Grinding Zone Research Articles

An analysis of centrifugal MQL supply system potential in the internal cylindrical grinding process

In the article the state of knowledge regarding the functions and supply methods of the cooling liquid into the grinding zone were presented. The new system for centrifugal supply of oil mist was described. The results of experimental investigations conducted into the internal cylindrical grinding process were given. The life of the wheel, machined surface roughness, grinding power and temperature in the machining zone were analyzed. Experimental results showed that compared to flood cooling, this new system provides double the lifespan of the wheel, significantly reducing the volume of wheel wear and enabling the slightly reduced roughness of machined surface and grinding power. Using a new coolant supply method caused an increase in the workpiece temperature, compared to the flood cooling.

Simulation and Experimental Research on Airflow Movement Characteristics of Grinding Zone

Simulation and Experimental Research on Airflow Movement Characteristics of Grinding Zone

Modeling and analysis of grinding forces based on the single grit scratch

Creating scratch by an abrasive grit is mostly investigated to enhance the finishing processes. The grinding process is such that a number of abrasives with a specific statistical distribution is engaged with the workpiece and performs the material removal. If we can consider the scratching and material removal processes for a single grit indicated on the grinding wheel as a smaller element, then the material removal process could be developed and extended for every engaged abrasive edge in the grinding. In this paper, a new analytical force model for grinding process is developed by modeling abrasive grits and their interaction with the workpiece individually. Grits are examined to determine their geometrical properties and distribution on the grinding wheel. Analytical equations for total normal and tangential force components are established. Especially, the model takes into account the microstructure of the grinding wheel given by the grain geometry and the grain density. Also, the effect of kinematical parameters and process inputs on the forces will be examined. The obtained results showed that the increasing in parameters such as the slope of abrasive grits on the surface of the grinding wheel and the number of active grits on the grinding zone lead to a reduction in forces. The validity of the model can be proved by comparison of experimental results. Modeling forces in the single grit scratch will be a key factor in accurate modeling of the grinding process, and the research findings provide important information for a better understanding of the process.

Experimental Investigation of the Heat Flux Distribution in Grinding of Titanium Alloy

Generally, grinding involves high specific energy, compared to other machining processes. Most of this energy is changed into heat which makes harmful effects on surface quality as well as tool wear. In this respect temperature measurement techniques enhance cutting performance in terms of increasing wheel life and improving the quality of the ground part, especially when grinding temperature sensitive material like γ-TiAl. The distribution of the total grinding heat flux along the grinding zone does not follow a linear form. It increases at the trailing edge with sharp gradients and then varies nearls linearly for the renaibder of the contact length. In this paper a new method to measure relative temperature in the grinding zone is presented. The approach demonstrates a flexible arrangement of the thermocouple in the workpiece to measure at variable depth of cuts. The results of the experiments are further investigated to cover the mentioned complex distribution of the heat flux in the workpiece. With the known relative temperature in the grinding zone and the net spindle power is a simple analytical approach presented to estimate the absolute grinding temperature. It is shown that the measured and the calculated temperature diver up to 600%.

Analysis of the Thermal Impact on Gamma Titanium Aluminide by Grinding with Internal Coolant Supply Based on Experimental Investigation and Transient Thermal Simulation

Gamma titanium aluminide as an intermetallic alloy is considered to be one of the materials which can substitute nickel based super-alloys in high duty applications e.g. in turbines of aircrafts. In this respect the grindability of γ-TiAl alloys is of high importance despite of the restrictions due to the alloy's thermal and metallurgical characteristics. High temperatures in the grinding zone effect the formation of micro cracks during the grinding operation. A more efficient cooling by an internal cooling supply can be seen as a suitable approach to tackle this obstacle. Thus the coolant flow is directly induced into the grinding zone through the abrasive. This kind of lubrication allows the reduction of the flow rate and a more effective cooling of the temperature sensitive materials, respectively. In order to investigate the effects of an internal coolant supply experimental investigations has been performed and the thermal impact on the workpiece has been detected by measurement. A newly designed measuring device based on a thermocouple, which is mounted on a ball screw, enables the automated adjustment in the workpiece according to the actual depth of cut. The results of these investigations are used as boundary conditions for a transient thermal simulation. Based on the finite element model the real grinding zone temperature can be calculated with respect to the influences of the heat transfer rate and the thermal inertia of the thermocouple as well as of the workpiece material

Dry grinding process with workpiece precooling

This paper proposes a workpiece cooling prior to grinding in order to allow a dry processing. Tests and simulation showed good potential. The obtained part quality is good, and there is no thermal damage since there is a higher heat flux from the grinding zone to the workpiece due to the much lower temperature of the last. The process design is a key task for good results and should include a precise determination of the cooling conditions that allow the grinding cycle heating to bring the part temperature close to the environment at the end of spark-out.

Appropriate application of pneumatic barrier for improving grinding performance

High grinding zone temperature is the primary reason behind several grinding defects. To control thermal defects, usually large quantity of grinding fluid is employed. However, much of applied grinding fluid is reported to be wasted because of the development of a stiff air layer surrounding the rotating wheel. In the present experimental work, an indigenously introduced setup utilising a pneumatic barrier is used for controlling the adverse effect of stiff air layer formed around the grinding wheel. Different parameters of the pneumatic barrier setup are optimised by using response surface methodology (RSM). Further, experiments are performed in surface grinding with the provision of pneumatic barrier. It is observed that applying conventional grinding fluid by providing the pneumatic barrier at optimised condition, tangential and normal force components are reduced significantly, and favourable grinding chips and good ground surface is generated in comparison with the conventionally used flood cooling.

Performance evaluation of Ti–6Al–4V grinding using chip formation and coefficient of friction under the influence of nanofluids

Nanofluid, fluid suspensions of nanometer sized particles are revolutionizing the field of heat transfer area. Addition of nano-particles to the base fluid also alters the lubricating properties by reducing the friction. In grinding process, friction between the abrasive grains and the workpiece is a key issue governing the main grinding output. It has a direct influence on grinding force, power, specific energy and wheel wear. Moreover, high friction force increases the heat generation and lead to thermal damage in the surface layer of the ground work. Hence, any effort towards the friction control will enhance the component quality significantly. In this study, nanofluid as metal working fluid (MWF) is made by adding 0.05, 0.1, 0.5 and 1% volume concentration of Al2O3 and CuO nano-particles to the water during the surface grinding of Ti–6Al–4V in minimum quantity lubrication (MQL) mode. Surface integrity of ground surface, morphology of the wheel, and chip formation characteristics are studied using surface profilometer, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and stereo zoom microscopy (SZM). Coefficient of friction was estimated On-Machine using the measured forces. The results showed that the type of nanoparticle and its concentration in base fluid and the MQL flow rate play a significant role in reducing friction. Application of nanofluid leads to the reduction of tangential forces and grinding zone temperature. The cooling effect is also evident from the short C-type chip formation. MQL application with Al2O3 nanofluid helps in effective flushing of chip material from the grinding zone, thereby solving the main problem during the grinding of Ti–6Al–4V.

Shaping the cutting ability of grinding wheels with zone-diversified structure

This article presents the results of experimental tests aimed at determining the influence of shaping the microgeometry of particular functional zones (rough and finish grinding) of the grinding wheel active surface in the dressing cut and what effect this would have on the results of the internal cylindrical grinding process of steel 100Cr6. Single-pass grinding processes and the grinding wheel used in them are described. Grinding wheels with zone-diversified structure, made from abrasive grains along the basis of Al2O3 (white fused alumina 99A and microcrystalline sintered corundum), are characterized, and the construction of a special device for precise shaping of the conic chamfer on the grinding wheel active surface is presented. The experimental test results form the basis for determining the influence of the chief dressing parameters (grinding wheel peripheral speed vsd, dressing axial feed rate vfd) on the selected machined surface roughness parameters ( Ra, Rz, RSm, Rdq), surface bearing ratio and grinding power P in the internal cylindrical traverse grinding process. It was proven that the most advantageous grinding results are obtained when using different dressing parameters for the conic rough grinding zone and the cylindrical finish grinding zone of the grinding wheel. When shaping the grinding wheel conic chamfer, increased values of the dressing feed rate vfd( cone) need to be used in order to reduce the grinding power. The most advantageous parameter values for describing the machined surface roughness were obtained with low values of axial table dressing feed rate vfd( cylinder), providing precise alignment and sharpening of the grinding wheel active surface cylindrical zone.

Advances and patents about grinding equipments with nano-particle jet minimum quantity lubrication.

In recent years, a large number of patents have been devoted to developing minimum quantity lubrication (MQL) grinding techniques that can significantly improve both environmentally conscious and energy saving and costeffective sustainable grinding fluid alternatives. Among them, one patent is about a controllable nano-fluids jet MQL grinding system based on electrostatic atomization. Using the principle of electrostatics, it can achieve the control of droplet transfer by charging the sprayed droplets. This system can improve the uniformity of the droplet spectrum, liquid deposition efficiency and effective utilization of liquid. It can also effectively control the movement patterns of the droplets, thereby reducing the pollution of the environment and providing better health protection for workers. Although researchers accomplished profound and systematic studies on MQL, especially on nano-particles jet MQL. It can solve the shortage of MQL in cooling performance, greatly improve the working environment, save energy and reduce costs to achieve a low-carbon manufacturing. The unique lubricating performance and tribological property of solid nano-particles form nano-particle shearing films at the grinding wheel/workpiece interface, which can enhance the lubricating performance of MQL grinding. Existing studies on MQL grinding equipments, however, cannot meet the needs of the technological development. Therefore, our research provided a general introduction of the latest patients and research progress of nanoparticles jet MQL grinding equipments presented by the research team from Qingdao Technological University.

Analysis and Simulation of Air Flow Field Surrounding Grinding Wheel

In grinding, high specific heat is generated and hence it is very important for the fluid to remove heat from the grinding contact zone to avoid thermal damage to the workpiece surface and/or sub-surface layers. In conventional grinding, a stiff air layer is generated due to the rotation of the porous grinding wheel at high speed. Hence, most of fluid isn’t penetrated into the grinding contact zone because of the stiff air layer around the grinding wheel. To improve grinding fluid cooling effection and avoid thermal damage, it is necessary to analyze the air flow and stiff air layer around the grinding wheel. Based on fluid dynamics and mathematical simulation method, the 3D finite element model of the air flow field around the grinding wheel is developed. The air flow pressure field and flow velocity near the grinding zone are analyzed. In results, the pressure and the velocity of the air flow near the grinding zone increase with the wheel speed increase, and the pressure and the velocity of the air flow near the grinding zone increase with the minimum gap between the grinding wheel and the workpiece reducing. After the air is drived by the grinding wheel into the high pressure area near the grinding zone, the air flows around both sides of the grinding wheel and there are no obvious returning air flow phenomena.

The Study on Optimum Thickness of Thermocouple Used for Measuring the Grinding Temperatures of Brittle Materials

The grinding temperatures were measured with half-cylindrical thermocouple which made by grinding method and measrued with foil thermocouple which made by rolling method respectively when grinding brittle granite with an Al2O3 wheel. Experimental results include average grinding zone temperatures and grains’ temperatures were analysed. The deviation of average grinding zone temperatures measured by them were within 6%. The foil thermocouples do not easily to lap due to the brittleness of the workpiece which usually makes the joint of thermocouples disconnected. But half-cylindrical thermocouples are more convenient to be prepared and be used than foil ones. However, the periodic “flash” impulses which reflect the grains’ temperature measured by half-cylindrical thermocouple were about 51% lower than the others. According to time constant, the thickness of the thermocouple less than 0.007mm is a necessary condition for measure the grains’ temperatures without distortion. The half-cylindrical thermocouple is too thick to have a momentary response time thus makes it out of the measurement accuracy range when it is used to measure the temperature of the grains. Therefore, foil thermocouple has an optimum thickness of 0.007mm is suitable for measuring the grains’ temperature while half-cylindrical thermocouple with average thickness less than 0.12mm is suitable for measuring the average grinding zone temperature.

Hardness control of grind-hardening and finishing grinding by means of area-based specific energy

The grind-hardening process uses the heat generated within the grinding zone in order to produce surface hardening of the workpiece. However, after the process, workpieces present dimensional inaccuracies and poor surface roughness. Thus, a final grinding operation has to be performed. For an industrial implementation of the whole process, two problems need to be solved. On the one hand, on-line control of the hardness penetration depth (HPD) should be achieved. On the other hand, excessive softening of the workpiece has to be avoided during the finishing grinding. This paper, firstly, investigates the feasibility of using the area based grinding energy (Ec″) for the prediction of the HPD. Surface grind-hardening tests carried out on 100Cr6, 42CrMo4 and AISI 1045 steels have shown that, for all the tested parameter sets, a linear correlation exists between Ec″ and HPD. Furthermore, the slope of this linear relationship can be estimated from the chemical composition of the hardened steel based on the equivalent carbon number. On the other hand, the influence of varying wheel dressing conditions on the Ec″–HPD relationship is analysed. Secondly, it has been found that a relationship exists between Ec″ and the surface softening during the finishing grinding operation. This relationship is independent of the grinding parameter combination when the maximum undeformed chip thickness is over a threshold value. Thus, Ec″ is a very appropriate parameter to control both the hardening and the finishing process of grind-hardened workpieces.

Investigation of Grinding Fluid Supply Parameters on Workpiece Surface Integrity

The grinding heat directly affected workpiece surface in the grinding process and it might produce some defects such as crack and burn. Meanwhile wear debris generated in the grinding process could easily embed grinding wheel blowhole and caused clogging and passivation. So it was particular important to avoid defects and improve the grinding workpiece surface integrity effectively. This paper established an incompressible turbulent fluid spray model based on the study of the existing airflow and the grinding fluid distribution in the grinding zone. Then according to different grinding fluid supply parameters established the two-phase gas liquid spray flow model by using CFD(computational fluid dynamics), simulated and calculated the model, compared the mass flow rate of the grinding fluid flow field with different spray distances, heights, speeds and spray angles in the grinding zone and determined the most reasonable spraying jet position. At the last, through researching on the workpiece surface integrity experiment, it provided an experimental basis to determine the most suitable spray jet position and verify the rationality of supply parameters selection.

An Innovative Cooling Method for Grinding Process Based on Heat Pipe Technology

The core idea of the existing cooling methods in grinding process is making a large quantity of coolant into the contact zone. However, the practical quantity of coolant injected in the grinding zone is limited, and the large amount of coolant employed can cause pernicious effect to human health and the environment, and will largely increase the expenses. In order to solve this problem, an environmental friendly idea about enhancing heat transfer in the contact zone based on heat pipe technology is put forward in this paper. The new system, heat pipe grinding wheel (HPGW), based on this high-efficiency cooling technology is developed and its heat transfer principle is illustrated. Eventually grinding experiments with HPGW were carried out to verify the cooling effect by comparing with non-HPGW in grinding plain carbon steel. Results show that using HPGW can significantly reduce the grinding temperature with no coolant.

Effect of parameters on grinding forces and energy while grinding Al (A356)/SiC composites

Grinding processes require a high energy input per unit volume of material removed, which is converted to heat at the grinding zone, resulting in increased force and wear. In the present study, the influence of grinding parameters like work speed and depth of cut on grinding forces and energy was studied. An attempt has been made to study the forces and energy involved while grinding aluminium alloy (A356)/silicon carbide (SiC) composite material with different grinding wheels. Experiments were carried out on a surface grinding machine. Three different types of wheels like SiC, cubic boron nitride (CBN) and diamond wheels were used. The grinding forces increased with increase in depth of cut and work speed. SiC exhibited high grinding force compared to the CBN wheel. In the case of the diamond wheel, it was even less. The specific grinding energy was highest for the diamond wheel followed by CBN and SiC wheels. The specific grinding energy decreased with increase in depth of cut and work speed.

Optimizing the Dry Grinding Process on the Basis of Bond Materials

In order to decrease the negative environmental impacts of the cutting fluids (for example, disposal of grinding sludge) and also to reduce the manufacturing costs and the required space for the machines the dry grinding can be a conceivable alternative for the conventional grinding processes. Nevertheless, dry grinding has not been widely introduced into industry because of the high temperature generated in the grinding zone and difficulties of heat transfer without coolants. Selection of the proper grinding wheel bonds, grit sizes and concentration has significant effect on the grinding performance and the generated heat in the contact zone. This paper addresses the effects of the grinding wheel bond and the concentration on the dry grinding process efficiency through comparing the results of the carried out experiments with three resin bonded cBN-cup-wheels, each consisting different bond components. For this purpose, surface roughness and thermal damages during dry and wet grinding (utilizing grinding oil) by three different resin bonds were measured. The results show almost identical surface roughness values for dry and wet grinding. Furthermore, using the resin-kryolith-graphite bonded wheel leads to a reduction in thermal damages on the workpiece. Through different experiments, it was shown that the different bonds, used in this study, have significant influence on the chip loading of the grinding wheels. This is contributed to the different chip formation mechanisms and induced grinding temperatures when grinding by the different wheel bonds.

Modeling and Simulation of the Single Grain Grinding Process of the Nano-Particle Jet Flow of Minimal Quantity Lubrication

Along with strengthening of people’s environmental protection awareness, the MQL technology has been used in grinding, but its limited cooling effect cannot satisfy the requirement of heat transfer enhancement in the grinding area. The new technology of nano-particle jet flow of MQL can effectively solve the heat transfer in the grinding zone and enhance the lubrication characteristics as well. This paper studies mainly the grinding process of the single grain under the condition of the nano-particle jet flow of MQL by establishing the kinematics model, elastic deformation model and plastic accumulation model of the single grain and simulating the value of the surface topography of the single-grain grinding workpiece with quenching 45# as the research subject. The results show that the grinding depth will exert a certain influence over the material deformation on the surface of the workpiece, the pile height and the length of the grinding crack. The yielding amount of the grain center δc and the elastic recovery amount of the materials on the surface of the workpiece δw increases with the grinding depth. The height of the material accumulation increases with the grinding depth. Furthermore, the change amplitude is large and the change gradient decreases correspondingly. The length of the grinding crack increases with the grinding depth, and the grinding depth and the height of the material accumulation have an approximate linear relationship.

Influence of Using Rexine-Pasted Wheel or Pneumatic Barrier on Air Layer Pressure around a Grinding Wheel

In grinding, high heat is generated at the grinding zone per unit volume of material removed. To control this temperature, generally, grinding fluid is employed. Due to formation of a stiff air layer around the grinding wheel, grinding fluid cannot enter easily inside the grinding zone. In this experimental work, formation of air layer around a rotating grinding wheel has been investigated to observe variation of air layer pressure around the wheel periphery under different wheel speeds. Bare wheel, rexine-pasted wheel and bare wheel with pneumatic barrier set up have been employed to find out their effect on formation of air layer. Significantly less air layer pressure is noted around the wheel with both faces rexine-pasted, and using pneumatic barrier set up. In aggregate, about 50% reduction in the air layer pressure is achieved in the pneumatic barrier set up compared to that with the rexine-pasted wheel. Pneumatic barrier set up is thus quite effective to facilitate grinding fluid reach deep inside the grinding zone.

Structure and Fluid Transportation Performance of Faults in the Changxing-Feixianguan Formation, Xuanhan County, Northeastern Sichuan Basin

On the basis of field observations, microscopic thin-sections and laboratory data analysis of ten faults in Xuanhan County area, northeastern Sichuan Basin, central China, the internal and megascopic structures and tectonite development characteristics are mainly controlled by the geomechanical quality in brittle formation of the Changxing-Feixianguan Formation. The fluid transportation performance difference between the faults formed by different geomechanics or different structural parts of the same fault are controlled by the megascopic structure and tectonite development characteristics. For instance, the extension fault structure consists of a tectonite breccia zone and an extension fracture zone. Good fluid transportation performance zones are the extension fracture zone adjacent to the tectonite breccia zone and the breccia zone formed at the early evolutionary stage. The typical compression fault structure consists of a boulder-clay zone or zones of grinding gravel rock, compression foliation, tectonite lens, and dense fracture development. The dense fracture development zone is the best fluid transporting area at a certain scale of the compression fault, and then the lens, grinding gravel rock zone and compression foliation zones are the worst areas for hydrocarbon migration. The typical tensor-shear fault with a certain scale can be divided into boulder-clay or grinding gravel rock zones of the fault, as well as a pinnate fractures zone and a derivative fractures zone. The grinding gravel rock zone is the worst one for fluid transportation. Because of the fracture mesh connectivity and better penetration ability, the pinnate fractures zone provides the dominant pathway for hydrocarbon vertical migration along the tensor-shear fault.