Pressure: a crucial parameter
Pressure is a key parameter in the extrusion process and can vary depending on the capacity of the press. Our presses differ in terms of maximum hydrostatic pressure, and these values depend on the container diameter and maximum pressing force. The hydrostatic pressure influences the flow of material through the tool and is crucial for the final shape of the profile.
Variations in pressure
During extrusion, the pressure in different parts of the tool varies, which can lead to pressure variations. The tool’s bearing lengths – the friction surface in the profile-forming gap – are designed to balance the pressure, but these pressure variations affect the flow through the tool. The pressure variations are not constant during the press cycle, causing the flow to change depending on the position of the tool. These variations in turn affect the profile shape obtained.
The forces and the extrusion rate
Another important parameter is the extrusion speed. As profile extrusion is an intermittent process, where each new ingot is stopped before the extrusion cycle starts again, the speed must be adjusted to optimize the material flow. If the speed is not adjusted correctly, it can affect the dimensional outcome of the finished profile.
Bollard force: controlling the profiles
When feeding profiles, the front end is guided by a pulling device called a puller. The puller has two purposes: to keep the profiles straight for further handling and to equalize differences in speed between different profiles in a multi-hole tool. If too much pulling force is applied to a profile, it can cause it to be overstretched, affecting the accuracy of the shape.
Temperature control: to maintain quality
A correct temperature treatment is crucial for the extrusion of aluminum alloys. The ingot must be heated to the right temperature to achieve dissolution and disperse alloying elements such as magnesium silicides. After the extrusion, a rapid cooling is required to avoid unwanted joining of these elements. This is done to prepare the material for the subsequent precipitation hardening which gives the material its final mechanical properties.
Casting temperature: customized heat management
To ensure a constant extrusion temperature, it is important to adjust the temperature of the ingot during the process. Adjusting the temperature at the front end can compensate for the temperature rise caused by the forming operation, ensuring a stable process.
Cooling: important for dimensional outcomes
Cooling is a critical process to achieve the desired profile shape and strength. Lighter alloys such as EN AW-6060 and EN AW-6063 can be air cooled, while harder alloys such as EN AW-6082 require rapid and vigorous water cooling. Effective cooling is essential to avoid thermal stresses in the material, which can lead to problems in subsequent processing.
The impact of cooling on the aluminum profile
The more intensive the cooling used, the greater the impact on the dimensional outcome. Uneven cooling can lead to thermal stresses that degrade the quality of the profile and can cause problems in handling and processing.
Stretching: correct profile shape after extrusion
After the profile has been cooled, a stretching operation is carried out to correct crookedness and reduce thermal stresses that occur during pressing and cooling. Stretching is done by gripping the entire length of the profile at the ends and stretching it by about 1%. This determines the final dimension and particularly affects flange angles and gap openings for profiles with semi-open sections.
Aging: final strength and quality
After stretching, the profiles are cut into handling lengths, usually 4-6 meters, and undergo an ageing process. During this process, the material is heated to 175°C – 185°C for 5-8 hours, which causes the alloying elements to bind to the grain boundaries and give the profile its final mechanical properties. Aging ensures that the material reaches its maximum strength and stability.
Executive summary
The parameters of the extrusion process are crucial to ensure high quality and precision of aluminum profiles. By carefully controlling factors such as pressure, temperature, cooling and stretching, you can optimize the result and create profiles with the desired properties. To achieve the best possible results, it is important to understand and control these parameters throughout production, from extrusion to aging.
