[China Aluminum Industry Net] In recent years, with the rapid advancement of large-scale infrastructure investment and industrialization in China, the output and consumption of aluminum profiles have increased rapidly, and China has also become the largest aluminum production in the world. Base and consumer market. After nearly 10 years of rapid growth, China's aluminum industry has entered a new stage of development, and shows many new trends.
Moreover, with the rapid development of industries such as construction, transportation, automobiles, and solar and LED industries, the requirements for high-precision and high-performance aluminum alloy extruded products are increasing, and the cross-sectional shape of the profiles is becoming more complicated and diversified, and the conventional common forms are designed. There are many deficiencies. Therefore, in order to obtain high-quality profiles, it is necessary to constantly learn and accumulate, constantly reform and innovate in production and life.
Mold design is an important part. Therefore, systematic analysis must be performed on the design of the extrusion profile mold, and problems should be gradually solved through production practices.
1. Six major points of aluminum profile mold design 1. Size analysis of aluminum extrusions The size and deviation of extrusions are determined by the die, extrusion equipment and other related process factors. Among them, the impact of changes in the size of the mold, and the impact of mold size changes are: the elastic deformation of the mold, mold temperature, mold material and mold manufacturing accuracy and mold wear and so on.
(1) Extrusion ratio of tonnage of aluminum extrusion press is numerically expressed in terms of ease of extrusion of the die. In general, an extrusion ratio of between 10 and 150 is applicable. When the extrusion ratio is lower than 10, the mechanical properties of the product are low; conversely, the extrusion ratio is too high and the product is prone to defects such as surface roughness or angular deviation. Solid profiles often recommend extrusion ratios of around 30 and hollow profiles around 45.
(2) Determination of external dimensions The external dimensions of the extrusion die refer to the outer diameter and thickness of the die. The dimensions of the mould are determined by the size, weight and strength of the profile section.
2. Reasonable Calculation of Extrusion Die Size When calculating the size of the die hole, the chemical composition of the extruded aluminum alloy, the shape of the product, the nominal size and its allowable tolerances, the extrusion temperature, and the material and the size of the die at this temperature are mainly considered. The coefficient of linear expansion of the extruded alloy, the geometry of the product section, its variation during straightening, the size of the extrusion force, and the elastic deformation of the die.
For profiles with very different wall thicknesses, the hard-to-shape thin-walled portions and the sharp corners of the edges should be appropriately enlarged.
For the die-holes of flat wide-walled thin-walled profiles and wallboard profiles with large aspect ratios, the dimensions of the purlins may be designed according to the general profile. The dimensions of the web thickness, in addition to the factors listed in the formula, still need to be considered Elastic deformation and plastic deformation and overall bending, distance from the center of the squeeze tube and other factors. In addition, the extrusion speed, the presence or absence of traction devices, etc., have a certain influence on the die hole size.
3. Reasonable adjustment of the metal flow rate The so-called reasonable adjustment is to ensure that in the ideal condition, every particle on the cross section of the product should exit the die hole at the same speed.
As far as possible, the porous symmetry arrangement is adopted. According to the shape of the profile, the difference in the thickness of each part and the difference in the circumference and the distance from the center of the squeeze tube are used to design the sizing tapes of different lengths. In general, the thinner the wall thickness of a section is, the larger the perimeter is, and the more complex the shape is. The farther away from the center of the squeeze tube, the shorter the sizing belt should be.
When it is still difficult to control the flow rate with a sizing belt, for the part with a particularly complex shape, a thin wall thickness, and a very long distance from the center, a flow promoting angle or a guide cone can be used to accelerate metal flow. Conversely, for those parts of the wall that are much thicker or closer to the center of the barrel, additional impediments should be used to retard the flow angle. In addition, it is also possible to use process balance holes, process margins, or to adjust the flow rate of the metal using an antechamber mold, a diversion mold, changing the number, size, shape, and position of the diverging holes.
4. Ensure sufficient mold strength Because the working conditions of the mold during extrusion are very poor, the mold strength is a very important issue in mold design. In addition to the rational placement of mold holes, the selection of suitable mold materials, and the design of a reasonable mold structure and shape, it is important to accurately calculate the extrusion force and verify the allowable strength of each dangerous section.
At present, there are many formulas for calculating the extrusion force, but the modified Berlin formula still has engineering value. The upper limit of the extrusion force method also has a good application value. It is relatively simple to calculate the extrusion force using the empirical coefficient method.
As for the check of the strength of the mold, it should be carried out according to the type of product and the structure of the mold. The general plane mold only needs to check the shear strength and bending strength; the tongue mold and the plane diversion mold need to check the shear strength, bending strength and compressive strength, and the tongue and the tip part must also consider the tensile strength.
An important basic problem in strength checking is to choose the appropriate strength theory formula and more accurate allowable stress. In recent years, the finite element method has been used to analyze the stress conditions and check the strength of particularly complex molds.
5. The working belt width dimension determines that the working belt of the splitting and combining mold is much more complicated than determining the working belt of the mold half, not only taking into account the poor wall thickness of the profile, the distance from the center, but also the fact that the mold hole is shielded by the distribution bridge. . The die hole below the splitter bridge must be considered thinner due to the difficulty of metal flow.
When determining the working zone, we must first find out where the thinner wall thickness of the profile under the diverging bridge is, that is, where the metal flow resistance is larger. Here, the smaller working zone is set to be twice the wall thickness, and the wall thickness is thicker or metal. Where it is easy to reach, the work belt should be given proper consideration for thickening, generally based on a certain proportion of the relationship, plus a correction value that is easy to flow.
6. Modular Hollow Knife Structure Modular Hollow Knife is a structure in which the die hole work has a cantilevered structure with an outlet end. When the profile wall thickness tâ‰¥2.0mm, it can use the easy-to-handle straight air knife structure; when t<2mm, or with the cantilever, it can use the oblique knife.
II. Common Problems in the Design of Molds 1. The Role of the Secondary Welding Chamber Extrusion dies play a crucial role in the production of aluminum extrusions, directly affecting the quality of extruded products. However, in actual production, the design of the extrusion die relies more on the experience of the designer, the quality of the die design is difficult to guarantee, and multiple attempts and repairs are required.
According to the deficiencies of the mold design, it is proposed to open the second welding room optimization design scheme in the lower mold, to make up for the lack of feeding material in the mold processing, to avoid the defects caused by the lack of supply, such as before and after the opening, closing, and out of shape. , And effectively solve the problem of uneven speed distribution in the design. Therefore, in the optimization scheme, the temperature distribution and stress distribution on the section of the profile are more even and the output is greatly improved.
2. Role of secondary diversion In the design of extrusion moulds, secondary diversions are used for solid sections with very different wall thicknesses. Example: The initial mold design is composed of ordinary molds and mold pads. It is very unsatisfactory on the previous machine, the angle is small, and the thin-walled part is ultra-thin and ultra-small. Rework of the mold is still not ideal even if the thin wall portion is enlarged and the working belt is lowered.
For the insufficiency of the initial mold design, the second time adopts the deflector design and proposes that the secondary diversion optimization design scheme is set up in the mold, which effectively solves the problem of uneven velocity distribution in the initial mold design.
Specifically through the thin-walled part of the direct flow, thick-walled part in the discharge opening 30 degrees wide, and the size of the thick-walled part of the mold hole slightly increased size, and the other 90-degree angle of the mold hole closed at 91 degrees The sizing work belt was also appropriately modified.
3. Summary After continuous learning, accumulation, and constantly inquiries related mold design information, after the transformation, innovation to optimize the mold design, and through production practices to verify the success.
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