Copper Workpiece Research Articles

Portable Machine Tools by Small Piezoelectric Robots for Scalable and Waviness‐Adaptive Fabrication of Surface Microstructures

Surface functional microstructures exhibit extensive application requirements in an array of breakthrough areas. One critical problem that restricts their industrial application is the lack of scalable fabrication techniques due to the limitation of conventional machine tools. This study proposes a scalable surface texturing technique using a portable small (30 × 19 × 22 mm) three‐leg robot that walks and works on the workpiece surface. Due to the elliptical tool vibration, microgrooves can be created on the workpiece surface periodically; meanwhile, the machining force drives the robot to walk forward. Surface texturing experiments are conducted on aluminum and copper workpieces to explore the machining performance of the small robot. The robot can reach a maximum moving velocity of 6.3 mm s−1 and can produce microstructures with a spacing of 4–14 μm on workpiece surfaces. Owing to its unique working principle, the small robot can maintain a constant depth of cut, demonstrating its capacity to adapt to the surface waviness of the workpiece. Finally, the motion straightness of the robot is greatly improved by combining it with the auxiliary track, and multiline microstructures are obtained. In short, the developed small robot presents a promising solution to the challenge of scalable surface texturing.

Cyclic biomachining of copper: Maximum metal removal rate with minimum depleted solution

Bacterially assisted leaching has been proposed for many innovative applications, such as urban mining or micromachining, but many technical challenges including substrate toxicity and downstream processing of the leach liquor must be solved before its industrial implementation. This study was conducted with the final goal of improving the average specific metal removal rate (SMRR) and reducing the amount of depleted solution generated in the leaching process of copper workpieces, with special attention paid to the detection of microbial activity inhibition.The copper leaching rate is almost entirely dependent upon the Fe3+ concentration with Fe3+/Fe2+ ratios higher than 0.3, after which A. ferrooxidans oxidation action becomes relevant. In both biotic and abiotic experiments, the SMRR peaked after the first hour of treatment, and it decreased sharply after three hours. A consecutive process alternating bioleaching and oxidant regeneration stages was proposed to improve performance, which considerably reduced both the time needed to dissolve a certain amount of metal and waste generation. The decrease in copper removal (25 %) and the increase in the time required for oxidant regeneration after five leaching cycles (longer than 90 h) were attributed to bacterial inhibition in the presence of 10.7 g Cu2+ L−1, which was established as the limiting metal concentration for reusing the biologically active solution.

Triple Effects of the Physicochemical Interaction between Water and Copper and Their Influence on Microcutting.

Water has been recognized in promoting material removal, traditionally ascribed to friction reduction and thermal dissipation. However, the physicochemical interactions between water and the workpiece have often been overlooked. This work sheds light on how the physicochemical interactions that occur between water (H2O) and copper (Cu) workpiece influence material deformations during the cutting process. ReaxFF molecular dynamics simulations were employed as the primary method to study the atomistic physical and chemical interactions between the applied medium and the workpiece. Upon contact with the Cu surface, H2O dissociated into OH- ions, H+ ions, and traces of O2- ions. The OH- and O2- ions chemically reacted with Cu to form bonds that weakened the Cu-Cu bonds by elongation, while the H+ ions gained electrons and diffused into the Cu lattice as H- ions. The weakening of surface Cu bonds promoted plastic deformation and reduced the difficulty of material removal. Meanwhile, further addition of H2O molecules saw a plateau in hydrolysis and more dominance of H2O physical adsorption on Cu, which weakens the elongation of Cu-Cu bonds. While the ideal case for atomic-scale material removal was found with an optimal number of 240 H2O molecules, the presented Cu material state with more H2O molecules could account for the observations in microcutting. The constricted nature of physical adsorption and hydrogen ion diffusion in the surface layer prevented the propagation of dislocations through the surface, which subsequently caused pinning points to be closer together during chip formation as observed by smaller chip fold widths on the microscale. Theoretical and experimental analysis identified the importance of accounting for physicochemical interactions between surface media and the workpiece when considering material deformations at micronanoscale.

Detailed characterisation of batch-manufactured flexible micro-grinding tools for electrochemical assisted grinding of copper surfaces

Precision machining is becoming more and more important with the increasing demands on surface quality for various components. This applies, for example, to mirror components in micro-optics or cooling components in microelectronics. Copper is a frequently used material for this purpose, but its mechanical properties make it difficult to machine. In this study, a process strategy for finishing copper surfaces with batch-manufactured micro-grinding tools in an electrochemically assisted grinding process is demonstrated. The tool heads are manufactured from a polyimide-abrasive-suspension and silicon as a carrier substrate using microsystems technology. The matching shafts are milled from aluminium. The tools are then used on pure copper and oxidised copper surfaces. By using finer abrasives grains (1.6–2.4 µm instead of 4–6 µm) than previously, similar surface roughness values could be achieved (Ra = 0.09 ± 0.02 µm, Rz = 1.94 ± 0.73 µm) with the same grinding process. An optimised grinding process that combines the use of rough and fine tools, on the other hand, achieves significantly better surface finishes in just four grinding iterations (Ra = 0.02 ± 0.01 µm, Rz = 0.83 ± 0.21 µm). In order to achieve a further increase in surface quality, this optimised grinding process is combined with the anodic oxidation of the copper workpieces. The surface modification is done to increase the machinability of the surface by creating an oxide layer. This is confirmed by the results of scratch tests carried out, which showed less force acting on the tool during machining with the oxide layer than with a pure copper surface. To realise this within the machine tool, an electrochemical cell is shown that can be integrated into the machine so that the oxidation can be carried out immediately before the grinding process. The copper layers produced inside the electrochemical cell in the machine tool show similar characteristics to the samples produced outside. Processing the oxidised samples with the optimised grinding process led to a further reduction of about 17% in the Rz values (Ra = 0.03 ± 0.01 µm, Rz = 0.69 ± 0.20 µm). The combination of the shown grinding process and the integration of anodic oxidation within the machine tool for the surface modification of copper workpieces seems to be promising to achieve high surface finishes.

Implementation of structurally pre-stressed piezo actuator based active vibration isolation system for micro milling

This paper presents the implementation of a structurally pre-stressed piezo actuator based active vibration isolation system incorporated with tool based micromachining setup for analyzing and comparing the milled pocket depth surface before and after isolation. A carbide micro end mill tool with 1 mm diameter and 4 flutes has been used for carrying out pocket milling experiments with and without vibrations on copper work pieces having 3 mm thickness. The machining parameters selected were spindle speed of 16,000 rev/min with 64 mm/min feed rate and 50 μm depth of cut. Two sets of pocket milling experiments were carried out using the proposed vibration isolation setup one with vibration and the other without vibration. In the first set of experiment, the source actuator was actuated for generating vibrations during pocket milling whereas in the second set of experiment, both source and isolator actuators were actuated for nullifying the vibrations generated during pocket milling. The macroscopic lens output images of the pocket depth surfaces before and after isolation were then compared corresponding to various actuation voltages at different frequencies using the proposed vibration isolation setup. Based on the macroscopic lens output images it was observed that the milled pocket depth surface obtained by actuating only source actuator showed distinct rings wherein the ring count matched with frequency and feed rate that has been provided during machining. However, the milled pocket obtained by actuating both source and isolator actuators resulted in surface characteristics with less pronounced rings similar to that of regular machining. Also the rings that has been formed showed more defined edges with the increase in actuator voltage indicating that these distinct patterns were caused due to the vibrations generated by the source actuator alone and not other factors.

Molecular dynamics simulations of nanometric cutting of single crystal copper sheets using a diamond tool

Nanometric cutting of a single crystal copper workpiece of different crystallographic orientations by a stiff cylindrical cubic diamond tool has been investigated by MD simulations using the freeware LAMMPS. The chip evolves during the cutting process and forms depending on crystal orientation, cutting velocity and tool geometry. It was found that no significant difference in the cutting force magnitude was observed for different crystallographic orientations despite significant differences in deformation patterns. After tool passage the surface is smooth and no elastic recovery was detected. Instead, a grain structure with areas surrounded by dislocation clusters form in the tool wake. Increasing the cutting velocity promotes chip formation and chip folding, thus increasing the chip thickness.

Experimental investigation on hydrophobic/superhydrophobic micro patterns: New manufacture method and performance

Hydrophobic/superhydrophobic micro patterns have broad application prospect due to their excellent water repellent ability. In order to manufacture hydrophobic micro patterns on metallic surface, a new flexible and high-efficient method called oscillation-loaded dynamic micro embossing (DME) was developed. In this work, the manufacture process and hydrophobic performance of micro patterns were experimentally investigated. Firstly, the oscillation-loaded DME process parameters designing method was provided to fabricate micro patterns with target dimensions. Then, pure copper workpiece with micro parallel channels and cubes array with different feature width were obtained through DME experiments. The experimental results of the geometrical morphology showed that dimensions of micro patterns were close to the theoretical value, demonstrating the effectiveness of the process parameters designing method. In addition, it was revealed that the roughness of the micro pattern top surface was enhanced significantly by increasing grain size and reducing punch width. Furthermore, the hydrophobic performance of the manufactured parallel channels and cubes array were investigated through water contact angle ( WCA ) test. It was demonstrated that the WCA of pure copper workpiece was improved significantly by the fabricated micro parallel channels and cubes array. Moreover, it was found that the WCA can be improved by reducing the feature width for both the parallel channels and cubes array. Lastly, superhydrophobic micro patterns with WCA up to 161.4° were obtained by utilizing the new oscillation-loaded DME process and plasma surface treatment.

Finite Element Analysis and Experimental Investigation of Tool Chatter in Ultra-Precision Diamond Micro-Milling Process

Ultra-precision milling with an aerostatic high-speed spindle and a single-crystal diamond micro-tool is promising for the fabrication of miniaturized complex parts. While tool chatter occurring in milling processes has a substantial effect on the machined surface formation, a fundamental understanding of the tool chatter behavior in ultra-precision milling is essentially required for achieving an ultra-high surface finish. In this paper, through a combination of finite element simulations and experimental validations, the machining mechanisms of the ultra-precision diamond micro-milling of a copper workpiece are revealed, in which the tool chatter behavior and its correlation with the machined surface morphology are emphatically studied. Specifically, the correlation between the tool chatter and the transient depth of cut is analytical established. Subsequently, we first establish a finite element model of diamond micro-milling with the consideration of milling tool deformation and material removal to reveal the tool chatter behavior during the milling process. Furthermore, a corresponding micro-milling experiment is also conducted to validate the simulation results in terms of the milling force, chip profile and morphology of machined surfaces. Finally, the effect of spindle speed on the milling process in particular tool chatter is investigated by FE simulations, through which a linear relationship between the spindle speed and microscopic roughness Rz of a machined surface is obtained. The research findings provide a theoretical basis for understanding the origination of tool chatter in the diamond micro-milling process, as well as the rational selection of machining parameters for suppressing the tool chatter.

Analysis of Surface Profile Error of Ultra-Precision Diamond Planing Based on Power Spectral Density

Vibration in ultra-precision machining is an inherent physical phenomenon and a key factor affecting surface generation. However, the influence of the vibration characteristics of aerostatic guideways on the machining morphology has not been fully studied. In this article, a diamond micro-planing experiment was carried out on an oxygen-free copper workpiece using a homemade three-axis machine tool, and a white-light interferometer was used to measure the surface topography of the planing surface. The power spectral density of the surface topography was analyzed, and the spatial wavelength components of the surface topography were extracted. Then, the vibration characteristics of the aerostatic guideway were measured in both the space domain and the time domain. A comprehensive analysis of the main components of the workpiece surface error morphology and the vibration characteristics of the guideway shows that the time-domain vibration of the aerostatic guideway is the main factor causing the surface topography error of the workpiece.

Electrorheological polishing performance of cerium-doped titanium dioxide particles

Electrorheological (ER) polishing as a new type of polishing technique has flexibility and controllability. However, ER polishing cannot be widely used in actual processing because the present ER polishing fluid is usually prepared by simple mixing abrasive materials into ER fluid, which is easy to occur phase separation and decreased ER performance. This paper develops a new type of ER polishing material based on cerium-doped titanium dioxide. As a classic abrasive, the cerium oxide not only has high polishing performance but also can enhance ER performance of titanium dioxide by doping effect, which endows the cerium-doped titanium dioxide with high ER polishing efficiency compared to ER polishing fluid prepared by a simple mixing method. Cerium-doped titanium dioxide particles were prepared by the sol-gel method. The size, surface morphology and elemental distribution were characterized. The ER properties were tested. The effects of different concentrations, machining gap, voltage and rotation speed on polishing performance were studied. Under the conditions of a 0.2 mm machining gap, 3 kV voltage and 200 r/min rotation speed, the surface roughness (Ra) of the copper workpiece decrease from 136 nm to 14.4 nm after 0.5 h of polishing, which is far higher than the polishing efficiency of simple mixed ER polishing fluid.

Towards obtaining high-quality surfaces with nanometric finish by femtosecond laser ablation: A case study on coppers

Femtosecond laser ablation is an essential technology for the fabrication of functional surfaces. However, the ablation quality in femtosecond laser processing is influenced by the excessive energy deposition and the heat accumulation, which results in a low ablated surface quality and even defects on the surface. This study performed femtosecond laser ablation to obtain surfaces with a nanometric finish. Different pulse overlap rates and multiple scanning strategies of the femtosecond laser to machine surfaces with reduction of debris, periodic striped micro-grooves, and micrometric ripples were investigated, which allowed an access to a high-quality surface with a nanometric finish. A mathematical model of femtosecond laser ablation was established to study the formation mechanism of ablated surface characteristics. The effects of the pulse overlap rate and scanning strategy on the generation of debris and microstructures were investigated. Experiments were carried out to verify the method by controlling the pulse overlap rate and scanning strategy of the laser. A femtosecond laser ablated copper workpiece with a surface roughness Sa of 0.056 μm was achieved.

Theoretical and experimental investigation into machining characteristics Of VHF micro-EDM

To further explore the machining characteristics of very high-frequency micro-electrical discharge machining (VHF micro-EDM), the range of radio frequency (RF) power amplifier was expanded to 110 MHz, and the power of the RF power amplifier was also greatly increased up to 91 W. The principle of the VHF pulse generator was discussed in detail, and an electro-thermal model suitable for VHF micro-EDM was established to determine the diameter of the plasma channel and the energy distribution ratio. Experimental studies for VHF micro-EDM were also carried out, and the effects of power and frequency on machining characteristics were then analyzed and discussed. The results show that at the same frequency, the higher the power is, the higher the material removal rate (MRR) and the larger the number of discharge craters. At the same power, both the MRR and the size of discharge craters first increase and then decrease with increasing frequency and peak at 65 MHz. For a copper workpiece, when the frequency is 110 MHz and the total power of the power amplifier is 8.0 W, 5.6% of the energy is used for the material removal of the workpiece and the finest processing surface is obtained with the surface roughness Ra = 12 nm. The average diameter of the discharge craters is as small as 0.268 μm, and the diameter of the plasma channel is only 0.350 μm. In addition, the effects of different workpiece materials and dielectric fluids are also analyzed in this paper.

Development and characterization of xanthan gum-based abrasive media and performance analysis using abrasive flow machining

Abstract In the Abrasive Flow Machining (AFM) process, a self-deformable abrasive media is used for the fine finishing of the workpiece. The development of polymer and rubber-based abrasive media includes long processing time, costly equipment and high preparation cost. The processing and disposal of these abrasive media harm both human health and the environment. Therefore, there need some alternate abrasive media which are not only cost-effective but also are eco-friendly. In this study, a low-cost hydrogel-based abrasive media has been developed for AFM. Xanthan Gum (XG) was used as the main constituent to develop hydrogel. Locust Bean Gum (LBG) and Fumed Silica (FS) were added as crosslinking and thickening agent, respectively. Finally, the abrasives were mixed in the hydrogel to develop abrasive media. The physical and thermal properties of developed XG-based abrasive media were characterized using Scanning Electron Microscopy (SEM), sweep tests, Thermo-Gravimetric Analysis (TGA), Differential Thermal Analysis (DTA), and Fourier Transform Infrared Spectroscopy (FTIR). The developed abrasive media showed shear-thinning behaviour during the sweep test and has also been found to be thermally stable in the operational temperature range of AFM. The required crosslinking and elasticity in abrasive media have been confirmed by FTIR analysis. The performance of developed abrasive media was evaluated by using it for the finishing of copper workpieces. The effect of extrusion pressure, number of cycles, and abrasive mesh size on the amount of material removed (MR) and percentage improvement in surface roughness ( % Δ R a ) have been discussed. The performance of XG-based abrasive media has also been compared with polymer-based abrasive media.

Hot embossing of aspherical Fresnel microlenses: design, process, and characterization

Hot embossing is a technique used to fabricate high-precision and high-quality polymeric components that combines low costs with high aspect ratio fidelity replication. In this study, we manufactured two aspherical Fresnel molds employing the single-point diamond turning process on an electrolytic copper workpiece, one with 10 μm constant height 30 zones and the other with 250 μm constant width 40 zones. The micromachined mold reproduced PMMA convex-plane lens optical quality replicas through the micro hot embossing technique. We used a scanning electron microscope (SEM), spectrophotometry, and non-contact optical profilometer to evaluate the replication fidelity qualitatively: the lens mold and the fine three-dimensional microstructures on the PMMA substrate surfaces. The results of the surface finish of the diamond machined mold sample are in the range of 4.92 nm (areal average surface roughness Sa) and 6.04 nm (areal root-mean-squared roughness Sq), respectively, and the values for the replicas being 4.73 nm and 5.94 nm, respectively. The results demonstrated that the geometry form accuracy obtained of the microfeatures was at the submicron level with little viscoelastic recovery. The surface roughness in the nanometer level got successfully replicated.

Modelling and measurements of gas tungsten arc welding in argon–helium mixtures with metal vapour

Argon–helium mixtures in gas tungsten arc welding of an iron workpiece are investigated using an axisymmetric computational model that includes the cathode, workpiece, and arc plasma in the computational domain. The three-gas combined diffusion coefficient method is used to treat diffusion of helium, argon, and iron vapour. Calculations for argon–helium mixtures without metal vapour are performed; good agreement with previous numerical results is found. A transition from a helium-like to an argon-like arc occurs when the argon mole fraction increases above about 0.3. Calculations for a wide range of argon–helium mixtures including iron vapour are then performed. Adding helium to argon alters the arc properties and affects the weld geometry. Iron vapour cools the arc for all argon–helium mixtures. Iron vapour is present above the workpiece, near the cathode and in the arc fringes for very low argon mole fractions. As the argon mole fraction increases, the iron vapour becomes increasingly confined to the region above the workpiece, with small amounts near the cathode tip. Emission spectroscopy measurements of arcs in argon–helium mixtures with water-cooled copper and uncooled iron workpieces were performed. The measured distributions of atomic helium and iron emission show good agreement with the predictions of the model.

The assessment of the process of drawing a cylindrical workpiece without pressing with alternating strain of the workpiece flange

The development of a method for drawing cylindrical parts without pressing the workpiece flange, which allows reducing the cost of production due to the use of dies without a fit ring and single-acting presses. The performed research revealed that this method results in obtaining cylindrical parts with drawing ratios typical for pressing drawing. In this case, the different thickness of the finished product is several times less compared with the same type of semi-finished products obtained by drawing with a fit ring. Steel, aluminum and copper workpieces were researched. The best results were shown by more plastic materials. This method is not applicable for materials with the less than 0.25 mm thickness.

Predicting the Tool Wear of a Drilling Process Using Novel Machine Learning XGBoost-SDA.

Tool wear negatively impacts the quality of workpieces produced by the drilling process. Accurate prediction of tool wear enables the operator to maintain the machine at the required level of performance. This research presents a novel hybrid machine learning approach for predicting the tool wear in a drilling process. The proposed approach is based on optimizing the extreme gradient boosting algorithm’s hyperparameters by a spiral dynamic optimization algorithm (XGBoost-SDA). Simulations were carried out on copper and cast-iron datasets with a high degree of accuracy. Further comparative analyses were performed with support vector machines (SVM) and multilayer perceptron artificial neural networks (MLP-ANN), where XGBoost-SDA showed superior performance with regard to the method. Simulations revealed that XGBoost-SDA results in the accurate prediction of flank wear in the drilling process with mean absolute error (MAE) = 4.67%, MAE = 5.32%, and coefficient of determination R2 = 0.9973 for the copper workpiece. Similarly, for the cast iron workpiece, XGBoost-SDA resulted in surface roughness predictions with MAE = 5.25%, root mean square error (RMSE) = 6.49%, and R2 = 0.975, which closely agree with the measured values. Performance comparisons between SVM, MLP-ANN, and XGBoost-SDA show that XGBoost-SDA is an effective method that can ensure high predictive accuracy about flank wear values in a drilling process.

Investigation of effect of uncut chip thickness to edge radius ratio on nanoscale cutting behavior of single crystal copper: MD simulation approach

Extremely small cutting depths in nanoscale cutting makes it very difficult to measure the thermodynamic properties and understand the underlying mechanism and behavior of workpiece material. Highly precise single-crystal Cu is popularly employed in optical and electronics industries. This study, therefore, implements the molecular dynamics technique to analyze the cutting behavior and surface and subsurface phenomenon in the nanoscale cutting of copper workpieces with a diamond tool. Molecular dynamics simulation is carried out for different ratios of uncut chip thickness ( a) to cutting edge radius ( r) to investigate material removal mechanism, cutting forces, surface and subsurface defects, material removal rate (MRR), and stresses involved during the nanoscale cutting process. Calculation of forces and amount of plowing indicate that a/ r = 0.5 is the critical ratio for which the average values of both increase to maximum. Material deformation mechanism changes from shear slip to shear zone deformation and then to plowing and elastic rubbing as the cutting depth/uncut chip thickness is reduced. The deformation during nano-cutting in terms of dislocation density changes with respect to cutting time. During the cutting process, it is observed that various subsurface defects like point defects, dislocations and dislocation loops, stacking faults, and stair-rod dislocation take place.

Performance of Ceramic-Metal Composites as Potential Tool Materials for Friction Stir Welding of Aluminium, Copper and Stainless Steel.

The aim of the research was to disclose the performance of ceramic-metal composites, in particular TiC-based cermets and WC-Co hardmetals, as tool materials for friction stir welding (FSW) of aluminium alloys, stainless steels and copper. The model tests were used to study the wear of tools during cutting of metallic workpiece materials. The primary focus was on the performance and degradation mechanism of tool materials during testing under conditions simulating the FSW process, in particular the welding process temperature. Carbide composites were produced using a common press-and-sinter powder metallurgy technique. The model tests were performed on a universal lathe at the cutting speeds enabling cutting temperatures comparable the temperatures of the FSW of aluminium alloys, stainless steels and pure copper. The wear rate of tools was evaluated as the shortening of the length of the cutting tool nose tip and reaction diffusion tests were performed for better understanding of the diffusion-controlled processes during tool degradation (wear). It was concluded that cermets, in particular TiC-NiMo with 75–80 wt.% TiC, show the highest performance in tests with counterparts from aluminium alloy and austenitic stainless steel. On the other hand, in the model tests with copper workpiece, WC-Co hardmetals, in particular composites with 90–94 wt.% WC, outperform most of TiC-based cermet, including TiC-NiMo. Tools from ceramic-metal composites wear most commonly by mechanisms based on adhesion and diffusion.

Atomistic Simulation Study of Nanoparticle Effect on Nano-Cutting Mechanisms of Single-Crystalline Materials.

Nanoparticle (NP), as a kind of hard-to-machine component in nanofabrication processes, dramatically affects the machined surface quality in nano-cutting. However, the surface/subsurface generation and the plastic deformation mechanisms of the workpiece still remain elusive. Here, the nano-cutting of a single-crystalline copper workpiece with a single spherical embedded nanoparticle is explored using molecular dynamics (MD) simulations. Four kinds of surface/subsurface cases of nanoparticle configuration are revealed, including being removed from the workpiece surface, moving as a part of the cutting tool, being pressed into the workpiece surface, and not interacting with the cutting tool, corresponding to four kinds of relative depth ranges between the center of the nanoparticle and the cutting tool. Significantly different plastic deformation mechanisms and machined surface qualities of the machined workpiece are also observed, suggesting that the machined surface quality could be improved by adjusting the cutting depth, which results in a change of the relative depth. In addition, the nanoparticle also significantly affects the processing forces in nano-cutting, especially when the cutting tool strongly interacts with the nanoparticle edge.