Some radiator profiles with small size and symmetrical shape are relatively easy to produce. Most radiator profiles are flat and wide, with large overall dimensions, and some are asymmetric. The groove depth width ratio between radiator fins is large, making it difficult to produce. The radiator profile can be successfully produced only through the coordination of ingot casting, mould and extrusion process. Alloys used to extrude radiator profiles must have good extrudability and thermal conductivity. Generally, 1A30, 1035 and 6063 alloys are used. At present, 6063 alloy is widely used because it has good mechanical properties in addition to good extrudability and thermal conductivity.
The production of aluminum alloy radiator profiles should start from the aspects of ingot quality, mold material and design, reduction of extrusion pressure and extrusion process.
1. Quality requirements for ingots
The alloy composition of ingot shall be strictly controlled to ensure the purity of alloy melt. For 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 should generally be controlled at the lower limit of the national standard. The content of Mg is 0.45% ～ 0.55%, and the content of Si is 0.25% ～ 0.35%. The ingot shall be fully homogenized to make its structure and properties uniform.
The surface of the ingot shall be smooth and free from segregation lump or sand mud. The end face of the ingot shall be flat and shall not be cut into steps or the cutting angle shall be too large (the cutting angle shall be within 3mm). Because of the step shape or too large cutting angle, when extruding the heat dissipation profile with a plane die, if there is no design of a guide rail, the ingot directly touches the mold. Because the end face of the ingot is uneven, some places contact the mold first, causing stress concentration, which is easy to extrude the tooth shape of the mold, or cause different discharging sequences, which is easy to cause mold plugging or poor extrusion.
2. Requirements for moulds
Because the die of radiator profile is made of many long and thin teeth, which must bear a large extrusion force. Each tooth must have a high strength and toughness. If there is a big difference in the performance between them, it is easy to fracture those teeth with poor strength or toughness. Therefore, the quality of die steel must be reliable. It is better to use H13 steel produced by reliable manufacturers, or select high-quality imported steel. The heat treatment of the die is very important. It is better to use vacuum heating quenching, and high-pressure pure nitrogen quenching, which can ensure the uniform performance of all parts of the die after quenching. After quenching, three times of tempering shall be adopted to ensure that the hardness of the die has sufficient toughness on the premise of HRC48~52. This is an important condition to prevent die tooth breakage.
The key to successful extrusion is to design the die reasonably and manufacture it accurately. Generally, the ingot shall not be directly squeezed onto the mold working belt. For the flat and wide comb shaped radiator profile, a guide die with smaller middle and larger two sides is designed to make the metal flow to both sides, reduce the extrusion force on the working belt of the die, and make the pressure distribution uniform. Due to the large wall thickness difference of the radiator profile section, their differences should be maintained when designing the mold working belt, that is, the working belt should be especially enlarged where the wall thickness is large, which can be as large as 20mm~30mm, while the position of the tooth tip should break through the convention and reduce the working belt to the minimum. In short, it is necessary to ensure the uniformity of metal flow everywhere. For the flat wide radiator, the thickness of the die shall be increased appropriately to ensure a certain rigidity of the die. The thickness increase is about 30%~60%. The mold should also be made very carefully. The empty cutter should be symmetrical from top to bottom, from left to right, and from the middle. The machining error between teeth should be less than 0.05mm. Large machining errors are likely to cause tooth deflection, that is, the thickness of the radiator is uneven, and even the tooth breakage may occur.
For the section with mature design, it is also a better method to use inlaid alloy steel die, because the alloy steel die has better rigidity and wear resistance, is not easy to produce deformation, and is conducive to the forming of radiator profiles.
3. Reduce extrusion force
In order to prevent die tooth breakage, the extrusion force should be reduced as much as possible, and the extrusion force is related to the ingot length, alloy deformation resistance, ingot state, deformation degree and other factors. Therefore, the cast rod of extruded heat dissipation aluminum profile should not be too long, which is about 0.6~0.85 times the length of the normal cast rod. Especially when testing the mold and extruding the first casting rod, in order to ensure the successful production of qualified products, it is better to use a shorter casting rod, that is, a casting rod with a length of (0.4~0.6) times of the normal casting rod to test the mold.
For the section of radiator profile with complex shape, in addition to shortening the length of casting rod, it can also consider using pure aluminum short casting as the first trial extrusion. After the trial extrusion is successful, normal ingot can be used for extrusion production.
Homogenization annealing of ingot can not only make the structure and properties uniform, but also improve the extrusion performance and reduce the extrusion force. Therefore, it requires homogenization annealing of ingot. As for the influence of deformation degree, because the sectional area of radiator profiles is generally large and the extrusion coefficient is generally within 40, the influence is small.
4. Extrusion process
The key to the production of radiator profiles is the first die test of the extrusion die. If possible, you can first do a simulation test on the computer to see whether the working belt of the die design is reasonable, and then try the die on the extruder. The first mold test is very important. The operator should make the main plunger move slowly under a low pressure lower than 8MPa when it is moving forward and pressing up. It is better for someone to look at the mold outlet with a flashlight light. After each radiator of the extrusion mold is evenly squeezed out of the mold hole, gradually pressurize and accelerate the extrusion. When continuing to extrude after successful die test, the extrusion speed shall be controlled to ensure smooth operation. During the production of radiator profiles, attention should be paid to the heating temperature of the mold to make the mold temperature close to the ingot temperature. If the temperature difference is too large, due to the slow extrusion speed when pressing, the metal temperature will drop, which is prone to die plugging or uneven flow rate.
