Jerzy Gronostajski

The recycling of metals by plastic deformation: an example of recycling of aluminium and its alloys chips

Abstract In this paper a new method of recycling aluminium and aluminium-alloy chips coming from the machining of semi-finished products, which are very difficult to recycle by conventional methods, is presented. The method consists in the conversion of the chips directly (without melting processes) into a finished product. Using a powder metallurgy technique followed by extrusion, the method has been applied to the production of composite materials, characterised by good properties. The new method is environmentally friendly and gives saving in material, labour and energy.

New methods of aluminium and aluminium-alloy chips recycling

Abstract A technology that has been developed systematically in recent years is that of the manufacturing of sintered products with pre-determined properties. It has been demonstrated that such products can be manufactured from waste such as aluminium and aluminium-alloy chips. The method consists in the conversion of the chips directly into a finished product. The method has been applied to the production of composite materials, characterised by good strength properties at room and elevated temperature, as well as for bearing materials.

Direct recycling of aluminium chips into extruded products

Abstract In the paper is described the method of direct convertion of aluminium and its alloys chips into final products. The chips were comminuted in cutting device, and for the future processing the granulated chips larger than 5 mm in length were eliminated. Such prepared chips were pre-pressed with the pressure of 210 MPa and hot extruded for final products. High density and good properties of products can be obtained at high extrusion temperature which makes possible the plastic flow of matrix into pores and voids and at relatively low extrusion rates which gives the time for diffusional transport of matter.

Sheet metal forming-limits for complex strain paths

Abstract The three non-quadratic yield criteria for a material with in-plane isotropy proposed by Hill (1979) were used to determine the effect of strain path on the forming-limit diagram (FLD). By this means, the experimentally determined FLD for different strain paths for Armco, copper, aluminium and steel were transformed to forming-limit stress diagrams (FLSD) in stress coordinates. Calculations were made for values of exponent m of 1.6, 1.8 and 2.0 in the yield criteria. The best yield criteria and values of m were found on the basis of good linear correlation between the calculated values of the principal stresses σ 1 and σ 2 at the point of instability. The FLSD obtained at the best yield criteria and values of m were then transformed to FLD, by means of which the formability of materials for different strain paths can be determined directly.

Production of composites on the base of AlCu4 alloy chips

Abstract This paper describes the experience obtained with the chips of Al and its alloy with addition of small amount of tungsten powder directly converted into the final product by hot extrusion process. The mechanical and physical properties of Al and AlCu4 based composites are presented. The effect of tungsten contents and heat treatment on the properties is described. Direct conversion method do not harmfully affect an environment and produced material can be used as a final product or can be further processed by another plastic working methods like forging or rolling.

Production of composites from Al and AlMg2 alloy chips

Abstract To avoid the troubles deriving from the conventional recycling process, an alternative process has been created, where chips of Al and its alloys are cut or milled convected directly by hot plastic working into final products. In the paper, the production of composites by the direct convertion of Al and AlMg2-alloy granulated chips with tungsten powder into final products by hot extrusion are described. The following extrusion parameters are the most important for the obtainment of high densities: (i) a high extrusion temperature, which enables the plastic flow of an extremely plastic matrix into pores and voids; and (ii) relatively low extrusion rates, which extend the time of plastic flow of the matrix material into the pores and voids and also the time for diffusional transport. The hardness and mechanical properties of Al and AlMg2 base composites are slightly lower than those of metallurgically-produced materials. The direct convertion method does not have any harmful effects on the environment and the material produced can be further processed by other plastic working methods such as forging and rolling.

A few methods of analytical calculation of forming-limit curves

Abstract The main aim of the present work is the modification of analytical calculation methods for forming limit curves. The calculated curves were compared with experimental data for steel and aluminium sheets and the best modifications were chosen. The following modifications were analysed: combination of the Swift diffuse instability criterion developed by Lian with the localized necking M-K theory developed by Jalinier and co-workers. The initial calculation, to some degree of deformation, was performed using: the Swift model and then the Jalinier localized theory until fully localization of the strain was applied; the application of Hills non-quadratic yield criteria for material with in-plane isotropy to the Jalinier theory; the application of the heterogeneity coefficient described by surface roughness to the Jalinier theory; and the development of the Gillis-Jones theory, which eliminates the necessity of the determination of the initial heterogeneity coefficient. The latter theory is based on the assumption that instability develops during successive cycles of deformation: uniform deformation, progressive strain localization, force drop and fully localized necking. Good correlation was found between theoretically calculated and experimentally determined curves for all modified methods, but the best agreement was for the Jalinier theory with the heterogeneity coefficient described by surface roughness and the Gills-Jones theory. The theories can be used successfully for the CAD of sheet forming processes.

Bearing materials obtained by recycling of aluminium and aluminium bronze chips

Abstract In this paper, a new method of chips recycling is presented. The method consists in the conversion of the chips directly (without intervening metallurgical processes) into a finished product, and has been applied to the production of conventional and composite materials. The sintering criterion for chips recycling is described and discussed. The application of the recycling method for the production of bearing materials is precisely described.

The effect of changing of heterogeneity with strain on the forming limit diagram

Abstract The heterogeneity coefficient of deformed sheet metal described by surface roughness was introduced into Jalinier theory of computation of forming limit diagrams. The surface roughness is changed during sheet deformation, and in the similar manner the heterogeneity coefficient is altered. Taking into account the changing of heterogeneity coefficient during forming of sheet the effect of grain size and strain paths on the limit strain of steel and aluminium was analysed.

Theoretical simulation of sheet behaviour in forming processes

Abstract In the paper the method of simulation of the forming-limit strain based on the Swift diffuse instability criterion combined with the localized instability theory of Marciniak and Kuczynski, developed by Jalinier, is presented. It has been found that the forming-limit curves of steel sheets calculated according to above-mentioned method give better correlation with the results of experiment, than do the forming-limit curves calculated on the base of Jaliniers theory alone.