DE102018203728B4 - Method and device for producing a spring dent in a sheet metal part - Google Patents

Abstract

Method for producing a spring bulge (3) in a sheet metal part (1) by plastic sheet metal forming, which spring bulge (3) can be transferred from a first position of use into a second position of use by the application of force and automatically springs back into the first position of use when the force is released or remains stable in the second position of use, wherein the plastic sheet metal forming is carried out by laser beam forming, in which at least one laser weld seam (11) is introduced into the sheet metal part (1) as a deformation seam by a laser device (10) along a predetermined application path (A) to form the spring bulge (3), wherein the finished spring bulge (3) is formed into the sheet metal part (1) as a dome-shaped curvature, wherein the spring bulge (3) has a bulge apex (9) at which the spring bulge (3) is curved with a maximum bulge height (h), characterized in that in the forming process the The laser weld seam (11) running along the application path (A) is guided in a spiral path around the dent apex (9), in that during the shaping process the laser beam exposure point (E) moves along the path with a reducing distance towards the dent apex (9), and in that the path is designed with a radial path distance (a) between a radially inner path section and a radially outer path section.

Description

The invention relates to a method for producing a spring dent in a sheet metal part according to the preamble of claim 1 and to a device for carrying out such a method according to claim 10.

A spring bulge can be realized through a conventional mechanical sheet metal forming process as a monostable or bistable spring section in the sheet metal part. When an external force is applied, it can pivot from a first position of use opposite to its forming direction into a second position of use, utilizing the so-called spring bulge effect. After this pivoting, the spring bulge is formed in the opposite direction. When the force is released, the spring bulge can either automatically return to its first position of use (monostable) or remain in the second position of use (bistable). A sheet metal part with such a spring bulge can be used in various technical fields, for example, to adjust the sheet metal part between a position with a reduced cross-section and a position with an expanded cross-section using the spring bulge effect.

In the state of the art, such a spring dent is produced, for example, by stretching, in which forming tools act on the sheet metal part in order to transfer the force required for forming.

Such a conventional sheet metal forming process has the following two disadvantages, which cause problems when forming rigid sheets. Rigid sheets (high sheet thicknesses with small dimensions of the dent to be created) cannot be easily mechanically formed, as this would otherwise result in excessive deformation. In this case, for example, cracks may form on the surface of the sheet. Furthermore, conventional forming processes result in poor dimensional accuracy. However, for the reliable creation of the spring dent effect, very high dimensional accuracy of the dent is crucial. This has so far been inadequately guaranteed, especially for rigid dents.

From the generic concept underlying claim 1 DE 10 2007 061 920 A1 or the EP 2 072 819 B1 A generic method for manufacturing a pump chamber in a pump is described. In this method, a curvature is introduced into a chamber wall by means of laser beam forming. EP 1 207 973 B1 A further method for removing dents from sheet metal parts is known, in which dents in the body of a motor vehicle can be removed by local heating using a laser device. From the method underlying claim 10 DE 20 2011 100 305 U1 , the DE 691 11 037 T2 , the DE 198 04 577 A1 , the US 2004 / 0 004 531 A1 and the DE 35 05 511 A1 Further methods and devices are known.

The object of the invention is to provide a method and a device for producing a spring dent in a sheet metal part, which can be carried out with reduced tool expenditure and with greater dimension accuracy compared to the prior art.

The object is achieved by the features of claim 1 or 10. Preferred developments of the invention are disclosed in the subclaims.

According to the invention, the bulge is introduced into the sheet metal part by laser beam forming. During laser beam forming, a laser device applies at least one laser weld seam as a deformation seam into the sheet metal part, forming the bulge.

According to the invention, so-called welding distortion is thus specifically utilized. This welding distortion results from shrinkage of the laser weld seam as the metal cools. This shrinkage then leads to residual stress and welding distortion. In laser beam forming, a laser device introduces heat into the sheet metal part to be formed, causing the spring bulge to develop due to the welding distortion. The resulting spring bulge geometry is continuously monitored inline during heat application: Dimensional deviations of the resulting bulge are responded to accordingly based on a target-actual comparison; the bulge is thus generated "intelligently."

If the heat input also causes structural changes, the effect of pure welding distortion is increased.

Using this inventive method, high-precision dents with high degrees of deformation can be reliably produced even with high component stiffness. The use of the joining processes mentioned above is simplified and their application spectrum is broadened.

The inventive production of dents is divided into the following steps: First, the generally flat sheet metal part is prepared. The sheet metal part to be formed is placed on a fixture table whose surface forms an inclined plane. The angle of the inclined plane is so large that the sheet metal can be bent up to a stop (static and sliding friction are overcome). The sheet metal is not firmly attached to the fixture table, but rather placed loosely on it.

The position is then checked using a distance measuring device. A handling device (e.g., a robot) feeds a laser device and the distance measuring device. After the sheet metal part is positioned, it should slide against the stop on the inclined fixture table. This is first checked using the distance measuring device, which determines the position of the sheet metal part's edges and performs a target-to-actual comparison. Only when the sheet metal part has completely slid into position and its edges are thus in the correct position can the next process step proceed.

The actual forming process then takes place. A laser device is used as the heat source, since laser welding involves a brief application of heat, which is followed by rapid cooling, which promotes possible structural transformations. The laser device is set so that it only welds up to approximately the neutral fiber of the later developing dent. This creates the greatest curvature, since the area below the neutral fiber is barely affected, while in the area above the neutral fiber a decrease in volume (i.e. shrinkage) occurs as a result of the solidification of the melt. The blind weld alone results in a concave curvature of the sheet material. If the material is made of a transformable material (e.g. steel), the curvature is further increased by the volume shrinkage during the martensitic transformation, for example.

The robot-guided laser device is moved from the outside inward in a spiral pattern over the desired dent in the sheet metal. To produce body components with spring dents, two parallel elongated holes are often drilled at suitable locations. In a variation of this concept, these elongated holes are cut out with the laser device in the same operation.

The distance measuring device attached to the laser unit measures the distance to the surface of the sheet metal part. Since the position of the robot, and thus also the position of the distance measuring device, is always known during heat application/forming, the measured distance can be used to determine the actual dent height at the point of current heat application. Thus, the distance measured by the distance measuring device during heat application/forming provides information about whether the heat application is resulting in the desired forming process.

During the creation of the dent, a target-actual comparison is carried out between the current dent height at the position of the laser and the respective target value.

If the target value deviates from the measured actual value, the laser power and feed rate can be adjusted accordingly. The following may apply: For example, if the actual value is too low, a higher laser power or a lower feed rate can be set. Conversely, the laser power can be reduced or the feed rate increased if the actual value is too high. However, there are limits to this setting, as welding beyond the neutral axis of the subsequently formed dent naturally no longer has a positive effect.

In another control situation, the spacing of the weld lines can be adjusted. If the measured actual value of the dent height is too high, the weld line spacing is increased. If, however, the measured actual value is too low, the weld line spacing is reduced accordingly.

Alternatively and/or additionally, in another standard situation, the weld line can be made locally wavy. If the dent height is too low at a particular location, a wavy weld line is drawn in that area. The curvature at this location naturally increases.

Alternatively and/or additionally, rework can be performed by adding additional weld lines. This means that even after the dent has been created, its shape can still be adjusted. Short weld lines or spots can be created in areas with insufficient curvature.

In principle, the effect described above can be exploited for all weldable sheet metal materials. Roughly speaking, the greater the volume shrinkage during solidification, the greater the expected distortion and thus the resulting spring buckling effect.

Since the distortion is created by welding down to the centerline of the sheet, the effect is relatively independent of the sheet thickness. The welding distortion can be utilized within a range of 0.5 mm to at least 5 mm. Only when the residual sheet thickness below the neutral axis becomes too large compared to the solidified volume do the residual stresses after welding no longer serve as distortion.

Further aspects of the invention are described in detail below: For example, the laser device can be integrated into a control loop. This can have a preferably contactless optical shape detection system with which an actual value (for example, an actual shape) of the bulge forming during the shaping process is detected. Furthermore, the control loop can have a control unit that generates at least one control signal based on the actual value and a target value. This control signal can be used to adjust laser parameters of the laser device (for example, power, feed rate of the laser device, laser beam diameter, and/or exposure time) and/or path parameters for specifying an application path along which the laser device advances during the shaping process.

In a technical implementation, the shape detection system can include a distance measuring device that detects the actual bulge of the bulge forming during the forming process. The control unit generates the aforementioned control signal based on a comparison of the actual bulge with a target value, which can be used to control the laser device.

The finished bulge can be formed, for example, into a flat base surface of the sheet metal part, as a dome-shaped curvature with a bulge apex at which the bulge protrudes from the sheet metal part's base surface with a maximum bulge height. Accordingly, the bulge height is not constant across the entire bulge surface, but rather increases starting from a radially outer edge of the bulge up to the maximum bulge height in the area of the bulge apex. Against this background, the target bulge height is not constant during the forming process, but rather depends on the current laser beam impact point at which the laser weld seam is formed by melting the sheet metal part material. Against this background, the control loop can have a target value acquisition unit that determines the current laser beam impact point during the forming process and assigns a corresponding target bulge height to it. This is then used as the basis for the target/actual value comparison in the control unit.

In one technical implementation, the distance measuring device can be provided with a motion-coupled connection to the laser device, in particular, mounted directly on the laser device. In this case, the distance measuring device can measure a distance to the developing bulge that correlates with the actual bulge height.

To ensure perfect curvature of the spring bulge, the laser weld seam running along the application path is guided in a continuous, spiral path (e.g., circular or elliptical) around the bulge apex during the forming process. With such a spiral path, the current laser beam exposure point is moved towards the bulge apex at a decreasing distance. The spiral path is designed (with a view to a welding distortion preferred for the spring bulge effect) such that an unprocessed radial path distance results between a radially inner path section and a radially outer path section. This radial path distance can be controlled as a path parameter in the control loop to increase control quality. If the actual bulge height is smaller than the target bulge height during the forming process, the radial path distance can be reduced accordingly to increase the actual bulge height.

In addition, a wave shape can be imposed on the spiral path locally or in sections in order to change the actual bump height.

With a view to further increasing dimensional accuracy, it is preferred if, after the above-mentioned forming process, a post-processing step is carried out in which at least one additional laser weld seam is introduced into the spring dent.

In a specific embodiment of the sheet metal part, it is preferred if the spring dent is assigned two relief slots, which have been machined into the sheet metal part during a cutting process. The spring dent is preferably positioned between the two relief slots, thereby reducing the actuation force required to fold the spring dent. It is preferred if the cutting process step is performed by laser cutting, specifically using the laser device.

The method described above is carried out in a device in which the sheet metal part is positioned correctly on a fixture table. Such correct positioning can be monitored by the shape detection system. Preferably, the sheet metal part is not fixed in a fixed bearing on the fixture table, but rather via a loose bearing in order to compensate for material stresses in the sheet metal part during the laser welding process. For such a loose bearing, the support surface of the fixture table can be inclined in the vertical direction and have a stop on the bottom. The sheet metal part, which is guided precisely on the fixture table, can be Gravity forces loosely support itself on the stop.

An embodiment of the invention is described below with reference to the attached figures.

• 1 in perspektivischer Darstellung ein fertiggestelltes Blechteil mit darin eingeformter Springbeule;
• 2 und 3 jeweils Schnittdarstellungen entlang von Schnittebenen aus der 1;
• 4 in einer grob schematischen Darstellung eine Vorrichtung zum Laserstrahlumformen des Blechteils sowie ein Blockschaltdiagramm, anhand dem eine Prozessregelung zur Erzeugung der Springbeule in dem Blechteil beschrieben wird;
• 5 in einer Ansicht von oben ein Blechteil mit einer Applikationsbahn, entlang der die Laserschweißnaht verläuft, die zur Formung der Springbeule führt;
• 6 und 7 jeweils weitere Ansichten entsprechend der 5.

They show:

• 1 in perspective view a finished sheet metal part with a spring bulge formed into it;
• 2 and 3 each section along section planes from the 1 ;
• 4 in a roughly schematic representation, a device for laser beam forming the sheet metal part and a block diagram describing a process control for generating the spring bulge in the sheet metal part;
• 5 in a top view of a sheet metal part with an application path along which the laser weld seam runs, which leads to the formation of the spring bulge;
• 6 and 7 further views according to the 5 .

In the 1 A three-dimensional view of a sheet metal part 1 is shown, in which a spring bulge 3 is formed. The spring bulge 3 is formed as a dome-shaped curvature in a plate-shaped base surface 5 of the sheet metal part. On both sides of the spring bulge 3, a relief slot 7 is positioned, with the aid of which an external actuating force to be applied can be reduced, so that the spring bulge 3 snaps from its shown basic state into a use state (not shown) by means of external force. The spring bulge 3 is in the 1 Starting from a flat sheet metal part base surface 5, it is curved downwards by a dent height h and has a dent peak 9 approximately in the middle, at which the spring dent 7 protrudes downwards from the sheet metal part base surface 5 with a maximum dent height h. The dent height h is not constant over the entire spring dent surface, but continuously reduces from the central dent peak 9 to the transition to the sheet metal part base surface 5 down to zero.

The spring bulge 3 is formed into the sheet metal part 1 by laser beam forming. During laser beam forming, a laser device 10 ( 4 ) a laser weld seam 11 is introduced into the sheet metal part 1 as a deformation seam. The curvature/bending of the sheet metal part 1 caused by the laser beam forming takes place towards the laser beam 12 ( 3 or 4 ), as it is in the 3 is indicated, in which a dashed line shows the curvature of a sheet metal part after laser beam forming.

As from the 3 As can be seen, the laser welding only takes place approximately up to the neutral fiber N of the sheet metal part 1. This results in the greatest curvature, since the area below the neutral fiber N is hardly affected, but in the area above the neutral fiber N a volume decrease (i.e. shrinkage) occurs as a result of the solidification of the melt in the laser weld seam 11, which is designed as a blind seam.

As from the 1 As can be seen, an application path A, along which the laser weld seam 11 (dashed double line) is guided, extends in a continuous, spiral path around the dent apex 9. The forming process starts at a starting point L1 on an edge side of the sheet metal part 1 and is then guided in a spiral path inwards to a radially inner end point L2, which is located near the dent apex 9.

The 1 The spiral application path A shown (or the spiral laser weld seam 11) is provided with a free radial path spacing a between a radially inner path section and a radially outer path section. Furthermore, the application path A, starting from the edge-side starting point L1, first leads to the two relief slots 7. Subsequently, the application path A is guided in a continuous spiral path around the dent apex 9 in the sheet metal area between the two relief slots 7 to the application end point L2, which is located near the dent apex 9.

The following is based on the 4 The device and the process control for producing the spring dent 3 are described: The device has a device table 13, the support surface 14 of which is inclined in the vertical direction. The support surface 13 merges into a stop 15 on the bottom side, on which the sheet metal part 1 is supported in a loose bearing in a precisely positioned manner. The laser device 10 is in the 4 mounted on an indicated robot arm 17. In addition, a distance measuring device 13 is attached directly to the laser device 10.

The distance measuring device 13 is - together with the laser device 10 and a control unit 21 - part of a control circuit R with which the process control is regulated.

By means of the distance measuring device 13, an actual dent height h _of the spring dent 3 being formed is recorded during the forming process and passed as a measurement signal to the control unit 21. In the control unit An actual value/setpoint comparison is performed in control unit 21, in which the actual dent height h _{actual is} compared with a target dent height h target. On this basis, control unit 21 generates a control signal S, with which laser parameters of laser device 10 can be adjusted, for example, power, feed rate of laser device 10, laser beam diameter, and/or exposure time. Furthermore, path parameters (for example, the radial path distance a) can be set using the control signal S to specify the application path A.

The 4 The distance measuring device 13 shown does _not detect the actual dent height h directly, but rather a distance b to the spring dent 3 _{that is} forming and correlates with the actual dent height h, from which the actual dent height h _can be determined in a simple manner.

The control loop R is also assigned a setpoint acquisition unit 23. This unit has a position acquisition unit 25 that determines the current laser beam impact point E during the forming process. The recorded current laser beam impact point E is read into a database 27 and assigned there to a corresponding dent height h ₁ , h ₂ , h ₃ . After the assignment has been made, the database 27 reads out a target dent height h _soll that correlates with the current laser beam impact point E and is applied to the signal input of the control unit 21 in order to perform the setpoint/actual value comparison.

If the control unit 21 detects an actual dent height h _ist that deviates from the target dent height h _soll during the forming process, the control circuit R can change the radial path distance a by appropriately controlling the robot arm 17 in order to change the actual dent height h _ist . Alternatively and/or additionally, if the actual dent height h _ist deviates from the target dent height h _soll, a waveform 31 (in the 6 highlighted with the detail X) to change the actual dent height h _ist .

After the forming process has been completed, a post-processing step can be carried out by means of which the dimensional accuracy of the produced spring bulge 3 can be further increased. In the post-processing step, an additional laser weld seam 29 can be introduced into the already formed spring bulge 3, as shown in the 7 indicated by detail X.

Claims (10)

Method for producing a spring bulge (3) in a sheet metal part (1) by plastic sheet metal forming, which spring bulge (3) can be transferred from a first position of use into a second position of use by the application of force and automatically springs back into the first position of use when the force is released or remains stable in the second position of use, wherein the plastic sheet metal forming is carried out by laser beam forming, in which at least one laser weld seam (11) is introduced into the sheet metal part (1) as a deformation seam by a laser device (10) along a predetermined application path (A) to form the spring bulge (3), wherein the finished spring bulge (3) is formed into the sheet metal part (1) as a dome-shaped curvature, wherein the spring bulge (3) has a bulge apex (9) at which the spring bulge (3) is curved with a maximum bulge height (h), characterized in that in the forming process the The laser weld seam (11) running along the application path (A) is guided in a spiral path around the dent apex (9), in that during the shaping process the laser beam exposure point (E) moves along the path with a reducing distance towards the dent apex (9), and in that the path is designed with a radial path distance (a) between a radially inner path section and a radially outer path section. Procedure according to Claim 1 , characterized in that the laser device (10) is integrated in a control circuit (R) which has a shape detection system (13) with which an actual value (h _ist ) of the spring bulge (3) forming in the shaping process is detected, and has a control unit (21) which, on the basis of the detected actual value (h _ist ) and a target value (h _soll ), generates at least one control signal (S) with which laser parameters of the laser device (10), such as power, feed speed of the laser device, laser beam diameter or exposure time, and/or path parameters (a) for specifying the application path (A) can be adjusted. Procedure according to Claim 2 , characterized in that the shape detection system (13) is a distance measuring device with which an actual dent height (h _ist ) of the spring dent (3) being formed is detected in the forming process, and in that the control signal (S) is generated in the control unit (21) on the basis of a comparison of the actual dent height (h _ist ) with a target value (h _soll ). Procedure according to Claim 3 , characterized in that the desired dent height (h _soll ) varies depending on the respective current laser beam impact point (E) of the laser device (10), and in that the control circuit (R) has a desired value detection (23) which determines the current laser beam impact point (E) in the shaping process and assigns thereto a corresponding desired dent height (h _soll ) which is used as the basis for the target/actual value comparison in the control unit (21). Method according to one of the Claims 3 or 4 , characterized in that the distance measuring device (13) is mounted on the laser device (10), and/or that the distance measuring device (13) detects a distance (b) to the spring bulge (3) being formed, said distance correlating with the actual bulge height (h _actual ). Procedure according to one of the Claims 2 until 5 , characterized in that the radial path distance (a) is set in the control loop (R) as a path parameter. Procedure according to Claim 6 , characterized in that in the event that the actual dent height (h _ist ) is smaller than the corresponding target dent height (h _soll ) in the shaping process, a wave shape (31) is locally impressed on the spiral-shaped path in order to increase the actual dent height (h _ist ), and/or in the event that the actual dent height (h _ist ) is smaller than the corresponding target dent height (h _soll ) in the shaping process, a reduced radial path distance (a) is locally impressed on the spiral-shaped path in order to increase the actual dent height (h _ist ). Procedure according to one of the Claims 6 or 7 , characterized in that after the shaping process, a post-processing step takes place in which at least one additional laser weld seam (29) is introduced into the spring bulge (3), specifically between a radially inner track section and a radially outer track section of the spiral-shaped laser weld seam (11). Method according to one of the preceding claims, characterized in that the spring dent (3) is assigned two relief slots (7), between which the spring dent (3) is positioned, and in that the relief slots (7) are introduced into the sheet metal part (1) in a laser cutting process, and in that the laser cutting process is integrated in the spring dent forming process. Device for carrying out a method according to one of the preceding claims, comprising a laser device (10), by means of which at least one laser weld seam (11) can be introduced into the sheet metal part (1) as a deformation seam by laser beam forming along a predetermined application path (A), specifically with formation of the spring bulge (3), wherein during the forming process the sheet metal part (1) is positioned on a fixture table (13), wherein the sheet metal part (1) is arranged in a loose bearing on the fixture table (13), and wherein the support surface (14) of the fixture table is inclined in the vertical direction and has a stop (15) on the bottom side, on which the sheet metal part (1) is loosely supported under the effect of gravity, characterized in that the laser device is set such that welding is carried out by means of the laser radiation of the laser device only up to the neutral fiber of the subsequently formed spring bulge (3).