Radiator extrusion technology

Aluminum alloys are widely used for radiator materials because of their light weight and beautiful appearance, good thermal conductivity, and ease of processing into complex shapes. There are three main types of aluminum alloy radiator materials: flat and wide, comb-shaped or fishbone-shaped; round or elliptical outer fins are radial and branch-shaped. Their common characteristics are: the distance between the fins is short, a groove shape is formed between two adjacent fins, and the depth-to-width ratio is large; the wall thickness difference is large, the fins are generally thin, and the bottom plate of the root is thick. Therefore, it brings great difficulty to the mold design, manufacture and production of heat dissipation profiles.

Some radiator profiles are relatively easy to produce with a small size and a symmetrical shape. Most radiator profiles are flat and wide, with large external dimensions, and some are asymmetrical. The groove-to-width ratio between the fins is very large. Production is more difficult. It is necessary to cooperate with the ingot, mold and extrusion process to successfully produce the radiator profile. The alloy used for extruding radiator profiles must have good extrudability and thermal conductivity. Generally, alloys such as 1A30, 1035 and 6063 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 quality of the ingot, the material and design of the mold, the reduction of extrusion force, and the extrusion process.

1. Quality requirements of ingot

The alloy composition of the ingot must strictly control the impurity content to ensure the purity of the 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%. The content of Mg and Si are generally controlled at the lower limit of the national standard. The content of Mg is 0.45% to 0.55% and the content of Si is 0.25% to 0.35%. The ingot must be fully homogenized to make the structure and performance of the ingot even and consistent.

The surface of the ingot should be smooth, and no segregation tumors or sand sticking are allowed. The end surface of the ingot should be flat, and cannot be cut into a step shape or the cutting slope is too large (the cutting slope should be within 3㎜). Because the stepped shape or the cut slope is too large, when the heat dissipation profile is extruded with a flat die, if there is no diversion design, the ingot directly touches the mold. Due to the uneven end surface of the ingot, some places first contact the mold, causing stress concentration , It is easy to squeeze the tooth shape of the mold, or cause different discharges, which is easy to cause mold blocking or poor extrusion.

2. Requirements for the mold

Because the mold of the radiator profile is composed of many slender teeth, to withstand a large squeezing force, each tooth must have a high strength and toughness, if the performance between each other is very different, it is easy Fracture those teeth with poor strength or toughness. Therefore, the quality of the mold steel must be reliable. It is best to use H13 steel produced by a reliable manufacturer or select high-quality imported steel. The heat treatment of the mold is very important. It is necessary to use vacuum heating for quenching, preferably high-pressure pure nitrogen quenching, which can ensure the uniform performance of each part of the mold after quenching. After quenching, three tempers should be taken to ensure that the hardness of the mold has sufficient toughness under the premise of HRC48-52. This is an important condition to prevent the mold from breaking teeth.

The key to the successful extrusion of radiator profiles is that the mold design should be reasonable and the manufacturing must be precise. Generally, try not to directly squeeze the ingot onto the working belt of the mold. For the flat and wide comb-shaped radiator profile, design a diversion die with a small center and large sides to make the metal flow to both sides, reduce the squeezing force on the working belt of the mold, and make its pressure distribution even. Due to the large difference in wall thickness of the section of the radiator profile, the difference should be maintained when designing the working belt of the mold, that is, the working belt should be particularly enlarged where the wall thickness is large, which can be as large as 20mm ~ 30mm, and the position of the tooth tip should be broken Routinely, minimize work bands. In short, to ensure the uniformity of metal flow everywhere. For flat and wide radiators, in order to ensure a certain rigidity of the mold, the thickness of the mold should be increased appropriately. The thickness increase is about 30% to 60%. The production of the mold should also be very delicate. The empty knife should be symmetrical up, down, left and right, and the middle. The processing error between the teeth should be less than 0.05mm. The large processing error is easy to produce eccentric teeth, that is, the thickness of the heat sink is uneven. There will even be broken teeth.

For the more mature section, using inlaid alloy steel molds is also a better method, because alloy steel molds have better rigidity and wear resistance, are not easy to deform, and are conducive to the formation of radiator profiles.

3. Reduce extrusion force

In order to prevent the broken teeth of the mold, the squeezing force should be reduced as much as possible, and the squeezing force is related to the length of the ingot, the size of the alloy deformation resistance, the state of the ingot, and the size of the deformation. Therefore, the cast rod of extruded heat dissipation aluminum profile should not be too long, about the length of normal cast rod (0.6 ~ 0.85 times). Especially when testing the mold and extruding the first casting rod, in order to ensure that a qualified product can be produced smoothly, it is best to use a shorter casting rod, that is, a casting rod with a length of the normal casting rod (0.4 to 0.6) times. mold.

In addition to shortening the length of the casting rod, the section of the radiator with a complicated shape can also be considered for the first trial extrusion with pure aluminum short casting. After successful trial extrusion, normal ingots are used for extrusion production.

Homogenizing annealing of the ingot not only can make the structure and performance uniform, but also can improve the extrusion performance and reduce the extrusion force, so the ingot must be uniformly annealed. As for the effect of the degree of deformation, the cross-sectional area of the radiator profile is generally relatively large, and the extrusion coefficient is generally within 40, so its impact is small.

4. Extrusion process

The key to the production of radiator profiles is the first test of the extrusion die. If conditions permit, a simulation test can be performed on the computer to see if the working band of the die design is reasonable, and then the die can be tested on the extruder. The first mold test is very important. The operator must allow the main plunger to advance slowly at a low pressure of less than 8MPa when it is pressurized. It is best for someone to look at the mold outlet with a torch light and wait for each heat of the extrusion mold After the pieces are evenly extruded out of the die hole, they can be gradually pressurized and accelerated for extrusion. When squeezing continues after a successful trial, attention should be paid to controlling the speed of extrusion to achieve smooth operation. Pay attention to the heating temperature of the mold when producing radiator profiles, so that the temperature of the mold is close to the temperature of the ingot. If the temperature difference is too large, due to the slow extrusion speed during the upper pressure, the metal temperature will drop, which is easy to cause mold blocking or uneven flow rate.

The heat sink profile extrusion process parameters are shown in Table 1.

Table 1 Process parameters of radiator profile extrusion

5. Conclusion

In addition to the above factors, the extrusion technology of the radiator profile is also related to the capacity and level of the extruder, the degree of automation of the rear equipment, and the operating skills of the workers. Measures cannot be generalized.