Browsing by Author "Varela, Sonia"
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Item Insertion behavior study of multi-material self-piercing rivet joints by means of finite element simulation(American Institute of Physics Inc., 2019-07-02) Varela, Sonia; Mangas, Ángela; Kotercova, Zuzana; Briskham, Paul; Giménez, María; Muñoz, Carlos; Molina, Ricardo; Santos, Maite; Arrazola, Pedro; Saenz de Argandona, Eneko; Otegi, Nagore; Mendiguren, Joseba; Saez de Buruaga, Mikel; Madariaga, Aitor; Galdos, Lander; PROMETAL; Tecnalia Research & Innovation; SGOver the last few years, fuel economy improvement has driven the use of efficient multi-material structures in the car industry. The combination of dissimilar materials, such as metal-metal and metal-polymer, is a complex issue that requires the use of different and emerging joining techniques. In this context, self-pierce riveting (SPR) is an extremely suitable technique for joining two or more metal sheets, particularly when other techniques are not applicable. SPR requires short manufacturing times and provides both high strength and high fatigue resistance. Yet, this technique still faces some hurdles, such as joining Ultra High Strength Steels (UHSS) with high strength low ductility aluminum alloys, which can result in rivet cracking or aluminum button tearing. Suitable process parameters, including the rivet size and the die profile, are usually obtained through a physical testing procedure to satisfy the required joint specification. This is both expensive and time consuming. Finite element simulations of SPR are being increasingly used to reduce the number of physical tests and to estimate the tensile strength of the joint. The capability to accurately simulate aluminum to aluminum riveting has been demonstrated in recent studies. However, very few simulation studies have been conducted on the riveting of UHSS to aluminum, mainly because this type of joint is a relatively new customer demand driven by the rapid adoption of mixed material car body structures. New rivet designs have recently been developed for joining UHSS to aluminum, these rivets have increased column strength and increased stiffness to enable piercing through UHSS materials. In this study the insertion behavior of these higher strength rivets has been simulated and numerical analysis has been conducted to investigate the influence of the key process parameters on the joining result. The simulation results were compared to physical experimental results and good correlation was achieved.Item Material saving by a combination of rotary forging and conventional processes: Hybrid forging for net-shape gear: Hybrid forging for net-shape gear(American Institute of Physics Inc., 2019-07-02) Varela, Sonia; Valbuena, Oscar; Armentia, Jorge; Larrucea, Francisco; Manso, Virginia; Santos, Maite; Arrazola, Pedro; Saenz de Argandona, Eneko; Otegi, Nagore; Mendiguren, Joseba; Saez de Buruaga, Mikel; Madariaga, Aitor; Galdos, Lander; PROMETAL; INDUSTRY_THINGS; SGIncreasing efficiency in raw material and energy usage is vital, even more in sectors, such as the hot forging industry, where material accounts for 50% of component price and energy costs are continuously rising. One of the methods to achieve this is to minimize material waste. Traditionally, high-quality gears for the automotive sector are machined to shape from forged preforms which is wasteful of both materials and energy. Attention has now turned to the forging of tooth gears by conventional forging. However, this could require high forging loads and therefore huge press sizes. Some gears may also be difficult to form due to the placement of their teeth. Forging of tooth gears is thus not a straightforward task. In this context, rotary forging is a powerful alternative. It uses incremental deformation locally with the material to achieve near net shape results, minimizing machining. Due to the reduction in contact, it also allows the forging load to be decreased substantially, resulting in smaller presses. This paper shows the development of the rotary forging process in combination with conventional forging to obtain crown gear teeth as a demonstration case. First, the hot conventional forging is shown, based on obtaining the rotary preform by a closed die forging operation. Then rotary forging is defined as a semi-finished operation to achieve the forged teeth. The objective is to reduce the initial billet weight, checking that folds and filling defects do not appear. A thermomechanical chained model has been developed based on FEM and experimental tests carried out in a pre-industrial environment. The prototypes result in increased yield from raw material (around 15% saving compared to machining) and they can be manufactured with less than 50% of the load required by conventional forging processes. Quality and metallographic requirements are also fulfilled.