Thanh-Hai Nguyen

This study examined the effect of billet preheating temperature ranging from 1220 to 1275 oC on the microstructure and performance of C45 steel ultrasonic horns. Six samples were fabricated and evaluated for microstructure and ultrasonic performance at 28 kHz through DEFORM-3D simulations and experimental forging trials. The unforged sample (Horn 1) exhibited the highest Qm (3,434), reflecting minimal energy loss under free resonance conditions. However, it failed during ultrasonic operation due to severe local heating and burning at the horn belly, indicating poor thermal reliability. The sample forged at 1,266 oC (Horn 5) showed refined, Dynamically Recrystallized (DRX) microstructures with reduced anisotropy and stable resonance frequencies close to 28 kHz. These results confirm that billet heating temperature strongly governs both microstructural evolution and acoustic behavior. The optimal preheating temperature of 1266 °C ensures a refined, homogeneous microstructure that provides the necessary mechanical integrity and thermal stability for reliable ultrasonic horn operation.

Traditional ultrasonic welding horns are primarily manufactured through CNC machining, which often leads to material wastage and non-uniform microstructure. This study explores an alternative hot forging-based manufacturing process for ultrasonic welding horns using 7075 aluminum alloy. The forming process, temperature variation, and microstructure evolution were simulated using finite element modeling (FEM) in QForm 10, considering key forging parameters such as temperature, deformation, and grain refinement. The results demonstrate that the proposed hot forging method significantly reduces material waste (by 58.41% compared to CNC machining), enhances grain refinement (from 250 µm to 60 µm), and improves mechanical properties. The study confirms the feasibility of using hot forging for mass production of ultrasonic welding horns while ensuring superior structural integrity and performance.

In general, the primary issues related to the present design are primarily the high temperature range, which is generating enormous thermal loads to the machinery, and the inability of achieving even temperature distribution in the workpiece. The new approach in this paper mitigates these issues for the aluminum alloy extrusion process using a screw extruder equipped with a Double Wave Screw (DWS). The extrusion screw is typically divided into three regions: the feeding region, the compression region, and the metering region. The DWS component is designed for the compression and metering regions to achieve maximum shear rate in extrusion, to create globular microstructure. Furthermore, our work aims to predict significant process parameters such as viscosity, shear rate, and material flow velocity to determine the feasibility of 3D printing. In order to validate the effectiveness of the material extrusion process in the 3D printing process, the model has been simulated through the finite element method (FEM) by employing the power-law model, which describes the non-Newtonian behavior of the composite semi-liquid aluminum needle. Simulation has demonstrated that control of the material outlet temperature can generate a semi-liquid state of aluminum. Besides, the DWS configuration enhances the shear rate and homogeneity of the molten metal, ultimately leading to enhanced mechanical properties of the product extruded.

This study explores the optimization of ultrasonic horn heat treatment conditions for enhanced mechanical quality (Q_m). The optimal parameters identified are a tempering temperature of 529°C and a 240-min soaking time, yielding a 1.3% experimental error. Frequency stability during welding is significantly improved, with the optimal horn exhibiting a minimal frequency variation of 64 Hz compared to 90 Hz and 82 Hz for other samples. Hardness varies with tempering temperature, reaching a peak of over 39.3 HRC at 450°C and dropping to 23.8 HRC at 650°C. Microstructural analysis reveals transformations in pearlite, spheroidization, and increased grain sizes in the optimal sample. Carbide precipitation is more pronounced in longitudinal sections and increases with higher tempering temperatures and soaking times. The presence of chromium alloying elements in SCM440 steel contributes to carbide formation. These findings underscore the critical role of heat treatment conditions in optimizing the performance of ultrasonic horns.

Ultrasonic welding is a welding method that has been applied for welding nonwoven fabrics, with many advantages such as fast speed, high reliability, easy automation and especially less pollution to the environment. This paper studies the optimization of technological parameters in the welding process such as welding time, pressure, and weld shape on the breaking strength of ultrasonic welding of Polypropylene (PP) nonwovens. To evaluate the influence level and find the reasonable technological parameters domain in the paper, the Taguchi method is used in combination with the face-centered central composite design (FCCCD) response surface method. The research results have determined the regression equations used to calculate the breaking strength for each weld shape as well as the optimal domain for the main technological parameters, ensuring the breaking strength of the weld. There are different degrees of influence of technological parameters (shape of the weld zone, welding time and welding pressure) on the breaking strength of ultrasonic welds. Among them, the influence level of welding time t is 45.31 %, the weld shape is Pattern 2 with the rate of 30.03 %, and the welding pressure is 24.66 %. Carrying out a verification test with the welding parameters: t=1.6 s, p=3.1 kgf/cm², two patterns ( Pattern 2 and Pattern 3), the result of breaking strength for patterns was achieved. Pattern 2 has a difference of 1.19 % between the regression equation results and the actual experimental results, while the figure for Pattern 3 is 0.77 %. From these results, it is possible to select the appropriate technological parameters for ultrasonic welding equipment when processing products from nonwoven fabrics to ensure the highest quality and productivity