What are The Design Ideas And Steps Of Aluminum Extrusion Die?
1. Factors to be considered when designing the extrusion die
1.1. Factors determined by the mold designer
The extrusion dies designer must follow the structure of the aluminum profile extrusion machine, the choice of the die machine and the customer’s product surface requirements, usage, the complexity of the product drawings, the structure and dimensions of the die, the die material, the number of die holes and the extrusion Compression coefficient, extrusion ratio, product shape, size, and allowable tolerances, die hole shape, orientation and size, die hole shrinkage, deformation deflection, strength deformation amount, performance ratio, the ratio of sizing band to obstruction flow rate, Sub-flow and so on.
1.2. Factors determined by the mold maker
Mold manufacturing includes turning, milling, drilling, grinding, beating, cutting, throwing, and welding. The accuracy of the mold size and shape must be processed in accordance with the design drawings, the processing accuracy of the sizing belt and the obstruction system, surface finish, heat treatment hardness, surface penetration Carbon, decarburization, surface hardness changes, end face parallelism, etc. must all meet the requirements of design drawings and customer surface requirements.
1.3 Factors determined by the extrusion producer
The assembly and support of the mold, the heating temperature of the ingot, the mold and the extrusion barrel, the extrusion speed, the process lubrication, the product variety and batch, the quality of the alloy and the ingot, the traction condition, the tension correction and the amount of stretch, are Specification of extruded alloy ingot, cooling condition of product exit.
Centering of tool and die, control and adjustment of industrial aluminum extrusion machine, setting of guide path, length of output table and straightener, industrial aluminum the capacity of the profile extrusion machine and the specific pressure of the extrusion barrel, the length of the extruded residue, etc.
2. Principles and steps of mold design
2.1.Determine the design cavity parameters
First, the designer gets the cross-section drawing. The first glance is to determine the machine. According to the extrusion ratio, the maximum circumscribed circle of the profile cross-section, and the complexity to decide which machine is suitable.
Second, the size of the mold is set. If it is smaller, it will affect the service life and moldability of the mold. Generally speaking, the specification of the large-section mold is set to a larger point, so that the mold is strong and the price of the mold is almost the same.
Third, the distribution of the split holes of the fixed mold and the deflector, the design of the flat die, and the design of the working belt, the design of the forming hole.
2.2. Reasonable arrangement of die holes on the die plane
The so-called reasonable arrangement is to distribute single or multiple die holes on the die plane reasonably, so as to obtain the best metal flow uniformity on the premise of ensuring the die strength.
For single-hole bars, pipes and profile die with good symmetry, the theoretical center of gravity of the die holes should be placed on the center of the mold. For products with different wall thicknesses and uneven symmetry in various parts of the aluminum profile, try to ensure the mold plane x.
The metal amounts of the upper, lower, left, and right sides of the shaft and l, the shaft are approximately equal, but the metal flow characteristics in the extrusion cylinder should also be considered so that the thin-walled part or the difficult-to-form part is as close to the center as possible.
The layout of the porous mold should mainly consider the number of mold holes, mold strength, the surface quality of the product, and uniformity of metal flow. Generally speaking, the porous die should be arranged on the concentric circle as much as possible, to maximize the symmetry of the arrangement, and to ensure the condition of the die strength, the die holes should be as compact as possible and as close as possible to the center of the extrusion cylinder.
2.3. Reasonable calculation of die hole size
When calculating the die hole size, mainly consider the chemical composition of the extruded alloy, the shape and nominal size of the product and its allowable tolerance, the extrusion temperature and the thermal expansion coefficient of the mold material and the extruded alloy at this temperature, the product cross-section, the characteristics of the geometry and its changes during extrusion and stretching straightening, the magnitude of the extrusion force and the elastoplastic deformation of the die and other factors. For profiles, the following formula is generally used for calculation:
A=A0+M+ (KY+KP+KT) A0
A0 in the formula-the nominal size of the profile;
M——The allowable deviation of the nominal size of the profile;
KY——For T-shaped and grooved profiles with long edges, consider the factor of reducing the size of the profile due to the pulling force;
KP——Considering the coefficient of size reduction when stretching and straightening;
KT——The heat shrinkage of the pipe.
Where t and t1 are the heating temperature of the blank and mold respectively;
α and α1——the coefficients of linear expansion of the blank and mold respectively.
For profiles with large wall thickness differences, the thin-walled parts and sharp edge areas that are difficult to form should be properly enlarged. For the die holes of flat, wide and thin-wall profiles and wall profiles with large width-to-thickness ratios, the size of the truss section can be designed according to the general profile, and the size of the web thickness, in addition to considering the factors listed in the formula, need to consider the mold Elastic deformation and plastic deformation and overall bending, the distance from the center of the extrusion cylinder and other factors.
2.4. Reasonably adjust the metal flow rate
Generally speaking, the thinner the wall thickness somewhere in the profile, the greater the perimeter, the more complicated the shape, and the farther away from the center of the extrusion barrel, the shorter the sizing zone.
When it is still difficult to control the flow rate with a sizing belt, the shape is particularly complicated, the wall thickness is very thin, and the part far away from the center can use a flow angle or a material guide cone to accelerate the metal flow.
On the contrary, for those parts with much larger wall thickness or very close to the center of the extrusion cylinder, the obstruction angle should be used to supplement the obstruction to slow down the flow velocity here.
In addition, you can also use process balance holes, process margins, or use anterior chamber mold, diversion mold, change the number, size, shape, and position of the distribution hole to adjust the metal flow rate.
Extrusion speed limit diagram
2.5. Ensure sufficient mold strength
In addition to rationally arranging the positions of the die holes, selecting appropriate die materials, and designing a reasonable die structure and shape, it is also very important to accurately calculate the squeezing force and check the allowable strength of each dangerous section.
At present, there are many formulas for calculating the extrusion force, but the modified Berrin formula still has engineering value. The upper limit solution of the squeezing force also has a good applicable value. It is relatively simple to calculate the squeezing force using the empirical coefficient method. As for the mold strength check, it should be done separately according to the type of product, mold structure, etc.
Generally, the flat mold only needs to check the shear strength and bending strength. The tongue die and plane split die need to check the shear, bending, and compressive strength, and the tongue and needle tip also need to consider the tensile strength. An important basic problem in strength checking is to choose the appropriate strength theoretical formula and more accurate allowable stress.
3. Aluminum profile extrusion process conditions
3.1. The heating temperature of ingot
The maximum allowable heating temperature of aluminum is 550 ℃, the lower limit temperature is 320 ℃, in order to ensure the structure and performance of the product, the heating temperature of the billet during extrusion should not be too high, the extrusion temperature should be reduced as much as possible.
3.2. The heating temperature of the extrusion cylinder
The composition of the mold is mostly alloy steel. Due to the poor thermal conductivity, the extrusion barrel must be preheated before extrusion to avoid thermal stress. To ensure the quality of the extruded product and have a good extrusion effect, the temperature of the extrusion barrel can be 400. ℃-450℃.
3.3. Extrusion temperature
During hot extrusion, the heating temperature is generally 0.75-0.95 times the absolute temperature of the melting point of the alloy, and the temperature during extrusion is controlled at about 500°C.
3.4. Squeeze speed
Although fast extrusion speed can improve productivity, too fast extrusion speed will affect the extrudability of the material and make the extrusion temperature too high, so the extrusion speed must be controlled.
Considering the squeezability of metals and alloys, product quality requirements, and equipment capacity limitations, the extruding speed of this design is 40-60m/min.
3.5. Extrusion ratio
Extrusion ratio calculation formula: area of extrusion barrel/cross-sectional area of the profile.
Extrusion ratio: one of the important parameters to measure whether this profile can be extruded in this extruder.
If the extrusion ratio is too small, the profile product deformation is insufficient, the density and surface quality is not good, the extrusion ratio is too large, the mold deformation is too severe, the extrusion is difficult, the profile size is difficult to guarantee, and even mold blocking is caused. Therefore, the ideal value of the extrusion ratio is 40-80.