Factors affecting the size of aluminum profile- Mold changes(一)

Working conditions of the mold

In the extrusion process, the working conditions of extruders and molds are very heavy. With the increase of extrusion product varieties and the large-scale specifications, complex shapes, precise sizes, high material reinforcement, and the continuous emergence of large-scale high-specific pressure extrusion cylinders and new extrusion methods, the working conditions of extrusion molds have become more and more harsh, and the requirements for them have become higher and higher.

1. Withstand long-term high temperature action. During the extrusion process, extrusion tools (extrusion cylinders, extrusion gaskets, needle back ends, punching pins, etc.) and dies (dies) that are in direct contact with the high-temperature ingots and are involved in deformation. The surface temperature of the mold pad, needle tip, tongue mold sleeve, mold support, etc.) can sometimes be as high as 550 ° C or more locally. The time to withstand high temperature action is generally a few minutes to tens of minutes, and for difficult-to-deform aluminum alloys with slow extrusion speed, sometimes up to several hours. The long-term high temperature effect greatly worsens the friction conditions between the metal and the tool, reduces the strength of the mold material, so that plastic deformation is produced and the accelerator is damaged.

2. Withstand long-term high pressure action.

3. Withstand the effect of cold and heat. Tools such as molds and extrusion gaskets, the temperature difference between working and non-working hours, can reach more than 200-300 ° C when extruding aluminum alloys. When the water-cooled mold is extruded and perforated, the temperature gradient in the mold is larger and the change is more intense. In addition, the heat transfer capacity of the tooling material is low. It is likely that large thermal stresses will be generated in the tooling, making their working conditions worse. Under the action of quenching and heating, the mold is very easy to produce micro-cracks or thermal fatigue cracks.

4. Withstand repeated circulating stress. During working hours, the mold is subjected to high pressure, while during non-working hours, it is suddenly unloaded and the stress drops to zero. Moreover, some tools (such as those of the perforation system) are sometimes pressurized and sometimes pulled during the extrusion process. Therefore, the stress states in the mold components are extremely complex and unstable. Under the stress of this repeated circulation and tension and pressure alternating, the mold is very easy to produce fatigue damage.