Creep Feed Grinding Process Research Articles

Study of the surface integrity and mechanical properties of turbine blade fir trees manufactured in Inconel 939 using laser powder bed fusion

In this study, Inconel 939 turbine blade fir tree samples were fabricated by the additive manufacturing method using a direct metal laser sintering (DMLS) machine. This critical gas turbine connection part requires high geometric accuracy and excellent mechanical properties. The fir tree profiles of turbine blades were machined using creep feed grinding (CFG) and wire electrical discharge machining (EDM) methods. The effects of CFG and wire EDM on the recast formation, heat affected zone (HAZ), geometrical accuracy, microhardness, and tensile strength were compared. The experimental results revealed that the CFG process was superior in recast formation, HAZ, and microhardness, whereas better geometrical accuracy and ultimate tensile strength values were measured for the wire EDM method. The ultimate tensile strengths of turbine blades shaped using wire EDM were higher than the CFG method and measured 769 MPa and 748 MPa, respectively. Profile deviation and recast formation were the most influential parameters on the ultimate tensile strength of the fir tree geometry. The specimens were fractured from the pressure faces of the fir tree root during the tensile tests. Microscopic voids, cracks, and chloride impurities that would facilitate the propagation of fatigue cracks were observed on the fractured surface.

Numerical Stress Analysis of Creep-Feed Grinding Through Finite Element Method in Inconel Alloy X-750

The present study developed a 2D finite element model for simulation of creep-feed grinding process. Fully-coupled mechanical-thermal analysis was used to predict the residual stresses distribution. As in the creep-feed grinding the thermal damages are considerable, so the best and worst cooling condition i.e. flood and dry grindings were studied. Convection heat transfer coefficient was utilized to shows the effect of coolant. The results show the maximum temperature of specimen has reduced by about 52% compared to non-use of coolant. The dominate residual stresses are tensile near the surface that a steep decline in stresses was observed in flood grinding. Also, by using the electro polishing layer removal technique the non-uniform residual stresses were measured to validate the model. The results demonstrated the presented model provides good congruency with the experiments

Creep feed grinding induced gradient microstructures in the superficial layer of turbine blade root of single crystal nickel-based superalloy

The service performance of the turbine blade root of an aero-engine depends on the microstructures in its superficial layer. This work investigated the surface deformation structures of turbine blade root of single crystal nickel-based superalloy produced under different creep feed grinding conditions. Gradient microstructures in the superficial layer were clarified and composed of a severely deformed layer (DFL) with nano-sized grains (48–67 nm) at the topmost surface, a DFL with submicron-sized grains (66–158 nm) and micron-sized laminated structures at the subsurface, and a dislocation accumulated layer extending to the bulk material. The formation of such gradient microstructures was found to be related to the graded variations in the plastic strain and strain rate induced in the creep feed grinding process, which were as high as 6.67 and 8.17 × 107 s−1, respectively. In the current study, the evolution of surface gradient microstructures was essentially a transition process from a coarse single crystal to nano-sized grains and, simultaneously, from one orientation of a single crystal to random orientations of polycrystals, during which the dislocation slips dominated the creep feed grinding induced microstructure deformation of single crystal nickel-based superalloy.

AN INVERSE OPTIMIZATION PROBLEM OF HEAT TRANSFER IN THE MACHINING PROCESS – A REVIEW

This paper reports on the results of research on thermal aspects in the process of material removal by inverse heat transfer problem. The research focuses on the identification, modeling and optimization of machining process based on the measured temperature at a particular point of the workpiece. The inverse approach determines the overall temperature distribution of the workpiece and the unknown heat flux at the tool/workpiece interface in machining. By introducing and minimizing an objective function based on the heat flux function, relationship of the heating power and duration on the surface layer of the workpiece is optimized. In this way, the most favourable machining conditions are determined in order to achieve high productivity and quality levels. The inverse optimization problem is solved by using the analytical, numerical and regularization methods. Formulation, application and analysis of the inverse optimization problem of heat transfer are shown on the example of creep-feed grinding. The creep-feed grinding process is a widely used abrasive machining process that is characterized by high thermal load of the workpiece. The results of the inverse optimization problem were verified by a series of experiments under different machining conditions.

An investigation on machined surface quality and tool wear during creep feed grinding of powder metallurgy nickel-based superalloy FGH96 with alumina abrasive wheels

In this study, the machined surface quality of powder metallurgy nickel-based superalloy FGH96 (similar to Rene88DT) and the grinding characteristics of brown alumina (BA) and microcrystalline alumina (MA) abrasive wheels were comparatively analyzed during creep feed grinding. The influences of the grinding parameters (abrasive wheel speed, workpiece infeed speed, and depth of cut) on the grinding force, grinding temperature, surface roughness, surface morphology, tool wear, and grinding ratio were analyzed comprehensively. The experimental results showed that there was no significant difference in terms of the machined surface quality and grinding characteristics of FGH96 during grinding with the two types of abrasive wheels. This was mainly because the grinding advantages of the MA wheel were weakened for the difficult-to-cut FGH96 material. Moreover, both the BA and MA abrasive wheels exhibited severe tool wear in the form of wheel clogging and workpiece material adhesion. Finally, an analytical model for prediction of the grinding ratio was established by combining the tool wear volume, grinding force, and grinding length. The acceptable errors between the predicted and experimental grinding ratios (ranging from 0.6 to 1.8) were 7.56% and 6.31% for the BA and MA abrasive wheels, respectively. This model can be used to evaluate quantitatively the grinding performance of an alumina abrasive wheel, and is therefore helpful for optimizing the grinding parameters in the creep feed grinding process.

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.

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.

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

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

A review of the design of grinding wheels operating at excessive speeds

The design of grinding wheels operating at excessive peripheral speeds has improved significantly since the 1970s, which was largely prompted by the development of the creep-feed grinding process (CFG) and its derivatives including high efficiency deep grinding (HEDG), peel grinding (PG), and the high-speed stroke grinding process (HSSG). The current work reviews the design of grinding wheels that operate within the specified safety factors that are applied by the industry through the application of various codes and industry standards developed since the introduction of high-speed grinding processes. The paper focuses on the design of plain and clamped homogeneous structure grinding wheels, reinforced and recessed grinding wheels, superabrasive segmented grinding wheels, and high-speed slotted grinding wheels that use both conventional bonded abrasive structures and vitrified and electroplated superabrasive materials such as cubic boron nitride (cBN) and diamond. The implications of grinding wheel safety are stressed, and recommendations are provided to ensure that grinding wheels continue to be operated safely at excessive peripheral speeds.

The prediction of profile deviations from multi process machining of complex geometrical features using combined evolutionary and neural network algorithms with embedded simulation

The capability to generate complex geometrical features at tight tolerances and fine surface roughness is a key element in the implementation of Creep Feed grinding process in specialist applications such as the aerospace manufacturing environment. Based on the analysis of 3D cutting forces this paper proposes a novel method of predicting the profile deviations of tight geometrical features generated using Creep Feed grinding. In this application, there are several grinding passes made at varying depths providing an incremental geometrical change with the last cut generating the final complex feature. With repeatable results from co-ordinate measurements both the radial and tangential forces can be gauged versus the accuracy of the ground features. The tangential force was found more sensitive to the deviation of actual cut depth from the theoretical one. However, to make a more robust prediction on the profile deviation its values were considered as a function of both force components (proportional to force: power was also included). For multi process, one machining platforms hole making was also investigated in terms of monitoring the force to ensure the mean cylinder was kept within required tolerances and with minimal subsequent machining (due to these imposed accuracies this is also considered a complex feature). Genetic programming (GP), an evolutionary programming technique, has been used to compute the prediction rules of part profile deviations based on the extracted radial and tangential force correlated with the said chosen “gauging” methodology (for grinding process). GP was also used to correlate the force and flank wear (VB) for hole deviations. It was found that using this technique, complex rules can be achieved and used online to dynamically control the geometrical accuracy of ground and drilled hole features. The GP complex rules are based on the correlation between the measured forces and recorded deviation of the theoretical profile (both grinding and hole making). The mathematical rules are generated from Darwinian evolutionary strategy which provides the mapping between different output classes. GP works from crossover recombination of different rules and the best individual is evaluated in terms of the given ‘best fitness value so far’ which closes on an optimal solution. The best obtained GP terminal sets were realised in rule-based embedded coded systems which were finally implemented into a real-time Simulink simulation. This realisation gives a view of how such a control regime can be utilised within an industrial capacity. Neural networks were used for GP decision verification ensuring less sensitivity to possible outliers giving more robustness to the integrated system.

The prediction of profile deviations when Creep Feed grinding complex geometrical features by use of neural networks and genetic programming with real-time simulation

The capability to generate complex geometry features at tight tolerances and fine surface roughness is a key element in implementation of Creep Feed grinding process in specialist applications such as the aerospace manufacturing environment. Based on the analysis of 3D cutting forces, this paper proposes a novel method of predicting the profile deviations of tight geometrical features generated using Creep Feed grinding. In this application, there are several grinding passes made at varying depths providing an incremental geometrical change with the last cut generating the final complex feature. With repeatable results from coordinate measurements, both the radial and tangential forces can be gauged versus the accuracy of the ground features. The results of the tangential force were found more sensitive to the deviation of actual cut depth from the theoretical one. However, to make a more robust prediction on the profile deviation, its values were considered as a function of both force components. In addition, the power signals were obtained as these signals are also proportional to force and deviation measurements. Genetic programming (GP), an evolutionary programming technique, has been used to compute the prediction rules of part profile deviations based on the extracted radial and tangential force and correlated with the initial “gauging” methodology. It was found that using this technique, complex rules can be achieved and used online to dynamically control the geometrical accuracy of the ground features. The GP complex rules are based on the correlation between the measured forces and recorded deviation of the theoretical profile. The mathematical rules are generated from Darwinian evolutionary strategy which provides the mapping between different output classes. GP works from crossover recombination of different rules, and the best individual is evaluated in terms of the given best fitness value so far which closes on an optimal solution. Once the best rule has been generated, this can be further used independently or in combination with other close-to-best rules to control the evolution of output measures of machining processes. The best GP terminal sets will be realised in rule-based embedded coded systems which will finally be implemented into a real-time Simulink simulation. This realisation gives a view of how such a control regime can be utilised within an industrial capacity. Neural networks were also used for GP rule verification.

Creep-Feed Grinding: An Overview of Kinematics, Parameters and Effects on Process Efficiency

Grinding kinematics is one of the main mechanisms affecting the behaviour and efficiency of the creep-feed grinding process; it is thus essential in understanding the interplay of its parameters in the material removal. This paper presents an overview of non-traditional process parameters, such as the apparent area of the removed material, the grinding force engagement angle, the ratio of normal-to-tangential grinding force, as well as the ratio between the depth of cut and the wheel diameter. The kinematic aspects of creep-feed grinding processes are illustrated in three different case studies for creep-feed grinding of turbine blades, gears and broaches, using highly porous, vitrified, alumina-oxide wheels at low speeds. Details about the experimental work, especially with regard to analysis and validation, are not included. Based on the case studies, however, some practical guidelines for improving process efficiency in terms of productivity and quality are provided.

The Morphology Analysis of Axial Creep-Feed Grinding about Engineering Ceramics with a Small Grinding Wheel

The plastic deformation and brittle fracture damage remained within a certain depth of the abrasive surface of ceramic materials during axial creep feed grinding process, which included much information about damage mechanism and removal mechanism of ceramic materials. The surface morphology analysis showed that the brittle fracture was the main removal mode of grinding surface in addition to some micro-cracks in the affected layer, and cracks were not found in the matrix. Compared with general grinding, only the surface deterioration layer is thicker than general grinding surface, and there is no obvious damage to the workpiece

Optimal Control of Workpiece Thermal State in Creep-Feed Grinding Using Inverse Heat Conduction Analysis

Due to intensive friction between grinding particles and workpiece material, a substantial quantity of thermal energy develops during grinding. Efficient determination of real heat loading in the surface layer of the workpiece material in grinding largely depends on the reliability of basic principles of distribution of heat sources and the character of the temperature field within the cutting zone. Therefore, this paper takes a different approach towards the identification of the thermal state of the creep-feed grinding process by using the inverse problem to approximate heat conduction. Based on a temperature measured at any point within a workpiece, this experimental and analytical method allows the determination of a complete temperature field in the workpiece surface layer as well as the unknown heat flux on the wheel/workpiece interface. In order to solve the inverse heat conduction problem, a numerical method using finite differences in implicit form was used. When the inverse heat conduction problem is transformed into an extreme case, the optimization of heat flux leads to an allowed heat loading in the surface layer of workpiece material during grinding. Given the state function and quality criterion, the control of workpiece heat loading allows the determination of optimal creep-feed grinding conditions for particular machining conditions.

An Approach to Reduce Experiments Quantity: A Case Study on Thermal Aspects of Creep Feed Grinding Process

Number of experiments has always been a critical criterion in analyzing and characterizing a process. The purpose of this work is to develop a generalized analytical-experimental model based on a typical curve fitting and normalizing method for reducing the number of required experiments to predict expected results. Firstly, the mathematical base of the suggested approach was explained. Then, the feasibility and practicality of the model were evaluated by a case study developed on data of an experimental study in thermal aspects of a creep feed grinding (CFG) process. The models were built by using the input parameters such as: grinding surface temperature and grinding energy at different feed rates, wheel speeds, and cutting depths. Grinding energy and surface temperature generalized models were set up using only the same seven experimental results, and then results of the rest of the experiments were predicted by models. Comparison between the predicted and experimental results shows the capability of the model in prediction of total grinding energy within an average absolute error of 3.8% and grinding surface temperature within an average absolute error of 4.2%. The capability of the approach in decreasing the number of experiments was proved as well. Besides the mentioned advantages, the proposed approach provides models based on both experimental data and mathematical methods which make it free of any assumptions required in mere analytical and numerical models.

An Investigation about the Effect of Depth of Cut on Surface Integrity in Creep Feed Grinding of INC 792-5A

Creep-Feed Grinding(CFG) is one of the none-traditional machining in which form grinding to full depth is performed in limited number of passes. One of the most significant criteria which is taken into account to display valid machining parameters, is surface integrity. Surface integrity in CFG process is influenced by four main factors including surface roughness, superficial micro-crack, burning and changes in micro-hardness. According to prior investigations in CFG process, depth of cut plays an important role in surface integrity. In this study, the influence of cutting depth on workpiece surface integrity of cast nickel-based superalloy with alummina wheels, was investigated. During this study, a sample part was machined with variable depth of cut while the other parameters were Constant. After machining, surface roughness of each specimen was measured and in order to investigate existence and dimensional situation of surface micro-cracks, Chemical Etch + FPI and Thermal shock + FPI were performed. For determining micro-structural changes in ground specimens as a clarifier criteria in measuring the level of residual stress, a set of recrystallization processes were carried out on them and average grain size were measured. The results show, however, changing in depth of cut hasn't influenced on micro-cracks, quality of surface roughness has descended in terms of increasing the cutting depth.

FEM Analysis of Single Grit Chip Formation in Creep-Feed Grinding of Inconel 718 Superalloy

Recent advances in materials science have necessitated the development and understanding of manufacturing processes for safe and repeatable utilization. Grinding is shown to be a promising material removal process especially for brittle and hard to cut materials such as superalloys. Grinding has always been associated with analysis and modeling complications regarding its nature which has limited its extension and reliability of use. The first step in analysis of grinding is considering the action of a single abrasive grit on workpiece surface. In this work the action of a single CBN abrasive grit in creep-feed grinding process of Inconel 718 superalloy is modeled and analyzed using a 3D FEM software, DEFORM. Thermal and mechanical characteristics of the mutual interaction between grit and workpiece surface, and different chip formation phases are defined which can further be used to analyze the whole process.

Statistical Modeling of Pin Gauge Dimensions of Root of Gas Turbine Blade in Creep Feed Grinding Process

Creep feed grinding is a recently invented process of material handling. It combines high quality of the piece surface, productivity, and the possibility of automatic control. The main objectives of this research is to study the influences of major process parameters and their interactions of creep feed grinding process such as wheel speed, workpiece speed, grinding depth, and dresser speed on the pin gauge dimensions of root of gas turbine blade by design of experiments (DOE). Experimental results are analyzed by analysis of variance (ANOVA) and empirical models of pin gauge dimensions of root are developed. The study found that higher wheel speed along with slower workpiece speed, lower grinding depth and higher dresser speed, cause to obtain best conditions for pin gauge dimensions of root.

Statistical Modeling of Pin Gauge Dimensions of Root of Gas Turbine Blade in Creep Feed Grinding Process

Creep feed grinding is a recently invented process of material handling. It combines high quality of the piece surface, productivity, and the possibility of automatic control. The main objectives of this research is to study the influences of major process parameters and their interactions of creep feed grinding process such as wheel speed, workpiece speed, grinding depth, and dresser speed on the pin gauge dimensions of root of gas turbine blade by design of experiments (DOE). Experimental results are analyzed by analysis of variance (ANOVA) and empirical models of pin gauge dimensions of root are developed. The study found that higher wheel speed along with slower workpiece speed, lower grinding depth and higher dresser speed, cause to obtain best conditions for pin gauge dimensions of root.

Optimum creep feed grinding process conditions for Rene 80 supper alloy using neural network

Creep feed grinding is widely used in manufacturing supperalloy materials. These materials are usually used in aircrafts, gas turbines, rocket engines, petrochemical equipments and other high temperature applications. The objective of this paper is to model and predict the grinding forces of the creep feed grinding of these materials using the neural network. This model is then used to select the working conditions (such as depth of cut, the wheel speed and workpiece speeds) to prevent the surface burning and to maximize the material removal rate. The results show that the combined neural network and an optimization system are capable of generating optimal process parameters. The outcomes of the paper are now used to apply the optimal working conditions for grinding the turbine blades.