Influence of laser heat treatment on microstructure and properties of surface layer of Waspaloy aimed for laser-assisted machining

In this study, a nickel-based superalloy, Waspaloy, was laser heat treated with diode laser. Single laser tracks were manufactured with different laser beam power densities between 63 and 331 kW/cm², and scanning laser beam speed ranged from 5 to 100 m/min. It was found that laser heat treatment of Waspaloy causes decrease in material hardness—the microhardness in laser tracks is about 300 HV0,1 while the microhardness of substrate is ranged from 300 to 600 HV0,1—which is a positive phenomenon for laser-assisted machining of investigated material. Impacts of laser heat treatment parameters on laser tracks properties were identified for obtaining multiple laser tracks with the most homogenous thickness. Moreover, roughness of heated layers was measured to specify surface quality after laser heat treatment. Multiple laser tracks were produced using different scanning laser beam speed and distances between laser tracks ranged from 0.125 to 1 mm. It was found that if scanning laser beam speed is 75 m/min and distance between laser tracks is equal to or lower than 0.25 mm, in microstructures of multiple laser tracks, cracks are occurring. The most suitable laser heat parameters for obtaining heated layers, and which can be used for laser-assisted machining, were identified as laser beam power density 178.3 kW/cm², scanning laser beam speed 5 m/min, and distance between laser tracks 0.125 mm.     

Experimental investigation on the electrochemical machining of 00Cr12Ni9Mo4Cu2 material and multi-objective parameters optimization

Special stainless steel 00Cr12Ni9Mo4Cu2 has multiple composition and inhomogeneous tissues; short circuiting will frequently occur when using conventional electrolyte processing. This article analyzes the reason why the process of machining is difficult from the material composition and structure. We used the NaNO₃ and NaClO₃ electrolyte composite to select the appropriate concentration, and then by using the orthogonal experiment and gray relational analysis method, we discussed how the voltage, feed speed, and electrolyte pressure solved the problem of the material removal rate (MRR), surface roughness (SR), and side gap. Under optimal conditions of 20 V, an electrolyte composite concentration of 178 g/l NaNO₃ and 41 g/l NaClO₃, a feed rate of 0.7 mm/min, and an electrolyte pressure of 0.8 MPa, a material removal rate of 100.8 mm3/min, a surface roughness of Ra 0.8 μm, and a side gap of 0.16 mm were produced. Given the same voltage, with an increasing cathode feed rate, the MRR was shown to increase while the surface roughness value and the side gap decreased. Under the same cathode feed rate, the MRR decreases, while the side gap and the surface roughness increase as the electrochemical machining application voltage increases. This study proves that using a certain concentration of electrolyte composite is a simple, low-cost, and feasible approach in improving efficiency and quality.     

Fabrication of multiple electrodes and their application for micro-holes array in ECM

In this study, a two-step composite processing technology combining the EDM process and electrochemical etching is introduced to fabricate a micro-electrodes array. Firstly, rectangular columns measuring 0.2×0.2 mm are machined by the wire-EDM (electrical discharge machining) machine tool, then electrochemical etching is used to erode the microelectrodes array into cylindrical columns. Results show that microelectrodes ranging from hundreds of micrometers to several millimeters could be prepared. Then the machined microelectrodes are used as a cathode tool for electrochemical drilling of micro-hole arrays in electrochemical micromachining (EMM). Furthermore, various parameters affecting the performance of EMM are discussed in detail. Results indicate that the production of EMM improves by using multiple microelectrodes. The pulse current shows strong localization in micro-hole drilling and improves the machining accuracy.     

Hybrid (LASER + CNC) process for lubricant groove on linear guides

A novel hybrid process [LASER?+?computer numerical control (CNC) machining] is used to fabricate a linear motion guide. A 20-W pulsed fiber laser and a three-axis CNC machining center were combined to fabricate microscale lubrication grooves on a 5-mm wide linear guide contact surface made of SCM-440H material. Ablation fabrication speed was increased up to 1,000 mm/min (or 16.7 mm/s) with a great ablation quality without any tool wear. The mean values of patterned sizes of lubrication grooves were measured to be between 40 and 80?μm in width and between 150 and 275?μm in depth with a laser pulse repetition of 25 kHz. A specially designed optical device was compact enough to be installed on CNC machine. It was mounted on the CNC spindle and proved to be flexible enough to deliver the laser beam on to the work piece. The microscale ablation quality of the surface was of sufficient quality to be adopted on most linear motion related applications.     

The effect of electrolyte current density on the electrochemical machining S-03 material

Selecting an appropriate electrolyte is very important for high-efficiency electrochemical machining novel S-03 special stainless steel aerospace component. A series of experiments were conducted with NaCl, NaNO₃, and their admixture solutions. This research focused on the relationship between current efficiency and current density. The current density effects on surface roughness, machining velocity, and grain boundary corrosion were analyzed. The results showed that: the current efficiency in NaCl electrolyte was 100 % with different concentrations. Under the conditions of 24 V voltage, 30 °C electrolyte, and 0.8 MPa electrolyte pressure, the 10 % NaCl electrolyte can obtain 3.6 mm/min cathode feed speed; the surface roughness is Ra 0.08 μm; and the material removal rate is 411.4 mm³/min. Comparing forward flow to forward flow with added backpressure, we found that: the surface roughness value decreased sharply at 3.6 mm/min in NaCl electrolyte.     

高回转精度多阶柱状微电极电化学高效制备试验研究

为实现高回转精度多阶柱状微电极的高效加工,对多阶柱状电极电化学刻蚀过程进行了深入的研究与改进。首先,根据电化学刻蚀理论推导了加工电流对电极直径变化的影响规律;通过试验证明了电极旋转可提高电流变化速率及有效起始电流进而提高加工效率,定性分析了电极旋转对电极回转精度的影响,提出了分阶变转速高效加工高回转精度多阶柱状微电极的方法;通过试验分析了各加工参数(电极转速、加工电压和切断电流)对电极形状及尺寸的影响;最后,在优化后的加工参数下,成功加工得到末端直径小于15μm且同轴度误差在1μm以内的多阶柱状微电极,与常规电化学刻蚀工艺相比,显著提高了加工效率。试验证明旋转电化学刻蚀是一种能够较好地提高微电极加工效率及回转精度的新工艺。     

Development and application of copper–nickel zirconium diboride as EDM electrodes manufactured by selective laser sintering

The production of electrical discharge machining (EDM) electrodes by conventional machining processes can account for over 50 % of the total EDM process costs. The emerging additive manufacturing (AM) technologies provide the possibility of direct fabrication of EDM electrodes. Selective laser sintering (SLS) is an alternative AM technique because it has the possibility to reduce the tool-room lead time and total EDM costs. The main difficulty of manufacturing an EDM electrode using SLS is the selection of an appropriate material. This work investigated the direct production of EDM electrodes by means of the SLS using a newly developed non-conventional metal–matrix composite material composed of a metallic matrix (CuNi) and an advanced ceramic (ZrB₂). The influence of important SLS parameters and material content on the densification behavior and porosity of the electrodes was investigated. EDM experiments were conducted to observe the electrodes behavior and performance. It was found that the ZrB₂-CuNi electrodes could be successfully manufactured by SLS. Interlayer bonding and porosity are directly influenced by the layer thickness. Smaller layer thicknesses improved bonding between layers and decreased the porosity of the parts. The laser scan speed has a significant effect on the densification behavior. The scan line spacing affects the pore structure by means of overlapping. The surface morphology of the samples was not affected by varying the scan line spacing. The ZrB₂-CuNi electrodes presented a much superior performance than SLS copper powder electrodes, but inferior to solid copper electrodes.     

Microstructure,chemical composition,wear, and corrosion resistance of FeB–Fe<Subscript>2</Subscript>B–Fe<Subscript>3</Subscript>B surface layers produced on Vanadis-6 steel using CO<Subscript>2</Subscript> laser

The paper presents the study results of laser modification of FeB–Fe₂B surface layers produced on Vanadis-6 steel using pack cementation method. Microstructure, x-ray phase analysis, chemical composition study using wave dispersive spectrometry method, microhardness, corrosion resistance as well as surface condition, roughness, and wear resistance were investigated. The diffusion boronizing processes were performed at 900 °C for 5 h in the EKabor® powder mixture. The boronized layers had a dual-phase microstructure composed of two types of iron borides, FeB and Fe₂B, and their microhardness ranged from 1800 to 1400 HV. The laser surface modification was carried out on specimens after diffusion boronizing process using CO₂ laser with a nominal power of 2600 W. Laser beam power used in this experiment was equal to 1040 W and was constant. While the three values of scanning speed were used: 19, 48, and 75 mm/s. During laser modification, the multiple tracks were made where distance between of axis tracks was equal to 0.5 mm. As a result of this process, microstructure consisted of remelted zone, heat-affected zone, and substrate was obtained. In remelted zone, the boron-martensite eutectic was observed. Boronized layers after laser modification were characterized by the mild gradient of microhardness from surface to the substrate and their value was dependent on the scanning speed used and was between 1700 and 1100 HV. Corrosion resistance tests revealed reducing the current of corrosion in case of laser modification process. Wear resistance of laser modified specimens was improved in comparison to diffusion boronized layers.     

Parametric analysis and optimization of Nd:YAG laser micro-grooving of aluminum titanate (Al2TiO5) ceramics

Pulsed Nd:YAG Laser offers an excellent role for various micro-machining operations of a wide range of engineering materials such as ceramics, composites, diamond etc. The micro-machining of ceramics are highly demanded in the present industry because of its wide and potential uses in various field such as automobile, electronic, aero-space, and bio-medical engineering applications etc. Aluminum titanate (Al₂TiO₅) has tremendous application in automobile and aero engine industry due to its excellent thermal property. The present research paper deals with the response surface methodology based mathematical modeling and analysis on machining characteristics of pulsed Nd:YAG laser during micro-grooving operation on a work piece of aluminum titanate. In this present study, lamp current, pulse frequency, pulse width, assist air pressure and cutting speed of laser beam are considered as machining process parameters during pulsed Nd:YAG laser micro-grooving operation. The response criteria selected for analysis are deviation of taper and deviation of depth characteristics of micro-groove produced on a work piece made of aluminum titanate (Al₂TiO₅). The analysis of variance test has also been carried out to check the adequacy of the developed regression mathematical models. The optimal process parameter settings are assist air pressure of 1.3 kgf/cm², lamp current of 20.44 amp, pulse frequency of 1.0 kHz, pulse width of 10% of duty cycle, and cutting speed of 10 mm/s for achieving the predicted minimum deviation of taper and deviation of depth of laser micro-groove. From the analysis, it is evident that the deviation of taper angle and deviation of depth of the micro-groove can be reduced by a great extent by proper control of laser machining process parameters during micro-grooving on aluminum titanate (Al₂TiO₅).     

An experimentally based thermo-kinetic phase transformation model for multi-pass laser heat treatment by using high power direct diode laser

Laser-based phase transformation hardening (LPTH), based on rapid heating and cooling cycles produces hard and wear-resistant layers only at the selective region of the components. However, the bulk mass of the material’s core property is retained. The advantages of high power direct diode laser in comparison with other high power lasers (CO₂ and Nd:YAG) have put this type of laser as a main heat source for localized heat treatment. However, a tempered zone is formed in overlapping regions of a large heat-treated area during multi-pass laser heat treatment (MPLHT) that affects the uniformity of heat-treated depth of material. This study is focused on the development of a uniform hardness distribution model to minimize the tempering effect during the MPLHT process. A tool steel AISI S7 is heat treated by using different levels of laser power (1,400–1,800 W) and scanning speeds (15–25 mm/s). An experimentally based finite element (FE) thermal model is developed to predict the cross-sectional as well as surface temperature history of the MPLHT process. The temperature-dependent material properties and phase change kinetics are taken into account in the model. The laser beam is considered as a moving rectangular-shaped heat source (12 mm?×?1 mm) with a uniform distribution (top-hat) of laser power. The temperature history acquired from the FE thermal model is coupled with thermo-kinetic (TK) equations to determine the corresponding phase transformations and hardness. The tempering effect of MPLHT is studied for different sizes of overlap (1 mm–3 mm) and lengths of scan (10 mm–35 mm). The TK model results are verified with experimental ones to optimize the processing parameters. The optimized processing parameters, including laser power, scanning speed, size of overlap, and the length of scan are used to achieve a uniform hardness distribution and an even depth of heat treatment in the MPLHT area.     

Application of Taguchi-based gray relational analysis for evaluating the optimal laser cladding parameters for AISI1040 steel plane surface

The effect of various laser cladding process parameters like laser power, scan speed, and powder feed rate on clad bead quality characteristics (or clad bead geometry) for AISI 1040 steel substrate have been studied by performing a number of experiments with L ₉ orthogonal array. In order to find the process parametric setting for best quality clad bead based on experimental results, a multiresponse optimization technique using gray relational analysis (GRA) is presented in this paper. The GRA is applied on laser cladding process to find out the gray relational grade for each experiment. On optimization, power of 1.25 kW, scan speed of 0.8 m/min, and a powder feed rate of 11 gm/min have been found to be the best parametric setting for laser cladding operation of AISI 1040 steel substrate. Moreover, the analysis of variance is also performed to determine the contribution of each control factor on the clad quality characteristics. Finally, to ensure the robustness of GRA, a confirmatory test is performed at selected optimal parametric setting.     

Study of laser butt welding of SUS301L stainless steel and welding joint analysis

This paper describes a study on laser butt welding of 4 and 2 mm SUS301L stainless steel and a detailed analysis of welding joints. The gap tolerance of butt joint was also studied with optimized process parameters. The electrolytic etching in 10 % oxalate solution was used to test the intergranular corrosion of the 4 mm SUS301L welded joint. Fatigue property of the 2 mm SUS301L welded joint was tested under the conditional cycle times of 1?×?10⁷. Using optical microscopy, the changes of metallurgical microstructure in the weld zone of 4 mm SUS301L were also studied. It has been found that laser butt welding of 4 mm SUS301L is able to achieve sound metallurgical morphology and high strength weld joint when the butt gap is within certain tolerance. The weld joint also has good resistance to intergranular corrosion and has a fatigue limit of 310 MPa.     

Surface quality improvement of EDMed Ti–6Al–4V alloy using plasma etching and TiN coating

This paper seeks to improve the surface quality of electrical discharge machining (EDM) Ti–6Al–4V using plasma etching treatment and TiN coating. The EDM parameter setting is optimized firstly based on grey-Taguchi method. Four EDM parameters, including current (A), voltage (V), pulse duration (μs), and duty factor (%), are selected for multiple performance of lower electrode wear rate (EWR), higher material removal rate (MRR), and better surface roughness (SR). An orthogonal array, signal-to-noise (S/N) ratios, and analysis of variance (ANOVA) are used to analyze the effects of these EDM parameters. Normality tests show that all the distributions fit normality assumption with p?=?0.276, 0.688, and 0.663, respectively. The EDM process is stable over time monitored by Shewhart control charts. It is observed that there is an EDM damaged layer on the surface consisting of debris, microcracks, molten drops, and solidified metals by scanning electron microscopy. The plasma etching and TiN coating are employed to improve surface quality of the EDMed Ti–6Al–4V alloys. The results demonstrate that using the oxygen plasma etching treatment, the damaged phenomena are decreased, and the mean SR value is reduced from Ra?=?2.91 to Ra?=?2.50 μm. In addition, when the plasma-treated alloy is coated with Ti buffer/TiN coating by physical vapor deposition, the surface morphology exhibits less defects and a better surface finish. The mean SR values are further reduced from Ra?=?2.50 μm to Ra?=?1.48 μm (for 740 nm TiN film) and Ra?=?0.61 μm (for 1450 nm TiN film), respectively.     

Investigations on precision finishing of space curve meshing wheel by electrochemical brushing process

In this study, a novel finishing process named electrochemical brushing (ECB) is proposed, which integrates the merits of electrochemical polishing (ECP) and mechanical finishing (MF). It executes finishing for the space curve meshing wheel (SCMW), which was manufactured by the selective laser melting (SLM) rapid prototyping process. First, finishing experiments of ECP and ECB were carried out with optimal parameters, including an applied voltage of 10 V, a cathode and workpiece gap of 1 mm, and an ingredient electrolyte of NaNO₃ (10 %)?+?Al₂O₃ (0.1 %)?+?H₂O. Advantages of the ECB process were shown by analyzing the machining mechanism and comparing the experimental results. Furthermore, the cathode tools and finishing experimental rigs were designed to process SCMW samples. Finally, kinematics experiments were carried out, and the relation between the transmission ratio and the surface roughness of meshing tines is discussed. After ECB, as the surface roughness of meshing tines was reduced from 34 to 0.5 μm, the average transmission ratio of SCMW samples was improved from 3.922 to 3.993 and approached the theoretical value of 4, and its standard deviation was improved from 0.0317 to 0.0077. Therefore, the ECB process could be a feasible process to finish the SCMW to be able to perform precision meshing transmission.     

A study of supersonic-aided electrolysis

In this study, a composite processing technology combined with supersonic and electrochemical machining is adapted to etch copper. Rod copper of diameter 3.0 mm is selected as a sample material. A series of experiments of supersonic-aided electrolysis by agitating anode, and electrolyte were carried out to investigate performance for copper etching. Faster metal removal rate can be achieved in supersonic-aided electrolysis machining by agitating either the anode or electrolyte. Removal rate can be raised up to 65% by supersonic-aided electrolysis by agitation both of anode and electrolyte. Deposition speed of cathode is lower in supersonic-aided electrolysis. Machined surface roughness of workpiece by supersonic-aided electrolysis is much better than no agitation.     

Electrochemical machining analysis on grid cathode composed of square cells

During the electrochemical machining (ECM), the cathodes designed by the existing methods are mainly unitary cathodes, which can be only used to produce the workpieces with the same shapes. However, there are few researches on designing cathodes for machining the different workpieces with the different surfaces. This paper presents the grid cathode composed of the square cells to produce the workpieces with different shapes. Three types of the square cells, 2.5 mm′2.5 mm, 3 mm′3 mm, and 4 mm′4 mm, are utilized to construct the plane, the slant, and the blade cathode. The material of the cathode and the anode is CrNi 18 Ti 9 , and the ingredient of electrolyte is 15% NaCl and 15% NaNO 3 . The machining equilibrium machining current and time are acquired and analyzed, the machining process and the workpiece quality are compared between using the grid cathode and the unitary cathode. Moreover, the machining errors on the workpiece surface are measured and analyzed, and the error reasons are traced and discussed to obtain the better surface quality of the workpiece. The experiment and analysis results show that the grid cathode can be used to manufacture the workpieces with complex shapes in certain range of the error. The workpiece quality improves with the size of the square cell being reduced, and if the square element is small enough, the workpiece quality is almost equal to the one machined by the unitary cathode. The proposed research realizes a single cathode machining the different workpieces with the different surfaces.     

Effect of machining parameters on surface roughness and tool wear for 7075 Al alloy SiC composite

In the present study, an attempt has been made to investigate the influence of cutting speed, depth of cut, and feed rate on surface roughness during machining of 7075 Al alloy and 10 wt.% SiC particulate metal-matrix composites. The experiments were conducted on a CNC Turning Machine using tungsten carbide and polycrystalline diamond (PCD) inserts. Surface roughness of 7075Al alloy with 10 wt.% SiC composite during machining by tungsten carbide tool was found to be lower in the feed range of 0.1 to 0.3 mm/rev and depth of cut (DOC) range of 0.5 to 1.5 mm as compared to surface roughness at other process parameters considered. Above cutting speed of 220 m/min surface roughness of SiC composite during machining by PCD tool was less as compared to surface roughness at other values of cutting speed considered. Wear of tungsten carbide and PCD inserts was analyzed using a metallurgical microscope and scanning electron microscope. Flanks wear of carbide tool increased by a factor of 2.4 with the increase of cutting speed from 180 to 240 m/min at a feed of 0.1 mm/rev and a DOC of 0.5 mm. On the other hand, flanks wear of PCD insert increased by only a factor of 1.3 with the increase of cutting speed from 180 to 240 m/min at feed of 0.1 mm/rev and DOC 0.5 mm.     

Parametric optimization of CNC turning process for hybrid metal matrix composite

Machining of hybrid metal matrix composite is difficult as the particulates are abrasive in nature and they behave like a cutting edge during machining resulting in quick tool wear and induces vibration. An attempt was made in this experimental study to evaluate the machining characteristics of hybrid metal matrix composite, and a mathematical model was developed to predict the responses, namely surface finish, intensity of vibration and work-tool interface temperature for known cutting condition while machining was performed in computer numerical control lathe. Design of experiments approach was used to conduct the trials; response surface methodology was employed to formulate a mathematical model. The experimental study inferred that the vibration in V _x, V _y, and V _z were 41.59, 45.17, and 26.45 m/s², respectively, and surface finish R _a, R _q, and R _z were 1.76, 3.01, and 11.94 μm, respectively, with work-tool interface temperature ‘T’ of 51.74 °C for optimal machining parameters, say, cutting speed at 175 m/min, depth of cut at 0.25 mm and feed rate at 0.1 mm/rev during machining. Experimental results were in close conformity with response surface method overlay plot for responses.     

Experimental investigation of machining characteristics and chatter stability for Hastelloy-X with ultrasonic and hot turning

Ultrasonic-assisted machining is a machining operation based on the intermittent cutting of material which is obtained through vibrations generated by an ultrasonic system. This method utilizes low-amplitude vibrations with high frequency to prevent continuous contact between a cutting tool and a workpiece. Hot machining is another method for machining materials which are difficult to cut. The basic principle of this method is that the surface of the workpiece is heated to a specific temperature below the recrystallization temperature of the material. This heating operation can be applied before or during the machining process. Both of these operations improve machining operations in terms of workpiece-cutting tool characteristics. In this study, a novel hybrid machining method called hot ultrasonic-assisted turning (HUAT) is proposed for the machinability of Hastelloy-X material. This new technique combines ultrasonic-assisted turning (UAT) and hot turning methods to take advantage of both machining methods in terms of machining characteristics, such as surface roughness, stable cutting depths, and cutting tool temperature. In order to observe the effect of the HUAT method, Hastelloy-X alloy was selected as the workpiece. Experiments on conventional turning (CT), UAT, and HUAT operations were carried out for Hastelloy-X alloy, changing the cutting speed and cutting tool overhang lengths. Chip morphology was also observed. In addition, modal and sound tests were performed to investigate the modal and stability characteristics of the machining. The analysis of variance (ANOVA) method was performed to find the effect of the cutting speed, tool overhang length, and machining techniques (CT, UAT, HUAT) on surface roughness, stable cutting depths, and cutting tool temperature. The results show both ultrasonic vibration and heat improve the machining of Hastelloy-X. A decrease in surface roughness and an increase in stable cutting depths were observed, and higher cutting tool temperatures were obtained in UAT and HUAT compared to CT. According to the ANOVA results, tool overhang length, cutting speed, and machining techniques were effective parameters for surface roughness and stable cutting depths at a 1% significance level (p ≤ 0.01). In addition, cutting speed and machining techniques have an influence on cutting tool temperature at a 1% significance level (p ≤ 0.01). During chip analysis, serrated chips were observed in UAT and HUAT.     

Ultrafast laser micromachining of 3C-SiC thin films for MEMS device fabrication

Femtosecond pulsed laser (800 nm, 120 fs) micromachining of thin films of 3C-SiC (β-SiC) semiconductor deposited on silicon substrate was investigated as a function of pulse energy (0.5 μJ to 750 μJ). The purpose is to establish suitable laser parametric regime for the fabrication of high accuracy, high spatial resolution and thin diaphragms for high-temperature MEMS pressure sensor applications. Etch rate, ablation threshold and quality of micromachined features were evaluated. The governing ablation mechanisms, such as thermal vaporization, phase explosion, Coulomb explosion and photomechanical fragmentation, were correlated with the effects of pulse energy. The results show that the etch rate is higher and the ablation threshold is lower than those obtained with nanosecond pulsed excimer laser ablation, suggesting femtosecond laser’s potential for rapid manufacturing. In addition, the etch rates were substantially higher than those achievable in various reactive ion and electrochemical etching methods. Excellent quality of machined features with little collateral thermal damage was obtained in the pulse energy range (1–10 μJ). The leading material removal mechanisms under these conditions were photomechanical fragmentation, ultrafast melting and vaporization. At very low pulse energies (<1 μJ), nanoscale material removal has occurred with the formation of nanoparticles that is attributed to Coulomb explosion mechanism. The effect of assist gas on the process performance at low and high energy fluences is also presented.