How to relieve machining stresses on aluminum profile

Aluminum profile is one of the most widely used non-ferrous metal structure materials. Aluminum profile with a low density but relatively high strength is close to or surpasses the high-quality steel and it also has good plasticity so that it can be processed in various. What’s more, with excellent conductivity, thermal conductivity and corrosion resistance, the applications of the aluminum profile are widely used in the aviation, aerospace, automotive, machinery manufacturing, ship and chemical industry.

Aluminum profile in the process of processing, especially in the machining process, is prone to greater stress to deformation causing the ultra-size scrapped, and some avoiding deformation at the time can deform still after installed, resulting greater system problems. For stress relief of aluminum profile, the current methods include thermal aging, vibration aging, mechanical stretching, the mold corrective cold-pressing, etc.

Thermal aging for stress relief is generally for small and medium machining aluminum parts, which is a traditional way to stress relief. Because a lot of aluminum profile material is very sensitive to temperature, the limited aging temperature can not be too high; otherwise it will reduce the strength of the material. Thus, the thermal aging is usually carried out at a temperature of not higher than 200 ° C, and the efficiency of the stress relief can only be removed by about 10-35% at the same time.

The vibration aging for stress relief is to use controlled vibration energy to act on the processed product by the exciter sandwiched on the product surface, and to carry out the vibration treatment at a certain frequency, so as to achieve the purpose of releasing and reducing the residual stress of the workpiece. This processing method is common in large structural parts, welding and casting parts, with removal effect of about 50-60%.

Mechanical stretching for machining stress relief is to exert a certain amount of permanent tensile along the rolling direction of the aluminum profile after the quenching plastic to deform. The tensile stress and the original quenching residual stress have plastic deformation after superimposing and the residual stress can be eased and released. The results show that the mechanical stretching method can relieve more than 90% of the residual stress. However, this method is only suitable for simple shape parts, and has high requirements on the uniformity of aluminum profile sheet before stretching, mostly used in aluminum processing plants.

The mold corrective cold-pressing method is to remove the residual stress in the complex shape aluminum profile forging die in a special finishing mold by means of a strictly controlled cold-shaped plastic, which is to adjust rather than to relieve the overall stress of the part. Through this method, the residual stress on some parts of the aluminum profile products is released, but it is possible to make the residual stress of other parts increase at the same time. In addition, in view of the workpiece has already a large residual stress, the excessive deformation may lead to cold hardening, cracking and fracture, the insufficient deformation may lead to poor effect of stress relief, and what’s more, the high cost of making plastic mold and difficult operation limit this method difficult to apply in practical.

How Aluminum Extruder Operation

First of all, as regard to the operation of the aluminum extruder, the operator must pay attention to the following matters before the formal operation to ensure the normal, safe and continuous aluminum production.

(1) To check: whether the aluminum equipment is normal, whether the operating parts of the machine are in place, the lubrication of the slide, the action of the induction switch, the fasteners (screws), whether the circulating cooling water is open, whether the Bit is enough, whether the oil temperature is normal, whether the pump has sound, whether the speed is normal, whether the action fluency is normal.

(2) To check: the situation of aluminum bars (see Article 1), the extrusion center line, the aluminum extrusion tube heating, the fluctuations of heating instrument, the traction machine, the material bed, and the rear equipment operation, whether all kinds of hardware tools for the operating equipment (mold, pad, pressure cake, platen, clip, hammer, pliers, wrench, screwdriver, screwdriver, crowbar, thermal tops, plastic tools, etc.) are fixed position the work site, driving, the mold furnace for aluminum extrusion profile is normal, all kinds of quenching cooling fan is running, whether all the measurement tools are completely correct.

(3) To check: whether there are any miscellaneous personnel at the scene, whether there are maintenance personnel, whether there is a visiting staff, whether there are new learners. It should be based on to the principle of safety first according to the actual situation to educate, comment, train, guidance, demonstrate the relevant personnel, and for the foreign personnel without the leadership, it is necessary to do confidential work. The operator should also co-ordinate production with team members and pay attention to the order of the various processes.

(4) It is a must to understand the production content, production requirements, production sequence, to record the corresponding real data of the production, writing clear with standard production date so that can be verified, traceable, learnt from, and cited. What’s more, the drawings, forms, information, documents, etc, of aluminum alloy profiles should be prepared in advance and well known before the production

Now, we take the 6082 aluminum extrusion profile as an example of the use of the extruder. There are these two points need to grasp: heating method of aluminum alloy casting rod; extrusion method of aluminum profile.

1. The heating method of aluminum alloy cast rod

A. Heating time is short to reach about 500 ℃in 3 minutes;

B. Extrusion temperature should be controlled accuracy, and the error should not be more or less then 3 ℃. (Through the resistance furnace slowly heating, it will lead to Mg2Si phase precipitation, affecting the strengthening effect.)

2. Extrusion methods of Aluminum profile

A. because of strong deformation resistance of 6082 alloy, the cast rod temperature should be near the upper limit (480-500℃);

B. Aluminum extrusion die temperature should be high;

C. In case of shrinkage or bubbles, oxide, or impurities involved, the pressure should be leave longer;

D. To ensure the Mg2Si completely solid solution, the quenching temperature is above 500 ℃, and to solid the profile, the extrusion exit temperature should be controlled at 500-530 ℃;

Lightweight trend stimulates demands in high precision aluminum

Today, it’s a popular trend to produce more light energy-efficient cars with aluminum profile instead of steel profile. In recent years, aluminum consumption in China's auto is significantly increased.

According to the related study, it shows that manufacturing vehicles with aluminum replacing steel can reduce the car weight of 30% to 40%: the aluminum-manufacturing engine can be reduced 30% weight; the aluminum-manufacturing wheels can be reduced 30% weight. In addition, the aluminum radiator is lighter 20% to 40% than the same copper products, and the aluminum car body is lighter more than 40% than the steel body light. In the vehicle running cycle, while its own weight reduces per 1000kg, you can reduce 4800L fuel consumption, and reduce 11.2 tons greenhouse gas emissions.

At present, the amount of aluminum profile used in the car, after the steel and cast iron, ranks the third, while the amount in the aluminum car is in the second place. The wheel is one of the living examples of aluminum using. In the last century 80's, most cars have already started to use aluminum alloy wheels, compared with ordinary steel wheels, which have strong shock-absorbing, good elasticity, strong corrosion resistance and durable, which can make the car's comfort and safety improved. In addition, the use of aluminum alloy wheels has significant environmental effect: for each 1kg reduction in the wheel quality, 1L gasoline can travel 800m more, and for each 1L gasoline saving, it can reduce 2.5kg carbon emissions.

It can be said that car weight reducing is an "eternal" topic, and aluminum is accompanied by the automobile industry. This history can be traced back to 1898 the advent of the old car De Dion Bouton which created a precedent for using aluminum in automotive. Since then, whether in rear axle, or cylinder block, there have been aluminum figure. However, the real opener of the era of aluminum cars was undoubtedly the Audi Company. From the beginning of the Audi Company in 1980, Audi80 and Audi100 both use the aluminum doors began, and it never stopped the pace of aluminum application. In 1994, Audi launched the world's first aluminum car, AudiA8, listed in Germany only 3 months, was sold 2000, from which the all-aluminum car -- AudiA8 began mass production. The so-called all-aluminum car refers to all the part can be made of aluminum machining parts has been aluminum in the current technical conditions. To AudiA8, for example, the body is made of aluminum profile, aluminum plate and aluminum extrusion profile so that their own quality is lighter 40% than the steel body; made of aluminum alloy extrusion profile, the space frame (ASF) like the human body supports the aluminum plate and the other parts.

In fact, in addition to Audi, the Mercedes-Benz, BMW, Ford, Land Rover and other international brands have become the pioneer of aluminum automotive, and aluminum profile in the automotive industry has maintained steady growth momentum. According to statistics, in the 1960s, the average amount of aluminum used in each vehicle was only 27.2 kg. By the mid-1990s, this data rose to 113 kg, accounting for about 8% of the vehicle's own quality, especially in Europe, the United States and other developed industries Countries. The Aluminum application in the automotive industry has continued to increase, and achieved good economic and social benefits.

China's auto aluminum market has entered a stage of rapid growth, some joint ventures with local auto brands made active attempts. From Xi'an Xiwo’s Volvo BIOM all-aluminum tourist bus, Zhengzhou Yutong's all-aluminum bus, to Shanghai Volkswagen's aluminum electric cars, and then to BYD's all-aluminum-body electric bus, due to large quantities of aluminum profile using, the weight loss of these vehicles is effect obviously, for example, the BYD’s all-aluminum-body electric bus compared to the previous steel body has reduced 1.2 tons.

Although the cost of aluminum is significantly higher than the steel, and the processing technology is more complex, it always can not stop the developing trend of aluminum replacing the steel. At present, the aluminum form for automobile is mainly castings, forgings, profiles and sheet metal, among which castings account for the most significantly, but from the application parts, the car body is the most potential market segments. According to statistics, the car body accounts about 30% of the total car quality, and in the no-load case, about 70% of the fuel consumption depends on the body quality, so the lighter body are of great benefit for the vehicle's economic fuel, control stability and collision safety, Which will undoubtedly to a certain extent stimulate the Chinese aluminum profile manufactures to R & D the automotive profiles and sheet.