In the extrusion process of aluminum profile, along the extrusion direction, a longitudinal continuous line is produced on the surface of the extruded aluminum profile product, which is called die mark
The causes of die marks come from three aspects: the extrusion die itself, the aluminum extrusion process and the material. In terms of molds, the smoothness, heating process and length of the working belt of the extrusion die will all have an impact on the mold marks. Molds with unpolished or poorly polished work belts will have mold marks on the surface of the extruded product, as shown in Figure 2. After the mold has been produced for a long time, through repeated heating and polishing, the base of the mold work belt will be damaged or damaged. The peeling of the nitrided layer will cause mold marks, which need to be re-nitrided and polished before being put into use; if the mold heating time is too long and the temperature is higher, the mold working belt will be oxidized or partial annealing will occur to reduce the strength (commonly known as ” “Red envelope”) will also lead to the production of mold marks; in addition, the longer the mold working belt, the longer the friction time during the extrusion process, which will cause the working belt to stick to aluminum, resulting in the surface of the extruded aluminum material becoming thicker and even forming molds. mark.
In terms of extrusion process, the higher the extrusion temperature, the increase in the viscosity of the aluminum alloy, which will increase the probability of die marks on the surface of the extruded product. At the same time, excessive extrusion speed will also cause die marks. When extruding 5××× alloy and 7××× alloy pipes, due to the high alloy content of the material, it is easy to precipitate a small amount of granular hard compound phase at the exit of the working zone of the extrusion die (Figure 3). Make the product surface produce mold marks, which are irregular and discontinuous in most cases. The causal diagram of mold marks is shown in Figure 4.
Die marks are inevitable in the extrusion process, but not all products with die marks on the surface are unacceptable. Through the subsequent mechanical polishing or anodizing process, the influence of die marks on the appearance of the product can be reduced, and some slight mold marks The marks can be removed.
When the depth of the mold mark is more than 8um, it will feel obvious when touched by hand, and ordinary anodizing cannot eliminate the influence of the mold mark on the appearance of the product. It can be seen that the degree of elimination of mold marks by anode treatment is limited. Only when the depth of mold marks is below 7um, ordinary anode treatment can basically eliminate the influence of surface mold marks on the appearance of the product. If the process is designed with a mechanical polishing process, the depth of the die mark of the extruded material can be allowed to relax to about 10um.
Summary: Die marks are one of the extrusion defects, which have a bad influence on the appearance of the product. However, the mold marks are controllable. Through the management of mold design and mold use, and the improvement of the extrusion process, the severity of mold marks can be reduced to a minimum. At the same time, by measuring the die marks of different depths, and then performing the subsequent anodizing and polishing tests, it is possible to establish the appearance limit standards of the die mark depths of the extruded materials with different quality requirements, which is effective in determining the appearance of the extruded materials. Guiding role.
Link to this article：Causes and Solutions of Die Marks in the Process of Aluminum Profile Extrusion
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