Papers by Keyword: Surface Integrity

Abstract: Additively manufactured titanium alloys such as Ti-6Al-4V have been used as functional components in industry due to their excellent mechanical properties. However, the machining of these alloys is a challenge due to their enhanced tensile/yield strength, low elastic modulus, poor thermal conductivity, and microstructural anisotropy. Thermal assisted machining (TAM), as a hybrid manufacturing technology, can improve the machinability of additively manufactured alloys. The main aim of this paper is to investigate the effect of temperature buildup on the machinability of additively manufactured Ti alloy with different build directions in the TAM process. It was found that the surface integrity was notably enhanced by preheating, and it was the best at 90° build orientation. Serrated chips were generated at room temperature, and curlier chips were formed in high-preheating machining environment. By analyzing the surface quality, the influence of the build-up orientation on the surface quality at different temperatures was evaluated.

Abstract: Additive manufacturing by laser powder bed fusion (LPBF) is increasingly applied to aluminium alloys; however, the resulting surface quality and machining behaviour remain critical challenges, particularly when post-processing is required. In this context, the interaction between LPBF process parameters and advanced cooling strategies during machining remains largely unexplored.This study examines the impact of cryogenic machining on the surface integrity of LPBF-produced AlSi7Mg components, fabricated with varying layer thicknesses. Specimens were machined under fixed cutting parameters using either conventional flood cooling or cryogenic cooling. Cutting forces, surface roughness, defect morphology, and subsurface microstructure were systematically evaluated.Cryogenic cooling consistently reduced cutting forces and improved surface quality, effectively suppressing tearing formation. In contrast, under flood cooling, the influence of the microstructural differences induced by layer thickness remained significant, with increasing LPBF layer thickness further enhancing both surface and subsurface integrity. Overall, the results reveal a strong interaction between LPBF parameters and cooling strategy, highlighting the unexpectedly beneficial role of cryogenic machining in improving the surface integrity of LPBF-processed AlSi7Mg alloys.

Abstract: Parallel turning is one among the advanced unconventional turning process. It employs two turning tools operating concurrently to cut the material from the workpiece. For turned rotary components, surface integrity is a major quality indicator that determines the fatigue life of the finished workpiece. Tool parting distance, rake angle and edge radius affects surface integrity. Part I dealt with numerical analyses to determine the effect of parting distance on surface integrity using finite element based commercial software Abaqus 6.14. Here in Part II, the impact of rake angle over surface integrity for various cutting speeds and feeds are numerically analyzed. It was observed that with the rise in negative rake angle the negative residual stresses decreased for the machined surface of leading and lagging cutting tool. When the rake angle is increased from-10 ̊ to-2 ̊, percentage reduction of negative residual stresses is same for the turned surfaces of both tools. The cutting velocity was 250 m/min and feed 0.2 mm/rev. With the rise in rake angle, the friction angle reduced but shear angle raised. When the cutting velocity increased, the shear angle of the leading and lagging cutting tool reduced. Lower shear angle causes higher stagnation region which further causes higher compressive surface residual stress.

Abstract: Additive Manufacturing of metal alloys offers unique advantages for producing net-shape components of complex geometries with very little waste of material. Nevertheless, machining operations may be needed on functional surfaces to get the required surface finish and geometrical tolerances. This poses challenging issues since the microstructural features characterizing the AM alloys are drastically different from those of the wrought alloys of the same chemical composition, which, in turn, may affect the mechanical and machining response to a great extent. This paper shows that both the machined surface integrity and tool wear are greatly affected by the microstructural features induced by the previous AM process as well as by the build-up orientation.

Abstract: Various novel 3D micro machining technologies were researched and developed for silicon micro mechanical system fabrication. Micro EDM is one of them. The material removal mechanism is thermal sparking erosion and is completely independent with regards to the crystalline orientation of silicon, therefore there is no orientation constraint in processing the complex 3D geometry of silicon wafers. As thermal sparking implied, the process features local area high temperature melting and evaporating, and this characteristic has an adverse side-effect on the sparked surface integrity. One important concern is the generation of micro cracks, which would provide an adverse effect on the fatigue life of the micro feature element made of silicon. For this consideration, in this paper, with the experiment and SEM picture analysis approach, the author explored the micro crack generation characteristics on mono crystalline silicon wafers under micro EDM with available sparking energies and on the different crystal orientation surface machining. The generation of micro cracking is not only related with the sparking energy but also related with the crystalline orientation. The {100} orientation is the strongest surface to resist crack generation. For a strong-doped P type silicon wafer, there exists a maximum crack energy threshold. If single sparking energy is over this threshold, micro cracks unavoidably would be generated on any orientation surface. Two types of chemical etching post processes that can remove cracks on sparked surfaces are also tested and discussed.

Abstract: The heat generation and subsequent temperature rise in the cutting zone due to plastic deformation and friction at tool-chip-workpiece interface are critical parameters that have a significant impact on tool wear, tool life and surface integrity. This paper aimed to analyse the effect of cutting parameters such as, cutting speed, feed and depth of cut on the cutting temperature in turning of hardened AISI 52100 alloy steel of 58 HRC using multilayer coated carbide cutting tool insert under high velocity pulsing jet minimal cutting fluid application (MCFA) environment. Response surface methodology based central composite design (CCD) was used to investigate and optimize the cutting parameters on cutting temperature response. The quadratic regression model in terms of cutting speed, feed and depth of cut for cutting temperature was developed. The diagnostic and confirmatory tests were carried out to check its validity. The implication of the process parameters and their interactions were tested using analysis of variance (ANOVA). The results showed that the cutting speed and feed were the main significant parameters affecting the cutting temperature, while depth of cut and quadratic term of cutting speed had a moderate effect. The predictive model developed indicates the 99% desirability level in turning of AISI 52100 hardened steel under the MCFA environment. The predicted values of cutting temperature response are in close agreement with the experimental results.

Abstract: This study focuses on the effect of cutting fluid on sample surface integrity and tool wear in milling additively manufactured Inconel 738LC. Sample surface integrity and tool wear characterization was undertaken using scanning electron microscopy, backscatter electron microscopy, energy dispersive spectroscopy, laser scanning confocal microscopy, ultra-depth of field digital microscope system and digital display hardness tester. Compared with dry milling, wet milling not only provides an entirely different result on surface morphology, but also shows less surface plastic deformation, and smaller surface roughness. In addition, the tool wear mechanisms of wet milling are found to be different compared to dry milling.

Abstract: Acoustic emission signal-based prediction of surface roughness has been utilized widely, yet little work has been done in this regard on RSA443. This paper seeks to study the correlation between acoustic emission (AE) signal parameters and surface roughness. Estimation of surface roughness using AE signal parameters and subsequent examination of the influence of AE signal parameters (root mean square, peak rate and prominent frequency) on the accuracy of the RSM model in surface roughness prediction are carried out. The experiment is designed using the Taguchi L9 orthogonal array to minimize the number of experiments. Emitted acoustic signals are captured using a Piezotron sensor. Three RSM models are formulated and compared in this study: a model that uses only critical machining parameters (cutting speed, depth of cut and feed rate), a model that uses only AE signal parameters (root mean square, peak rate and prominent frequency) and a model that uses both critical machining parameters and AE signal parameters. An assessment based on the models’ mean absolute percentage error (MAPE) is made to see if AE signal parameters have any contribution towards surface roughness prediction accuracy. The order of parameter significance in the most accurate model is investigated in this paper. The mean absolute percentage error results for the models indicate that the model in which AE signal parameters are utilized in conjunction with critical machining parameters has the highest prediction accuracy of 97.32%. The model that utilizes only critical machining parameters has a prediction accuracy of 96.35% while the one that utilizes only AE signal parameters has a prediction accuracy of 84.43%. It is observed that the order of parameter significance from the most to the least significant is as follows: feed rate, cutting speed, peak rate, AErms, depth of cut and prominent frequency.

Abstract: Turning of hardened alloy steel (Hard turning) is a replacement for grinding operation. The heat generation and temperature during hard turning at the cutting zone and due to the friction at tool-chip-workpiece interface are significant parameters which influence chip formation mechanism, tool wear, tool life, surface integrity and hence the machining quality. Cutting fluid performs key role in metal cutting due to its cooling and lubrication action. Flood cooling is a common method of cutting fluid application, in which large quantity of cutting fluid is applied at the cutting zone. Due to environmental, health and safety concerns, the usage of cutting fluid in abundant quantity is being restricted. Most of the researchers have varied the cutting parameters like cutting speed, feed rate and depth of cut to machine different work materials with different cutting tools and studied its effects on cutting force and cutting temperature. It is thus essential to study the combine effect of cutting and jet parameters in machining. This research article focusses on study and optimization of cutting and jet parameters on tool-chip interface temperature and cutting forces during turning hardened alloy steel AISI 4140 steel of 50 HRC using Finite Element Analysis and Taguchi’s Technique. Three levels of cutting speed, feed rate, depth of cut, jet angle and jet velocity are chosen. A suitable L27 Orthogonal array is selected based on Taguchi’s Design of Experiments (DoE) and the output quality characteristics such as tool-chip interface temperature and cutting forces are analyzed by Signal-to-Noise (S/N) ratio. Analysis of Variance is performed to determine the most contributing factor, which shows that the feed and depth of cut are the most prominent contributing parameter followed by cutting speed, jet impingement angle and jet velocity.

Abstract: Nickel based super alloys, such as Inconel 625 is amongst the most difficult to machine, due to its low thermal conductivity and high strength at higher temperature. Although, they are used in aerospace exhaust systems and other applications, the strain hardening that results during the machining operation, which adversely affects surface integrity of machined surface of such materials especially in extensive applications, is a cause for concern. In this context, this study was carried out, involving the milling operation, using solid carbide tools coated with TiAlSiN, under specifically developed conditions for dry machining of the difficult to cut materials. The cutting parameters were 4 in number, namely radial rake angle, feed per tooth, cutting speed and radial depth of cut and the response parameters included surface integrity characteristics, such as residual stresses, surface roughness and micro-hardness. Based on the experimental analyses, it was found that the micro-hardness of machined surface was higher. Micro hardness of sub surface decreases with the depth (50,100,150,250μm) due to a reduction in the work hardening of the Inconel 625, underneath the surface layer. The residual stresses were analyzed using main effect plot, and it was seen that the residual stresses were significantly influenced by the radial rake angle, followed by feed per tooth.