Bar Extrusion
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Bar Extrusion Erman A. Tekkaya and Sami Chatti Institute of Forming Technology and Lightweight Design, Technische Universität Dortmund, Dortmund, Germany
Synonyms Extrusion; Extrusion of sections
Definition Pushing a billet enclosed in a container through a die to form an extrudate.
Theory and Application Introduction Bar extrusion is a process in which a block of metal (billet) is forced to flow by compression through a tool (die) opening of a smaller crosssectional area than that of the original billet. There are two basic types of bar extrusion: direct and indirect. The most important and common method used is the direct extrusion (Lange 1988). Fig. 1 shows the principle of direct bar extrusion where the billet is placed in the container and pushed through the die by moving a ram towards the die (Saha 2000).
In indirect bar extrusion, the die at the front end of the hollow ram moves relative to the container, but there is no relative displacement between the billet and the container as shown in Fig. 2. Therefore, indirect extrusion is characterized by the absence of friction between the billet surface and the container. The absence of friction leads to reduced axial extrusion forces compared to direct extrusion. Therefore, indirect extrusion is used for the forming of heavy extrudable alloys. But the major disadvantage of the method is the strong limited die design due to the required hollow ram geometry. A third type of bar extrusion, which is rarely applied, is hydrostatic bar extrusion. This process utilizes a hydrostatic medium and there is no direct contact between ram and billet (Fig. 3). The pressure of the ram is transferred though the hydrostatic medium to the billet. In hydrostatic extrusion, friction as well as shear forces take place only between the billet and the die (Bauser et al. 2001; Sheppard 1999). It is difficult to seal the container, which is a drawback of the hydrostatic extrusion. Stages of Bar Extrusion In the most common direct extrusion process, pressure reaches a maximum when the material filled the container. The process can be described with three different phases:
# CIRP 2016 The International Academy for Production Engineering et al. (eds.), CIRP Encyclopedia of Production Engineering, DOI 10.1007/978-3-642-35950-7_20-4
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Bar Extrusion
1. The billet is upsetting and pressure rises to its peak value. 2. The pressure decreases as the billet length is decreasing. 3. The pressure shows a sharp rise as the discard material is compressed (usually the process ends at this point and the rest material is removed).
Bar Extrusion, Fig. 1 Direct bar extrusion
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1 Extruded Material 2 Die 3 Billet 4 Container 5 Ram
Bar Extrusion, Fig. 2 Indirect bar extrusion
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1 Extruded Material 2 Die 3 Billlet 4 Container 5 Hydrostatic medium 6 Ram 1 7 Sealing
A typical force-displacement curve is shown in Fig. 4. The parameters that influence the force can be given as: • Temperature of container, die, and associated tooling • Billet material • Extrusion temperature •
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