Simulation of Welding Conditions in Porthole die Extrusion
In aluminum extrusion with porthole dies, the welding of material seams represents a major manufacturing problem inasmuch it affects the integrity of the final product. The way the problem is treated is yet not consistent in literature, and different qual
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Department of Mechanical Construction Engineering (D.I.E.M.), University ofBologna, Italy
KEYWORDS: extrusion, alumirrum alloy, welding conditions, FEM, die stress. ABSTRACT: In alumirrum extrusion with porthole dies, the welding of material seams represents a major manufacturing problern inasmuch it affects the integrity of the final product. The way the problern is treated is yet not consistent in literature, and different quality parameters for welding are still used in practice. In this work a new parameter for evaluating the welding quality is proposed. lts effectiveness is tested in comparison with other parameters by means of a parametric FEM analysis in which the distribution of pressure and velocity along the welding line is considered. The investigated geometry is a simple two-seams plane-strain die. Many die shapes have been considered, by varying the position and the shape of the leg, in order to understand the sensitivity of the parameters in a wide range of operative conditions. The solutions are also significant for evaluating process Ioad, productivity and die-stresses.
INTRODUCTION In the extrusion of hollow sections of alurninum, the billet is pressed through a die that determines the outer shape and over a mandrei that determines the inner shape. The material must, therefore, flow through a narrow gap. In porthole dies, as well as in bridge and spider dies, the material divides around the core supports which holds the stub mandrel, and then welds together in the welding chamber before passing through the gap. In this way, hollow or semihollow sections of great complexity can be produced. The process conditions in the welding chamber must be set at a Ievel to produce perfect welds of the material fluxes and final products free of defects. The production of good seam joints depends on many process parameters: pressure, temperature, residence time in the welding chamber, surface conditions and presence of contaminants. The complexity of the matter led historically to different ways of evaluating the welding conditions and different guidelines are still used in practice. Meier [ 1] suggests that both the width Published in: E.Kuljanic (Ed.) Advanced Manufacturing Systemsand Technology, CISM Coursesand Lectures No. 437, Springer Wien New York, 2002.
L. Donati, L. Tomesani
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and height of the welding chambers should be equal to 6 to 8 times the wall thickness of the hollow shape in the area under the support. Akeret [2] recommends that the local extrusion ratio in the final step has to be on the order of at least three for any part of the shape. More recently, Plata and Piwnik [3] proposed a quality factor as the integral of hydrostatic pressure for the time of contact on a definite path. Finally, the authors [4] stated that a modified parameter with material flow could also give interesting informations about the welding quality. In particular the last two methods can be successfully used as a guideline in die design, when finite element simulation (FEM) of the process is performed. In fact, t
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