Explore the vast range of titles available.

Cold metal transfer (CMT)-based wire-arc additive manufacturing (WAAM) is a promising method for the production of large-scale and complex metallic parts because of its high efficiency, less heat input and low cost. However, a critical and common problem with the arc welding processes is the irregular geometry at the beginning and end parts of the bead due to the ignition and extinction of the arc. Based on experimental investigations of the irregularities and different possible optimization methods, an improvement strategy consisting of configurations with a varying travel speed and an extra return path is presented in this paper. Experimental results show that this strategy can effectively enhance the geometric accuracy at the beginning and end parts of different single beads. In the manufacturing of a thin-wall part and a multi-pass cladding, the improvement of geometric accuracy has also been achieved by this strategy.

Existing precision design methods cannot directly guide the tolerance design. Therefore, in this study, an optimization design method of machine tool static geometric accuracy based on tolerance modeling is proposed. In this methodology, the mapping relationship between the geometric error of machine tools and tolerance design is established using the small displacement torsor to represent the tolerance information and the Monte Carlo simulation method is used to establish the response model of the torsor parameters and the tolerance variation bandwidths. An assembly accuracy model is then established by combining a machine tool topology analysis and the forming mechanism of the joint surface error. To calculate the tolerances of the component joint surface, a tolerance response model related to the component joint surface tolerance and torsor parameters is developed. Finally, according to the state function of assembly accuracy reliability, a function response model of the assembly accuracy, reliability, and tolerance is developed. Combining the assembly’s processing cost model with the accuracy, reliability, and tolerance principles, a tolerance optimization model of the static geometric accuracy of a CNC machine tool, a linear axis motion guide, is constructed as a case study. Using a simulated annealing genetic algorithm to solve the tolerance optimization model, the tolerance optimization value is obtained, thereby verifying the effectiveness of the proposed method.

Ti6Al4V alloys are often employed in conjunction with carbon fiber–reinforced polymers (CFRPs) to create hybrid structures for aerospace applications. The introduction of the fibrous composites brings significant challenges to the titanium alloys with extremely poor machinability. Since the minimum quantity lubrication (MQL) is reported as a technologically feasible method to improve the machinability of individual titanium alloys, the current work aims to investigate the impacts of the MQL on the machining behavior of titanium-related stacks through the comparison with the dry cutting condition. Drilling tests were carried out to evaluate the machinability and hole quality of CFRP/Ti6Al4V stacks using the TiAlN-coated and diamond-coated drills. The obtained results indicate that the MQL yields a reduction of the drilling torque and the minimization of specific cutting energy consumption during the drilling process of CFRP/Ti6Al4V stacks. The machining qualities are also improved by the help of the MQL, and better surface morphologies of CFRP holes and less titanium burr formation are achieved under the MQL condition. Moreover, the MQL drilling produces better geometrical accuracy of cut composite holes, and the diamond-coated drills outperform the TiAlN-coated ones in terms of higher geometrical accuracy of cut stack holes.

Geometrical accuracy is currently one of the important parameters regarding the machined surfaces of components used in modern technical equipment. Even though the WEDM technology belongs to the precise final machining technologies, the most demanding requirements for the geometrical accuracy of the machined surface are not always met. These geometrical deviations consequently manifest themselves not only in the assembly of particular parts of the final product but also in their operation. In addition, errors of the geometrical accuracy of the machined surface also have negative effect on the serviceability of the finished parts and their overall service life. Even though these shortcomings are only minimally reflected in planar cuts, the production of circular profiles is a problem in particular. The important factors causing this poor quality are the technological parameters in combination with the specific physical and mechanical properties of the workpiece and wire electrode. Experimental research was therefore focused on identifying the influence of selected technological parameters and material properties of the workpiece on the size of geometrical deviations of the machined surface that occur at WEDM using CuZn37 wire electrode. In general, it is also a serious problem to maintain the prescribed geometrical tolerance of the machined surface in a narrow tolerance field. By exceeding it, the product becomes unsatisfactory. However, the problem is also achieved quality, which significantly exceeds the expected values. This essentially reduces productivity and worsens the economic efficiency of production. For this reason, it is ideal to achieve the exact required quality of the machined surface in terms of geometrical accuracy. Therefore, an algorithm of simulation software was proposed, which includes empirically determined mathematical models, based on which the software can predict the necessary setting of technological parameters, derived from the dimensional and material properties of the workpiece and wire. The mentioned solution thus will bring the geometrical accuracy of the production of circular holes in a narrow tolerance field to the customer’s requirements with a significant increase of the economic efficiency of production.

Since the microchannels have a vital role in microelectromechanical systems (MEMS), microfluidic and lab-on-a-chip devices, the surface quality, material removal rate (MRR), and geometrical accuracy of microchannels should be controlled well. The electrolyte nature is one of the dominant and important factors that affect the accuracy and performance of electrochemical discharge machining (ECDM). In this contribution, two alkaline electrolytes, NaOH and KOH, were mixed in equal proportion. It was observed that using NaOH + KOH mixed electrolyte at 15 and 25 wt% concentrations provides more electrical conductivity than KOH and NaOH separately at the same concentrations. It results in the fabrication of deeper microchannel with sharper sidewalls compared to KOH and NaOH, while its surface quality is preserved as well. Also, using 25, 30, and 35 wt% mixed electrolyte, due to higher viscosity compared to KOH, improved the surface quality of channels up to 35, 42, and 36%, respectively. Analyzing the waveform of the current response of various electrolytes showed that the microchannel with poor MRR and surface quality will be fabricated in the presence of salt electrolytes due to the generation of very low energy and unstable electrochemical sparks. In another part of the experiments, scanning electron microscopy (SEM) images and energy-dispersive X-ray (EDX) analysis of the tungsten carbide (WC) tool used in different electrolytes showed that the tools used in NaOH and NaNO 3 had more severe wear compared to KOH and mixed electrolyte. Also, at the applied voltages of 50 V, the tool erosion was more serious compared to tool erosion at 35 V.

The geometrical accuracy of incrementally formed products is the key focus in the incremental sheet forming (ISF) process. Pillow defect hinders the material’s formability, which limits geometrical accuracy. Therefore, considering the pillow defect as the major objective, the present study is aimed to evaluate the benefits of adding vacuum to the conventional ISF process for limiting the pillow effect. This work also studies the impact of forming parameters like tool diameter and vertical step increments on pillowing. Using the digital image correlation (DIC) technique, the material characteristics of AA5052 Al alloy were determined from a room-temperature tensile test. The vacuum-assisted ISF (VISF) experiments were then conducted, and the shape error was computed using the 3D scan data to check the part’s geometrical accuracy. The test results revealed that the forming tool diameter is the most important parameter, followed by the vertical step increment, affecting pillowing; with a small forming tool diameter, vacuum presence greatly reduced material pillowing. Besides, the vacuum uniformly deforms materials and controls shear deformation by balancing local element strain accumulation; however, when the tool diameter increased, the produced parts had no shear deformation. The numerical results showed that pillow formation largely relied on stress values from the forming tool motion and transverse directions and that the pillow height was lowered when the stress values were decreased in magnitude; however, there was no change in direction with a vacuum. In conclusion, the meaningful outcomes from the VISF process confirm the benefits of using vacuum to control pillowing.

One of the major drawbacks of selective laser melting (SLM) is the accumulation of tensile residual stresses (TRS) in the surface and subsurface zones of produced parts which can lead to cracking, delamination, geometrical distortions, and a decrease in fatigue life. 3D laser shock peening (3D LSP) is a novel hybrid method which introduces a repetitive LSP treatment during the manufacturing phase of the SLM process. In this paper, the ability of 3D LSP to convert TRS into beneficial compressive residual stresses and their subsequent effect on the geometrical accuracy of produced parts were investigated. Samples made of Ti6Al4V were manufactured with the 3D LSP process and treated with different processing parameters. Cuboidal samples were used for residual stress measurements, and the evolution of residual stresses was evaluated. Geometrical distortions were measured on bridge-like samples, and the influence on the final sample geometry was quantified. A significant improvement in geometrical accuracy resulting from reduced distortions was observed in all selected 3D LSP processing conditions.

A comprehensive investigation of the size and geometry dependency of the dimensional accuracy of direct metal laser sintering (DMLS) for Ti-6Al-4V ELI is presented. For features such as walls, squares, tubes, and rods with different sizes, the percent error significantly increases with decreasing the feature size. The polynomial function a t - b is suggested to describe this size dependency of the dimensional error where a and b are parameters depending on the geometry, material, and DMLS process parameters. This function is used to successfully predict the dimensional error in DMLS of two spinal cages. Therefore, these functions can be used to account for these errors in DMLS by design change or by adjusting DMLS scaling factors. Furthermore, the inconsistency of the DMLS-manufactured dimensions within the feature is shown to be in the same range of the dimensional inconsistency for features located at different positions on the build platform, implying that the location of the feature on the build platform has a negligible effect on the dimensional accuracy. Finally, it is shown that the error in the position accuracy of DMLS-manufactured features is negligible when the size dependency of the dimensional features is considered in the measurements.

The Gaofen-1 (GF-1) and Gaofen-6 (GF-6) satellites have acquired many GF-1 and GF-6 wide-field-view (WFV) images. These images have been made available for free use globally. The GF-1 WFV (GF-1) and GF-6 WFV (GF-6) images have rational polynomial coefficients (RPCs). In practical applications, RPC corrections of GF-1 and GF-6 images need to be completed using the rational function model (RFM). However, can the accuracy of the rational function model satisfy practical application requirements? To address this issue, a geometric accuracy method was proposed in this paper to evaluate the accuracy of the RFM of GF-1 and GF-6 images. First, RPC corrections were completed using the RFM and refined RFM, respectively. The RFM was constructed using the RPCs and Shuttle Radar Topography Mission (SRTM) 90 m DEM. The RFM was refined via affine transformation based on control points (CPs), which resulted in a refined RFM. Then, an automatic matching method was proposed to complete the automatic matching of GF-1/GF-6 images and reference images, which enabled us to obtain many uniformly distributed CPs. Finally, these CPs were used to evaluate the geometric accuracy of the RFM and refined RFM. The 14th-layer Google images of the corresponding area were used as reference images. In the experiments, the advantages and disadvantages of BRIEF, SIFT, and the proposed method were first compared. Then, the values of the root mean square error (RSME) of 10,561 Chinese, French, and Brazilian GF-1 and GF-6 images were calculated and statistically analyzed, and the local geometric distortions of the GF-1 and GF-6 images were evaluated; these were used to evaluate the accuracy of the RFM. Last, the accuracy of the refined RFM was evaluated using the eight GF-1 and GF-6 images. The experimental results indicate that the accuracy of the RFM for most GF-1 and GF-6 images cannot meet the actual use requirement of being better than 1.0 pixel, the accuracy of the refined RFM for GF-1 images cannot meet practical requirement of being better than 1.0 pixel, and the accuracy of the refined RFM for most GF-6 images meets the practical requirement of being better than 1.0 pixel. However, the RMSE values that meet the requirements are between 0.9 and 1.0, and the geometric accuracy can be further improved.

In modern constructions, especially aircraft, the aim is to minimize the weight of the components used. This necessitates the use of innovative construction materials, or the production of these parts with ever-decreasing wall thicknesses. To simplify assembly and improve strength properties, so-called structural elements are being used in the form of monolithic elements, which are replacing the assemblies of parts joined by, for example, riveting. These structures often have a complex, thin-walled geometry with deep pockets. This paper attempts to assess the accuracy of manufacturing thin-walled elements, in the shape of walls with different geometries, made of various aluminum alloys. Machining tests were conducted at different cutting speeds, which allowed comparisons of the geometric accuracy of parts manufactured under conventional and high-speed cutting conditions. Based on the result obtained, it was found that the elements made of EN AW-7075 T651 alloy underwent the greatest deformations during machining in comparison to other two materials (EN AW-6082 T651 and EN AC-43000). An increase in the geometrical accuracy of the manufactured elements was also observed with the increase in the cutting speed for the HSC range. Hence, to minimize the postmachining deformation of thin-walled elements, the use of high-speed cutting is justified.