Text/Yao Jiangang, Zhao Lanlei, You Jiaqi Jiangsu Xingforging Intelligent Equipment Technology Co., Ltd
The world is pursuing carbon neutrality and carbon peaking, and countries have put forward clear goals to achieve it, and new energy vehicles are one of the key elements to achieve carbon neutrality and carbon peaking. The lightweight of the car is particularly outstanding in terms of energy saving and consumption reduction, that is, under the premise of ensuring the strength and safety performance of the car, the curb weight of the car is reduced as much as possible, so as to improve the power of the car, reduce fuel consumption and reduce exhaust pollution. Experiments have shown that if the mass of the car is reduced by half, the fuel consumption will also be reduced by almost half. Due to the need for environmental protection and energy saving, the lightweight of automobiles has become the trend of world automobile development. Experiments have shown that if the quality of the vehicle is reduced by 10%, the fuel efficiency can be increased by 6%~8%; For every 100kg reduction in the curb weight of the car, the fuel consumption can be reduced by 0.3 ~ 0.6L per 100 km; the vehicle mass can be reduced by 1%, and the fuel consumption can be reduced by 0.7%.
At present, the main automobile lightweight measures are the use of lightweight materials, of which aluminum alloy is a very ideal material, its density is about 1/3 of steel, is the most widely used lightweight material. Lightweight materials have obvious advantages: from a cost point of view, high-strength steels are significantly ahead, followed by aluminum alloys. In terms of weight reduction potential, aluminum alloys are weaker than carbon fiber and magnesium alloys, and significantly stronger than high-strength steels. From the perspective of manufacturing process, the aluminum alloy process is relatively mature, efficient and moderately costly. Aluminum alloy has gradually become the mainstream material for automobile lightweight. Taking the automotive products produced in the United States as an example, the aluminum alloy used in each vehicle was only 39kg in 1976, reached 62kg in 1982, and reached 100kg in 1998, and the amount of aluminum used in pure electric vehicles in North America in 2020 was as high as 291.7kg.
Aluminum alloy forging characteristics
The forging deformation temperature range is small. The forging deformation temperature of most aluminum alloys is in the range of 350 ~ 450 °C, the deformation temperature range is about 100 °C, and the deformation temperature range of a few alloys is even only 50 ~ 70 °C, allowing the forging operation time to be short. This undoubtedly brings great difficulties to the forging operation, in order to strive for a longer forging time, it is necessary to heat the blank to the upper limit temperature as much as possible, increase the forging fire and preheat the tool to a higher temperature.
Sensitive to strain rate. Aluminum alloys are sensitive to strain rate, and it is necessary to choose forging equipment with low working speed and stable speed for forging. For ingots, in order to prevent forging cracking, it is usually necessary to open blanks at low speeds, extrusion and forging or rolling. When aluminum alloy die forging, it often needs to be carried out on hydraulic press or mechanical press, and it is not carried out on forging hammer forging equipment as much as possible, and the choice of forging equipment is relatively small.
Strict requirements for heating and forging temperature. Due to the small deformation temperature range of aluminum alloy forging, in order to extend the forging operation time, it should be heated to the upper limit of the allowable deformation temperature as much as possible, which requires the use of high-precision heating furnace and temperature control instrument to control the heating temperature, otherwise, it is easy to overheat. Most of the aluminum alloy semi-finished products after billet have high plasticity, in general it is not easy to forge crack, but in the forging process should avoid intense deformation, so as not to affect the structure and performance of the forgings due to excessive temperature, if you do not pay attention to the operation, the use of high speed (such as the use of forging hammer), large amount of deformation forging, a large number of deformation energy into heat energy may make the temperature of the forging exceed the upper limit of the forging temperature, causing overburning, and causing the structure and performance of the forging unqualified.
Good thermal conductivity. The thermal conductivity of aluminum alloy is 3 ~ 4 times that of steel, and its advantage is that the blank is small and does not need to be preheated, and can be directly loaded into a high-temperature furnace for heating. The disadvantage is that the surface heat dissipation is too fast during the forging process, which will cause the temperature difference between the inside and outside of the forging process to be too large, so that the deformation is uneven, resulting in local critical deformation, easy to cause local coarse crystals of the forging, so that the structure of the forging is uneven. Most aluminum alloys, especially aluminum-manganese alloys with extrusion effect, the coarse crystal rings common on the surface of the extruded bar may be related to the fast heat dissipation and friction on the surface of the blank, and the uneven deformation of the inner and outer layers falling into the critical deformation zone. To prevent heat from dissipating too quickly, the mold and the tool in contact with the workpiece must be preheated to a temperature of 300°C or higher.
The coefficient of friction is large and the fluidity is poor. The friction coefficient between aluminum alloy and steel mold is large, and the fluidity is poor during deformation, making it difficult for the metal to fill the mold groove during die forging, usually need to increase the steps and mold, and increase the corner radius of the mold.
High adhesion. Aluminum alloy viscosity, when the fierce large deformation forging, the blank will often be bonded to the mold, easy to cause forgings peeling, warping and other defects, but also cause mold wear, serious will lead to forgings and molds are scrapped.
Strong crack sensitivity. Aluminum alloys are sensitive to cracks, and if the cracks generated during the forging process are not cleaned up in time, they will expand rapidly in subsequent forging, resulting in the scrapping of forgings.
Analysis of the current situation of aluminum alloy forging
At present, there are three forms of aluminum alloy forging wire in China: manual line, semi-automatic line, and imported automatic line, all of which have certain drawbacks and defects. Its prominent problems are as follows:
Manual thread. The proficiency requirements for workers are relatively high, and the operation time is short; Off-duty or temporary substitution, product differentiation; Low production efficiency.
Semi-automatic line. Manual combined with automated production methods, limited production efficiency; Most of the manual work is to operate the trimming process.
Fully automated line imported. Multi-station forging press combined with robot production mode, usually adopts jumping process in production, and the production cycle is only 3 ~ 4 times/min; Complex molds; Equipment procurement and maintenance costs are high and time-sensitive is poor.
Aluminum alloy control arm forging process planning
Control arm is one of the key parts of the automobile suspension system, in addition to bearing the weight of the entire body, in the driving will also be subject to the action of external dynamic torque and real-time road conditions test, which makes the control arm manufacturing requirements more strict and fine, optimize the aluminum alloy control arm forming technology has been one of the focus of continuous research and exploration of personnel in the industry. Aluminum alloy control arm includes straight arm, curved arm, L arm and triangle arm, etc., which has the characteristics of diversification and complex shape, control arm forming difficulty, need multiple forming steps to turn simple shape blanks into complex shape control arm parts, its forging process is complex, feasibility, stability, forming quality, material utilization and forming load, improve mold life, etc. are the focus of its forming process. The application of forged aluminum alloy control arm products is a symbol of the improvement of automobile manufacturing level, and it is also a powerful measure for vehicles to achieve weight reduction and energy saving and improve market competitiveness. At present, there are two forging methods for aluminum alloy control arms: one is conventional extrusion rod + forging; The second is special-shaped ingot + forging, which can increase the yield of materials by 15%~20%, greatly reducing the process. However, the European and American systems usually adopt conventional forging methods, which pay more attention to the mechanical properties of forgings. Based on the above analysis, this paper mainly takes the typical aluminum alloy triangle arm in the control arm as an example to discuss the forging forming process of the control arm.
The conventional process of aluminum alloy triangle arm is shown in Figure 1: "extrusion cutting roll forging bending heating rough die forging cutting edge heating die forging forming cutting edge", this line is a manual process route, in order to make the forging form full and ensure product quality, to the greatest extent to avoid through, filling, folding, grain unevenness and other defects, the entire forging circulation and forming process, need more and relatively high proficiency requirements. With the increasing cost of labor, the domestic demographic dividend is gradually decreasing, facing the problems of difficult to find forgings, expensive labor, and serious labor loss, so how can we improve production efficiency and reduce production costs?
Figure 1 Conventional process of aluminum alloy triangle arm
Based on this, this paper proposes the process route of automatic forging, as shown in Figure 2. That is, the bar stock is cut by sawing and then heated to the specified temperature with a medium frequency induction furnace, and after "roll forging, billet bending and flattening pre-forging final forging cutting edge", the forging process of the aluminum alloy triangle arm is completed to achieve the final required forging shape.
Figure 2 Automatic forging process of aluminum alloy triangle arm
Due to the small deformation temperature range of aluminum alloy forging, sensitive strain velocity, strict requirements for heating and forging temperature, high friction coefficient in the deformation process, high viscosity in material flow and other main factors. The types and shapes of the control arm are diversified, and under the premise of forging tonnage and forging size permitting, in order to increase the adaptability to multi-variety, multi-product specifications and ensure the stability and high precision of the forging process, the line adopts multi-machine connection, multi-process forming, and the layout mode of multiple automation devices, and the layout diagram of the whole line equipment is shown in Figure 3. It is composed of bending machine, cutting edge press, hot die forging press, automatic mold changing trolley, product transfer robot, spraying robot, forging mold, high temperature resistant wedge clamping hydraulic lock and graphite automatic spraying system and other main parts, among which the press bending press mainly adopts small table, long stroke, automatic overload elimination, high rigidity press transmission structure; The hot die forging press adopts new hydraulic mechanical swing arm type material ejecting device, servo adjustment hydraulic lever type anti-stuffy car seal height adjustment device, plate dry clutch and high bearing capacity herringbone gear structure; The mold changing trolley adopts one vehicle, two molds, and drag-tow traction structure; The product transfer robot adopts tandem arrangement structure and visual online temperature monitoring device; The spraying robot adopts the control mode of tracing spraying; The forging mold adopts quick-change mold frame structure and online automatic heating device of the mold base; High temperature resistant wedge clamping hydraulic lock, looking at the influence of temperature on the mold clamping device, the beveled clamping snap-on locking structure and internal circulation cooling structure are adopted; The graphite automatic spraying system is composed of high-pressure pump, graphite automatic proportioning, automatic level monitoring and spraying atomization device.
Figure 3 Layout diagram of the entire line
Interpretation of innovative points
Hot die forging press (pre-forging and final forging): In terms of forging process, hydraulic press is an ideal equipment for aluminum alloy forging, but due to its low working frequency and production efficiency, it is difficult to adapt to the needs of mass production. Because the mechanical press has the characteristics of high strength, good rigidity, stable action, high precision of forgings, high material utilization rate, high productivity, good consistency of mechanical properties of forgings and easy automation, it is especially suitable for the production of aluminum alloy forgings sensitive to deformation speed of die forging. Starting from the requirements of the aluminum alloy forging process, in order to ensure the stability of the production process, considering the project and automatic handling, and then comprehensively considering the structural characteristics of the equipment, the required process parameters have broken the traditional concept. The new disc friction clutch and brake with non-mechanical interlocking structure are installed at the low-speed shaft, that is, the left and right sides of the eccentric shaft, and its main transmission gear adopts a herringbone gear structure with high bearing capacity; In order to meet the needs of mold demolding and robot handling of forgings in the production of forgings, starting from the aspects of maintenance characteristics and multi-variety adaptation characteristics, the upper ejection adopts the hydraulic mechanical swing arm lever structure, and the lower ejection adopts the hydraulic structure with real-time feedback with adjustable stroke; In order to prevent the main problems caused by blank, temperature, lubrication, misoperation, etc. in the forging process, and to meet the requirements of one-key automatic mold change of the whole line, this project is the first time to use the servo-adjusted hydraulic lever type anti-stuffy car seal height adjustment device to prevent the stuffy car of the equipment and the accuracy of the slider adjustment position.
Press (bending, flattening, trimming): Conventional forgings are cut and edged using special trimming presses, and this innovation improves the universal press to realize the function of cutting edge bending. In order to meet the requirements of aluminum alloy forging and bending process, the processing and assembly process of large eccentric crankshaft is developed on the basis of the general machine to improve the transmission structure of the fuselage; At the same time, it is not limited to the traditional general-purpose machine, fully combines the automation and mold-related needs, and reasonably configures the upper and lower hydraulic ejection module on the basis of the general-purpose machine, and the real-time feedback of the ejection stroke is controllable. Through a series of improvements and upgrades to the general machine, the large-stroke transmission is realized on the basis of the small table general-purpose machine, which fully meets the process requirements of large stroke and high rigidity required for bending and cutting.
Automated mold change system
Automatic mold change trolley.
Hot die forging has great difficulties in realizing multi-machine automatic mold change: the environment is harsh, and it must be waterproof and dustproof; The mold base weighs a lot; The mold has heating requirements, and the temperature of the pulled mold base is high (about 200 °C). At present, China is basically dominated by manual mold change or semi-automatic mode to achieve mold change, and all are single-station layout. Based on the requirements of fully automated one-key mold change, the key technologies that have been broken through are: the mold changing trolley adds a thermal insulation layer to ensure that non-load-bearing parts are not affected by heat; Select high-temperature resistant materials and structures for parts in contact with the mold base; Two-station design layout. The design goal of 10~15 minutes fast mold change (including automatic adjustment of closed height) has been achieved.
High temperature resistant large load clamp clamp.
A high temperature resistant hydraulic lock with a wedge chuck (fig. 4), comprising a master cylinder and a cage that can be fixed with the table, and the main cylinder and the cage are detachable connection, the cage has a guide hole, the piston of the main cylinder passes through the guide hole, and can be telescopic and moved in the guide hole, at the same time, the end of the piston has a chuck that can fix the mold base, the main cylinder further comprises a cylinder block, and the cylinder block has a cooling channel arranged around the piston. The main oil cylinder and the cage are set separately, so that during the hot forging process, the heat of the mold base is not easy to be conducted from the cage to the main cylinder, and the cooling medium in the cooling flow channel can take away the heat of the main cylinder, thereby reducing the possibility of aging damage to parts caused by excessive temperature of the main cylinder, and then oil leakage. At present, this type of hydraulic clamp can withstand a maximum load of 63 tons, and the heat resistance is as high as 160 °C; It provides the underlying core technology for automatic mold change.
Figure 4 Wedge chuck hydraulic lock
Aluminum alloy special spraying technology has higher requirements than steel parts, which not only requires the pipeline (gas path/graphite tube) pressure to be in a high-pressure and stable state during spraying, but also requires graphite liquid atomization to be more sufficient, and the spraying amount is also strictly limited. The spraying system is generally composed of three parts: spraying device, nozzle unit and electrical control.
The spraying device is used in conjunction with the forging press, and the corresponding spraying time and angle are given according to the spindle encoder. The spraying device must have the functions of graphite emulsion storage, stirring, graphite transportation, pipeline cleaning and so on, so as to achieve full automation and perfect combination with the process.
The nozzle unit now features dual nozzle mounts, with two nozzles on each seat and two nozzles on each nozzle. In principle, the spraying control of a single nozzle can be achieved to ensure that the spraying time and amount of each point can be adjusted at will to meet the requirements of the production process.
New automatic line progress
At present, the project equipment (Figure 5) has been installed in place, is still in the robot debugging stage, has successfully typed qualified products, the beat has reached 5 / minute, and reached the pre-planning target. This line is compared to other production lines in Table 1.
Table 1 Comparison table of manual line, import line and newly planned domestic line
Figure 5 Aluminum alloy control arm forging press
The project was successfully developed by Jiangsu Xingforg Intelligent Equipment Co., Ltd., which broke the embarrassing situation of aluminum alloy control arm automatic line dependence on imports, not only greatly reduced procurement costs, improved production time, but also brought additional value and experience to users. In addition, in terms of after-sales service, timely response, reduce maintenance costs, for users to seize and expand the market to lay a solid foundation.
——Article selected from: Forging & Stamping, Issue 7, 2022