La relevancia del material did��ctico dentro del aula : Una investigaci��n sobre las principales ��reas de inter��s de los estudiantes de ELE

El material did��ctico influye considerablemente en la ense��anza y es de gran importancia que fomente el inter��s y la motivaci��n en el aprendizaje de ELE. De ah�� que este estudio ha tenido como objetivo comprobar si la ense��anza de espa��ol como lengua extranjera est�� enfocada en base a los intereses personales de los estudiantes. La autora ha realizado una encuesta donde diecinueve estudiantes en el bachillerato han respondido a diez preguntas respecto a diferentes materiales. Los resultados muestran que es importante que el material se enfoque en aspectos como el inter��s personal, la utilidad pr��ctica para el futuro y la realidad fuera del aula. Adem��s, se ha comprobado que materiales como el libro de texto, los medios de comunicaci��n, el Internet y las pel��culas responden a los intereses de los estudiantes en algunos sentidos. Sin embargo, no son tan relevantes en todos los aspectos, por lo que hace falta combinar diferentes materiales y usarlos de una manera cr��tica y creativa.

Tribology in Metal Working

This thesis focuses on the tribological performance of tool surfaces in two steel working operations, namely wire drawing and hot rolling. In all forming operations dimensions and surface finish of the products are of utmost importance. Forming basically includes three parts – forming conditions excluded – that may be changed; work material, tool and (possibly) lubricant. In the interface between work material and tool, the conditions are very aggressive with – generally or locally – high temperatures and pressures. The surfaces will be worn in various ways and this will change the conditions in the process. Consequently, the surface finish as well as the dimensions of the formed product may change and in the end, the product will not fulfil the requirements of the customer. Therefore, research and development in regard to wear, and consequently tribology, of the forming tools is of great interest. The investigations of wire drawing dies focus on coating adhesion/cohesion, surface characteristics and material transfer onto the coated steel both in laboratory scale as well as in the wire drawing process. Results show that it in wire drawing is possible to enhance the tribological performance of drawing dies by using a lubricant together with a steel substrate coated by a polished, dual-layer coating containing both hard and friction-lowering layers. The investigations of hot rolling work rolls focus on microstructure and hardness as well as cracking- and surface characteristics in both laboratory scale and in the hot strip mill. Results show that an ideal hot work roll material should be made up of a matrix with high hardness and a large amount of complex, hard carbides evenly distributed in the microstructure. The surface failure mechanisms of work rolls are very complex involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. This knowledge may be used to develop new tools with higher wear resistance giving better performance, lower costs and lower environmental impact.

Minimization of stock weight during close-die forging of a spindle

In this paper, Finite Element method and full-scale experiments have been used to study a hot forging method for fabri-cation of a spindle using reduced initial stock size. The forging sequence is carried out in two stages. In the first stage, the hot rolled cylindrical billet is pre-formed and pierced in a closed die using a spherical nosed punch to within 20 mm of its base. This process of piercing or impact extrusion leads to high strains within the work piece but requires high press loads. In the second stage, the resulting cylinder is placed in a die with a flange chamber and upset forged to form a flange. The stock mass is optimized for complete die filling. Process parameters such as effective strain distribution, material flow and forging load in different stages of the process are analyzed. It is concluded from the simulations that minor modifications of piercing punch geometry to reduce contact between the punch and emerging vertical walls of the cylinder appreciably reduces the piercing load. In the flange chamber, a die surfaces angle of 52�� instead of 45�� is pro-posed to ensure effective material flow and exert sufficient tool pressure to achieve complete cavity filling. In order to achieve better compression, it is also proposed to shorten both the length of the inserted punch and the die ���tongues��� by a few mm.