Properties Of Machined Surface Research Articles

Estimation of Hardness and Residual Stress on End-Milled Surfaces Using Linear Regression Model

This study presents a novel method for estimating the surface integrity of end-milled workpieces. It is well known that the mechanical properties of machined surfaces in cutting affect the quality of the final product. In particular, hardness and residual stress often require strict control; however, nondestructive inspection remains a challenge. This study proposes a method to estimate the hardness and residual stress of end-milled surfaces by analyzing cutting forces and images of the tool during machining to obtain approximate temperature and stress distributions. These state quantities are highly correlated with the dislocation density and its distribution on the machined surface, which in turn is strongly correlated with residual stress and surface hardness. Despite this strong correlation, few research studies have been conducted on the topic. In the proposed method, cutting forces, measured by a dynamometer, are analyzed to estimate the specific cutting forces and edge force coefficients. Simultaneously, the flank wear width is recorded using an image-based on-machine measuring device installed in the machine tool. From this information, the average stresses at the primary and tertiary cutting zones are estimated, while the cutting temperature in the primary cutting zone is roughly estimated by considering the traditional shear-angle prediction theory. Using these estimations, hardness and residual stress are calculated based on a simple linear regression model. Parameter identification for the model is performed based on measured hardness and residual stress in end-milling experiments. The model was validated against experimental measurements, which showed that the proposed method can accurately estimate hardness and residual stress, although it was observed that the selection of explanatory variables has a significant effect on accuracy.

Multi-mechanism-based twinning evolution in machined surface induced by thermal-mechanical loads with increasing cutting speeds

Microstructural features are an important factor in the evaluation of machined surface integrity. In particular, twins and twin boundaries have a significant impact on the physical and mechanical properties of components. This study investigates twin boundary evolution mechanisms in the machined surface during orthogonal cutting of oxygen-free-high-conductivity copper with cutting speeds ranging from 125 m/min to 2000 m/min. Pertinent features including twin boundaries, grain morphologies, textures, etc. Are characterized by electron backscattered diffraction and transmission electron microscope. The results show that the machined surface is divided into the refined layer, the deformed layer, and the matrix. An abnormal gradient distribution of a 60°<111> twin boundary is discovered for the first time. Specifically, the annealing twins mostly diminish in the deformed layer and regenerate in the refined layer. In the refined layer, a temperature-dominated process of twin formation and dynamic recrystallization occur. In the deformed layer, the resolved shear stress along the twin system is calculated through a novel approach, which reveals the stress-induced detwinning mechanism. The results of this research are beneficial for understanding both the deformation mechanism of medium stacking fault energy face-centered cubic metal under extreme loading conditions and the underlying effects of twins on the mechanical properties of machined surface.

New insights into the surface features of SKD61 steel at heat-treated and non-heat-treated states as processed by powder-mixed EDM

In this paper, the two states of SKD61 steel include heat-treated (HT) and non-heat-treated (NHT), were processed by powder-mixed electrical discharge machining (PMEDM) using tungsten compound powder. Several machined surface properties were investigated by methods such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), 3D Laser Scanning Microscope, and X-ray diffraction (XRD). In both states, their surfaces were changed in chemical composition and content of elements (CCCE), and tungsten carbide phase (W2C) was created. In comparison with the HT state, some surface features of NHT specimens, such as: the percentage of micro-crack acreage per surface (PCAS) is better improved, the penetration of the W element into surfaces and the intensity of the tungsten carbide phase are larger, the distribution of C and W elements on the surface is a more even, and the surface topography has more uniformity and flatness.

Experimental Investigation of Tribology-Related Topography Parameters of Hard-Turned and Ground 16MnCr5 Surfaces

Several surface topography parameters are available for the quantification of tribological properties of machined surfaces. Although these parameters and their influences are widely studied, there are contradictory findings due to the nature of the topography parameters, i.e., the behavior of different materials and cutting tool interactions lead to relatively varying numerical results. A comprehensive study of these interactions can contribute to more exact industrial machining applications. In this study, tribology-related 3D topography parameters of hard-machined (hard-turned and ground) surfaces were analyzed. The machining experiments were carried out based on a detailed design of the experiment; the analyzed material was case-hardened low-carbon content steel, which is widely used for automotive, industrial components such as bearings or gears. From the topography data, response function, correlation, and relative deviation analyses were carried out for the analyzed topography parameters, and tribology maps were created to support the selection of optimal cutting parameter values.

Effects of multi-pass turning on surface properties of AISI 52100 bearing steel

Hard turning is extensively used in the machining of bearings. The turning process has a significant influence on the properties of machined surface. In this paper, multi-pass turning experiments were machined on AISI 52100 bearing steel, and corresponding simulation model was established. The effects of multiple pass turning on microhardness and residual stress were investigated. The results demonstrate that the machined surface hardness of single, double, and triple pass turning is 30.0%, 25.2%, and 24.5% higher than the initial surface, respectively, at a turning depth of 0.1mm and a speed of 100m/min. Double pass turning significantly reduces the residual stress of machined surface. With the change of turning speed, the residual stress after double pass turning is 88 MPa lower than single pass on average, while the difference of residual stress is relatively minor after double pass and triple pass turning. At a cutting depth of 0.05 mm, the residual stresses after double pass turning and triple pass turning are 152 MPa lower than those after one-pass turning. As the turning depth increases, the influence of the previous pass turning gradually decreases in terms of residual stress.

Unveiling sub-bandgap energy-level structures on machined optical surfaces based on weak photo-luminescence.

Sub-bandgap defect energy levels (SDELs) introduced by the point defects located in surface defect areas are considered the main factors in decreasing laser-induced damage thresholds (LIDTs). The suppression of SDELs could greatly increase LIDTs. However, no available method could detect SDELs, limiting the characterization and suppression of SDELs. Herein, a self-designed photo-luminescence detection system is developed to explore the weak transient-steady photo-luminescence properties of machined surfaces. Based on the excitation laser wavelength dependence of photo-luminescence properties, a sub-bandgap energy-level structure (SELS) containing SDELs is unveiled for the first time. Based on the developed mathematical model for predicting LIDTs, the feasibility of the detection method was verified. In summary, this work provides a novel approach to characterize SDELs on machined surfaces. This work could construct electronic structures and explore the transition behaviors of electrons, which is vital to laser-induced damage. Besides, this work could predict the LIDTs of the machined surfaces based on their PL properties, which provides convenience for evaluating the LIDTs of various optical elements in industrial production. Moreover, this work provides a convenient method for raising the LIDTs of various optical elements through monitoring and suppressing the SDELs on machined surfaces.

Improvements of surface tribological properties by magnetic assisted ball burnishing

The effect of the magnetic assisted ball burnishing on a general, C45 steel was investigated considering tribological aspects. In engineering practice, the tribological properties of machined surfaces are characterized by amplitude roughness parameters from roughness profiles, as Rpk, Rk, Rvk, Rsk and Rku. Information about the sliding properties can be described by these parameters together with the oil retention capacity of the surface. Despite the conventional burnishing processes used as a post-machining operation, the authors applied a newly designed magnetic assisted ball burnishing method and tool, which can also burnish flat or harmonically changing surfaces and is able to round the edge of the workpiece in one pass as well, immediately after milling. To increase efficiency of the applied burnishing process, different types of burnishing strategies were applied and compared. The results of the investigations showed that the magnetic assisted ball burnishing decreases the frictional resistance, and at the same time it creates advantageous oil pockets on the machined surface.

Study on Slicing of Conductive SiC Ingot by Oil and Water type WEDM

In this paper, the slicing of a conductive SiC ingot is performed by an oil and a water type WEDM. The machining characteristics by the both type WEDM are investigated. The survey items are volumetric removal rate, average machined groove width, machined surface roughness, and machined surface properties. Regarding the results of the investigation with a discharge current of 1A, the volumetric removal rate of the water type WEDM is about 1.1 times faster than that of the oil type WEDM. Comparing the average machined groove widths, it of the water type WEDM is about 30% wider than that of the oil type WEDM. As a result, it was found that the surface roughness of the machined surface of water type WEDM was about 3 times as rough as the surface roughness of the machined surface of oil type WEDM. The machined surface properties of the both type WEDM are completely different. Specifically, the molten recast layer is hardly seen on the machined surface of the oil type WEDM, but it is clear that the machined surface of the water type WEDM is covered with the molten recast layer. This result suggests that the EDM phenomenon differs between the oil and the water type WEDM. From the above results, it was clarified that the oil type WEDM gives better results than the water type WEDM for slicing of a conductive SiC ingot.

Investigation of Coatings, Corrosion and Wear Characteristics of Machined Biomaterials through Hydroxyapatite Mixed-EDM Process: A Review.

Together, 316L steel, magnesium-alloy, Ni-Ti, titanium-alloy, and cobalt-alloy are commonly employed biomaterials for biomedical applications due to their excellent mechanical characteristics and resistance to corrosion, even though at times they can be incompatible with the body. This is attributed to their poor biofunction, whereby they tend to release contaminants from their attenuated surfaces. Coating of the surface is therefore required to mitigate the release of contaminants. The coating of biomaterials can be achieved through either physical or chemical deposition techniques. However, a newly developed manufacturing process, known as powder mixed-electro discharge machining (PM-EDM), is enabling these biomaterials to be concurrently machined and coated. Thermoelectrical processes allow the migration and removal of the materials from the machined surface caused by melting and chemical reactions during the machining. Hydroxyapatite powder (HAp), yielding Ca, P, and O, is widely used to form biocompatible coatings. The HAp added-EDM process has been reported to significantly improve the coating properties, corrosion, and wear resistance, and biofunctions of biomaterials. This article extensively explores the current development of bio-coatings and the wear and corrosion characteristics of biomaterials through the HAp mixed-EDM process, including the importance of these for biomaterial performance. This review presents a comparative analysis of machined surface properties using the existing deposition methods and the EDM technique employing HAp. The dominance of the process factors over the performance is discussed thoroughly. This study also discusses challenges and areas for future research.

Prediction of microstructure gradient distribution in machined surface induced by high speed machining through a coupled FE and CA approach

Surface integrity is the permanent pursuit of industries for decades, and microstructure is a key factor controlling physical and mechanical properties of machined surfaces. During machining, a complicated non-uniform distribution of deformation fields will be applied to machined surfaces, as a result, microstructure evolution will be significantly influenced. In this study, a coupled finite element (FE) and cellular automata (CA) approach is used to characterize and predict microstructure evolution during high-speed machining oxygen-free high-conductivity (OFHC) copper, where a unique material model is presented to describe both constitutive behaviors and microstructure evolution, and a mixed mechanism of continuous dynamic recrystallization (cDRX) and discontinuous dynamic recrystallization (dDRX) is adopted to show grain refinement and grain growth procedure under gradient distributed fields of strains, strain rates and temperatures in machined surfaces. A similar gradient distribution of grain sizes is obtained through both simulation and experimental results, which validates the predictive model and presents an in-depth understanding of microstructure evolution process during surface formation, and it shows the primary factors influencing the grain size distribution in sub-surface are cDRX-induced grain refinement and dDRX-induced grain growth. Moreover, the gradient distribution of microstructures in refined sub-surfaces could be used to explain mechanisms of sub-surface damage in the future.

EDMed Inconel 718 using powder metallurgy (P/M) sintered electrode made with nano and micron sized powders

This work presents experimental data carried out for surface modification of Inconel 718 using WC/Cu composite powder metallurgy (P/M) electrodes made of nano and micron sized particles. Both machine and tool parameters were selected for study and experiments were planned as per Taguchi’s L18 mixed orthogonal array in order to find the influence of parameters on surface roughness (SR) and micro-hardness (MH). Peak current, particle size and pulse on time were found to be most significant on both SR and MH. High reactive surface area of nano particles made surface alloying greater than the other tool electrodes and has shown its influence positively on both SR and MH. The EDX analysis reveals the migration of WC and Cu elements and deposition of carbon and oxygen particles on the surface. The XRD spectrum confirms presence of carbides (WC, W2C, Fe5C2, Cr7C3, Fe7C3 and Fe3C), oxides (Fe3O4, WO3 and Cr3O) and other intermetallics at different machining conditions indicating the influence of Pulse on time (TON) and Peak current (IP) on discharge energies and in turn on the properties of machined surface. The carbides generated on the machined surface increased the hardness to 845HV without much sacrifice of the roughness of the machined surface. The range of roughness values obtained in the present investigation is 2.443 to 4.098µm.

Laser-Based Ablation of Titanium-Graphite Composite for Dental Application.

Biocompatible materials with excellent mechanical properties as well as sophisticated surface morphology and chemistry are required to satisfy the requirements of modern dental implantology. In the study described in this article, an industrial-grade fibre nanosecond laser working at 1064 nm wavelength was used to micromachine a new type of a biocompatible material, Ti-graphite composite prepared by vacuum low-temperature extrusion of hydrogenated-dehydrogenated (HDH) titanium powder mixed with graphite flakes. The effect of the total laser energy delivered to the material per area on the machined surface morphology, roughness, surface element composition and phases transformations was investigated and evaluated by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), confocal laser-scanning microscopy (CLSM) and X-ray diffraction analysis (XRD). The findings illustrate that the amount of thermal energy put to the working material has a remarkable effect on the machined surface properties, which is discussed from the aspect of the contact properties of dental implants.

Experimental investigation on surface quality in ultrasonic-assisted honing of 304 stainless steel

Honing is a surface finishing technology, which plays an important role in improving the surface quality and working performance of workpieces. However, with the extensive application of hard-to-machine materials and the increasing requirement for the surface properties of workpieces, the performance of conventional honing (CH) is becoming more and more difficult to meet the production needs. The ultrasonic vibration provides a way to overcome the technological constraints of CH and improve the machined surface properties. To realise the ultrasonic vibration of honing stone, a slotted block horn was used as a vibration transmission component and a supporting component of honing stone in this study. Finite element method was used to analyse and optimise the block horn to improve the uniformity of the amplitude on the output surface, to provide stable and efficient vibration for the honing stone. In this study, the effects of processing parameters on surface roughness in CH and ultrasonic-assisted honing (UAH) of stainless steel SUS304 were studied. The results indicated that the application of ultrasonic vibration in honing made a significant contribution to the formation of a dense punctiform morphology and reduction of the defects of the workpiece surface. Moreover, interactions between ultrasonic vibration, speed of revolution, and honing time in UAH make the changes of surface roughness much different from the CH. On the whole, for UAH, it is a feasible approach to improve the surface roughness by using a smaller amplitude, increasing the speed of revolution appropriately, and extending honing time.

Prediction of machined surface properties by Boolean calculation using 3D CAD

Prediction of machined surface properties by Boolean calculation using 3D CAD

Interference- and chatter-free cutter posture optimization towards minimal surface roughness in five-axis machining

Five-axis CNC machining of sculptured surfaces plays a significant role in aerospace industry, such as blisk machining. The key issue involved is the determination of cutter posture in tool path planning. As the interference will cause the cutter to intrude the workpiece or machine tool and then seriously damage the cutter or machine tool, cutter posture must be well planned to avoid interference. Meanwhile, as the machined surface quality will be deteriorated inevitably when chatter arises, chatter must be eliminated as well. In this paper, posture accessibility and stability diagram (PASD) is firstly constructed by identifying interference- and chatter-free cutter postures based on geometric analysis and machining dynamic analysis. Furthermore, as surface roughness is an important characteristic to evaluate the surface properties of workpieces and should be generally minimized, its prediction model is also established for optimization. As is well known, surface roughness is mainly affected by cutter deflection due to inevitable cutter deformation force (CDF). By analyzing the relationship between surface roughness and maximum CDF, a novel surface roughness prediction model is proposed from a new viewpoint, i.e., the maximum CDF. Compared with the traditional prediction models considering only geometry, the proposed prediction model is much more straightforward, and the prediction results are more accurate (the average prediction error is only about 9.0%). This study reveals that the cutter posture has a great effect on surface roughness, which implies that surface roughness can be optimized from a new perspective (cutter posture). Finally, based on the proposed PASD and surface roughness prediction model, a new cutter posture optimization algorithm is proposed to minimize surface roughness. The algorithm considers both geometrical and dynamical constraints (interference and chatter) simultaneously, and it is verified by machining experiments under different cutter postures. According to the validation experiments, the proposed algorithm can effectively avoid the interference and chatter while minimizing the surface roughness (the optimized Ra is only 0.3589 μm compared to normal one 0.5476 μm). To the authors’ best knowledge, it is the first time to optimize cutter posture by considering the following three aspects simultaneously: avoiding interference, eliminating chatter and reducing surface roughness. It will greatly improve the machined surface properties, while optimizing the utilization of the machine tool and cutter (extending their service life by avoiding various potential damages). This also will provide a new perspective that optimizes the machining process of complex and precise parts from cutter posture, which is of great significance to aviation and aerospace industries.

Effect of machining processes on the residual stress distribution heterogeneities and their consequences on the stress corrosion cracking resistance of AISI 316L SS in chloride medium

The effects of machining such as grinding and turning on the microstructural and mechanical changes of the machined surfaces of AISI 316L stainless steel (SS) have been studied. Surface aspects and surface defects have been examined by scanning electron microscopy (SEM). Machining-induced nanocrystallization has been investigated by transmission electron microscopy (TEM). Surface and subsurface residual stress distribution and plastic deformation induced by the machining processes have been assessed by X-ray diffraction (XRD) and micro-hardness measurements, respectively. The susceptibility to stress corrosion cracking (SCC) has been assessed by SEM examination of micro-crack networks which are characteristics of a machined surface immersed in boiling (140 ± 2 °C) solution of MgCl2 (40%) during a 48 h-period. The machined surface properties have been correlated to severe plastic deformation (SPD) resulting from specific cutting state of each process. High cutting temperature and plastic rate are considered to be at the origin of near-surface austenitic grain refinement that leads to equiaxed nanograins with a size ranging from 50 to 200 nm. Ground surface residual stress distribution heterogeneities at the micrometric scale are attributed to the random distribution of the density and the geometry of abrasive grains that represent micro-cutting tools in the grinding process. The relationship between residual stress distribution and susceptibility of the AISI 316L SS to SCC has been demonstrated, and an experimental criterion for crack initiation has been established.

Crystallographic texture evolution and tribological behavior of machined surface layer in orthogonal cutting of Ti-6Al-4V alloy

The machining-induced crystallographic orientation variation in the plastic deformation layer on the mesoscopic scale usually occurs when severe plastic deformation undergoes in the machined surface layer, which will further affect the macroscopic mechanical performance of the machined parts. The orthogonal cutting experiments of Ti-6Al-4 V titanium alloy were carried out to confirm the effectiveness and reliability of the established finite element method (FEM) simulation cutting model with ABAQUS. From the perspective of macroscopic deformation, the shear strain and strain rate history were obtained, and this provided the fundamental data to simulate the machining-induced surface crystallographic texture evolution process using a visco-plastic self-consistent (VPSC) code. The pole figures and orientation distribution function (ODF) maps of crystallographic texture were produced and analyzed using a toolbox of Matlab. In order to validate the existence of crystallographic texture orientation with anisotropy, friction and wear tests were performed to explore the influence of crystallographic texture variation on the macroscopic properties of machined surface. The difference of friction coefficients and wear track width in the cutting direction and vertical cutting direction confirmed the hypothesis, and the machining-induced crystallographic texture evolution will alter the surface integrity and eventually the mechanical behavior of machined parts.

Investigation of Machined Surface Properties and Tool Wear for Drilling of Nickel-Based Superalloy FGH97

Nickel-based superalloy is widely used in aviation, aerospace, shipping and petrochemical industry. The effect of drilling parameters on work hardening and machined surface roughness of nickel-based superalloy FGH97 is summarized according to investigation of its drilling process. Machined surface roughness will increase with the increasing of feed per revolution or drilling speed. With the increase of drilling speed, the hardness of workpiece surface is decreasing. The influence of feed rate on the surface hardness of the workpiece is not significant. With the increase of drilling speed, the depth of workpiece hardening layer becomes smaller and smaller. The wear of the flank can be divided into two stages: uniform wear and rapid failure: when the wear of the flank of the bit is less than VB0.16mm, the wear of the flank is more uniform; when the wear of the flank exceeds VB0.16mm, the flank of drill bit becomes urgent from the outermost edge to the core of drill bit. The wear and tear of the play until the tool fails.

Investigations of micro-textured surface generation mechanism and tribological properties in ultrasonic vibration-assisted milling of Ti–6Al–4V

Ultrasonic machining (UM) as a non-traditional manufacturing technology has been recognized as an effective machining method for improving surface topography and surface quality. Although substantial experiment studies have been conducted and reported, the generation mechanism of textured surfaces in UM is still ambiguous, in which trajectories of tool-tips is not equal to actual cutting path due to separate-type cutting mechanism. Besides, the influence of ultrasonic vibration texture on tribological performance of machined surfaces is uncertain. This paper focuses on investigating the micro-texture generation mechanism and the effect of textured surface characteristics on tribological properties of machined surfaces in ultrasonic vibration-assisted milling (UVAM) process. Firstly, based on detailed analysis of tool-tips trajectories and rapid separate-type cutting process in UVAM, the generation mechanism of micro-texture was theoretically studied and the visualization of intermittent cutting process was given. Secondly, both conventional milling (CM) and UVAM experiments on Ti–6Al–4V were conducted to distinguish surface morphology features between CM and UVAM surfaces. Thirdly, the characterization methods of surface morphology, roughness parameters etc. were employed to characterize textured surfaces by comparing with CM surfaces. Finally, friction experiments were carried out to investigate influence of micro-texture on surface tribological properties, which was of great significance to functional property, wear property and service life of components. Experiment results showed that compared to common surfaces, uniform micro-texture could significantly improve surface morphology and surface quality. Friction test results also verified that micro-vibration-texture had a significant influence on improving tribological properties by reducing friction coefficients and its fluctuations.

Surface Modification of Ti6Al4V Alloy Using EDMed Electrode Made with Nano- and Micron-Sized TiC/Cu Powder Particles

The present study is an experimental work carried on for surface modification of Ti6Al4V alloy using TiC/Cu powder metallurgy (P/M) electrode. Both, machine and tool parameters were selected for study, and these experiments were planned as per Taguchi’s L18 mixed orthogonal array. Optimal combination of parameters was obtained using Taguchi’s method, and analysis of variance was performed to evaluate the influence of parameters on surface roughness (SR) and micro-hardness (MH). Peak current, particle size and pulse on time were found to be the most significant accordingly on both SR and MH. High reactive surface area of nanoparticles made greater surface alloying than the other tool electrodes and has shown its influence positively on both SR and MH. The EDS analysis reveals the migration of Ti and Cu elements, deposition of carbon and diffusion of oxygen particles on the surface. The XRD spectrum confirms the presence of carbides (TiC, $$\hbox {Ti}_{2}\mathrm{C}$$ , $$\hbox {Fe}_{5}\mathrm{C}_{2}$$ and $$\hbox {Fe}_{3}\mathrm{C}$$ ) and oxides (TiO and $$\hbox {Ti}_{3}\mathrm{O}$$ ) at different machining conditions which indicates the influence of TON and IP on discharge energies and in turn on the properties of machined surface. The carbides, generated on the machined surface, increased the hardness as high as 912 HV, without much sacrifice of the roughness of the machined surface. The range of roughness values obtained in the present investigation is 1.88–4.449 $$\upmu \hbox {m}$$ .