Integrated die-cast mobile terminal middle frame structure and preparation method thereof

Abstract

The invention discloses an integrally die-cast mobile terminal middle frame structure and a preparation method thereof. The preparation method comprises the following steps: forming a first middle frame structure through a die-casting process; the first middle frame structure comprises a middle plate and a frame which are integrally formed, and a machining allowance is reserved on the outer side of the frame; cNC machining before injection molding is conducted on the first middle frame structure, and a second middle frame structure is obtained; forming a plastic structure on the second middle frame structure through injection molding; cNC machining is conducted on the second middle frame structure and the plastic structure, and a third middle frame structure is obtained; and spraying the surface of the frame to form a paint spraying coating. According to the mobile terminal middle frame and the manufacturing method thereof, the mobile terminal middle frame is manufactured in a die-casting integrated forming mode, the process of welding the middle plate and the frame can be omitted, and the overall structural integrity and stability of the mobile terminal middle frame can be ensured; the spraying process is adopted to replace a traditional anode process, the problem that the traditional anode process is difficult to cover bubble flaws is effectively solved, and the appearance quality of the product is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of mobile terminal manufacturing, and in particular relates to an integral die-cast mobile terminal frame structure and its preparation method. Background Technology

[0002] The mid-frame of a mobile terminal is a crucial component. For example, the mid-frame of a mobile phone forms the foundation of the entire device, providing a robust and stable mounting platform for all its delicate internal components. Furthermore, the mid-frame acts as a large "heat sink," quickly and evenly dissipating heat from the phone's interior across the entire surface and then releasing it into the air. In addition, the mid-frame provides electromagnetic shielding and signal leakage protection. Moreover, the mid-frame is a key element of a phone's aesthetics; its material and manufacturing process directly determine the phone's feel and premium appearance. Therefore, the phone's frame directly impacts its durability, performance, signal strength, and overall quality.

[0003] The conventional manufacturing method for mobile terminal frames generally involves first fabricating the frame and middle plate separately, then welding them together as a single unit. Next, the frame and middle plate are CNC machined, followed by injection molding to form a plastic structure, and then another CNC machining process. Finally, surface treatments such as anodizing are applied. The frame and middle plate are typically made of stainless steel through stamping. However, when using stainless steel to manufacture mobile terminal frames, the CNC machining process is complex due to the properties of stainless steel, requiring multiple steps and increasing production costs and difficulty. Furthermore, stainless steel has a high density, resulting in a heavier mobile phone frame, which is detrimental to lightweight phone design and contradicts the current market demand for thin and light phones. While aluminum alloy can be used to make mobile terminal frames to reduce weight, the manufacturing process remains complex. Using traditional aluminum alloy CNC machining to process a single mobile phone frame takes approximately 85 minutes, resulting in low efficiency, long production cycles, and difficulty meeting the needs of large-scale rapid production. Additionally, the structural strength of mobile terminal frames made of aluminum alloy is reduced. Summary of the Invention

[0004] To address the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide an integrally die-cast mobile terminal frame structure and its preparation method.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for fabricating a mobile terminal mid-frame structure by integral die casting includes the following steps: S100. A first middle frame structure is formed by die casting process; the first middle frame structure includes an integrally formed middle plate and a frame, and the outer side of the frame has a machining allowance. S200. Perform CNC machining on the first middle frame structure before injection molding to obtain the second middle frame structure; S300, a plastic structure is formed on the second middle frame structure by injection molding; S400. The second middle frame structure and the plastic structure are CNC machined to obtain the third middle frame structure. S500: Spray paint onto the surface of the frame to form a paint coating.

[0006] Furthermore, in step S100, magnesium alloy material is used for die casting, and the die casting process temperature is 650℃~680℃.

[0007] Furthermore, in step S100, aluminum alloy and magnesium alloy materials are mixed for die casting. Before die casting, an Al-Mg diffusion layer is formed in the die casting mold. During die casting, aluminum alloy melt is injected first at a temperature of 660±10℃, and then magnesium alloy melt is injected after an interval of 1.5s to 2.5s at a temperature of 580±10℃. The confluence pressure of the two runners is 80MPa to 100MPa.

[0008] Furthermore, step S200 includes the following sub-steps: S210. Perform CNC machining on the outer side of the frame to remove some machining allowance on the outer side of the frame. S220, positioning holes, antenna slots, adhesive-coated structures, and Type-C holes are machined on the first middle frame structure.

[0009] Furthermore, in step S100, the machining allowance thickness on the outer side of the frame is 1.8mm to 2.0mm; In step S210, a machining allowance of 0.3mm to 0.5mm is removed from one side of the outer edge of the frame by CNC milling, leaving a machining allowance of 1.5mm ± 0.05mm.

[0010] Furthermore, step S400 includes the following sub-steps: S410. Perform CNC machining on the frame and plastic structure to obtain the required structural features; S420. Perform CNC machining on the outer side of the frame to remove any remaining machining allowance on the outer side of the frame. S430, The required side hole structure is formed on the frame.

[0011] Furthermore, step S500 includes the following sub-steps: S510. The surface of the frame is sandblasted. S520. Apply epoxy primer and PU topcoat sequentially to the surface of the frame to form a paint coating. S530: Remove excess paint coating using CNC to obtain the mid-frame structure of the mobile terminal.

[0012] Furthermore, in step S520, the spraying method is electrostatic spraying, the curing temperature is 170℃~190℃, and the curing time is 15min~25min.

[0013] Furthermore, in steps S200 and S400, the CNC machining tool material is PCD diamond end mill, the rotation speed is 12000rpm~15000rpm, and the feed rate is 2000mm / min~3000mm / min.

[0014] A mobile terminal mid-frame structure integrally die-cast is prepared by the method for preparing an integrally die-cast mobile terminal mid-frame structure as described in any of the above claims.

[0015] In this invention, by using a die-casting integrated molding method for the middle plate and frame, the subsequent welding process for the middle plate and frame can be eliminated. Furthermore, the integrated molding of the frame and middle plate ensures the overall structural integrity and stability of the mobile terminal's frame. The tight fit reduces potential loosening issues caused by weak connections. Moreover, the main body of the middle plate can largely retain its original die-cast shape, requiring only pre-processing of the areas around the positioning holes. This maximizes the preservation of die-cast characteristics, making the middle plate structure more stable and better supporting other internal components of the phone, ensuring the structural strength of the mobile terminal's frame and guaranteeing the overall performance of the phone. In actual production, since most of the main body of the middle plate requires no additional processing, the total CNC machining workload is reduced by 60%, and the single-piece machining time is shortened from 85 minutes using traditional aluminum alloy CNC machining to 48 minutes, reducing processing costs and production cycle time, and effectively improving production efficiency. Furthermore, this embodiment, through improvements to materials and die-casting processes, and by employing a spray coating process instead of the traditional anodizing process, achieves a surface defect coverage rate of >99%, effectively solving the problem of traditional anodizing processes failing to conceal bubble defects. This significantly improves the product's appearance quality, resulting in substantial commercial value and market competitiveness. It also enables significant weight reduction in mobile terminals such as smartphones, enhancing user comfort. This embodiment effectively reduces defects and flaws during the production process, leading to a substantial increase in the yield rate of the mid-frame. Compared to traditional processes, the yield rate is significantly improved, reducing production costs. Attached Figure Description

[0016] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1This is a flowchart of an embodiment of the method for preparing the integral die-cast mobile terminal frame structure of the present invention.

[0017] Figure 2 and Figure 3 This is a structural diagram of the first middle frame structure.

[0018] Figure 4 and Figure 5 This is a structural diagram of the second middle frame structure.

[0019] Figure 6 and Figure 7 This is a schematic diagram of the structure after the plastic structure is formed on the second middle frame structure.

[0020] Figure 8 This is a schematic diagram of a plastic structure.

[0021] Figure 9 and Figure 10 This is a schematic diagram of the structure after CNC machining of the frame and plastic structure.

[0022] Figure 11 This is a schematic diagram of the structure after removing the remaining machining allowance on the outer side of the frame.

[0023] Figure 12 This is a structural diagram of the third middle frame structure.

[0024] The diagrams in the instruction manual are labeled as follows: First middle frame structure - 110; Second middle frame structure - 120; Third middle frame structure - 130; Frame - 200; Antenna slot - 210; Type-C hole - 221; Volume through hole - 222; Card slot hole - 223; Middle plate - 300; Positioning hole - 310; Plastic structure - 400; Plastic allowance layer - 410. Detailed Implementation

[0025] The following specific examples illustrate the implementation of the present invention. The illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0026] Please see Figure 1 , Figure 1 This is a flowchart illustrating an embodiment of the method for fabricating the integrally die-cast mobile terminal frame structure according to the present invention. The method for fabricating the integrally die-cast mobile terminal frame structure in this embodiment includes the following steps: S100, please refer to Figure 2 and Figure 3The first middle frame structure 110 is formed by die casting. The first middle frame structure 110 includes an integrally formed middle plate 300 and a frame 200, with a machining allowance on the outer side of the frame 200. The machining allowance thickness on the outer side of the frame 200 is generally 1.8mm to 2.0mm. By using die casting to integrally form the middle plate 300 and the frame 200, the subsequent welding process between the middle plate 300 and the frame 200 can be omitted, and the integral forming of the frame 200 and the middle plate 300 ensures the overall structural integrity and stability of the middle frame. The tight connection between the two reduces potential loosening problems caused by loose connections.

[0027] Die casting can form most of the characteristic structures of the middle plate 300 of the mobile terminal frame. Subsequently, only the positioning holes 310 (hole diameter ≤ 3mm) need to be pre-machined on the middle plate 300, allowing more than 95% of the die-cast surface to be retained on the middle plate 300. This reduces subsequent machining steps, improves production efficiency, and also preserves the advantageous characteristics of magnesium alloy die casting. Furthermore, through advanced die casting technology, magnesium alloy die-cast mobile phone frames can achieve high dimensional accuracy, meeting the installation requirements of precision electronic components inside the mobile phone. For example, the machining accuracy of key parts such as the positioning holes 310 can be controlled within an extremely small range.

[0028] However, if aluminum alloy is used for die casting, deformation is prone to occur after casting. This is because aluminum alloy has relatively low strength, and the stress generated during the die casting process is difficult to release effectively. If not controlled, the deformation may be significant, affecting the dimensional accuracy and assembly performance of the phone's mid-frame. Furthermore, defects such as bubbles are easily found on the surface of die-cast aluminum alloy, affecting the appearance quality of the mid-frame, and traditional processes are difficult to effectively solve these problems. Therefore, improvements to die-casting materials and processes are needed to reduce or avoid these defects.

[0029] In this step, magnesium alloy (e.g., AZ91D magnesium alloy) can be used for die casting. The preferred die casting temperature is 650℃~680℃. This temperature range ensures that the magnesium alloy melts fully, achieving good die casting results, ensuring the forming quality of the mobile terminal's frame, and reducing defects such as deformation and bubbles after die casting. Furthermore, since the density of AZ91D magnesium alloy is 1.8g / cm³... 3 Compared to the density of conventional aluminum alloy materials (2.7 g / cm³), 3 The significant reduction in weight allows mobile devices such as smartphones to achieve substantial weight reduction, improving the comfort of holding them for users.

[0030] In this step, aluminum alloy and magnesium alloy materials can also be mixed for die casting. In this case, an Al-Mg diffusion layer needs to be formed in the die casting mold before die casting (this can be achieved by spraying a 50μm thick Al-12%Mg powder coating as the Al-Mg diffusion layer). During die casting, aluminum alloy melt is injected first at a temperature of 660±10℃, followed by magnesium alloy melt injected after an interval of 1.5s to 2.5s at a temperature of 580±10℃. The dual-channel confluence pressure is 80MPa to 100MPa. This process yields a first middle frame structure 110 made of magnesium-aluminum alloy, achieving good die casting results, ensuring the forming quality of the mobile terminal's middle frame, and reducing defects such as deformation and bubbles after die casting. The density of the magnesium-aluminum alloy material is 2.60 g / cm³. 3 The weight is reduced by about 4.7% compared to conventional aluminum alloy materials, which also provides a basis for the lightweighting of mobile terminal frames.

[0031] In this embodiment, by reserving a certain machining allowance on one side of the outer edge of the frame 200, the machining allowance can be processed in stages, thereby gradually releasing the stress caused by the die-casting process; in addition, the improvement of the die-casting material can effectively control the deformation of the mobile terminal frame, and also provide adjustment space for subsequent processing steps, which helps to ensure the dimensional accuracy of the final product.

[0032] S200, please refer to Figure 4 and Figure 5 The first middle frame structure 110 is CNC machined before injection molding to obtain the second middle frame structure 120. During CNC machining, PCD diamond end mills are preferred. PCD diamond has high hardness and wear resistance, ensuring tool life and machining accuracy during finishing. The rotational speed is generally 12000rpm to 15000rpm. Higher speeds improve machining efficiency while ensuring the surface finish of the middle frame and reducing tool marks. In this embodiment, the preferred speed is 15000rpm. The feed rate is generally 2000mm / min to 3000mm / min. A reasonable feed rate matches the rotational speed, allowing the tool to run smoothly during machining and ensuring the dimensional accuracy of the middle frame. In this embodiment, the preferred feed rate is 2000mm / min. This step may include the following sub-steps: S210. Perform CNC machining on the outer side of the frame 200 to remove some of the machining allowance on the outer side of the frame 200. In this step, 0.3mm to 0.5mm of machining allowance is removed on one side of the outer side of the frame 200 by CNC milling, so that a machining allowance of 1.5mm ± 0.05mm is retained before injection molding; the retained machining allowance is then removed after injection molding. This staged machining method helps to release the stress caused by the die casting process and control the deformation of the mobile terminal frame.

[0033] S220. Positioning holes 310, antenna slots 210, a glue-pulling structure (not shown in the figure), and a Type-C hole 221 are machined on the first mid-frame structure 110. The glue-pulling structure can be a T-slot or a dovetail slot. By creating holes and a glue-pulling structure before injection molding for pulling the plastic material, the plastic structure 400 formed in subsequent processes can be prevented from separating from the mobile terminal mid-frame. The positioning holes 310 and the antenna are generally machined in the same clamping position to ensure machining accuracy. Key dimensional information can also be marked on the antenna slot 210 to ensure the machining accuracy of the antenna slot 210, guaranteeing the normal installation and working performance of the mobile terminal antenna. The manufacturing methods of the positioning holes 310, antenna slots 210, and glue-pulling structure are conventional techniques and will not be described in detail here.

[0034] S300, please refer to Figure 6 , Figure 7 and Figure 8 A plastic structure 400 is formed on the second frame structure 120 by injection molding. In this step, a 0.5mm thick plastic allowance layer 410 can be formed on the inner side of the frame 200 by injection molding. The injection molding process can precisely control the material filling to ensure the uniformity and integrity of the allowance layer. In this embodiment, the plastic structure 400 covers the outer surface of the frame 200 after processing and the antenna slot 210 area, enhancing the protective performance of the frame 200 and also providing a certain degree of insulation to protect the antenna and other electronic components.

[0035] Using a suitable injection molding material ensures a good bond with the magnesium alloy frame 200, improving the overall quality and durability of the mid-frame. In this step, a PC + GF 30% composite material is preferably used as the injection molding material. PC + GF 30% composite material is a glass fiber reinforced polycarbonate composite material, a high-performance plastic granule produced by mixing and melting 30% chopped glass fibers and 70% polycarbonate resin through an extruder. This composite material exhibits excellent properties; by observing the structure of the injection molding joint, it can be clearly seen that the PC + GF 30% composite material is tightly bonded to the magnesium alloy (or magnesium-aluminum alloy) frame 200, enhancing the overall performance of the mid-frame.

[0036] PC stands for polycarbonate, which is the matrix material. Polycarbonate is a high-performance engineering plastic with high impact resistance, high transparency, good dimensional stability, and heat resistance. While pure PC has many advantages, it also has some significant drawbacks: poor fatigue resistance, making it prone to cracking under long-term repeated stress; poor stress cracking resistance, especially in the presence of chemicals (such as certain solvents), easily leading to streaks and cracking; relatively insufficient rigidity, with strength and modulus not high enough for structural components requiring high rigidity; and a large and anisotropic molding shrinkage rate, making dimensional accuracy control of parts challenging.

[0037] GF30% is 30% by weight glass fiber, a reinforcing material added to PC. The addition of 30% glass fiber significantly improves upon the aforementioned shortcomings of pure PC. For example, the addition of 30% glass fiber significantly increases strength and rigidity; the glass fiber acts as a load-bearing skeleton, greatly enhancing the material's tensile strength, flexural strength, and modulus of elasticity (stiffness). It improves heat resistance, significantly increasing the heat deflection temperature (HDT), allowing parts to maintain their shape and function at higher temperatures. It improves dimensional stability, greatly reducing molding shrinkage, resulting in higher dimensional accuracy and less susceptibility to temperature changes. It improves fatigue and creep resistance, leading to less deformation under long-term loads and a longer lifespan.

[0038] Therefore, PC + GF 30% composite material is a classic example of a "strong-strong combination" engineering plastic. It sacrifices some of the high impact toughness and transparency of pure PC, but gains extremely high rigidity, strength, heat resistance, and dimensional stability. It is an ideal choice for parts that need to withstand structural loads and operate for extended periods at certain temperatures.

[0039] S400, CNC machining is performed on the second middle frame structure 120 and the plastic structure 400 to obtain the third middle frame structure 130.

[0040] S410, please refer to Figure 9 and Figure 10 The frame 200 and the plastic structure 400 are then CNC machined to obtain the required structural features. This step is a standard process and will not be described in detail here.

[0041] S420, please refer to Figure 11 The outer side of the frame 200 is CNC machined to remove any remaining machining allowance. By precision milling the frame 200 to its final thickness using CNC, the dimensional accuracy of the middle frame is ensured, meeting design requirements and effectively releasing stress accumulated during the die-casting process.

[0042] S430, please refer to Figure 12 The required side hole structures, such as volume through hole 222 and card tray hole 223, are formed on the frame 200. Of course, since a plastic layer is formed in the Type-C hole 221 during injection molding, the excess plastic layer in the Type-C hole 221 also needs to be removed in this step.

[0043] S500: Spray paint onto the surface of the frame 200 to form a paint coating, thus obtaining the mobile terminal frame structure. Traditional anodizing processes have poor adaptability to magnesium alloy materials and cannot adequately meet the surface treatment requirements of the frame 200 after magnesium alloy die casting, failing to achieve the desired surface quality. Therefore, in this embodiment, a spraying process is used to treat the surface of the frame 200. This step may include the following sub-steps: S510. The surface of the frame 200 is sandblasted. In this embodiment, #200 mesh quartz sand is used for sandblasting to eliminate tool marks, making the surface of the frame 200 smoother and improving the appearance quality.

[0044] S520. Apply epoxy primer and PU topcoat sequentially to the surface of frame 200. The paint coating formed in this step can cover the entire area of ​​frame 200, effectively filling the micropores on the surface of frame 200, improving the appearance quality of frame 200, and making the surface of frame 200 smoother and flatter.

[0045] The total thickness of the epoxy primer and PU topcoat is preferably 40μm ± 5μm, which can cover the surface micropores of the frame 200, further improving the protective performance and appearance of the frame 200. In this step, electrostatic spraying is used, which allows the paint to adhere evenly to the surface of the frame, improving the quality and coverage of the coating. The curing temperature is 170℃~190℃, preferably 180℃ in this embodiment. Curing at this temperature allows the epoxy primer and PU topcoat to react fully, forming a strong coating and improving its protective performance. The curing time is 15min~25min, preferably 20min in this embodiment. A suitable curing time ensures complete curing of the coating, achieving optimal hardness and gloss, and improving the appearance quality.

[0046] The spray coating also provides some protection, preventing oxidation and corrosion of the mobile terminal's frame surface and extending its service life. In this embodiment, a spray coating process is used instead of the traditional anodizing process. By spraying epoxy primer and PU topcoat, the micropores and imperfections on the magnesium alloy surface can be better covered, improving the appearance quality of the frame.

[0047] Traditional anodizing processes have limited coverage capabilities when treating surface defects in die-cast aluminum alloy frames, making it difficult to completely conceal surface defects such as bubbles, resulting in a low appearance yield (<85%). In this embodiment, after using a spraying process for surface treatment, the coverage rate is >99%. Therefore, this embodiment has a significant advantage in improving surface quality by adopting the spraying process.

[0048] S530: Excess paint coating is removed using CNC machining to obtain the mobile terminal's frame structure. For example, excess paint in the side hole structure.

[0049] In this embodiment, by using a die-casting integrated molding method for the middle plate 300 and the frame 200, the subsequent welding process for the middle plate 300 and the frame 200 can be omitted. Furthermore, the integrated molding of the frame 200 and the middle plate 300 ensures the overall structural integrity and stability of the mobile terminal's frame. The tight connection reduces potential loosening issues caused by weak connections. Moreover, the main body of the middle plate 300 can largely retain its original die-cast shape, requiring only pre-processing of the relevant areas of the positioning holes 310. This maximizes the preservation of die-cast characteristics, making the structure of the middle plate 300 more stable and better supporting other internal components of the phone, ensuring the structural strength of the mobile terminal's frame and guaranteeing the overall performance of the phone. In actual production, since most of the main body of the middle plate 300 requires no additional processing, the total CNC machining workload is reduced by 60%, and the single-piece machining time is shortened from 85 minutes using traditional aluminum alloy CNC machining to 48 minutes, reducing processing costs and production cycle, and effectively improving production efficiency.

[0050] To address the issue of surface bubble defects that easily appear on the surface of die-cast aluminum alloys, this embodiment improves the materials and die-casting process, and replaces the traditional anodizing process with a spray coating process. This achieves a surface defect coverage rate of >99%, effectively solving the problem that traditional anodizing processes struggle to conceal bubble defects, significantly improving the product's appearance quality, and demonstrating significant commercial value and market competitiveness. Furthermore, because magnesium alloys and magnesium-aluminum alloys have a significantly lower density than conventional aluminum alloys, this allows for a significant weight reduction in mobile devices such as smartphones, improving user comfort. This embodiment effectively reduces defects during the production process, resulting in a substantial increase in the yield rate of the mid-frame. Compared to traditional processes, the yield rate is significantly improved, reducing production costs.

[0051] This invention also discloses a one-piece die-cast mobile terminal frame structure, which is prepared using the one-piece die-cast mobile terminal frame structure preparation method described in any of the above embodiments. In this embodiment, the mobile terminal frame structure is formed by die-casting a middle plate 300 and a frame 200, ensuring the overall structural integrity and stability of the mobile terminal frame and reducing potential loosening issues caused by loose connections. Furthermore, the middle plate 300 has a more stable structure, better supporting other internal components of the phone and ensuring the structural strength of the mobile terminal frame, thus guaranteeing the overall performance of the phone. Moreover, the surface defect coverage rate is >99%, significantly improving the product's appearance quality and enabling a significant weight reduction in the mobile terminal, enhancing user comfort and demonstrating broad application prospects.

[0052] The above embodiments merely illustrate preferred implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention should be determined by the appended claims.

Claims

1. A method for manufacturing a mobile terminal frame structure integrally die-cast, characterized in that, Includes the following steps: S100. A first middle frame structure is formed by die casting process; the first middle frame structure includes an integrally formed middle plate and a frame, and the outer side of the frame has a machining allowance. S200. Perform CNC machining on the first middle frame structure before injection molding to obtain the second middle frame structure; S300, a plastic structure is formed on the second middle frame structure by injection molding; S400. The second middle frame structure and the plastic structure are CNC machined to obtain the third middle frame structure. S500: Spray paint onto the surface of the frame to form a paint coating.

2. The method for preparing the integrated die-cast mobile terminal frame structure as described in claim 1, characterized in that: In step S100, magnesium alloy material is used for die casting, and the temperature of the die casting process is 650℃~680℃.

3. The method for preparing the integrated die-cast mobile terminal frame structure as described in claim 1, characterized in that: In step S100, aluminum alloy and magnesium alloy materials are mixed for die casting. Before die casting, an Al-Mg diffusion layer is formed in the die casting mold. During die casting, aluminum alloy melt is injected first at a temperature of 660±10℃, and then magnesium alloy melt is injected after an interval of 1.5s to 2.5s at a temperature of 580±10℃. The confluence pressure of the two runners is 80MPa to 100MPa.

4. The method for preparing the integrated die-cast mobile terminal frame structure as described in claim 1, characterized in that, Step S200 includes the following sub-steps: S210. Perform CNC machining on the outer side of the frame to remove some machining allowance on the outer side of the frame. S220, positioning holes, antenna slots, adhesive bonding structure and Type-C holes are machined on the first middle frame structure.

5. The method for preparing the integrated die-cast mobile terminal frame structure as described in claim 4, characterized in that: In step S100, the machining allowance thickness on the outer side of the frame is 1.8mm to 2.0mm; In step S210, a machining allowance of 0.3mm to 0.5mm is removed from one side of the outer edge of the frame by CNC milling, leaving a machining allowance of 1.5mm ± 0.05mm.

6. The method for preparing the integrated die-cast mobile terminal frame structure as described in claim 1, characterized in that, The S400 step includes the following sub-steps: S410. Perform CNC machining on the frame and plastic structure to obtain the required structural features; S420. Perform CNC machining on the outer side of the frame to remove any remaining machining allowance on the outer side of the frame. S430, The required side hole structure is formed on the frame.

7. The method for preparing the integrated die-cast mobile terminal frame structure as described in claim 1, characterized in that, The S500 step includes the following sub-steps: S510. The surface of the frame is sandblasted. S520. Apply epoxy primer and PU topcoat sequentially to the surface of the frame to form a paint coating. S530: Remove excess paint coating using CNC to obtain the mid-frame structure of the mobile terminal.

8. The method for preparing the integrated die-cast mobile terminal frame structure as described in claim 7, characterized in that: In step S520, electrostatic spraying is used, the curing temperature is 170℃~190℃, and the curing time is 15min~25min.

9. The method for preparing the integral die-cast mobile terminal frame structure as described in any one of claims 1 to 8, characterized in that: In steps S200 and S400, the CNC machining tool material is PCD diamond end mill, the rotation speed is 12000rpm~15000rpm, and the feed rate is 2000mm / min~3000mm / min.

10. A mobile terminal frame structure integrally die-cast, characterized in that: The mobile terminal mid-frame structure is prepared by the method of integral die casting as described in any one of claims 1 to 9.

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