From billet to profile: the extrusion process
Extrusion is a continuous production method in which heated aluminium is pushed through a die to form a constant-section profile.
The process consists of heating the billet, pressing it through the die, quenching the emerging profile, stretching it straight, cutting it to length and, if needed, artificial ageing. Temperatures and speeds vary with alloy and section; the ranges below are general references.
- Billet preparationThe cylindrical billet cast in the chosen alloy is homogenised (soaking at roughly 550–600 °C) to balance its structure.
- Billet heatingBefore pressing the billet is heated to roughly 430–500 °C.
- ExtrusionA hydraulic press pushes the billet through the container into the die; the die opening defines the section.
- QuenchingThe profile is cooled with air or water at the rate required for the alloy and temper.
- Stretching and cuttingThe profile is stretched a few percent to remove curvature and twist, then cut to length.
- Artificial ageingFor T5/T6 tempers it is baked at roughly 160–200 °C for several hours; strength develops at this stage.
Die types
- Solid die: Solid sections such as bar, flat bar and angle.
- Semi-hollow die: Sections with a partly enclosed void (e.g. narrow-mouth channels).
- Hollow (porthole/bridge) die: Box, tube and multi-chamber sections; the metal splits and re-welds inside the die.
Tolerances
Dimensional and shape tolerances are defined in EN 755-9, and for precision EN AW-6060 and 6063 profiles in EN 12020-2. Critical dimensions and tolerances should be stated in writing in the quote and drawing.