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Chinese Journal of Mechanical Engineering
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Dressing Mechanism and Evaluations of Grinding Performance with Porous cBN Grinding Wheels

Chinese Journal of Mechanical Engineering volume 37, Article number: 106 (2024) Cite this article

Abstract

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.

1 Introduction

The cubic boron nitride (cBN) grinding wheels have gained widespread applications in various fields such as high-speed, ultra-high-speed grinding, high-performance grinding and efficient form grinding of difficult-to-machine materials, owing to their exceptional grinding performance and surface quality [1,2,3,4,5,6,7,8,9]. During grinding processes, the abrasive grains on the surface wheel undergo passivation as a result of the combined effects of grinding force, elevated and adhesion within the grinding zone [10,11,12]. The occurrence of uneven wear also leads to the loss of the wheel's original geometry, while fine chips are produced during high-speed grinding processes, thereby obstructing the chip storage space on the wheel surface [13,14,15]. Porous cBN grinding wheel with high porosity has presented increasing popularity in grinding difficult-to-machine materials. However, frequent dressing is needed to ensure the sharpness of the wheels, whereas proper dressing methods are lacking.

The conventional dressing method for grinding wheels leads to rapid wear on turning dressing tools. In contrast, roller dressing offers both efficiency and precision [16, 17]. However, the complex roller and high manufacturing cost present challenges [18, 19]. Electrical discharge machining (EDM) dressing is not efficient [20, 21], whereas electrolytic dressing has high efficiency at the expense of difficult shaping [22, 23]. Most of these methods are complicated to operate with limited potential for promotion and application [24,25,26,27,28,29]. Although oilstone dressing is widely used, it cannot obtain a large exposed height of abrasive grain. It is usually only 1/600 of the abrasive grain diameter and cannot be used to dress porous cBN grinding wheels for high-efficiency deep grinding (HEDG) [30]. Therefore, the air-borne abrasive blasting dressing method is the most suitable method for HEDG of porous cBN grinding wheels. However, the current air-borne abrasive blasting dressing method primarily relies on blasting nozzles to dress the surface of grinding wheels. The blasting time(tps), blasting distance (Lps), and abrasive size exhibit inherent variability, thereby compromising the control of the grinding wheel dressing process. Meanwhile, silicon carbide (SiC) is suitable for blasting owing to its stable chemical properties and good wear resistance [31, 32]. Alexandre et al. [33] adopted acoustic emission (AE) technology and digital signal processing to monitor the dressing process of cBN wheels. After applying digital filtering to the original signal, the average count statistics can effectively determine the optimal termination point of the dressing process excessive wear on the grinding wheels. Chen et al. [34, 35] investigated the morphology of abrasive grains on the surface of a grinding wheel following numerous dressing periods, but they did not analyze the dressing process of the grinding wheel. If the dressing period is inadequate and the distance is excessive, it may lead to a reduction in the exposed height of abrasive grains or the filling of open pores with metal bonds. Conversely, if the dressing period is excessive and the distance is too short, cBN grains may experience macro-fracture. Moreover, removing metal bonds is likely to result in partial chipping of the grinding wheel, which poses challenges to surface accuracy and prolongs its lifespan. Yu et al. [36] observed that surpassing the threshold resulted in the compressed gas flow influencing the configuration of the abrasive beam by adjusting the blasting parameters, leading to convergence of the beam and a decreasing erosion rate and the average roughness on the sample surface. Zhang et al. [37] demonstrated that wet micro-abrasive blasting primarily relies on micro-cutting action of abrasives when processing carbide cutting tools, which generates an insert mixture with rounded cutting edges while effectively eliminating defects such as cavities and cracks located at insert peripheries. Zhao et al. [38] conducted an experiment to dress a resin-bonded cBN grinding wheel using white corundum and silicon carbide, wherein the characterization parameters of the abrasive grain cutting height and grinding density were established. The dressing parameters and mechanism have not and thoroughly investigated, despite the evaluation of the dressing of both types of abrasive grains. The optimization of blasting parameters for porous cBN grinding wheels and the exploration of the abrasive blasting and mechanism are therefore essential.

This article proposes conducting an air-borne abrasive blasting experiment alongside a 2D simulation model for abrasive blasting to reveal the dressing mechanism and validate the advantages of dressed porous cBN grinding wheels through comparative grinding experiments. Additionally, Section 2 introduces the air-borne abrasive blasting device, preparation of raw materials, abrasive blasting experiment process, establishment of abrasive blasting simulation model and process of comparative grinding performance experiment. Section 3 presents the impact of blasting parameters on metal-bonded segments and abrasive erosive wear, dressing mechanism of porous cBN grinding wheels and the evaluation of grinding performance. The article concludes with a summary in the final section.

2 Experiment Details

2.1 Fabrication of Raw Materials and Air-borne Abrasive Blasting Device

The matrix materials of the working layer of wheels compose the gas atomized Cu-Sn powder (i.e., about 20 at.%Sn, average diameter of 20 μm) mixed with titanium powder (i. e., 98% purity, average diameter of 30–50 μm), using the ball milling method at a speed of 120 r/min for 3 hours. According to Ref. [10], the total concentration of solid phase additives, including molybdenum disulfide (MoS2) and graphene particles, was fixed at 7.5 wt.%. Pure metal-bonded segments (length × width × height: 40 mm × 10 mm × 4 mm) were fabricated by vacuum sintering with cold compression molding. And the segments’ surfaces were ground to reduce their roughness (Ra) below 0.4 μm. A single 40/45# cBN grain with full crystal form was brazed on an AISI 1045 steel substrate to investigate the erosive wear of the abrasive grain. The pure metal-bonded segment fabrication process is depicted in Figure 1. Figure 2 shows the developed air-borne abrasive blasting device for the abrasive blasting dressing experiment.

Figure 1
figure 1

Fabrication process of pure metal-bonded segments

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Figure 2
figure 2

Air-borne abrasive blasting device: a 3D structure and b abrasive air-blasting device

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The device consists of a rotating component for the grinding wheel, a horizontal moving component, an abrasive blasting nozzle, and other auxiliary, which is equipped with the capability to regulate the distance of abrasive blasting and adjust the abrasive’s size. By adjusting the rotating speed, the duration of abrasive blasting can be controlled to facilitate the optimization of blasting parameters.

2.2 Erosion Experiment and Microstructural Characterization

The research findings of both domestic and foreign scholars on abrasive blasting technology [39, 40] indicate that when the abrasive size is large or the Lps is too short, it can lead to accelerated wear of certain abrasive grains, thereby posing challenges in achieving precise Lps control. When the abrasive size is small or the Lps is too long, the removal efficiency of the metal bond also decreases, necessitating a significant increase in tps to ensure effective dressing. The effects of dissociated SiC particle size, Lps and tps on the erosive wear rate and micro-morphology of grains and the metal bond were conducted by an air-borne abrasive blasting device. The morphology of the blasting SiC particle used in the experiment is shown in Figure 3. The corresponding experiment parameters are given in Table 1. To facilitate the observation and acquisition of the wear rate and morphology of abrasive grains after each blasting experiment, a 3D video microscope (Hirox KH-7700) and a scanning electron microscope (COXEM EM30) were used to collect the 3D data and microscopic morphology of the abrasive grains after each abrasive blasting experiment.

Figure 3
figure 3

SiC particles with different sizes: a 36#, b 60#, and c 100#

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Table 1 Abrasive blasting experiment parameters
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Additionally, the 3D entity reconstruction method was employed to quantify the amount of worn grains caused during blasting processes. The 3D topography profilometer (Sensorfar S Neox) was utilized to obtain the Ra value of the metal-bonded segments subsequent to each abrasive blasting experiment, while the erosive wear amount of the metal bond was weighed by calculating the weight difference of segments. The objective is to ascertain the optimal parameters for abrasive blasting and subsequently apply them in the dressing porous cBN grinding wheels.

2.3 Establishment of Porous Grinding Wheel Dressing Simulation Model

The 2D simulation model for abrasive blasting of the cross-sectional layer in operation was created utilizing Abaqus software, as illustrated in Figure 4. The working layer consists of unobstructed macro-pores and numerous micro-pores. The abrasive grains are simplified as regular hexagons, while the 100# SiC particles are simplified as spheres with a diameter of 0.15 mm. Material property parameters of cBN, metal-bonded segments and SiC particles are listed in Table 2 [11, 41]. Firstly, the time value of the erosion process from completion is calculated by considering the relative position of abrasives to the material matrix and the magnitude of motion velocity (v = 50 m/s).

Figure 4
figure 4

2D abrasive blasting simulation model

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Table 2 Material properties of cBN, mental bond and SiC particle
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The contact property between the abrasives and the metal-bonded segment components in the interaction module should be set as surface-to-surface contact, with frictionless tangential direction and hard contact in the normal direction. The default output variables set by the system should be selected for field output management. In addition, the unit failure variable in the field output is configured to automatically be removed upon unit failure. A denser mesh is employed for the matrix region, and CPE3 units chosen as the unit type are utilized to define the impact region mesh, and other settings remain at their default values.

2.4 Comparative Grinding Performance Experiment

The high-speed Blohm Profimat MT 408 grinding instrument was used in comparative grinding performance experiments. As shown in Figure 5, the workpiece (length × width × height: 30 mm × 9 mm × 60 mm) was Ti–6Al–4V and fixed on the workbench by a bench vise.

Figure 5
figure 5

Setup schematic of comparative grinding performance of experiment

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In order to reduce the measurement error of the grinding force (F) caused by the coolant nozzle on the working table during the grinding process, a breakwater was constructed on top of the workbench. A Kistler 9253B force sensor was connected to the workbench to collect the signal of the F at different material removal rates (Q′w). When each set of 4000 mm3 material removal volume was completed, the detachable lumps on the grinding wheel were removed, cleaned, and then observed through a 3D video microscope and SEM to track the changes in the surface morphology of the wheel, as well as the state of wear, and then reassembled to carry out the next set of wear experiments. Meanwhile, the Ra of the workpiece was measured and recorded.

3 Results and Discussion

3.1 Effect of Blasting Parameters on Metal Bond Erosive Wear

Figure 6 illustrates the material removal rate per unit (η) derived by calculating the mass loss of the metal bond before and after the tps value of 15 s and converted to the removal height of metal-bonded segments (Δh). The SiC abrasive sizes of 36#, 60#, and 100# were selected as the Lps increased from 30 mm to 90 mm, resulting in respective decreases in material removal rates by 45.0%, 43.9%, and 33.3%. The data suggest that the reduction in abrasive size has a relatively smaller impact on the material Q′w of metal bond compared to the increase in Lps value. In other words, the sensitivity of Q′w to Lps is higher than that of abrasive size, and opting for a smaller abrasive size is more advantageous in controlling the dressing outcome of grinding wheels.

Figure 6
figure 6

Effect of blasting parameters on the removal rate of metal-bonded segments

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Owing to the proportions of the porous cBN grinding wheel working layer and the metal bond being consistent, the material density of the metal bond is approximately 7.9627 g/cm3. Consequently, the Δh value can be calculated by the amount of metal bond removed. In addition, cBN grain size in the porous cBN grinding wheel is 40/50#, with a diameter of 300–425 μm. When the Lps value is fixed to 30 mm, as the SiC particle size decreases from 36# to 100#, the Δh value is 373.3 μm, 254.4 μm, and 149.7 μm respectively, which is approximately 102.9%, 70.2%, and 41.3% of the average abrasive diameter. When the Lps value reaches 60 mm, the Δh value is 281.4 μm, 188.7 μm, and 143.9 μm respectively, which is approximately 77.6%, 52.1% and 39.7% of the average abrasive diameter. When the Lps value is 90 mm, the Δh value is 206.3 μm, 131.1 μm, and 99.8 μm respectively, which is about 56.9%, 36.2% and 27.5% of the average abrasive diameter. In order to meet the requirements of the requirement of porous cBN grinding wheels, the abrasive grains should be exposed as much as possible without macro-fracture and have sufficient holding strength. The Δh value is selected to be 30% to 50% of the average diameter of the abrasive grains. Upon examination of the reference line in Figure 6, it can be seen that the experiment requirements are met when the SiC particle size is 100# and the Lps value is set to 30 mm or 60 mm. The SiC particle size is 60# and the Lps value is set to 90 mm.

Figure 7 shows the Ra value of metal-bonded segments after continuous abrasive blasting for 15 s and 60 s. There is a significant reduction in Ra values as the Lps value increases and SiC particle size decreases. As the tps value increases, the Ra value of the segments will decrease to varying degrees. When the Lps value is fixed at 30 mm and various SiC particle sizes (i.e., 36#, 60#, and 100#) are used to carry out abrasive blasting experiments, a decrease in abrasive size results in a decrease in the Ra value of the segments. The Ra values of the segments are 5.73 µm, 3.67 µm, and 2.24 µm, respectively, displaying a decrease of 60.9%. When the Lps value reaches 60 mm, the Ra values of the segments become 5.14 µm, 2.83 µm, and 1.73 µm, by 66.3%, as the abrasive size decreases. When the abrasive Lps value is increased to 90 mm, the Ra values of the segments are reduced to 3.50 µm, 2.12 µm, and 1.42 µm, decreasing by 59.4%.

Figure 7
figure 7

Effect of blasting parameters on the surface roughness: a tps = 15 s and b tps = 60 s

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When the tps value is increased to 60 s and the Lps value is set to 30 mm, as the abrasive size decreases, the Ra values of the segments are 4.16 µm, 2.88 µm, and 2.21 µm respectively, decreasing by 46.9%. When the Lps value reaches 60 mm, as the abrasive size decreases, the Ra value of the segments is 3.79 µm, 2.41 µm and 1.65 µm respectively, with a reduction of 56.5%. When the Lps value is increased to 90 mm, the Ra values of the segments are changed into 3.34 µm, 1.72 µm, and 1.26 µm, decreasing by 62.3%. By comparison, it becomes evident that when the Lps value remains constant, there is a linear decrease in the Ra value of the segments as the size of the abrasive decreases. However, this decreasing trend exhibits varying degrees of attenuation compared to 15 s. The results demonstrate that an increase in the distance of abrasive blasting or a decrease in abrasive size leads to a gradual reduction in Ra of metal-bonded segments after abrasive blasting, while an increase in the duration of abrasive blasting results in a progressively flatter surface.

The typical morphological characteristics of the erosive wear area were observed using Sensofar, as shown in Figure 8. The abrasive blasting process was conducted at the Lps value of 60 mm for 15 s. The analysis reveals the presence of abrasive impact stripping-induced pits in the erosive wear area, which are formed by metal bond peeling. The size and quantity of pits gradually decrease, and the erosion area becomes more uniform as the abrasive size. The surface quality achieved through 100# SiC particle blasting is evidently superior.

Figure 8
figure 8

Typical morphologies of erosive wear area under different abrasive sizes: a 36#, b 60#, and c 100#

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3.2 Effect of Blasting Parameters on Single Grains Erosive Wear

Figure 9 depicts the variation of cBN grains’ erosive wear rate with dissociated SiC particle size and Lps, highlighting the significant impact of Lps on the change in the abrasive erosive wear rate. The erosive wear rate of cBN grains exhibits an upward trend as the size of dissociated SiC particles increases, with a fixed Lps value of 30 mm. When 36# SiC particles are utilized at a tps value of 15 s, the erosive wear rate of cBN grains experiences a rapid increase to 80.5%, resulting in the loss of grinding ability for the cBN grains. When the duration is extended to 30 s, the erosive wear rate of the abrasive grains reaches 99.8%, resulting in the removal of almost all particles. The erosive wear rate of cBN abrasive grains in the initial 15 s is only 35.8% when utilizing 60# SiC particles for abrasive blasting experiments, which demonstrates a significant reduction compared to the rapid erosive wear and removal observed with the use of 36# abrasives.

Figure 9
figure 9

Effect of abrasive sizes on cBN grain erosive wear rate: a Lps = 30 mm, b Lps =  60 mm, and c Lps = 90 mm

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When the tps value is increased to 30 s, the erosive wear rate of the abrasive grains reaches 90.4%, resulting in their complete removal after being subjected to abrasive blasting for 45 s. In experiments utilizing 100# SiC particles, the erosive wear rate of cBN grains initially exhibits a rapid increase followed by a slower rate as the duration of abrasive blasting increases. When the distance is set to 60 mm (Figure 9b), the abrasive wear erosion rate of the three sizes of SiC particles at 15 s is only 20%, and when the time reaches 60 s, only the cBN grains eroded by 36# SiC particles have reached a complete removal state, and the abrasive erosive wear rates of 60# SiC and 100# SiC particles are 84.4% and 67.1%, respectively.

When the distance increases to 90 mm (Figure 9c), the abrasive erosive wear rates of the three sizes of SiC particles in the initial 15 s are all less than 20%, and then the abrasive erosive wear rate of the 36# SiC particles increases rapidly, resulting in complete removal being achieved at 60 s. Meanwhile, the erosion abrasive wear rate of 60# and 100# SiC particles increases with time. Abrasive wear rates are only 44.2% and 32.1% with a tps value of 60 s. It can be observed that when employing short Lps, particularly with large-diameter SiC particles (36#), the rapid wear of abrasive grains can induce macro-fracture within a brief duration of abrasive blasting time (i.e., tps < 15 s), leading to complete removal. The upward trend in the erosive wear rate of the abrasive grains significantly decelerates as the distance for abrasive blasting increases, particularly when fine abrasives are employed.

This demonstrates that an increase in the size of abrasives results in higher kinetic energy for each individual abrasive grain. Consequently, the cBN experiences macro-fracture due to the continuous impact of powerful erosion kinetic energy, thus intensifying wear. Furthermore, the size and proximity of the dissociated SiC particles directly determine the instantaneous kinetic energy upon impact with the surface of cBN grains, subsequently converting it into internal energy within the abrasives. This process also disrupts chemical bonds between material atoms, ultimately initiating cracks and facilitating their gradual expansion. However, cBN grains exhibit anisotropic characteristics, resulting in significant variations in impact resistance and strength among different crystal faces of the grains. When SiC particles continuously impact cBN grains, the weaker crystal faces are more susceptible to crack initiation. Subsequently, these cracks gradually propagate due to continuous abrasion, ultimately resulting in macro-fracture of the grains.

Figure 10 shows the micro-morphology of cBN grains under different abrasive blasting distances and abrasive sizes at 15 s. When 36# SiC is used at the Lps value of 30 mm, cBN grains undergo macro-fracture, and the broken cracks can be clearly seen. When the SiC particle size is reduced to 60# and 100#, the covered matrix material on the surface of cBN grains is removed, and the fracture degree of grains is slightly reduced, but macro-fracture still exists. At the Lps of 60 mm, it is observed that as the sizes of the SiC particles decrease, the degree of erosive wear of the cBN grains diminishes. The surface of the abrasive grains eroded with 36# SiC particles also exhibits macro-fracture while preserving the localized metal bond coating on the abrasive grain surface. When the Lps value is increased to 90 mm, the macro-fracture and cleavage fracture of the abrasive grains can be observed in comparison to the Lps of 30 mm and 60 mm. The morphology of the abrasive grains is enhanced, leading to a reduction in fracture occurrence, thereby achieving effective removal of metal bonds.

Figure 10
figure 10

Micro-morphology of cBN grains under different abrasive blasting distances and abrasive sizes at 15 s

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This is due to the high instantaneous speed and impact kinetic energy of SiC particles hitting the surface of abrasive grains at the Lps value of 30 mm during abrasive blasting, resulting in rapid macro-fracturing of the grains (i.e., tps < 15 s). The precise control of the abrasive wear state is hindered by its lack of conduciveness. Achieving precise control of the abrasive wear state becomes challenging due to the larger size of dissociated SiC particles, specifically those for 36# and 60#. The abrasive blasting nozzle is prone to blockages during the blasting process, and the abrasive wear rate significantly increases due to the force of high impact energy. Therefore, in order to ensure that they possess high impact kinetic energy and effectively remove the metal bond without causing excessive wear on the abrasive grain, it is necessary to reduce the tps value of the porous cBN grinding wheel. The preferred parameters of the porous grinding wheel for this experiment are a 100# SiC particle size, a Lps value of 60 mm, and a tps value of 15 s.

Figure 11 illustrates that SEM morphologies of a single cBN grain are tracked and observed, with the SiC particle size of 100# and Lps value of 60 mm. The results indicate that as the tps value increases from 0 to 30 s, there is a continuous removal of the metal bond wrapping the abrasive grains, gradual micro-fracture of cBN grains, and eventual macro-fracture of -abrasive grains. Additionally, the edges of the abrasive grains gradually become rounded due to the removal of metal bonds and micro-fracture. The edges exhibit multiple micro-fractures due to their low strength. From the evolution of abrasive grain morphology, it can be inferred that cracks easily initiate on weaker crystal planes during the erosion process attributed to the uneven distribution of crystal plane strength. With continuous abrasion, these cracks propagate throughout the entire abrasive grain, resulting in both micro-fractures and macro-fractures.

Figure 11
figure 11

Evolution of cBN grain morphology: a tps = 0 s, b tps = 15 s, and c tps = 30 s

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3.3 Dressing Mechanism of Porous cBN Grinding Wheels

Figure 12 shows the optical microscope morphology and SEM micro-morphology for the surface of porous cBN grinding wheels before and after the blasting processes. It can be found that there are a lot of scratches on the surface of the working layer of the porous cBN grinding wheel before abrasive blasting (Figure 12a). The cBN grains are significantly encapsulated by the metal bond, thereby not being exposed in the conventional manner. Additionally, certain pores are obstructed and covered by the metal bond. After undergoing abrasive blasting and dressing with optimized process parameters, the morphology of the grinding wheel's working layer indicates the removal of the metal bonds wrapped in the outer layer of cBN grains (Figure 12b). As a result, the cutting edge is clearly exposed, and a significant reduction in open pores filled with metal bonds is observed. Consequently, the grinding wheel successfully regains its chip-holding capacity. Moreover, the SEM micro-morphology of the same area of a certain working layer before and after abrasive blasting and dressing has been tracked (Figure 12c and d) for a further understanding of the erosive wear state of cBN grains and open pore characteristics of the porous cBN grinding wheel.

Figure 12
figure 12

Comparison of surface morphology and microscope morphology of porous cBN grinding wheel before and after abrasive blasting: a surface morphology before abrasive blasting, b surface morphology after abrasive blasting, c microscope morphology before abrasive blasting and d microscope morphology after abrasive blasting

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It is found that after abrasive blasting and dressing, with the removal of a large amount of metal bond, the cBN grains and open pores are exposed significantly, and some of the cBN grains on the working surface of the grinding wheel are partially micro-fracture or macro-fracture under the impact of abrasives, while most of the cBN grains with lower exposure height remain intact.

The cross-sectional results of the working layer's 2D abrasive blasting simulation are presented in Figure 13. The findings indicated that when the abrasives contact with the surface of the working layer, the fatigue strength of the cBN grains is higher than that of the metal-bonded segments. The crystal form of the cBN grains remains intact during impact, but the surface of the metal-bonded segments is impacted by the SiC particles and continuously eroded, and the local stress continues to increase, eventually forming the initial source of the cracks. Furthermore, the direction of crack expansion follows the direction of stress concentration in the walls of micro-pores and macro-pores in the working layer. Owing to the continuous impact of abrasives, the metal bond reaches its fatigue limit. Consequently, large sections of the metal bond tend to detach along the hole wall. The wrapped open pores are exposed leading to the greatly increasing chip holding space. Some cBN grains on the outer surface experience micro-fracture at the stress concentration point of the cutting edge under the impact of abrasives. When the tps value continues to increase, a large amount of the metal bond around the cBN grains is removed. It can be observed that while the surface bond deteriorates, the abrasive grains may also experience macro-fracture or even detachment, gradually exposing the subsequent working layer.

Figure 13
figure 13

Evolution of the working layer during blasting process: a tps = 15 s, b tps = 30 s and c tps = 45 s

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3.4 Evaluation of Grinding Performance

The porous cBN grinding wheels are dressed with optimal blasting parameters. Figure 14a depicts the F of the porous cBN grinding wheels and the vitrified cBN grinding wheels compared based on various Q′w values. The grinding wheel speed (vs) is set at 120 m/s while the depth of cut (ap) is maintained at 0.1 mm. With Q′w value increasing, the specific grinding force (F′) of both grinding wheels gradually increases. Additionally, the F′ value of the porous cBN wheel is always lower than that of the vitrified cBN wheel, whether normal or tangential. When the Q′w value increases from 1 mm3/(mm·s) to 10 mm3/(mm·s), the specific normal grinding force (F′n) of the vitrified cBN wheel increases from 25.7 N/mm to 43.4 N/mm and the specific tangential grinding force (F′t) increased from 7.9 N/mm to 11.7 N/mm. While the F′n value of the porous cBN wheel increases from 9.5 N/mm to 21.5 N/mm, the F′t value only increases from 4.1 N/mm to 7.9 N/mm. This is because the number of effective grinding edges of the dressed porous cBN wheel is more than that of the vitrified cBN wheel. Therefore, the dominant force between the wheel and the workpiece is the cutting force, which in turn weakens the sliding friction force, resulting in a decrease in the F′ value. According to the variation of the grinding force ratio (F′n/F′t) in Figure 14b, it can be observed that F′n/F′t value of the porous cBN grinding wheel is lower, stable between 2.35 and 2.86, while the F′n/F′t value of the vitrified cBN grinding wheel is between 3.24 and 3.87. This observation leads to the conclusion that the porous cBN grinding wheel has a better sharpness.

Figure 14
figure 14

Effect of material removal rate on specific grinding force and force ratio of both wheels: a specific grinding force and b grinding force ratio

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Figure 15 shows a comparison of the Ra value of workpieces ground with the porous cBN wheel and the vitrified cBN wheel at the vs value of 120 m/s and the ap value of 0.1 mm, respectively. As the Q′w value increases, the Ra value of the workpieces ground by both grinding wheels increases gradually. However, the average Ra value and the rate of Ra value are very different. When Q′w value rises from 1 mm3/(mm·s) to 10 mm3/(mm·s), the Ra value of the workpiece with the porous cBN grinding wheel rises gradually and steadily from 0.803 μm to 1.13 μm, which is an increase of 40.7%. The Ra value of the workpiece ground by vitrified cBN grinding wheels rises rapidly from 0.806 μm to 1.731 μm at the Q′w value of 6 mm3/(mm·s) or less, and then rises slowly, and finally the Ra value reaches 1.731 μm. Finally, the Ra value reaches 2.077 μm, which is 157.7% higher than the initial Ra value. The micro-morphology of the workpiece surface ground by both grinding wheels at a Q′w value of 10 mm3/(m·s) is obtained by SEM (Figure 16).

Figure 15
figure 15

Effect of material removal rate on surface roughness of workpieces under both wheels

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Figure 16
figure 16

Micro-morphology of workpiece surfaces ground by two wheels: a vitrified cBN wheel and b porous cBN wheel

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The micro-morphology of the workpieces after grinding with the vitrified cBN wheel shows deeper scratches and pile-up on both sides of the scratches, as well as severe chip adhesion on the surface. This is due to the high wheel speed which leads to a reduction in the maximum undeformed chip thickness. The relatively small size of the chips produced during the grinding process resulted in the blockage of the vitrified cBN grinding wheel. The heat of grinding can’t be dispersed in a timely manner, leading to an increase in the temperature of the grinding process, resulting in the adhesion of chips. As a result, the material pile-up and grinding burns make the Ra value of the workpiece unstable. The porous cBN grinding wheel exhibits greater chip storage space due to its open connecting pores and larger pore size. This feature reduces chip adhesion and promotes the evacuation of grinding heat.

4 Conclusions

The cBN grain samples and metal-bonded segments are prepared by cold pressing and vacuum sintering. An air-borne abrasive blasting device is used to conduct an abrasive blasting erosion experiment on metal bonds and single cBN grains. Detailed discussion on the effects of erosion on the metal bond and cBN grains is provided, with consideration given to parameters such as SiC particle size, Lps, and tps. The blasting process parameters of the porous grinding wheel working layers have been optimized. In addition, an abrasive blasting and dressing model has been developed using Abaqus software to illustrate the abrasive blasting and dressing mechanism of the grinding wheel's working layer. Finally, the advantages of dressed porous cBN wheel are proved. The main research results are summarized as follows:

  1. (1)

    The Lps has the most significant influence on the change rate of abrasive erosive wear. When subjected to high kinetic energy impacts, the abrasive grains are more prone to experiencing macro-fracture and cleavage fracture, ultimately leading to failure.

  2. (2)

    After considering the Q′w value of the metal bond, as well as the morphology and wear rate of the abrasive grains, the optimal parameters for dressing the working layer of the porous grinding wheel are as follows: a SiC particle size of 100#, an Lps value of 60 mm, and a tps value of 15 s.

  3. (3)

    According to the simulation, it is demonstrated that the initial formation of cracks in the metal-bonded segments can be attributed to the progressive impact and erosion caused by increasing local stress exerted by SiC particles on the surface. The incorporation of a metal bond effectively mitigates the internal propagation of cracks within cBN abrasive grains.

  4. (4)

    Compared to vitrified cBN grinding wheels, porous cBN wheels with high sharpness after dressing can achieve a reduction of 50.5%–63.0% in F′n and 32.5%–48.1% in F′t, respectively. Additionally, the increased chip storage capacity of porous cBN wheels helps minimize chip adhesion and enhances surface quality.

Data availability

Data available on request from the authors.

References

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Acknowledgements

Not applicable.

Funding

Supported by National Natural Science Foundation of China (Grant Nos. 92160301, 92060203, 52175415, 52205475, and 52205493), Science Center for Gas Turbine Project (Grant Nos. P2022-AB-IV-002-001 and P2023-B-IV-003-001), Jiangsu Provincial Natural Science Foundation (Grant No. BK20210295), the Huaqiao University Engineering Research Center of Brittle Materials Machining (Grant No. 2023IME-001),  Foundation of Graduate Innovation Centre in NUAA (Grant No. XCXJH20230509), and Fundamental Research Funds for the Central Universities (Grant Nos. NS2023028 and NG2024015).

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Authors and Affiliations

  1. National Key Laboratory of Science and Technology on Helicopter Transmission, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, China

    Jiahao Song, Yu Yao, Shandong Feng, Biao Zhao, Wenfeng Ding & Guodong Xiao

  2. China Aeronautical Radio Electronic Research Institution, Shanghai, 200233, China

    Guodong Xiao

  3. Department of Mechanical Engineering, University of Bath, Bath, UK

    Qi Liu

  4. School of Mechanical Engineering, Tongji University, Shanghai, China

    Dongdong Xu

  5. State Key Laboratory for High Performance Tools, Zhengzhou Research Institute for Abrasives and Grinding Co. LTD, Zhengzhou, China

    Yanjun Zhao & Jianhui Zhu

Authors
  1. Jiahao Song
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  2. Yu Yao
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  3. Shandong Feng
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  4. Biao Zhao
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  5. Wenfeng Ding
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  6. Guodong Xiao
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  7. Qi Liu
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  8. Dongdong Xu
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  9. Yanjun Zhao
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  10. Jianhui Zhu
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Contributions

JS, BZ, GX and YY were in charge of the whole trial; JS wrote the manuscript; SF, WD, QL, DX, YZ and JZ assisted with sampling and laboratory analyses. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Biao Zhao.

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Song, J., Yao, Y., Feng, S. et al. Dressing Mechanism and Evaluations of Grinding Performance with Porous cBN Grinding Wheels. Chin. J. Mech. Eng. 37, 106 (2024). https://doi.org/10.1186/s10033-024-01083-9

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  • DOI: https://doi.org/10.1186/s10033-024-01083-9

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