CN106825160A - The method for reducing bend pipe cross section distortion using magnetorheological packing material - Google Patents

Abstract

A method for reducing the cross-sectional distortion of a bent pipe by using a magnetorheological filling material, comprising the following steps: (1) injecting a magnetorheological material into the inner cavity of a pipe to be bent, and sealing both ends of the pipe with rubber plugs; (2) placing the pipe Put it into the corresponding position of the bending mold; (3) energize the induction coil fixed on the side of the pipe and generate a magnetic field, apply a magnetic force to the deformation area of the pipe, and change the rheological characteristics of the magnetorheological material in the pipe; (4) Perform bending, adjust the current to change the magnetic field strength, and adjust the rheological properties of the magnetorheological material in real time; (5) After the bending is completed, turn off the current and take the pipe out of the bending mold; (6) Remove the rubber at both ends of the pipe Stopper, pour out the magnetorheological material and collect it in a special container for recovery. The invention is suitable for various bending processes such as winding, pressing and stretching, can reduce the section distortion of the bent pipe, is convenient to operate, and the magnetorheological fluid can be used repeatedly with low cost.

Description

A Method for Reducing Sectional Distortion of Elbows Using Magnetorheological Filling Materials

technical field

The invention belongs to the field of metal plastic forming, and in particular relates to a method for reducing the cross-sectional distortion of an elbow by using a magneto-rheological filling material.

Background technique

Bend pipe fittings are a type of hollow profile parts that are widely used. They are usually made by bending and plastically deforming straight pipe blanks by using some plastic forming method. So far, according to different needs, people have developed a variety of pipe bending methods such as winding, pressing, rolling and stretching, and have been widely used in production practice. However, due to the thin-walled and hollow special structural form of the pipe, the existing pipe bending methods have corresponding limitations in practical application, especially the bending quality is difficult to meet the requirements of precision. For example, in these pipe bending methods, different types and degrees of forming defects often appear in the deformation zone when the tube blank is bent, including cross-sectional distortion (flattening or ovalization), local collapse, inner wrinkles, and outer cracks. It is especially serious when bending with a small radius of curvature with a large degree of deformation. For the bending of thin-walled tubes in the form of rectangular equal cross-sections, there are also other forms of defects such as twisting. These forming defects not only affect the appearance of the product and reduce the precision of the workpiece, but also lead to a decrease in the bearing capacity of the tube structure, seriously affecting its service performance.

The flattening of the section during bending of the tube blank exists in almost all bending processes. In order to reduce this section distortion, various methods have been proposed, such as using reverse deformation mold grooves, adding a mandrel inside the tube blank or filling steel balls, sand and other fillers. However, these methods either have very limited effects on improving the distortion of the curved section, or lose their practical value due to difficult operation, or are prone to pipe wall rupture due to the uncontrollable increase in internal pressure caused by the filler. In short, the existing methods are difficult to meet the requirements of precision forming of pipe fittings in practice.

Magnetorheological material (Magnetorheological material) is a new type of material whose rheological properties will change drastically under the action of an external magnetic field, including magnetorheological fluid, magnetorheological elastomer, and powder with ferromagnetic effect. Among them, the magnetorheological fluid is a Newtonian liquid that can flow freely without the action of an external magnetic field, but under the action of a strong magnetic field, the magnetorheological fluid can change from liquid to semi-solid or even solid in an instant (milliseconds), showing a controllable yield strength, and this change is reversible. Utilizing the special properties of magnetorheological fluid, it has been used in a wide range of fields including automobile damping and shock absorption, bearing sealing and so on. The initial state of the magnetorheological elastomer is a solid elastomer, and its yield strength will also change instantaneously with the change of the applied magnetic field.

Soft molding is a special sheet plastic forming process that uses different types of substances such as gas, fluid (such as liquid water or oil), viscous medium, solid polyurethane rubber, and discrete particles as pressure transmission media to bulge thin-walled parts. , can obtain thin-walled parts such as corrugated pipes that are difficult to form by ordinary sheet metal stamping methods. However, traditional force transmission media such as gas, water or oil, viscous medium, solid polyurethane rubber, and discrete particles are only suitable for a certain range of sheet forming processes, and there are generally problems such as difficult sealing and poor force transmission effect. Due to the above-mentioned special properties of magnetorheological materials, in recent years there have also been researches on applying them as pressure transmission media to soft mold forming processes such as thin plate bulging, such as Chinese patent CN102615164A (a soft mold forming of magnetorheological fluid for plates device and method), CN103273644A (a device and method for soft mold forming of a plate based on a magnetorheological elastomer), CN104874662A (a device and method for forming a special-shaped plate with magnetic medium damping), etc. However, the main purpose of applying magnetorheological fluid/elastomer as pressure transmission medium to soft mold forming is to solve the problems of difficult sealing and poor force transmission effect of traditional pressure transmission medium. In addition, magnetorheological materials have not been applied in other aspects of the field of sheet metal forming.

Contents of the invention

The invention provides a method for reducing the section distortion of the bent pipe by using the magneto-rheological filling material aiming at the requirement of forming the precise bent pipe. In order to achieve the above object, the present invention comprises the following steps:

(1) The magnetorheological material is injected into the inner cavity of the pipe fitting to be bent, and the two ends of the pipe fitting are sealed with rubber plugs. The magnetorheological material can be magnetorheological fluid, iron powder and steel balls with ferromagnetic effect;

(2) Put the pipe fittings into the corresponding position of the bending mold;

(3) Energize the induction coil fixed on the side of the pipe fitting, apply magnetic force to the bending deformation zone of the pipe fitting by using the magnetic field generated by the induction coil, and change the rheological properties of the magnetorheological material inside the pipe fitting;

(4) Bending the pipe fittings with a bending die. While the pipe is deforming, the magnetic field strength can be changed by adjusting the current in the induction coil, and the rheological characteristics of the magnetorheological material in the pipe can be adjusted, so as to control the internal pressure of the pipe bending deformation area in real time and minimize the pipe deformation. The purpose of the distortion of the area section;

(5) After the bending operation is completed, the current passing through the induction coil is turned off, and the pipe is taken out from the bending mold at the same time;

(6) Remove the rubber plugs at both ends of the pipe fitting, pour out the magnetorheological material in the inner cavity of the pipe fitting and collect it in a special container for recovery.

The invention has the following beneficial effects: the magnetorheological material is used as the filling body of the inner cavity when the hollow pipe is bent, which can provide support for the deformation zone when the pipe is bent. The rheological mechanical properties of magnetorheological materials can realize the intelligent regulation of the internal pressure of pipe fittings, thereby reducing the cross-sectional distortion of pipe fittings and other forming defects, and meeting the needs of precision bending pipe forming. In addition, since the magnetorheological material has good fluidity without the action of a magnetic field, the filling and removal of the magnetorheological material in the pipe fittings can be easily realized, and the magnetorheological material can be recycled and used repeatedly. low cost. The invention is suitable for various types of thin-walled pipe bending processes such as winding, stretching and pressing.

Description of drawings

Below in conjunction with accompanying drawing, the present invention will be further described.

Fig. 1 is a schematic diagram of using magnetorheological fluid to fill and control the distortion of the cross-section of the pipe fittings in the present invention;

Fig. 2 is a schematic diagram of the present invention using magnetorheological fluid filling to control the deformation of the section of the pipe fittings during bending;

Fig. 3 is the cross-sectional shape of the deformation zone of the tube blank after the MR fluid-filled tube is bent and formed by the finite element simulation.

From Fig. 1 to Fig. 2, 1—bending die, 2—clamping insert around bending die, 3—clamping block around bending die, 4—induction coil, 5—pressure die, 6—pipe fitting, 7—magnetorheological fluid, 8—rubber plug, 9—wrinkle-proof block, 10—bending die, 11—roller.

detailed description

Taking the bending and bending forming of pipe fittings (6) as examples, the method of using magnetorheological material as the filling medium to realize the internal pressure regulation and reduce the distortion of the bent pipe section in the present invention will be described.

In the two embodiments, the magnetorheological material used is magnetorheological fluid (7) obtained by mixing iron powder and silicone oil, and its Young's modulus is 1500MPa. The induction coil (4) is a DC coil, and the variation range of the magnetic field strength B applied to the pipe fitting (6) is 0-14000Gs, and the variation range of the shear yield strength K of the magnetorheological fluid (7) corresponding to different magnetic field strengths B is 0.003-0.2 MPa, the Coulomb friction coefficient μ between the magnetorheological fluid (7) and the inner wall of the pipe fitting (6) varies linearly with K, and the range is 0.38-0.5.

After the pipe fitting (6) is bent and formed, the calculation method of the ellipticity Φ of the cross section of the deformation zone is as follows:

Φ＝(D _max -D _min )/D _max ×100％

D _max and D _min are respectively the major axis and the minor axis of the cross-sectional ellipse at the middle position of the deformation zone of the pipe fitting (6) after bending.

Example 1 - Bending

The material of the bending forming pipe is Al 6061 aluminum alloy, the outer diameter is 18mm, the wall thickness is 2mm, the density is 2.89g/mm ² , the Poisson’s ratio v is 0.33, the Young’s modulus is 68900MPa, the yield strength is 65MPa, and the bending angle is uniform. is 90°.

The steps of bending forming are as follows:

1. Inject magnetorheological fluid (7) into the inner cavity of the pipe fitting (6) to be bent, and seal both ends of the pipe fitting (6) with cylindrical rubber plugs (8);

2. Put the pipe fitting (6) into the bending forming mold, that is, the bending mold (1), the clamping insert of the bending mold (2), the clamping block of the bending mold (3), the pressure mold (5) and the anti-wrinkle block ( 9) the corresponding position between;

3. Apply power to the DC induction coil (4) fixed on the side of the pipe fitting (6), and use the magnetic field generated by the DC induction coil (4) to exert a magnetic force on the bending deformation zone of the pipe fitting (6), thereby changing the internal magnetic current of the tube blank The rheological properties of variable liquid (7);

4. Use the bending mold to perform bending and forming operations on the pipe fitting (6), and at the same time adjust the current in the induction coil (4), and control the rheological properties of the magnetorheological fluid (7) inside the pipe fitting (6) in real time by changing the magnetic field strength ;

5. After the bending operation is completed, the pipe fitting (6) is taken out from the pipe bending mold, and the current passing through the induction coil (4) is turned off;

6. Remove the rubber plugs (8) at both ends of the pipe fitting (6), pour the magnetorheological fluid (7) in the inner cavity of the pipe fitting (6) into a special container, and recycle the magnetorheological fluid (7).

The following table shows the numerical simulation results of the bending radii of 70mm, 40mm and 30mm respectively. It can be seen that when the magnetorheological fluid (7) is not filled, the ellipticities of the pipe fittings (6) after bending under the three bending radii are 12.08, 16.93 and 20.18 respectively; after adding the magnetorheological fluid (7), the ellipticity Φ appears The sharp drop indicates that the section distortion of the pipe fitting (6) after bending has been effectively controlled.

Example 2 - Bending

The outer diameter of the pipe fitting (6) is 18mm, the wall thickness is 2mm, the material is 20 steel, the density is 7.85g/mm ² , the Poisson’s ratio v is 0.3, the Young’s modulus is 206000MPa, the yield strength is 275MPa, and the bending angle is 90°. The steps of bending and forming are the same as before.

The attached table shows the numerical simulation results of bending with bending radii of 70mm, 50mm and 30mm respectively. In the table, K is the shear yield stress of the magnetorheological fluid (7) under the corresponding magnetic field strength, and μ is the Coulomb friction coefficient between the magnetorheological fluid (7) and the pipe wall under the corresponding magnetic field strength.

When the magnetorheological fluid (7) is not filled, the bending ellipticity Φ of the pipe fitting (6) under three bending radii is 5.49, 7.93 and 14.01 respectively, and after adding the magnetorheological fluid (7), the ellipticity Φ decreases, Sectional distortion is reduced.

Claims (3)

1. A method utilizing magnetorheological filling material to reduce the distortion of the elbow section, characterized in that, the method is realized through the following steps: (1) Inject the magnetorheological material into the inner cavity of the pipe fitting to be bent, and seal the two ends of the pipe fitting with rubber plugs; (2) Put the pipe fittings into the corresponding position of the bending mold; (3) Energize the induction coil fixed on the side of the pipe fitting, apply magnetic force to the bending deformation zone of the pipe fitting by using the magnetic field generated by the induction coil, and change the rheological properties of the magnetorheological material inside the pipe fitting; (4) Bending the pipe fittings by using a bending die; (5) After the bending operation is completed, the current passing through the induction coil is turned off, and the pipe is taken out from the bending mold at the same time; (6) Remove the rubber plugs at both ends of the pipe fitting, pour out the magnetorheological material in the inner cavity of the pipe fitting and collect it in a special container for recovery. 2. The method for reducing the cross-sectional distortion of an elbow by using a magnetorheological filling material as claimed in claim 1, characterized in that: said magnetorheological material can be magnetorheological fluid, and iron powder with ferromagnetic effect and steel ball. 3. The method of using magnetorheological filling materials to reduce the distortion of the elbow section as claimed in claim 1, characterized in that: while the pipe is deformed, the magnetic field strength can be changed by adjusting the current in the induction coil, and the inner diameter of the pipe can be adjusted. Rheological properties of magnetorheological materials.