Extrusion defects

Irregularities during the process of Extrusion.
These are mainly due to Non uniform flow and stress distribution

1. Presentation on: EXTRUSION DEFECTS Presented by: Nishat Riaz MME-13-27 IAM,BZU,MULTAN

2. Extrusion Defects: Irregularities during the process of Extrusion These are mainly due to Non uniform flow and stress distribution Number of defects depends upon: Wall friction Wall temperature

3. Types of Extrusion defects: Surface Cracking Internal Cracking Piping Defect

4. Surface Cracking: Surface cracks are developed due to High extrusion temperature High ram speed High Friction

5. It occurs at High temperature such as Hot hardness Can also occur at low temperature These cracks are intergranular

6. Internal Cracking: Cracks are developed in the center of extruded material This is also named as Center Cracking Center Burst Chevron Cracking Arrow head Cracking These are hard to detect in the material

7. It occurs due to difference in velocity and tensile stresses in center of the material These can be prevented by using appropriate die angle Friction Extrusion Ratio

8. Piping Defect: It occurs during hot extrusion due to presence of impurities and oxides It is also known as: Tail pipe Fish Tailing Propagates as Funnel Shaped Void.

9. Metal in contact with walls cools down rapidly as compared to center part resulting in non uniform flow of metal

10. Prevention: Modifying flow pattern by controlling temperature and friction Machining billet surface prior to extrusion Using dummy block