A high strain rate-controllable soft die coupling precision forming device and method for a plate

Abstract

The present application belongs to the technical field of plate forming, and relates to a plate high-strain-rate-controllable-soft-mold coupling precision forming device and method. The device comprises an electromagnetic pulse generating unit, a driving plate, a plunger, a pressure ring, a medium bin, a magnetic field auxiliary device, a coil and a female die. The female die is arranged at the lower end of the medium bin, and the plate is placed between the medium bin and the female die. The cavity between the medium bin and the plate is filled with magnetorheological fluid. The plunger is placed at the upper end of the cavity of the medium bin, the driving plate is placed on the upper end surface of the plunger, and the electromagnetic pulse generating unit is located on the upper end of the driving plate. In the initial stage of forming, the magnetic field auxiliary device is arranged at the periphery of the bottom of the plunger. In the later stage of forming, the magnetic field auxiliary device is arranged at the center of the bottom of the plunger. The device can realize the precision forming of the plate under the coupling action of high strain rate and controllable soft mold, improve the plasticity of the material under high strain rate from the inside of the material, provide suitable soft mold stress state for different deformation regions of the plate from the outside, regulate the deformation, and realize the precision forming of the part.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of plate forming, and particularly relates to a plate high-strain-rate-controllable soft die coupling precision forming device and method. BACKGROUND

[0002] In recent years, the application of light alloy complex thin-walled components in the fields of aerospace and automobiles is increasingly widespread, which plays an important role in improving the lightweight and high reliability of equipment. However, the low plasticity of light alloy itself and the characteristics of large deformation degree and local features of complex components result in obvious local stress difference in the deformation process, which leads to problems such as cracking and wrinkling in the forming process of conventional processes.

[0003] Research shows that high-rate forming can effectively improve the formability of plates. Plate impact hydraulic forming technology is a high-strain-rate forming technology, which has two characteristics of dynamic impact loading and liquid flexibility in the machining process, and has the advantages of large impact energy, high forming limit and high forming part quality. However, the impact hydraulic forming equipment has a complex structure, and water or hydraulic oil is used as the force transmission medium in the impact hydraulic forming technology, which is easy to leak. According to Pascal's principle, the liquid pressure in the cavity is equal everywhere. However, the pressure requirements of different areas are different during the forming of complex thin-walled parts, which is contradictory, so it is difficult to provide a suitable stress state for different areas during the plate forming process. SUMMARY

[0004] In order to solve the above problems, the purpose of the present application is to provide a plate high-strain-rate-controllable soft die coupling precision forming device and method, which solves the problem that the existing forming method is difficult to provide a suitable stress state for different areas during the plate forming process.

[0005] The present application is realized by the following technical solutions:

[0006] A plate high-strain-rate-controllable soft die coupling precision forming device, comprising an electromagnetic pulse generating unit, a driving plate, a plunger, a pressure ring, a medium bin, a magnetic field auxiliary device, a coil and a concave die;

[0007] The pressure ring is arranged at the upper end of the medium bin, the concave die is arranged at the lower end of the medium bin, and the plate is placed between the medium bin and the concave die;

[0008] The cavity between the medium bin and the plate is filled with magnetorheological fluid, and the coil is sleeved outside the medium bin;

[0009] The plunger is placed at the upper end of the cavity of the medium bin, the driving plate is placed on the upper end surface of the plunger, and the electromagnetic pulse generating unit is located at the upper end of the driving plate;

[0010] In the initial stage of forming, the magnetic field auxiliary device is arranged at the bottom periphery of the plunger; in the later stage of forming, the magnetic field auxiliary device is arranged at the bottom center of the plunger.

[0011] Further, the plunger comprises a lower section, an intermediate section and an upper section which are integrally connected, the diameter of the lower section is the same as the inner diameter of the medium bin, the diameter of the intermediate section is smaller than that of the lower section and the upper section;

[0012] The length of the intermediate section ranges from 200mm to 300mm.

[0013] Further, the die is provided with exhaust holes.

[0014] Further, sealing rings are arranged between the medium bin and the die and the plunger.

[0015] Further, the plunger, the pressure ring, the medium bin and the die are made of non-magnetic steel, the magnetic field auxiliary device is made of pure iron, and the material of the driving plate is red copper.

[0016] Further, the magnetorheological fluid comprises methyl silicone oil, hydroxyl iron powder and a stabilizer; the volume fraction of the hydroxyl iron powder is 30% to 50%.

[0017] The application further discloses a plate high-strain-rate-controllable-soft-mold coupling precision forming method, which comprises the following steps:

[0018] S1: according to the shape of the part to be formed, a corresponding matching die is processed;

[0019] A plurality of magnetic field auxiliary devices are arranged along the annular edge on the lower side of the plunger, and the plunger is arranged in the medium bin;

[0020] S2: the pressure ring is clamped to the plate by applying a pressure force, current is passed through the coil, and under the action of the magnetic field auxiliary device, a non-uniform magnetic field distribution is generated in the cavity, so that the magnetorheological fluid has different constitutive relation parameters at the center and the edge in the cavity;

[0021] S3: after the electromagnetic pulse generating unit is charged and discharged, a strong pulse current generates a strong instantaneous magnetic field through the working coil, the driving plate generates a downward impact force and impacts the plunger, the plunger moves downward and extrudes the magnetorheological fluid, so that the plate deforms under the pressure of the magnetorheological fluid and enters the die, the plate is partially attached to the die, and preforming is completed;

[0022] S4: the magnetic field auxiliary device installed in S1 is disassembled, the magnetic field auxiliary device is reinstalled at the bottom center of the plunger, the current passed through the coil is adjusted, and under the action of the magnetic field auxiliary device, a non-uniform magnetic field distribution is generated in the cavity, so that the magnetorheological fluid has different constitutive relation parameters at the center and the edge in the cavity;

[0023] S5: Adjust the discharge of the electromagnetic pulse generating unit so that the driving plate impacts the plunger again, the plunger high-speed downwardly extrudes the magnetorheological fluid to form a soft die, extrudes the plate material, and makes the plate material completely adhere to the concave die to meet the forming requirements.

[0024] Further, in S2, the constitutive relation parameters include a strength coefficient k and a strain rate sensitivity index m, and the magnetorheological fluid has different constitutive relation parameters at the center and the edge of the cavity, specifically:

[0025] The strength coefficient k1 of the center region ranges from 0.02 to 0.15, and the strain rate sensitivity index m1 of the center region ranges from 0.55 to 0.65.

[0026] The strength coefficient k2 of the edge region ranges from 0.20 to 0.30, and the strain rate sensitivity index m2 of the edge region ranges from 0.45 to 0.55.

[0027] The relationship between the strength coefficient k and the magnetic field strength B is K=0.033+1.569·B-2.101·B 2 .

[0028] The relationship between the strain rate sensitivity index m and the magnetic field strength B is m=0.644-1.362·B+3.423·B 2 .

[0029] Further, in S4, the constitutive relation parameters include a strength coefficient k and a strain rate sensitivity index m, and the magnetorheological fluid has different constitutive relation parameters at the center and the edge of the cavity, specifically:

[0030] The strength coefficient k1 of the center region ranges from 0.20 to 0.30, and the strain rate sensitivity index m1 of the center region ranges from 0.45 to 0.55.

[0031] The strength coefficient k2 of the edge region ranges from 0.02 to 0.15, and the strain rate sensitivity index m2 of the edge region ranges from 0.55 to 0.65.

[0032] The relationship between the strength coefficient k and the magnetic field strength B is K=0.033+1.569·B-2.101·B 2 .

[0033] The relationship between the strain rate sensitivity index m and the magnetic field strength B is m=0.644-1.362·B+3.423·B 2 .

[0034] Further, in S5, when the formed part has one or more local feature regions, the number of impacts is increased according to the geometric features of the formed part, and the discharge energy of the electromagnetic pulse generating unit ranges from 2 to 15 kJ.

[0035] Compared with the prior art, the present application has the following beneficial technical effects:

[0036] The application discloses a plate high-strain-rate-controllable soft die coupling precision forming device, which comprises an electromagnetic pulse generating unit, a plunger, a medium bin, a magnetic field auxiliary device, a coil and a female die; the cavity between the medium bin and the plate is filled with magnetorheological fluid, and the coil is sleeved outside the medium bin. Under the action of the coil and the magnetic field auxiliary device, a non-uniform step-type changing magnetic field can be obtained in a forming area, and then the controllable adjustment of the soft die performance is realized, so that the magnetorheological fluid has different constitutive relation parameters at the center and the edge in the cavity; the magnetic field auxiliary device is located inside the soft die, the magnetic field regulation and control effect is stronger, and the non-uniform magnetic field regulation and control range is wider. The device can realize the coupling loading of the magnetic field, the force field and the pulse current, and avoid the interference between the devices. The device uses electromagnetic pulse force as an energy source, has high energy utilization rate, the electromagnetic pulse generating unit is used for generating a strong pulse current to promote the plunger to extrude the magnetorheological fluid and complete pre-deformation; the position of the magnetic field auxiliary device is adjustable, and the magnetic field auxiliary device is moved according to needs for secondary forming.

[0037] Further, the magnetorheological fluid comprises methyl silicone oil, hydroxyl iron powder and a stabilizer; the volume fraction of the hydroxyl iron powder is 30%-50%, the magnetorheological fluid with the volume fraction has a good mechanical property regulation and control range and is a good mechanical transmission medium, and the suitable volume fraction has beneficial mechanical transmission characteristics and a regulation and control range. If the volume fraction of the hydroxyl iron powder is too small, the mechanical property regulation and control range is small; and if the volume fraction of the hydroxyl iron powder is too large, the magnetorheological fluid is excessively saturated, and particle agglomeration and uneven mixing occur.

[0038] Further, the force transmission section of the plunger should have a sufficient length, and the length should be 200mm-300mm, and the purpose is mainly to prevent magnetic field interference between the electromagnetic pulse generating unit and the coil.

[0039] Further, the lower end of the female die is provided with an exhaust hole, the exhaust hole can be increased, decreased and arranged according to small feature areas of a part, and the purpose is to prevent the air in the female die from generating a reaction force and damaging the stress state of the plate.

[0040] Further, sealing rings are arranged between the medium bin and the female die and between the medium bin and the plunger, and the purpose is to improve the sealing performance of the equipment and prevent the magnetorheological fluid from overflowing.

[0041] Further, the materials of the plunger, the edge ring, the medium bin and the female die are non-magnetic steel, so that the magnetic field generated by the coil can pass through the magnetorheological fluid and change the rheological property of the magnetorheological fluid; the material of the magnetic field auxiliary device is pure iron, so that the magnetic field can be flexibly and locally concentrated; and the material of the driving plate is red copper, so that the electromagnetic pulse generating unit can convert electromagnetic force into impact force of the plunger.

[0042] The application discloses a plate high-strain-rate-controllable soft mold coupling precision forming method, which can control a soft mold of a magnetorheological fluid to generate different mechanical properties according to the local small feature topography of a forming component through one or more times of electromagnetic impact loading, and the electromagnetic impact loading gap is changed by adjusting a coil and a magnetic field auxiliary device to change the local mechanical properties of the magnetorheological fluid, so that the part with small features is formed in stages and precisely. The application can realize the precision forming of the plate under the coupling action of the high-strain-rate-controllable soft mold, promote the plasticity of the material under the high-strain-rate from the inside of the material, provide suitable soft mold stress states for different deformation regions of the plate from the outside, control the deformation, and realize the precision forming of the part by combining the inside and the outside. The performance regulation and control of the soft mold in different regions can effectively relieve the local stress concentration caused by the high-speed impact, the wall thickness distribution of the formed part is more uniform, and the rebound of the small feature area of the plate after the impact is reduced.

[0043] Further, in S2, the magnetorheological fluid has different constitutive relation parameters at the center and the edge of the cavity, wherein the strength coefficient k of the center region ranges from 0.02 to 0.15, the strain rate sensitivity index m ranges from 0.55 to 0.65, the strength coefficient k of the edge region ranges from 0.20 to 0.30, and the strain rate sensitivity index m ranges from 0.45 to 0.55. In this stage, the coil provides a magnetic field for the magnetorheological fluid to convert mechanical properties, and the magnetic field auxiliary device controls the constitutive relation of the magnetorheological fluid at the center and the edge, so as to realize the local mechanical property regulation and control of the magnetorheological fluid.

[0044] Further, in S4, the magnetorheological fluid has different constitutive relation parameters at the center and the edge of the cavity, wherein the strength coefficient k of the center region ranges from 0.20 to 0.30, the strain rate sensitivity index m ranges from 0.45 to 0.55, the strength coefficient k of the edge region ranges from 0.02 to 0.15, and the strain rate sensitivity index m ranges from 0.55 to 0.65. In this stage, the coil provides a magnetic field for the magnetorheological fluid to convert mechanical properties, and the magnetic field auxiliary device controls the constitutive relation of the magnetorheological fluid at the center and the edge, so as to realize the local mechanical property regulation and control of the magnetorheological fluid.

[0045] Further, in S4, multiple impacts can be performed in one forming process. When there is one or more small feature regions at the bottom of the part, the number of impacts can be increased to form the plate. For the part with small features, the overall stress state of the part is unbalanced, and there is one or more dangerous stress points and surfaces. Multiple impacts can effectively control the rebound phenomenon of the plate forming and make the plate completely formed. The discharge energy range of the electromagnetic pulse generating unit is 2-15 kJ, which can provide appropriate forming force required by the plate forming and corresponding forming rate. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 is a schematic diagram of the overall structure of the present application;

[0047] Figure 2 is a front view of the shell-shaped convex bottom part forming device of Example 1 when fully assembled;

[0048] Figure 3 is a front view of the shell-shaped convex bottom part forming device of Example 1 in an intermediate state;

[0049] Figure 4 is a force relationship diagram of the shell-shaped convex bottom part forming device of Example 1 in an intermediate process;

[0050] Figure 5 is a front view of the shell-shaped convex bottom part forming device of Example 1 at the completion of forming;

[0051] Figure 6 is a force relationship diagram of the shell-shaped convex bottom part forming device of Example 1 at the completion of forming.

[0052] In the figure: 1, electromagnetic pulse generating unit; 2, drive plate; 3, plunger; 4, edge ring; 5, sealing ring; 6, medium bin; 7, magnetic field auxiliary device; 8, magnetorheological fluid; 9, coil; 10, plate; 11, concave die. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical scheme and advantages of the present application more clear and obvious, the following will be further described in detail in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application, that is, the described examples are only a part of the examples of the present application, but not all the examples.

[0054] It should be noted that the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, element, method, article or equipment including a series of elements includes not only those elements, but also other elements not explicitly listed, or further includes the elements inherent to the process, element, method, article or equipment.

[0055] The features and performances of the present application will be further described in detail in combination with the examples below.

[0056] As shown in Figure 1 A specific device for realizing the present application is shown, which is used as an example to specifically explain the plate high strain rate-controllable soft die coupling precision forming method of the present application, which does not constitute a limitation of the present application. The method of the present application can be realized by using any existing device capable of realizing its step-by-step function.

[0057] The device includes an electromagnetic pulse generating unit 1, a drive plate 2, a plunger 3, a pressure ring 4, a dielectric chamber 6, a magnetic field auxiliary device 7, a coil 9, and a die 11. The pressure ring 4 is located at the upper end of the dielectric chamber 6, and the die 11 is placed at the lower end of the dielectric chamber 6. The cavity between the dielectric chamber 6 and the plate 10 is filled with magnetorheological fluid 8, and the coil 9 is sleeved on the outside of the dielectric chamber 6. The plunger 3 is placed at the upper end of the cavity of the dielectric chamber 6, and the magnetic field auxiliary device 7 is installed on the lower side of the plunger 3. The drive plate 2 is placed on the upper end face of the plunger 3, and the electromagnetic pulse generating unit 1 is located at the upper end of the drive plate 2.

[0058] The lower end of the die 11 is provided with an exhaust hole, the diameter of which ranges from 0.5mm to 3mm. The exhaust hole can be added, removed, or arranged according to the small feature areas of the part. Its purpose is to prevent the air inside the die 11 from generating a reaction force and thus damaging the stress state of the sheet metal.

[0059] A sealing ring 5 is provided between the medium chamber 6, the die 11, and the plunger 3. The sealing ring 5 can be an O-ring.

[0060] Specifically, the plunger 3, the pressure ring 4, the medium chamber 6, and the die 11 are made of non-magnetic steel, the magnetic field auxiliary device 7 is made of electrical pure iron, and the drive plate 2 is made of copper.

[0061] like Figure 1 As shown, the plunger 3 includes an integrally connected lower section, middle section and upper section. The diameter of the lower section is the same as the inner diameter of the medium chamber 6, and the diameter of the middle section is smaller than that of the lower section and the upper section. The middle section of the plunger 3 is the force transmission section and should have sufficient length, with a range of 200mm to 300mm. Its main purpose is to prevent magnetic field interference between the electromagnetic pulse generating unit 1 and the coil 9.

[0062] This invention also discloses a high strain rate-controllable soft mold coupling precision forming method for sheet metal, comprising the following steps:

[0063] S1: Based on the shape of the part to be formed, process the corresponding matching die 11;

[0064] Multiple magnetic field auxiliary devices 7 are installed along the annular edge on the lower side of the plunger 3, and the plunger 3 is installed in the medium chamber 6;

[0065] S2: Apply a clamping force to the clamping ring 4 to clamp the plate 10. Current is passed through the coil 9. Under the action of the magnetic field auxiliary device 7, a non-uniform magnetic field distribution is generated in the cavity, so that the magnetorheological fluid 8 has different constitutive parameters at the center and the edge in the cavity.

[0066] S3: the electromagnetic pulse generating unit 1 is discharged after charging, the strong pulse current passes through the working coil to generate a strong instantaneous magnetic field, the driving plate 2 generates an impact force downward and impacts the plunger 3, the plunger 3 moves downward and extrudes the magnetorheological fluid 8, so that the plate material 10 is deformed into the concave die 11 under the pressure of the magnetorheological fluid, and the plate material 10 is partially attached to the concave die 11, and the preforming is completed;

[0067] S4: the magnetic field auxiliary device 7 installed in S1 is disassembled, the magnetic field auxiliary device 7 is reinstalled at the bottom center of the plunger 3, the current flowing into the coil 9 is adjusted, and under the action of the magnetic field auxiliary device 7, a non-uniform magnetic field distribution is generated in the cavity, so that the magnetorheological fluid 8 in the cavity has different constitutive relation parameters at the center and the edge;

[0068] S5: the discharge of the electromagnetic pulse generating unit 1 is adjusted, so that the driving plate 2 impacts the plunger 3 again, the plunger 3 extrudes the magnetorheological fluid 8 at high speed, forms a soft die, and extrudes the plate material 10, so that the plate material 10 is completely attached to the concave die 11, and the forming requirement is reached.

[0069] The constitutive relation parameters include the strength coefficient k and the strain rate sensitive index m, the magnetorheological fluid 8 in the cavity has different constitutive relation parameters at the center and the edge, and in S2, the constitutive relation parameters are as follows:

[0070] The strength coefficient k1 of the center region ranges from 0.02 to 0.15, and the strain rate sensitive index m1 of the center region ranges from 0.55 to 0.65;

[0071] The strength coefficient k2 of the edge region ranges from 0.20 to 0.30, and the strain rate sensitive index m2 of the edge region ranges from 0.45 to 0.55;

[0072] The relationship between the strength coefficient k and the magnetic field strength B is K=0.033+1.569·B-2.101·B 2 .

[0073] The relationship between the strain rate sensitive index m and the magnetic field strength B is m=0.644-1.362·B+3.423·B 2 .

[0074] In S4, the constitutive relation parameters are as follows:

[0075] The strength coefficient k1 of the center region ranges from 0.20 to 0.30, and the strain rate sensitive index m1 of the center region ranges from 0.45 to 0.55;

[0076] The strength coefficient k2 of the edge region ranges from 0.02 to 0.15, and the strain rate sensitive index m2 of the edge region ranges from 0.55 to 0.65;

[0077] Wherein, the relationship between the intensity coefficient k and the magnetic field intensity B is K=0.033+1.569·B-2.101·B 2 ;

[0078] The relationship between the strain rate sensitive index m and the magnetic field intensity B is m=0.644-1.362·B+3.423·B 2 .

[0079] The following will be further explained by a plate member processing process:

[0080] As Figures 2-4 , the shell-shaped convex bottom part needs to be processed in this embodiment, and the difficulty of the part forming is that there is a convex small feature area in the bottom section. When the material convexity reaches a certain degree, the stress concentration point is seriously thinned. For the shell-shaped convex bottom part, the forming process is divided into two stages of impact, and different magnetic field auxiliary devices 7 are used in the two impact processes. The first stage makes the plate 10 preliminarily deform and accumulate materials under the influence of the magnetic field, and the second stage makes the plate 10 completely fit the concave die 11 and keeps the pressure for a period of time to reduce the springback of the plate 10.

[0081] The specific processing steps are as follows:

[0082] S1: According to the shape characteristics of the shell-shaped convex bottom part, the matching concave die 11 bottom surface structure is designed;

[0083] S2: As Figure 1 shown, the plate 10 is placed on the upper end surface of the processed concave die 11, the medium bin 6 is placed on the upper surface of the plate 10, the magnetorheological fluid 8 is injected into the medium bin 6, the coil 9 is placed outside the concave die 11 and the medium bin 6, a plurality of magnetic field auxiliary devices 7 are installed along the annular edge on the lower side of the plunger 3, the plunger 3 is installed in the medium bin 6, and the plunger 3 is installed in the medium bin 6. The upper side of the plunger 3 is provided with a driving plate 2, and the upper surface of the driving plate 2 is provided with an electromagnetic pulse generating unit 1;

[0084] S3: As Figure 2 shown, the edge pressure force F is applied to clamp the plate 10, the current is passed through the coil 9 to make the magnetorheological fluid 8 become a soft mold with specific mechanical properties, at this time the intensity coefficient k of the central region of the magnetorheological fluid 8 is 0.03, the strain rate sensitive coefficient m of the central region is 0.65, the intensity coefficient k of the edge region is 0.26, and the strain rate sensitive coefficient m of the edge region is 0.51; The electromagnetic pulse generating unit 1 is charged and discharged, and the discharge energy is 15kJ. At this time, the plunger 3 is driven by the damping effect of the driving plate 2 to impact the magnetorheological fluid 8 at high speed, and the magnetorheological fluid 8 extrudes the plate 10, as Figure 3 shown, the plate 10 is stressed and deformed to form a W-shaped bottom surface, and the material accumulation preforming is completed; the part pressure distribution is as Figure 4As shown, P1>P2, P3>P2, the intermediate region pressure is small, and the edge region pressure is large, and the edge region is the main deformation region.

[0085] S4: as shown, the magnetic field auxiliary device 7 is reinstalled at the bottom center of the plunger 3, the input current of the coil 9 is adjusted, so that the magnetorheological fluid 8 becomes a soft mold with specific mechanical properties, at this time, the strength coefficient k of the central region of the magnetorheological fluid 8 is 0.26, the strain rate sensitivity coefficient m of the central region is 0.51, the strength coefficient k of the edge region is 0.03, and the strain rate sensitivity coefficient m of the edge region is 0.65; Figure 5

[0086] S5: the electromagnetic pulse generating unit 1 is charged and discharged again, at this time, the plunger 3 is driven by the driving plate 2 to extrude the magnetorheological fluid 8, and then extrude the plate material 10, so that the plate material 10 is completely attached to the concave die 11; the part pressure distribution is as shown in Figure 6 As shown, P2>P1, P2>P3, the intermediate region pressure is large, and the edge region pressure is small, and the intermediate region is the main deformation region.

[0087] S6: after the shape requirement of the formed part is reached, the coil 9 is powered off, the plunger 3 is withdrawn to the starting position, the blank holder 4 is removed, the equipment is opened, and the formed part is taken out.

[0088] The adjustment of the strength coefficient k and the strain rate sensitivity coefficient m is: by controlling the input current of the coil 9, if necessary, the position of the magnetic field auxiliary device 7 can also be adjusted, and then the magnetic field distribution of the position where the magnetorheological fluid 8 is located is adjusted, and the performance parameters thereof are changed.

[0089] More preferably, in S5, multiple impacts can be performed in one forming process, when there is one or more small feature regions at the bottom of the part, the number of impacts can be increased to form the plate material 10; for such parts with small feature regions, the overall stress state of the part is uneven, there is one or more dangerous stress points and surfaces, multiple impacts can effectively control the plastic flow of the material, and can effectively control the springback phenomenon of the part, and can make the plate material 10 completely formed.

[0090] The discharge energy range of the electromagnetic pulse generating unit 1 is 2-15kJ, which can provide appropriate forming force required for the forming of the plate material 10, and can also provide corresponding forming rate.

[0091] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them, although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that: the specific embodiments of the present application can still be modified or replaced by equivalents without departing from the spirit and scope of the present application, any modification or equivalent replacement without departing from the spirit and scope of the present application should be covered in the protection scope of the claims of the present application.​

Claims

1. A high strain rate-controllable soft mold coupling precision forming device for sheet metal, characterized in that, It includes an electromagnetic pulse generating unit (1), a drive plate (2), a plunger (3), a pressure ring (4), a dielectric chamber (6), a magnetic field auxiliary device (7), a coil (9), and a die (11). The pressure ring (4) is located at the upper end of the medium chamber (6), the die (11) is located at the lower end of the medium chamber (6), and the plate (10) is placed between the medium chamber (6) and the die (11). The cavity between the dielectric chamber (6) and the plate (10) is filled with magnetorheological fluid (8), and the coil (9) is sleeved on the outside of the dielectric chamber (6); The plunger (3) is placed at the upper end of the cavity of the medium chamber (6), the drive plate (2) is placed on the upper end face of the plunger (3), and the electromagnetic pulse generating unit (1) is located at the upper end of the drive plate (2). In the early stage of forming, the magnetic field auxiliary device (7) is set on the outer periphery of the bottom of the plunger (3); in the later stage of forming, the magnetic field auxiliary device (7) is set at the center of the bottom of the plunger (3); The plunger (3) includes an integrally connected lower section, middle section and upper section. The diameter of the lower section is the same as the inner diameter of the medium chamber (6), and the diameter of the middle section is smaller than that of the lower section and the upper section. The length of the middle section ranges from 200mm to 300mm; In the initial stage of forming, under the action of the magnetic field-assisted device (7), a non-uniform magnetic field distribution is generated in the cavity, so that the magnetorheological fluid (8) has different constitutive parameters at the center and the edge in the cavity; the constitutive parameters include the strength coefficient k and the strain rate sensitivity index m. The magnetorheological fluid (8) has different constitutive parameters at the center and the edge in the cavity, specifically: The strength coefficient k1 in the central region ranges from 0.02 to 0.15, and the strain rate sensitivity index m1 in the central region ranges from 0.55 to 0.

65. The strength coefficient k2 of the edge region ranges from 0.20 to 0.30, and the strain rate sensitivity index m2 of the edge region ranges from 0.45 to 0.

55. The relationship between the intensity coefficient k and the magnetic field strength B is as follows: ; The relationship between the strain rate sensitivity index m and the magnetic field strength B is as follows: ; In the later stage of forming, under the action of the magnetic field-assisted device (7), a non-uniform magnetic field distribution is generated in the cavity, so that the magnetorheological fluid (8) has different constitutive parameters at the center and the edge of the cavity; the constitutive parameters include the strength coefficient k and the strain rate sensitivity index m. The magnetorheological fluid (8) has different constitutive parameters at the center and the edge of the cavity, specifically: The strength coefficient k1 in the central region ranges from 0.20 to 0.30, and the strain rate sensitivity index m1 in the central region ranges from 0.45 to 0.

55. The strength coefficient k2 of the edge region ranges from 0.02 to 0.15, and the strain rate sensitivity index m2 of the edge region ranges from 0.55 to 0.

65. The relationship between the intensity coefficient k and the magnetic field strength B is as follows: ; The relationship between the strain rate sensitivity index m and the magnetic field strength B is as follows: .

2. The high strain rate-controllable soft mold coupling precision forming device for sheet metal according to claim 1, characterized in that, The die (11) is provided with an exhaust hole.

3. The high strain rate-controllable soft mold coupling precision forming device for sheet metal according to claim 1, characterized in that, A sealing ring (5) is provided between the medium chamber (6), the die (11), and the plunger (3).

4. The high strain rate-controllable soft mold coupling precision forming device for sheet metal according to claim 1, characterized in that, The plunger (3), pressure ring (4), medium chamber (6), and die (11) are made of non-magnetic steel, the magnetic field auxiliary device (7) is made of electrical pure iron, and the drive plate (2) is made of copper.

5. The high strain rate-controllable soft mold coupling precision forming device for sheet metal according to claim 1, characterized in that, The magnetorheological fluid (8) includes methyl silicone oil, hydroxyl iron powder and stabilizer; wherein the volume fraction of hydroxyl iron powder is 30%~50%.

6. A high strain rate-controllable soft mold coupling precision forming method for sheet metal based on the forming apparatus according to any one of claims 1-5, characterized in that, Includes the following steps: S1: Based on the shape of the part to be formed, process the corresponding matching die (11). Multiple magnetic field auxiliary devices (7) are installed along the annular edge on the lower side of the plunger (3), and the plunger (3) is installed in the medium chamber (6); S2: Apply a clamping force to the clamping ring (4) to clamp the plate (10), and pass current into the coil (9). Under the action of the magnetic field auxiliary device (7), a non-uniform magnetic field distribution is generated in the cavity, so that the magnetorheological fluid (8) has different constitutive parameters at the center and the edge in the cavity. S3: After the electromagnetic pulse generating unit (1) is charged and discharged, the strong pulse current generates a strong instantaneous magnetic field through the working coil, which drives the plate (2) to generate a downward impact force and impacts the plunger (3). The plunger (3) moves downward and squeezes the magnetorheological fluid (8), causing the plate (10) to deform under the pressure of the magnetorheological fluid and enter the die (11), so that the plate (10) and the die (11) are partially attached to each other, and the pre-forming is completed. S4: Disassemble the magnetic field auxiliary device (7) installed in S1, reinstall the magnetic field auxiliary device (7) at the bottom center of the plunger (3), adjust the current flowing into the coil (9), and under the action of the magnetic field auxiliary device (7), generate a non-uniform magnetic field distribution in the cavity, so that the magnetorheological fluid (8) has different constitutive parameters at the center and the edge in the cavity. S5: Adjust the electromagnetic pulse generating unit (1) to discharge, so that the drive plate (2) impacts the plunger (3) again. The plunger (3) descends at high speed to squeeze the magnetorheological fluid (8) to form a soft mold and squeeze the plate (10) so that the plate (10) and the die (11) fit together completely to achieve the forming requirements.

7. The high strain rate-controllable soft mold coupling precision forming method for sheet metal according to claim 6, characterized in that, In S2, the constitutive parameters include the strength coefficient k and the strain rate sensitivity index m. The magnetorheological fluid (8) has different constitutive parameters at the center and edge of the cavity, specifically: The strength coefficient k1 in the central region ranges from 0.02 to 0.15, and the strain rate sensitivity index m1 in the central region ranges from 0.55 to 0.

65. The strength coefficient k2 of the edge region ranges from 0.20 to 0.30, and the strain rate sensitivity index m2 of the edge region ranges from 0.45 to 0.

55. The relationship between the intensity coefficient k and the magnetic field strength B is as follows: ; The relationship between the strain rate sensitivity index m and the magnetic field strength B is as follows: .

8. The high strain rate-controllable soft mold coupling precision forming method for sheet metal according to claim 6, characterized in that, In S4, the constitutive parameters include the strength coefficient k and the strain rate sensitivity index m. The magnetorheological fluid (8) has different constitutive parameters at the center and edge of the cavity, specifically: The strength coefficient k1 in the central region ranges from 0.20 to 0.30, and the strain rate sensitivity index m1 in the central region ranges from 0.45 to 0.

55. The strength coefficient k2 of the edge region ranges from 0.02 to 0.15, and the strain rate sensitivity index m2 of the edge region ranges from 0.55 to 0.

65. The relationship between the intensity coefficient k and the magnetic field strength B is as follows: ; The relationship between the strain rate sensitivity index m and the magnetic field strength B is as follows: .

9. The high strain rate-controllable soft mold coupling precision forming method for sheet metal according to claim 6, characterized in that, In S5, when the formed part has one or more local feature areas, the number of impacts is increased according to the geometric features of the formed part, and the discharge energy range of the electromagnetic pulse generating unit (1) is 2~15kJ.

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