Process flow of aluminum extrusion

1、 Overview of Process Flow

Preparation of raw materials

Firstly, it is necessary to choose a suitable aluminum rod as the billet. The quality of aluminum bars has a significant impact on the performance of the final profile, and it is generally required that the purity and microstructure of the aluminum bars meet certain standards. For example, for aluminum profiles used in construction, 6063 alloy aluminum bars are usually chosen, which contain magnesium and silicon elements and can achieve good mechanical properties and surface quality after heat treatment.

Aluminum bars need to be heated before extrusion because appropriate temperature can reduce the deformation resistance of aluminum, making the extrusion process easier. The heating temperature depends on the alloy composition of the aluminum rod and the complexity of the profile, generally around 400-500 ℃. For example, the heating temperature during extrusion of 6061 alloy aluminum rod may be around 480 ℃.

Squeezing process

The heated aluminum rod is sent to the barrel of the extruder. The extruder is mainly composed of a main cylinder, an extrusion rod, and a mold seat. When the master cylinder pushes the extrusion rod, the extrusion rod pushes the aluminum rod towards the mold. The mold is a key component of the extrusion process, and its shape determines the cross-sectional shape of the aluminum profile. For example, if you want to produce hollow aluminum profiles, you need to use molds with hollow needles.

Aluminum bars are extruded into profiles with the desired shape through the mold holes under immense pressure. This pressure is usually very high, usually between 10-100MPa. During the extrusion process, the metal flow characteristics of aluminum are crucial as they can affect the quality of the profile. For example, for complex shaped profiles, it is necessary to design the mold and extrusion process reasonably to ensure that aluminum flows evenly around all parts of the mold and avoid defects.

Cooling and straightening

The newly extruded aluminum profile has a high temperature and needs to be cooled. Usually, air or water cooling is used. The air cooling speed is slow, but it has little effect on the microstructure and properties of the profile; The water cooling speed is fast, but if not controlled properly, it may cause residual stress in the profile. For example, for some industrial profiles that require high dimensional accuracy, air cooling may be used for initial cooling before water cooling.

The cooled profile may experience deformation such as bending or twisting, and needs to be straightened. Straightening can be achieved through a mechanical straightening machine, which applies appropriate pressure to the profile to restore it to a straight state.

Finishing and surface treatment

The straightened profile needs to be polished, including cutting to the appropriate length. Cutting can use equipment such as sawing machines to cut profiles into finished or semi-finished products of a certain length according to customer requirements.

In order to improve the corrosion resistance and aesthetics of aluminum profiles, surface treatment is usually required. Common surface treatment methods include anodizing, electrophoretic coating, powder coating, etc. Anodizing can form a dense oxide film on the surface of aluminum profiles, enhancing their corrosion resistance; Electrophoretic coating and powder coating can provide rich color choices and have good decorative properties.

2、 The Importance of Die in Extrusion Process

Mold structure and type

The mold mainly includes parts such as the mold head, mold core, and mold pad. The mold head is the part that directly contacts the aluminum rod, and its shape and size determine the outer contour of the profile; The mold core is used to form the internal shape of profiles, such as hollow parts; The mold pad plays a role in supporting and fixing the mold head and core.

According to the shape of the profile and the requirements of the extrusion process, molds can be divided into solid profile molds and hollow profile molds. Solid profile molds have a relatively simple structure and are mainly used for producing solid aluminum profiles; Hollow profile molds are more complex and require devices such as hollow needles to ensure that aluminum can form a uniform hollow structure when flowing around the hollow needles.

Factors to Consider in Mold Design

When designing molds, it is necessary to consider the flow characteristics of aluminum. For complex shaped profiles, it is necessary to guide the flow of aluminum through reasonable diversion hole design, adjustment of working belt length, and other methods. For example, when designing and producing aluminum profile molds with multiple reinforcing ribs, it is necessary to ensure that aluminum can be evenly filled into the reinforcing rib areas to avoid defects such as insufficient reinforcing ribs or wrinkles on the surface of the profile.

The material selection of the mold is also crucial. Due to the high pressure and friction experienced by the mold during the extrusion process, it is necessary to choose mold materials with high hardness, strength, and good wear resistance. The commonly used mold materials include H13 steel, and appropriate heat treatment is also required during the mold manufacturing process to improve its performance.

3、 Key points of quality control

Dimensional accuracy control

The dimensional accuracy of aluminum profiles includes aspects such as cross-sectional dimensions, wall thickness, and length. During the extrusion process, it is necessary to strictly control the dimensional accuracy of the mold and the extrusion process parameters to ensure that the dimensions of the profile meet the standards. For example, for aluminum door and window profiles used in construction, the tolerance requirement for wall thickness is generally around ± 0.1mm, which requires precise control of factors such as the diameter of the aluminum rod, the size of the mold holes, and the extrusion speed.

Regular inspection and calibration of extrusion equipment and molds are also important measures to ensure dimensional accuracy. If the accuracy of the equipment decreases or the mold wears out, it is easy to cause deviations in the size of the profile.

Surface quality control

Surface quality mainly includes the flatness, glossiness, and presence of defects of the profile surface. During the extrusion process, it is necessary to prevent defects such as scratches, strains, and bubbles from appearing on the surface of the aluminum profile. This requires ensuring the smoothness of the mold surface, controlling the flow velocity and temperature of aluminum reasonably, and avoiding turbulence or local overheating of aluminum inside the mold.

For surface treated profiles, it is necessary to strictly follow the surface treatment process standards to ensure that the thickness and color uniformity of the oxide film meet the requirements. For example, the thickness of the anodic oxide film is generally required to be between 5-20 μ m, and the color should be uniform and consistent, without significant color differences.