Internal Cylindrical Grinding Process Research Articles

Simulation Studies on Centrifugal MQL-CCA Method of Applying Coolant during Internal Cylindrical Grinding Process.

This paper describes simulation studies regarding the application of the centrifugal minimum quantity lubrication (MQL) method simultaneously with the delivery of a compressed cooled air (CCA) stream in the internal cylindrical grinding process. The idea of a new hybrid cooling and lubrication method connecting centrifugal (through a grinding wheel) lubrication by MQL with a CCA stream is described. The methodology of computational fluid dynamics (CFD) simulation studies, as well as the results of numerical simulations, are presented in detail. The aim of the simulations was to determine the most favourable geometrical and kinematic parameters of the system in the context of air-oil aerosol and CCA flow, as well as heat exchange. In the simulation, the variables were the grinding arbor geometrical parameters, the angle of CCA supply line outlets, and the grinding wheel and workpiece peripheral speed. As a result of the simulation studies, the most favourable geometrical parameters were designated, determining the orientation of the ends of the two CCA supply line outlets before and after the grinding zone, the number of openings in the drilled-out grinding arbor, and the influence of the grinding speed on the parameters of the coolant flow and temperature of objects in the grinding zone. In addition, the results of simulation tests made it possible to visualise the velocity vectors of the two-phase coolant flow in a complex system of air-oil aerosol delivery centrifugally through an open structure of a very fast rotating porous layer (grinding wheel), with an additional supply of CCA using an external cold air gun (CAG).

Experimental Studies on the Centrifugal MQL-CCA Method of Applying Coolant during the Internal Cylindrical Grinding Process.

This paper presents the results of experimental research concerning the possibility of supporting the cooling function during internal cylindrical grinding using the minimum quantity lubrication (MQL) method by additional delivery of a compressed cooled air (CCL) stream. The article presents a description of a hybrid method of cooling and lubrication of the grinding zone integrating centrifugal (through a grinding wheel) lubrication with the minimum quantity of lubricant and cooling with a compressed cooled air stream generated by a cold air gun (CAG). The methodology and results of experimental studies are also presented in detail, with the aim of determining the influence of the application of the hybrid method of cooling and lubrication of the machining zone on the course and results of the internal cylindrical grinding process of 100Cr6 steel in comparison with other methods of cooling and lubrication, as well as compared with dry grinding. The research results obtained using the described hybrid method of cooling and lubrication of the grinding zone are related to the results obtained under the conditions of centrifugal MQL method, cooling with a stream of CCA, cooling and lubrication with a stream of oil-in-water emulsion delivered using the flood method, and dry grinding. The efficiency of the grinding process is evaluated (based on the average grinding power Pav, grinding wheel volumetric wear Vs, material removal Vw, and grinding ratio G), along with the thermal conditions of the process (based on the analysis of thermograms recorded by infrared thermal imaging method), the textures of machined surfaces (based on microtopography measured by contact profilometry), the state of residual stress in the surface layers of workpieces (determined by X-ray diffraction method), and the state of the grinding wheels’ active surfaces after grinding (based on microtopography measured by laser triangulation and images recorded with a digital measuring microscope). The obtained results of the analyses show that the application of the hybrid method allows for the longest wheel life among the five compared grinding methods, which is about 2.7 times the life of grinding wheels working under the flood cooling and centrifugal MQL methods, and as much as 8 times the life of grinding wheels working under the conditions of CCA only and dry grinding.

Internal Cylindrical Grinding Process of INCONEL® Alloy 600 Using Grinding Wheels with Sol-Gel Alumina and a Synthetic Organosilicon Polymer-Based Impregnate.

The development of modern jet engines would not be possible without dynamically developed nickel–chromium-based superalloys, such as INCONEL® The effective abrasive machining of above materials brings with it many problems and challenges, such as intensive clogging of the grinding wheel active surface (GWAS). This extremely unfavorable effect causes a reduction in the cutting ability of the abrasive tool as well as increase to grinding forces and friction in the whole process. The authors of this work demonstrate that introduction of a synthetic organosilicon polymer-based impregnating substance to the GWAS can significantly improve the effects of carrying out the abrasive process of hard-to-cut materials. Experimental studies were carried out on a set of a silicon-treated small-sized sol–gel alumina 1-35×10×10-SG/F46G10VTO grinding wheels. The set contained abrasive tools after the internal cylindrical grinding process of INCONEL® alloy 600 rings and reference abrasive tools. The condition of the GWAS after the impregnation process was studied, including imaging and measurements of its microgeometry using confocal laser scanning microscopy (CLSM), microanalysis of its elemental distribution using energy dispersive X-ray fluorescence (EDXRF), and the influence of impregnation process on the grinding temperature using infrared thermography (IRT). The obtained results confirmed the correctness of introduction of the impregnating substance into the grinding wheel structure, and it was possible to obtain an abrasive tool with a recommended characteristic. The main favorable features of treated grinding wheel concerning the reduction of adhesion between the GWAS and grinding process products (limitation of the clogging phenomenon) as well as reduction of friction in the grinding process, which has a positive effect on the thermal conditions in the grinding zone.

Experimental Studies on MoS2-Treated Grinding Wheel Active Surface Condition after High-Efficiency Internal Cylindrical Grinding Process of INCONEL® Alloy 718.

This work demonstrates that molybdenum disulfide can be successfully used as an impregnating substance that is introduced in the abrasive tool structure for improving its cutting properties and favorably affecting the effects of the abrasive process. For the experimental studies, a set of MoS2-treated small-sized grinding wheels with a technical designation 1-35×10×10×109A5X60L10VE0 PI-50 before and after the reciprocating internal cylindrical grinding process of rings made from INCONEL® alloy 718 was prepared. The condition of grinding wheel active surface was analyzed using an advanced observation measurement system based on stylus/optical profilometry, as well as confocal and electron microscopy. The obtained results confirmed the correctness of introduction of the impregnating substance into the grinding wheel structure, and it was possible to obtain an abrasive tool with a given characteristic.

Quality evaluation of internal cylindrical grinding process with multiple quality characteristics for gear products

Gears are among the most crucial components in the transmission systems of machine tools. Gear manufacturing includes a number of processing procedures. The grinding process is an important procedure involving high precision and fairly small grinding surfaces. For this reason, this study aimed at developing a quality assessment model for the internal cylindrical grinding process of gears. The Six Sigma quality indices (SSQIs) were used to directly assess the quality of the internal cylindrical grinding process due to their ability to directly reflect quality level and process yield. Since the process may include nominal-the-best (NTB), larger-the-better (LTB) and smaller-the-better (STB) quality characteristics, so we used the variable transformation method to normalise the specifications of each quality characteristic for the convenient and effective management and analysis of process performance for multiple quality characteristics. We then constructed a multi-characteristic process quality analysis chart (MPQAC) to simultaneously assess the quality levels of various quality characteristics. Furthermore, the MPQAC can provide references for process improvement. This ensures the quality of internal cylindrical grinding and enhances the quality of gear and machine tool products. Finally, a real-world application and numerical experiments demonstrate the effectiveness and practical applicability of the proposed method.

Multi-objective Optimization of Dressing Parameters of Internal Cylindrical Grinding for 9CrSi Aloy Steel Using Taguchi Method and Grey Relational Analysis

Abstract This study has been done to optimize the dressing parameters in internal cylindrical grinding process for 9CrSi tool steel to minimize surface roughness and maximize material removal rate (MRR) using Taguchi method and Grey Relational Analysis (GRA). This multi-objective optimization is obtained by optimizing five three-level and one six-level dressing parameters in eightteen experiments based on an orthogonal array L18(35×16). The results show that the optimal dressing parameters to obtain the minimal roughness average and maximal MRR are the coarse dressing depth of 0.02 mm, the coarse dressing times of 1 time, the fine dressing depth of 0.005 mm, the fine dressing times of 3 times, the non-feeding dressing of 5 times and the dressing feed rate of 1.4 m/min, respectively. The differences of the roughness average and MRR from the experiments and the predict model are small. Thus, the proposed method has been proven and it can be further applied in other studies.

Estimation of the active grains load in different kinematic variations of the internal cylindrical grinding process

This article presents indexes referred to in literature and used when describing the working conditions of abrasive grains in internal cylindrical grinding processes: equivalent chip thickness heq, material removal rate Qw and the proper grinding material removal rate Q′w, as well as the average cross-section of the cut layer AD. From consideration of these indexes, it became apparent that there was a need to develop a new index which would synthetically combine all of the key grinding parameters, as well as the geometric structure of the grinding wheel active surface. A new index was defined, marked as SIQ (synthetic index of single abrasive grain material removal rate), in which the material removal rate Qw was related to the number of active grains on the grinding wheel surface and the converse speed ratio q = vs/vw. The work presents example calculations and charts detailing the changes within the SIQ index values for the following kinematic variations of internal cylindrical grinding processes: traverse grinding, reciprocating grinding, plunge grinding and plunge grinding with grinding wheel oscillations. The work includes an analytical and experimental example of how the SIQ index can be used to determine the grinding parameters within which the grain load remained at a similar level in various kinematic variations of the grinding process. The analyses performed show that application of the proposed index allows for: a comparison of various kinematic variations of internal cylindrical grinding, the selection of machining parameters in instances where the grinding kinematics may need to be altered, the necessity for maintaining the active grains load at the same level, determination of the changes of the active cutting vertexes load during the functioning of select machining parameters, and the comparison of grinding wheels with a variety of active surface geometric structures.

The effect of the grinding wheel modification on the state of the workpiece surface layer after internal cylindrical grinding of steel C45

Internal cylindrical grinding is one of the most difficult grinding processes due to the very long zone of contact between the grinding wheel and the workpiece surface. Such conditions limit delivery of the grinding fluid into the grinding zone, as well as impeding the removal of chips from it. As a result, during the internal cylindrical grinding process, difficult thermal conditions occur in the machining zone which finally could lead to grinding defects. One of the most efficient and cost-effective ways of improving the grinding stability and repeatability is modifying the grinding wheel structure. As such, modifications usually do not require interfering with the construction of the grinding machine or its equipment, they are universal and, possibly, widely applicable. This article presents a modified grinding wheel with helical grooves shaped on its active surface. Such modification was developed to reduce the thermal load of the workpiece surface and the occurrence of thermal defects. The effectiveness of the proposed grinding wheel modification was examined experimentally in the reciprocal circumferential internal cylindrical grinding process of 45C steel. The goal of the described tests was to determine the influence of the suggested grinding wheel modification on the condition of the workpiece surface layer (the surface roughness and residual stresses). The test results obtained indicated that application of the modified grinding wheel has a positive influence on the residual stresses in the workpiece surface layer, resulting in better delivery of the grinding fluid into the area of contact between the wheel and the machined material. Moreover, a decrease of the Ra parameter value by approximately 7–19%, as compared to the results of the process carried out with the (unmodified) reference grinding wheel was indicated.

Potential for improving efficiency of the internal cylindrical grinding process by modification of the grinding wheel structure—Part II: Grinding wheels made of superabrasive grains

This article offers an overview of 11 grinding wheel construction modifications used in the peripheral grinding of flat, shaped, internal, and external cylindrical surfaces, when grinding wheels made of superabrasive grains are used (natural and synthetic diamonds, as well as mono- and microcrystalline cubic boron nitride). The text contains characteristics of grinding wheels with: bubble corundum grains, glass-crystalline bond, conic chamfer, zones of different diameters, a centrifugal provision of the coolant into the grinding zone, aggregate grains, zone-diversified structure, as well as impregnated (self-lubricating), multiporous, segment and “intelligent” grinding wheels. Each of the presented structural modifications were described by giving construction scheme, used abrasive grains, range of applications, advantages as well as disadvantages. Modifications of the grinding wheel construction allow for effective improvement of both the conditions and the results of the grinding process. A wide range of the known modifications allow for their proper selection depending on the required criteria of effective evaluation and taking into account the specific characteristics of superabrasive grains. As a result, it is possible to obtain positive influence on a number of technological factors of the grinding process. The described modifications of the grinding wheel structure can be also an inspiration and the basis for creating new solutions in this field.

Potential for improving efficiency of the internal cylindrical grinding process by modification of the grinding wheel structure—Part I: Grinding wheels made of conventional abrasive grains

This article offers an overview of 14 grinding wheel construction modifications used in the peripheral grinding of flat-shaped internal and external cylindrical surfaces, when grinding wheels made of conventional abrasive grains are used (Al2O3, sol-gel alumina, SiC, etc.). The text contains characteristics of grinding wheels with mixed grains, glass-crystalline bond, a centrifugal provision of the coolant into the grinding zone, aggregate grains, zones of different diameters, radial rough grinding zone, extended finish grinding segments, active surface macro- and micro-discontinuities, as well as multiporous, impregnated (self-lubricating), sandwich, sectional and segment grinding wheels. Each of the presented structural modifications was described by giving construction scheme, used abrasive grains, range of applications, advantages as well as disadvantages. Modifications of the grinding wheel construction allow for effective improvement of both the conditions and the results of the grinding process. A wide range of the known modifications allows for their proper selection depending on the required criteria of effective evaluation and taking into account the specific characteristics of conventional abrasive grains. As a result, it is possible to obtain positive influence on a number of technological factors of the grinding process. The described modifications of the grinding wheel structure can be also an inspiration and the basis for creating new solutions in this field.

A multi-criteria methodology for effectiveness assessment of internal cylindrical grinding process with modified grinding wheels

One of the possible engineering solutions in developing grinding technology is modifying the structure of the grinding wheels. This solution is applicable and feasible for industrial conditions as it does not require interfering with the construction of the grinding machine. This article presents an important aspect of the development of new grinding wheels, which uses multiple criteria to evaluate their effectiveness in the grinding process. An analysis of previously used methods of grinding effectiveness evaluation was performed. A number of criteria for evaluating the most important expenditures and effects of these processes were highlighted. Next, a comparative evaluation of effectiveness of the six suggested grinding wheel modifications with sintered microcrystalline corundum grains and ceramic bond was performed. These grinding wheels were characterized by the following structural modifications: zone-diversified structure, modification of the bond microstructure, microdiscontinuities of the grinding wheel active surface, sandwich structure with a centrifugal system for provision of the coolant into the grinding zone as well as impregnated grinding wheel. Additionally, a grinding wheel whose structure was composed of a number of modifications was considered. The essential advantages and disadvantages of the structural types of small-sized grinding wheels for peripheral grinding were determined. The results of the analysis of the effectiveness of the suggested solutions showed that it is possible to adjust the grinding wheel construction to the expected results of the given grinding operation as well as the technological conditions. It is also possible to combine these modifications in order to obtain additional synergetic effect of their positive influence on the grinding process.

Building a Dynamic Model of the Internal Cylindrical Grinding Process

The accounting of change and assessment of impact of the revolting factors on the technological process demand making a mathematical description. It is necessary to add dynamic models of the technological process and the corresponding mathematical models of the influencing factors to such description. The ratios allowing estimation of form deviations upon studying of dynamic properties in a static form have been received. For more detailed analysis of communication between basic elements of the technological system, the cutting zone with the actual cutting depth is separately determined. The dependencies allowing to characterize the technological system condition in relation to the actual cutting depth are received. The offered ratios have allowed to characterize the power balance and can be used for the analysis of dynamic properties and upon program corrections for CNC machines.

Morphology of Near- and Semispherical Melted Chips after the Grinding Processes Using Sol-Gel Abrasives Based on SEM-Imaging and Analysis

Selected issues related to SEM-imaging and image analysis of spherical melted chips formed during the grinding process are presented and discussed. The general characteristics of this specific group of machining products are given. Chip formation phenomena, as well as their overall morphology, are presented using selected examples of near- and semispherical melted chips occurring singly or concentrated in clusters on the grinding wheel surface after the machining process. Observation of the spherical melted chips and acquisition of their images were carried out for grinding wheel active surfaces with microcrystalline sintered corundum abrasive grains SG™after the internal cylindrical grinding process of a 100Cr6 steel and Titanium Grade 2® alloy by use of a scanning electron microscope, JEOL JSM-5500LV. Analysis of the obtained SEM micrographs was carried out by Image-Pro® Plus 5.0 software to determine the selected geometrical parameters describing the morphological features of the assessed chips.

Small-dimensional sandwich grinding wheels with a centrifugal coolant provision system for traverse internal cylindrical grinding of steel 100Cr6

The following article characterizes the problems occurring in the traverse internal cylindrical grinding process. It has been concluded that an effective way of influencing the quality and stability of the grinding process and repeatability of its results is through controlling the machining allowance and method of coolant provision. This issue is of exceptional importance from the perspective of costs related to buying, using and maintaining coolants, as well as the impact the disposal of these fluids – classified as hazardous waste – has on the environment. The construction of a small-dimensional sandwich grinding wheel with a centrifugal coolant provision system was described against the background of known methods of limiting grinding fluid flow rate, usually involving its effective provision into the machining zone. Results of simulation analyses regarding the influence of grinding speed and diameter, as well as the number of channels on the speed of the coolant outflow through holes in the grinding wheel arbor were presented. Taking into consideration the results of simulation, a prototype of the sandwich grinding wheel was made and a number of experimental tests on the process of internal cylindrical grinding of steel 100Cr6, with 62 ± 2 HRC hardness, were carried out. The experiment results obtained were then compared with the results obtained when using the flood cooling method. The test results showed that application of the sandwich grinding wheel allows for a fivefold limiting of the grinding fluid flow rate, from 5.0 to 1.0 l/min, with simultaneous limitation of the machined surface roughness and without considerable influence on the grinding power. The last part of the article also presents an improved construction solution which facilitates centrifugal coolant provision.

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.

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.

Wear phenomena of grinding wheels with sol–gel alumina abrasive grains and glass–ceramic vitrified bond during internal cylindrical traverse grinding of 100Cr6 steel

This article presents the results from a traverse internal cylindrical grinding process conducted using grinding wheels with sol–gel alumina abrasive grains and varying volumes of glass–ceramic vitrified bond. The aim was to determine how changing the bond volume within the range of V b = 11.5–14.5 % influenced the wear phenomenon of the microcrystalline sintered corundum abrasive grains and the ceramic bond bridges with glass-crystalline structure. The paper presents grinding wheels with conic chamfer and the most important wear phenomena of the grinding wheel components occurring in the area of contact between the tool and the workpiece material. The work includes the methodology of the experimental tests on the traverse internal cylindrical grinding of bearing rings made from steel 100Cr6 (62 ± 2 HRC). A wide range of test results were analyzed, including machined surface roughness parameters (Ra, Rz, Sm, Δa), grinding power, grinding wheel volumetric wear V s , material removal V w , G-ratio, root-mean–square roundness deviation from mean circle (Δ, rms), grinding wheel edge wear, grinding wheel microtopography parameters (Sa, St, Sdr, Sds), and SEM images of the wear marks on the grinding wheel active surface. The dominant wear phenomena of the grinding wheels with conic chamfer and the influence of the bond volume share on its intensity were experimentally determined. The results show that the decrease in bond volume from V b = 14.5 to 11.5 % increases the grinding wheel life by twofold. This was due to a decrease in abrasive wear and plastic flow phenomena and to a greater fracture wear (mostly fatigue and thermal-fatigue). These events led to a periodic shedding of the oxide layer and the plastically deformed grain layer and also revealed the crystals’ sharp edges, located below the plastically deformed surface layer.

Regeneration of grinding wheel active surface using high-pressure hydro-jet

The possibility of applying a high-pressure hydro-jet for renewal of the grinding wheel cutting ability was presented. This work was conducted in the internal cylindrical grinding process of the Titanium Grade 2® alloy, which belongs to the group of hard-to-cut materials. The analysis shows that the impact on the erosion effectiveness of the grinding wheel active surface (GWAS) depends upon the hydro-jet inclination angle and working pressure. Experimental results reveal that application of hydro-jet working pressure of 25 MPa allows for effective cleansing of the grinding wheel surface. Depending on the initial GWAS condition and the level of its smearing with chips of machined material, it is possible to increase the number of grinding wheel unevenness apexes by as much as 4.5 times.

The effect upon the grinding wheel active surface condition when impregnating with non-metallic elements during internal cylindrical grinding of titanium

The following article describes the results of experimental works connected with the possibility of limiting the adhesion of grinding products to the grinding wheel active surface, as a result of introducing an impregnate, in the form of sulphur or allotropic carbon variants, into the grinding wheel volume. The methods of sulphurizing, as well as impregnation with graphite and amorphous carbon, were described. The results of experimental tests conducted in the internal cylindrical reciprocal grinding process in Titanium Grade 2® alloy, using impregnated grinding wheels, were presented and compared to the results of grinding with a non-impregnated grinding wheel. What was also determined was the influence of the type of impregnate on the grinding wheel active surface stereometric features after the grinding process, especially the degree to which smearing with machined material chips occurred. Moreover, the influence of impregnation on the machined surface roughness was also estimated. The results of the conducted experiments indicate that application of the impregnate, in the form of graphite, allowed for a 10-fold reduction in the number of smeared areas in comparison with the non-impregnated grinding wheel.

Stepwise approach to reduce the costs and environmental impacts of grinding processes

Grinding is a common finishing process to meet specific technological requirements; however, it is energy, resource and time consuming. Thus, the improvement of grinding processes should not only consider the technological requirements but also environmental and economic impacts. There are a number of factors involved in grinding processes. Besides the process parameters and workpiece properties, there are three enabling factors for improvement opportunities, such as tool, cutting fluid and machine tool. However, in practice, not all factors can be changed or modified easily at the same time. To support process improvement, this paper proposes a stepwise approach to compare alternative enabling factors in conjunction with the process parameters in order to reduce the costs and environmental impacts of a grinding process under consideration of technological requirements. The proposed approach is demonstrated by means of an internal cylindrical grinding process and applications of different tools, cutting fluid and machine tools.