Microstructure Of Machined Surface Research Articles

Investigation of the influence of cryogenic‐temperature machining on ultrafine‐grained chips and machined surface quality of solution‐treated aluminum 7075 alloys

AbstractIn this study, cryogenic‐temperature formal machining technique was used to process solution‐treated aluminum 7075 alloys, the mechanical properties, morphology, and microstructure of machined surface and produced chips are investigated. Results show machining temperature has a huge influence on chip and machined surface morphology, cryogenic‐temperature machining chips and machined surfaces possess better surface integrity, chips are continuous and smoother, and machined surfaces are flatter. In contrast, room‐temperature formal machining chips exhibit serrated cracks on their free surface and the machined surface produces more serious scaly spines phenomenon. Both cryogenic‐temperature and room‐temperature samples experience severe deformation, cryogenic‐temperature machining alumium 7075 alloys max microhardness has enhanced from 98 HV 0.1 to 174 HV 0.1, and cryogenic‐temperature samples’ microhardness is higher than corresponding room‐temperature samples’ microhardness among all machining parameters. Cryogenic‐temperature can effectively suppress dynamic recovery thus chips could store more dislocations and then possess smaller ultrafine‐grained structures, accounting for higher microhardness. Besides cryogenic‐temperature inhibits precipitation of solute cluster and second phase particles and plays a lubrication effect at tool‐chip interface, thus cryogenic‐temperature machining aluminum 7075 alloys could obtain superior machined surface quality/chip morphology to improve processability. (*: Equal contributi)

Multi-objective parametric optimization of electrochemical machining of Inconel-625 superalloy

The high hardness value of Inconel-625 super alloy makes it difficult to machine with traditional machining methods. In this study, the machining of Inconel-625 has been attempted with electrochemical machining. The influence of input process parameters—voltage, feed rate, and flow rate of electrolyte has been studied on the output responses—material removal rate (MRR) and average surface roughness (SR). The experiments were performed following the central composite rotatable design of the response surface methodology. Analysis of variance has been used to test the significance of the process parameters and the model. A comprehensive empirical model representing the relationship between the process parameters and the response parameters has been developed. Further, the desirability function approach was used to acquire the optimal set of parameters. The optimal values of MRR and SR obtained in the study are 0.192837 gm./min and 0.99 μm, respectively, corresponding to the optimum settings of voltage, feed rate of the tool, and flow rate of electrolyte at 13.7 V, 0.20 mm/min, and 2.8 lit/min, respectively. The optimum settings so attained have been substantiated using confirmation experiments. The Confirmation tests show that the error between predicted and experimental values of MRR and SR was 2.02% and 4.8%, respectively, which fall in the acceptable range. Moreover, the surface characteristics of the machined area have been investigated using field emission scanning electron microscopy and 3D optical profilometer to analyze the machined surface's microstructure and 3D surface characteristics.

Experimental investigations and parametric optimization during micro-EDM drilling of Ti -5.6Al-3.6V using ABC algorithm

This work presents experimental investigations and parametric optimization during micro-Electric discharge Machining (EDM) drilling of Titanium alloy Ti-5.6Al-3.6V. The experiments have been designed by response surface methodology (RSM) based central composite design (CCD) taking current, pulse-on-time and pulse-off-time as input parameters; and drill rate and tool wear ratio as performance measures. After carrying out experiments, the effect of each input parameter on performance measures has been found. In order to study the microstructure of machined surface, scanning electronic microscope (SEM) has been performed. Single objective and multi-objective optimization have been done using artificial bee colony (ABC) algorithm to find the optimal combination of input parameters for the best yield of the process. Experimental verification of the obtained results has also been performed and a difference of less than 5% has been observed between experimental values and that obtained using ABC algorithm.

Optimization of abrasive water jet machining process parameters of Al 7071 using design of experiments

In recent times, Taguchi’s statistical approach in favour of development of face excellence and product types in abrasive water jet machining of aluminium and its alloys has turn out to be increasingly more widespread in various aircraft, ship building, and automation sectors. The present work made an attempts to identify the optimized parameter combination in abrasive water jet machining (AJWM) of aluminium 7071alloy (Al 7071). AJWM experiments were conducted based on Taguchi design of experiments. Machining parameters of traverse speed, SiC-abrasive flow rate and stand-off distance were taken as input parameters. For this purpose, Taguchi’s design of experiments selecting L9 orthogonal array was carried out in order to collect the material removal rate and surface roughness values. Furthermore, the control of process parameters on material removal rate as well as surface roughness has been measured by means plots and analysis of variance. Experiment number 9 through traverse speed of 300 mm min−1, 500 g min−1 of SiC-abrasive flow rate and 1 mm stand-off distance were identified as the best parameter combinations for maximum material removal rate. However, experiment number 1 through traverse speed of 100 mm min−1, 300 g min-1 SiC-abrasive flow rate and 0.5 mm stand-off distance were identified as the best parameter combination for improved surface finish. The microstructure of machined surfaces using scanning electron microscopy reveled that AWJM produced different zones along the cut surface of Al 7071and waviness and striations were increased marginally with SiC-abrasive flow rate.

Measurement and analysis of machining induced tribological characteristics in dual jet minimum quantity lubrication assisted turning of duplex stainless steel

In this work, the sustainable machining approach is promoted by implementing the dry and minimum quantity lubrication (MQL) cooling conditions in the turning of duplex stainless steel. Initially, the turning experiments were performed under dry as well as MQL conditions and then, the influence of different positions of MQL nozzles on tribological and machining performance of 2205 duplex steel was investigated. The cutting parameters were kept fixed and the performance is evaluated in terms of surface roughness, micro-hardness, energy consumption, tool wear, machined surface microstructure and chips morphology. The results demonstrated that the highest average surface roughness values were obtained under dry conditions, with a value of 2.20 µm while MQL (flank + rake directions) produces the lowest surface roughness value of 1.55 µm with an improvement of 30%. Moreover, dual-jet MQL gives the lowest energy consumption (229 kJ) and tool wear (0.15 mm) with 23.67% and 52.38% enhancement, respectively.

Effect of ultrasonic vibration-assisted face milling on the surface microstructure and tribological properties

The surface with a certain microstructure and morphology has a better wear resistance and allows reduction in the drag and noise. In this work, we supplemented an ultrasonic vibration and thereby proposed the underlying mechanism in the formation of the surface microstructure of ultrasonic vibration face milling using the kinematics model. Furthermore, we established the theoretical model of the machined surface microstructure. The cutting test of TC4 titanium alloy was conducted. The rationality of the theoretical model verified by adjusting the corresponding cutting parameters and the ultrasonic parameters. In addition, the friction and wear tests of the machined surface were also performed. The results showed that the amplitude had a significant influence on the micro-morphology, roughness, and friction coefficient of the ultrasonic vibration-assisted face milling. With the increase in the amplitude, the surface roughness and friction coefficient showed an initial decreasing trend with a subsequent increase. The surface roughness declined with the increase in the cutting speed, while had little effect on the surface friction coefficient of the material.

Influence of cutting velocity on gradient microstructure of machined surface during turning of high-strength alloy steel

The microstructure of machined surfaces is crucial to the overall performance and service life of mechanical structures. In this study, we performed cutting experiment, test analyze, and theoretical calculation to investigate the evolution in gradient microstructures of the superficial layer on machined surface, including grain size, dislocation density, grain boundary and misorientation angle, in the turning of high strength alloy steel with a self-developed coated carbide microstructure turning tool under different cutting velocities. Single-factor cutting experiments and corresponding tests were carried out using X-ray diffraction (XRD) and electron back scattered diffraction (EBSD) to investigate effects of cutting velocity on the microstructure of the machined surface during the cutting process. In addition, the performance and quality of the machined surfaces were assessed using a micro-hardness tester, laser scanning confocal microscopy, and atomic force microscopy. The relationship between microstructure and performance of the machined surface was explored by establishing a cutting model. The results showed that higher cutting velocities before exceeding the transition threshold with a larger relative evaluation coefficient can raise the thickness of the strengthening layer. This changes the gradient-distribution of dislocation density, grain boundary, and misorientation angle in the machined surface resulting in finer grains, thereby strengthening the machined surface. Moreover, the thickest agglomerate layer of equiaxed crystals was also observed under the higher cutting velocity, which was found to improve the performance of the workpiece (Micro-hardness of 318.07 HV and roughness of 0.05 μm), suggesting the approach to control cutting conditions to achieve better machined surfaces by evaluating the comprehensive function of mechanical load and thermal load in the metal machining process is effective.

High Stock Removal Hard Turning of Hardened 52100 Steel with High-Pressure Coolant Applied

Hard turning experiments were conducted on hardened 52100 steel utilizing high-pressure (10.3 MPa) coolant. CBN inserts were used. The cutting conditions were investigated to obtain high stock removal with a feasible tool life on the large part hard turning process. A small thermocouple was mounted in a ground slot underneath the CBN insert tip, close to the cutting edge, to effectively measure the insert’s temperature during cutting. The cooling effect of the high-pressure coolant was evaluated by monitoring CBN insert crater wear and the time for the edge to become prematurely fractured. The temperature measurements show that the high-pressure coolant cools the insert more efficiently and has better lubrication capability leading to longer cut time without edge fracture. The study revealed that conventional low-pressure (0.4 MPa) coolant could not economically achieve high stock removal hard tuning due to high cutting temperature leading to premature fracture of the cutting edge. When using the high-pressure coolant and the optimized parameters, the tool life was enhanced by nearly 100%. The machined surface microstructure did not degrade even with the generation of very high shearing and friction heat energy in the cutting zone. Based on validation cut results and production part cycle assessment, the application of high-pressure coolant enables feasibility of high stock removal in hard turning with the ability to improve the productivity of large part rough stage turning by about 46%.

Microstructural assessment of drilled cross-sections on titanium generated under different cooling strategies

High heat generation during machining of titanium alloy causes microstructural damage on machined surfaces. Different cooling strategies in machining of titanium alloy have been studied to understand their effectiveness in improving heat dissipation and machined surface microstructure. In this work, heat-sink based cooling has been used to channelize an ice water for effecting positive heat dissipation. Before drilling experiments, solution annealing was performed on all Ti-6Al-4V samples to achieve an equiaxed microstructure. Extensive drilling experiments under dry, flood cooling and heat-sink based cooling environments were performed under different cutting parameters. Electron Backscatter Diffraction (EBSD) technique was utilized to characterize microstructure of titanium drilled entry and exit hole surfaces. Dry drilling showed the highest average of 40 μm of machining affected zone (MAZ), whereas the least MAZ average 3 μm which was evident in the heat-sink based cooling. Image quality (Kikuchi pattern intensity) quantification revealed the highest normalized IQ value, indicating the lowest deformation in heat-sink based cooling over dry and flood cooling at the entry and exit surfaces of the drilled samples. Misorientation maps show that low angle grain boundaries misorientation is reduced in heat-sink based cooling by maximum 75 % over dry drilling, and by 57 % over flood cooling, at the exit hole surfaces. Kernel average misorientation (KAM) analysis at the exit drilled hole surfaces shows that the local misorientation in heat-sink based cooling is reduced by 90 % as compared to dry drilling and by 60 % over flood cooling.

Surface and sub-surface analysis of rotary ultrasonic elliptical end milling of Ti-6Al-4V

Ultrasonic vibration has received widespread attention for its dramatic effect on grain refinement and microstructure modification during casting, additive manufacturing, cold rolling, and cutting, changes which can significantly improve the mechanical and physical properties of components. As a novel ultrasonic vibration cutting method, rotary ultrasonic elliptical milling (RUEM) has been introduced to mill the alloy Ti-6Al-4V. However, the effects of ultrasonic elliptical vibration on the microstructures of machined surfaces in end milling of Ti-6Al-4V are still unclear. A comprehensive study on the surface characteristics and sub-surface microstructure in RUEM of Ti-6Al-4V was conducted. The results show that the uniform textures, in the form of ridges mapped on the machined surface in RUEM, varied with the cutting speed. Compared with conventional milling, microchip debris adhesion on the machined surface was significantly reduced by using RUEM. Moreover, intense plastic deformation in the sub-surface was obtained, and nanocrystalline layers, with grain dimensions of 10 nm to 100 nm, were fabricated on the processed surfaces of RUEM. Additionally, the improvement in sub-surface microstructure increased the surface micro-hardness from 21.22% to 33.84%. This study allows an in-depth understanding of sub-surface deformation and surface nanocrystallization in RUEM of Ti–6Al–4V.

Comparative analysis of dry, flood, MQL and cryogenic CO2 techniques during the machining of 15-5-PH SS alloy

The Precipitation Hardening (PH) Stainless Steel (SS) is considered as a promising alternative for aerospace and marine sectors owing to its good mechanical properties with high corrosion resistance. But the lower thermal conductivity and the presence of precipitates lower its machinability in terms of rapid tool wear. In this context, this study aims to analyze the dry, flood, MQL (Minimum Quantity Lubrication), and cryogenic machining with LCO2 in terms of tool wear for the turning tests of 15-5 PH SS. Apart from progressive flank wear, the machining performance of different cutting fluid strategies is compared by analyzing the crater wear, progressive power consumption, and surface roughness, microhardness, and microstructure of machined surface and chip. The performance of sustainable cryogenic machining is found superior in terms of lower tool wear, power consumption, subsurface microhardness. The relatively finer grain size and helical chip with smaller diameter are produced in the cryogenic machining while the better surface finish is observed for the flood machining in contrast to other cutting fluid strategies.

Exploration on Surface Roughness in Abrasive Water Jet Cutting of AA6063-TiC Composites for Vehicle Structural Applications

This paper deals a set of studies performed on AA6063-TiC composites produced by adding 3%, 6% and 9% wt. of TiC in aluminium alloy 6063 and processed with abrasive water jet cutting that are formed with garnet abrasive of 80 mesh size. These studies are effectively meant to evaluate the surface roughness (Ra) of abrasive water jet cutting on various compositions of AA6063-TiC produced by stir casting route. Abrasive water jet cutting was carried out on cylindrical samples of various compositions of AA6063-TiC composites by varying traverse speed, stand-off distance and abrasive flow rate at three different levels. The experiments were performed using Taguchi’s L27 orthogonal array. Contribution of these parameters on the Ra was determined by ANOVA and regression analysis to optimize the process parameters for effective machining. Among the interaction effects, traverse speed and stand-off distance combinations contribute more to the Ra. The microstructures of machined surfaces were also analysed by scaning electron microscope images and F-profile plots.

Surface Integrity of Powder Metallurgy Superalloy FGH96 Affected by Grinding with Electroplated CBN Wheel

Abstract Powder metallurgy superalloy FGH96 is a key material for manufacturing aero-engine high temperature parts due to its excellent high-temperature mechanical performances. Machined surface integrity has a directly influence on the fatigue behavior. Unique properties of FGH96, like high-temperature strength and poor machinability, make it extremely difficult to control the machined surface integrity. Grinding technology utilizing super abrasive wheel is widely used in finish machining of powder metallurgy superalloy. Therefore, improving the fatigue property of parts by controlling grinding surface integrity is significantly important. Experimental results of grinding FGH96 with CBN electroplated wheel show that the grits size of wheel is the main factor influencing on surface roughness. With the decreases of the grits size, the surface roughness decreases gradually. Surface roughness of workpieces machined with 400#CBN wheel is Ra=0.76 μm, while that with 600#CBN wheel is Ra=0.56 μm. In the experimental conditions, feed speed and grinding depth have little influence on surface roughness. Grinding speed has hardly any influence on surface roughness. Meanwhile, the surface microhardness of workpieces is maintained at 460 HV to 500 HV and the surface residual stress is -700 MPa to -620 MPa. There is almost no plastic deformation in the microstructure of machined surface. Therefore, grits size of grinding wheel has a tremendous influence on surface integrity of powder metallurgy superalloy FGH96 in the range of experimental parameters, and controlling the surface roughness is a crucial method to improve the fatigue behavior of FGH96 parts.

On the machinability and properties of Ti-6Al-4V biomaterial with n-HAp powder-mixed ED machining.

Nano-hydroxyapatite powder was used in electric discharge machining to modify the surface of Ti-6Al-4V medical alloy. Herein, electric discharge machining was performed, with and without powder-mixed flushing for evaluation of the material erosion rate and surface roughness. In addition to dielectric type, several process parameters including current, pulse-on duration, pulse-off duration, and electrode hole diameter were considered. The experiments were planned by Taguchi design technique and conducted to analyze the material erosion rate and surface roughness. After machining, scanning electron microscope, energy-dispersive X-ray spectrometry, and X-ray diffraction techniques were used to evaluate the surfaces of the samples. Furthermore, wear and corrosion tests were also carried out on the Ti alloy with modified surfaces. The influential factors were identified based on analysis of variance results. Current and dielectric type were the significant factors, both for the material erosion rate and surface roughness. The scanning electron microscope images of Ti-6Al-4V samples highlighted that the process parameters exhibited a vital influence on the topology and microstructure of machined surface. Furthermore, energy-dispersive X-ray spectrometry and X-ray diffraction analyses confirmed the presence of hydroxyapatite on Ti alloy surface after machining. Moreover, the results of wear and corrosion tests revealed lower wear and corrosion rates of the surface-treated workpiece with nano-hydroxyapatite.

Effect of the cutting speed on the cutting mechanism in machining CFRP

Cutting mechanism of CFRP is different from that of a homogeneous metal. For metal, high speed cutting can improve machining quality and efficiency. However, there is no agreed conclusion on the effect of cutting speed on the cutting mechanism of CFRP. This paper studies the effect of cutting speed on cutting mechanism of CFRP and damage formation by using finite element and experiment methods. A three-dimensional finite element model of orthogonal cutting CFRP is established considering the strain-rate-dependent mechanical properties of resin and the anisotropy of fiber. By this model, cutting processes at micro level are simulated. Fracture evolution processes of fiber and resin are characterized. Furthermore, experimental data of cutting forces are obtained, and the machined surface microstructure are observed based on orthogonal cutting experiments. Subsurface morphology and degree of resin cracking extension in simulation and experiment are consistent with each other. Results show that with the increase of cutting speed, the fiber deformation and the affected area before fiber fracture obviously deceases. Accordingly, the resin cracking and extension degree caused by the excessive deformation of fiber also be greatly reduced. In addition, there is a trend that the specific energy gap for different chip formation modes becomes smaller and smaller.

Grain refinement mechanism under high strain-rate deformation in machined surface during high speed machining Ti6Al4V

The mechanical and physical properties of component surfaces are determined by the evolution of microstructures during high speed machining (HSM). In order to investigete the crystalline structure and formation mechanism of the highly perturbed surface layer, a novel characterization technique, precession electron diffraction (PED), is applied for quantitative characterization of the nano-scaled microstructures of machined surfaces, including phase distribution, grain size, character of grain boundary, grain orientation distribution and geometrical necessary dislocation (GND) density distribution. The deformation conditions of machined surface are used to analyze the evolution of microstructure under the effects of high strain-rate during machining process. Nano-crystalline structures are observed under high strain-rate deformation in the highly perturbed layer of machined surfaces. The calculation results based on crystal orientation information show that high GND density up to 106/m2 is generated and deformed nano-twins boundary is 14% of total grain boundary, which demonstrate that both dislocation slip and twinning contribute to the plastic deformation during HSM. Composite stress state and rapid heating of HSM surface produce large numbers of nanoscale β phase precipitations, which has critical pinning effects on dislocation and grain boundary movement, and will inhibit grains recovery and growth until nanoscale grains are formed. As high strain rate combined with precipitation of second phase particles is the main factor for nanoscale grains formation, HSM could be considered as an effective method to control the deformation conditions through selecting proper machining parameters in order to acquire component surface with nanocrystalline structure.

Investigation of mechanical properties of hard finish turned and grinded surfaces

The main topic of the research conducted by the authors of this article is the study of the mechanical properties of surface layers after finish machining by two methods. The material of the test samples is 33NiCrMoV steel. The main aim of the authors is to compare hardness of the machined surface layers of this steel after hard finish turning and grinding. In the experimental process, quasi-static nanoindentation technique with the cube corner was used, and the microstructural analysis was performed by atomic force microscopy (AFM). Even before the start of the measurements that investigated the influence of hard finish turning technology against round grinding, it was necessary to subject the investigated 33NiCrMoV15 steel to basic research with regard to its chemical composition, fundamental microstructure and also microstructure of machined surfaces and basic mechanical and nano-mechanical properties. The microstructure was realized on the Oxford Instruments MFP-3D Infinity atomic force microscope AFM. All of these measurements were performed for investigating material properties using AF-FM viscoelastic mapping mode, which can register nanomechanical properties of materials. Chemical composition of investigated steel was performed on the spectral analyzer Spectrolab Jr CCD. Nano-mechanical properties, like nanohardness H and reduced Young modulus Er were subsequently performed on the Hysitron TI950 Triboindenter with a Cube Corner measuring tip, and then evaluated by the Triboscan software. Based on the acquired values, a 2D nanostructure of the distribution map of s H and Er was then evaluated in Matlab. This scientific research, together with all measured and calculated values, is the fundamental that will help to optimizing the quality and used all these results to optimize presented material and technological finishing processes in term of surface integrity.

Investigation of hole quality in rotary ultrasonic drilling of borosilicate glass using RSM

The present article emphasizes on reducing the edge chipping and taper during rotary ultrasonic drilling of one of the most demanded ceramic glasses “BK-7.” Statistical tools of design of experiments and backing plate were adopted as two distinct approaches to curb the chipping damage. Central composite design has been conjugated with desirability function for framing the design matrix. This investigation also emphasizes to study the effect of process variables—spindle speed, ultrasonic power and feed rate—on the chipping width (CW) and taper (T). After developing the second-order regression models for the CW and T, analysis of variance was used to check the fitness of regression models and recognizing the significant model terms. Then impact of each process parameter was analyzed on responses of interest through 3-D surface plots. The feed rate came forth as the most dominating factor by having maximum influence over the qualitative aspects “CW” and “T” of the drilling process. Interactions of higher rpm and power with lower feed effectively reduced the CW and T. The backing material, employed during main experimentation, also proved its effectiveness to reduce CW when main experiments results were compared to the results of pilot experimentation, which was performed without backing plate. Scanning electron microscope (SEM) was used to analyze the different tool wear modes and microstructure of machined surfaces. Tool weight measurement revealed the dominance of bond fracture and grain fracture during the early stage of the drilling process. Apart from brittle fracture, SEM also affirmed the presence of plastically deformed regions over the machined surfaces. Little deviations between the predicted values and experimental values during the confirmatory tests validated the prediction accuracy of regression models at 95% confidence level.

Surface microstructure of titanium alloy thin-walled parts at ultrasonic vibration-assisted milling

Milling of the titanium alloy thin-walled workpiece is a critical challenging task and the machining vibration is a major effect on the accuracy of the final part due to difficult machining properties and low stiffness. The common milling (CM) is very hard for titanium alloy thin-walled parts to get high-quality machined surface microstructure, so finding an effective way of processing to obtain better surface microstructure is particularly important. In this article, the longitudinal-torsional composite ultrasonic vibration-assisted milling (LTCUVM) is proposed to overcome the problems of the common milling. The cutting method of the high-frequency vibration separation of a workpiece and the tool reduces an average cutting force. Thereby suppressing the tool relieving and further providing a good machined surface. In this study, firstly, the kinematic model of LTCUVM was established and the variations of the movement of the cutting edge flank with the spindle speed change were analyzed. Then the finite element model (FEM) of the two processing methods was developed and significant differences between the CM and LTCUVM in the micro-milling were revealed. Further, related experiments were designed and conducted. Finally, the experimental analysis showed that the LTCUVM effectively reduced an average cutting force, and further reduced surface roughness and height of chatter marks compared to the CM with the same processing parameters.

Material driven machining process modeling

A material driven machining process modeling framework is proposed to incorporate thermal-mechanical-microstructural coupling in which the material microstructure dynamics and process mechanics are computed simultaneously. The material microstructure evolution in the machining process is obtained from dynamic recrystallization model which takes the strain, strain rate and temperature history as input. A microstructure sensitive flow stress model is used to correlate the material microstructure with material mechanical properties. The detailed implementation of the proposed framework is illustrated by the machining of titanium alloy. As the output of the model, the machining forces, residual stress profile and machined surface microstructure states are validated against the experiments.