Hot stamping forming device and method for large aluminum alloy thin-wall part

Abstract

The invention provides a hot stamping forming device and method for a large aluminum alloy thin-wall part. The device comprises a hot stamping die, a single-loop cooling unit and a control system. An integrally-machined variable cross-section cooling flow channel is embedded in the hot stamping die, and the flow channel is composed of a high-speed flow channel area, a low-speed flow channel area and a transition flow channel area which are different in hydraulic diameter. The single-loop cooling unit provides a cooling medium for the flow channel through a single variable-frequency hydraulic pump; and the control system is used for roughly adjusting the overall cooling strength by adjusting the pump power. Passive distribution of the flow velocity of a cooling medium is achieved through geometric differences of flow channel sections, a complex multi-loop active control system can be replaced with a single-loop system only, soft and hard gradient performance distribution is achieved on a formed part, and the system has the advantages of being simple in structure, high in reliability and low in energy consumption and maintenance cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum alloy plastic forming, in particular to an aluminum alloy large thin-walled part hot stamping forming device and method. BACKGROUND

[0002] Aluminum alloy large thin-walled components are key structural components for lightweighting in the aerospace field. During the hot stamping forming process of such parts, there are severe challenges: on the one hand, complex curved thin-walled parts after forming due to uneven internal stress distribution produce significant springback, resulting in difficulty in controlling shape accuracy; on the other hand, components have different requirements for performance in different service areas, such as high strength in areas such as mounting points and stiffeners to withstand loads, and high toughness in large curvature or energy absorption areas to suppress cracking. The traditional hot stamping process uses overall heating and uniform cooling, which is difficult to balance "shape control" and "property control", and cannot achieve gradient distribution of component performance.

[0003] With the development of hot forming technology, zoned active temperature control technology is introduced to solve the above problems. The existing technology usually adopts a multi-loop independent cooling system, by embedding multiple independently controlled electromagnetic choke valves and cooling channels in the die, to apply different cooling rates to different areas, thereby regulating the microstructure and performance of the material. Although this method can achieve performance gradient distribution, the system is complex, the manufacturing cost is high, the electromagnetic valve has poor reliability and frequent maintenance in harsh conditions of high temperature and high humidity, and the multi-loop hydraulic system has huge energy consumption, which is difficult to meet the strict requirements of industrial mass production on economy and stability.

[0004] At present, the gradient hot forming device based on multi-loop active control has achieved performance regulation to some extent, but its high cost and complex maintenance limit its popular application in batch production. How to greatly reduce system complexity, improve equipment reliability and reduce energy consumption while ensuring accurate "soft and hard gradient" performance control of components has become a core problem that needs to be solved by technical personnel in the field. SUMMARY

[0005] The present application provides an aluminum alloy large thin-walled part hot stamping forming device and method. The purpose is to replace the complex multi-loop active control system with a passive, high-reliability single-loop cooling system, to achieve accurate "soft and hard gradient" performance distribution on large thin-walled aluminum alloy components, thereby simultaneously solving the dual problems of part forming accuracy and performance requirements, and greatly reducing device cost and energy consumption.

[0006] The technical scheme adopted by the present application to achieve the above purpose is:

[0007] An aluminum alloy large thin-walled part hot stamping forming device, comprising:

[0008] Hot stamping dies with an internal single-circuit cooling system;

[0009] A single-loop cooling unit is used to provide cooling medium for a single-loop cooling system;

[0010] The control system is electrically connected to the single-loop cooling unit.

[0011] The single-loop cooling system is characterized by being an integrated variable cross-section flow channel, which consists of at least two flow channel partitions with different hydraulic diameters. The different flow channel partitions correspond to different temperature control areas on the mold surface, and the passive distribution of the cooling medium flow rate is achieved through the geometric difference in the cross-sectional area of ​​the flow channel.

[0012] Furthermore, the variable cross-section flow channel includes:

[0013] The high-speed flow channel region has a small hydraulic diameter, which corresponds to the high-strength hardened region required for large thin-walled aluminum alloy parts.

[0014] The low-speed flow channel region has a large hydraulic diameter, which corresponds to the high toughness softening region required for large thin-walled aluminum alloy parts;

[0015] The transition channel region has a continuously changing hydraulic diameter, corresponding to the performance transition area of ​​large thin-walled aluminum alloy components.

[0016] Furthermore, the ratio of the cross-sectional area of ​​the high-speed flow channel region to that of the low-speed flow channel region is no greater than 1:2.

[0017] Furthermore, the inner wall of the high-speed flow channel region is processed with a turbulence enhancement structure, which is a series of uniformly distributed V-shaped microgrooves or an array of micro-protrusions.

[0018] Furthermore, the upper and lower dies of the hot stamping die are both provided with the variable cross-section flow channels, and the flow channel partitions of the upper and lower dies match the temperature control area of ​​the large thin-walled aluminum alloy part after the mold is closed.

[0019] Furthermore, the single-loop cooling unit includes a variable frequency hydraulic pump, a liquid storage tank, and a heat exchanger, wherein the variable frequency hydraulic pump is controlled by the control system.

[0020] Furthermore, the control system is configured to: receive feedback signals from temperature sensors installed inside the mold, and adjust the overall flow rate of the cooling medium by regulating the power of the variable frequency hydraulic pump in the single-loop cooling unit, thereby coarsely adjusting the overall cooling intensity of the mold.

[0021] A method for hot stamping forming of large thin-walled aluminum alloy parts, using the above-mentioned apparatus, includes the following steps:

[0022] S1, heat the aluminum alloy sheet to the solution temperature and hold it at that temperature;

[0023] S2, the heated sheet metal is quickly transferred to the hot stamping die, and the die is immediately closed and pressure is applied and maintained;

[0024] S3, while maintaining pressure, the single-loop cooling unit is activated, and the cooling medium enters the variable cross-section flow channel in the mold with a single total flow rate;

[0025] S4, the cooling medium is automatically distributed to different flow rates in the flow channel due to the change in cross-section. The high-speed flow channel zone performs strong quenching on the corresponding area of ​​the large thin-walled aluminum alloy part, while the low-speed flow channel zone performs weak quenching on the corresponding area of ​​the large thin-walled aluminum alloy part, thereby achieving a gradient distribution of the performance of the large thin-walled aluminum alloy part.

[0026] S5. After cooling, the mold is opened and the molded component with soft-hard gradient properties is obtained.

[0027] Furthermore, in step S4, the control system dynamically adjusts the power of the variable frequency hydraulic pump based on the temperature sensor signal to control the temperature of key points on the mold surface within the temperature fluctuation range of the quenching process.

[0028] The above-described solution of the present invention has the following beneficial effects:

[0029] 1) This invention achieves the zoned gradient cooling function, which previously required multiple solenoid valve circuits, using only a single-loop cooling system through an integrated variable cross-section flow channel design. This mechanical solution avoids the inherent defects of solenoid valves, such as easy damage and short lifespan in high-temperature and humid environments, thus improving system reliability.

[0030] 2) This invention simplifies the system configuration, eliminating multiple sets of electromagnetic throttle valves, corresponding independent hydraulic control units, and complex control programs, thus significantly reducing the energy consumption and maintenance costs of the device.

[0031] 3) This invention achieves stable and passive control of the cooling medium flow rate without feedback through the hydraulic diameter design, cross-sectional ratio, and built-in turbulence enhancement structure of the flow channel. It eliminates flow fluctuations and interference caused by frequent valve operation in multi-loop systems and improves the consistency of performance gradient distribution of large thin-walled aluminum alloy parts. Attached Figure Description

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0033] Figure 1 Schematic diagram of a hot stamping forming device for large thin-walled aluminum alloy parts;

[0034] Figure 2 This is a schematic diagram of the hot stamping die structure in an embodiment of the present invention;

[0035] Figure 3 This is a schematic diagram of a single-loop cooling unit structure in an embodiment of the present invention;

[0036] Figure 4 This is a schematic diagram of a partially variable cross-section cooling channel in an embodiment of the present invention;

[0037] Figure 5 This is a schematic diagram illustrating the matching of material performance regions and flow velocity distribution in an embodiment of the present invention.

[0038] Figure 6 This is a partially enlarged schematic diagram of the V-shaped microgroove turbulence enhancement structure on the inner wall of the high-speed flow channel in an embodiment of the present invention;

[0039] Figure 7 This is a partially enlarged schematic diagram of the array-type micro-bump turbulence enhancement structure on the inner wall of the high-speed flow channel in an embodiment of the present invention.

[0040] In the diagram: 1-Hot stamping die, 2-Single-loop cooling unit, 3-Control system, 4-Large thin-walled aluminum alloy part, 5-Variable cross-section cooling channel, 6-V-shaped micro-groove, 7-Micro-bump, 101-Upper die, 102-Lower die, 103-Temperature sensor, 201-Variable frequency hydraulic pump, 202-Heat exchanger, 203-Storage tank, 501-High-speed flow channel area, 502-Low-speed flow channel area, 503-Transition flow channel area. Detailed Implementation

[0041] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0042] A hot stamping forming apparatus for large thin-walled aluminum alloy parts, such as Figure 1 As shown, it includes:

[0043] Hot stamping die 1, which has an integrated variable cross-section cooling channel 5 embedded inside;

[0044] The single-loop cooling unit 2 is connected to the variable cross-section cooling channel 5 via a variable frequency hydraulic pump 201 to provide cooling water medium.

[0045] The control system 3 is electrically connected to the variable frequency hydraulic pump 201 in the single-loop cooling unit 2.

[0046] The hot stamping die 1 consists of an upper die 101 and a lower die 102. Temperature sensors 103 and 104 are installed inside the die. After the die is closed, a cavity matching the shape of the large thin-walled aluminum alloy part 4 is formed. Figure 2 As shown.

[0047] Reference Figure 4The variable cross-section cooling channel 5 is machined inside the upper mold 201 and the lower mold 202, and includes a high-speed channel area 501, a low-speed channel area 502 and a transition channel area 503 connecting the two.

[0048] Reference Figure 5 The high-speed flow channel region 501 corresponds to the high-strength areas such as the mounting points and reinforcing ribs of the large thin-walled aluminum alloy component 4. Its designed hydraulic diameter is 12mm, and its cross-sectional shape is circular. The low-speed flow channel region 502 corresponds to the high-toughness areas such as the large curvature surfaces and energy-absorbing areas of the large thin-walled aluminum alloy component 4. Its designed hydraulic diameter is 18mm, and its cross-sectional shape is circular. The ratio of the cross-sectional areas of the high-speed flow channel region 501 to the low-speed flow channel region 502 is 1:2.25. The hydraulic diameter of the transition flow channel region 503 smoothly transitions from 12mm to 18mm, and its length is 150mm to ensure a smooth transition in cooling intensity.

[0049] Example 1: V-shaped microgroove turbulence enhancement structure

[0050] Reference Figure 6 V-shaped microgrooves 6 are machined on the inner wall of the high-speed flow channel region 501 to enhance heat transfer. The V-shaped microgrooves 6 extend along the flow channel axis, with specific parameters: groove depth 0.9 mm, groove apex angle 45°, and spacing between adjacent microgrooves 1.2 mm. This structure can disrupt the laminar sublayer on the flow channel wall, significantly increasing the heat transfer coefficient at the same flow rate. CFD simulation and experimental verification show that its heat transfer efficiency is approximately 25% higher than that of a smooth flow channel.

[0051] Example 2: Array-type distributed micro-bump turbulence enhancement structure

[0052] Reference Figure 7 An array of micro-bumps 7 is machined on the inner wall of the high-speed flow channel region 501. The micro-bumps 7 are hemispherical and formed by CNC milling or EDM machining. Their specific parameters are: bump height 0.3 mm, bottom diameter 0.6 mm, arranged in an array on the inner wall of the flow channel, with a center-to-center distance of 1.0 mm between adjacent bumps. This array of micro-bumps effectively disturbs the boundary layer, generating eddies to enhance heat transfer. Its heat transfer efficiency is approximately 18% higher than that of a smooth flow channel, and the weakening of the flow channel structure strength is less than that of a V-shaped microgroove.

[0053] Reference Figure 1 , Figure 2 , Figure 4 and Figure 5The working principle of this invention is as follows: After heating the aluminum alloy sheet to the solution temperature, it is quickly transferred to the preheated hot stamping die 1 cavity. The upper die 201 moves downward to close the die and form and hold the sheet under pressure. At the same time, the control system 3 immediately starts the single-loop cooling unit 2, and the variable frequency hydraulic pump 201 pumps cooling water into the variable cross-section cooling channel 5 of the hot stamping die 1 at a set total flow rate. The cooling water is automatically distributed in the channel due to the difference in cross-sectional geometry: in the high-speed channel region 501, due to the small cross-sectional area and the presence of turbulence-enhancing structures within the cross-section, the flow velocity of the cold water near the wall of the pipe is greatly increased, the convective heat transfer capacity is enhanced, the temperature gradient at the contact interface between the large thin-walled aluminum alloy part 4 and the hot stamping die 1 is increased, the heat transfer coefficient at the contact interface increases, and the cooling rate of the large thin-walled aluminum alloy part is increased, reaching 100℃ / s, achieving strong quenching of the corresponding area of ​​the large thin-walled aluminum alloy part 4; in the low-speed channel region 502, due to the large cross-sectional area, the flow velocity decreases, achieving weak quenching of the corresponding area of ​​the large thin-walled aluminum alloy part. Through this passive flow rate distribution, the large thin-walled aluminum alloy part 4 is gradient cooled under pressure, thereby achieving a gradient performance distribution of high strength (hard area) and high toughness (soft area) in the corresponding regions. The control system 3 dynamically fine-tunes the power of the variable frequency hydraulic pump 201 based on the temperature signals fed back by the mold temperature sensor 103 and temperature sensor 104, controlling the temperature fluctuation of the key mold surfaces within ±8℃.

[0054] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make other changes or modifications based on the above disclosure, such as changing the cross-sectional shape of the flow channel, or adjusting the geometric parameters and arrangement of the V-grooves or micro-protrusions, and these changes or modifications are still within the scope of this disclosure.

Claims

1. An apparatus for hot press forming of an aluminum alloy large thin-walled member, comprising a hot press die (1), a single-circuit cooling unit (2), and a control system (3), characterized by, The hot stamping die (1) is internally embedded with an integrated machining variable cross-section cooling channel (5); the variable cross-section cooling channel (5) is composed of at least two flow channel partitions with different hydraulic diameters, including a high-speed flow channel zone (501), a low-speed flow channel zone (502), and a transition flow channel zone (503) connecting the two, the different flow channel partitions corresponding to different temperature control areas on the die surface; the single-circuit cooling unit (2) is connected with the variable cross-section cooling channel (5) through a variable frequency hydraulic pump (201) for providing cooling medium; through the geometric difference of the flow channel cross-sectional area, passive distribution of the cooling medium flow rate is realized.

2. The apparatus for hot press forming of an aluminum alloy large thin-walled part according to claim 1, characterized in that, The hydraulic diameter of the high-speed flow channel zone (501) is smaller than that of the low-speed flow channel zone (502), and the ratio of the cross-sectional areas of the high-speed flow channel zone (501) and the low-speed flow channel zone (502) is not greater than 1:

2.

3. The apparatus for hot stamping forming of an aluminum alloy large thin-walled part according to claim 2, characterized in that, The inner wall of the high-speed flow channel zone (501) is processed with a turbulent flow strengthening structure.

4. The apparatus for hot press forming of an aluminum alloy large thin-walled part according to claim 3, characterized in that, The turbulent flow strengthening structure is a series of V-shaped micro grooves (6) extending along the flow channel axis.

5. The apparatus for hot press forming of an aluminum alloy large thin-walled part according to claim 3, characterized in that, The turbulent flow strengthening structure is an array of micro convex points (7).

6. The apparatus for hot press forming of an aluminum alloy large thin-walled part according to claim 1, characterized in that, The upper die (101) and the lower die (102) of the hot stamping die (1) are both internally provided with the variable cross-section cooling channel (5), and the flow channel partitions of the upper and lower dies match the workpiece temperature control areas after the die is closed.

7. The apparatus for hot press forming of an aluminum alloy large thin-walled part according to claim 1, characterized in that, The control system (3) is configured to receive feedback signals of temperature sensors (103, 104) arranged in the die, and change the overall flow rate of the cooling medium by adjusting the power of the variable frequency hydraulic pump (201).

8. A method of hot press forming of an aluminum alloy large thin-walled member using the apparatus according to any one of claims 1 to 7, characterized by, The method comprises the following steps: S1: heat the aluminum alloy sheet to the solid solution temperature and keep it; S2: quickly transfer the heated sheet to the hot stamping die (1) and close the die to pressurize; S3: while pressurizing, start the single-circuit cooling unit (2), and the cooling medium enters the variable cross-section cooling channel (5) in the die at a single total flow rate; S4: the cooling medium is automatically distributed to different flow rates in the flow channel due to the cross-section change, and gradient quenching is implemented on different areas of the workpiece; S5: after cooling, the die is opened, and a formed component with soft and hard gradient performance is obtained.

9. The method of claim 8, wherein, In step S4, the control system (3) dynamically adjusts the power of the variable frequency hydraulic pump (201) according to the temperature sensor signal, and controls the temperature of the key points of the die surface within the process requirement range.

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