3. 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
6. • It occurs at High temperature such as Hot hardness
• Can also occur at low temperature
• These cracks are intergranular
7. 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
8. • 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
9. 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.
10. • Metal in contact with walls cools down rapidly as compared to center
part resulting in non uniform flow of metal
11. Prevention:
• Modifying flow pattern by controlling temperature and friction
• Machining billet surface prior to extrusion
• Using dummy block