Determination of aluminium properties under bulk cold forming processes

Abstract

Consulta en la Biblioteca ETSI Industriales (7816)

[EN] This work is about analysis of structural, mechanical and technological properties of aluminium assigned to bulk forming processes. Almost in all metal forming processes the tools are operating with pressure on deformed material surface. This results in arising friction forces on tool ¿ material contact surface and it is the reason of inhomogeneity of stress and strain on the inside of deformed material. As a result of external friction forces, non-uniform distribution of unit pressure and its essential growth over yield stress occurs on contact surfaces, too. Tensile test is commonly used to determine mechanical properties of materials. Such properties as yield point, tensile ultimate strength, unit elongation, reduction of specimen area, obtained in tensile test are very important in strength of materials. These parameters are often used in metal forming to estimate the usability of a material, but they are not technological parameters. The opposite of tensile test, with respect to the direction of loading, is compression test. In compression test the specimen is squeezed and friction forces, which arise on thrust surface, are diminished (for instance by lubricants). Compression test results in mechanical properties that include the compressive yield stress, compressive ultimate stress, compressive modulus of elasticity and others. These strength values are calculated using the original cross sectional area of specimen and are named nominal or engineering values, what is likewise in tensile test. Upsetting test is like a compression test realized between flat dies and it is close to technological conditions of metal forming. During the test, on the die-specimen contact surface friction forces arise and the barrelling of specimen side surface occur. The barrelling is the result of non-homogeneous stress and strain in the process. When press load and ram displacement are recorded, unit pressure - strain curves can be determined up to very high strains, considerably greater than in tensile test. The upsetting force and strain are not only material dependent but also the test conditions. The hardness test is, together with the one of traction, one of the most used in the selection and control of quality of metals. Intrinsically the hardness is a condition of the surface of the material and it does not represent any fundamental property of the matter. It is evaluated conventionally by two procedures. The hardness is a fundamental property of the materials and this related to the mechanical resistance.