In July 2019, Tesla issued a new patent titled “Multi-directional body-integrated molding machine and related molding methods for automobile frames”, proposing frame-integrated molding technology and related molding machine design. At the Tesla Battery Day conference on September 22, 2020, Musk said that the Tesla Model Y will use integrated die-casting to produce the body’s rear floor assembly, replacing the initial need for more than 70 parts and more than 1,000 welds, Tesla officials said. that this technology will reduce the quality of the lower body assembly by 30%, reduce the manufacturing cost by 40%, save 20% of the cost of Model Y vehicle, and reduce the manufacturing cost by 30%. At the same time, Tesla plans to use three large die-cast parts to assemble the entire lower body and replace the original 370 parts, which could reduce the overall quality of the vehicle by 10% and increase the autonomy of 14%. Tesla led the entire industry to follow and change. OEMs and die casting related manufacturers such as NIO, Xpeng and Gaohe are currently carrying out 0 to 1 verification work and 1 to 100 development work. Volvo, Volkswagen, Mercedes-Benz Traditional. OEMs such as FAW and FAW are also actively deploying.
The technology mentioned above is “integrated die casting technology”. It redesigns and heavily integrates dozens or even hundreds of parts that need to be assembled into the original design. It uses a very large tonnage die-casting machine and advanced technologies. casting technology to form super large size die casting machine to achieve original functionality. The most important feature of this technology is the ultra-large size of products, which leads to ultra-large tonnage die casting machines, ultra-large complex structural molds, extreme process parameters and demanding requirements. extremely high CAE analysis ratings. it also solves the problem of deformation of large, thin-walled parts. Heat-treated aluminum alloy has become one of the hot spots of integrated die-casting technology.
This article combines traditional die casting technology with a detailed introduction and analysis of the production factors of integrated die casting technology, namely “people, machines, materials, methods, environment and measure “.
Material properties
Integrated die-casting parts generally have the characteristics of large size, thin wall thickness and complex structure, which imposes higher requirements on the performance of aluminum alloy materials. Taking into account factors such as performance, process characteristics and production conditions, die-casting aluminum alloy integrated materials not only have higher overall performance requirements than ordinary die-casting, but have also unique requirements.
1. General performance requirements
Good thermoplastic rheological properties: It must have good thermoplastic rheological properties when the superheat is not higher than the liquid and solidus temperatures to achieve the filling of complex cavities, form a good casting surface and avoid the appearance of defects. withdrawal.
Lower linear shrinkage avoids cracking and warping during the die casting process, allowing die casting parts to maintain high dimensional accuracy.
The smaller solidification temperature range facilitates rapid simultaneous solidification and reduces defects such as internal shrinkage holes.
Better casting interface (mold) properties will not cause chemical reaction with the die casting mold and have low affinity to reduce mold sticking and mutual alloying.
2. Unique performance requirements
(1) High strength and toughness For traditional aluminum alloys, heat treatment is a necessary way to ensure the mechanical properties of parts. However, in fact, the heat treatment process can easily cause surface defects and dimensional deformation of parts, which will be a problem. problem for large built-in parts. This will inevitably lead to an increase in scrap rate and bring huge cost risks. Therefore, special heat-treatable aluminum alloys are required to ensure that the material maintains good mechanical properties after being formed without heat treatment. The structural design of parts is carried out according to the strength of the material, and the higher the strength of the material, the more obvious the weight reduction. Additionally, for vehicle body structural parts, crash and fatigue performance requirements must also be considered. Therefore, integrated die-cast structural parts require materials with high strength and plasticity in the cast state.
(2) Excellent casting performance includes many aspects for integrated die-cast structural parts, the mold filling ability of the material is essential. At present, the farthest process can reach about 2.7 m. If the mold filling capacity is insufficient, it will cause problems such as under-pouring.
(3) High connection tolerance Since large integrated die-casting body structural parts cannot achieve uniform performance in different parts of the part, different connection methods can be selected in different parts of the part. For example: welding, SPR and bonding, etc.
Different connection methods also have different performance requirements for materials. For example, SPR requires the material to have high toughness, while welding requires the material to be pore-free.
(4) Higher tolerance of trace elements and impurities. Currently, the yield of integrated castings is around 60% (each company’s data is inconsistent, this data is a rough average), which means that around 40% of parts are affected. must be returned to the oven for reuse. In this process, some impurity elements will inevitably be introduced, and some elements will also be burned. With the determination of the double carbon goal, it is hoped that in the future, recycled materials can be integrated into the production process without heat. Therefore, the material must have a high tolerance to elements and impurities to ensure casting economy and performance.
(5) Durable and efficient modifier Due to the characteristics of heat-free materials, the heat treatment process is eliminated. The currently commonly used AlSi10MnMg material improves the mechanical properties of parts through heat treatment. However, materials without heat treatment have no means of tracking and can only acquire mechanical properties through the structure formed during the casting process. The strength and plasticity of materials are achieved by controlling the structure formed during solidification. At present, the key point for controlling the structure of materials without heat treatment lies in controlling the eutectic structure. Aluminum-silicon alloys focus on controlling the morphology and size of the eutectic silicon; Aluminum-magnesium-silicon alloys focus on controlling the morphology and size of magnesium disilicon. Currently, the element lanthanum (La), the element gadolinium (Gd) or the existing rare earth element is used as a modifier for tissue regulation. In the actual production process, the process requires the melted material to be kept hot for a long time. If the efficiency of the modifier decreases or even fails, it will pose a great challenge to the continuity of production.
Therefore, aluminum alloys without heat treatment have become the only choice for integrated die casting products. Major universities, scientific research institutes, enterprises and institutions have developed materials resistant to heat treatment, showing a flourishing trend. At present, heat-treatable aluminum alloys can be divided into two categories: aluminum-silicon series (Al-Si series) and aluminum-magnesium series (Al-Mg series) within this framework. . At present, mature materials without heat treatment often have a non-heat treatment alloy quality system, such as Alcoa, Rheinfield, Tesla and Shanghai Jiaotong University.
By sorting the components of different grades of heat-treatable aluminum alloy materials, it can be seen that some materials have been refined in their composition and production process based on existing patents. Companies that have successfully developed heat-treatable aluminum alloy materials. will apply for patents as soon as possible for protection; OEMs To avoid patent disputes, patent-protected alloy grades will be selected. Patents are the threshold for preliminary testing and certification of complete vehicles. Barriers to R&D and certification – Although there is no unattainable technical threshold for research and development of alloys without heat treatment, it requires cooperation between upstream materials companies, die casting plants pressure, mold factories and automobile manufacturers for R&D. The obstacles to R&D lie not only in adjusting alloy composition and adjusting process routes. The bottom line is that material manufacturers cooperate with die-casting plants and automobile manufacturers to continually conduct trial and error to produce materials that meet vehicle performance requirements.
Process flow
Integrated die-casting technology changes the traditional body production process (produce the structural parts first, then weld and assemble them), which can greatly reduce welding and gluing links and greatly simplify the overall process bodywork production. Integrated die casting parts mainly include processes such as melting, die casting, grinding, X-ray machine assembly and machining. The production process is shown in Figure 1. Compared to body structural parts such as shock towers and longitudinal beams, heat treatment. is omitted (orthopedic process), this section focuses on the die casting process.
Integrated die-cast parts include the rear wheelhouse interior panels on the left and right sides of the vehicle, rear longitudinal beams, floor connection plates and interior beam reinforcement plates. They are larger and more complex in shape than ordinary die castings. with different shapes, sections and materials, thick changes are more dramatic. It also puts forward higher requirements for the die casting process: the flow pattern, specific injection pressure and process speed are more strictly controlled, as well as the requirements for precision and threshold of the equipment and the ability of the mold to resist shock. the deformations are stricter.
The integrated die casting process includes: spraying, mold clamping, pouring, injection, pressure holding, mold opening, picking up, integrity inspection, cooling, trimming and conveyor belt.
The die casting process parameters mainly include pressure, speed, time, temperature and vacuum. The casting pressure is 80 MPa for airtight products, 60 MPa for general products, and all integrated die casting products are less than 40 MPa. The reason is that the pressure is too high and the clamping force is insufficient, resulting in serious material leakage. the air pressure injection speed of the die casting machine generally requires more than 10m/s, the actual maximum speed of the punch is 6-8m/s, the speed of the inner door. It is 40 to 55 m/s; the filling time is 50 to 80 ms; aluminum liquid temperature is 700-710℃, mold temperature is 220-280℃, integrated die casting has high requirements for mold heat balance; vacuum degree is 30~50 mbar (1 bar = 105 Pa), actually can be less than 30 mbar.
In addition, because the precrystallized structure greatly weakens the mechanical properties of integrated die casting parts, the casting process of aluminum alloy is very critical. Precrystallization is usually controlled by processes such as the temperature of the molten aluminum during melting. cup, barrel heating and die casting process.
Basic material
The size and quality of integrated die casting structural parts continue to improve, and the tonnage of die casting machines reaches new heights. Integrated die-casting technology adopts die-casting hosts with a capacity of more than 6,000 tons. -The die casting machines that have been installed and debugged so far include 6000t, 6100t, 6600t, 6800t, 7200t, 8800t and 9000t. In addition to 12,000 t, another 16,000 t die casting machine has entered production. scene, 20 000 ton die casting machine enters the development stage.
1. Die casting machine
The die casting machine is an industrial casting machine that hydraulically injects molten metal into a die mold to cool and form it. Once the mold is opened, a solid metal casting is primarily obtained. producing a variety of parts and components by installing different die casting molds. According to industry experience, die casting machines of different tonnages are generally selected according to the contour, size and quality of die casting parts. According to Bühler China, the tonnage of die-casting machines required for traditional body parts has remained in the range of 1,600-4,400t for a long time, of which the front shock absorber tower requires 1,600-2,500t, while the The front shock absorber and rear door frames, tailgate boxes, rear longitudinal beams and A-pillars require 4,000 t. Door requirements are 4,400 t. As the size and quality of integrated die-casting structural parts continue to increase, the requirements for the tonnage of the die-casting machine also increase, as shown in Figure 2, the mid-size SUV model. The rear floor and front cabin of the Y use a 6,000t die-casting machine; the half-piece rear floor of Weilai ET5 B-class coupe uses a 6,000t die-casting machine; and the rear floor (or front floor) of the largest electric Cybertruck pickup will use 8,000; up to 9,000 t Die casting machines; battery packs, A00 level lower body, etc. require die casting machines with a tonnage of 12,000 t and more.
There are difficulties in the research, development and production of ultra-large die casting machines. The difficulty of manufacturing ultra-large die casting machines is mainly reflected in the two aspects of research, development and production.
In terms of research and development, the currently widely used automotive aluminum die-casting structural parts have the characteristics of large size (500~1500mm), thin wall (about 2.5mm), ‘a complex structure, etc., which combine traditional aluminum castings. Cast structural parts with highly integrated one-piece die-cast structures. In contrast, the shape of the integrated die-casting structural parts is more complex, the wall thickness is uneven, and the size and mass are greatly increased. This affects the clamping force, mold gap size, injection force, maximum air injection speed and. safety of the very large die casting machine. It places higher demands on design capabilities for performance and reliability. Previously, die casting machine manufacturers only had experience in the research and development of die casting machines under 5,000t. Facing the growth of tonnage of ultra-large die casting machines, 6,000t→7,000t→8,000t→9,000t→. 12,000t → 16,000t → 20,000t, the R&D curve of die casting machine factory is very steep.
In terms of production, the time from research and development to delivery of ultra-large die casting machines is long, and die casting machine factories need to continue to invest large sums, which tests in a to some extent production capacities. die casting machine factories. Domestic die-casting machine factories lead in layout, and Lijin Group is far ahead in order volume.
Domestic die casting machine manufacturers are leaders in research and development progress, delivery speed and order volume. The representative companies are Lijin Co., Ltd. (13522079385), Yizumi (18210062835) and Haitian Metal (15910974236).
Among them, Lijin Group delivered its first large-scale die casting unit of 6,000 tons as early as November 2019 and successfully became a global supplier of Tesla. Later, he received orders for 30 sets of ultra-large die-casting machines from Tesla. After that, Lijin Group continued to receive ultra-large integrated die casting orders from various domestic die casting factories, and the tonnage of its delivered die casting machines continued to break new highs. Foreign die casting machine factories are progressing slowly and will only officially deliver a 6,100 ton die casting machine to customers in June 2022.
2. Die casting mold
Die casting molds are also one of the basic equipment in die casting production. Integrated die casting places higher demands on the design of large-scale die casting molds. The size of the integrated die casting mold is larger. The product size of traditional die casting mold is less than 1m. The size of the integrated die casting product reaches 1.6~2m, and the corresponding mold size should be. more than 3 m, which leads to increased processing difficulty. The quality of integrated die casting mold reaches 150t or more. The vacuum die casting environment and integrated die casting have high requirements for mold sealing performance. The required vacuum environment is less than 30 MPa. Due to the large number of mold parts, the requirements for sealing rings are higher; The development cycle is long and the development cost is higher. The development cycle of very large die casting molds is 150-180 days. The cost of traditional die casting molds does not exceed 4 million yuan, and the cost of very large molds. die casting molds generally cost more than 10 million yuan. The molds are highly personalized and orders are generally accepted as private customization. They need to be designed according to different car models, which requires the mold factory to constantly communicate with the car manufacturer and the die casting factory, for design, proofing and improvement. and optimization, and production. The cycle is long and the level of reuse of design solutions is low. , usually the second mold needs to be redeveloped; the material performance requirements are high, because the injection speed of the large die casting machine is faster, the mold needs to withstand greater pressure, and secondly, the quenching performance, toughness, and Thermal expansion coefficient requirements of the material are high, as well as surface treatment and other technologies are difficult.
Support Equipment
In addition to die casting machine and die casting mold, other equipment involved in die casting production is called supporting equipment. It mainly includes peripheral equipment, melting equipment, heat treatment and post-processing equipment, among which post-processing includes machining, surface treatment and assembly, etc. The peripheral equipment, together with the die casting machine and the die casting mold, form a die casting unit. The peripheral equipment includes machine side oven, spray system and spray robot, picking robot, vacuum system, integrity inspection and cooling. water tank, slag removal bag, trimmer and coding machine, conveyor belt. , mold temperature controllers, cooling stations, thermal imagers and dust hoods, and more than 20 sets of melting equipment including centralized melting furnaces, transfer sets, metering furnaces, holding furnaces and post-processing machines including machining, deburring, surface treatment and assembly equipment. Among the above equipment, the difference between integrated die casting technology and traditional die casting technology lies in the machine side oven, spray system, thermal camera, trimming equipment and equipment machining.
1. Machine side oven
There are two types of ovens on the machine side: the dosing oven and the holding oven + soup feeder. Generally, a dedicated centralized melting furnace is equipped alongside the two. The dosing oven is characterized by a large, fully enclosed dosing system. The fully enclosed laundromat adopts a closed design, so that the aluminum liquid is no longer in contact with the air during the soup feeding process, and the soup feeding time is greatly reduced. should be equipped with 4-8 ton dosing furnace, single/double pump can provide soup volume of 150/200 kg, dosing speed of 10 kg/s and dosing accuracy of ±1% . In addition, the metering furnace is divided into three types: integrated sealed air pressure metering holding furnace, split open air pressure metering holding furnace and split open air vacuum metering holding furnace. Relatively speaking, the holding furnace + soup feeding machine has disadvantages in work efficiency, energy consumption, combustion loss and soup feeding time, but the investment in equipment is weak. Currently, both types of machine-side furnaces are used, as shown in Figure 3.
2. Spray system
Most use micro-spray or electrostatic spray technology, using pulse spray technology, equipped with profiling nozzles and multi-spray devices, as shown in Figure 4.
Spraying is a large cycle time hog and traditional spraying methods seriously affect the efficiency of producing large parts. The design of a set of movable and fixed molds or double spraying on one side is adopted to minimize the installation and maintenance area and avoid further mechanical interference. In terms of technical solutions, micro-spraying or electrostatic spraying technology can be selected to reduce the cycle time and improve production efficiency to the greatest extent, but it also imposes higher requirements on the control of the thermal balance of the molds.
3. Thermal imager
As shown in Figure 5, the integrated die casting is basically equipped with a real-time online mold temperature monitoring system, including infrared thermal cameras, monitoring systems, acquisition software and temperature analysis, etc., which work with mold temperature machines, spot coolers and spray robots to adjust and control the mold temperature.
During the die casting production process, the mold temperature real-time online monitoring system is connected with the control system of the die casting machine, and can also communicate with other peripheral equipment such as spray robots, mold temperature controllers and spot coolers to complete closed-loop control. The monitoring system can accurately and quickly collect, record, analyze and compare the mold surface temperature with the set value during the two stages of mold opening and spraying, and complete the corresponding evaluation, thereby precisely controlling the mold temperature to achieve the stabilization objective. the mold temperature should ultimately achieve stable production processes and stable product quality.
4. Paring plan
Integrated die casting generally uses plasma cutting machine + edge cutting machine, plasma cutting is used in the small batch stage, and edge cutting machine is used in the mass production stage. Trimmer solutions involved in die casting production include trimmers, plasma, lasers, high-speed saws and manual labor, as shown in Figure 6.
The speed of hydraulic edge trimming machine is relatively faster, but a certain margin should be left to control the deformation, and the investment is large, so it is more suitable for mass production, the cutting performance is similar to those of the laser; , or even slightly better, and the total price of the equipment It is low, has high versatility and flexibility. All kinds of castings with complex shapes can be processed on the same equipment, but the consumables are more expensive; Light cutting is more common in small batch production in Europe. The advantage is that the cuts are clean, except for the corners, great versatility and flexibility. However, the cutting cost is high and is suitable for cutting thicknesses less than 10mm; -rapid sawing can be used on thin-walled workpieces. It is easy to cause product deformation due to stress; Manual edge trimming is more suitable for traditional small die-casting parts in small and medium-sized die-casting factories.
5. Machining solutions
There are currently largeHorizontalFive-axis machining centerAndFive-axis double gantry machining centerconsultation phone: 13501282025.
The processing characteristics of large-scale integrated die casting parts: large-size stroke is more than 2000mm; there are many processing points, but the processing volume of a single point is mainly drilling, tapping, etc. and there are many spatial angle holes. The specific selection should be based on factors such as product characteristics, order volume, investment funds, etc. In addition, in order to improve processing flexibility and reduce investment costs, using robotic clamping tools to process integrated die-casting parts has become another goal. There are already mature cases of robotic processing of interior door panels. overall rigidity of the robot, there is no such case yet. Applied to integrated die casting products.
Testing process
Compared with other die casting products, the testing of integrated die casting products is nothing special, which mainly includes six types: appearance quality, defect detection, outline size, mechanical properties, temperature testing. bench and road tests. Among them, appearance quality refers to cold sealing, flow marks, deformation and cracks; Defect detection mainly checks internal defects such as pores, shrinkage cavities, inclusions, etc. ; , elongation); outline dimensions involve inspection tools, three-dimensional coordinates, etc. ; Bench tests include static strength in different directions, durability performance under real working conditions, and road crash tests mainly include: Performance test (test acceleration, climbing, starting and maximum speed vehicle and other performance indicators), braking performance test (testing the vehicle braking distance, brake force distribution and braking stability and other indicators), handling performance test ( test the vehicle’s handling performance, such as driving in bends, bends and merges, etc.) and reliability testing (testing the vehicle’s driving performance in different road conditions and the reliability of the components).
Staff quality
Integrated die casting technology imposes high-level comprehensive requirements on R&D, technology and on-site personnel, involving four major aspects: product design, material development, processing molds and production management. site.
Product design requires reserves of knowledge in structural mechanics, vehicle structure, mechanical drawing, Catia, Abqus, etc. Materials development requires mastery of solidification principles, alloy formulas, basic knowledge of materials mechanics, etc. In terms of process molds, you have mastery of fluid mechanics, process parameters and casting systems, mold design, thermodynamics and surface treatment technology, etc. On-site management has many skills such as familiarity with equipment operation, electrical/hydraulics, automation programming, lean production, quality management and staff training. .
There are only more than 300,000 employees in the die casting industry. It is a niche industry, but it is also a typical multidisciplinary field that has comprehensive requirements for employee knowledge reserves and practical on-site operations. Integrated die casting technology will be improved by several orders of magnitude.
Conclusion
Integrated die casting technology is basically a die casting technology supporting a vacuum system, as well as the characteristics of oversized products. It is always an improvement and expansion of traditional technology. However, oversized sizes have moved the entire industrial chain from quantitative to. qualitative changes.
Before that, the maximum tonnage of die casting machines had been at the level of 4,000 tons for more than 20 years, while highly integrated die casting products continued to touch the tonnage ceiling and have been under development since 20 years old. 000 ton die casting machine, with the subsequent increase of equipment processing difficulty and control precision; in the die casting process of large products, the filling distance exceeds 2m, and the casting and drainage system is particularly important; the quality is above 100kg and the filling time is tens of milliseconds, the process window has been greatly reduced, and high requirements have been put forward for equipment performance, mold level and quality staff; to meet the comprehensive requirements of medium strength, high elongation, no need for heat treatment, good casting performance and low cost.
Therefore, the promotion and application of integrated die casting technology requires the collaborative cooperation of multiple industries and the whole chain, including automobiles, equipment, die casting, molds, materials and scientific research, to contribute to a soft landing of integrated die casting. .
Authors: Yu Deshui (1), He Tingyu (2), Liu Qing (1) Li Dongyang (1), Gao Jie (3), Han Xing (4)
(1) Suzhou Yadelin Co., Ltd.
(2) Dongguan Pingze Hardware Products Co., Ltd.
(3) BYD Co., Ltd.
(4) Shandong Hongqiao Lightweight Technology Co., Ltd.
Daguang focuses on providing solutions such as precision CNC machining services (3-axis, 4-axis, 5-axis machining), CNC milling, 3D printing and rapid prototyping services.
