A forming method using magneto-rheological fluid pressure to suppress springback

Abstract

The application discloses a forming method and system for suppressing springback by using the pressure of magneto-rheological fluid, and belongs to the technical field of plate forming. By applying an intermittent constant magnetic field to the plate at the end of stamping forming and cooperating with the downward movement of the plunger, the effect of repeatedly adhering to the concave die under gradually increasing pressure is realized, so that the plate reduces the springback amount. In the process of adhering to the concave die, the residual stress in the plate is gradually released, the degree of springback is gradually reduced, and after repeated several times, the forming precision of the plate is improved and the springback amount of the plate is reduced, realizing efficient, economical and high-quality plate bending springback control. The whole adjusting process is short in time, does not need redundant calculation and die changing steps, correspondingly reduces the equipment and process cost, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of sheet metal forming technology, specifically relating to a forming method that uses magnetorheological fluid pressure to suppress springback. Background Technology

[0002] Bending is common in sheet metal stamping, and it is a process of bending sheet metal into a certain shape. Springback is a common problem during bending. This is partly because some residual stress and elastic deformation remain after processing, and partly due to the inherent properties of the sheet metal, namely its yield strength and modulus of elasticity. When the applied pressure is removed after forming, the release of residual stress within the sheet metal leads to springback, which can cause part failure. Therefore, the magnitude of springback depends on the amount of residual stress within the sheet metal before the pressure is released.

[0003] Currently, many low-plasticity metal sheets, during the forming process, exhibit low plasticity, leading to adverse phenomena such as springback in the formed parts. These phenomena result in low dimensional accuracy and even part failure. Therefore, effective measures are needed to prevent and control springback. Current methods for controlling springback include: first, selecting materials with low yield strength and high elastic modulus, and optimizing the local bending structure to reduce springback; second, using die compensation and over-bending methods to provide geometric compensation for springback; third, applying pressure to the sheet near the end of deformation to induce tensile strain in the deformed portion, reducing springback; and fourth, the tension-bending method, which uses external tension to bend the sheet, altering the internal stress distribution and converting compressive stress into tensile stress, ultimately controlling springback.

[0004] Current methods for controlling springback are time-consuming and expensive. Compensation methods require additional calculations to estimate the degree of springback after unloading the sheet material, and offer limited improvement in dimensional accuracy. Therefore, they cannot quickly, economically, or effectively control springback. It is necessary to explore an efficient and economical method for controlling bending springback. Summary of the Invention

[0005] In order to overcome the defects in the prior art, the present invention aims to provide a forming method that uses magnetorheological fluid pressure to suppress springback, which can create multiple springback suppression effects on the sheet metal, allowing the sheet metal to repeatedly conform to the die, gradually reducing springback, and achieving efficient and economical sheet metal bending springback suppression.

[0006] This invention is achieved through the following technical solution:

[0007] A forming method for suppressing springback using magnetorheological fluid pressure includes:

[0008] S1: Fix the die on the press worktable, place the medium chamber above the die, place the coil around the medium chamber and the die, and clamp the plate between the die and the medium chamber; install the plunger inside the medium chamber and fill the medium chamber with magnetorheological fluid;

[0009] S2: Apply downward pressure to the medium chamber to clamp the plate, and energize the coil to generate a magnetic field B1, so that the magnetorheological fluid becomes a soft mold;

[0010] S3: The plunger moves downward at a speed of V1, squeezing the magnetorheological fluid, causing the sheet to deform under the pressure of the magnetorheological fluid and enter the die cavity to fit into the cavity of the die. At this time, the peak value of the equivalent pressure on the sheet is P1.

[0011] S4: Adjust the current in the coil to reduce the magnetic field strength generated by the coil to 0. The plunger continues to move downward at a speed of V2 for a duration of T. Adjust the magnetic field strength generated by the coil to B2, so that the plunger continues to move downward at a speed of V3. At this time, the peak value of the equivalent pressure on the plate is P2 for a duration of T.

[0012] S5: Check the forming shape of the part, and repeat S4 several times according to the inspection results until the part is completely molded; turn off the coil, retract the plunger to the starting position, remove the magnetorheological fluid and remove the medium chamber, and take out the formed part.

[0013] Preferably, the magnetorheological fluid comprises methyl silicone oil, hydroxyl iron powder, and a stabilizer, wherein the volume fraction of hydroxyl iron powder is 30% to 50%.

[0014] Preferably, the magnetorheological fluid has an intensity coefficient of 0.02 to 0.2 and a strain rate sensitivity coefficient of 0.55 to 0.65.

[0015] Preferably, the equivalent pressure peak value P1 is directly proportional to the yield strength of the plate, the equivalent pressure peak value P1 is inversely proportional to the elastic modulus of the plate, and P2 > P1.

[0016] Preferably, the magnetic field strength B2 = B1 - B, where 0 < B < B1, B1 > 0.2T.

[0017] More preferably, B is proportional to the downward velocity V2 of the plunger and to the interval T of the magnetic field change.

[0018] Preferably, the interval T between the changes in the magnetic field is 2 to 8 seconds.

[0019] Preferably, V1 is 0.5 ~ 2.0 mm / s.

[0020] Preferably, V2 is 0.02 ~ 0.05 mm / s.

[0021] Preferably, V3 is 0.05 ~ 0.1 mm / s.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] This invention discloses a forming method for suppressing springback using magnetorheological fluid pressure. Taking advantage of the rapid response of magnetorheological fluid to a magnetic field, the mechanical properties of the fluid are altered by adjusting the magnetic field. Through plunger movement, the sheet metal repeatedly conforms to the die under the pressure of the magnetorheological fluid after bending, gradually reducing the degree of springback and releasing residual stress within the sheet, thus controlling the bending springback. This method does not require additional die compensation design, is suitable for controlling the bending springback of most low-plasticity materials, has a short adjustment time, and eliminates the need for additional calculations and die replacement steps, thereby reducing equipment and process costs.

[0024] Furthermore, the magnetorheological fluid comprises methyl silicone oil, hydroxyl iron powder, and stabilizers. The volume fraction of hydroxyl iron powder is 30% to 50%. This volume fraction of magnetorheological fluid has a good range for mechanical property regulation and can serve as a good mechanical transmission medium.

[0025] Furthermore, the magnetorheological fluid has an intensity coefficient of 0.02~0.2 and a strain rate sensitivity coefficient of 0.55~0.65. Under this constitutive relationship, the magnetorheological fluid can rapidly respond to changes in the magnetic field and the transmission of corresponding shock waves.

[0026] Furthermore, the equivalent pressure peak value P1 is directly proportional to the yield strength of the plate and inversely proportional to the elastic modulus of the plate, and P2 > P1. The range of the equivalent pressure peak value can be flexibly adjusted according to the different materials of the plate, namely the different yield strength and elastic modulus.

[0027] Furthermore, the magnetic field strength B2 = B1 - B, where 0 < B < B1, B1 > 0.2T. The range of values ​​for this magnetic field strength meets the requirements for changes in the mechanical properties of magnetorheological fluid and can be adjusted according to the interval between magnetic field changes and the downward speed of the plunger. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0029] Figure 2 This is a front view of the U-shaped forming device in the embodiment when it is fully assembled.

[0030] Figure 3 This is a front view of the device for completing the forming of the U-shaped part according to the embodiment;

[0031] Figure 4 This is a schematic diagram of the molded state at the end of the forming process of the U-shaped part in the embodiment.

[0032] Figure 5 This is a schematic diagram showing the correspondence between the magnetic field applied to the U-shaped component and the magnitude of the pressure in the embodiment.

[0033] Figure 6 This is a schematic diagram of the U-shaped component before and after springback, as shown in the embodiment.

[0034] Figure 7 This is a schematic diagram of the U-shaped component being re-molded after the magnetic field is changed, as shown in the embodiment.

[0035] Figure 8 This is a schematic diagram of the U-shaped component before and after its second springback, as shown in the embodiment.

[0036] Figure 9 This is a schematic diagram of the state of the U-shaped component before and after the nth springback, as shown in the embodiment.

[0037] Figure 10 This is a schematic diagram of the V-shaped forming mold structure.

[0038] In the diagram: 1 is the plunger, 2 is the medium chamber, 3 is the sealing ring, 4 is the coil, 5 is the magnetorheological fluid, 6 is the plate, and 7 is the die. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. These descriptions are intended to explain the invention and not to limit it.

[0040] like Figure 1 The present invention is explained in detail using a specific apparatus for implementing the forming method of suppressing springback by magnetorheological fluid pressure, which is an example of the present invention. This explanation does not constitute a limitation of the present invention. The method of the present invention can be implemented using any existing apparatus capable of performing its step-by-step functions.

[0041] The device includes a plunger 1, a medium chamber 2, a coil 4, a magnetorheological fluid 5, a plate 6, and a die 7. The die 7 is fixed on the press worktable, the medium chamber 2 is placed on the die 7, the coil 4 is placed around the medium chamber 2 and the die 7, and the plate 6 is sandwiched between the die 7 and the medium chamber 2. The plunger 1 is installed inside the medium chamber 2, and an annular groove is formed on the outer wall of the plunger 1, with a sealing ring 3 installed inside. The magnetorheological fluid 5 is filled into the medium chamber 2. The strength coefficient of the magnetorheological fluid 5 is... k The value range is 0.02~0.2, strain rate sensitivity coefficient m The value range is 0.55 to 0.65.

[0042] The following explanation uses the manufacturing process of the U-shaped component to further illustrate the invention:

[0043] like Figure 2 , 3 In this embodiment, a typical U-shaped bent part needs to be processed. When this part is processed using some metals with high yield strength, it will produce obvious springback. The die is designed according to the characteristics of this part. After the stamping is completed, a constant magnetic field is intermittently applied to the magnetorheological fluid and the plate is squeezed repeatedly by a plunger movement to make the plate re-fit the die, gradually reducing the springback and improving the part accuracy.

[0044] The specific processing steps are as follows:

[0045] S1: Fix the die 7 on the press worktable, place the medium chamber 2 on the die 7, place the coil 4 around the medium chamber 2, and sandwich the plate 6 between the die 7 and the medium chamber 2. Install the plunger 1 inside the medium chamber 2 and fill the medium chamber 2 with magnetorheological fluid 5;

[0046] S2: Press the medium chamber 2 and clamp the plate 6. The coil 4 is energized to generate a magnetic field B1 with a magnetic field strength of 0.3T, so that the magnetorheological fluid 5 becomes a soft mold with specific mechanical properties.

[0047] S3: The plunger 1 moves downward at a speed of V1=0.2mm / s, squeezing the magnetorheological fluid 5, and causing the plate 6 to deform under the pressure of the magnetorheological fluid 5 and enter the cavity of the die 7 to fit together. At this time, the peak value of the equivalent pressure on the plate 6 is P1=10Mpa.

[0048] S4: The plunger 1 continues to move downward at a speed of V2 = 0.02 mm / s. At the same time, the current flowing through the coil 4 is adjusted so that the magnetic field it generates drops to 0. After an interval of T = 5s, the magnetic field generated by the coil 4 is adjusted to B2 = 0.15T and the plunger 1 is adjusted so that the plunger 1 continues to move downward at a speed of V3 = 0.1 mm / s. At this time, the peak value of the equivalent pressure on the plate 6 is P2 = 12 MPa.

[0049] S5: After the magnetic field B2=0.15T generated by coil 4 lasts for 5 seconds, coil 4 is turned off, plunger 1 returns to the starting position, magnetorheological fluid 5 is removed and medium chamber 2 is removed, and the formed part is taken out.

[0050] The magnitude of the equivalent pressure peak P1 increases with increasing σs and decreases with increasing E, where σs is the yield strength of plate 6 and E is the elastic modulus of plate 6. Generally, the amount of springback after bending is directly proportional to the yield strength and inversely proportional to the springback modulus of plate 6. That is, when a material with larger σs and smaller E is used, the springback tendency of plate 6 is greater, and a larger equivalent pressure peak P2 is needed to control the springback of plate 6; conversely, when a material with smaller σs and larger E is used, the springback tendency of plate 6 is smaller, and a smaller equivalent pressure peak P2 is needed to complete the springback control.

[0051] The magnetic field B2 = B1 - generated by coil 4 B, where 0 < B < B1, B1 > 0.2T, the The magnitude of B is related to the plunger's descent speed V2 and the magnetic field change interval T. B increases with the increase of the descent speed V2 and the increase of the magnetic field change interval T. That is, the greater the descent speed V2 of the plunger, the greater the increase of the magnetic field change interval T. The larger the value of B, the greater the reduction in volume within the medium chamber. In this case, a smaller B2 is needed to enhance the mechanical properties of the magnetorheological fluid. The larger the value of B, the greater the magnetic field change interval T; conversely, the smaller the plunger's descent speed V2, the greater the change in magnetic field. The smaller the value of B, the less the volume decreases within the medium chamber. In this case, a larger B2 is needed to enhance the mechanical properties of the magnetorheological fluid. The smaller the value of B, the more consistent the time interval T between magnetic field changes.

[0052] When the U-shaped part is formed, sheet 6 will spring back. The springback of the U-shaped part mainly occurs in the R-corner area and the flat bottom area. Let the standard radius of the R-corner be R, and the radius after springback be approximately r. The radius after springback on the left side of the U-shaped part is r1, and the radius after springback on the right side is r2. The springback amount in the flat bottom area is d, which ranges from d1 to d10 from left to right. Figure 6 , 7 As shown in Figures 8 and 9, r1, r2, and d1~d10 continuously decrease under the action of intermittent equivalent pressure P, eventually completely conforming to the mold.

[0053] like Figure 5As shown, the changes in the magnetic field, the equivalent pressure on the sheet 6, and the piston movement are correlated throughout the forming process. The sheet 6 reaches its equivalent pressure peak P1 at the end of forming, and its equivalent pressure peak P2 at the end of the first cycle of the springback control stage. Under the intermittent constant magnetic field and the downward movement of the piston, the pressure in the medium chamber repeatedly decreases and increases. When the pressure inside the medium chamber decreases, the sheet springs back; when the pressure increases, the sheet re-fits the die. This alternation of pressure decrease and increase repeats. As the equivalent pressure gradually increases, the sheet repeatedly fits the die, and the amount of springback gradually decreases. When the residual stress inside the sheet is insufficient to cause springback, the sheet achieves a macroscopic bending springback effect. This invention utilizes the sensitivity of magnetorheological fluid to magnetic fields to control the bending springback of the sheet by applying a decaying magnetic field. This method is rapid, economical, and produces high precision after forming, while being applicable to most low-plasticity metal sheets.

[0054] like Figure 10 The present invention can also be used for forming processes such as V-shaped parts, by processing the cavity of the die 7 into the required shape.

[0055] It should be noted that the above description is only a part of the embodiments of the present invention, and all equivalent changes made to the system described in this invention are included within the protection scope of this invention. Those skilled in the art can make similar substitutions to the specific examples described, as long as they do not deviate from the structure of the invention or exceed the scope defined in these claims, all of which fall within the protection scope of this invention.

Claims

1. A forming method for suppressing springback using a magneto-rheological fluid pressure, characterized by, It comprises: S1: fixing the concave die (7) on the worktable of the press, placing the medium bin (2) above the concave die (7), placing the coil (4) on the periphery of the medium bin (2) and the concave die (7), and fixing and clamping the plate (6) between the medium bin (2) and the concave die (7); installing the plunger (1) inside the medium bin (2) and filling the medium bin (2) with the magnetorheological fluid (5); S2: applying downward pressure to the medium bin (2) to clamp the plate (6), and energizing the coil (4) to generate a magnetic field B1, so that the magnetorheological fluid (5) becomes a soft die; S3: the plunger (1) moves downward at a speed V1, extruding the magnetorheological fluid (5), so that the plate (6) deforms under the pressure of the magnetorheological fluid (5) and enters the concave die (7) and conforms to the cavity of the concave die (7), at this time the peak equivalent pressure of the plate (6) is P1, and V1 is 0.5-2.0 mm / s; S4: adjusting the current in the coil (4) to reduce the magnetic field strength generated by the coil (4) to 0, and continuing to move the plunger (1) downward at a speed V2 for a duration T, adjusting the magnetic field strength generated by the coil (4) to B2, and continuing to move the plunger (1) downward at a speed V3, at this time the peak equivalent pressure of the plate (6) is P2, the duration T, the interval time T of the magnetic field change is 2-8 s, V2 is 0.02-0.05 mm / s, and V3 is 0.05-0.1 mm / s; S5: checking the forming shape of the part, and repeating S4 several times according to the checking result until the part completely conforms to the die; turning off the coil (4), returning the plunger (1) to the starting position, taking out the magnetorheological fluid (5) and removing the medium bin (2), and taking out the formed part.

2. The forming method of claim 1, wherein the composition of the magnetorheological fluid (5) comprises methyl silicone oil, hydroxyl iron powder and a stabilizer, and the volume fraction of the hydroxyl iron powder is 30%-50%.

3. The forming method of claim 1, wherein the strength coefficient of the magnetorheological fluid (5) is 0.02-0.2, and the strain rate sensitivity coefficient is 0.55-0.

65. The peak equivalent pressure P1 is proportional to the yield strength of the plate (6), and inversely proportional to the elastic modulus of the plate (6), and P2>P1. The magnetic field strength B2=B1-ΔB, wherein 0<ΔB<B1, and B1>0.2T.

4. The forming method of claim 1 wherein the magnetic field is applied to the magnetorheological fluid by a plurality of electromagnets. ΔB is proportional to the downward speed V2 of the plunger (1) and the interval time T of the magnetic field change.

5. The forming method of claim 1 wherein the magnetic field is applied to the magnetorheological fluid by a plurality of electromagnets. ​ 6. The forming method of claim 5 wherein the magnetic field is applied to the magnetorheological fluid by a plurality of electromagnets. ​

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