Grinding Zone Temperature Research Articles

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.

DEVELOPMENT OF WOOD GRINDING 4. EVALUATION OF THE THEORETICAL GRINDING MODEL

"Spruce wood was ground under certain fixed conditions to achieve data for interpretation of the grinding mechanism. For this purpose, wood moisture content, wood feeding rate and grindstone peripheral speed were given five, three and two different levels, respectively. The data obtained by application of a laboratory grinder were accordingly most reliable, because the grinder was run under well controlled conditions, and the wood samples represented one and the same wood quality, but at five moisture content levels. The grinding zone temperature was measured at the outlet from the grinding zone, and accordingly it would indicate the average grinding zone temperature. The grinding model suggests that the energy specific fibre production ( w/Pt) evaluated at various power friction levels (Pc/Pt) would help understanding the wood grinding mechanism. The energy specific fibre production showed significant dispersion, when evaluated as a function of the power friction. However, detailed analysis of the data revealed that there could be two linears, one representing moisture saturated wood, and one representing fresh wood that also contains free water in the lumina. Surprisingly, this linear also included data representing air-dry wood. Increasing wood moisture ratio from 0.2 kg to 1.4 kg per kg o.d. wood decreased the average grinding zone temperature significantly from about 98° to 88 °C. Further, there was roughly a difference of 8–12° C in grinding zone temperature due to the wood moisture, when evaluated as a function of the force friction coefficient (Ft/Fc). The two highest moisture ratios resulted in a low-level linear, as the other moisture ratios produced a high-level linear. The wood moisture content seems to affect the grinding process in different ways due to the moisture content level. Since moisture is absorbed in the fibre wall material and evidently linked to various lignin and cellulose components by hydrogen bonds, it will affect the grinding in a certain mode. However, the air-dry wood sample seemed to act as the fresh wood samples, which cannot be explained properly unless also considering fibrillation and fibre properties."

Enhancing grinding parameters of TC4 titanium superalloy by using hybrid eco-friendly cooling system

Grinding, a popular surface finishing operation with high dimensional accuracy is widely used for machining superalloy, ceramic, and composite materials. The trouble that arises while grinding is attributed to excessive specific energy consumption and high grinding zone temperature. This problem enhances for low thermal conductivity materials like TC4 titanium superalloy. An optimal method to minimize heat is the application of cutting fluids. However, the conventional method is inefficient and ineffective to penetrate coolant satisfactorily into the compact grinding zone. Therefore, to enhance the performance of TC4 titanium superalloy hybrid eco-friendly grinding which is the modern manufacturing process is used in this research work. Implementation of a hybrid cooling system using MQL coolant with a jet of Liquid CO2 at a higher feed rate provides a better surface morphology and eliminates biological problems. The experimental result shows that there is an eminently reduction of grinding force using a hybrid method as compared with conventional flood and MQL environmental conditions. This is generally due to better infiltration of fluid in the grinding zone and there is breakage of air turbulence which is formed around the porous grinding wheel. Moreover, MQL reduces overall manufacturing costs by reducing the amount of coolant and disposal difficulties. Significant reduction of heat flux was observed in a hybrid system which minimizes thermal-related problems and enhances the longevity of grinding wheel.[copyright information to be updated in production process]

On grinding force ratio, specific energy, G-ratio and residual stress in SQCL assisted grinding using aerosol of MWCNT nanofluid

In the present investigation, water based multi-walled carbon nanotube (MWCNT) dispersed nanofluid was produced and used as a cutting fluid in small quantity cooling lubrication (SQCL) assisted grinding of hardened AISI52100 steel. The work material was ground by an alumina wheel. The SQCL technology utilizes atomized aerosol of liquid grinding fluid. Use of MWCNT nanofluid aerosol in place of soluble oil was found to be substantially beneficial in reduction of specific energy and development of compressive residual stress on ground surface. The steady and lower value of the force ratio (tangential to normal grinding force, Ft/Fn) was suggestive of the superior lubrication and grit sharpness retention ability of the aerosol of MWCNT nanofluid. Higher compressive residual stress on the ground surface under MWCNT nanofluid environment suggests lesser grinding zone temperature, which can be attributed to its superior wettability, lubricity and heat dissipation ability of the MWCNT nanofluid. The consumption rate of grinding fluid in SQCL was varied. It could be reduced to 200 ml/h for MWCNT nanofluid to obtain an almost similar or better effect to that of 500 ml/h for soluble oil. Lesser surface tension of MWCNT nanofluid, compared to its counterpart, seemed to facilitate wetting, thus improving lubrication and heat transfer capability further.

Temperature of Grinding Carbide With Castor Oil-Based MoS2 Nanofluid Minimum Quantity Lubrication

Abstract Nanofluid minimum quantity lubrication (NMQL) has better stability, higher thermal conductivity, and excellent lubrication performance compared with traditional flood lubrication. The heat transfer model and finite difference model were established to verify the feasibility of NMQL conditions in grinding cemented carbide. Based on them, the grinding temperature of cemented carbide is calculated numerically. Results show that the grinding zone temperatures of flood grinding and NMQL are lower, 85.9 °C and 143.2 °C, respectively. Surface grinding experiments of cemented carbide YG8 under different working conditions are carried out. Dry grinding (227.2 °C) is used as the control group. Grinding zone temperatures of flood grinding, minimum quantity lubrication, and NMQL decrease by 64.2%, 39.5%, and 20.4%, respectively. The error is 6.3% between theoretical calculation temperature and experimental measurement temperature. Based on machining process parameters (specific grinding force, force ratio) and experimental results (microstructure of grinding wheel, workpiece, and grinding debris), the effects of different working conditions on wheel wear are studied. NMQL achieves the highest G ratio of 6.45, the smallest specific grinding force, and the smallest Fn/Ft ratio of 2.84, which further proves that NMQL is suitable for grinding cemented carbide.

Effects of local strain rate and temperature on the workpiece subsurface damage in grinding of optical glass

Subsurface damage (SSD) generated during the grinding process directly affects the optical quality and the service life of optical components. It is of great significance to accurately predict and effectively control the depth of the SSD layer of the ground workpiece. However, most of the existing SSD depth prediction models are based on quasi-static and room temperature conditions. This paper presented a prediction model of SSD depth, which considered the combined effect of local strain rate and temperature on the SSD generation during grinding process. The variation of strain and strain rate in the local shear zone of an average abrasive grit on the grinding wheel was analyzed, considering the dynamic density of abrasive grits; Strain rate effect of the material was described by introducing a dynamic fracture toughness KID, which would increase with the strain rate; Grinding zone temperature and especially the temperature on the abrasive grits were analyzed. Combining the strain rate effect and temperature effect, a thermodynamic fracture toughness KIDT model was further developed. On the basis of classic brittle material crack system and the kinematics of grinding, the SSD prediction model considering the dynamic variation of mechanical properties in grinding process was derived. The effects of local strain rate and temperature in grinding of BK7 optical glass were systematically studied under different grinding wheel speeds. The predicted SSD values using a conventional static model and current models considering the strain rate or grinding temperature effect or both, were compared with the measured values. The predicted SSD values using the theoretical model including both the strain rate and grinding temperature effects, agree well with the measured values. The proposed model therefore is anticipated to be meaningful to understand of the SSD of hard and brittle materials involved in a precision grinding process.

Thermal damage control for dry grinding of MgO/CeO2 glass ceramic

MgO/CeO2 glass ceramic is a key solid catalyst and accelerant produced by raw mixing, prilling and pressure sintering. Grinding, as a high-efficiency machining method was used to obtain MgO/CeO2 glass ceramic components with accurate size to meet the size requirements of design. However, thermal damage occurring on the ground surface may change the properties of the components and affect their performance in subsequent applications. In this work, a grinding thermal model was established and validated by experiments. On the basis of this thermal model, the grinding temperature can be controlled to < 100 °C by selecting optimal grinding parameters and thus prevent grinding burn. The mechanism of potential chemical reactions on the grinding surface was further studied by analysing the transient temperature jump at a grain wear flat area and comparing the change in element mass fraction before and after grinding. The performance of a normal resin bond diamond wheel and a resin bond wheel with Ni–P alloy coating on the diamond grains was compared. Results showed that the latter intensified the redox reaction because of the catalytic actions of Ni and P, and the mass fraction of each elements on the workpiece surface shows obvious uneven distribution due to the surface spalling of Ni–P alloy. All these results indicated that key issues are the optimal setup of process parameters to control the grinding zone temperature and the selection of a proper grinding wheel to avoid catalytic elements such as Ni and P.

The temperature field study on the three-dimensional surface moving heat source model in involute gear form grinding

Form grinding is one of the most important finishing processes for obtaining high surface quality gears. Nevertheless, to avoid thermally induced burning and structural change poses a major challenge for this manufacturing technology. Based on the moving heat source model and the superposition principle of heat sources, a comprehensive analytical thermal model for analyzing the heat transfer mechanism of involute gear form grinding was derived. A three-dimensional distribution model of equivalent grinding heat source considering the non-linear distribution of tangential grinding force, grinding parameters, and heat partition ratio was proposed. The FEM (finite element method) simulation of the grinding temperature field was carried out to predict the grinding temperature field using a nested net heat flux equation. Research results have shown that the grinding temperature increases nonlinearly with the rolling angle increasing and the evident peak grinding zone temperature appearing near the tip of the tooth. Through the comparison with the previous experimental measurement results, it is found that the temperature distribution of analytical calculation and numerical simulation agrees well with the measured results.

Experimental Evaluation of the Lubrication Performance in MQL Grinding of Nano SiC Reinforced Al Matrix Composites

Metal matrix composites (MMCs) are materials which have been extensively used in the aerospace and automobile industries and have been categorized as hard-to-machine materials.Lubricants participate a significant role in machining, particularly in the grinding process. As a effect of the rising require for environmental safety and the growing number of health problems faced by workers, traditional lubricants are gradually being replaced. This research evaluate the performance of MQL grinding of nano SiC reinforced Al matrix composites using SAE20W40, Cashew nut shell oil and nano Tio2 filled Cashew nut shell oil as base oils. Experiments for grindability study were approved on a horizontal spindle cylindrical grinding machine using Response Surface Methodology. In this research, the influences of n grinding parameters including wheel speed, work piece speed, depth of cut and wt% nano SiC have been considered on the basis of the grinding forces and temperature to develop optimum grinding narration such as lubrication, high biological and ecological safety. The result shows that the application of nano fluid leads to the reduction of tangential forces and grinding zone temperature. Surface integrity of machined surface were studied using Scanning electron microscopy (SEM).

Analytical Modelling of Temperature in Cylindrical Grinding to Predict Grinding Burns

The direct measurement of grinding temperature is always difficult due to coolant cover and very size of work and wheel interaction zone. At the same time, high heat generation in grinding often leads to grinding burns thereby affecting surface integrity; in this context, theoretical evaluation of temperature could facilitate early detection of the grinding burns. This paper therefore presents an analytical model to evaluate grinding temperature and correlates it with the occurrence of grinding burns in terms of BNA. In general, the analytical approach involves evaluating real contact length, grinding forces and finally grinding zone temperature for the plunge cylindrical grinding. The maximum rise in grinding temperature at the surface was calculated, for the wet grinding process by considering the total heat flux entering into the grinding system. Model validation experiments have been performed to measure BNA and identify parametric conditions that produce grinding burns. The model estimate of grinding zone temperature of 631 °C is in good agreement (92%) with other research works. Further, when the calculated grinding temperature reaches beyond 631 °C, the grinding burns are observed on the work surface with a BNA value of the order of 100 mp for the micro alloyed steel. The minimum thermal damage in terms of BNA is observed at higher levels of wheel speed and spark-out time and lower levels of depth of cut.

Grinding of WC-Co cermets using hexagonal boron nitride nano-aerosol

WC-Co cermets (ceramic-metal composites) were ground by a resin bonded diamond grinding wheel using hexagonal boron nitride (hBN) nano-aerosol to improve the grindability. This is a new generation grinding fluid and was produced by dispersing nano-sized hBN platelets in deionized water. Small quantity cooling-lubrication (SQCL) technology was employed to deliver hBN nanofluid in the form of nano-aerosol so that volumetric consumption rate could be kept at a very low value of 200 ml/h. The nanofluid, when separately characterized, demonstrated good lubrication and heat dissipation capability in reference with soluble oil, which is a commonly used cutting fluid for grinding. The superior tribological characteristics of hBN nanofluid were more pronounced at a high sliding speed of 1 m/s, as observed during a ball-on-disc test. However, the beneficial effect of using hBN nanofluid could be extracted more efficiently only in aggressive grinding condition. A clear drop in specific energy, favourable values of residual stress indicate the same. Prevalence of low grinding zone temperature was reflected through low specific energy values and finer but complex chip micromorphology. Overall the aqueous hBN nanofluid was proven to be a high performing grinding fluid suitable for SQCL application and WC-Co cermet grinding.

Influence of minimum quantity lubrication on surface integrity of ground hardened H13 hot die steel

In grinding process, cutting fluids play an important role to control high grinding zone temperature. However, their use causes detrimental effect on the operator’s health and environment. On the other hand, dry grinding not only results in thermal damage to ground surface but also deteriorates the surface quality and dimensional accuracy of the ground component. The possible solution is to apply cutting fluids using minimum quantity lubrication (MQL) technique. The objective of present research work is to investigate and compare the effect of different grinding environments: dry, flood, MQL with deionized water (DIW), MQL with liquid paraffin oil (LP), and MQL with castor oil based on vegetable oil (VO) during grinding of hardened H13 hot die steel. Grinding performance was evaluated in terms of specific grinding force, specific grinding energy, grinding force ratio, surface roughness, and microhardness. Ground surface and debris morphology were also analyzed using scanning electron microscope, atomic force microscope, and energy-dispersive X-ray spectroscopy to validate the grinding performance. The results showed that MQL-VO grinding leads to minimum specific grinding force, specific grinding energy, and grinding force ratio. Further, surface roughness was considerably reduced under MQL-VO grinding, where Rɑ and Rz were 0.245 μm and 1.846 μm, respectively. AFM analysis indicated that the surface roughness of MQL-VO grinding was nearly 29.88% less as compared to dry grinding. Smooth ground surface topography, as well as long, thin, and no wear track grinding debris, were observed under MQL-LP and MQL-VO conditions. Moreover, dry grinding resulted in lower microhardness in comparison to other grinding conditions.

Research on force and temperature characteristics of novel point grinding wheels

We propose a novel point grinding wheel (NPGW) with coarse grinding zone angle θ. According to earlier studies, this type of grinding wheel has high grinding efficiency, long service life, and generates very little surface roughness. The contact zone between the grinding wheel and workpiece is modified by the addition of the NPGW with the coarse grinding zone angle θ and the inclined angle α of point grinding process, and as a result, grinding force and grinding zone temperature are also altered. The grinding force theoretical model of NPGW was established and the grinding zone temperature was simulated by the finite element method, based on the theory of grinding heat generation and distribution and triangular heat source distribution model. At the same time, seven pieces of NPGW with different angles θ used for grinding experiments were fabricated. The theoretical model of grinding force and the simulation of grinding temperature coincided with experimental results. Therefore, the grinding force theoretical model and the grinding temperature simulation provide an auxiliary and predictive method for the actual process. Moreover, the influence of parameters on grinding force and grinding zone temperature can be obtained, and the results indicate that the NPGW and point grinding process can reduce grinding force and grinding zone temperature. Finally, plastic deformation is attributed to the production of compressive stress and grinding heat is attributed to the production of tensile stress. Therefore, the residual stress is influenced by the grinding force and the grinding temperature coupled. The residual stress of workpiece surface and subsurface was studied. In conclusion, the NPGW and point grinding process can reduce residual stress of workpiece surface and subsurface, in the case of tensile and compressive stress.

Simulation of Part Surface Residual Stress Based on Grind-hardening Process

Grind-hardening is a new technology for steel parts surface enhancing which uses thermal and mechanical composite effects on the parts in the grinding process. During the process, the workpiece surface generates hardened layer which improves the surface quality. As a key performance indicator of measuring the part surface quality, the residual stress of the hardened layer affects the strength, fatigue life and corrosion performance of the part directly. Therefore, the study of residual stress in hardened layer plays an important role in the effective control of hardened layer quality. First, grinding temperature field is analysed for studying the distribution characteristics of surface residual stress after grind-hardening process. Then, different grinding parameters an effect on the temperature field is studied by establishing the mathematical model and the heat transfer model of the grinding zone temperature field. Furthermore, combined with the grinding force generated in the grinding process, the thermo-mechanical coupling analysis with finite element method is adopted to obtain the residual stress and its distribution of the part. Also, the influence mechanism of the part residual stress formation is revealed.

Grindability Improving of Titanium alloy by Using Minimum Quantity Lubrication with Pneumatic Nozzle

Major problem associated while grinding titanium alloy are high specific energy and high grinding zone temperature. To reduce temperature, grinding fluid was used but majority of them was wasted due to formation of stiff air layer around porous grinding wheel rotating at high speed which deflects grinding fluid away from grinding wheel.This paper presents an innovative improvement of MQL process by adding pneumatic nozzle. High compressed air jet from pneumatic nozzle is impinged on grinding wheel surface at an angle of 45° which suppress stiff air layer and clean machined chip, clogged wheel pores from grinding wheel surface. In this work, titanium grade I with alumina grinding wheel is ground at an infeed of 30 μm under flood cooling, MQL and MQL with pneumatic Nozzle conditions. Experimental result shows grindability of titanium grade I alloy under MQL with pneumatic nozzle proves to be an extremely efficient in order to lower grinding force, force ratio, wheel wear, wheel loading and surface roughness.

Investigation of the grinding temperature and subsurface quality of a novel point grinding wheel

In this paper, a novel point grinding wheel (NPGW) with coarse grinding area angle θ is proposed. According to earlier studies, this type of grinding wheel has the advantages of high grinding efficiency, a long service life, and very little surface roughness generated. The contact zone between the grinding wheel and workpiece is modified by the addition of the NPGW with the coarse grinding area angle θ and the inclining angle α of the point grinding process, and as a result, the grinding zone temperature is also altered. Using the finite element method, the grinding zone temperature can be simulated based on the theory of grinding heat generation and distribution, and the triangular heat source distribution model. From this, the distribution of the point grinding temperature field and influence of different grinding parameters on the grinding zone temperature were obtained. To verify the simulation, thermocouple measurements for different NPGWs were taken during the grinding experiments. The simulation provides an auxiliary and predictive method for the actual process. Moreover, an L16(45) orthogonal experiment was designed. Analyzing this range, primary and secondary factors affecting grinding zone temperature, and the optimum combination of parameters for reducing the grinding zone temperature, are determined. Finally, the grinding heat can affect the quality of the workpiece subsurface; therefore, the influence of the various parameters on subsurface quality, including metallographic structure, work hardening, and residual stress, was studied. In conclusion, the NPGW and point grinding process can reduce the degree of work hardening and residual stress of the subsurface of the workpiece, and it was demonstrated that the residual stress changes from compressive to tensile with increasing depth.

Effect of nozzle angle and depth of cut on grinding titanium under cryogenic CO2

ABSTRACT Grinding force and grinding energy are the significant factors associated with the grinding process. The higher heat at the contact zone leads to dulling grits and frequent breakage of grit particle resulting in increase of the grinding force. This problem can be met by bringing down the temperature at the contact zone. The oil-based coolant fails to eliminate the heat at the grinding zone. Hence, the approach of cryogenic coolant is required for this problem. In the present study, an experimental work has been made on the grinding Ti-6Al-4V under cryogenic carbon dioxide (CO2) and conventional coolant condition. Grinding experiments were performed with an electroplated cubic boron nitride (CBN) wheel, with two factors such as nozzle inclination angle and depth of cut (DOC). The output response parameters considered were surface roughness (R a), tangential force (F t), normal force (F n) grinding zone temperature (GT), and specific energy. The effect of CO2 and wet coolant on the chip morphology and surface modification in grinding Ti-6Al-4V was analyzed. The experimental result indicates when cryogenic CO2 was used as a coolant the F t is reduced from 3 to 21% and 2 to 99% in F n. The R a was reduced by 333% and GT by 48% over conventional grinding.

Increasing the operational stability of running surfaces of aluminothermiс welded rail joints by hot grinding

Welded joints have traditionally been a weak point in a design of continuous welded rail (CWR) tracks. Grinding can be used as a resource-saving technology. The purpose of this paper is to study the grinding technology for welded rail joints at different temperatures. The temperature in the weld grinding zone varied from 560 to 850 °С. Using methods of microstructural analysis and hardness measurement, it has been established that different temperature conditions for weld grinding lead to the creation of non-identical mechanical properties of metal and a surface structure of the rail head in the weld zone. As a result of the research, an optimum temperature range, 600 ... 560 °C, was determined. This range is recommended for grinding aluminothermic welded joints.

Characteristics of aerosol produced by an internal-mix nozzle and its influence on force, residual stress and surface finish in SQCL grinding

A tiny amount of cutting fluid is atomised and consumed at a very low rate in SQCL (small quantity cooling lubrication) grinding process and delivered in grinding zone. Grindability is significantly influenced by aerosol characteristics. In the present work, CFD (computational fluid dynamics) based modelling of the aerosol (air atomised water) produced by an internal-mix nozzle was carried out and validated. Various parameters, which are significantly pertinent to grindability, like droplet diameter, droplet velocity and heat transfer coefficient, were in the focus of the study. The model suggests that the SQCL technology can be effectively used at comparatively high atomising pressure with reduced flow rate for achieving adequate level of heat transfer coefficient. It was further concluded that higher flow rates or atomising pressure increases the wettable area, helping in reduction of the grinding zone temperature. Intensity of the tensile residual stress and tangential grinding force were found to be reduced in both cases but the former one was more sensitively influenced by increase in atomising pressure.

SELECTION OF APPROPRIATE FLUID DELIVERY TECHNIQUE FOR GRINDING TITANIUM GRADE-1 USING THE ANALYTIC HIERARCHY PROCESS

&lt;p class="abstract"&gt;Grinding is commonly used in industry for the finishing or semi-finishing of different mechanical components. In this process, a wheel is rotated at a high speed. The wheel is made of abrasive particles known as grits. During grinding, high grinding zone temperature is experienced leading to several grinding defects. To control these thermal defects grinding fluid is usually employed mainly to cool and lubricate the grinding region. However, most of the applied grinding fluid cannot reach the grinding zone as it is deflected by the stiff air layer formed around the wheel periphery. Several attempts have been made in the past to overcome this problem in order to guarantee better fluid delivery. In this paper, two newly developed methods, a pneumatic barrier and a compound nozzle are considered to serve this purpose. Grinding experiments are conducted on titanium grade-1 specimens under four environmental conditions, which include dry, flood cooling, flood cooling with pneumatic barrier set up and cooling using a compound nozzle. Under each environment, 10 grinding passes are undertaken using 10, 20 and 30 mm infeed. Data obtained are used to optimize the grinding performance by employing the Analytic Hierarchy Process (AHP). The AHP results show compound nozzle fluid delivery at 20 mm infeed to be the appropriate condition for grinding titanium grade-1 within this experimental domain. This condition is supposed to deliver grinding fluid deep into the grinding zone thereby controlling grinding temperature effectively and may be recommended to the industry. &lt;/p&gt;