Die for double-angle bending of flat parts

Abstract

FIELD: mechanical engineering.SUBSTANCE: used in the manufacture of parts from flexible sheet material. The die contains a punch with a lateral undercut, a container, an ejector and two elastic curved slats. The lower part of the slats is rigidly fixed in the container. The upper working part of the slats is made rounded along the radius. The bending angle of the said upper working part and the angle of the lateral undercut of the punch are greater than the springback angle of the part.EFFECT: improving the quality of the obtained parts.1 cl, 7 dwg

Description

[0001] The invention relates to the field of mechanical engineering and is intended for the production of a wide range of U-, S-, V-, U-shaped parts obtained by bending from sheet material and widely used in aircraft construction, rocket construction, shipbuilding, petrochemical and agricultural engineering and other fields.

[0002] The accuracy of angular dimensions depends on the correct accounting for springback compensation of the workpieces during bending. The most radical method of springback compensation is bending at angles less than 90° by additionally moving the bending tools at the end of the bend. However, the use of such systems is limited due to increased cost and decreased dies' performance. The advantage of these systems is the ability to adjust the bending angle. Furthermore, bending in such dies can damage the workpiece surface, which is unacceptable in some cases.

[0003] A two-angle bending scheme with a hinged connection of bending tools is known (patent No. 784967, IPC B21D 22 / 02, published 07.12.80), which allows to avoid damage to the surface of the workpieces.

[0004] The disadvantage of this patent is the impossibility of regulating the bending angle, i.e. the springback is always compensated for equally, therefore the accuracy of the angular dimensions depends on the stability of the properties and thickness of the workpieces.

[0005] Dies for U-shaped bending with simultaneous elastic bending of the bottom part of the product, the straightening of which compensates for springback and ensures parallelism of the walls, have become widely used (patent No. 1706750, MKI B21D 22 / 02, published on 23.01. and patent No. 297557, MKI B21D 5 / 01, published on 16.01.92).

[0006] The disadvantage of these schemes is the exclusion of the possibility of regulating the springback compensation in case of instability of the workpiece properties.

[0007] Methods for manufacturing U-shaped parts are known (patent No. 1750789, MKI B21D 22 / 02, published on July 30, 1992 and patent No. 1655597, MKI B21D 5 / 00 published on June 15, 1991), which indicate that the parallelism of the walls of U-shaped section products can be ensured by pulling the blanks into gaps that are 3-5% smaller than the thickness of the material being bent.

[0008] The disadvantage of these methods is that they are not applicable to parts whose outer surfaces must not have burrs or scratches. In this case, it is recommended to create residual stress fields in the areas of the workpiece to be bent, which reduce or completely eliminate springback during bending. This is achieved by pressing the projections of the stamping tool into the bending areas to a depth of 0.05-0.10 mm of the workpiece thickness, with the deformation zones being 1.3-2.0 times the length of the internal curved section of the workpiece.

[0009] There is a method (RU Patent No. 2078634, IPC B21D 22 / 02, published March 10, 2002) in which, to compensate for springback, the central portion of the workpiece is pressed, the end sections are freely bent, and then pulled into a die. Moreover, the bending of the end sections during the free bending stage is achieved by the edges of the punch and die, with a distance between them equal to three times the length of the developed radius of the part.

[0010] This method has the disadvantage of needing to accurately capture the gap Z, since if the gap is insufficient there will be underbending, and if there is excessive gap there will be overbending.

[0011] A known method for bending sheet material using flat plates (patent SU 1526870 A1, B21D 5 / 01, published July 12, 1989) is aimed at improving the surface quality of manufactured parts and extending the service life of the die. This is achieved by installing two flat plates between the die and the workpiece in the bending zone before bending, positioning them on either side of the die axis. A spacer, curved to match the shape of the punch, is placed between the punch and the workpiece. As the punch moves downward, the two flat plates move with the workpiece into the die's working space, sliding along the die's curvature radius and preventing the workpiece metal from rubbing against the plate along the die's curvature radius. The spacer and plates are made of high-strength metal. The use of such spacers and plates significantly increases the wear resistance of the punch and die working surfaces.This sheet metal bending method ensures high-quality parts, with no scratches on the inner or outer surfaces. Furthermore, the linings are not deformed during bending and can be reused multiple times. Furthermore, the service life of the die is extended, as wear on the punch and die surfaces is compensated for by the thickness of the plates and linings.

[0012] The disadvantage of this method is the inclusion of expensive die tooling components, as well as additional preliminary heating before bending.

[0013] A known design of a stamp for constrained bending of sheet metal parts and cutting blanks from a strip in a single press stroke (Patent No. 40230, U1, No. 2004112655 / 22, published September 10, 2004) is in this stamp. In this stamp, the punch is made of elastomer, an elastomer rod is located between the punch holder and the housing, and an elastomer rod is installed between the die and the ejector. The blank is bent into a semi-cylinder until it descends toward the ejector, which begins to compress the rod. Simultaneously, the housing compresses the rod until the projections on the housing rest against the punch holder. The elastic punch is deformed under further pressure, bending the blank from a semi-cylindrical to an angular cross-section. The straightening of the blank wall and the frictional forces exerted by the punch force the blank material into its corners. The final deformation of the blank is achieved by the ledges of the body, which transfer the force of the press to the ends of the bending flanges.The stamp provides thickening of the material in the bending zone, reducing the bending radius and springback, which increases the strength, rigidity, quality and service life of parts, as well as labor productivity.

[0014] The disadvantage of this method is the complexity of the design and the inability to control the springback angle after bending is completed.

[0015] A known method for bending long hollow products with an open profile includes placing a set of inserts inside a workpiece and jointly bending the workpiece and the inserts (patent No. 2691478, C1, No. 2018132021, published on June 14, 2019). A set of inserts made of steel strips is installed in each of the open cavities of the workpiece with the possibility of their longitudinal displacement of each of the strips relative to each other and, accordingly, relative to the workpiece during the bending process, while the insert is located in the open cavity of the workpiece along the entire length of the profile, and bending of the workpiece with a set of inserts is performed on rolls made in the form of rollers with a working part width between stops equal to the width of the workpiece with the inserts placed in it, wherein the bending of the profile is carried out in the zone of plastic deformations, and the bending of the steel strips in the region of elastic deformations.

[0016] The disadvantage of this method is the lack of versatility of the bending method.

[0017] The closest to the claimed stamp is the stamp for flat parts with an elastic bar (patent RU No. 153887 U1, B21D 5 / 02, published on 15.04.2015), selected as a prototype. A stamp for bending flat parts with an elastic bar, comprising a side punch with a lateral undercut equal to the springback angle, a matrix and an ejector, characterized in that it is provided with elastic bars, wherein the lower part of the elastic bars is rigidly fixed to the matrix, and the upper part is free and its working plane is made at an angle to the punch equal to the springback angle of the workpiece, and the height of the elastic bars is equal to the height of the bending parts of the workpiece.

[0018] The disadvantage of this method is that if a similar part needs to be manufactured with a different thickness or material, or if the blank properties vary significantly, new strips will need to be manufactured. This significantly limits the capabilities of the proposed two-angle bending method in a die with bilinear strips.

[0019] The technical result of the proposed solution is the use of the elastic properties of the die tooling, improving the quality of the part, compensating for elastic springback due to the bending of the workpiece by an elastic bar and the shape of the punch, eliminating the calibration operation from the technological process, and the ability to regulate the bending angle by changing the stroke of the punch.

[0020] The technical result is achieved due to the fact that the stamp consists of a container, an ejector, a punch, pins and elastic curved strips that ensure constant pressure of the part shelf to the punch during bending and consist of two sections, one of which is curved with a radius R пл , and the second is straightforward.

[0021] For the practical application of this invention, equations for calculating the main process parameters have been derived.

[0022] When used in a die tooling, an elastic curved bar must bend the workpiece, thereby compensating for its springback, and at the same time be sufficiently strong, rigid, and stable. To achieve this, it is necessary to select the appropriate geometric dimensions of the elastic bilinear bar: the bar thickness S пл , bending angle of the elastic bar α пл , the height of the bar h пл , radius of curvature of the elastic bar R пл , radius of rounding of the edge of the bar r пл (Fig. 3).

[0023] Bending angle of the elastic bar α пл must include the springback angle of the part Da, as well as the additional angle α доп , which is necessary for a slight bending of the workpiece in order to compensate for variations in the properties of the workpiece and process parameters:

[0024] α пл =Δα+α доп .

[0025] In α calculations допshould be taken equal to the tolerance value for the angular dimension of the part or determined based on the results of finite element modeling of the bending process.

[0026] As the punch moves downward, the ejector moves in the same direction. In the ejector's extreme lower position, the curved section of the bar is released. In this position, an internal torque M acts on the released inclined section. пл , which tends to return the bar to its original position and, as a result, presses it against the workpiece. On the other hand, the elastic springback of the workpiece tends to bend the elastic bar with a moment equal to the bending moment of the workpiece M. и The lower part of the bar, always located between the ejector and the die, does not experience loads, therefore calculations are carried out only for the curved section of the elastic bar, with the moments acting on it.

[0027] Thus, tensile deformations occur on the side of the bar facing the workpiece, and compression deformations occur on the side of the matrix.

[0028] Then after the transformations we obtain a formula for calculating the thickness of the elastic bar:

[0029]

[0030] It is advisable to assign the radius of curvature of the elastic curved strip based on the limit value of elastic deformation of the strip material [ε пл ].

[0031]

[0032] Edge rounding radius r пл The elastic bar is selected based on reference data.

[0033] The height of the bar, inclined at the bending angle α пл to the axis of the stamp, it is recommended to assign it equal to the height of the part shelf h пол In this case, the height of the elastic bar is the sum of the height h пол shelf of the part and the height of the ejector h выт (Fig. 4):

[0034] h пл =h пол +h выт .

[0035] We will find the height of the elastic curved bar as follows:

[0036] h пл =h выт +l а'b +r пл+ r п+ s o .

[0037] The height of the elastic curved bar is determined by the required bending angle of the workpiece α пл On the other hand, to create the possibility of adjusting the bending angle of the workpiece with a curved bar, it is recommended to set the length of its working part equal to l a'b =(5 - 10)S0. In this case, the maximum bending angle of the workpiece - the angle of inclination of the curved bar in the extreme maximum lower position of the ejector will be equal to:

[0038]

[0039] a punch stroke h, at which the intermediate bending angle α is achieved пл , we define:

[0040] h=R пл sin2α пл +r пл +r п

[0041] The essence of the invention is explained by the following drawings:

[0042] - Fig. 1 shows a diagram of the process of two-angle bending with elastic curved bars (the beginning of the process is on the left, the middle of the process is on the right);

[0043] - Fig. 2 shows a diagram of the process of two-angle bending with elastic curved bars (on the left is the middle of the process, on the right is the end of the process);

[0044] - Fig. 3 shows a diagram for calculating the geometric dimensions of an elastic curved bar

[0045] - Fig. 4 shows a geometric diagram for determining the length of the working part of a curved bar;

[0046] - Fig. 5 shows a diagram of bending a V-shaped part with a bending angle of no more than 90°;

[0047] - Fig. 6 shows a diagram of bending an S-shaped part;

[0048] - Fig. 7 shows a diagram of bending two symmetrically located U-shaped parts, the dimensions of which differ greatly.

[0049] The bending die consists of a container (1), an ejector (3), a punch (4), elastic curved strips (5) and pins (7).

[0050] The invention operates as follows. At the beginning of the process, workpiece 2 is secured to container 1 and ejector 3, which is in its uppermost position. The curved section of bar 5 is straightened by the action of ejector 3. As punch 4 moves downward, ejector 3 is lowered, and the released section of the bar returns to its original position and bends to a radius R. пл , creating a bending moment and pressing the vertical shelves of part 6 to the punch 4. The amount of bending of the shelf of part 6 is determined by the angle of inclination of the bar, which increases as the punch 4 moves deeper into the container, characterized by the value h, since the elastic bars 5 are made curved with a radius of curvature R плAnd releasing them from the constraint between ejector 3 and container 1 gradually returns the bars to their original position. The maximum bar tilt angle is achieved at the ejector's lowest position. Bars 5, moving in a direction perpendicular to the die axis, press on the part's flanges, bending them in the same direction until the final bending angle reaches the required value.

[0051] During the return stroke, ejector 3 removes part 6 from container 1, while elastic curved bars 5 gradually straighten and return to their original position. After completion of the process, part 6 is removed from punch 4 in a direction perpendicular to the drawing plane.

[0052] Curved strips allow you to adjust the bending angle α плBy changing the punch stroke. Thus, if the flange is under-bent, the displacement h must be increased, and if it is over-bent, it must be decreased. Once the process is fine-tuned, it can be repeated repeatedly without any further adjustments. If the workpiece properties change or if the material or thickness needs to be changed, the process can be adjusted again without reworking the die tooling, simply by changing the punch stroke.

Claims

A die for double-angle bending of flat parts, comprising a punch with a lateral undercut made at an angle, a container, an ejector and two elastic curved bars, the lower part of which is rigidly fixed in the container, characterized in that the upper working part of the elastic curved bars is made rounded along the radius, and the bending angle of the said upper working part of the elastic curved bars and the angle of the lateral undercut of the punch are greater than the springback angle of the part.

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