Unsteady-State Grinding Technology (II) Experimental Studies of Grinding Forces and Force Ratio

As is known to all, grinding force is one of the most important parameters to evaluate the whole process of grinding. Generally, the grinding force is resolved to three component forces, namely, normal grinding force F n, tangential grinding force F t and a component force acting along the direction of longitudinal feed which is usually neglected because of insignificance. The normal grinding force F n has influence upon surface deformation and roughness of workpiece, while the tangential grinding force F t mainly affect power consumption and service life of grinding wheel. In order to study deep into the process of the unsteady state grinding, we set up a measurement system to monitor the change of grinding force during the course of grinding and try to find some difference in the change of grinding force between the steady state grinding and unsteady state grinding. In the test, the normal and tangential grinding forces, F n and F t were measured by using a set of equipments including sensor, amplifier, oscilloscope and computer monitor. From the results, we can conclude that: 1) In the unsteady state grinding process, the values of the grinding forces are much lower than those of the steady state grinding process and the grinding force ratio showed a nonlinear fluctuation. 2) The tendency of the grinding forces in the process of the unsteady state grinding proved the existence of the cutting and micro-cutting actions. 3) Because the grinding force signals of the unsteady state grinding are much weaker than those of the steady state grinding, to obtain accurate value of the grinding forces, wave filtering is needed to be done. The whole process to filter the perturbation wave can be separated into three steps in order, changing the grinding force signals from analog signals into digital signals, FFT (fast Fourier transform) treatment to the digital signals, and IFFT(inversion fast Fourier transform) treatment to the digital signals after spectrum limitation.

Prediction of Grinding Force by an Electroplated Grinding Wheel with Orderly-Micro-Grooves

The ability to predict a grinding force is important to control,monitor,and optimize the grinding process.Few theoretical models were developed to predict grinding forces when a structured wheel was used in a grinding process.This paper aimed to establish a single-grit cutting force model to predict the ploughing,friction and cutting forces in a grinding process.It took into the consideration of actual topography of the grinding wheel,and a theoretical grinding force model for grinding hardened AISI 52100 by the wheel with orderly-micro-grooves was proposed.The model was innovative in the sense that it represented the random thickness of undeformed chips by a probabilistic expression,and it reflected the microstructure characteristics of the structured wheel explicitly.Note that the microstructure depended on the randomness of the protruding heights and distribution density of the grits over the wheel.The proposed force prediction model was validated by surface grinding experiments,and the results showed(1)a good agreement of the predicted and measured forces and(2)a good agreement of the changes of the grinding forces along with the changes of grinding parameters in the prediction model and experiments.This research proposed a theoretical grinding force model of an electroplated grinding wheel with orderly-micro-grooves which is accurate,reliable and effective in predicting grinding forces.

Dry Grinding of Titanium Alloy Using Brazed Monolayer cBN Wheels Coated with Graphite Lubricant

The purpose of this study is to investigate the effect of graphite lubricant on the dry grinding performance of Ti-6Al-4Valloy,using graphite-coated,brazed monolayer,cubic boron nitride(cBN)wheels.Brazed monolayer cBN wheels both with and without a coating of polymer-based graphite lubricant are fabricated and subsequently compared for grinding performance based on measurements of grinding temperature,surface microstructure and grinding.In terms of grinding temperature,considerable improvement in dry grinding performance of titanium alloy is achieved using coated brazed monolayer cBN wheels,with 42%—47%reduction in grinding temperature as opposed to uncoated wheels.The grinding force ratio with the coated wheels is observed to remain between 1.45to1.85despite material removal rates reaching up to 1 950mm3/mm.No tangible change in ground titanium surface microstructure is noted as a result of grinding with the graphite coated wheels as opposed to the uncoated ones.

Face Grinding Surface Quality of High Volume Fraction SiC_(p)/Al Composite Materials

The existing research on SiC_(p)/Al composite machining mainly focuses on the machining parameters or surface morphology.However,the surface quality of SiC_(p)/Al composites with a high volume fraction has not been extensively studied.In this study,32 SiC_(p)/Al specimens with a high volume fraction were prepared and their machining parameters measured.The surface quality of the specimens was then tested and the effect of the grinding parameters on the surface quality was analyzed.The grinding quality of the composite specimens was comprehensively analyzed taking the grinding force,friction coefficient,and roughness parameters as the evaluation standards.The best grinding parameters were obtained by analyzing the surface morphology.The results show that,a higher spindle speed should be chosen to obtain a better surface quality.The final surface quality is related to the friction coefficient,surface roughness,and fragmentation degree as well as the quantity and distribution of the defects.Lower feeding amount,lower grinding depth and appropriately higher spindle speed should be chosen to obtain better surface quality.Lower feeding amount,higher grinding depth and spindle speed should be chosen to balance grind efficiently and surface quality.This study proposes a systematic evaluation method,which can be used to guide the machining of SiC_(p)/Al composites with a high volume fraction.

Force Characteristics in Continuous Path Controlled Crankpin Grinding

Recent research on the grinding force involved in cylindrical plunge grinding has focused mainly on steady-state conditions.Unlike in conventional external cylindrical plunge grinding,the conditions between the grinding wheel and the crankpin change periodically in path controlled grinding because of the eccentricity of the crankpin and the constant rotational speed of the crankshaft.The objective of this study is to investigate the effects of various grinding conditions on the characteristics of the grinding force during continuous path controlled grinding.Path controlled plunge grinding is conducted at a constant rotational speed using a cubic boron nitride（CBN）wheel.The grinding force is determined by measuring the torque.The experimental results show that the force and torque vary sinusoidally during dry grinding and load grinding.The variations in the results reveal that the resultant grinding force and torque decrease with higher grinding speeds and increase with higher peripheral speeds of the pin and higher grinding depths.In path controlled grinding,unlike in conventional external cylindrical plunge grinding,the axial grinding force cannot be disregarded.The speeds and speed ratios of the workpiece and wheel are also analyzed,and the analysis results show that up-grinding and down-grinding occur during the grinding process.This paper proposes a method for describing the force behavior under varied process conditions during continuous path controlled grinding,which provides a beneficial reference for describing the material removal mechanism and for optimizing continuous controlled crankpin grinding.

Ceramics Grinding Under the Condition of Constant Pressure

To meet the increasing demand on the quality and co st of precision components for the semiconductor industries, extensive studies on high efficiency and precision machining of ceramic materials have been conducted over the past several years. It is found that the effects of grinding pressure and rotational speed of spindle in the machining for the ceramic materials are v ery significant on the quality of the grinding process. In order to achieve stab le grinding conditions for improved performance, a new grinding control scheme i n which the grinding pressure is maintained constant throughout the grinding pro cess was carried out in the present study. The surface quality of ground ceramics depends on the mechanism of material remo val in the vertical grinding process. For grinding of Si 3N 4 and glass under the condition of constant pressure, increasing pressure enhances material remova l rate, and at the same time causes more machining-induced microcracks on the g round surfaces. Along with the analysis of tangential forces, specific grinding energy, and the micro observations on ground surfaces, it can be found that low pressure and high wheel speed should be selected to high efficiently remove cera mics in ductile mode in the vertical grinding. From the theoretically analytical and measured grinding temperatures in the vert ical grinding of ceramics, it is found that the analytical temperature profile w ithε= 55% has the same trend with the measured one. The measured temperature is higher that the analytical one at the beginning stage of grinding process, whic h might be contributed to the unstable grinding condition of this stage. The gri nding temperatures in the vertical grinding of ceramics under a constant are not high enough for glassy phase formation, and may not reduce surface fracture as expected. However, the temperature in dry grinding may cause thermal damage to t he resin bond diamond wheel, thereby resulting in low quality workpiece surface.

External grind-hardening experiments and its grinding force

The grind-hardening method suitable for external grinding is proposed in this paper and the experiments are carried out on M1432B grinding machine. The hardened layer of the workpiece with cut depth 0.3 mm and speed 0.2 m/min is analyzed. The result indicates the metallurgical structure of the hardened layer is martensite and the top hardness value is 754 HV （about 62.3 HRC）. At the same time, the grinding force, one of the most important factors of external grind-hardening process is modeled, and the measurement method is provided with elastic core clampers. The measurement result shows that the values of both the tangential force and the normal force increase when the cut depth increases, and the top value is 146 N and 656 N with the cut depth value of 0.4 mm. The increment speed and the value of the normal force are larger than the tangential force.

Derivation of Grinding Force of Online Roll Grinder

The force of grinding particle was disintegrated to study the physical and mathematical models. The grinding wheel can be characterized by grinding ratio, C, a steady constant. The moment and C of grinding wheel can be estimated with electrical parameters. The grinding force can be calculated quite easily in this way.

Experimental Study on Grinding Force of Electrostatic Coated Grinding Wheel

In order to deal with the hard machining of TC4 alloy,coated graphite on grinding wheel surface by electrostatic device is proposed in this paper.This paper mainly completed the design of graphite electrostatic spraying grinding wheel device,force experimental analysis of grinding TC4 alloy with coated graphite grinding wheel,and summary of the influence of different grinding speeds and grinding depths on grinding force and grinding force ratio.The experimental results show that the lubrication coating can reduce the grinding force and grinding force ratio in the process of grinding TC4 alloy with graphite powder-coated wheel under electrostatic field force,compared to dry grinding with the uncoated wheel.

Investigation on the Grindability of CSS-42L Stainless Steel

Plunge grinding experiments were carried out on CSS-42L stainless steel with the white fused alumina wheel.The grinding forces were measured with variations in accumulated material removal volume.Then the morphological features of worn grinding wheel were analyzed by optical microscopy and the grinding temperatures were measured with a thermocouple.For comparison,C45 steel was ground under the same conditions.The results indicated that the grinding forces of CSS-42L were at least twice that of C45 steel.When the accumulated removal volume overcame 375mm^3,strong adhesion was found between the abrasives and workpiece CSS-42L.Nevertheless,adhesion was hardly found after 800mm^3 workpiece C45 steel was removed.In order to enhance the machining property of CSS-42L,a brazed CBN wheel was incorporated into the grinding of CSS-42L,and the grinding forces and temperatures were found significantly decreased,whose maximum decreasing amplitude was about 70%and 80%,respectively.

Analysis of grinding mechanics and improved grinding force model based on randomized grain geometric characteristics

Too high grinding force will lead to a large increase in specific grinding energy, resulting in high temperature in grinding zone, especially for the aerospace difficult cutting metal materials,seriously affecting the surface quality and accuracy. At present, the theoretical models of grinding force are mostly based on the assumption of uniform or simplified morphological characteristics of grains, which is inconsistent with the actual grains. Especially for non-engineering grinding wheel,most geometric characteristics of grains are ignored, resulting in the calculation accuracy that cannot guide practical production. Based on this, an improved grinding force model based on random grain geometric characteristics is proposed in this paper. Firstly, the surface topography model of CBN grinding wheel is established, and the effective grain determination mechanism in grinding zone is revealed. Based on the known grinding force model and mechanical behavior of interaction between grains and workpiece in different stages, the concept of grain effective action area is proposed. The variation mechanism of effective action area under the influence of grain geometric and spatial characteristics is deeply analyzed, and the calculation method under random combination of five influencing parameters is obtained. The numerical simulation is carried out to reveal the dynamic variation process of grinding force in grinding zone. In order to verify the theoretical model, the experiments of dry grinding Ti-6Al-4 V are designed. The experimental results show that under different machining parameters, the results of numerical calculation and experimental measurement are in good agreement, and the minimum error value is only 2.1 %, which indicates that the calculation accuracy of grinding force model meets the requirements and is feasible. This study will provide a theoretical basis for optimizing the wheel structure, effectively controlling the grinding force range, adjusting the grinding zone temperature and improving the workpiece machining quality in the industrial grinding process.

Machinability of ultrasonic vibration-assisted micro-grinding in biological bone using nanolubricant

Bone grinding is an essential and vital procedure in most surgical operations.Currently,the insufficient cooling capacity of dry grinding,poor visibility of drip irrigation surgery area,and large grinding force leading to high grinding temperature are the technical bottlenecks of micro-grinding.A new micro-grinding process called ultrasonic vibration-assisted nanoparticle jet mist cooling(U-NJMC)is innovatively proposed to solve the technical problem.It combines the advantages of ultrasonic vibration(UV)and nanoparticle jet mist cooling(NJMC).Notwithstanding,the combined effect of multi parameter collaborative of U-NJMC on cooling has not been investigated.The grinding force,friction coefficient,specific grinding energy,and grinding temperature under dry,drip irrigation,UV,minimum quantity lubrication(MQL),NJMC,and U-NJMC micro-grinding were compared and analyzed.Results showed that the minimum normal grinding force and tangential grinding force of U-NJMC micro-grinding were 1.39 and 0.32 N,which were 75.1%and 82.9%less than those in dry grinding,respectively.The minimum friction coefficient and specific grinding energy were achieved using U-NJMC.Compared with dry,drip,UV,MQL,and NJMC grinding,the friction coefficient of U-NJMC was decreased by 31.3%,17.0%,19.0%,9.8%,and 12.5%,respectively,and the specific grinding energy was decreased by 83.0%,72.7%,77.8%,52.3%,and 64.7%,respectively.Compared with UV or NJMC alone,the grinding temperature of U-NJMC was decreased by 33.5%and 10.0%,respectively.These results showed that U-NJMC provides a novel approach for clinical surgical micro-grinding of biological bone.

Developing a novel radial ultrasonic vibration-assisted grinding device and evaluating its performance in machining PTMCs

Particle-reinforcing titanium matrix composites(PTMCs)exhibit the sharp raising applications in modern industries owing to its extraordinary physical and mechanical properties.However,the poor grindability and unstable grinding processes due to the existence of TiC particles and TiB short fibres inside PTMCs,leading to the sudden grinding burn and low material removal rate.In this work,a novel radial ultrasonic vibration-assisted grinding(RUVAG)device with a special cross structure was developed to improve machining efficiency and avoid grinding burns.Meanwhile,the resonant modal and transient dynamic characteristics of radial ultrasonic vibration system were discussed.Comparative grinding performance experiments were then conducted under the conventional grinding(CG)and RUVAG using mono-layer cubic boron nitride abrasive wheels,in views of the grinding forces and force ratio,grinding temperature,and ground surface morphology.Results show that the ultrasonic vibration direction can be transformed effectively using the special cross structure of vibration converter,and better vibration homogeneity can be obtained.RUVAG has a smaller tangential grinding force by 5.0%–17.2%than that of CG,but a higher normal grinding force of 6.5%–14.9%,owing to the periodic impact of grinding wheels.In addition,RUVAG possesses a remarkable lower grinding temperature in range of 24.2%–51.8%and a higher material removal rate by 2.8 times compared with CG,resulting from the intermittent cutting behavior between the grinding wheel and workpiece.In this case,the sudden burn can be avoided during high-speed grinding processes.Moreover,the proportion of micro-fracture defects on machined surface is slightly increased once the ultrasonic vibration mode is employed because of the periodic impact on reinforced particles,whereas the pull-out defects of reinforced particles are reduced significantly.

An iterative blending integrating grinding force model considering grain size and dislocation density evolution

The dynamic force load in grinding process is considered as a crucial factor affecting the quality of parts,and a better understanding of the mechanism of force generation is conducive to revealing the evolution of material microstructure more precisely.In this study,an iterative blending integrating grinding force model that comprehensively considers the impact of grain size and dislocation density evolution of the material is proposed.According to the grinding kinematics,the interaction of grit-workpiece is divided into rubbing,plowing,and chip formation stages in each grinding zone.On this basis,the evolution of material microstructure in the current chip formation stage will affect the rubbing force in the next grinding arc through flow stresses,which in turn will influence the total grinding force.Therefore,the flow stress models in rubbing and chip formation stages are firstly established,and then the dislocation density prediction model is established experimentally based on the characteristics of grain size.The effects of the evolution of grain size and dislocation density on the grinding forces during the grinding process are studied by means of iterative cycles.The results indicate that the implementation of an iterative blending scheme is instrumental in obtaining a higher accurate prediction of the grinding force and a deeper insight of the influence mechanisms of materials microstructure on grinding process.

Vibration characteristics and machining performance of a novel perforated ultrasonic vibration platform in the grinding of particulate-reinforced titanium matrix composites

Ultrasonic vibration-assisted grinding(UVAG)is an advanced hybrid process for the precision machining of difficult-to-cut materials.The resonator is a critical part of the UVAG system.Its performance considerably influences the vibration amplitude and resonant frequency.In this work,a novel perforated ultrasonic vibration platform resonator was developed for UVAG.The holes were evenly arranged at the top and side surfaces of the vibration platform to improve the vibration characteristics.A modified apparent elasticity method(AEM)was proposed to reveal the influence of holes on the vibration mode.The performance of the vibration platform was evaluated by the vibration tests and UVAG experiments of particulate-reinforced titanium matrix composites.Results indicate that the reasonable distribution of holes helps improve the resonant frequency and vibration mode.The modified AEM,the finite element method,and the vibration tests show a high degree of consistency for developing the perforated ultrasonic vibration platform with a maximum frequency error of 3%.The employment of ultrasonic vibration reduces the grinding force by 36%at most,thereby decreasing the machined surface defects,such as voids,cracks,and burnout.

Grinding temperature and energy ratio coefficient in MQL grinding of high-temperature nickel-base alloy by using different vegetable oils as base oil

Vegetable oil can be used as a base oil in minimal quantity of lubrication (MQL). This study compared the performances of MQL grinding by using castor oil, soybean oil, rapeseed oil, corn oil, sunflower oil, peanut oil, and palm oil as base oils. A K-P36 numerical-control precision surface grinder was used to perform plain grinding on a workpiece material with a high-temperature nickel base alloy. A YDM-III 99 three-dimensional dynamometer was used to measure grinding force, and a clip-type thermocouple was used to determine grinding temperature. The grinding force, grinding temperature, and energy ratio coefficient of MQL grinding were compared among the seven vegetable oil types. Results revealed that (1) castor oil-based MQL grinding yields the lowest grinding force but exhibits the highest grinding temperature and energy ratio coefficient; (2) palm oil-based MQL grinding generates the second lowest grinding force but shows the lowest grinding temperature and energy ratio coefficient; (3) MQL grinding based on the five other vegetable oils produces similar grinding forces, grinding temperatures, and energy ratio coefficients, with values ranging between those of castor oil and palm oil; (4) viscosity significantly influences grinding force and grinding temperature to a greater extent than fatty acid varieties and contents in vegetable oils; (5) although more viscous vegetable oil exhibits greater lubrication and significantly lower grinding force than less viscous vegetable oil, high viscosity reduces the heat exchange capability of vegetable oil and thus yields a high grinding temperature; (6) saturated fatty acid is a more efficient lubricant than unsaturated fatty acid; and (7) a short carbon chain transfers heat more effectively than a long carbon chain. Palm oil is the optimum base oil of MQL grinding, and this base oil yields 26.98 N tangential grinding force, 87.10 N normal grinding force, 119.6 degrees C grinding temperature, and 42.7% energy ratio coefficient. (C) 2015 The Authors. Production and hosting by Elsevier Ltd. on behalf of Chinese Society of Aeronautics and Astronautics.

Grinding force and surface quality in creep feed profile grinding of turbine blade root of nickel-based superalloy with microcrystalline alumina abrasive wheels

Creep feed profile grinding of the fir-tree blade root forms of single crystal nickel-based superalloy was conducted using microcrystalline alumina abrasive wheels in the present study. The grinding force and the surface quality in terms of surface topography, subsurface microstructure,microhardness and residual stress obtained under different grinding conditions were evaluated comparatively. Experimental results indicated that the grinding force was influenced significantly by the competing predominance between the grinding parameters and the cross-sectional root workpiece profile. In addition, the root workpiece surface, including the root peak and valley regions, was produced with the large difference in surface quality due to the nonuniform grinding loads along the root workpiece profile in normal section. Detailed results showed that the surface roughness, subsurface plastic deformation and work hardening level of the root valley region were higher by up to25%, 20% and 7% in average than those obtained in the root peak region, respectively, in the current investigation. Finally, the superior parameters were recommended in the creep feed profile grinding of the fir-tree blade root forms. This study is helpful to provide industry guidance to optimize the machining process for the high-valued parts with complicated profiles.

Prediction on grinding force during grinding powder metallurgy nickel-based superalloy FGH96 with electroplated CBN abrasive wheel

In this article,a grinding force model,which is on the basis of cutting process of single abrasive grains combined with the method of theoretical derivation and empirical formula by analyzing the formation mechanism of grinding force,was established.Three key factors have been taken into accounts in this model,such as the contact friction force between abrasive grains and materials,the plastic deformation of material in the process of abrasive plowing,and the shear strain effect of material during the process of cutting chips formation.The model was finally validated by the orthogonal grinding experiment of powder metallurgy nickel-based superalloy FGH96 by using the electroplated CBN abrasive wheel.Grinding force values of prediction and experiment were in good consistency.The errors of tangential grinding force and normal grinding force were 9.8%and 13.6%,respectively.The contributions of sliding force,plowing force and chip formation force were also analyzed.In addition,the tangential forces of sliding,plowing and chip formation are 14%,19%and 11%of the normal forces on average,respectively.The pro-posed grinding forcemodel is not only in favor of optimizing the grinding parameters and improving grinding efficiency,but also contributes to study some other grinding subjects(e.g.abrasive wheel wear,grinding heat,residual stress).

Grinding behavior and surface appearance of(TiC_p+ TiB_w)/Ti-6Al-4V titanium matrix composites

（TiCp＋ TiBw）/Ti-6Al-4V titanium matrix composites（PTMCs） have broad application prospects in the aviation and nuclear field. However, it is a typical difficult-to-cut material due to high hardness of the reinforcements, high strength and low thermal conductivity of Ti-6Al-4V alloy matrix. Grinding experiments with vitrified CBN wheels were conducted to analyze comparatively the grinding performance of PTMCs and Ti-6Al-4V alloy. Grinding force and force ratios, specific grinding energy, grinding temperature, surface roughness, ground surface appearance were discussed. The results show that the normal grinding force and the force ratios of PTMCs are much larger than that of Ti-6Al-4V alloy. Low depth of cut and high workpiece speed are generally beneficial to achieve the precision ground surface for PTMCs. The hard reinforcements of PTMCs are mainly removed in the ductile mode during grinding. However, the removal phenomenon of the reinforcements due to brittle fracture still exists, which contributes to the lower specific grinding energy and grinding temperature of PTMCs than Ti-6Al-4V alloy.

Study into grinding force in back grinding of wafer with outer rim

Back grinding of wafer with outer rim(BGWOR)is a new method for carrier-less thinning of silicon wafers.At present,the effects of process parameters on the grinding force remain debatable.Therefore,a BGWOR normal grinding force model based on grain depth-of-cut was established,and the relationship between grinding parameters(wheel infeed rate,wheel rotational speed,and chuck rotational speed)and normal grinding force was discussed.Further,a series of experiments were performed to verify the BGWOR normal grinding force model.This study proves that the BGWOR normal grinding force is related to the rotational direction of the wheel and chuck,and the effect of grinding mark density on the BGWOR normal grinding force cannot be ignored.Moreover,this study provides methods for reducing the grinding force and optimizing the back thinning process of the silicon wafer.