Aluminium profiles of radiators have a small size and symmetrical shape. It is easy to produce. Most of the radiator profiles are flat and wide, with large dimensions and some asymmetry. The groove width between the fins is very large. Its production is difficult. It is necessary to cooperate with the ingot, mold and extrusion process in order to smoothly produce the radiator profile. Alloys for extruded radiator profiles must have good extrudability and thermal conductivity. Alloys such as 1A30, 1035 and 6061 are commonly used. At present, the 6061 aluminum plate is commonly used because it has good mechanical properties in addition to good squeezability and thermal conductivity.
The production of aluminum alloy radiator profiles begins with the quality of the ingot, the material and design of the mold, the reduction of the pressing force and the extrusion process.
1. Quality requirements of ingots
The alloy composition of the ingot must be strictly controlled to ensure the purity of the alloy. For the 6063 alloy, the content of Fe, Mg, and Si should be controlled. The content of Fe should be less than 0.2%, and the content of Mg and Si is generally controlled at the lower limit of the national standard, the Mg content is 0.45% to 0.55%, and the Si content is 0.25% to 0.35%. The ingot is subjected to sufficient homogenization treatment to make the structure and performance of the ingot uniform.
The surface of the ingot should be smooth and no segregation or sticking of sand is allowed. The end face of the ingot should be flat and cannot be cut into steps or the slope is too large (the cutting slope should be within 3 mm). Because the step shape or the cutting inclination is too large, when the heat sink profile is pressed by the plane die, if the guide vane is not designed, the ingot directly hits the mold, and because the end surface of the ingot is not flat, some places first contact the mold to generate stress concentration. It is easy to squeeze the tooth shape of the mold, or cause the discharge to be successively different, which is prone to the phenomenon of blockage or poor extrusion.
2, the requirements of the mold
Because the molds of the radiator profile are many elongated teeth, they have to withstand a large pressing force, and each tooth has high strength and toughness. If the performance between them is very different, it is easy. Those teeth that are poor in strength or toughness are broken. Therefore, the quality of the mold steel must be reliable, it is best to use H13 steel produced by reliable quality manufacturers, or use high-quality imported steel. The heat treatment of the mold is very important. It is necessary to use vacuum heating and quenching. It is best to use high-pressure pure nitrogen quenching to ensure uniform performance of the various parts of the mold after quenching. After quenching, three times of tempering should be taken to ensure the hardness of the mold is sufficient under the premise of HRC 48-52. This is an important condition to prevent the mold from breaking.
The key to the successful extrusion of the radiator profile is that the design of the mold should be reasonable and the manufacturing must be precise. Generally, the ingot is generally prevented from being directly extruded onto the working belt of the mold. For the flat and wide comb-shaped radiator profile, a small flow guiding mold with a small middle and two sides is designed to make the metal flow to both sides, reduce the pressing force on the working belt of the mold, and make the pressure distribution uniform. Due to the large wall thickness difference of the section of the radiator profile, the difference between the working belts of the molds should be maintained accordingly, that is, the working belts with large wall thickness should be specially enlarged, which can be as large as 20mm~30mm, and the position of the tooth tips should be broken. Regularly, minimize the work band. In short, we must ensure the uniformity of the flow of metal everywhere. For the flat wide heat sink, in order to ensure a certain rigidity of the mold, the thickness of the mold should be appropriately increased. The thickness increase is about 30% to 60%. The production of the mold should also be very fine. The empty knife should be symmetrical about the top, bottom, left and right, and the machining error between the tooth and the tooth should be less than 0.05mm. The machining error is easy to produce partial teeth, that is, the thickness of the heat sink is not uniform. There is even a phenomenon of broken teeth.
For the relatively mature design section, the inlay alloy steel mold is also a better method, because the alloy steel mold has better rigidity and wear resistance, is not easy to deform, and is favorable for the formation of the radiator profile.
3, reduce the pressing force
In order to prevent the mold from breaking the teeth, the pressing force should be minimized, and the pressing force is related to the length of the ingot, the magnitude of the alloy deformation resistance, the state of the ingot, and the degree of deformation. Therefore, the cast rod of the extruded aluminum profile should not be too long, about the length of the normal cast rod (0.6 to 0.85 times). Especially in the trial and extrusion of the first cast rod, in order to ensure the smooth production of qualified products, it is best to use a shorter cast rod, that is, a normal cast rod length (0.4 ~ 0.6) times the cast rod to try mold.
For the shape of the complex heat dissipation profile section, in addition to shortening the length of the cast rod, it is also considered to use the pure aluminum short casting for the first trial extrusion. After the successful extrusion, the normal ingot is used for extrusion production.
The ingot homogenization annealing not only makes the structure and properties uniform, but also improves the extrusion performance and reduces the extrusion force, so the ingot must be homogenized and annealed. As for the influence of the degree of deformation, since the sectional area of the heat sink profile is generally large, the extrusion coefficient is generally within 40, so the influence is small.
4, extrusion process
The key to the production of radiator profiles is the first trial of the extrusion die. If conditions permit, you can first do a simulation test on the computer to see if the working belt of the mold design is reasonable, and then try the mold on the extruder. It is very important to test the mold for the first time. The operator should let the main plunger advance slowly when moving under the low pressure of less than 8MPa. It is best to use the flashlight to look at the exit of the mold, and so on. After the sheets are evenly extruded into the die holes, the pressurization can be accelerated and gradually pressed. When the extrusion is continued after the successful test, attention should be paid to controlling the extrusion speed to achieve smooth operation. When manufacturing the radiator profile, pay attention to the heating temperature of the mold, so that the mold temperature is close to the temperature of the ingot. If the temperature difference is too large, the temperature of the metal will decrease due to the slow extrusion speed when the pressure is applied, and the phenomenon of blockage or uneven flow rate may occur.
The extrusion process parameters of the radiator profile are shown in Table 1.
Table 1 Radiator profile extrusion process parameters
Alloy Ingot Temperature / °C Extrusion Cylinder Temperature / °C Mold Temperature / °C Extrusion Coefficient Extrusion Speed min-1
1035, 1A30 400 ~ 470 400 ~ 440 400 ~ 460 20 ~ 60 15 ~ 50
6063 500～520 400～450 480～500 15～40 10～30
5. Conclusion The extrusion technology of the radiator profile is related to the above factors, as well as the capacity and level of the extruder, the automation of the rear equipment, and the operation skills of the workers. The sections of the heat dissipation profiles should be based on their characteristics. Taking appropriate measures cannot be generalized.
Key words: aluminum alloy profile aluminum alloy extrusion process aluminum alloy