Process for shearing sheet metal with subsequent forming and a cutting tool intended for this purpose

Abstract

Method for shearing processing of sheet metal (3) to produce a recess (4), in which the sheet metal (3) thus processed is subjected to subsequent forming of at least the area enclosing the recess (4), characterized in that, starting from the desired contour (2) of the recess (4), a cutting contour (5) deviating from the desired contour (2) and extended by additional curves compared to the desired contour (2) is determined and the recess (4) is introduced into the sheet metal (3) in accordance with this cutting contour (5).

Description

[0001] The invention relates to a method for shearing sheet metal to produce a recess, in particular an opening in the sheet metal, in which the thus processed sheet metal is subsequently formed at least in the area enclosing the recess. Furthermore, the invention relates to a cutting tool for use in the method.

[0002] In the series production of sheet metal components with a sheet thickness of more than 1.5 mm as well as with high-strength, high-strength and ultra-high-strength sheet materials with a tensile strength of more than 300 MPa, it has been shown that an increased sensitivity to edge cracking occurs during forming.

[0003] This problem is particularly pronounced when the sheet metal is first separated in a cutting process and then cold formed. The resulting work hardening in the shear zone reduces the residual formability of the sheet metal and thus its ability to withstand further forming processes in the cold forming process. This results in deterioration of the cut edges, which can lead to complex post-processing.

[0004] Known approaches to preventing cracks or imperfections in general involve dividing complex forming processes into several sub-steps or localized heating with a laser to partially soften the workpiece. This involves additional design effort, particularly for the tools.

[0005] In practice, components for highly stressed automotive parts often consist of several individual parts that are connected to each other, for example by welds.

[0006] In addition, the use of so-called tailored blanks can achieve a wall thickness distribution that is better adapted to the component load.

[0007] Furthermore, internal high-pressure forming is known for complex forming processes of a tubular element, for example, from DE 102 41 406 A1. This usually requires post-processing of the tubular element from the semi-finished product to the final product using a laser.

[0008] In contrast, DE 10 2006 014 730 A1 describes a deep-drawing process for manufacturing a component for a motor vehicle wheel suspension, which is made from a sheet metal blank made of lightweight steel. The high strain hardening that occurs during forming is utilized, enabling a stiff, thin-walled design of the spring link. This results in significant weight savings by allowing the use of a sheet metal with a thickness of 1.6 to 1.8 mm. Appropriately trimmed blanks are formed in several deep-drawing steps until the final shape of the component is achieved.

[0009] DE 10 2010 007 944 A1 describes a bearing holder for a bearing, which is produced by forming the sheet metal blank in a forming tool in order to insert a collar for receiving a bearing.

[0010] DE 196 43 194 A1 relates to a punching die with a cutting plate designed as an indexable insert, which has a round or non-round cross-section.

[0011] Against this background, the invention is based on the object of significantly simplifying the production of a sheet metal component using the process steps of shearing and forming. Furthermore, a cutting tool suitable for this purpose is to be created.

[0012] This object is achieved by a method according to the features of patent claim 1. The subclaims relate to particularly expedient developments of the invention.

[0013] According to the invention, a method is provided in which, starting from the desired contour of the recess, a cutting contour is determined that deviates from the desired contour and is extended by additional curves compared to the desired contour, and the recess is introduced into the sheet metal according to this cutting contour. The invention is based on the surprising finding that undesirable cracking during the subsequent forming of the sheet metal provided with the recess can be easily avoided if the recess is introduced not along the desired contour, i.e., according to the geometrically predetermined course, but in a wave-like manner in the region of this desired contour, for example, running tangent to it.The extension of the cutting line during shearing machining results in a reduction in hardening in the area of ​​the cutting line compared to the target contour, so that at the same time the risk of undesirable crack formation is significantly reduced.

[0014] In this case, not only is an enclosed area larger than the target contour selected, with a longer peripheral surface correspondingly spaced from the target contour. Rather, the cutting contour is preferably determined such that it touches or intersects the target contour at several points, in particular in a wave-like manner, in order to create the conditions for the target contour to be easily achieved during the subsequent forming process, for example by drawing. Since the effect according to the invention is noticeable even with a slight extension of the cutting contour as a shear line or parting line compared to the target contour, the dimensional deviations as the amplitude of the curve compared to the target contour can often be within the tolerance range in practice, so that no post-processing is necessary. According to the invention, the division of the forming process into a large number of individual steps can thus be dispensed with.

[0015] It is also advantageous if the cutting line has several convex and concave curves and that the cutting contour runs within a region delimited by the maximum and minimum amplitudes. This means that the target contour lies within the outer boundary line delimited by the maximum and minimum amplitudes and the inner boundary line, for example, between a great circle and a small circle. Since the cutting lines run in sections on one or the other side of the target contour, a desired contour can be easily created through subsequent forming. With respect to the target contour, the cutting contour can, for example, also have a sinusoidal shape.

[0016] In a simple variant of the process, the target contour is circular and the recess is introduced according to a wave-shaped cutting contour enclosing the target contour, so that the wave-shaped cutting contour does not fall below the target contour at any point, but rather runs tangent to it in sections.

[0017] The curves extending the cutting contour could be limited to individual circumferential sections. However, it is particularly advantageous if the curves are directly adjacent to one another, so that the beneficial effect of reduced work hardening occurs evenly across the circumference, thus reliably preventing crack formation across the entire circumference.

[0018] At the same time, it proves to be particularly useful if the cutting contour has a continuous course, so that the curves extending the cutting line are continuous, in particular in turn connected to one another by curves.

[0019] Preferably, matching curves are evenly distributed over the circumference of the cutting contour, for example, to create a point-symmetrical contour of the cutting line. For this purpose, the cutting contour can, for example, have cloverleaf-shaped radial extensions, with all curves having a matching geometric shape.

[0020] In another variation, which is also particularly promising, the curves have a constant radius that is smaller than the radius of the circular nominal contour of the opening.

[0021] In principle, it can be assumed that a significant extension of the cutting line relative to the target contour has a correspondingly beneficial effect and thus results in a reduction in the risk of crack formation. However, it is particularly advantageous if the distance between the cutting contour and the target contour corresponds to a maximum of 25% of the sheet thickness. Surprisingly, it has been shown that even a slightly longer cutting contour compared to the target contour leads to a clearly discernible beneficial effect. The increase in the length of the cutting contour is in the range of up to 5%, preferably up to 1%, relative to the target contour.

[0022] The effect according to the invention can generally be advantageously utilized in conjunction with various forming processes. However, it is particularly advantageous if the sheet metal is subjected to cold forming after the recess has been created. Due to the adjusted cutting contour, the residual formability is sufficient for cold forming, and at the same time, the hardening results in a high load-bearing capacity of the resulting component.

[0023] The recess could be introduced into the sheet metal in any known manner. However, it is particularly practical if the recess is introduced using a punching process, because the hardening of the sheet metal resulting from shearing can be particularly advantageously limited or reduced in the desired manner by introducing the curved extensions according to the invention.

[0024] Following the creation of the recess, the recess is widened or expanded by drawing a collar enclosing the recess. The opening plane of the sheet metal part thus created is spaced from the base plane of the sheet and can have a circular cross-sectional shape, regardless of the introduced curves, which, due to the forming process, run in particular in a plane perpendicular to the base plane of the sheet. In particular, the forming of the sheet metal results in the passage opening not being defined by the recess, but by the annular collar that protrudes from the sheet and runs perpendicular to the sheet plane and thus to the opening plane.

[0025] Of course, the process is not limited to specific sheet thicknesses. However, the beneficial effect is particularly significant when the sheet to be formed has a thickness of more than 1.5 mm and is made of a high-strength, higher-strength, or ultra-high-strength sheet material with a tensile strength of more than 300 MPa.

[0026] The object of the invention is further achieved with a cutting tool, in particular a punching tool, in that the cutting tool has a cross-sectional area delimited by a circumferential line which deviates from a desired contour in that it has concave and / or convex shapes as bulges and / or indentations compared to the desired contour, and in that the cutting contour thus defined by the bulges is longer than the circumferential line of the desired contour, and in that the cutting contour and the desired contour coincide at points or in sections. Thus, by having a plurality of convex or concave bulges or indentations on the circumference of the cutting tool, the cutting line is significantly lengthened, whereby, in contrast, the desired contour enclosed by the cutting contour is defined to coincide with the latter at least at points.In a surprisingly simple way, the resulting work hardening can be limited to favor the subsequent forming process. In particular, the subsequent degree of deformation can be increased, eliminating the need for costly stepwise forming with a low degree of deformation, which is unavoidable in the current state of the art due to work hardening.

[0027] A particularly advantageous embodiment of the invention is also achieved in that the cutting tool has a cutting edge which is arranged in at least two planes inclined to one another, so that during shearing processing the cutting line is not introduced simultaneously over the entire cutting contour, but is introduced and extended continuously due to the roof shape starting from two tips of the cutting tool through the end ring depth of the punch.

[0028] The invention permits numerous embodiments. To further clarify its basic principle, one of them is shown in the drawing and is described below. This shows in Fig. 1. a cutting tool in a top view; Fig. 2 the cutting tool in a side view; Fig. 3 the cutting tool in a perspective view; Fig. 4 a sheet metal component provided with a recess and produced by forming in a side view; Fig. 5 that in Fig. 4 shown sheet metal component in a perspective view.

[0029] The cutting tool 1 according to the invention is described below with reference to Fig. 1 to 3. The cutting tool 1, which is designed as a punching tool, serves to cut a desired contour 2, shown only in dashed lines, of the workpiece in a Fig. 4 shown sheet metal 3 to be introduced. For this purpose, the cutting tool 1 is delimited by a circumferential line which is provided with regular concave and convex formations 6 which form bulges and / or indentations. The resulting wave-shaped contour of the regularly successive formations 6 in plan view is convex and concave in equal parts. Because the recess 4 is not introduced into the sheet metal 3 along the desired contour 2, but rather in a wave-shaped manner within a corridor extending on both sides of the desired contour 2, the cutting line in the sheet metal 3 is extended during shearing. The associated hardening in the area of ​​the cut edges of the sheet metal 3 can thereby be significantly limited. Thus, in the following, using the example of the Fig. The complex cold forming of the sheet metal component 7 shown in Figure 4 did not lead to crack formation.

[0030] In the Fig. 4 and Fig.5 shows an enlarged side view and a perspective view of a sheet metal part 7 provided with a recess and produced by forming the sheet metal 3, in which, after the recess 4 has been created, the recess 4 has been widened by pulling a collar 8 enclosing the recess 4. The plane of the opening 9 of the sheet metal part 7 thus created is spaced from the base plane of the sheet metal 3 and is delimited by a collar 8 which, regardless of the wavy course along the cut edge of the recess 4, has a circular cross-sectional shape due to the forming process in a plane transverse to the base plane of the sheet metal 3.In particular, the forming of the sheet metal 3 results in the passage opening being defined not by the recess 4, whose undulating course with convex and concave formations 6 is recognizable, but by the annular collar 8 protruding from the sheet metal 3 and extending perpendicular to the sheet metal plane. This results in the cutting contour 5 according to the invention, which deviates from the target contour 2, significantly simplifying the forming process, and the resulting complex geometry presents no practical limitations compared to comparable sheet metal components manufactured according to the prior art in a sequence of multiple partial forming steps. List of reference symbols 1 cutting tool 2 Target contour 3 sheet metal 4 recess 5 Cutting contour 6 Forming 7 Sheet metal part 8 collars 9 Opening

Claims

[1] Method for the shearing processing of sheet metal (3) for producing a recess (4), in which the sheet metal (3) thus processed is subjected to a subsequent forming of at least the area enclosing the recess (4), characterized by that starting from the target contour (2) of the recess (4), a cutting contour (5) is determined which deviates from the target contour (2) and is extended by additional curves compared to the target contour (2), and the recess (4) is introduced into the sheet (3) in accordance with this cutting contour (5). [2] Method according to claim 1, characterized by that the cutting contour (5) intersects the target contour (2) in several points and / or areas and / or the cutting contour (5) has a course identical to the target contour (2) only in sections. [3] Method according to claims 1 or 2, characterized bythat the cutting line has several convex and concave curves and that the cutting contour (5) runs in the area of ​​an area limited by the maximum and the minimum amplitude. [4] Method according to at least one of the preceding claims, characterized by that the target contour (2) is circular and the recess (4) is introduced according to a wave-shaped cutting contour (5) enclosing the target contour (2). [5] Method according to at least one of the preceding claims, characterized by that several curves are inserted directly next to one another. [6] Method according to at least one of the preceding claims, characterized by that the cutting contour (5) is introduced with a continuous course. [7] Method according to at least one of the preceding claims, characterized by that matching curves are introduced evenly distributed over the circumference of the cutting contour (5). [8] Method according to at least one of the preceding claims, characterized by that all curves are introduced with a consistent geometric progression. [9] Method according to at least one of the preceding claims, characterized by that the curves are introduced with a constant radius which is smaller than the radius of the circular nominal contour (2) of the recess (4). [10] Method according to at least one of the preceding claims, characterized by that the distance of the cutting contour (5) from the target contour (2) corresponds to a maximum of 25% of the thickness of the sheet (3). [11] Method according to at least one of the preceding claims, characterized by that the sheet (3) is subjected to cold forming after the recess (4) has been made. [12] Method according to at least one of the preceding claims, characterized by that the recess (4) is made by means of a punching process. [13] Method according to at least one of the preceding claims, characterized by that after the recess (4) has been made, the recess (4) is widened by pulling a collar (8) enclosing the recess (4). [14] Cutting tool (1) for use in the method according to at least one of the preceding claims, characterized by that the cutting tool (1) has a cross-sectional area which is delimited by a circumferential line which deviates from a desired contour (2) and has concave and / or convex formations (6) as bulges and / or indentations compared to the desired contour (2), so that the cutting contour (5) defined by the formations (6) is longer than the circumferential line of the desired contour (2), and that the cutting contour (5) and the desired contour (2) coincide at points or in sections. [15] Cutting tool (1) according to claim 14, characterized bythat the cutting tool (1) has a cutting edge which runs in at least two planes inclined to one another.

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