Elimination of Transverse Deformation on Bars

In the production process at Impol PCP, we extrude aluminium and its alloys in various geometric shapes (round, square, hexagonal, flat…) and profiles of different shapes according to customer orders. Extrusion is also referred to by another term as direct compression extrusion, in which the billet can be partially extruded or pushed entirely through an opening in the die or tool, where its cross-section and shape are reduced. The most common transverse deformations that occur are surface cracks, transverse marks, joints, torn material, defects on bars due to the extractor, and damage to bars that occurs during packaging. In the diploma thesis, most attention will be devoted to the defect called 'stop marker'.

Problem

In the production process at Impol PCP, we extrude aluminium and its alloys in various geometric shapes (round, square, hexagonal, flat…) and profiles of different shapes according to customer orders.

Solution and Method

Extrusion is also referred to by another term as direct compression extrusion, in which the billet can be partially extruded or pushed entirely through an opening in the die or tool, where its cross-section and shape are reduced. The advantages of extrusion are the creation of very complex cross-sections and the possibility of extruding brittle materials. With the latter, during the processing procedure, we encounter shear and compressive stresses, which enable deformation without tearing the material.

The extrusion process also enables the shaping of products with an excellent surface. The 55 MN press is a direct press intended for direct extrusion of bars and profiles from aluminium and its alloys. Direct extrusion, also known as conventional pressing, is the most widespread throughout the world and is among the main processing methods for aluminium.

In this method of metal processing, the billet is inserted into the container, whereupon the press ram begins pressing through the die to the other side. It is understood that the tool has a smaller cross-section than the billet. Pressing conditions are specified in work orders, tables, graphs, and master technology.

During bar extrusion, transverse deformations can occur due to deviations of alloying elements in the alloy or due to incorrect speed of the main ram movement.

Results

The most common transverse deformations that occur are surface cracks, transverse marks, joints, torn material, defects on bars due to the extractor, and damage to bars that occurs during packaging. In the diploma thesis, most attention will be devoted to the defect called 'stop marker'. 'Stop marker', or in workers' jargon a joint, appears on bars during press malfunctions.

A joint is a transverse deformation on a bar that occurs when the press stops in the tool area; this bar is discarded and remelted. Among the most common faults that occur on the press are: extractor fault, full bar storage track, power failure, or human error. One of the main objectives in the diploma thesis will be to determine how to eliminate the defect called 'stop marker'.