The latest technology and equipment for aluminum alloy extrusion

1. Preface

China's aluminum extrusion processing started from the 1950s, and has experienced the former Soviet Union's assistance in the 1950s, independent development in the 1960s and 1970s and the high-speed development period in the 1980s and 1990s. Before the eighties, China only has the production of hard aluminum alloy tube, bar, type, line mainly in the northeast light alloy processing plant, northwest aluminum processing plant and southwest aluminum processing plant three major manufacturers and a few production of ordinary material local enterprises, has developed to nearly a thousand aluminum extrusion enterprises, with more than 2,500 extrusion machine, the annual production capacity of more than 2,000kt, become a large aluminum extrusion production country, the number of extrusion enterprises, the number of extrusion machine and production capacity and the number of aluminum extrusion enterprises. The number of extrusion enterprises, the number of extrusion machines and production capacity and annual output are among the top in the world. The number of extrusion enterprises, the number of extrusion machines, the production capacity and the annual output are among the highest in the world. Aluminum profile processing equipment is constantly being improved and enhanced, and its equipment level is close to the advanced level of foreign countries in the 1990s. However, from the perspective of the whole processing industry, there is still a large gap compared with the developed countries in the West. This paper explains the current situation of China's extrusion industry and compares it with foreign extrusion industry. Described the foreign extrusion new technology and new equipment.

2 domestic aluminum extrusion industry status

2.1 Product varieties and product quality

China's aluminum extrusion industry to produce mainly architectural aluminum profiles, industrial aluminum production has just begun, aviation with hard aluminum alloy profiles stagnant, the output is very little. Alloy 6063 is the main, because the vast majority of manufacturers after the extrusion machine is not equipped with a suitable online water quenching device or quenching furnace, rarely develop and produce industrial heat treatment to strengthen the other 6000 series, 7003, 7005, 7201 and other alloys of medium strength, the production of a single variety of alloy. Most manufacturers of product structure, equipment level and production technology is the same, the market competition is very fierce, a large surplus of production capacity. Due to the limitations of equipment, production technology and molds, the precision and quality of the products produced is not high, and some high-precision pipes and industrial materials still need to be imported.

2.2 Technology and equipment level

China's three major aluminum processing plants built before the eighties, extrusion machines are mostly water presses, extrusion, heat treatment, finishing using non-continuous production mode, the main production of hard aluminum alloy material, equipment for the fifties and sixties equipment level. Most of the aluminum extrusion plants built in the eighties and nineties are mainly based on Taiwan equipment and domestic self-designed and manufactured extrusion machines, and only a few manufacturers have introduced advanced foreign extrusion machines. Extrusion production are used extrusion, online air-cooled or water-cooled quenching, finishing flow production method, extrusion machine using oil pump transmission, the entire production line is mostly PLC control. In technology, although digested and absorbed the technology of western industrial developed countries, but still dominated by Taiwan technology. Most of the extruders are small tonnage extruders, mainly single extrusion, manual operation, low production efficiency, low yield, product accuracy and surface quality is not high, most of the factories use the ingots without homogenization, which does not meet the requirements of the new national standards.

2.3 Mould processing technology

China's specialized extrusion mold processing plant is not much, some large and medium-sized enterprises have mold processing center, mold standardization is not high. Mold design more traditional design methods, in recent years the development of plane die and shunt combination die computer-aided design (CAD) system has been applied. Due to the use of new die materials and surface treatment technology, improve the die hole surface hardness, die life has also been improved. In the extrusion production, the new die usually has to go through 2-3 times of mold trial and more than one mold repair.

3 The gap between domestic and foreign aluminum extrusion industry

China's aluminum extrusion industry and the gap between the developed countries in the West, see Table 1.

4 foreign extrusion new branch technology

4.1 long ingot heating

Small and medium-sized extrusion production lines in Europe and the United States more than the use of long ingot heating, hot billet shear production method. The use of hot billet shear, in the extrusion production according to the different specifications of the ingot length required to set the shear length, a long ingot shear the remaining short ingot can be connected with the next long ingot shear into the required ingot length, therefore, the shear does not produce waste, improve the yield, but also reduce the amount of sawdust. In the production, the reasonable ingot length can be determined according to the requirements of the cut-to-length, and the ingot length can be adjusted at any time, thus improving the yield.

4.2 Isothermal extrusion

In the extrusion process, in order to improve production capacity, it is often desired to produce at a speed close to the critical extrusion speed, while in actual production, a more conservative extrusion speed is often used. During the extrusion process, the temperature of the extruded material becomes higher and higher due to the friction between the ingot and the extrusion barrel and the heat generated by the extrusion deformation, and the temperature difference between the front and rear of the extruded material is large, which leads to uneven organizational properties along the length of the profile, and cracks are likely to appear on the surface of the profile if the extrusion speed is too high in the middle and late stages of extrusion. To prevent this temperature rise, the isothermal extrusion method is proposed to keep the extruded material exit temperature consistent throughout the extrusion process. The isothermal extrusion method is especially suitable for the production of hard aluminum alloys such as 2000, 7000 and some 5000 series with low critical extrusion speed. For soft alloys with high extrusion speed, the extruder usually adopts the method of isothermal extrusion such as ingot heating or gradient cooling and extrusion deceleration control to simulate isothermal extrusion.

Ingot gradient heating is based on the temperature difference between the front and rear of the extruded material during the extrusion process to determine the heating temperature gradient of the ingot. Ingot induction furnace is usually divided into several zones along the length of the heating coil, the heating power of each zone is different, the front end of the ingot heating power is high, the back end of the heating power is low, so as to get the ingot front temperature is high and the back temperature is low, the temperature gradient is generally 0-15 ℃ / 100mm. long ingot gas heating is usually used to heat the ingot out of the furnace gradient cooling method, so that the ingot also in the Longitudinal formation of a high temperature gradient before and after the low temperature gradient.

Extrusion deceleration control is to gradually reduce the extrusion speed in the middle and late stages of extrusion to reduce the temperature rise of the extruded material. This deceleration control is usually used to control the extrusion speed of soft alloy materials, and the average extrusion speed of this control method is greater than the speed of ordinary isothermal extrusion.

In order to achieve isothermal extrusion, also take the extrusion barrel partition heating measures, in more than 25MN extrusion machine extrusion barrel heating in 4-6 zones, by SCR or PID control extrusion barrel heating temperature. The extrusion barrel is also equipped with a cooling path, and a spiral groove is set in the inner part of the extrusion barrel jacket (or middle sleeve) near the die, and compressed air is passed in the middle and late stages of extrusion to take away the frictional heat between the ingot and the extrusion barrel, so as to control the temperature rise of the ingot.

4.3 Extrusion process temperature control

In the extrusion process, it is usually necessary to control the ingot heating temperature, extrusion profile exit temperature and quenching and cooling temperature to ensure that the required extrusion properties and obtain longitudinal properties consistent, excellent mechanical properties of the product. With the development of far-infrared temperature measurement technology, some foreign factories have been in the ingot out of the furnace, the front sorghum outlet and quenching device after the measurement accuracy is relatively high (accuracy ± 1%, response time 0.05-1s) non-contact infrared thermometer, can continuously measure, display and record the ingot and extrusion material temperature, while over-temperature alarm. The temperature of the ingot is measured and the optimum extrusion speed parameters can be determined by the computer. The temperature of the extrusion die exit is measured, and the temperature of the extrusion die exit is kept in the required temperature range by adjusting the heating temperature of the ingot, and the extrusion speed and the heating temperature gradient of the ingot can be appropriately adjusted by the computer to achieve more accurate isothermal extrusion. The application of this temperature measurement technology will promote the development of isothermal extrusion technology.

4.4 High-speed extrusion

The current advanced extrusion line to improve production efficiency, in addition to mechanical considerations to minimize the extruder fixed cycle (non-extrusion time) in addition to the use of high-speed extrusion method. As is known, the quality of extruded material and extrusion exit speed and extrusion temperature is closely related. In the extrusion process, when the extrusion speed is too fast, the uneven deformation intensifies, the ingot temperature rises faster, the metal flow is not uniform and the exit temperature is too high, easy to cause extrusion material surface tear, roughness and die damage. Domestic in order to improve the extrusion speed, generally only using low-temperature extrusion. Foreign advanced extrusion line in addition to the use of reasonably designed die to take the die, extrusion cylinder cooling, take away part of the metal deformation, heat generated by friction, to prevent the die temperature rise, inhibit the profile surface defects, and extend the life of the die.

For hard alloys (2000, 7000 series alloys and some 5000 series), liquid nitrogen is used to cool the die. Soft alloys (6000 series alloys) can adopt gas nitrogen cooling mold.

In the design of the die, consider reducing the uneven deformation rate to make the metal flow pressure equal and flow smoothly, and set up a guide cavity with a shape similar to the profile shape at the entrance end of the chess piece to make the metal flow more uniform and extend the die life.

4.5 Computer optimization of extrusion process parameters

The quality of the extruded material depends on the extrusion process extrusion ratio, extrusion speed and ingot preheating temperature and other process parameters. At present, foreign manufacturers have used the computer to optimize the extrusion process parameters. The computer uses the stored material properties, extrusion characteristics, processing range, extruder tonnage, ingot diameter, extrusion barrel size, maximum extrusion bar speed, and product data to derive the extrusion criticality diagram (Figure 4) [1]. This diagram describes the relationship between extrusion temperature and speed, there are three critical lines in the diagram, the first is the pressure critical line corresponding to the capacity of the extruder, the second is the mechanical properties of the material critical line, the third is the appearance of surface defects surface critical line, in the pressure critical line and surface critical line under the intersection of the two lines near the region for the best process parameters range, the computer after computing, simulation of the extrusion process, the analysis of the best The computer calculates and simulates the extrusion process to analyze the best process parameters, including extrusion speed, ingot heating temperature and ingot size.

4.6 Online control of product dimensional accuracy

Foreign advanced production lines have started to use laser measurement technology and laminar X-ray camera inspection technology to inspect the geometric dimensions of the profile online.

The laser inspection system measures the profile size of the continuous extruded products from different directions and controls the dimensional accuracy of the products by comparing with the computer stored images. It also manages the die.

The laminar X-ray camera inspection system uses the principle of CT used in general medicine to scan a section of a hollow or solid profile online, generates an image to be displayed on the computer screen, compares it with the design data stored in the computer (CAD file of the profile section graphics), automatically detects all critical dimensions, shows whether they are out of tolerance, and stores the inspection data, with a typical inspection cycle time of 1 - 2min [2]. This technology is used for online control of complex sections and profile geometries with narrow tolerance ranges. Based on the inspection results, the operator decides whether to change the mold or not, and for new molds, the inspection data can also be sent to the mold manufacturing department via a computer network.

The adoption of online geometric dimension inspection of profiles greatly improves the precision control and yield of products.

4.7 Mold design and manufacturing

The metal flow, temperature and pressure changes in the extrusion process of aluminum profiles are very complicated, and the more complex the profile section is, the greater the degree of uneven deformation. When using unsuitable extrusion die or extrusion speed, it will cause the profile to twist, bend and produce waves, and it is usually necessary to repeatedly test and repair the die in order to produce qualified products. Advanced foreign enterprises adopt CAD system for auxiliary design of dies, and according to the processing parameters (ingot temperature and size, extrusion speed, etc.), adopt 3D finite element processing model to dynamically simulate the material flow, deformation rate distribution, temperature distribution and pressure distribution in the extrusion process, and optimize the design of extrusion dies through computer analysis and calculation. Through the CAM (Computer Aided Manufacturing) system, CNC (Computer Numerical Control) machine tools are used for die processing. The resulting design and manufacture of the die, extrusion, metal flow uniformity, high precision products, and greatly reduce the number of die trials, die repair.

4.8 Reverse extrusion technology

Aluminum and aluminum alloy hot extrusion is usually used in two ways: forward extrusion and reverse extrusion, and the forward extrusion method is now commonly used internationally. Reverse extrusion due to than the forward extrusion required squeezing pressure is reduced by 10-30%, ingot and extrusion cylinder surface without friction, temperature rise is small, metal flow uniform, the organization of the product properties of uniform, high dimensional accuracy, can use a higher extrusion speed, extrusion AA2000, 5000, 6000 and 7000 series alloy, its extrusion speed for forward extrusion 1.7-4.2 times [3]. Therefore, in recent years, the reverse extrusion machine has been more and more widely used in the extrusion of hard alloys. However, reverse extrusion requires high ingot surface quality and high cost of extrusion tools. At present, foreign countries are vigorously research to solve these problems, in order to make the reverse extrusion technology is more widely used.

4.9 three-dimensional extrusion technology

Three-dimensional extrusion technology is a set of extrusion and mechanical processing in one step molding technology. Such as the installation of a rotary die at the exit of the extrusion die, along the profile longitudinal processing of the required indentation; after the extruder installed a set of bending devices, the extruded profile will be bent into the required shape, such as Figure 2, 3 [4].

5 Foreign extrusion equipment new progress

5.1 Extrusion machine

5.1.1 Extrusion press structure

5.1.1.1 Pre-stressed tension column

The extruder adopts pre-stressed tension column structure, that is, a certain tensile stress is applied to the tension column to reduce its elastic extension during extrusion, improve the rigidity of the extruder, greatly reduce the movement of the front beam during extrusion, reduce the die deformation, improve the dimensional accuracy of the extruded profile, and also extend the life of the tension column. The old structure of the tension column is mostly solid cylinders, each pair of open nuts to the tension column and the front and rear beams fixed. The tension column of this structure is subjected to tensile stress from 0 to maximum squeezing pressure during extrusion, and the deformation is large. The new prestressed tension column structure is in the front and rear beams between the tension column outside of a square casing or round casing, to the tension column after the application of prestress, the formation of the tension column under tensile stress, casing under compressive stress structure, in the extrusion tension column to bear the tensile force and casing under pressure and the residual tension applied to the tension column and the residual tension, the residual tension with the increase in squeeze pressure and decrease, the tension column tension stress always in the prestress The tensile stress of the tension column always changes between the pre-stress and the tensile stress when squeezing, and the stress changes are small, and the elastic elongation of the tension column during the squeezing process is also small.

5.1.1.2 Short-stroke extrusion machine

Short-stroke extrusion machine has long been put into production, but began not to attract attention, only in recent years to promote the use of Europe, this short-stroke extrusion machine is the ingot for between the extrusion cylinder and die or the use of lifting the extrusion shaft structure, the extrusion shaft stroke is short, shorten the empty journey time, improve productivity. At the same time also shorten the length of the whole machine, improve the rigidity of the extruder.

5.1.1.3 Rotating extrusion barrel type extruder

Rotary extrusion barrel type extruder is developed in recent years, the extruder is equipped with three extrusion barrels are placed in the extrusion, loading ingot, cleaning three stations, three extrusion barrels can be rotated, the extrusion is completed, the completion of the extrusion barrels rotate to clean up the position, loaded ingot extrusion barrels are rotated to the extrusion position to start the next extrusion cycle. This extruder non-extrusion time within 10 seconds, the production efficiency is high.

5.1.1.4 movable beam, extrusion barrel seat, extrusion pad, residual material shear

Active cross-beam and extrusion cylinder seat for the "X" type guide, to ensure the concentricity of the extruder. The fixed extrusion pad structure eliminates the need for a shim return mechanism and reduces the thickness of the residue. The residue shear moves up and down along the square guide rail and has a beating mechanism. At the end of shearing, the cylinder pushes the beating head to flush out the residue left on the die. To prevent the cutting edge of the aluminum stick, with automatic lubrication device for cutting edge.

5.1.1.5 extrusion tool replacement

Extrusion tool replacement to simple, fast direction. Modern extrusion machine with translating or rotating fast die change mechanism, die change time only a dozen seconds. Some extruders are also equipped with die support shear mechanism under the sliding die frame, before the die change, the extruded material in the die support and support pad between the cut, extruded material pulled out, the support pad without cutting off the material head, so that the die change operation more convenient. This mechanism is especially suitable for large extruders where it is difficult to separate the die support from the support pad. The extrusion cylinder and extrusion shaft are equipped with a quick locking device, which is easy to assemble and replace, and shorten the time of tool change.

5.1.2 Extruder hydraulic system

The current advanced extruder hydraulic system are used hydraulic integrated block, compact structure, the main cylinder and most of the other cylinders using logic cone valve control, this valve switching fast response, small impact, less leakage, good stability, accurate and reliable control. The extrusion speed control adopts volumetric speed regulation, and the main pumps are all large-capacity axial piston variable pumps. For the simple production of construction profiles and soft alloy products extrusion machine, the use of inexpensive electro-hydraulic proportional valve to adjust the main pump discharge, open-loop control of extrusion speed. For the production of hard alloy extrusion machine, the use of electro-hydraulic proportional servo valve closed-loop control of the extrusion speed, the actual extrusion speed measured by the extrusion rod tachometer or the position of the main pump variable mechanism measured by the position of the sensor and its corresponding set value for comparison, the deviation signal feedback to the electro-hydraulic proportional servo valve control of the main pump discharge, so as to achieve closed-loop control of the extrusion speed.

Extruder hydraulic system tends to use higher pressure, currently more than 275bar, increase the system pressure, will reduce the size of the cylinder, pipe, valve and pump flow, reduce the size and weight of the extruder. But need to be equipped with good seals, keep the hydraulic oil clean, oil filtration accuracy ≤ l0μm.

5.1.3 Extruder column automatic control system

5.1.3.1 Computer control system and data processing system

In the 80s, the extrusion line using PLC (programmable logic controller) to control the operation of the entire production line. 90s, advanced foreign extrusion machine are equipped with PLC communication with the host computer - computer (PC) and special software to monitor, control and record the whole process of extrusion, and the whole plant computer system network, in This computer through the multi-screen menu input work parameters, display the work status diagram and the main work parameters, hydraulic drive system diagram and auxiliary equipment action diagram, fault alarm and display, record and store the process and operating parameters, die numbering management, storage of daily, class, time product data and finished product volume, according to the need to be able to call out and print the above parameters at any time. In recent years, the more advanced production line computer is also equipped with extrusion process parameters optimization and die design software as mentioned before, storing information on extruders, properties of various aluminum alloys, processing range and processing characteristics, etc. When extrusion materials, section shapes and specifications, product requirements are given, the best process parameters (extrusion speed, extrusion temperature, ingot size and ingot gradient heating temperature) can be determined through this software to achieve isothermal and high-speed extrusion. Realize isothermal and high-speed extrusion. The PC can also be connected to the plant-wide computer network system.

5.1.3.2 Extrusion centering detection system

Extrusion Jane and extrusion rod with sensor detection system to detect its alignment, and display the test results on the operating panel, so that the operator timely adjustment.

5.2 Auxiliary machine after the machine

5.2.1 After the machine double traction machine

Some extruders are equipped with double tractors with flying saws after the machine, which can avoid the requirement of short fixed cycle (non-extrusion time) of extrusion due to the long return time of the tractor, and the interruption of the profile can be carried out during the extrusion process. In the extrusion process, the profiles can be interrupted at the welding of the two profiles extruded before and after, or when extruding profiles with large deformation coefficients in a single hole, long ingots can be used to interrupt the multiple profiles extruded continuously in the extrusion process to improve the yield.

5.2.2 Water - air cooling quenching device

Water-air cooling and quenching device is commonly provided, and water pipes and air ducts equipped with nozzles are arranged longitudinally to prevent profile deformation.

5.2.3 Tension straightening machine

The tension straightening machine of advanced extrusion line is mostly operated by one person or no one, realizing automatic feeding and moving out, adopting comb-type or vertical clamping jaws, and shortening the length of the stretching chuck.

5.2.4 Automatic sawing

High-precision automatic sizing and automatic batch sawing of profiles, with a section of head exclusion device at the sizing table near the sawing machine to automatically allocate the cut head and tail waste to the waste basket, and the finished product is automatically removed.

5.2.5 Automatic stacking of profiles

The advanced and large extruders are equipped with automatic profile stacker, as shown in Fig. 4. The stacker places the profile pads at certain intervals between the finished product transfer belts, and when the profile is moved to the pads, the stacker clamps the two ends of the pads and puts the profile into the material basket.

5.3 Mould heating

Multi-bore mold heating furnace is adopted, and each set of molds is heated separately to improve heating quality and prolong mold life.

5.4 Profile roller straightening machine

In order to improve the sectional accuracy of the profile, foreign countries are generally equipped with roll-type straightening machine to correct the defects such as angle and flare of the profile that do not meet the technical standards.

6. Suggestions for the development of China's aluminum extrusion industry

1) adjust the production scale of enterprises, merge small enterprises, the formation or development of large-scale extrusion production lines, the elimination of some of the technical equipment backward small extrusion production lines.

2) adjust the product structure, and increase efforts to develop and produce industrial profiles. Some medium and large extrusion machine for appropriate transformation, the use of advanced extrusion technology and equipment to meet the production of industrial materials and high-precision profiles.

3) extrusion equipment manufacturers, production plants, universities and research institutes to join together to develop isothermal extrusion, online temperature and product size measurement, computer control and process parameter optimization software, reverse extrusion technology, three-dimensional extrusion technology and other advanced extrusion technology and equipment, and applied to China's extrusion industry.

4) The establishment of specialized die processing center, the development of die set juice and manufacturing software to improve product accuracy. Design multi-hole extrusion die and adapt to high-speed extrusion die, in order to improve the extrusion equipment single machine production capacity.

5) Construction of large-scale technology and equipment level of the melting and casting plant, eliminating energy consumption, backward technology and equipment, the production of ingots of poor quality of small melting and casting production lines, to provide quality ingot billets for the extrusion line.

7. Conclusion

China is a large extrusion production country, the vast majority of extrusion machine technology and equipment is far behind the world's advanced level, low production efficiency, single product, product quality is not high, the market competition is fierce. For some conditional manufacturers, should draw on foreign advanced technology, accelerate the extrusion of mechanical, hydraulic and electrical systems to transform, and the use of increasingly popular computer and some measurement technology, as soon as possible to develop some software, operation control extrusion machine and processing of some production data, in order to catch up with the world's advanced level of technology and equipment, to adapt to the production of domestic shortage of high-precision small and large extrusion products. Participate in the international market competition.