A Tube Variable Axis Forming Device and Forming Method Based on Magnetorheological Elastomer

Abstract

The present invention discloses a tube variable-axis forming device and a forming method based on magnetorheological elastomer, belonging to the technical field of tube forming. The forming device includes a mold, a punch, a tube blank, a magnetorheological elastomer and an electromagnet. This method uses a magnetorheological elastomer to replace fillers such as polyurethane, metal particles and mandrels. According to the characteristics that the surface roughness and elastic modulus of the magnetorheological elastomer can be changed by an externally applied magnetic field, through this tube variable-axis forming device with magnetic field control, the internal pressure of the tube is regulated, and by changing the concentration of magnetic particles in the magnetorheological elastomer, the friction force between the inner and outer sides of the tube bending and the filler is adjusted. According to the characteristics of the bending radius, tube blank diameter and wall thickness of the part, through the cooperation between the feeding of the plunger and the externally applied magnetic field, the forming effect of the part can be effectively guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of pipe forming, and specifically to a pipe variable-axis forming device and forming method based on magnetorheological elastomer. Background Technique

[0002] In recent years, industries such as aerospace, nuclear energy engineering, and automotive engineering have developed rapidly, and the demand for high-performance lightweight metal pipe parts has been increasing day by day. Traditional forming techniques for pipe parts include bending processes, press bending processes, roll bending processes, and stretch bending processes, etc. However, these processes all have their own limitations, restricting their application scope. When facing some pipe parts with characteristics of large diameter, relatively small wall thickness, and relatively small bending radius, the formed bent pipes may have defects such as excessive thinning on the outer side of the bend, wrinkling on the inner side, and cross-sectional distortion.

[0003] Chinese invention patent CN 110576089 A discloses a push-bending forming method for large-diameter small-bending-radius thin-walled bent pipes assisted by particle fillers, which uses pressure-holding punches on both sides to feed to achieve internal pressure control, and adjusts the stress state during pipe bending by real-time control of the axial force of the pipe by the pusher and the pressure of the particle fillers. However, the two punches required by this method are not in the same direction, and additional devices are needed to achieve the experimental conditions, thus increasing the production cost. Summary of the Invention

[0004] In order to solve the above deficiencies of the existing technology in the pipe bending process, the purpose of the present invention is to provide a pipe variable-axis forming device and forming method based on magnetorheological elastomer. Magnetorheological elastomer is used as the internal filler during the pipe forming process. Through the cooperation of an electromagnet and a punch, the stress state during the pipe deformation process is changed, and the variable-axis forming of pipe parts is realized. Among them, the magnetorheological elastomer can be prefabricated so that the concentration of local magnetic particles is different, thereby differentiating the local stress on the pipe blank and controlling the local flow ability of the material. This method has improved efficiency compared with traditional bending processes and press bending processes, and can effectively improve the forming performance of pipes, further improving the thickness distribution of the formed parts. For some bent pipe parts with characteristics of large diameter, relatively small wall thickness, and relatively small bending radius, multiple processes may be required. This method can reduce the processes, and can ensure the surface quality of the parts and improve the part stiffness.

[0005] To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0006] A tube variable-axis forming device based on magnetorheological elastomer, comprising a mold, a punch, a tube blank, a magnetorheological elastomer and an electromagnet; wherein: the mold includes a front mold and a rear mold (the mold closing method is split mold closing), the front mold and the rear mold are mirror-symmetric structures, and a tube bending cavity is formed inside after mold closing; the punch is horizontally placed, and the feeding direction is horizontal; the magnetorheological elastomer is placed in contact with the inner wall of the tube blank to be formed; one end of the tube blank is sealed, and the punch pushes the magnetorheological elastomer in the tube blank to make it fit against the sealed end of the tube blank, and the internal pressure of the tube blank is provided by the magnetorheological elastomer; there are two electromagnets, which are respectively arranged above and below the cavity and the mold.

[0007] The size of the electromagnet is equivalent to that of the mold, and the magnetic field action range generated by it is larger than the working area of the forming device; the input current of the electromagnet is 0 - 30A, and the magnetic induction intensity range generated in the mold cavity is 0 - 2T.

[0008] The shape of the magnetorheological elastomer is adapted to the mold cavity. The magnetic particles in the magnetorheological elastomer are ferromagnetic micron-scale particles such as hydroxyl iron powder or carbonyl iron powder; the concentration range of the magnetic particles in the magnetorheological elastomer is 0% - 80%, and the concentration distribution method is uniform concentration in each part or locally variable concentration; when the magnetic particles in the magnetorheological elastomer are locally variable concentration distribution, the magnetic particle distribution methods are up-and-down distribution (different concentrations in the upper and lower parts) or left-and-right distribution (different concentrations in the left and right parts), etc.

[0009] The materials of the mold and the punch are non-magnetic metal materials such as superalloy, austenitic stainless steel or aluminum alloy.

[0010] The punch is an equal-diameter punch or a stepped punch. If it is a stepped punch, its maximum diameter is smaller than the diameter of the mold cavity. For the stepped punch, the outer diameter size change range is 10 - 300mm, and the inner diameter is 1 - 8mm smaller than the outer diameter.

[0011] The length L of the tube blank should be greater than the sum of the central axis arc length of the bending section of the mold cavity and the straight line section lengths at both ends of the bent tube after forming.

[0012] The method for forming a tube with a variable axis based on a magnetorheological elastomer using the forming device includes the following steps:

[0013] (1) Prepare the tube blank to be formed: the length of the tube blank should be greater than the sum of the central axis arc length of the bending part of the cavity and the straight line section lengths at both ends of the bent tube after forming, and one end of the tube blank is sealed by welding;

[0014] (2) Adjust the distribution method and distribution concentration of the magnetic particles inside the magnetorheological elastomer according to the bending structure characteristics of the tube and the relative bending radius of the tube;

[0015] (3) Place the magnetorheological elastomer in step (2) inside the tube blank, then place the tube blank in the mold cavity, and then close the mold.

[0016] (4) Align the center of the punch with the center of the magnetorheological elastomer, push the tube blank to move, and at the same time, apply a magnetic field. According to the bending structure characteristics and deformation characteristics of the tube, the performance of the magnetorheological elastomer is changed in real time; through the cooperation of the magnetic field and the punch feed, the tube gradually deforms in the cavity.

[0017] (5) Withdraw the punch, open the mold, and take out the formed part.

[0018] The design mechanism of the present invention is as follows:

[0019] The magnetorheological elastomer is a polymer composite material with magnetic particle additives. Compared with its matrix material, the performance of the magnetorheological elastomer can be changed by applying a magnetic field. Regarding the surface roughness of the magnetorheological elastomer, under the action of a magnetic field, the magnetic particles in the magnetorheological elastomer are prone to form magnetic dipole pairs and generate mutual forces, resulting in microscopic changes on the surface of the magnetorheological elastomer, thereby changing the surface roughness. During the bending deformation process of the tube, using a magnetorheological elastomer with adjustable surface roughness as the internal filler can realize the function of real-time adjusting the friction force between the magnetorheological elastomer and the tube, and further improve the fluidity of the material to avoid the defect of excessive thinning. At the same time, under the action of a magnetic field, the elastic modulus of the magnetorheological elastomer changes, realizing the function of real-time adjusting the internal pressure of the tube.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. Compared with the traditional tube bending forming process with internal fillers, the present invention uses a magnetorheological elastomer as the internal filler, which can realize the functions of real-time controlling the elastic modulus and surface friction of the internal filler. According to parameters such as the wall thickness, diameter, and relative bending radius of the bent tube, by changing the magnitude of the applied magnetic field, the stress state of the tube during bending is changed in real time, so as to accurately control the bending deformation of the tube.

[0022] 2. The device of the present invention is simple, the reaction of the magnetic field regulating the internal filler is rapid, effectively reducing the production cost, shortening the process flow, having high forming efficiency, and the surface quality of the formed plate-like parts is good and the forming accuracy is high.

[0023] 3. The present invention can formulate a magnetorheological elastomer filler with a corresponding locally non-uniform magnetic particle concentration according to the tube structure, thereby changing the friction coefficient and elastic modulus of the magnetorheological elastomer in a local range, making the material more likely to flow to the position with a large deformation and obvious thinning, effectively preventing the excessive thinning of the part thickness, and increasing the strength and stiffness of the formed part. Description of the Drawings

[0024] Figure 1 Schematic diagram of the variable-axis forming device of the present invention. At this time, the cavity is closed with the mold, and the pipe has not deformed.

[0025] Figure 2 Schematic diagram of the variable-axis forming process of the present invention. At this time, the pipe deforms at the bending part of the mold cavity.

[0026] Figure 3 Schematic diagram of the variable-axis forming process of the present invention. At this time, the pipe completely enters the mold cavity and bends.

[0027] In the figure: 1 - mold; 2 - punch; 3 - tube blank; 4 - high-density magnetorheological elastomer; 5 - low-density magnetorheological elastomer; 6 - electromagnet. Specific embodiments

[0028] The following will describe the present invention in detail with reference to the accompanying drawings. However, the present invention is not limited to the variable-axis forming of the following one kind of part, and is equally applicable to pipe parts with the same type but different structural features and dimensions.

[0029] The present invention is improved based on the pipe push-bending forming process, uses magnetorheological elastomer as the internal filler, and adds an electromagnet outside the mold. Through the cooperation of the magnetic field and the punch, the variable-axis forming of the part is completed. The structure of the pipe variable-axis forming device proposed by the present invention is as Figure 1 shown. The forming device includes a mold 1, a punch 2, a tube blank 3, a magnetorheological elastomer and an electromagnet 6; wherein: the mold includes a front mold and a rear mold (the closing method is split closing), the front mold and the rear mold are mirror-symmetrical structures, and a pipe bending cavity is formed inside after closing; the punch is placed horizontally, and the feeding direction is horizontal; the magnetorheological elastomer is placed in contact with the inner wall of the tube blank to be formed; one end of the tube blank is sealed, and the punch pushes the magnetorheological elastomer in the tube blank to make it fit against the sealed end of the tube blank, and the internal pressure of the tube blank is provided by the magnetorheological elastomer; there are two electromagnets, which are respectively arranged above and below the cavity and the mold.

[0030] The size of the electromagnet is equivalent to that of the mold, and the magnetic field action range generated by it is larger than the working area of the forming device; the input current of the electromagnet is 0 - 30 A, and the magnetic induction intensity range generated in the mold cavity is 0 - 2 T.

[0031] The shape of the magnetorheological elastomer is adapted to the mold cavity. The magnetic particles in the magnetorheological elastomer are ferromagnetic micron-scale particles such as hydroxyl iron powder or carbonyl iron powder; the concentration range of the magnetic particles in the magnetorheological elastomer is 0% - 80%, and the concentration distribution method is uniform concentration in each part or local variable concentration; when the magnetic particles in the magnetorheological elastomer are distributed with local variable concentration, the local concentration distribution method of the magnetic particles is different up and down, such as Figure 1As shown, the upper half of the tube blank is a high-density magnetorheological elastomer (i.e., a relatively high concentration of magnetic particles) 4, and the lower half of the tube blank is a low-density magnetorheological elastomer (i.e., a relatively low concentration of magnetic particles) 5; alternatively, the distribution pattern of the magnetic particles is such that the concentrations on the left and right parts are different, etc.

[0032] The materials of the die and the punch are non-magnetic metal materials such as superalloys, austenitic stainless steels, or aluminum alloys.

[0033] The punch is a punch with a constant diameter or a stepped punch. If it is a stepped punch, its maximum diameter is smaller than the diameter of the die cavity. For the stepped punch, the range of variation of its outer diameter is 10 - 300 mm, and the inner diameter is 1 - 8 mm smaller than the outer diameter.

[0034] The length L of the tube blank should be greater than the sum of the arc length of the central axis of the bent section of the die cavity and the lengths of the straight sections at both ends of the bent tube after forming.

[0035] Example 1

[0036] This example is a method for bending a tube using the Figure 1 forming device in, and is specifically implemented according to the following steps:

[0037] Step 1: Cut the tube blank 3. The length of the tube blank should be greater than the sum of the arc length of the central axis of the cavity bend and the lengths of the straight sections at both ends of the bent tube after forming. One end of the tube blank can be sealed by welding. Since the outer side of the tube is thinned under tension during the bending process, to avoid excessive thinning and cracking, the material on the outer side of the tube can be appropriately increased.

[0038] Step 2: Design the distribution pattern and concentration of the magnetic particles inside the magnetorheological elastomer according to the forming characteristics of the tube and the relative bending radius of the tube. For example, the magnetorheological elastomer can be designed to be of the type with a dense inner part and a sparse outer part. In this way, the surface roughness of the low-density magnetorheological elastomer 5 under the magnetic field is higher than that of the high-density magnetorheological elastomer 4, which helps the flow of the material on the outer side of the tube and avoids thinning of the tube.

[0039] Step 3: Place the magnetorheological elastomer obtained in step (2) inside the tube blank, then place the tube blank in the die cavity, and then close the die 1.

[0040] Step 4: The diameter of the punch 2 is equal to the inner diameter of the tube. The center of the punch 2 is aligned with the center of the magnetorheological elastomer, and the tube blank 3 is pushed to move to the right. At the same time, the electromagnet 6 applies a magnetic field. According to the structural characteristics and deformation characteristics of the bent tube, the magnitude of the applied magnetic field is changed to control the elastic modulus and Poisson's ratio of the magnetorheological elastomer. Since the magnetorheological elastomer will maintain a fixed strain after the maximum diameter of the punch contacts the tube blank, changing its elastic modulus can control the stress magnitude, and thus the internal pressure of the tube can be adjusted in real time. Through the cooperation of this magnetic field and the punch feed, the tube is gradually deformed in the cavity.

[0041] Step 5: Withdraw the punch 2, open the die 1, and take out the formed part.

[0042] The inner surface of the part formed in this embodiment is smooth. Compared with the method of pushing and bending a pipe filled with particles, this method will not cause damage to the inner surface of the pipe. In addition, by reasonably regulating the magnitude of the magnetic field, the thickening rate of the inner side of the formed pipe decreases (the inner side thickening rate is less than 30%), the thinning rate of the outer side of the bend decreases (the outer side thinning rate is less than 30%), the wall thickness distribution is uniform, and there is no wrinkling phenomenon.

Claims

1. A tube variable-axis forming device based on magnetorheological elastomers, characterized in that: The forming device includes a mold, a punch, a tube blank, a magnetorheological elastomer, and an electromagnet; wherein: the mold includes a front mold and a rear mold, the front mold and the rear mold are mirror-symmetrical structures, and a tube bending cavity is formed inside after mold closing; the punch is placed horizontally, and the feeding direction is horizontal; the magnetorheological elastomer is placed in contact with the inner wall of the tube blank to be formed; one end of the tube blank is sealed, and the punch pushes the magnetorheological elastomer inside the tube blank to make it contact with the sealed end of the tube blank, and the internal pressure of the tube blank is provided by the magnetorheological elastomer; there are two electromagnets, which are respectively arranged above and below the cavity and the mold; the length L of the tube blank should be greater than the sum of the arc length of the middle axis of the bending section of the mold cavity and the straight-line section lengths at both ends of the bent tube after forming. The shape of the magnetorheological elastomer is adapted to the mold cavity. The magnetic particles in the magnetorheological elastomer are ferromagnetic micron-scale particles such as hydroxyl iron powder or carbonyl iron powder; the concentration range of the magnetic particles in the magnetorheological elastomer is 0%-80%, and the concentration distribution method is uniform concentration in each part or locally variable concentration; when the magnetic particles in the magnetorheological elastomer are locally variable concentration distribution, the magnetic particle distribution method is up-down distribution or left-right distribution.

2. The tube variable-axis forming device based on magnetorheological elastomer according to claim 1, wherein: The size of the electromagnet is comparable to that of the mold, and the magnetic field action range generated by it is greater than the working area of the forming device; the input current size of the electromagnet is 0-30A, and the magnetic induction intensity range generated in the mold cavity is 0-2T.

3. The tube variable-axis forming device based on magnetorheological elastomer according to claim 1, characterized in that: The materials of the mold and the punch are non-magnetic metal materials such as superalloy, austenitic stainless steel or aluminum alloy.

4. The tube variable-axis forming device based on magnetorheological elastomer according to claim 1, characterized in that: The punch is an equal-diameter punch or a stepped punch. If it is a stepped punch, its maximum diameter is smaller than the diameter of the mold cavity.

5. The tube variable-axis forming device based on magnetorheological elastomer according to claim 1, characterized in that: The punch is a stepped punch, and the variation range of its outer diameter size is 10-300mm, and the inner diameter is 1-8mm smaller than the outer diameter.

6. A method for forming a tube with a variable axis based on magnetorheological elastomer using the forming device according to any one of claims 1-5, characterized in that: This forming method includes the following steps: (1) Prepare the tube blank to be formed: the length of the tube blank should be greater than the sum of the arc length of the middle axis of the bending part of the cavity and the straight-line section lengths at both ends of the bent tube after forming, and one end of the tube blank is sealed by welding. (2) Adjust the distribution method and distribution concentration of the magnetic particles inside the magnetorheological elastomer according to the bending structure characteristics of the tube and the relative bending radius of the tube. (3) Place the magnetorheological elastomer in step (2) inside the tube blank, then place the tube blank in the mold cavity, and then close the mold. (4) Align the center of the punch with the center of the magnetorheological elastomer, push the tube blank to move, and at the same time, apply a magnetic field. According to the structural characteristics and deformation characteristics of the bent tube, the performance of the magnetorheological elastomer is changed in real time; through the cooperation of the magnetic field and the punch feeding, the tube gradually deforms in the cavity. (5) Withdraw the punch, open the mold, and take out the formed part.

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