Creep Feed Grinding Research Articles

Creep feed grinding mechanism from grinding forces acted on single-grain cutting edge

Creep feed grinding mechanism from grinding forces acted on single-grain cutting edge

Surface Integrity Study of Creep-Feed Grinding

Surface Integrity Study of Creep-Feed Grinding

Tool wear behavior of vitrified microcrystalline alumina wheels in creep feed profile grinding of turbine blade root of single crystal nickel-based superalloy

Different aspects on the tool wear behavior of profiled vitrified microcrystalline alumina wheels during creep feed grinding of Ni alloy blade root were investigated. Experimental results indicate that the wheel peak regions had the higher wear values than the wheel valley regions by around 21.7%, 42.8%, 34.5%, in terms of the profile heights, circle radii and angles respectively. Furthermore, the wear flats, workpiece material adhesion, and the fractures of grains and bond bridges occurred in the wheel peak regions; while in the wheel valley regions, heavy wheel clogging, fractures of grains, and workpiece material adhesion were produced. Based on the experimental results, an analytical model with the average error of 17.3% to predict the wheel profile wear was finally developed.

Comparison on grindability and surface integrity in creep feed grinding of GH4169, K403, DZ408 and DD6 nickel-based superalloys

Comparative study was conducted on the grindability of wrought GH4169, equiaxial cast K403, directionally solidified cast DZ408 and single crystal DD6 superalloys by using the brown alumina wheels during the creep feed grinding process with regard to the grinding force, grinding ratio, wheel wear and surface integrity. The grinding forces were found to increase in the following order: DD6, GH4169, K403 and DZ408; and DD6 alloy had the largest grinding ratio, followed by GH4169, K403 and DZ408. In addition, the workpiece material adhesion and grain wear flats were found to be the main pattern of wheel wear in the grinding of DZ408, K403 and GH4169 alloys, while it was the wheel clogging for DD6 alloy. Irrespective of the workpiece material, the microhardness alternation of subsurface induced by thermal effect dominated over the mechanical effect with the increasing material removal rate (up to 6 mm3/(mm s)) and the softened level was 10–16.5 % to a depth of around 40 μm in this study. The surface defects, the highly deformed subsurface and the generation of micro cracks within the workpiece were found to be the main types of damage induced by the grinding operation. These results can provide insights into the effect of workpiece material on the grindability of different nickel-based superalloys in the investigation.

Determining the conditions for decreasing cutting force and temperature during machining

The theoretical approach to calculating and controlling the force and temperature parameters of edge cutting and abrasive machining processes taking into account the provision of the minimum possible power consumption of the cutting process is given. The conditions for reducing cutting force and temperature and improving the quality and rate of grinding and edge cutting machining are theoretically determined. They consist mainly in reducing the relative shear angle of the machined material and, accordingly, power consumption by increasing the cutting capacity of the tool. It is analytically found that in grinding, cutting force and temperature are greater than in edge cutting machining due to the intense friction of the grinding wheel bond with the machined material and the presence of negative rake angles of cutting grains. It is shown that cutting temperature during grinding can be reduced using the multipass grinding pattern, as well as patterns of high-velocity creep-feed wheel-face and double-disc grinding. On this basis, the approach to creating technologies of effective high-velocity defect-free edge cutting and abrasive machining of machine parts and carbide cutting tools is developed. The developed technology of form grinding on the modern HOFLER RAPID 1250 gear grinding machine using a special highly porous form abrasive wheel tapered on both sides received practical application. This wheel has a high cutting capacity in conditions of high-velocity creep-feed grinding. Compared to the conventional method of gear grinding by the generating process, carried out under conditions of multipass grinding, this allowed increasing machining rate up to 5 times. The technology of high-velocity creep-feed external grinding of multipoint carbide cutting tools (milling cutters, reamers) with high-strength metal-bonded diamond wheels using the electrical discharge dressing method is developed. This made it possible to increase the rate by 2–3 times and provide high-quality defect-free machining of carbide tools

On the temperature field in the creep feed grinding of turbine blade root: Simulation and experiments

Although there have been many theoretical, numerical and experimental studies focusing on grinding temperature, very few of them investigated the temperature domain when performing profile grinding of free-form surfaces, where excessive heat can be considered as the key issue due to the long and complex contact zone. In this study, the finite element (FE) based thermal model of the Creep Feed Grinding (CFG) process of Inconel 718 turbine blade root was established in terms of energy partition, material properties, geometry, and thermal boundary. The validation experiments aided with the imbedded thermocouples showed the reasonable match with the experimental results where the average difference was of about 20% proved the simulation feasibility and accuracy. The effects of the blade root profiling and root geometry on the grinding temperature were discussed based on the validated FE model. Considering the research gaps mentioned above, this work is not only expected to be meaningful to deepen the understandings of the temperature field distribution in the CFG of turbine blade root, but also helpful to provide industry guidance to optimize the process physics in precision machining of high-valued parts with complex profiles.

Effect of the grit shape on the performance of vitrified-bonded CBN grinding wheel

Abstract This paper deals with the effect of the CBN grit shape on the grindability of a low alloy chrome steel, 100Cr6. Firstly, a simple wheel-workpiece interaction model is introduced to investigate the grinding response. The formulation considers the global grinding forces, which embodies all the properties of the wheel acting at the interface. The use of this approach eliminates the need to consider the interaction of each individual grit with the workpiece during the grinding process. Next, a series of tailored grinding tests conducted with a creep-feed grinding machine are used to evaluate the grinding performance and the wheel wear. The results have shown that the specific grinding energy ( u e ) is affected by the CBN grit shape, and the wheel wear is proportional to the ratio of the CBN shape factor (Aspect Ratio) and the overall bearing surface of the wheel-workpiece contact area ( a f ).

ТЕХНИКО-ЭКОНОМИЧЕСКОЕ ОБОСНОВАНИЕ ЭФФЕКТИВНОСТИ ПРИМЕНЕНИЯ ПЛАНЕТАРНЫХ ШЛИФОВАЛЬНЫХ ГОЛОВОК

The development of aviation technology is based on the introduction of new progressive technologies, the use of new materials, the improvement of technological equipment and tools. Improving aircraft engines often leads to greater use of wear-resistant, heat-resistant, heat-resistant materials based on nickel and titanium, which are characterized by low machinability. Blade processing of such alloys faces many difficulties: increased equipment wear, increased machine setup time for the operation, high cutting forces, increased wear of the cutting tool, increased processing time, etc. All this harms productivity, an increase in production time and a decrease in economic efficiency. The use of the operation of creep feed grinding instead of blade milling operations, pulling, planning and abrasive operations (pre-grinding, final grinding) reduces the time to manufacture parts while maintaining its quality and accuracy. The study of the technical and economic aspect of the proposed technology of creep feed grinding instead of preliminary and final grinding operations is of interest. The paper compares two methods of abrasive machining: traditional grinding and creep feed grinding on the SPD-30B surface grinder from Jotes (Poland) with a planetary grinding head (PGH) installed on its spindle. The study was conducted when grinding the castle part of turbine blades. The removable allowance was 3.8 mm. The processing according to the traditional grinding scheme took place in 10 passes, while the processing time was about three and a half minutes. The processing under the scheme of creep feed grinding with the use of PGH for 4 passes took about a minute of machine time. It should be noted a significant increase in productivity at the first transition when removing an allowance of 3.5 mm in the mode of deep grinding compared to traditional grinding 2.1 times. On the second and third transitions, the performance of both methods is virtually the same.

Study on material removal mechanism of electrochemical deep grinding

Deep grinding, such as creep-feed grinding and high efficiency deep grinding, offers the possibility of high process efficiency. However, deep grinding is also suffering from grinding heat and grinding wheel wear, resulting in serious surface damage and precision error. Hybrid machining process is generally regarded as effective way to improve the machining performances. Electrochemical machining (ECM) is an anodic electrochemical dissolution process that can effectively remove materials without limitations in terms of the mechanical properties of the alloys. Therefore, this paper attempts to combine deep grinding with ECM process, which can be named electrochemical deep grinding (ECDG). During ECDG process, mechanical grinding and ECM process are simultaneously applied on the anode workpiece. With the aid of high-speed ECM process, the cut-depth is greatly increased without damaging the workpiece. The feed rate and machining stability are also further improved by scraping the electrolyte product and insoluble components. The removal mechanism of anode material during ECDG process was studied through experiments in detail. Based the detailed analysis of material removal phenomenon, a qualitative model of material removal mechanism of ECDG was established. This research provides valuable insights into the material removal mechanism and the dependence of MRR and surface quality on machining conditions in the hybrid process of ECM and deep grinding.

Comparative investigation on wear behavior of brown alumina and microcrystalline alumina abrasive wheels during creep feed grinding of different nickel-based superalloys

This study investigates the comparative wear behavior of brown alumina (BA) and microcrystalline alumina (MA) alumina abrasive wheels and its effect on the creep feed ground surface of different nickel-based superalloys, such as wrought alloy GH4169, directional solidified alloy DZ408 and single crystal solidified alloy DD6. The abrasive wheel wear topography was characterized and an analytical model was developed to evaluate the abrasive wheel wear comprehensively. Finally, the effects of tool wear on the grinding performance and ground surface were discussed. Results obtained indicate that, compared with BA abrasive wheel, the MA wheel performed better in terms of the grinding ratio and tool wear behavior. Strong adhesion wear and attritious wear of the abrasive wheels were generated during grinding of GH4169 and DZ408 alloys, while great wheel clogging occurred during grinding of DD6 alloy. Moreover, DZ408 alloy produced the most severe tool wear and largest grinding forces, followed by GH4169 and DD6 alloys. The defects pattern of ground surface with BA wheel was unparallel to the grinding direction due to the grain dislodging and fracture; however, when grinding with MA wheel, groove defects were created along the grinding direction due to high ductility and hardness of grains.

Experimental studies of the grinding process by planetary grinding head

The object of research is the process of creep feed grinding of parts of aircraft engines with hard-to-machine materials. In the aviation industry from such materials (steel 4Х5МФ1С, ХН53КВМТЮБ, etc.) blades and disks of turbines, segments of nozzle apparatuses, sectors of input guide vanes, plungers, pistons, gears, etc. similar details are made. Blade processing methods are not very effective in creating such parts. Increased wear of technological equipment and tools leads to an increase in temperature in the cutting zone, adversely affects the quality indicators and reduces the life of the product as a whole. Constant sharpening, editing or changing the tool to a new, additional adjustment of the process equipment leads to an increase in the cost of manufacturing parts from difficult-to-work materials. The introduction of creep feed grinding in technological processes allows to avoid the above negative factors. The increase in the technological modes of grinding reduces the processing time, but it becomes a cause of burn in the surface layers and damage to the processed surface. Experimental studies of the process of creep feed grinding are carried out to determine the temperatures in the subsurface layers of the part during its processing and subsequent comparison with the theoretically obtained results of the developed mathematical model. Processing was performed on a surface grinding machine Jotes SPD-30b (Poland). The temperature is measured by the contact method (measuring instrument ОВЕН МВА 8, Russia) and contactless (using a pyrometer СТ 3M, Germany). The results of the experimental temperature values are given in tabular form. According to the research results, it is found that the use of a planetary grinding head for the technology of creep feed grinding of machine-building and aviation parts of difficult-to-process, corrosion-resistant materials leads to a decrease in the power-process parameters. In addition, there is an improvement in the surface cleanliness class (surface roughness Ra is between 1.25-1.8 μm). The results suggest that the technology of creep feed grinding should be introduced into technological processes instead of milling, external pulling and traditional grinding.

The influence of grinding speed on the creep-feed grinding process

The influence of grinding speed on the creep-feed grinding process

The Effect of the Operating Speed and Wheel Characteristics on the Surface Quality at Creep-Feed Grinding Titanium Alloys

The paper dwells upon flat creep-feed grinding of grooves in Ti6Al4V workpieces. Those were machined with high-porosity silicon carbide wheels of I, H grades at a speed of 20-30 m/s. Machined surfaces were analyzed using a Versa 3D electron microscope. The paper demonstrates the formed morphology of ground surfaces along the workpiece. Higher-speed grinding results in greater concentrations of silicon on the machined titanium alloy surface. Altering the characteristics of the abrasive tool does not have a significant effect on the concentration of silicon on machined surfaces. The paper analyzes how the grade of wheel and the grinding speed affect Ra surface roughness parameter. The article demonstrates the difference in grades of wheels along the surface, at the stage of constant length of arc and the stage of exit.

An Analysis of Electroplated cBN Grinding Wheel Wear and Conditioning during Creep Feed Grinding of Aeronautical Alloys

Cubic boron nitride (cBN), in addition to diamond, is one of the two superabrasives most commonly used for grinding hard materials such as ceramics or difficult-to-cut metal alloys such as nickel-based aeronautical alloys. In the manufacturing process of turbine parts, electroplated cBN wheels are commonly used under creep feed grinding (CFG) conditions for enhancing productivity. This type of wheel is used because of its chemical stability and high thermal conductivity in comparison with diamond, as it maintains its shape longer. However, these wheels only have one abrasive layer, for which wear may lead to vibration and thermal problems. The effect of wear can be partially solved through conditioning the wheel surface. Silicon carbide (SiC) stick conditioning is commonly used in the industry due to its simplicity and good results. Nevertheless, little work has been done on the understanding of this conditioning process for electroplated cBN wheels in terms of wheel topography and later wheel performance during CFG. This work is focused, firstly, on detecting the main wear type and proposing a manner for its measurement and, secondly, on analyzing the effect of the conditioning process in terms of topographical changes and power consumption during grinding before and after conditioning.

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

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

Влияние скорости глубинного шлифования на морфологию и химический состав поверхности титанового сплава

Влияние скорости глубинного шлифования на морфологию и химический состав поверхности титанового сплава

A Statistical Model of Equivalent Grinding Heat Source Based on Random Distributed Grains

Accurate information about the evolution of the temperature field is a theoretical prerequisite for investigating grinding burn and optimizing the process parameters of grinding process. This paper proposed a new statistical model of equivalent grinding heat source with consideration of the random distribution of grains. Based on the definition of the Riemann integral, the summation limit of the discrete point heat sources was transformed into the integral of a continuous function. A finite element method (FEM) simulation was conducted to predict the grinding temperature field with the embedded net heat flux equation. The grinding temperature was measured with a specially designed in situ infrared system and was formulated by time–space processing. The reliability and correctness of the statistical heat source model were validated by both experimental temperature–time curves and the maximum grinding temperature, with a relative error of less than 20%. Finally, through the FEM-based inversed calculation, an empirical equation was proposed to describe the heat transfer coefficient (HTC) changes in the grinding contact zone for both conventional grinding and creep feed grinding.

Research on operation mode of abrasive grain during grinding

The processing of materials by cutting with an abrasive tool is carried out by means of thousands of grains bonded together as a single whole. The quality of the abrasive tool is defined by cutting properties of abrasive grains and depends on features of spreading the temperature field in time and in the abrasive grain volume. Grains are exposed to heating and cooling during work. It leads to undesired effects such as a decrease of durability of grain retention in the binder, hardness, intensification of diffusion and oxidation processes between the binder and the grain, the occurrence of considerable temperature stresses in the grain itself. The obtained equation which allows calculation of temperature field of grain for one rotation of grinding wheel shows that the temperature of the wheel depends on grinding modes and thermophysical properties of abrasive material. Thus, as the time of contact of grain with processed material increases, the temperature in the cutting area rises. As thermophysical properties increase, the temperature in cutting area decreases. Thermal working conditions are determined to be different from each other depending on contact time of the grain and the material. For example, in case of creep-feed grinding, the peak value of temperature is higher than during multistep grinding; the depth of expansion is greater. While the speed of the thermal process in creep-feed grinding is 2-3 times lower than in multistep grinding, the gradient reduces 3-4 times. The analysis of machining methods shows that creep-feed grinding ensures greater depth of grain heating, a smaller heating rate and a reduced velocity gradient. It causes a decrease of probable allotropic modifications and prevents from occurring of heat strokes - cracking of grains due to high temperature falls. Consequently, it is necessary to employ creep-feed grinding to increase the efficiency of abrasive tool employing. Three operation modes of grinding wheel including blunting, full self-sharpening, emergency wear and tear are determined as the result of the research on evaluation of cutting ability of grinding wheels. Recommendations for working capacity of grinding wheels in each operation mode and with a transition from one mode to another are given. As a result of the research, different dependencies were determined. They include dependencies, governing the extent of influence of granularity, difference in height and concentration of grains, geometry parameters of the detail to be machined and the grinding wheel on machining modes and the thickness of the layer cutoff by one grain. They have an influence on the grinding process.

Wheel Working Surface Topography and Grinding Force Distributions in Creep Feed Grinding

This paper discusses the topographic features of wheel working surfaces and the grinding force distributions in wheel-work contact zones of creep feed grinding. Grain cutting edge wear is observed by a Scanning Electron Microscope (SEM) and quantitatively evaluated in terms of attritious wear flat percentage, which is able to characterize the wear behavior. By measuring the normal and tangential grinding force distribution in the grinding zone, the distribution form of grinding forces can be approximated to be triangular and the grinding forces increased rapidly due to workpiece burn. It is shown that the variation of the grinding force and the distribution are closely related to cutting edge wear characteristics.

INVESTIGATION OF THE INFLUENCE OF CREEP FEED GRINDING SPEED AND ABRASIVE TOOLS CHARACTERISTICS ON THE QUALITY OF TITANIUM ALLOY SURFACE CONDITION

The process of creep feed grinding of titanium alloy Ti6Al4V with high porosity circles of silicon carbide of 64CF80H12V and 64CF100I12V characteristics produced by JSC "Volzhsky Abrasive Plant" is considered. The morphology and chemical composition of the surfaces obtained at a grinding speed of 20-30 m / s were examined with a double-beam electron microscope. Surface roughness control was performed using a modern profilograph, profilometer. The chemical composition and roughness of the machined surface were determined in 10 sections, uniformly distributed along the length of the workpiece. It was found out that abrasive tool characteristic does not influence the general character of the formation of the morphology of the titanium alloy surface. It was proved that, as a result of adhesion-cohesive interaction, concentration of silicon on the machined surface of the titanium alloy increases with increasing grinding speed The increase of the grinding speed by 1.5 ensures the increase in the average silicon concentration by 1.6-1.8 times. The change in the hardness of the grinding wheel does not significantly affect the transfer of the abrasive material to the titanium alloy. The influence of the grinding speed and tool hardness on the values of the arithmetic mean deviation of the profile Ra on the entire length of the workpiece, the stages of the constant length of the arc of the contact and the output was considered. It was found out that the values of Ra parameter at the stage of constant contact arc length are greater than at the output stage by 30-40% when machined with a wheel of 64CF80H12V and by 15-30%, respectively, when machined with a wheel of 64CF100I12V. The increase of the grinding speed from 20 m / s to 30 m / s has a significant effect on the roughness of the machined surface only at the output stage.