pressure at the outlet. The temperature and velocity fields of the grinding process were simulated to verify the feasibility of the designed structure theoretically. The optimal process parameters for the bonding among the metal bond, the abrasive grains, and the substrate were determined by orthogonal and full-scale factorial experiments. The chemical metallurgical reactions between CBN grain and metal bond, as well as between the metal bond and substrate, were formed, increasing the holding force of CBN grains. The method can realize the fabrication of high-strength and long-life structured grinding wheels with an orderly arrangement of abrasive grains. The micro-mechanism of fabrication was analyzed using element distribution measurement and XRD analysis.

Dressing Mechanism and Evaluations of Grinding Performance with Porous cBN Grinding Wheels

Cubic boron nitride (cBN) grinding wheels play a pivotal role in precision machining, serving as indispensable tools for achieving exceptional surface quality. Ensuring the sharpness of cBN grains and optimizing the grinding wheel's chip storage capacity are critical factors. This paper presents a study on the metal-bonded segments and single cBN grain samples using the vacuum sintering method. It investigates the impact of blasting parameters—specifically silicon carbide (SiC) abrasive size, blasting distance, and blasting time—on the erosive wear characteristics of both the metal bond and abrasive. The findings indicate that the abrasive size and blasting distance significantly affect the erosive wear performance of the metal bond. Following a comprehensive analysis of the material removal rate of the metal bond and the erosive wear condition of cBN grains, optimal parameters for the working layer are determined: a blasting distance of 60 mm, a blasting time of 15 s, and SiC particle size of 100#. Furthermore, an advanced simulation model investigates the dressing process of abrasive blasting, revealing that the metal bond effectively inhibits crack propagation within cBN abrasive grains, thereby enhancing fracture toughness and impact resistance. Additionally, a comparative analysis is conducted between the grinding performance of porous cBN grinding wheels and vitrified cBN grinding wheels. The results demonstrate that using porous cBN grinding wheels significantly reduces grinding force, temperature, and chip adhesion, thereby enhancing the surface quality of the workpiece.

Heterogeneous components removal mechanism and grinding force model from energy aspect in ultrasonic grinding continuous fiber reinforced metal matrix composites

Continuous fiber reinforced metal matrix composites (CFMMCs) offer higher specific strength, specific modulus, and operating temperature than matrix metals due to the unique enforcement mechanism of the one-to-one scale arrangement of matrix and reinforced phases. Due to the heterogeneous characteristics between the plastic matrix and brittle fibers, the removal mechanism of CFMMCs during processing is exceptionally complex. Ultrasonic vibration-assisted grinding (UVAG) shows great advantages in machining difficult-to-cut materials (i.e., ceramics and composites) by changing the motion trajectory between grains and workpieces, effectively reducing grinding force and improving machining quality. However, little is known about the removal mechanism of UVAG for CFMMCs composed of the ductile (i.e., metal matrix) and brittle (i.e., SiC fiber) phases with highly anisotropic structure characteristics. This raises the question of how CFMMCs with heterogeneous components perform under abrasive processing and how to predict their processing forces. Hence, UVAG and conventional grinding (CG) experiments with single CBN grain were carried out on SiC fiber reinforced TC17 matrix composites (SiCf/TC17) in this work. A grinding force model considering both phases and materials structure from energy aspect was proposed. A theoretical model for suppressing SiC fiber damage has been proposed, which is expected to guide low-damage processing of brittle materials. According to the results, the removal models of CFMMCs are revealed including: i) macro fracture of SiC fiber, ii) neat fracture of SiC fiber, and iii) TC17 matrix massive adhesion on the SiC fiber. Besides, no cracks crossing fibers are observed on the subsurface of SiC fiber under both UVAG and CG due to the good support of the TC17 matrix on SiC fibers. The grinding force predicted model error decreases as ap increases. When ap is 50 μm, the errors between predicted and experimental values are 7.8 % and 9.1 % for normal forces (Fn) and tangential forces (Ft), respectively. Ultrasound suppresses the severe wear behavior of grains, thereby improving the tool life. This paper aims to comprehensively reveal the characteristics of abrasive processing of CFMMCs from various aspects (surface morphology, subsurface features, grinding force prediction, and tool wear), which will promote the industrial application of CFMMCs.

Constructing coherent/semi-coherent phase boundaries to enhance toughness of superhard cBN-B composite

Harsh synthesized pressure is required in constructing of excellent grain boundary (GB) connection for nano-polycrystalline cubic boron nitride (nPcBN) to yield high hardness and toughness. Therefore, it is urgent to fabricate robust nPcBN composite under relatively mild pressure by developing the hard nonmetal binders to form coherent/semi-coherent phase boundary (cPB, scPB) with cBN. Here, the slight content of nano‑boron was composited with nPcBN to achieve superhard property of 45.2 GPa and high fracture toughness 8.4 MPa‧m0.5 under a relatively mild condition of 5 GPa and 1800 °C. The hardness is comparable with single crystal cBN and the toughness is about three times higher than single crystal cBN. The nano boron connects the nano cBN grains by cPB and scPB, and nano boron filled the triangular space of cBN crystals, which eliminates the defects to prohibit the crack trigger sources and enhances the strength. This work provides a reference and a new strategy on composite engineering in superhard materials with high toughness by relatively mild synthesized pressure.

СТРУКТУРНИЙ СТАН КОМПОЗИТІВ, СПЕЧЕНИХ ІЗ ПОРОШКІВ сBN З ПОКРИТТЯМ ЗІ СПОЛУК Ті

The paper presents the results of experimental studies of the structural state of composites obtained at high temperatures and pressures from cBN powders with coatings deposited by CVD from Ti compounds using a gas transport reaction. The features and quantitative parameters of the structure of the composites depending on the presence of Ti in the coating were determined. It has been experimentally established that the matrices of the obtained composites are formed by submicron grains of TiN and TiB2, the quantitative differences of which correspond to the concentration of Ti in the coating - from 3 to 8 %. The structure of the obtained composites is characterized by a uniform distribution of the ceramic matrix between the cBN grains, which is achieved due to the high-quality encapsulation of individual grains of the superhard phase in the coating. The ceramic layers have the largest dimensions (up to 10-12 μm) in the area of triple joints, the width of the zone between two adjacent cBN particles is < 1 μm. When moving from a coated powder to a composite, the shape of the diffraction peaks changes, which is associated with the stresses of the first and/or second kind inherent in the studied samples. Sintering of the powder leads to a decrease in the size of the blocks from 56 nm to 27 nm, an increase in the lattice strain from 0.11 to 0.24 %, in TiN - to an increase in the lattice parameter in the composite by 10% (from 0.4244 nm to 0.4253 nm), a decrease in the size of crystallites within individual grains from 100 nm to 20 nm, and an increase in the lattice strain by 0.47 %. At the same time, TiN nitride is supersaturated with nitrogen, which is a significant increase in its lattice parameter, and the coating formed in this case is exclusively oriented in the (022) direction.

Effect of radial ultrasonic vibrations on wear properties of CBN grains in high-speed grinding of PTMCs

Effect of radial ultrasonic vibrations on wear properties of CBN grains in high-speed grinding of PTMCs

Grinding Characteristics of MoS2-Coated Brazed CBN Grinding Wheels in Dry Grinding of Titanium Alloy

As an important green manufacturing process, dry grinding has problems such as high grinding temperature and insufficient cooling capacity. Aiming at the problems of sticking and burns in dry grinding of titanium alloys, grinding performance evaluation of molybdenum disulfide (MoS2) solid lubricant coated brazed cubic boron carbide (CBN) grinding wheel (MoS2-coated CBN wheel) in dry grinding titanium alloys was carried out. The lubrication mechanism of MoS2 in the grinding process is analyzed, and the MoS2-coated CBN wheel is prepared. The results show that the MoS2 solid lubricant can form a lubricating film on the ground surface and reduce the friction coefficient and grinding force. Within the experimental parameters, normal grinding force decreased by 42.5%, and tangential grinding force decreased by 28.1%. MoS2 lubricant can effectively improve the heat dissipation effect of titanium alloy grinding arc area. Compared with common CBN grinding wheel, MoS2-coated CBN wheel has lower grinding temperature. When the grinding depth reaches 20 μm, the grinding temperature decreased by 30.5%. The wear of CBN grains of grinding wheel were analyzed by mathematical statistical method. MoS2 lubricating coating can essentially decrease the wear of grains, reduce the adhesion of titanium alloy chip, prolong the service life of grinding wheel, and help to enhance the surface quality of workpiece. This research provides high-quality and efficient technical support for titanium alloy grinding.

Synthesis and characterization of environment-friendly spherical cubic boron nitride magnetic abrasives by plasma molten metal powders bonding with hard materials

In this investigation, globular cubic boron nitride magnetic abrasive powders (cBN-MAPs) were synthesized with additive-free via plasma molten metal powders bonding with hard materials (PM2BH) for finishing hard and brittle materials. Experiments were carried out with cBN powder flow rates of 60–300 g/min, which significantly affected the performance and microstructure of the composites. It illustrates that: the composites are composed of cBN and α-Fe; the cBN is not transformed into hBN, which can be reused; a linear increase in the amount of cBN grains bound to the apparent layer of the ferrous substrate with increasing powder flow rate, the proportion of MAPs in the 180–230 μm size distribution and the magnetic permeability decrease; when the powder flow rate is maximum, the powder embedded in ferrous substrate completely covers the surface of the matrix, forming spherical MAPs, after 50 min of machining, surface finish of AlN ceramics improved from 342 nm to 93.5 nm, with cBN-MAPs showing normal wear within 80 min. A novel, highly efficient strategy for additive-free cBN/Fe composites is presented in this paper.

Influence of wire electrical discharge conditioning on the grinding performance of metal-bonded diamond grinding tools

Wire Electrical Discharge Conditioning (WEDC) is an efficient non-conventional method for conditioning metal, resin, and hybrid bonded super-abrasive grinding tools. Since the diamond and CBN grains are not affected directly by the WEDC and only the electrically conductive bond material is eroded by the process, high grain protrusions are achievable. Therefore, unlike the common mechanical conditioning methods using WEDC, the microtopography of the grinding tool can be influenced by the process parameters, directly affecting the grinding efficiency. However, the selection of WEDC process parameters is influenced by the specifications of the grinding tool, particularly the grain size and concentration. This study aims to investigate the effects of WEDC parameters and strategies on the microtopography and material removal rate of metal-bonded grinding tools, considering different grain sizes and concentrations. Additionally, the correlation between the microtopography of grinding tools conditioned by the WEDC process and their grinding efficiency was investigated by analyzing tool wear, grinding forces, and surface roughness of tungsten carbide workpieces. The results indicate that the material removal rate of the WEDC process decreases as the grain size and concentration of metal-bonded diamond grinding tools increase. Furthermore, it was observed that employing high spark energy parameters reduces the grain protrusion of grinding wheels with small grain sizes. However, the utilization of high-energy sparks is necessary to create larger spark gaps and achieve a higher material removal rate.

Grinding damage in the fabrication of polycrystalline cubic boron nitride micro-drill

Micro superhard cutting tool such as polycrystalline cubic boron nitride (PCBN) tool are increasingly demanded in high-end manufacturing field. The grinding is a widely used technology in the manufacture of superhard micro-tools, but its grinding damage is often difficult to control. In order to improve the grinding quality of superhard micro-tools, it is necessary to further understand the damage behavior during tool grinding process. This study aims to reveal the damage form and damage formation mechanism in the grinding process of PCBN micro-drills. The PCBN micro-drill grinding experiment is conducted under different process parameters, and the morphology characteristics of the micro-drill surface and cutting edge are observed and analyzed. The influence of grinding process parameters on the grinding quality of PCBN micro-drill is quantitatively investigated. The results indicate that, the grinding damage of PCBN micro-drill is mainly manifested as micro chipping and micro fracture of the cutting edge, material adhesion on the chisel edge, and micro cracks, micro pits and micro scratches on the grinding surface. For the ground surface of flank and helical flute of PCBN micro-drill, the material removal mechanisms of plastic removal and brittle removal work together. The material in the area with more binder inclusions is removed by plastic removal mode, and the material brittleness removal mode mainly includes cleavage brittleness removal and intergranular brittleness removal. The edge impact fracture brings grinding damage to the main cutting edge of PCBN micro-drill. The CBN grains at the fracture surface mainly undergo cleavage fracture, while the fracture of the binder occurs in the form of micro pit aggregation. The reduction of grinding depth and feed rate will lead to the decrease in the surface roughness of flank and helical flute, the cutting edge radius, and the edge chipping width, thus improve the grinding quality of PCBN micro-drill. These findings contribute to expand the understanding of process characteristics for grinding PCBN micro-tools, and thus to restrain the grinding damage and improve the grinding quality of micro-tools.

Grinding Force and Surface Formation Mechanisms of 17CrNi2MoVNb Alloy When Grinding with CBN and Alumina Wheels

The 17CrNi2MoVNb alloy is widely used for manufacturing heavy-duty gears in vehicles' transmission systems, where grinding is a significant process affecting gears' working performance and service life. This work comprehensively analyzed the grinding force, surface morphology, and surface roughness when grinding 17CrNi2MoVNb alloy using alumina and CBN grinding wheels. Results showed that the maximum normal grinding force from the CBN wheel was only ~67% of the one from the alumina wheel. Due to the small size and limited cutting depth of CBN grains, the grinding force increased by about 20% when the grinding depth increased from 0.02 to 0.03 mm for CBN grinding wheels. Surface defects, including cavities and material tearing, were mainly found on the ground surface when using an alumina grinding wheel. The surface roughness Ra recorded from the CBN grinding wheel mainly ranged from 0.263 to 0.410 μm, accounting for less than 40% of the one from the alumina grinding wheel. The information from this work could provide benchmark data and references for optimizing grinding tools and parameters when manufacturing gears in the vehicle industry.

Effect of the Granularity of Cubic Boron Nitride Vitrified Grinding Wheels on the Planar Technical Blades Sharpening Process.

The most widely used method for shaping technical blades is grinding with abrasive tools made of cubic boron nitride (cBN) grains and vitrified bond. The goal of this work was to determine the effect of grinding wheel grain size (cBN grain number according to FEPA standards: B126, B181 and B251), kinematics (grinding with the circumference, face and conical surface of the wheel) and feed rate (vf = 100; 150; 200 mm/min) on the effects of the grinding process evaluated by the cutting force of the blade after machining F, blade surface texture parameters (Sa, St, Smvr, Str, Sdq, Sdr and Sbi) as well as blade surface morphology. An analysis of output quantities showed that grinding wheels made of B181 cBN grains are most favorable for shaping planar technical blades of X39Cr13 steel in the grinding process.

CBN grain wear and its effects on material removal during grinding of FGH96 powder metallurgy superalloy

CBN grain wear and its effects on material removal during grinding of FGH96 powder metallurgy superalloy

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 air-borne 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.

Production of nano- and micropowders of cubic BN from mechanically activated graphite-like BN under high pressures and temperatures using aluminium as a phase convertion initiator

An effect of mechanical activation of graphite-like (hexagonal) boron nitride (hBN) on catalytic synthesis of nano- and micropowders of cubic boron nitride (cBN) under conditions of high pressures and temperatures is shown in the article. It has been suggested that nuclei of dense phases of boron nitride (cubic and wurtzite) are formed in the hBN structure during mechanical activation they serve as crystallization centers stimulating the formation of cBN crystals under subsequent thermobaric treatment. Additional chemical-thermal modification of hBN with aluminum as a catalyst (initiator) for the phase transformation of hBN into cBN leads to a significant increase in the content of cBN along with an increase in the synthesis pressure. Thus, the introduction of Al additives in the amount of 10 wt.% leads to an increase in the content of the cBN phase from 10–15 % under synthesis pressure of 2.5 GPa up to 90 % under pressure of 5.5 GPa. In this case, the grain size of cBN, estimated by scanning and atomic force microscopy, is mainly 200–400 nm and 40–120 nm for the samples synthesized under pressure of 2.5 and 5.5 GPa, respectively. The increase in the content of the initiator from 10 to 40 wt.% with an increase in isothermal holding time from 15 to 60 s in the studied range of pressures and temperatures leads to the formation of intergrowths of cBN grains in nano- and submicron sizes and individual cBN single crystals of a cubic habit with a grain size of 1–4 µm, as well as polycrystalline cBN particles from 10 to 50 µm. In this case, the maximum size distribution of cBN micropowders in the range up to 50 µm falls on particles up to 5 µm (~ 70 %). In the submicron grain size range the maximum yield (~ 50 %) is marked for cBN particles 0.5–0.7 µm in size. The obtained powders can be used to make abrasive and cutting tools.

Wear behaviors of cubic boron nitride tools with various binders in high-speed turning of compacted graphite irons

Compacted graphite iron (CGI) is a promising material as diesel engines in automotive industry, but the poor machinability and low machining efficiency have further hindered the employment of CGI in the potential applications. Cubic boron nitride (cBN), possessing extreme hardness and chemical inertness, is the best candidate as tools to machine ferrous metals. In this paper, we attempt to explain the disparities in wear behaviors of cBN tool with different binders by implementing high-speed turning of CGI. The effects of various binders on cBN tool flank wear, cutting force, cutting temperature, and machined surface roughness was systematically investigated. Additionally, the response relationship among flank wear, cutting force, temperature and surface roughness was obtained. Further, the underlying reasons of the wear mechanism of cBN tool were revealed. The results indicated that the cBN tool performances strongly depend on the affinity of binders with CGI. The contributions of binder phases, cBN content, and cBN grain size under the employed machining conditions: the binders are dominated, and followed by cBN grain size or cBN content in the high-speed cutting of CGI. The small cBN grain size, and TiCN, TiC, TiN binders of cBN tools have superior cutting performance than the Co binders.

Micro-fracture behavior of a single-aggregated cBN grain and its relation to material removal in high-speed grinding of Ti–6Al–4V alloys

Aggregated cubic boron nitride (cBN) abrasive grains were developed using high-temperature liquid phase sintering processes and then the single-grain scratching trial was conducted to study the grain wear behavior and material removal characteristics. Characterizations of grain wear evolutions and related surface scratches grinded by aggregated and monocrystalline cBN grains are performed, respectively. The evaluations of wear-resistance and self-sharpening abilities of both abrasive grains are carried out based on the proposed indicators of volumetric pile-up ratio, volumetric groove removal rate, and grain grinding ratio. Compared to the monocrystalline cBN grain, the as-developed aggregated cBN grain exhibits the more stable grinding process, excellent self-sharpening ability as well as a higher material removal volume provided by the dynamic balance between microfracture and partial macrofracture of multi-layer micro cBN particles.

Performance and wear mechanisms of different PcBN tools when machining superalloy AD730

Nickel-based superalloys are known to be difficult to machine. These alloys are generally machined with cemented carbide tools under low productivity process conditions. Superhard polycrystalline cubic boron nitride (PcBN) tooling offers the possibility of increased production rates, however, a thorough understanding of the material performance and degradation is required before a transition from carbide tools occurs. This study investigated the performance and wear mechanism of three different PcBN tools with low (50 vol. %), medium (65 vol. %), and high (90 vol. %) cBN content, when turning AD730, a new Ni–Co-based superalloy. Due to the novelty of the material, little research has been done on its machinability with carbide and even less with PcBN tooling. The results showed the high-cBN grade was the best performer in terms of machining time. However, an undesirable wear morphology is generated, leading to excessively high cutting forces. Both the medium-cBN and low-cBN showed promise with stable rake and flank wear, but with notching as a drawback. Degradation analysis of medium-cBN grade revealed diffusional dissolution of cBN and formation of a reaction layer atop the cBN grains. The reaction layer, which acts as a diffusional barrier, consisted of three sub-layers: (1) Al2O3, (2) (Ti, Nb, Zr)N, and (3) (Ti, Cr, Nb, Zr)N. The low-cBN grade also showed a reaction layer; however, the smaller cBN grain size of this grade did not allow the layer to sufficiently stabilize.

RESEARCH ON THE STRUCTURE OF THE MATERIAL BASED ON NANO-AND MICRO-SIZED CUBIC BN SYNTHESIZED FROM MECHANICALLY ACTIVATED GRAPHITE-LIKE BN WITH THE ADDITION OF ALUMINUMUNDER HPHT CONDITIONS

In the article the structure and phase composition of the material based on nano-and micro-sized cubic boron nitride (cBN) obtained under high pressure and high temperature conditions from mechanically activated graphite-like boron nitride (hBN) in the presence of aluminum (Al), which plays the role of an initiator for the phase transformation hBN → cBN, are investigated. It has been shown that the use of mechanical activation contributes to the formation of cBN nuclei in hBN, which makes it possible to increase the dispersion of the final product. The technological parameters of the cBN synthesis and the amount of Alhave a significant effect on the structure of the material as well as the content of the cubic BN phase in it. The increase in the pressure for the hBN (MA) -10% Al system from 2.5 to 5.5 GPa and the temperature from 1550 °C to 1750 °C contributes to the increase of the content of the cBN phase from 10-15% to 90%. In this case, the size of cBN grains synthesized at pressures of 2.5 and 5.5 GPa is in the range of 200-500 nm and 40-120 nm, respectively. The increase in the amount of Al, temperature and duration for the cBN synthesis leads to the formation of large cBN grains with a size of about 10-50 μm.

Influence of regeneration process parameters on geometry and defects of clearance surface of planer knives used in wood planing process

A properly implemented strategy regarding the planer knife regeneration process, may not only restore the original cutting ability of the tool, but even increase its operational quality, including its durability for industrial woodworking processes. This article presents experimental results and discussion in respect of sharpening planer knives with cubic boron nitride grinding wheels. Both the grinding conditions and machining surface quality were analyzed. Application of improper size or loads of abrasive grains may lead to the appearance of grinding burns on a machined surface, or result in a surface with cracks and grooves. The results of the measurements carried out indicate that surfaces with reduced values of roughness and waviness parameters can be obtained, even up to 22% (as in the case of the reduced peak height parameter, Spk) in relation to new knives, prepared at a factory. The value of St and Sds parameters are almost the same as reference knife (deviation up to 3%). Due to machining marks, the total waviness exceeds 33%. Our research also shows that due to the technological quality of the knife surfaces, it is beneficial to use CBN grains with a low depth of cut (ae no more than 0.02 mm), but a moderate or high feed rate (the best choice is about 470 mm/min for vft). Presented results constitute an important know-how for the grinding process with the use of grinders used by operators (like WEINIG Rondamat 980) during the sharpening of planer cutter heads in the wood industry.