Preface:

As early as September 2020, Tesla CEO Musk announced for the first time that integrated die-casting technology will be used in the production of the Model Y rear body panel. Integrated die-casting technology is a new change in die-casting technology. By redesigning multiple independent parts that need to be assembled in the original design, and using a super-large die-casting machine to die-cast in one go, complete parts can be directly obtained to realize the original functions. But in terms of technological maturity, it still has a long way to go.

Introduction

The Future of Die-casting Production

Traditional automobile production processes are stamping, welding, painting, and assembly in 4 steps, generally, the steel plate is stamped into small parts, following the design drawings welded into large parts, assembled into the body, and finally painted.

Tesla has opened up a whole new field of automobile production, i.e., utilizing the characteristics of the traditional die-casting process and launching integrated casting with advanced concepts and materials, which has changed the conventional automobile production method by combining the two steps of stamping and welding into one step and casting the large parts directly, which is a new process that has greatly provided the efficiency of production and lowered the cost in the long run. Moreover, it increases the recycling rate of all-aluminum body materials to more than 95%, which becomes simpler and more efficient.^[1]

The materials used in the integrated die casting of its automotive parts are new and can be free heat treatment. Its characteristic is that it does not need to go through high-temperature solution treatment and artificial aging, only through natural aging can achieve better strength and plasticity. No heat treatment die casting aluminum alloy mainly through microalloying to regulate the microstructure and size morphology of the alloy, combined with solid solution strengthening, fine grain strengthening, and the second phase dispersion strengthening to strengthen the material. The use of free heat treatment aluminum alloy can improve the quality of castings, enhance the mechanical properties of the alloy, and save energy, reduce carbon emissions so that the body structure parts in terms of cost and performance have greater advantages.

At present, automotive parts integrated die-casting its four major thresholds are mold, material, machine, and process.

Mold

1. Mold manufacturing

Mold manufacturing is difficult, and one of the difficulties in manufacturing die-casting molds is design. Die-casting molds are complex and have high processing costs. The difficulty in mold design lies in the need to consider many issues such as thermal balance, demoulding, and slurry feeding direction.^[2]

(1) Thermal balance in the mold production cost accounted for a relatively small but will affect the solidification, quality, circle, and so on, affecting the overall service life of the mold is a key factor. The design of heat balance is the design of the cooling pipe, including the location, cooling water flow rate, and so on;
(2) Melt liquid direction affects the quality of the die casting and raw materials, the design is not reasonable, it will cause the problem of under injection of blanks, thus affecting the product yield rate;
(3) Air in the cavity will lead to product molding yield is not high, generally can be used to facilitate the discharge of gas, high-end precision molds also use vacuum casting technology, to solve the problem of air is not excluded;
(4) The demolding design is reflected in the product after molding to take out the step, the design is not reasonable and will make the product stuck in the mold can not be removed.

2. Mold raw material selection

Molds need to be injected into the molten metal, molding after cooling, the process of the cavity and high-temperature metal direct contact, repeatedly subjected to extreme cold and heat, and harsh working conditions, so improving the life of the mold is the key to cost control. In addition to reasonable design to enhance the service life, mold raw material selection and innovation are crucial. The material needs high thermal stability, high-temperature strength, wear resistance, toughness, thermal conductivity, and other properties. Specific ways to enhance the service life are

(1) remove the metal gas and other non-metallic elements, thereby improving the purity, such as the steel sulfur content of the element is controlled at 0.003% or less, the mold life enhancement of 1.3 times.
(2) Reduce the content of alloying elements such as Mn\Si\Cr to reduce the segregation of steel.
(3) mold has a short-plate effect, any one direction of the performance is low, which will affect the overall life, so you can improve isotropy and uniformity.

With the large-scale die-casting molds and precision increase, these difficulties will be raised. The higher the precision of the mold, the more complex the heat balance design, the higher the difficulty of machining, the more considerations for mold eject design, and the higher the technical difficulty. The larger the mold corresponds to the thermal balance of the range increases, and the material requirements such as isotropic, uniformity, and purity are higher.

3. Mold frame

Mold frame is one of the main costs of the mold, and requires regular maintenance. In the cost structure of super-large molds, the cost of the die holder accounts for about 40%, and the structure and manufacturing accuracy of the die holder directly affect the structure of the mold and the accuracy of the forgings. To ensure the accuracy of the die holder, the die holder should be inspected and maintained regularly and overhauled regularly (generally should be inspected and maintained annually).

We believe that the die frame is developing towards non-standardization, complexity, and precision. Mold is too large, precise, and complex direction, The mold frame also supports the upgrade:

(1) non-standardized development. Die frame manufacturing enterprises following the plan to produce standard die frames based on the beginning to provide a variety of non-standard die frame supplies, that is, according to the requirements of the standard die frame for deep processing and finishing. 2010 non-standard die frame accounted for all die frame sales of 60-70%, and mostly for large, precision molds. With the integration of the die-casting technology revolution, we expect non-standard mold frames will continue to improve;
(2) complexity, precision development. Along with the mold manufacturing specialization division of labor in-depth, mold manufacturing enterprises will be more finishing links transferred to the mold manufacturing enterprises, so the standard mold products on the finishing project increasing, such as processing runner holes, pulling rod holes, core holes, push rod holes, cooling water holes, oblique guide pillar holes, oblique push rod holes and so on, installing the positioning ring, locator, sprue set, push the plate guide pillar, support blocks and so on. These complex finishing projects on the mold manufacturing process and their accuracy to put forward higher requirements;
(3) The degree of standardization of non-standardized mold frames is constantly improving. Standardization is conducive to the company’s cost reduction and efficiency, with the development of the mold frame industry, specialized manufacturing technology continues to deepen, and non-standardized mold frame structure continues to pattern, standardization, and specialized production.

Material

Traditional die-casting machines have high-temperature solution treatment and artificial aging processes. For the integrated oversized products, the material needs to be free of post-processing heat treatment in addition to the traditional imperfections in the die-casting process, which is also a very high challenge. Therefore, to meet these challenges, there are some solutions for the material as follows.

1. The role of alloying elements on Al-Mg system heat treatment-free die-casting aluminum alloys

Mg as die-casting Al-Mg alloy in addition to Al in the highest content of elements, in Al solid solubility up to 17.4%, has a good solid solution strengthening effect, in improving the strength of the alloy at the same time does not affect the toughness of the alloy, but also improve the fluidity of the alloy and resistance to thermal cracking tendency, and to reduce the phenomenon of sticking mold. However excessive Mg will not only cause oxidation, but also reduce the casting performance of the alloy, and with Al to form Al₃Mg₂ phase, the mechanical properties of the alloy and corrosion resistance performance have adverse effects ^[3]. Free heat treatment die casting Al-Mg alloy casting organization is mainly dendritic crystal, large size granular α₁-Al grains, fine spherical α₂-Al grains, and eutectic organization, see Figure 1 ^[4].

The mechanical properties of the alloy can be significantly improved by regulating the elemental composition and adding trace elements. JIS et al. ^[5] based on the influence of each alloying element on the mechanical properties of the material, the optimal composition was obtained as 5.0% ~ 5.5% Mg, 1.5% ~ 2.0% Si, 0.5% ~ 0.7% Mn, 0.15 ~ 0.2% Ti and not more than 0.25% Fe, with the balance of Al. The yield strength of the alloy in the cast state can reach 150 MPa, tensile strength of 300 MPa, and elongation greater than 15%. Wu Han ^[6]through orthogonal tests to determine the optimal composition of die-casting aluminum-magnesium alloy for 5.4% Mg, 2.0% Si, 0.77% Mn, ≤ 0.22% Fe, the balance of Al, so that the cast alloy tensile strength of 353.58 MPa, yield strength of 204.53 MPa, the elongation of 12.46%. Si can be with Mg to form the Mg₂Si eutectic phase, which is the Al-Mg system free of heat. Si can form the Mg₂Si eutectic phase with Mg, which is the main reinforcing phase of the Al-Mg system heat-treatment-free die-casting aluminum alloy, and the influence of Mg and Si on the alloy properties is shown in Fig. 2 ^[5].

To improve the strength, ductility, and corrosion resistance of the alloy in the as-cast state, all Mg and Si should be formed into ideal Mg₂Si particles, so the mass ratio of Mg and Si should be 1.73∶1 (corresponding to the 2∶1 chemical measurement ratio of Mg₂ Si) ^[7]. To enhance the solid solution strengthening of the alloys in the as-cast state, the Mg and Si content of the alloys should be in the vicinity of the maximum solubility of Mg2Si in Al of 1.85%. HU Z Q et al. ^[8]>found that when the Mg content ranged from 5.7% to 7.2%, the yield strength and hardness were increased by 11% and 9%, respectively, but elongation was decreased significantly, and the fatigue resistance of the alloys increased with the increase of the Mg content. YUAN L Y et al ^[4] to chemical composition, eutectic phase fraction, average grain size, Mg solid solution, and tensile properties of the relationship between the establishment of contour plots, as a guide to the development of high strength and toughness die casting Al-Mg-Si alloys, determined that when the Mg content of 6.5% ~ 7.5%, Si content of 2.4% ~ 3.0%, the elongation can be greater than 10%, and at the same time have a high yield strength and tensile strength.

Mn is an important constituent element in Al-Mg system alloys. Adding 1% Mg to aluminum alloys can increase the tensile strength of the alloy by 35 MPa, and the strengthening effect of Mn is twice as much as that of the same amount of Mg ^[9]. At present, Mn is mainly added instead of Fe to improve the mold release of the alloy and make the Al₃Mg₂ phase precipitate uniformly to improve the corrosion resistance and welding performance of the alloy. The Al₆Mn phase formed in the alloy can reduce the hot cracking tendency of the alloy. In addition, Mn can also increase the Fe content in α-AlFeSi intermetallic compounds, and inhibit the formation of needle-like β-AlFeSi, AlFe₃ phase, thus improving the performance of the alloy, especially plastic toughness. The best Mn content in the alloy is 0.3% to 0.8%, when the Mn content of 0.8%, the maximum elongation, the content continues to increase, the plasticity is significantly reduced, and Mn, Si combined with the formation of the AlMnSi phase so that the strength of the alloy decreased.

Cu can be solidly dissolved in α-Al matrix or granular compounds that exist in Al-Mg alloys, can significantly improve the strength and hardness of the alloy, and in the later baking process promotes the formation of β″ phase, improves the baking hardening properties, but the cracked Al₂CuMg phase and Cu-rich reticulation compounds will make the elongation slightly decreased ^[10-11]. The presence of Cu also increases the tendency of intergranular corrosion of the alloy and the tendency to thermal cracking, so generally control the Cu content of 0.3% to 0.8%, and minimize the content of Cu.

Ti is the main element added to refine the alloy casting organization, reduce cracking tendency, and improve mechanical properties ^[12]. The Al₃Ti particles and TiC formed after the addition of Ti to the alloy can promote the nucleation of the α-Al matrix to refine the grain size, and at the same time, Al₃Ti can make the precipitation phase diffusely distributed in the alloy, effectively pinning grain boundaries and dislocations, hindering the recrystallization of the occurrence of the strength, and improve the elongation. When Ti and B are added together, B can not only form the Al₂B sub-stable phase as the spontaneous nucleation point of the matrix, but also reduce the solubility of Al₃Ti or form the TiB₂ phase as the heterogeneous nucleation point, which promotes the nucleation of the Al₃Ti phase, and significantly enhances the refining effect. However, it should be noted that Ti and Cr, Zn, Mn, and other impurity elements produce poisoning reactions ^[13].

2. The role of alloy elements on Al-Si system heat treatment-free die-casting aluminum alloy

Si in the heat treatment-free die-casting Al-Si system alloy content, in general, is 4.0% ~ 11.5%. With the increase of Si content, α-Al dendritic grains continue to be refined, the Mg₂Si strengthening phase and the number of eutectic Si phases continue to increase, in which the size and morphology of the eutectic Si phase significantly affect the alloy properties, should try to make the eutectic Si phase is spherical or fibrous uniformly distributed, to improve the alloy’s strength and toughness ^[14]. Free heat treatment die casting Al-Si system alloys cast state organization is mainly uniform fine α-Al dendrites, eutectic Si, and other granular second phase ^[15]. Strengthening of this alloy requires the control of alloy composition and the addition of refining agents and densifying agents to refine the primary α-Al phase, reduce the spacing of the secondary dendrite arms, and improve the morphology of eutectic Si. Figure 3 shows the microstructure solidification diagram of Al-Si-Mg alloy after the addition of the metamorphic element Sr and composite addition of Sr and refiner Al-Ti-B ^[16]. ZHANG P et al. ^[15] developed Al-10Si-1.5Cu-0.8Mn-0.15Fe alloy by adjusting the content of Cu, Mn, and Fe, which showed better mechanical properties, the yield strength was 190 MPa and the tensile strength was 308 MPa.

BOSCH D et al. ^[17] pointed out that the addition of Mn to Al-Si die-casting aluminum alloys with a w(Mn)/w(Fe) ratio of 1, combined with a high cooling rate, results in alloys with excellent plasticity (elongation >10%). Cu added to Al-Si alloys significantly increases strength, but corrosion resistance and resistance to thermal cracking tend to decrease significantly, and the solidification temperature range of the alloy will increase significantly. At low Cu content, the properties of the alloy mainly depend on the presence of the Al₂Cu phase, when the Al₂Cu phase is uniformly distributed in the matrix in the form of spherical particles, the strength of the material can be significantly increased and the plasticity is maintained at a high level; if it is distributed along the grain boundaries in the form of a continuous mesh, the strength is almost unchanged but the ductility decreases significantly ^[18]. With the increase of Cu content, the eutectic segregation of Cu will deteriorate the plasticity of the material, and the formation of a large number of Al2Cu phases significantly reduces the corrosion resistance. Therefore, the amount of Cu added to heat treatment-free die-casting aluminum alloys should be strictly controlled, or other elements to replaced, such as Zr, V, Mo, and so on.

Mn in Al-Si system alloys can inhibit recrystallization, increase the recrystallization temperature, significantly refine the recrystallized grains, improve the high-temperature performance of the alloy, improve fatigue resistance, and reduce shrinkage ^[15]. In addition, Mn can also eliminate the adverse effects of the Fe element, in the Al-Si system alloys, Mn can form spherical or kanji Al₁₂Mn₃Si₂ and AlFeMnSi phases, to avoid the formation of the long needle-like β-AlFeSi phase, but also with the formation of a uniform precipitation of Mg, to improve the corrosion resistance of alloys and welding performance. However the content of too high Mn will reduce the elongation of the alloy, so it is generally controlled at 0.8% or less.

Mg in the Al-Si system alloys can improve the material tensile strength, hardness, and corrosion resistance, effectively reducing the Sr, and Cu elements added to the casting microporous tendency. In the high Si aluminum alloy added 0.3% ~ 0.4% of Mg, the formation of the binary reinforced phase Mg₂Si can make the α-Al and eutectic Si morphology refinement and distribution tends to be orderly, significantly increase the tensile strength and yield strength of the alloy material, improve the alloy’s machinability, but the plasticity of the material will be a significant decline ^[18-19]. When the Mg content of more than 0.5%, the yield strength of the alloy is no longer increased; excessive Mg, on the contrary, will reduce the casting process performance of the alloy, increase the solidification shrinkage of the casting during cooling, so that the tendency of hot cracks, shrinkage holes, shrinkage and other defects increased dramatically.

3. Rare earth element mechanism

Heat treatment-free die-casting aluminum alloy is mainly strengthened by microalloying control material microstructure, and its main way of strengthening for fine crystal strengthening, so in the melting process need to add refining agent and metamorphic agent to improve the microstructure size and morphology, commonly used metamorphic elements such as Na, Ca, Sr, La, Ce, etc., of which the metamorphic effect of rare earth elements has a long-lasting and remelting, can make the alloy casting organization obviously Refinement. The refining mechanism is that the solid solubility of rare earth elements in the α-Al matrix is limited, and they will be enriched on the surface of secondary dendrites, increasing the supercooling degree of the composition, improving the nucleation rate, and thus realizing grain refinement.

In addition, rare earth elements will change the growth mechanism of eutectic Si phase grains, so that the eutectic Si phase is transformed from plate-like, needle-like to laminated, fibrous, or spherical ^[20]. Rare earth elements additive amount is too high, easy to form a coarse rare earth element compound phase, resulting in a reduction in the content of rare earth elements used for modification, the modification effect is reduced.

For the study of rare earth elements to improve the properties of die-casting aluminum alloys, MAO F et al ^[21] found that the addition of rare earth elements Eu can affect the growth mode and morphology of the eutectic Si phase. When adding 0.3% of Eu, the eutectic Si phase from needle-like, plate-like transformation to fiber-like, see Figure 4. MUHAMMAD A et al. ^[22] use Sc to die casting Al-Mg-Si alloy modification and found that when the Sc content of 0.4%, the grain size was reduced by 80%, tensile strength, and hardness compared to the unadded Sc was increased by 28% and 19%, respectively, the elongation increased by 165%.

PRACHO et al. ^[23] obtained the best strength and plasticity in cast Al-5Mg-2Si alloys by adding 0.2% of Sc, with a yield strength of 206 MPa, a tensile strength of 353 MPa, and an elongation of 10%. ZHENG Q J et al. ^[24] found that the addition of 0.06% La to Al-Si alloys could improve the morphology of the eutectic Si phase and increase the elongation from 6.7% to 12.9% while refining the α-Al grains. JIN H N et al. ^[25]found that when 0.1% Ce is added to Al-Mg-Si alloy, the smallest secondary dendrite arm spacing of grains (25.95 μm).

Machine

New energy vehicles mostly use cold room die-casting machines, is the core equipment of integrated die-casting, according to the size of clamping force can be divided into small (<4,000 kN), medium-sized (4,000 ~ 10,000 kN) and large (≥10,000 kN) die-casting machine. Due to the die casting machine clamping force size needs to cover the projected area of the pressed parts, so the large body structural parts such as the rear floor, front cabin frame, etc. need to clamp force of at least 60 000 kN die casting machine, and structural parts of the projected area, the larger the need for die casting machine clamping force, such as the die casting of the battery tray, the middle floor need to clamping force of 80 000 ~ 120 000 kN, die casting of the entire chassis, the body-in-white need clamping force of 120 000 ~ 200 000 kN, the die casting machine clamping force of 120 000 ~ 200 000 kN, the die casting of the whole chassis, the body in white. Die casting the entire chassis, body-in-white required a clamping force of 120 000 to 200 000 kN.

At present, the world has more than 60,000 kN super-large die-casting equipment production capacity of manufacturers Switzerland Buhler, Haitian Die-casting, YIZUMI, L.K. technology and its sub-brand IDRA, and so on. Integration die-casting with large die-casting equipment development situation is shown in Table 3. Future new energy automobiles to use integration die-casting technology must purchase a large number of ultra-large die-casting equipment, so mass production of ultra-large integration die-casting equipment is still one of the key barriers to the rapid development of the current integration die-casting technology.

At present to cope with one-time large-scale die-casting production requirements, the trend of the development of ultra-large die-casting machines is:

1. Die casting machine clamping force is getting bigger.

1.1. Improvement of production efficiency

Die casting machine in the process, needs to press the molten state of the metal into the mold so that it is cooled and solidified, to form the required products. And the size of the clamping force will directly affect the speed and quality of die-casting molding. The larger the clamping force, the higher the compaction of the casting, the casting quality is also better. In addition, the clamping force can also fundamentally increase the production efficiency of die-casting machines, such as in the high-temperature melting process, shorten the casting time, and save production time.

1.2 optimize product quality, improve accuracy

Die casting processing by injecting the molten metal into the mold, through cooling and solidification, forming the desired product. Large clamping force can promote the uniform compaction of metal in the mold, thus making the casting quality more stable. Insufficient clamping force, on the other hand, will result in the casting not being able to fill the mold, creating problems such as defects and burrs, and affecting the service life of the product. Therefore, a large clamping force can ensure the stability of casting quality and improve the service life of the product.

1.3 reduce cost

Die casting is generally used in industrial manufacturing, clamping force can use less material to produce more solid and durable products, and thus reduce production costs. In addition, a large clamping force can shorten the production cycle, and improve production efficiency and quality, while reducing production costs.

However, in the long run, the clamping force should be determined by the demand of the product, and the pursuit of a large clamping force will result in the waste of resources.

2. High efficiency

2.1 High-efficiency press injection

By optimizing the pressing and ejection system, the speed and stability of pressing and ejection can be improved, so as to increase production efficiency.

2. 2 Efficient Cooling

Adopting more efficient cooling technology to speed up the cooling speed of the mold and shorten the production period

3. Automation and Intelligence

3.1 Automation control

Through the introduction of industrial IoT and artificial intelligence technology, automated control and optimization of die-casting machines are realized.

3.2 Intelligent detection

Utilize non-destructive testing technology and artificial intelligence algorithms to realize intelligent detection and defect prediction of die-casting parts.

4. Equipment long life

Due to the equipment for a long time in the high temperature and high-pressure conditions of work, which puts forward high requirements for the life of the machine itself, research and development of new alloy materials, high-strength steels, and composite materials, design considered reasonable use of the life of the machine has become a necessary road.

Summarized: high-performance die-casting machine using advanced processing technology and precision control system, so that it has high accuracy, high speed, high stability, and other characteristics, to meet the continuous upgrading of the manufacturing needs, while the use of advanced hydraulic system, electrical control system, and mold design technology, can improve productivity, reduce energy consumption and reduce the number of times the mold maintenance. And then through the optimization of design and the use of high-performance materials, realize the lightweight and high strength of the die-casting machine, the use of new alloy materials, high-strength steel and composite materials, etc., to improve the rigidity and durability of the die-casting machine.

Process

Integrated die-casting body technology not only covers metal material science, high-pressure physics, rheology, and other disciplines field, also embodies the mechanical engineering and modern manufacturing technology cross-fusion. In the process, the focus is how to maintain the mechanical properties of metal materials at the same time, safeguard their stability and mobility in high temperature and high-pressure environments, to ensure the quality of the final product, which on the alloy melting and pre-treatment, pouring and solidification method, spraying and demolding process, high-vacuum die-casting equipment and so on puts forward higher technical requirements, and at the same time, in the production control requirements for the injection pressure, filling speed, circle time, holding time and pressurized solidification parameters also put forward high requirements.

1. Challenges of integrated body design

1.1 Structure complexity on the impact of the die-casting process

Structural complexity requires that the mold design must achieve higher precision to adapt to the complex body structure. This means that when the mold is manufactured, it is necessary to use more delicate CNC machining technology, as well as higher-grade materials to ensure the accuracy and durability of the mold. Complex structure molds also require a more complex cooling channel design to ensure uniform temperature distribution of the castings during the cooling process, avoiding internal stress and deformation due to excessive temperature differences.

The complex structure of large auto body design in the die-casting process of metal fluidity put forward higher requirements. Due to the complex structure, the molten metal needs to flow through a more tortuous path in the mold, which requires precise control of pressure and speed in the die-casting process, to ensure that the metal can fill every corner of the mold, at the same time to avoid in the high-speed flow of air bubbles and other defects, the requirement of die casting machine with higher pressure control accuracy and faster response speed.

Due to the complex structure of the body parts in the cooling process is easy to produce uneven shrinkage, so the die-casting process of cooling control is particularly critical, with the help of accurate mold temperature control and a cooling rate adjustment system, ensure that the casting in the cooling process of the size and internal quality.

1.2 Balance between energy saving, emission reduction and cost control

Material selection plays a key role in energy saving and cost control. Choosing lightweight materials such as high-strength aluminum alloys or magnesium alloys may increase the material cost at the initial stage, but due to its lower melting point, it can reduce energy consumption in the high-pressure die-casting process, and at the same time, reduce the weight of the body and improve the fuel efficiency of the vehicle. In the long run, the application of such materials can help reduce overall operating costs and environmental impact.

Optimization of the high-pressure die-casting process is another important strategy for reducing energy consumption and costs. Improving the energy efficiency of die-casting machines and optimizing the melting and injection processes can significantly reduce energy consumption. The use of advanced temperature control systems and energy recovery technology can effectively reduce heat loss while improving production efficiency and casting quality. In addition, precise control of die-casting parameters, such as pressure and injection speed, can not only improve the material utilization rate, but also reduce the scrap rate, and thus reduce the consumption of materials and energy.

2. Integration of high-pressure die-casting process flow

2.1 Alloy melting and transportation

The purpose of the alloy melting process is to heat the selected metal raw materials to a liquid state to ensure that they have suitable fluidity for subsequent injection and molding. This process involves complex thermodynamic and material science principles that require precise control of the furnace temperature, the chemical composition of the liquid metal, and its physical properties. Particularly where multiple alloying elements are involved, such as aluminum or magnesium alloys, the proportion and purity of each element can significantly affect the mechanical properties and durability of the final product. During the melting process, the furnace design and the choice of operating parameters have a direct impact on energy efficiency and metal quality.

Furnaces need to have efficient thermal energy conversion capability and good heat retention performance to minimize energy consumption and maintain a uniform temperature of the metal liquid. At the same time, atmosphere control during the melting process is critical, and oxidation or other undesirable chemical reactions of the metal must be avoided. In addition, inclusions or air bubbles may be present in the metal solution and need to be removed by appropriate treatment methods to ensure the internal quality of the castings. After the metal is melted, its transfer to the die-casting machine is equally critical. This process needs to maintain the appropriate temperature and fluidity of the liquid metal to ensure that it can fill the mold when injection molding.

2.2 Casting preparation

Casting preparation is a key prerequisite to ensure efficient and high-quality die-casting, involving mold design, material handling, machine adjustment, and other aspects. Mold design, as the core of casting preparation, not only requires precise geometric construction to ensure the casting dimensional accuracy but also needs to consider factors such as heat treatment, surface coating, and cooling channel layout to improve the durability and productivity of the mold, as shown in Figure 4. The key to mold design is to optimize the cooling and solidification process of the casting, which requires consideration of the thermal conductivity of the mold material, the layout of the cooling channels, and the geometry of the casting.^[26-27]

Effective cooling channel design can accelerate the solidification process of the casting, reduce residual stress and deformation, and improve the dimensional accuracy and mechanical properties of the casting. At the same time, the coating treatment on the mold surface is also the key to improving the life of the mold and the surface quality of the casting. If surface treatment technologies such as carbonitriding and nickel plating are used, the wear resistance and corrosion resistance of the mold can be effectively improved. In terms of material processing, the chemical composition and temperature of the molten metal directly affect its flow and solidification characteristics, thereby determining the internal and surface quality of the casting ^[28]. Therefore, the molten metal needs to be strictly analyzed for chemical composition and temperature control to ensure that it meets the requirements of high-pressure die-casting. For non-ferrous metals such as aluminum alloys, the content of alloying elements such as silicon, magnesium, and copper needs to be precisely controlled to regulate their fluidity and solidification characteristics.

In addition, machine adjustment is the key to ensuring that the molten metal can efficiently and accurately fill the mold in the die-casting process, including the precise setting of the pressure and speed of the injection system of the die-casting machine, as well as the strict control of the mold temperature. The pressure and speed of the injection system need to be optimized according to the size and complexity of the casting, to ensure that the molten metal can fill the mold quickly and uniformly, and the control of the mold temperature directly affects the cooling rate of the casting and solidification process.

2.3 Pressure casting

Pressure casting is a high-precision, high-efficiency metal forming process, the key lies in the rapid injection of molten metal material under high-pressure into a precision-designed mold, especially the application of a hot chamber die-casting machine, which improves the quality and efficiency of pressure casting and allows for the formation of castings with complex shapes and fine details.

The successful implementation of this process is critical to realizing the integrated design of automobile bodies, which involves the integrated application of several fields such as materials science, thermodynamics, fluid mechanics, and mechanical engineering. In the pressure casting process, precise temperature control of the molten metal is first required to ensure that the metal liquid maintains proper fluidity before it is injected into the mold. Improper temperature control may result in cold segregation or underfilling of the casting. In addition, precise control of the injection pressure and velocity is required to ensure that the metallic fluid fills every space in the mold while preventing bubbles and vortices from being generated by excessive velocity ^[29]. During this process, the flow characteristics of the fluid, the pressure distribution, and its effect on the mold are the technical details that need to be focused on.

The design and build quality of the mold are also critical for pressure casting. Molds must withstand continuous high-temperature and pressure environments and have high precision and good thermal conductivity to ensure the dimensional accuracy and shape stability of the castings. The choice of mold material, the heat treatment process, and the layout of the cooling channels all have a direct impact on the quality of the casting. Uneven cooling may lead to internal stresses or even cracks in the castings.

Quality control during the casting process is another key role. This includes fine inspection of the microstructure, mechanical properties, and dimensional accuracy of the castings. By using non-destructive testing techniques such as X-rays or ultrasound, defects within the casting, such as porosity, inclusions, or underfilling, can be detected on time.

In addition, a real-time monitoring system plays a vital role in the pressure casting process, which can adjust real-time parameters such as temperature, pressure, and filling speed in response to the various changes that occur during the casting process.

2.4 Cleaning inspection

The cleanup inspection step is an indispensable part of the high-pressure die-casting process, directly affecting the final quality and performance of the castings. The cleanup process involves removing the casting on the gate, fly edge, burrs, and other excess parts, as well as cleaning the surface, to ensure that the casting achieves the required dimensional accuracy and surface roughness. The inspection process involves a comprehensive evaluation of the casting’s dimensions, shape, and physical and chemical properties to ensure that each casting meets stringent quality standards, as shown in Table 1 for the cleaning and inspection process steps. The cleaning process begins with the mechanical cutting or grinding of the casting to remove gates and flying edges. This step requires precise control of cutting forces and grinding speeds to prevent unnecessary internal stresses or distortion of the casting ^[30]. Oxidized layers and other impurities are removed from the surface of the casting with the help of sandblasting or chemical cleaning methods to improve its surface quality, and parameter control of the mechanical and chemical cleaning methods is essential to ensure the overall quality of the casting. The inspection session carried out after the castings have been cleaned is aimed at ensuring that the geometric dimensions, surface roughness, and material properties of the castings meet the design requirements.

Dimensional inspections are usually carried out using high-precision gauges and CMMs to ensure the dimensional accuracy of the castings. Surface roughness inspections are conducted by surface roughness gauges to assess the microscopic unevenness of the casting surface.

Material property inspection includes hardness test, tensile test, and impact test, which are the key indexes to evaluate the mechanical properties of castings. The hardness test can be performed using a Brinell or Rockwell hardness tester, while the tensile test requires the use of a universal material testing machine to measure the tensile strength and elongation of the castings ^[31].

Conclude

（1）The booming development of the new energy automobile industry for integrated die-casting aluminum alloy material research and development and ultra-large integrated die-casting machine manufacturing provides a development drive force.

（2）Compared with the traditional die-casting process, integrated die-casting molding manufacturing of materials, molds, processes, and equipment have put forward higher technical requirements. The process elements, including alloy melting and pretreatment, pouring solidification mode, spraying and de-molding process, high vacuum die-casting equipment, and so on put forward higher technical requirements; In the production elements, the injection pressure, filling speed, filling time, holding time and pressurized solidification parameter control put forward more demanding production control requirements; In the mold manufacturing, in addition to the mold strength and plastic toughness put forward higher technical indicators. Higher technical indicators, but also on the mold surface quality, resistance to thermal cracking, resistance to high-temperature oxidation and service life, and other aspects of the proposed higher requirements; In the ultra-large die-casting machine, to meet the future integration of die-casting in the new energy automobile industry rapid popularization, the realization of the ultra-large die-casting equipment, low-cost, high-precision, long-life design and development and mass production manufacturing will be the future of the new energy automobile industry will be concerned about the hotspot.

（3）Currently used for integrated die-casting heat treatment-free manufacturing of lightweight alloy materials are still Al-Si system and Al-Mg system mainly through microalloying design combined with solid solution strengthening and fine crystal strengthening as its toughness mechanism. Limited by the strength of the material, can only be used as a medium load-bearing part of integrated die-casting manufacturing; future take into account the static load strength, coating hanging performance, process performance, fatigue life, corrosion resistance and recyclability of die-casting aluminum alloy materials research and development will become the focus of the field of aluminum alloy materials research.

---