Key Engineering Materials Vol. 1034

Abstract: In this study, a hot stamping process, which delivers ready-to-use parts for the production of aircraft components is applied as an alternative manufacturing method to, for instance, machined parts. The research has been focused on examining the formability of an aluminium alloy at high temperatures. An extensive experimental campaign has been conducted to establish the optimal hot stamping process parameters. As a final stage of the development, a demonstrator corresponding to a wing rib with AA2198 aluminium-lithium alloy has been successfully produced. After the corresponding heat treatment, material properties have been restored.

Abstract: Surface coatings are crucial for improving the thickness distribution by reducing the interfacial friction between the component and forming die during superplastic forming process. In addition, these coatings act as an oxygen barrier to minimise the formation of alpha case. In this paper, the effect of friction was studied with a single-sheet superplastic forming component using finite-element (FE) analysis and validated through experimental trials. Tensile tests of Ti-6Al-4V were conducted at 900° C according to ASTM E2448 standard, and time-hardening creep power law was used to estimate the material parameters for FE simulation. Herein, two cases were studied. Firstly, a uniform friction condition (one frictional constant) for the whole die surface was studied and a pressure cycle using a strain rate control algorithm was derived using Abaqus. Four different friction constants were studied using the pressure cycle. Low, medium and high fiction coefficients were analysed, along with frictionless conditions. A comparison of FE and experimental results indicated that combining a new coating variant and Boron nitride (BN) achieved similar results to that observed with FE simulation with low friction constant, while results with Boron nitride coating correlated with FE simulation with a medium friction constant. Secondly, a varying friction approach was studied wherein the die surface geometry was segmented and assigned heterogeneous coefficient of friction (COF) values. The obtained FE results suggest that varying friction can introduce slight improvement in the thickness distribution for the selected component geometry.

Abstract: Experimental studies show the significant improvement of superplastic formability of AA5083 alloy under oscillating loads. Tensile tests are performed to determine the benefits of oscillatory stress at 450°C. Microstructural analysis of the tested specimen indicates an improvement in the grain boundary sliding mechanism with oscillation. Based on the knowledge from the tensile tests, a Gas-Oscillation Superplastic Forming (GO-SPF) process is developed. The cycle time of the GO-SPF process to form a AA5083 part in a dual-cavity tool without failure is impressively 4.5 times shorter than the required one of a conventional superplastic forming (SPF) process, while the GO-SPF process is found to provide practically identical forming quality to the conventional SPF process. Significant potential benefits of the GO-SPF process are presented.

Abstract: Laser engraving of elements for injection molds is a technology that allows precise and durable engraving of various details on the surface of the molds. This method uses a focused laser beam to remove material from the mold surface, creating high-resolution patterns, text or codes. This study investigates the influence of various parameters on the laser engraving process, utilizing factorial experimental design to systematically analyze their effects. The parameters considered include power, speed, frequency, number of cuts, stepover, focal distance, and engraving strategy. The objective function of the study is the processing time, which is critical for optimizing efficiency in laser engraving applications. By employing a factorial approach, we aim to identify the interactions between these factors and their collective impact on processing time. The results indicate that certain parameters significantly affect the engraving efficiency, providing insights into optimal settings for enhanced performance. This research contributes to the understanding of laser engraving dynamics and offers practical guidelines for practitioners seeking to improve operational efficiency in laser-based manufacturing processes. Due to the high precision, and flexibility, laser engraving allows the creation of fine and very complex details with high efficiency and durability.

Abstract: The paper presents a comparison of CNC (Computer Numerical Control) turning technologies. In the conventional turning: one cutting tool is dedicated for roughing and another cutting tool for finishing. One cutting tool can cut only in one direction it is not possible to cut in two directions. In the paper all this “standard lathe methods” was replaced with new concepts, with new modalities to understand turning operation. A new method was underlined to turn the material. Considering the development and constructive diversification of numerical control lathes, the evolution of CNC equipment, the development of new cutting tools, new CAM (Computer Aided Manufacturing) programs, and new CNC turning technologies appear. Such a new technology: "Prime technology", is analyzed and tested and the results are presented in the paper. It starts from the presentation of new technologies, which are the requirements and the advantages it brings, all of them being particularized on a real example implemented in the "CNC training center” from Politehnica University of Timisoara, Romania, Faculty of Mechanics, Department of Materials and Manufacturing Engineering. The tests that were conducted and validation of these new methods are the real value of the paper.

Abstract: During metal machining, under certain conditions, vibrations occur, both at the cutting tool, at the workpiece and at the machine tool. The appearance of vibrations during the cutting process is troublesome, because vibrations reduce the durability of cutting tools (especially in tools with inserts). It also increases machine tool wear and worsens the quality of the machined surface (roughness). The problem of vibration is vast and will represent a permanent research topic for tool makers, machine tool builders and process engineers. This paper presents the study and finite element analysis of the vibrations of a cutting tool, a tool used in the longitudinal turning process, both for deburring and finishing operations. The behavior of the tool, the natural frequencies and the elastic deformations that lead to the impairment of the processing precision and the quality of the surface obtained after processing were demined by calculation. We believe that this study is useful both to the manufacturers of cutting tools, but especially to the technological engineers, for the optimization of the process, by avoiding the cutting parameters that lead to resonance with the tool's own frequencies.

Abstract: This paper presents the design and structural analysis of a support system for a 3D printer, developed to improve resin drainage by enabling rotational movement along two axes. Three design variants were created, and after evaluating their performance, the second variant was chosen for its higher torque capacity and potential for future enhancements. This variant showed the most promise in achieving the desired functionality while allowing for further optimization. Finite element analysis (FEA) was utilized to investigate the structural behavior of the support system under loading conditions, ensuring the design remained within the elastic range. The FEA simulations were performed using Beam, Solid, and Shell element types, which provided insights into stress and strain distribution within the structure. This analysis guided the design process, allowing for refinements that improved the structural integrity and load-bearing capacity of the support. Alongside FEA, analytical calculations were performed to assess the bending stress and shear forces on the aluminum profile under three-point bending conditions. These calculations confirmed that the support structure was capable of handling the operational loads while staying within the elastic domain, ensuring reliable performance. This study demonstrates the effectiveness of combining finite element analysis with analytical methods to optimize the design of 3D printer support systems. The results highlight the potential for enhancing the performance and efficiency of additive manufacturing processes through improved structural designs.

Abstract: Cu ribbons were manufactured through continuous casting to 6 mm thick wire, drawing to 0.51 mm fine wire and rolling to 200 μm thickness and 1000 μm ribbons. Annealing treatments with applying an electrical current of 34 Amp led to an average breaking load of 4.2 Kgf, elongation of 38.0% and hardness of 76.2 Hv. Nanotwinned Cu films were sputtered on SiC dies as stress buffer layer to prevent the chip cratering during the ultrasonic bonding using Cu ribbons. The results indicated that satisfactory joints were obtained with shear strengths of 6.3 Kgf and 7.5 Kgf at the interface of Cu ribbon/SiC chip and Cu ribbon/DBC substrate, respectively. The joints after shear tests fractured in the Cu ribbon, rather than along the bonding interfaces, displaying a tight interconnection for the power modules.

Abstract: The high surface diffusivity of (111)- preferred orientation nanotwinned films has been suggested to apply for the low temperature direct bonding of chip to chip in 3D-IC advanced packages. The beneficial effects have also been reported for the Ag sintered die bonding of SiC power modules. In this research, an innovative pre-formed Ag sintered sheets with and without surface deposition of nanotwinned films are proposed for the die bonding of SiC. It shows that the bonding layer porosity decreased from 8.1% to 0.7% as the sintered material changed from traditional Ag paste to pre-formed Ag sheets in the case of die bonding of nanotwinned film metallized SiC chips with DBC alumina substrates. Another example showed that porosities of 3.7% and 4.6% were achieved for the die bonding of SiC/DBC power modules using Ag nanotwinned films coated on the smooth and rough surfaces of the pre-formed Ag sintered sheets, respectively, much preferer to the value of 26.8% for the conventional Ag sintered die bonding without employment of nano-twinned films.