Semi-solid injection molding method for thin-wall battery end plate

Abstract

The invention belongs to the technical field of semi-solid alloy injection molding, and discloses a thin-wall battery end plate semi-solid injection molding method, which comprises the following steps: S1, material pretreatment: cutting a magnesium alloy material into particles, and carrying out surface cleaning treatment under the protection of inert gas; s2, preparing semi-solid slurry: adding magnesium alloy particles into a semi-solid injection molding machine, and heating to enable the magnesium alloy particles to form the semi-solid slurry; s3, injection molding: injecting the semi-solid slurry into the thin-wall battery end plate mold, solidifying and molding, opening the mold, and taking out a molded workpiece; and S4, post-treatment is conducted, specifically, corrosion-resistant treatment is conducted on the surface of the formed workpiece. Magnesium alloy is adopted as a material, and the magnesium alloy with light weight, high strength, corrosion resistance, high precision, low roughness and low wall thickness is obtained by applying the semi-solid injection molding method provided by the invention; the thin-wall battery end plate with the thickness of 1.5 mm meets the assembly requirement of a battery module, the forming temperature is reduced by 100 DEG C, and the service life of the mold is greatly prolonged.

Description

Technical Field

[0001] This invention belongs to the technical field of semi-solid alloy injection molding, and particularly relates to a semi-solid injection molding method for thin-walled battery end plates. Background Technology

[0002] With the rapid development of the new energy vehicle industry, battery systems, as core power components, have become a core requirement for the industry in terms of lightweighting, high safety, and high energy density, directly affecting the vehicle's range, handling performance, and operational safety. As a core structural component of the battery module, the battery end plate undertakes the critical functions of fixing the battery cells, transferring loads, and assisting in heat dissipation. Therefore, it must simultaneously possess high strength to ensure structural stability, high thermal conductivity for efficient heat transfer, and good corrosion resistance to adapt to complex operating environments.

[0003] Currently, battery end plates are mainly produced using aluminum alloy die casting. However, this technology has two major drawbacks that make it difficult to meet the upgrade requirements of battery systems: First, weight control is limited. Aluminum alloy has a density of 2.7 g / cm³, which significantly limits the weight reduction potential of battery systems given the increasingly stringent requirements for lightweight battery modules, indirectly affecting the overall vehicle range. Second, the molding quality is unstable. During the liquid aluminum alloy molding process, traditional die casting is prone to internal defects such as porosity and shrinkage due to the flow characteristics of the molten metal and poor venting. This leads to fluctuations in the mechanical properties of the product, making it impossible to consistently meet the structural strength requirements of the end plate and posing safety hazards.

[0004] To overcome the lightweighting bottleneck of aluminum alloys, magnesium alloys, with their outstanding advantages of low density (1.74 g / cm³, only about 64% of aluminum alloys) and high specific strength (strength per unit weight superior to aluminum alloys), have become an ideal alternative material for battery end plates, potentially significantly reducing end plate weight while maintaining structural strength. However, the traditional magnesium alloy liquid die-casting process faces four major technical bottlenecks when applied to battery end plate production, hindering its industrial application:

[0005] Severe Oxidation Inclusions: Magnesium alloys have high chemical activity and are prone to react with oxygen and nitrogen in the air in the high-temperature liquid state to form hard oxide inclusions such as MgO and Mg3N2. These inclusions not only reduce the mechanical and thermal conductivity of the end plate, but may also become stress concentration points during the stress process, leading to the risk of cracking.

[0006] High porosity: During the liquid die casting process, air is easily trapped when the molten metal fills the mold cavity at high speed. In addition, the volume shrinkage rate of magnesium alloy is large during solidification. Existing processes are difficult to effectively remove gas, resulting in the porosity of the molded end plate generally exceeding 5%, which greatly weakens the strength and sealing of the product.

[0007] Short mold life: When high-temperature liquid magnesium alloy (pouring temperature is usually 650-700℃) comes into contact with the mold, it will generate severe thermal shock, which will cause thermal fatigue cracks and accelerated wear on the surface of the mold cavity. The mold life is only 50,000-100,000 cycles, which is far lower than that of aluminum alloy die casting molds (usually 200,000-300,000 cycles), significantly increasing production costs.

[0008] Thin-walled parts are difficult to form: In order to achieve further weight reduction, the battery end plate needs to be designed as a complex thin-walled structure with a wall thickness of <1.5mm. However, in the traditional magnesium alloy liquid die casting process, the flow of molten metal is prone to problems such as insufficient filling and cold shut in the thin-walled area, making it difficult to achieve the complete forming of such complex thin-walled structures and limiting the structural design freedom of the end plate.

[0009] In summary, existing battery endplate materials and molding processes can no longer meet the upgrade requirements of new energy vehicle battery systems for lightweighting and high reliability. There is an urgent need to break through the technical bottleneck of traditional magnesium alloy die casting process and develop new process solutions adapted to battery endplate production. Summary of the Invention

[0010] The purpose of this invention is to provide a semi-solid injection molding method for thin-walled battery end plates. Using high-strength, corrosion-resistant magnesium alloy as raw material, and employing a semi-solid injection molding machine with the specified process parameters, a semi-solid slurry is injected into a mold for the thin-walled battery end plate, which has a curved parting surface and a fan-shaped manifold gating system. The slurry solidifies and is then molded. The surface of the molded workpiece undergoes anti-corrosion treatment, resulting in a lightweight, high-strength, corrosion-resistant, high-precision, low-roughness thin-walled battery end plate with a wall thickness of <1.5mm, meeting the assembly requirements of battery modules. Compared to traditional die casting, the semi-solid injection molding method can reduce the molding temperature by 100℃, significantly extending the mold's service life.

[0011] The specific details of the plan are as follows:

[0012] A semi-solid injection molding method for thin-walled battery end plates, comprising the following steps:

[0013] S1. Material Pretreatment: Magnesium alloy material is used. The magnesium alloy material is cut into particles and surface cleaned under inert gas protection. S2. Semi-solid Slurry Preparation: The magnesium alloy particles are added to a semi-solid injection molding machine and heated to form a semi-solid slurry. S3. Injection Molding: The semi-solid slurry is injected into the thin-walled battery end plate mold, solidified, and the molded part is removed after opening the mold. S4. Post-treatment: The surface of the molded part is treated with corrosion resistance.

[0014] Furthermore, the magnesium alloy in step S1 is AZ91D or AM60B.

[0015] Furthermore, in step S1, the content of magnesium alloy particles with a length between 1.4mm and 2.8mm after cutting reaches 85%, and the minimum particle size of magnesium alloy is not less than 0.9mm.

[0016] Furthermore, in step S2, a semi-solid injection molding machine is used, with a screw diameter of 100mm, a length-to-diameter ratio of 20:1, and the barrel temperature is controlled in stages: the temperature of the barrel feeding section is 200-250℃, the temperature of the barrel compression section is 350-400℃, and the temperature of the barrel metering section is 450-590℃.

[0017] Furthermore, the screw speed is 200-300 rpm; the back pressure is 5-10 MPa.

[0018] Furthermore, in step S2, the melt temperature is 605-610℃, the shear rate is 160-180 rpm, the stirring time is 30 seconds, and the solid fraction is 3-8%.

[0019] Furthermore, in the semi-solid slurry prepared in step S2, the solid particles are spherical with an average particle size of <50μm, are uniformly distributed, and show no agglomeration.

[0020] Furthermore, in step S3, the parting surface of the thin-walled battery end plate mold is curved, the gating system is a fan-shaped sprue, the venting system is equipped with multi-stage venting grooves, and the cooling system adopts conformal oil circuit.

[0021] Furthermore, in step S3, the injection pressure is 20-30 MPa, the holding pressure is 110-130 MPa, the mold temperature is 180-220℃, the holding time is 7-9 seconds, the injection speed is 3.3-3.4 m / s, and the mold dwell time is 21.5-23.5 s.

[0022] Furthermore, in step S4, an electrophoresis process is used to treat the surface of the molded workpiece for corrosion resistance.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] This invention uses high-strength, corrosion-resistant magnesium alloy as raw material, which achieves lightweighting compared to aluminum alloy raw materials in the prior art. The alloy composition is optimized to expand the semi-solid temperature range, ensuring the fluidity of the semi-solid slurry and meeting the needs of the semi-solid injection molding method of this invention.

[0025] The semi-solid injection molding method of this invention uses a semi-solid injection molding machine and, in accordance with process parameters, injects semi-solid slurry into a thin-walled battery end plate mold with a curved parting surface and a fan-shaped manifold gating system. The slurry solidifies and is then molded. The surface of the molded workpiece is treated with anti-corrosion measures to obtain a lightweight, high-strength, corrosion-resistant, high-precision, low-roughness, and thin-walled battery end plate with a wall thickness of <1.5mm, which meets the assembly requirements of battery modules.

[0026] Compared to traditional die casting, semi-solid injection molding can reduce the molding temperature by 100°C, significantly extending the mold's lifespan. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0028] The terminology used in this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0029] This invention provides a semi-solid injection molding method for thin-walled battery end plates, the steps of which include:

[0030] S1. Material Pretreatment: Magnesium alloy material is used. The magnesium alloy material is cut into particles and surface cleaned under inert gas protection. S2. Semi-solid Slurry Preparation: The magnesium alloy particles are added to a semi-solid injection molding machine and heated to form a semi-solid slurry. S3. Injection Molding: The semi-solid slurry is injected into the thin-walled battery end plate mold, solidified, and the molded part is removed after opening the mold. S4. Post-treatment: The surface of the molded part is treated with corrosion resistance.

[0031] The magnesium alloy in step S1 is AZ91D or AM60B.

[0032] The material used in this invention is a high-strength, corrosion-resistant magnesium alloy. The material used in this invention is not limited to AZ91D or AM60B, but can also be other magnesium alloy materials, as long as they can meet the performance requirements of this invention for raw material strength, good corrosion resistance, and semi-solid temperature range.

[0033] In step S1, the content of magnesium alloy particles with a length between 1.4mm and 2.8mm after cutting reaches 85%, and the minimum particle size of magnesium alloy is not less than 0.9mm.

[0034] In step S2, a semi-solid injection molding machine is used with a screw diameter of 100mm and a length-to-diameter ratio of 20:1. The barrel temperature is controlled in stages: the temperature of the barrel feeding section is 200-250℃, the temperature of the barrel compression section is 350-400℃, and the temperature of the barrel metering section is 450-590℃.

[0035] The core function of segmented temperature control in the barrel is to match the functions of each section and ensure the "orderly transformation" of materials. The feeding section, compression section, and metering section of the barrel undertake the progressive tasks of "conveyance, compaction, semi-solidification, and precise metering." The essence of segmented temperature control is to provide the optimal temperature environment for each stage, avoiding problems such as feed blockage and uneven material state in the metering section caused by single temperature control. The temperature of the feeding section is controlled at 200-250℃, which allows the material to soften initially but not yet enter the semi-solid state. If the temperature is too high, the material will soften prematurely and stick to the screw or the inner wall of the barrel, causing the material to clump and block at the feed inlet, making it impossible to convey downwards. If the temperature is too low, the material hardness is high and the friction with the barrel is large, the screw conveying resistance increases sharply, which can easily lead to conveying interruption. The core task of the compression section is to compact the loose material conveyed by the feeding section, reduce voids, expel air and volatiles from the material, and gradually raise the material temperature to the "semi-solid critical range." A temperature of 350-400℃ allows the material to soften further but remains predominantly solid. During screw compression, it tightly adheres to the barrel, expelling air, oil, and volatiles from the material. This avoids the internal defects such as porosity and shrinkage that easily occur in the liquid aluminum alloy forming process of traditional die casting due to the flow characteristics of molten metal and poor venting, leading to fluctuations in product mechanical properties and an inability to consistently meet the end plate's structural strength requirements. The temperature in the compression section is between 200-250℃ in the feeding section and 450-590℃ in the metering section, forming a gentle gradient from low to medium temperature. This prevents localized overheating (coarse grains) or uneven temperature distribution (partially semi-solid, partially solid) caused by a direct jump from low to high temperatures. The metering section is the core control area for semi-solid molding. Its temperature range of 450-590℃ perfectly matches the semi-solid temperature range of magnesium alloys, ensuring consistent material viscosity and preventing slippage or uneven thrust during screw advancement. This guarantees accurate material injection each time, ensuring stable dimensions and weight of the molded workpiece. Segmented temperature control keeps temperature fluctuations in the metering section within ±5℃, significantly improving metering accuracy and enhancing the quality of the molded workpiece.

[0036] Compared with the traditional magnesium alloy die casting process, the semi-solid injection molding method of the present invention can reduce the molding temperature by 100°C and significantly improve the service life of the mold.

[0037] Screw speed: 200-300 rpm; back pressure: 5-10 MPa; back pressure 5-10 MPa.

[0038] In step S2, the melt temperature is 605-610℃, the shear rate is 160-180 rpm, the stirring time is 30 seconds, and the solid fraction is 3-8%.

[0039] In the semi-solid slurry prepared in step S2, the solid particles are spherical with an average particle size of <50μm, are uniformly distributed, and do not exhibit agglomeration.

[0040] In step S3, the parting surface of the thin-walled battery end plate mold is curved, the gating system is a fan-shaped manifold gate, the venting system is equipped with multi-stage venting grooves, and the vacuum degree is <50mbar; the cooling system adopts conformal oil passages, with an oil flow rate of 10-15L / min and an oil temperature of 210-220℃.

[0041] The thin-walled battery end plate mold selected in this invention has a curved parting surface, which can reduce flash and improve sealing; the gating system is a fan-shaped manifold gate, which ensures uniform filling and minimizes warping deformation of the flat plastic part; the gate residue is thin, easy to remove, and does not affect the appearance. Other parting surfaces and gating systems can also be selected to improve the quality of the molded workpiece.

[0042] In step S3, the injection pressure is 20-30 MPa, the holding pressure is 110-130 MPa, the mold temperature is 180-220℃, the holding time is 7-9 seconds, the injection speed is 3.3-3.4 m / s, and the mold dwell time is 21.5-23.5 s.

[0043] In step S4, an electrophoresis process is used to treat the surface of the molded workpiece for corrosion resistance.

[0044] The present invention preferably uses an electrophoresis process to treat the surface of the molded workpiece for corrosion resistance, but is not limited to an electrophoresis process.

[0045] The following detailed description is provided with reference to the embodiments:

[0046] Example 1:

[0047] AM60B magnesium alloy ingots were cut into particles. The content of magnesium alloy particles with a length between 1.4mm and 2.8mm reached 85%, and the minimum particle size of magnesium alloy was 1mm. The particles were then cleaned under inert gas protection.

[0048] Magnesium alloy particles were added to a semi-solid injection molding machine with a screw diameter of 100 mm and an aspect ratio of 20:1. The barrel temperature was controlled in stages: the temperature of the barrel feeding section was 200℃, the temperature of the barrel compression section was 350℃, and the temperature of the barrel metering section was 450℃. The screw speed was 200 rpm, the back pressure was 5 MPa, the melt temperature was 605℃, the shear rate was 160 rpm, the stirring time was 30 seconds, and the solid fraction was 8%. After heating, the magnesium alloy particles formed a semi-solid slurry. The solid particles in the prepared semi-solid slurry were spherical with an average particle size of <50 μm, uniformly distributed, and without agglomeration.

[0049] Semi-solid slurry was injected into the thin-walled battery end plate mold. The holding pressure was 100MPa, the holding pressure was 110MPa, the mold temperature was 180℃, the holding time was 8 seconds, the injection speed was 3.3m / s, the mold dwell time was 21.5s, the slurry solidified, the mold was opened, and the molded part was removed.

[0050] The surface of the molded workpiece was treated with an electrophoretic process to achieve corrosion resistance. Measurements showed the wall thickness of the molded workpiece to be 0.9 mm.

[0051] Example 2:

[0052] AZ91D magnesium alloy ingots were cut into particles. The content of magnesium alloy particles with a length between 1.4mm and 2.8mm reached 85%, and the minimum particle size of magnesium alloy was 1mm. The particles were then cleaned under inert gas protection.

[0053] Magnesium alloy particles were added to a semi-solid injection molding machine with a screw diameter of 100 mm and an aspect ratio of 20:1. The barrel temperature was controlled in stages: the temperature of the barrel feeding section was 250℃, the temperature of the barrel compression section was 400℃, and the temperature of the barrel metering section was 590℃. The screw speed was 300 rpm, the back pressure was 10 MPa, the melt temperature was 610℃, the shear rate was 180 rpm, the stirring time was 30 seconds, and the solid fraction was 3%. After heating, the magnesium alloy particles formed a semi-solid slurry. The solid particles in the prepared semi-solid slurry were spherical with an average particle size of <50 μm, uniformly distributed, and without agglomeration.

[0054] Semi-solid slurry was injected into the thin-walled battery end plate mold. The holding pressure was 110MPa, the holding pressure was 130MPa, the mold temperature was 220℃, the holding time was 9 seconds, the injection speed was 3.3m / s, the mold dwell time was 21.5s, the slurry solidified, the mold was opened, and the molded part was removed.

[0055] The surface of the molded workpiece was treated with an electrophoretic process to achieve corrosion resistance. Measurements showed the wall thickness of the molded workpiece to be 0.8 mm.

[0056] Example 3:

[0057] AZ91D magnesium alloy ingots were cut into particles. The content of magnesium alloy particles with a length between 1.4mm and 2.8mm reached 85%, and the minimum particle size of magnesium alloy was 0.9mm. The particles were then cleaned under inert gas protection.

[0058] Magnesium alloy particles were added to a semi-solid injection molding machine with a screw diameter of 100 mm and an aspect ratio of 20:1. The barrel temperature was controlled in stages: the temperature of the barrel feeding section was 230℃, the temperature of the barrel compression section was 390℃, and the temperature of the barrel metering section was 510℃. The screw speed was 300 rpm, the back pressure was 7 MPa, the melt temperature was 608℃, the shear rate was 170 rpm, the stirring time was 30 seconds, and the solid fraction was 6%. After heating, the magnesium alloy particles formed a semi-solid slurry. The solid particles in the prepared semi-solid slurry were spherical with an average particle size of <50 μm, uniformly distributed, and without agglomeration.

[0059] Semi-solid slurry is injected into the thin-walled battery end plate mold. The holding pressure is 130MPa, the mold temperature is 200℃, the holding time is 7 seconds, the injection speed is 3.4m / s, the mold dwell time is 22s, the material solidifies and is then removed from the mold.

[0060] The surface of the molded workpiece was treated with an electrophoretic process to achieve corrosion resistance. Measurements showed the wall thickness of the molded workpiece to be 0.8 mm.

[0061] The surface roughness and dimensional accuracy of the molded workpieces prepared in Examples 1-3 were tested respectively. The test standards were: surface roughness: GB / T 1031-2009; dimensional accuracy: GB / T 6414-2017. The results are shown in Table 1.

[0062]

[0063] The test results of the molded parts in Examples 1-3 show that, compared with the traditional die casting process using aluminum alloy as raw material, the semi-solid injection molding method of this invention, which uses high-strength and high-corrosion-resistant magnesium alloy as raw material, can obtain lightweight, high-strength, corrosion-resistant, high-precision, low-roughness, and thin-walled battery end plates with a wall thickness of <1.5mm, meeting the battery module assembly requirements, reducing the molding temperature by 100℃, and significantly improving the service life of the mold.

[0064] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A thin-walled battery end plate, semi-solid injection molding method characterized by the steps of The method comprises the following steps: S1, pretreatment of the material: cutting the magnesium alloy material into particles and performing surface cleaning treatment under inert gas protection; S2, preparation of semi-solid slurry: adding the magnesium alloy particles into a semi-solid injection molding machine and heating the magnesium alloy particles to form a semi-solid slurry; S3, injection molding: injecting the semi-solid slurry into a thin-walled battery end plate mold, solidifying and molding, opening the mold, and taking out the molded workpiece; S4, post-treatment: performing corrosion-resistant treatment on the surface of the molded workpiece.

2. The thin-walled battery end plate semi-solid injection molding process of claim 1, wherein, The magnesium alloy in step S1 is AZ91D or AM60B.

3. The thin-walled battery end plate method of claim 1, wherein, In step S1, the length of the cut magnesium alloy particles is between 1.4 mm and 2.8 mm, and the content of the magnesium alloy particles with a length of not less than 0.9 mm is 85%.

4. The thin-walled battery end plate method of claim 1, wherein, In step S2, a semi-solid injection molding machine is used, the screw diameter is 100 mm, the length-diameter ratio is 20:1, the barrel temperature is controlled in sections, the temperature of the barrel feeding section is 200-250℃, the temperature of the barrel compression section is 350-400℃, and the temperature of the barrel metering section is 450-590℃.

5. The thin-walled battery end plate semi-solid injection molding process of claim 4, wherein, The screw rotation speed is 200-300 rpm, and the back pressure is 5-10 MPa.

6. The thin-walled battery end plate semi-solid injection molding process of claim 4, wherein, In step S2, the melt temperature is 605-610℃, the shear rate is 160-180 rpm, the stirring time is 30 seconds, and the solid phase rate is 3-8%.

7. The thin-walled battery end plate method of claim 1, wherein, In the semi-solid slurry prepared in step S2, the solid phase particles are spherical, the average particle size is <50μm, the distribution is uniform, and there is no agglomeration phenomenon.

8. The thin-walled battery end plate method of claim 1, wherein, In step S3, the parting surface of the thin-walled battery end plate mold is curved, the gating system is a fan-shaped collector gate, the exhaust system is provided with multiple exhaust grooves, and the cooling system adopts a conformal oil way.

9. The thin-walled battery end plate method of claim 1, wherein, In step S3, the injection pressure is 20-30 MPa, the holding pressure is 110-130 MPa, the mold temperature is 180-220℃, the holding time is 7-9 seconds, the injection speed is 3.3-3.4 m / s, and the mold dwelling time is 21.5-23.5 S.

10. The thin-walled battery end plate method of semi-solid injection molding of claim 1, wherein, In step S4, an electrophoresis process is used to perform corrosion-resistant treatment on the surface of the molded workpiece.

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