High Grinding Temperature Research Articles

The Process Optimization Analysis of CBN Abrasive Cu-Sn-Ti Coating Fabrication via the Ultrasonic-Vibration-Assisted Laser Cladding Method

Ultra-precision machining has higher requirements for the performance of abrasive tools, but the traditional grinding wheel has some problems such as irregular grain arrangement, limited chip space, and high grinding temperature. Therefore, a structured grinding wheel suitable for ultra-precision machining is proposed. In this study, the laser cladding method and ultrasonic vibration technology were combined to study the preparation process of a structured grinding wheel. Firstly, the quality evaluation system of the printing layer was established, and the shape coefficient and dilution rate were used to evaluate the laser cladding quality. The effects of laser power, sweep speed, powder feeding speed, and ultrasonic power on the shape coefficient and dilution rate of the printing layer were analyzed by single-factor experiments. The level range of each factor in the orthogonal experiment was established to optimize the process parameters. The surface morphology was observed, and the influence of ultrasonic vibration on the morphology was analyzed. The structured grinding wheel was prepared according to the optimized parameters.

Effects of the Impacting Velocity and Angle on the Grinding Force, Force Ratio and Deformation Behavior During High-shear and Low-pressure Grinding

Background: Background: The normal grinding force is generally larger than the tangential one during conventional grinding processes. Consequently, several machining issues arise, such as a low material removal rate, a high grinding temperature, and poor surface integrity. To overcome the constraints associated with conventional grinding methods, a novel “high-shear and low-pressure” flexible grinding wheel is utilized. A thorough investigation of the influence of machining parameters on the highshear and low-pressure grinding performance from a microscopic perspective is focused. Objective: The effect of the impacting angle and velocity on the grinding force, grinding force ratio, and fiber deformation displacement is explored at the microscopic level. Methods: An impact model was established using ABAQUS software to explore and analyze the interaction results of micro-convex peaks with the abrasive layer under different processing conditions. Results: It was found that the normal grinding force Fn increased with both impact angle and velocity. Similarly, the tangential grinding force Ft is enhanced with increasing velocity. However, its magnitude is reduced with impact angle. Conclusion: The grinding force ratio is primarily affected by the impact angle, which displays a declining trend. The maximum fabric deformation displacement reaches 72.4 nm at an angle of 60° and at a velocity of 9 m/s.

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.

Fabrication of PCD face grinding wheel with positive rake angle by femtosecond laser and its performance evaluation in cemented carbide grinding

Super-hard abrasive grinding is considered to be the main approach to realize precision and ultra-precision machining of difficult-to-machine materials such as cemented carbide, engineering ceramics, titanium alloys and superalloy materials encountered. However, heavy grinding force, high grinding temperature and poor surface integrity are prone to be encountered in conventional negative rake angle grinding of difficult-to-machine materials. In response to these problems, a novel concept of positive rake angle grinding is first proposed and an abrasive grain regularly arranged binder-less polycrystalline diamond face grinding wheel with positive rake angle has been designed and fabricated by femtosecond laser ablation. To evaluate the grinding performance of the face grinding wheel with positive rake angle, grinding experiments of YG8 cemented carbide are conducted and compared with the traditional electroplated diamond grinding tool with equivalent abrasive grain dimension and distribution. The results show that compared with the conventional negative rake angle grinding, the normal and tangential forces in positive rake angle face grinding are reduced by 30.3 % ∼ 36.4 % and 21.1 % ∼ 29.3 %, respectively, and the ratio of normal to tangential force is reduced by 12.6 % ∼ 20.3 %. The surface roughness and average depth of subsurface metamorphic layer are also significantly smaller. The laser fabricated polycrystalline diamond face grinding wheel also has better wear resistance in the grinding of cemented carbide. Therefore, it can be concluded that better ground surface quality is obtained by the novel grinding wheel with positive rake angle. The innovative grinding method can fill the research gap on the grinding mechanism of positive rake angle grinding and further enrich the grinding theory of difficult-to-machine materials.

Start-up behavior of oscillating heat pipe in grinding wheel under axial-rotation conditions

• Start-up timing behavior of AR-OHP is characterized and studied. • AR-OHP filled with acetone has a fast start-up speed followed by methanol & water. • Start-up mode turns from over-damped to under-damped/ transient mode with increase of cooling. • Centrifugal acceleration improves AR-OHP flow motion and increases start-up time. • Start-up mode becomes over-damped mode @ a =738m/s 2 and benefits temperature control. High efficiency grinding of difficult-to-machine materials can generate a good amount of heat in a short time. If the heat is not timely transferred, the accumulation of heat will cause a high grinding temperature and can be harmful to the machining quality. The oscillating heat pipes (OHP) are designed in the grinding wheel to directly transfer out grinding heat when axial rotating with the grinding wheel. To avoid sudden burnout of the workpiece in high efficiency grinding, the OHPs in the grinding wheel are supposed to dissipate a high heat flux in a very short time, therefore, such OHPs should start-up very quickly. The start-up speed of the OHP plays an important role in the grinding efficiency and quality, while the study on the start-up behavior of the OHP under axial-rotation is insufficient. Given that, the start-up process of the OHP under axial-rotation is here described and characterized, and the insurgence of the start-up is evaluated by the settling time and the rising time. Besides, the influences of the working fluids, cooling conditions, and centrifugal accelerations are studied. As expected for other kinds of OHP, also for the present OHP, the OHP filled with acetone has the shortest start-up time (20s), followed by the OHP filled with methanol (45s), while the water as the working fluid has the longest start-up time (46.5s). Along with the increase of cold air pressure, the settling and the rising time decreases significantly, e.g., for acetone, the settling time decreases by 59% - 87%. The centrifugal acceleration promotes the OHP flow motion and heat transfer, in turn, increases the start-up time. Besides, the start-up behavior turns from under-damped mode to over-damped mode, which has no temperature overshoot and is beneficial to the temperature control for thermal management in axial-rotation scenarios.

Analysis of grain tribology and improved grinding temperature model based on discrete heat source

A high grinding temperature will cause thermal damage to a workpiece surface and deterioration of surface integrity, which is the bottleneck of grinding. The present grinding temperature theoretical model is based on grain homogeneity and the continuous heat source distribution in the grinding zone. However, the random change in interference between the effective grains and a workpiece during the machining process causes a change in the grain tribological properties, resulting in varying transient grinding temperatures. Based on the current situation, the grain tribological mechanism and an improved temperature model based on a discrete heat source are proposed to reveal the temperature variation law of a workpiece in an actual grinding process. First, the surface topography model of a grinding wheel is established based on the geometric characteristics of grains, and the determination mechanism of effective grains is revealed. Furthermore, the interference mechanical behavior of the grains and workpiece is analyzed according to the kinematic law of grains in the sliding, plowing, and cutting stages. The mechanical model and specific grinding energy model at different stages are established, and the thermal distribution mechanism of effective grains is revealed. Finally, a temperature field mathematical model of a discrete heat source is established, and numerical simulation is performed to demonstrate the dynamic temperature change process of different grains. A new experimental method for measuring temperature at different positions of the workpiece with a bipolar thermocouple array is designed, and a regional numerical simulation and experimental temperature comparison method is innovatively proposed. Experimental results show that the grinding temperature measured under different cutting depth conditions is in good agreement with the numerical results, and the variation law is consistent. The minimum error in 64 groups of experimental measuring and numerical calculation comparison zones can reach 4.9%, and the proportion of zones with errors less than 10% can approach 86%. This study will provide a theoretical basis for the accurate suppression of workpiece surface thermal damage and the development of precision grinding in engineering discipline and machinery industry.

A study of dynamic energy partition in belt grinding based on grinding effects and temperature dependent mechanical properties

• A dynamic energy partition calculating model in abrasive belt grinding is proposed. • Cutting and ploughing dominate material removal for soft material while ploughing is more dominant for hard material. • Heat accumulation of grains reduces cooling capacity of abrasive belt during grinding. • High grinding temperature softens workpiece and makes cutting action occur easily. Analyzing and modelling the dynamic energy partition is of great significance to revealing the mechanism of belt grinding and improving grinding quality. However, there is lack of comprehensive studies on energy partition in belt grinding, especially when the dynamic characteristics are under consideration. To fill this gap, this paper analyzed the grinding energy partition from the perspective of grinding effects and thermal aspects. Grinding effects are distinguished by combination of single grain scratch tests and force balance of one grain in view of dynamic and elastic contact conditions. Thermal aspects are obtained by a fusion method of finite element method (FEM) and optimization algorithm. Then, by utilizing the iterative approach, heat accumulating effect and temperature dependent mechanical properties of workpieces are taken into account either and the dynamic energy partition is calculated in a continuous grinding process. Validations on two workpieces (made by SUS304 and AA6061-T6) prove that the proposed dynamic energy partition calculating method is effective and the maximum error of q w is 17.2 %. The proposed method not only enhances the understanding of dynamic energy partition in robotic belt grinding, but also offers a new venue for studying abrasive belt grinding.

Surface burn behavior in creep-feed deep grinding of gamma titanium aluminide intermetallics: characterization, mechanism, and effects

This article presents the surface burn behavior when creep-feed grinding gamma titanium aluminide (γ-TiAl) intermetallic. First, the main characteristics of burnt surface morphology were detected. Subsequently, surface burn mechanism was revealed by analyzing compositional changes in the surface layer via X-ray photoelectron spectroscopy. Lastly, the effects of grinding temperature on grinding force and surface integrity were discussed. Finding showed that a high grinding temperature would lead to a heavy color, from light brown to hyacinthine, on the burnt surface. The burning process was dominated by oxidation of Ti and Al. Ti was generally in the state of TiO2 on the ground surface, whereas lower valence oxide of Ti was found on the subsurface. This oxide layer could produce a reduced ratio of the tangential grinding force to the normal one. Elevated temperature would produce grinding and quenching cracks on a burnt surface, and tensile residual stress might be developed if the temperature is extremely high. Surface morphology and topography characteristics indicated that, unlike conventional titanium alloys (e.g., Ti-6Al-4V), a marginal physical reaction occurred on the workpiece surface during the burning process of γ-TiAl intermetallics due to poor material ductility.

Micro-magnetic characterisation of ground AISI D2 tool steel using hysteresis loop technique

According to tooling industries, grinding is the most effective and economical machining for AISI D2 tool steel owing to its low thermal conductivity. The first objective is to investigate the effect of grinding environments on surface integrity of AISI D2 tool steel. Grinding performance like force ratio and grinding temperature was investigated under wet and dry environments. The second objective is to qualitatively assess the thermal damage of ground surface using non-destructive hysteresis loop (HL) technique. The result shows that higher force ratio and surface roughness were obtained under flood grinding. Maximum thermal damage in terms of drastic variation in microstructure and microhardness were observed under dry grinding owing to serious plastic deformation at higher grinding temperature. HL outcomes like lower average permeability, higher coercivity and remanence were obtained with higher thermal damage on ground surface. Finally, linear correction was obtained between HL outcomes and microhardness of ground samples.

Micro-magnetic characterisation of ground AISI D2 tool steel using hysteresis loop technique

According to tooling industries, grinding is the most effective and economical machining for AISI D2 tool steel owing to its low thermal conductivity. The first objective is to investigate the effect of grinding environments on surface integrity of AISI D2 tool steel. Grinding performance like force ratio and grinding temperature was investigated under wet and dry environments. The second objective is to qualitatively assess the thermal damage of ground surface using non-destructive hysteresis loop (HL) technique. The result shows that higher force ratio and surface roughness were obtained under flood grinding. Maximum thermal damage in terms of drastic variation in microstructure and microhardness were observed under dry grinding owing to serious plastic deformation at higher grinding temperature. HL outcomes like lower average permeability, higher coercivity and remanence were obtained with higher thermal damage on ground surface. Finally, linear correction was obtained between HL outcomes and microhardness of ground samples.

Research on the metamorphic layer of silicon nitride ceramic under high temperature based on molecular dynamics

The high temperature of the grinding area at the engineering ceramic materials processing is one of the main factors affecting the quality of processing and the performance of parts. In order to reveal the law of temperature distribution of silicon, nitride ceramic grinding and its mechanism of action on surface quality. The process of machining silicon nitride ceramic material is simulated based on the established molecular dynamics model of the nanometric grinding of silicon nitride. The influence of grinding parameters on the nanometric grinding process is studied from the variation law of grinding temperature and the evolution of system energy, as well as the formation of grinding surface and metamorphic layer during machining. And the results of the experiment were compared with the theoretical research. With the increasing of grinding depth and speed of diamond grains, the energy released during the deformation and amorphous phase change of the atomic lattice get increased, and the grinding temperature get increased. The high grinding temperature will cause amorphous phase change in silicon nitride ceramics, and the amorphous atoms are recombined with the atomic bonds of the processed surface to form a metamorphic layer of the processed surface. The effect of grinding parameters on temperature changes from large to small is grinding wheel line speed, workpiece feeding speed, and grinding depth. There is an important effect on improving the surface machining quality and the service life of parts of engineering ceramics such as silicon nitride from the results of this paper, and it also plays an important role in reducing the effect of grinding temperature on the surface quality.

Atmospheric pressure plasma jet and minimum quantity lubrication assisted micro-grinding of quenched GCr15

High-strength alloys have significant application values in aerospace industry due to their excellent mechanical properties. However, grinding of these alloys, which is generally used for precision machining, suffers from problems like high grinding temperature and poor surface quality. Having relatively lower grinding temperature and smaller grinding force, micro-grinding is a high-efficient manufacturing method for precision machining of difficult-to-cut materials. Nevertheless, the side effects induced by current composite grinding methods, such as temperature gradient and chatter marks, tend to be more obvious in the micro-machining process. Atmospheric pressure plasma jet (APPJ) can effectively improve metal surface wettability without changing surface structures. On the other hand, minimum quantity lubrication (MQL) can more efficiently cool and lubricate the grinding area. Here, we propose to induce APPJ and MQL cooling media into the micro-grinding area, and adjust the cooling and lubricating characteristics. Quenched GCr15 workpieces are machined under five different conditions (dry micro-grinding, nitrogen jet assisted micro-grinding, APPJ assisted micro-grinding, MQL assisted micro-grinding, and APPJ+MQL assisted micro-grinding), and grinding temperature, grinding force, surface roughness, and surface morphology of workpieces in each group are investigated and analyzed. The results indicate that APPJ can reduce grinding force and that APPJ+MQL micro-grinding can obtain surfaces with much better surface quality. Tensile experiments demonstrate that APPJ can reduce material elongation rate and promote material fracture, which contributes to its positive effect on the micro-grinding process. The environmentally-friendly method is expected to have promising application potentials in machining of difficult-to-cut materials.

Subsurface damage and material removal of Al–Si bilayers under high-speed grinding using molecular dynamics (MD) simulation

By performing three-dimensional molecular dynamics (MD) simulations, the effects of the tool radius, depth of cut and grinding speed are thoroughly studied in terms of the workpiece deformation, material removal, dislocation movement, atomic trajectory, grinding temperature and average grinding force. The strength of ductile/brittle (Al/Si) bilayers is largely enhanced, because the interface can hinder the passage of dislocations. The interface in brittle/ductile (Si/Al) bilayers contributes to its ductility by increasing the movability of dislocations when gliding on it. The brittle to ductile transition of bilayers, which strongly depends on the interface debond energy, has a key role in controlling the dislocation slipping mechanism. The investigation also reveals that a larger tool radius, higher grinding speed or deeper depth of cut results in more chipping volume and higher grinding temperature in both bilayers. At the same machining parameters, the above changes in brittle/ductile (Si/Al) bilayers are more apparent than that in ductile/brittle (Al/Si) bilayers, since Si is stiffer and has a higher yield strength than Al.

Surface integrity in grinding of Ti-6Al-4V using monolayer superabrasive wheel

ABSTRACTTitanium alloy is considered to be difficult to grind due to its low thermal conductivity, relatively high grinding temperature and its reactivity with almost all grit materials. Residual stress on the ground surface, which is one of the major aspects of surface integrity, has not been studied well in case of grinding of Ti- alloys. Further, investigations assessing the effectiveness of emulsion of vegetable oil in water as a grinding fluid applied in minimum quantity lubrication (MQL) mode are lacking. The present work endeavours to experimentally study the effect of different grinding fluids applied in MQL mode in comparison to flood cooling with soluble oil on different grindability characteristics with particular emphasis on residual stress. Neat oil, applied in MQL mode, has provided a reduction in grinding forces, even in comparison to flood cooling. It has also yielded overall competitive performance in comparison to flood cooling from the perspective of surface roughness, residual stress, and ground surface topography.

Experimental investigation of cooling characteristics in wet grinding using heat pipe grinding wheel

High grinding temperature restricts the machining efficiency and precision of some aeronautical difficult-to-machine materials. Aiming to enhance heat exchange with the grinding zone and reduce grinding temperature, heat pipe grinding wheel (HPGW) provides a novel method through improving the thermal conductivity of grinding wheel assisted by heat pipe. In this paper, the structure of HPGW is introduced and the workpiece temperature and energy partition in wet grinding using HPGW based on a wheel-fluid composite surface model is analyzed. Wet grinding experiments including creep feed grinding, high-speed shallow grinding and high-efficiency deep grinding (HEDG) are carried to investigate the cooling characteristics of HPGW according to the workpieces of titanium alloy Ti-6A1-6 V and Inconel 718. Compared with using the traditional grinding wheel, the results show that using HPGW in creep feed grinding and HEDG can maintain a lower grinding temperature and avoid the burnout under a relatively high removal rate, but cooling effect of HPGW is not obviously different from the traditional grinding wheel in high-speed shallow grinding due to a small heat input at the evaporator of HPGW.

Grinding Titanium grade 1 alloy with an alumina wheelusing soap water

Grinding is a manufacturing process used mainly for semi finishing/ finishing operations. Many problems, such as high specific energy requirement, high grinding temperature and rapid wheel loading are associated with this process. These difficulties become more pronounced when grinding a difficult-to-grind material, such as titanium, a metal used mainly in aerospace, automotive, biomedical and nuclear industries. Inability of the conventional fluid in effective lubrication and cooling along with their adverse environmental impact has prompted a worldwide need for an alternative grinding fluid and its delivery systems. This paper focuses on the effect of soap water delivered in two ways- firstly, in a drop by drop method, and secondly, as a high velocity jet. Results show that using soap water drop by drop, high grinding ratio is achieved; however, forces increase and poor surface quality is observed. On the other hand, a jet of soap water applied during grinding results in lowest tangential force, acceptable surface quality and lower surface roughness; also, chips obtained are of shear type, indicating better grindability.

Analytical modeling of grinding-induced subsurface damage in monocrystalline silicon

Monocrystalline silicon is a predominant type of semiconductors. However, subsurface damage (SSD) of silicon has been widely reported during the mechanical grinding process. Although relevant efforts have been reported, most theoretical studies only qualitatively explained the SSD formation mechanism rather than quantitatively evaluate SSD values, while most experimental measurement techniques unavoidably damaged (even destroyed) the ground surfaces and therefore could only be ultilised ex-situ. To fill this gap, this paper suggests an analytical model of grinding-induced SSD in silicon, where the explicit relationship between SSD and the ground surface roughness Rz is analytically established considering the (i) ductile-regime effect, (ii) crystallographic orientation effect, and (iii) material property degradation due to high grinding temperature. Based on the model, grinding-induced SSD could be nondestructively, quickly and conveniently evaluated, in-situ or ex-situ, by measuring Rz values based on a handheld profilometer. Grinding trials indicated the model could accurately evaluate SSD depths along both the 〈100〉 and 〈110〉 crystallographic orientations in both dry and wet silicon grinding processes. Further discussion on how the model could guide and monitor the industrial silicon grinding is also presented. The proposed model therefore is anticipated to be meaningful to facilitate design, manufacture, and applications of monocrystalline silicon.

Prediction of high-speed grinding temperature of titanium matrix composites using BP neural network based on PSO algorithm

High grinding temperature is the key reason of workpiece burnout, which hinders the improvement of the machining quality. In this work, the prediction of high-speed grinding temperature of titanium matrix composites is investigated using back propagation (BP) neural network based on particle swarm optimization (PSO) algorithm (also called as PSO-BP). Furthermore, a comparison has been carried out among GD-BP (the BP neural network trained with gradient descent method), LM-BP (the BP neural network trained with Levenberg-Marquardt (LM) algorithm), and PSO-BP. Results obtained show that the PSO-BP method has a more significant advantage in terms of convergence speed, fitting accuracy, and prediction accuracy than the other two methods (such as GD-BP and LM-BP) in predicting the grinding temperature. Accordingly, the grinding temperature is predicted by applying the PSO-BP method and the grinding parameters are optimized, which could avoid the burnout behavior of the titanium matrix composites.

Crack-free ductile mode grinding of fused silica under controllable dry grinding conditions

A crack-free ductile mode grinding of fused silica was realized by a controllable dry grinding process in this research, which is attributed to the improvement of fused silica's ductile machinability induced by the high grinding temperature. The plastic deformation of fused silica consists of shear flow and densification. Plastic deformation mechanisms and cracking behaviors related to densification were investigated firstly by high temperature nanoindentation experiments to reveal the ductile–brittle transition mechanisms. Fused silica exhibits less densification and more shear flow at high temperature than room temperature. The critical ductile–brittle transition load of fused silica is higher at high temperature than room temperature. These results may lead to the improvement of the fused silica's ductile machinability at high temperature. Dry grinding experiments were conducted to investigate the effect of grinding depth. A mathematical model is established to predict the maximum temperature in workpiece. A novel infrared radiation (IR) transmission on-line measurement method was presented to acquire the workpiece temperature in the contact zone directly. The predicted results coincide well with the experiment results. Contrary to the conventional experience, a large grinding depth is beneficial for the surface quality and integrity in the dry grinding of fused silica due to the increased grinding temperature; however, the excessive grinding depth results in grinding wheel burn. The ductile grinding depth of the fused silica increases from sub-micrometers to 5μm by dry grinding which makes the grinding process more controllable and effective.

An investigation on surface burn during grinding of Inconel 718

Grinding nowadays is extensively used for machining of superalloys. Inconel 718 is a Ni-based superalloy which is known as difficult to grind material (DTG) due to its inherent properties like high hardness, high hot strength, severe strain hardening and low thermal conductivity. In the present work, grindability of Inconel 718 using conventional abrasive grinding wheels has been experimentally explored. Ground surfaces have been characterized after grinding with silicon carbide (SiC) and alumina (Al2O3) wheels under dry condition. Surface integrity of the ground product has been studied using surface characterization techniques like Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Further, the surface behavior of the ground surface has been investigated using microscopic images, micro-hardness tests, and surface roughness measurements. The major conclusion of the present work is that Inconel 718 can be ground more efficiently using alumina grinding wheels compared to the SiC grinding wheel. In the case of SiC wheel, it has been found that the severe attritious wear of the wheel took place primarily due to the chemical reaction between SiC grits and workpiece material at a higher grinding temperature. The mechanism for such attritious wear has been studied, and it appears to be a dissociation of SiC at higher temperature.