Common defects include:
- Die Lines: Fine lines running the length of the profile caused by imperfections in the die. Prevention: Proper die polishing and maintenance.
- Twisting/Bowing: Longitudinal curvature. Prevention: Uniform cooling, proper die design for balanced metal flow, and stretching.
- Piping/Back-End Defect: A funnel-shaped void at the end of the billet, extruded into the profile. Prevention: Proper billet preparation and discard of the back-end material.
- Blistering: Small raised areas caused by trapped gas under the surface. Prevention: Ensure billets are homogeneous and dry; control extrusion speed.
- Poor Surface Finish (Roughness): Can be due to billet temperature, speed, or die condition. Prevention: Optimize process parameters.
Working closely with an experienced extruder during the design phase is the best prevention.