[China Aluminum Industry Network] 1. Problems to be considered in mold design
The design of the mold must meet the calculation requirements of stiffness and strength to reduce the amount of elastic deformation of the mold when it is under pressure. When determining the working belt, the length of the working belt, the form of the empty knife, the form of the neck and the form of the welding chamber should all be considered in the optimum value of the parameters. The selection of the coefficient of the diversion hole and the diversion hole of the mold is as large as possible within the allowable range to achieve the purpose of reducing the pressure. Aluminum formwork is generally produced by hard alloy such as 6061, which makes the production technology more difficult. When extrusion production, there are often cases where the material is dragged, pressed, and discharged too slowly. Therefore, the design of the mold plays a role in the production process. A big key role.
2. Mold design
Diversion hole, split hole design
When designing the mold, the position of the diversion hole and the diversion hole should be evenly distributed, so that the various parts of the profile can absorb the same amount of metal. The size of the diversion hole and the diversion hole are proportional to the area of the profile. Under the condition of not affecting the strength of the mold and the surface quality of the profile, the diversion hole and the diversion hole should be maximized. When the extrusion, the metal flows into the welding chamber and the diversion The larger the hole and the split hole, the smaller the force of the bridge area is. The displacement of the metal flow from the bridge reduces the resistance and the discharge speed increases, but does not affect the mold strength. Therefore, the mold having a small feed hole and a large bridge position may not necessarily have a stronger mold strength than the feed hole.
The bridge position is an important part of the mold organization. It is the supporting bridge of the mold. When designing the mold bridge position, it must be considered that it has sufficient support for the mold. In order to meet the support strength of the mold, the general bridge angle is designed to be between 18 and 25 ° C. If the angle is too large, the friction between the metal flow and the bridge will increase, and the flow of the metal flow will be slowed. The smaller the angle, the easier the metal is to be welded. The discharge rate will increase. At the same time, when designing the bridge angle intersection, it should be as smooth as possible to avoid or reduce the dead angle of welding.
Welding chamber design
The welding chamber should not be too deep. If the welding chamber is too deep, the volume of the metal in the welding chamber will increase. When the volume of the welding chamber increases, the welding process will be lengthened and the pressing pressure will increase.
Work belt design
The mold work belt should be carefully polished to ensure flatness and verticality. No turtle back or unevenness can be found. The length of the working belt can be calculated reasonably and the metal flow rate should be uniform.
3. Extrusion process
Aluminum rod heating (440-460 ° C)
Mold heating (420-460 ° C, 3-6h) → extrusion (outlet temperature 530-570 ° C) → spray air quenching → take
Ingot heating (410-420 ° C)
Plate self-test → (200 ° C or less) → stretch straightening (70 ° C or less, elongation rate ≤ 1.5%) → cut-to-length sawing → basketing (checking) → aging → hardness test → unpacking (or oxidation, spraying ).
Aluminum rod heating
For 6061 alloy, it must be heated to above 500 °C, Mg and Si can be completely solid solution. Before extrusion, the ingot is above 440 °C. The temperature rises due to the heat of extrusion deformation, and the metal temperature reaches 530-570 through the die hole. °C, the solution treatment state is reached, therefore, the aluminum rod must be heated to between 440 and 460 °C before extrusion.
The temperature of the mold before heating on the machine is: flat die 410-440 ° C, split die 430-460 ° C; mold heating time in the furnace is not allowed to exceed 10 h, the time is too long, the die hole work belt is prone to pitting corrosion points.
The extrusion speed must be carefully controlled during the extrusion process. The extrusion speed has an important influence on the deformation heat effect, deformation uniformity, recrystallization and solid solution process, mechanical properties of the product and surface quality of the product. In order to improve production efficiency, according to years of production discussion and experience accumulation, at present our main extrusion methods follow the "low temperature high speed" production process, that is, the aluminum rod temperature is inversely proportional to the extrusion speed, the aluminum rod temperature is high, and the extrusion The speed is appropriately slowed down, the aluminum rod temperature is low, and the extrusion speed is appropriately accelerated. Through this adjustment mode, the extrusion production is adjusted to the optimum state. Under normal circumstances, when the upper mold is produced to the third rod, the temperature can be accelerated, and the temperature of the flat mold aluminum rod is kept at 390-410 °C. The temperature of the aluminum alloy rod is reduced to 410-430 °C. good.
The quenching is to preserve the Mg2Si which is solid-solubilized in the base metal at a high temperature and is rapidly cooled to room temperature after being discharged. 6061 contains Mg2Si 0.6-0.9%, from 500 degrees to 204 degrees critical cooling temperature range, the minimum cooling rate is not less than 180 °C / min, water-coolable, 6061 alloy aluminum template hardness requirements ≥ 15HW, its large section quenching Cooling is recommended at 549 ° C / min. Squeeze in-line quenching, the cooling rate should be based on the principle that the supersaturated solid solution can be condensed. For products that can be straightened, the warpage caused by quenching can be corrected.
The mechanical properties of 6061 alloy aluminum formwork generally require tensile strength of 265 (σь) MPa and Vickers hardness of ≥ 15HW. Therefore, the aging temperature is generally 180-200 ° C, time 5-6 h; sometimes in order to improve its strength properties, (170-180) ° C × (6-8) h process can also be used.