Ultrasonic welding is a process that has been in continuous development since it was first introduced in the 1940s. The process is widely used to join or reform plastic or metal materials using mechanical vibrations propagated at frequencies ranging from 20.000 Hz to gigahertz levels. These vibrations produce heat that melts the materials to be welded at their contact surface. In addition to the heat produced by the vibrations, a preset pressure is applied from the control panel of the welding machine to ensure perfect contact between the welded parts.[1] The ultrasonic welding process is time-efficient, taking less than 0.2 seconds in some cases, and does not damage the outer surface of the parts. The whole paper is structured in two parts, one theoretical and one practical, these parts are divided into six chapters. The first chapter of the paper explains the propagation process of ultrasound and what it actually is, as well as a brief history of ultrasound. In the second chapter there are generalities about ultrasonic welding and how this process is carried out and a history of ultrasonic welding. The third chapter introduces us to the subject of the paper, namely ultrasonic welding of plastics. Chapter four deals with the materials used to produce seat belts and their evolution over time. In chapter five we present all the equipment used for the case study. Chapter six is the case study and the explanation of all the steps performed to find out some results about ultrasonic welding of seat belt samples. Finally, I presented the conclusions drawn from the whole research process and the results obtained for the ultrasonic welding process of seat belts.

This study presents a comparative evaluation of two widely used chemical analysis techniques: scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX) and spectrophotometry. SEM-EDX is renowned for its ability to provide qualitative and quantitative elemental analysis at microscopic levels, making it a powerful tool for material characterization. On the other hand, optical emission spectroscopy, which analyses the light emitted by excited atoms, is highly effective for the rapid and precise quantification of elements in various sample types, especially metals and alloys. The research aims to assess the effectiveness, accuracy, and applicability of these techniques, by analysing identical samples (welding wire) using both SEM-EDX and spectroscopy, this study highlights the strengths and limitations of each method. Key parameters such as sensitivity, detection and data interpretation are compared to provide a comprehensive understanding of their performance in chemical analysis.

Over the past 30 years, the medical sector has increasingly used 3D printing to offer personalized and fast solutions for patients. The lack of biocompatible and biomechanically efficient polymers, hydrogels, biomaterials and bioinks is a major barrier to the widespread adoption of 3D printing in biomedical manufacturing. For this aim, a variety of synthetic and biological polymers can be employed. Combining biological and synthetic materials can enhance their physicochemical and biological qualities, as each has advantages and downsides. This paper discusses the types of synthetic, natural and hybrid materials that can be used for medical purpose 3D printing.