METHOD FOR PRODUCING A TUBULAR FRAME

Abstract

A method that makes it possible to produce actual cutting contours on tubes with only rough tolerances, to which contours others of the tubes can be joined and welded, wherein, as a result of the actual cutting contours being modified, the rough shape tolerance of the tubes does not enter the tolerance chain, or enters the latter only a little, for the tubes to be fully welded to form a tubular frame. It also allows the automated reception of only pre-oriented tubes by a gripping arm and the infeed thereof to a laser cutting device.

Claims

1. A method for producing a tubular frame comprising a plurality of tubes which are welded together at several actual interfaces in each case via two respective joining surfaces, at least one of the two joining surfaces representing an actual cutting contour along which one of the two tubes to be welded in each case was cut out or cut off with a laser beam before welding, the method comprising calculating a tolerance envelope for each individual tube of the plurality of tubes and storing the calculated tolerance envelope with reference to a coordinate system related to a tube feeder, defining a desired cutting contour pattern with desired cutting contours, which are each assigned to one of the actual cutting contours, for the tubular frame and storing the desired cutting contours in relation to the tolerance envelopes of the individual tubes, picking up one of the tubes in each case with a gripping arm of the tube feeder and transporting the tube relative to an optical measuring device with a known spatial position in the coordinate system, and optically recording and measuring the tube, spatially moving the tube using the gripping arm until the tube lies within the tolerance envelope calculated for the tube, feeding the tube using the tube feeder to a laser cutting device in such a way that the tolerance envelope calculated for the tube assumes a predetermined position relative to the laser cutting device, the tube having thus assumed a spatial position defined by a spatial position of the tolerance envelope relative to the laser cutting device, and wherein the laser beam of the laser cutting device describes the desired cutting contour related to the tolerance envelope and the actual cutting contour is cut on the tube, the actual cutting contour corresponding to a projection of the desired cutting contour onto the tube.

2. The method for producing a tubular frame according to claim 1, wherein the actual cutting contour is in the form of a cutout surface in a shell of one of the tubes, which corresponds, for tubes inserted in the same tolerance envelope with different tolerance deviations, to a differently modified image of the desired cutting contour, so that another one of the tubes welded to the actual cutting contour assumes a same relative position to the tolerance envelope of the inserted tube, regardless of the position of the inserted tube in the tolerance envelope.

3. The method for producing a tubular frame according to claim 1, wherein the actual cutting contour is in the form of an end face of one of the tubes, which has a different angle with a tube axis of the tube for the tubes inserted into the same tolerance envelope with different tolerance deviations, so that a different one of the tubes welded to the actual cutting contour assumes a same relative position to the tolerance envelope of the inserted tube, regardless of the position of the inserted tube in the tolerance envelope.

4. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In the drawings:

[0023] FIG. 1a shows a tubular frame comprising four tubes in an exploded view;

[0024] FIG. 1b shows a representation of the assembled tubular frame according to FIG. 1a;

[0025] FIG. 1c shows a desired interface pattern for the tubular frame according to FIGS. 1a and 1b with reference to a coordinate system;

[0026] FIG. 2 shows the tubular frame according to FIG. 1 in an exploded view with tolerance envelopes for the tubes;

[0027] FIG. 3a shows an ideal tube ideally lying within the tolerance envelope;

[0028] FIG. 3b shows a faulty tube lying within the tolerance envelope;

[0029] FIG. 3c shows another faulty tube lying within the tolerance envelope;

[0030] FIG. 4a shows the relative position of a tube, which lies with its shell surface against the cutting contour of another tube;

[0031] FIG. 4b shows an ideal tube lying ideally within the tolerance envelope;

[0032] FIG. 4c shows a tube lying tilted in the tolerance envelope;

[0033] FIG. 4d shows another tube lying tilted in the tolerance envelope, and

[0034] FIG. 5 shows a schematic diagram of a device suitable for performing the method.

DETAILED DESCRIPTION

[0035] By way of example, FIG. 1a shows an exploded view of a tubular frame consisting of tubes R, in this case four tubes R.sub.1-R.sub.4, which are welded together at actual interfaces S.sub.ACTUAL, i.e. five actual interfaces S.sub.ACTUAL1-S.sub.ACTUAL5 in this specific case. The actual interfaces S.sub.ACTUAL1-S.sub.ACTUAL5 are each formed by weldable joining surfaces V on the two tubes R, each forming a welding partner. FIG. 1b shows these four tubes R.sub.1-R.sub.4 welded together as intended. FIG. 1c shows a desired interface pattern with desired interfaces S.sub.DESIRED for the tubular frame. Each of the desired interfaces S.sub.DESIRED is assigned to one of the actual interfaces S.sub.ACTUAL.

[0036] There are basically three different types of interfaces:

[0037] The first type of interface is obtained by pairing two tubes R via two end faces. An example of this is shown in FIGS. 1a-1b with reference to the actual interface S.sub.ACTUAL1, where an end face of the tube R.sub.3, as joining face V.sub.R31, is welded to an end face of the tube R.sub.1, as joining face V.sub.R11.

[0038] The second type of interface is obtained by pairing two tubes R via a cutout surface and a shell surface. An example of this is shown in FIGS. 1a-1b with reference to the actual interface S.sub.ACTUAL2, where a cutout surface of the tube R.sub.1, as joining surface V.sub.R12, is welded to the shell surface of the tube R.sub.2, as joining surface V.sub.R22.

[0039] The third type of interface is obtained by pairing two tubes R via an end face and a shell surface. An example of this is shown in FIG. 1 with reference to the actual interface S.sub.ACTUAL3, where an end face of the tube R.sub.4, as joining face V.sub.R42, is to be welded to the shell surface of the tube R.sub.3, as joining face V.sub.R33.

[0040] Each of the interface types has at least one joining surface V, which represents a desired cutting contour K.sub.DESIRED. According to the invention, their desired position of the latter is determined neither in relation to the ideal tube R nor to the real tube R, but rather in relation to a calculated tolerance envelope H. This tolerance envelope H envelops the ideal tube R. It also envelops the real tube R, whose external dimensions are in tolerance. The tolerance envelope H can also be defined for individual sections of individual tubes R.

[0041] Prior to cutting the tubes R for the tubular frame, tolerance ranges for the dimensional accuracy of the shape of the relevant tubes R are calculated as the so-called tolerance envelopes H at least for the tubes R on which cutting is to be performed, see FIG. 2. Assuming that the tubes R are manufactured with sufficient accuracy in terms of their tube cross section and length, the possible shape deviation mainly concerns the deviation of the line of the actual tube axis from a desired tube axis due to the deviation of actual bending radii from desired bending radii on the tube R and a possible twisting of the actual tube axis in the bending areas.

[0042] Each actual interface S.sub.ACTUAL is assigned the desired interface S.sub.DESIRED, which is related to the tolerance envelope H, see FIG. 1b in combination with FIG. 1c. The desired interfaces S.sub.DESIRED are stored in a desired interface pattern in a fixed relative position to each other. This means that the relative spatial position of the desired cutting contours K.sub.DESIRED to each other is stored for the respective joining surfaces V to be produced by cuts.

[0043] The tolerance envelopes H are each calculated in such a way that on each tube R fitting into the tolerance envelope H the actual cutting contours K.sub.ACTUAL can be cut in such a way that the suitable joining surface V for welding is created. FIG. 3a shows the ideal tube R lying ideally within the tolerance envelope H. The tube axes of the ideal tube R and of the tolerance envelope H coincide. Advantageously, the desired cutting contours K.sub.DESIRED are calculated in such a way that they coincide with the actual cutting contours K.sub.ACTUAL in this case. This would no longer be the case if the ideal tube R were tilted within the tolerance envelope H.

[0044] FIGS. 3b and 3c show two tubes R.sub.1, each fitting into the tolerance envelope H.sub.1 and deviating differently from the shape of an ideal tube R.sub.1. In relation to the tolerance envelope H.sub.1, the desired cutting contours K.sub.R11DESIRED, K.sub.R12DESIRED, K.sub.R13DESIRED have the same relative position to one another, but the actual cutting contours K.sub.R11ACTUAL, K.sub.R12ACTUAL, K.sub.R13ACTUAL cut on the real tubes R.sub.1, as shown in an exaggerated manner herein, have a slightly different spatial position and also a different shape and/or size. A cutout surface as joining surface V.sub.R12 for the actual interface S.sub.2ACTUAL extends more or less deeply into tube R.sub.1. An end face as joining face V.sub.R11 for the actual interface S.sub.1ACTUAL is cut at different points along the tube axis of the tube R and at a different angle to the tube axis.

[0045] The tube R.sub.3, in which an end face and a cutout surface are to be produced as joining faces V.sub.R31 and V.sub.R21 for the actual interfaces S.sub.1ACTUAL and S.sub.5ACTUAL respectively, is processed in the same way as the tube R.sub.1.

[0046] On the tube R.sub.4, only one end face is cut as joining surface V.sub.R42 for the actual interface S.sub.3ACTUAL. The tolerance with respect to the second actual interface S.sub.4ACTUAL is compensated by welding the tube R.sub.4 with a moving part of its shell surface to a joining surface V.sub.R13, which is a cutout surface.

[0047] The tube R.sub.2 has no actual cutting contours K.sub.ACTUAL. Its joining surfaces V.sub.R21, V.sub.R22 are areas on shell surfaces whose relative position to each other is created during the production of the tube R. This means that in contrast to the joining surfaces V, which are created in different manners by cutting actual cutting contours K.sub.ACTUAL on the tubes R due to the different position of the tube R in the tolerance envelope H, whereby the tolerances can be compensated, a tolerance deviation must be accepted here. Accordingly, either the tolerance envelope H must be kept sufficiently tight at least in the area of the joints V.sub.R21 and V.sub.R22, or the tube R is designed in such a way that it is aligned with the joining surfaces V of the other tubes R by a positional adjustment. Specifically, the U-shaped tube R.sub.2 is to be constructed here in such a way that its two arms do not run parallel to each other, but enclose a small angle with each other, allowing positional adjustment by shifting in the direction of the arms. After the tubes R.sub.1 and R.sub.2 have been welded together at the actual interface S.sub.1ACTUAL and the tube R.sub.4 has been welded on, the tube R.sub.2 is inserted from above between the tubes R.sub.1 and R.sub.3 and welded so as to protrude upwards to a greater or lesser extent at the actual interfaces S.sub.2ACTUAL and S.sub.5ACTUAL.

[0048] FIGS. 4b to 4d again show in simplified form, with reference to a straight tube R, how a desired cutting contour K.sub.DESIRED is projected, in relation to a tolerance envelope H, onto the tubes R lying in the tolerance envelope H. Actual cutting contours K.sub.ACTUAL projected onto the shell of the respective tube R are modified compared to the desired cutting contour K.sub.DESIRED by a change in position, size and/or shape, depending on the spatial position of the shell of the respective tube R relative to the desired cutting contour K.sub.DESIRED. The other of the tubes R, which is welded to the at least one actual cutting contour K.sub.ACTUAL, has the same spatial position as shown in FIG. 4a with reference to three tubes R lying differently in the tolerance envelope H, as shown in FIGS. 4b- 4d.

[0049] FIG. 5 shows a schematic diagram of a device suitable for carrying out the method. The device includes a feed surface 1, a feeding device, tube feeder or feeding means 2 with a gripping arm 2.1, an optical measuring device 3, e.g. a 3D camera, a laser cutting device 4 with a cutting nozzle 4.1, a storage and control unit 6 and advantageously a further optical measuring device 5. The latter is used to check whether there are one or several tubes R and how they are two-dimensionally aligned on the feed surface 1. Based on this knowledge, the gripping arm 2.1 can be adjusted, in order to grip the tube R optimally, in case of positional deviations from a desired position, which may also be due to a shape deviation of the tube R.

[0050] For machining the tubes R, i.e. for producing desired cutting contours K.sub.DESIRED, the tubes R are each picked up from a feed surface 1 by the gripping arm 2.1 of the feeding means 2. Ideally, the tubes R lie pre-sorted, pre-positioned and pre-oriented on the feed surface 1, so that the gripping arm 2.1, moving to a predetermined gripping position, picks up the tube R, lying pre-oriented to the gripping arm 2.1. It is not necessary to position the tubes R so precisely on the feed surface 1 that they are picked up in a reproducible spatial position to the coordinate system of the feeding means 2, which also benefits the comparatively large shape tolerance of the individual tubes R.

[0051] The gripping arm 2.1 is preferably a multi-axis gripping arm 2.1, which can freely move a gripped workpiece, in this case the tube R, within a limited working area. Arranged within the working area are the feed surface 1, the optical measuring device 3 and the laser cutting device 4, each having a known spatial position within the coordinate system.

[0052] The gripping arm 2.1 transports the tube R to the optical measuring device 3, where the tube R is optically recorded and measured. Then, the tube R is inserted by the gripping arm 2.1 into a tolerance envelope H, thereby confirming that the tube R is in tolerance. The spatial position of the tube R within a coordinate system defined by the feeding means 2 is thus determined by the spatial position of the tolerance envelope H in the coordinate system.

[0053] Afterwards or at the same time, the gripping arm 2.1 feeds the tube R to the laser cutting device 4 in such a way that the tolerance envelope H is in a predetermined relative position to the laser cutting device 4. The laser cutting device 4 then cuts the actual cutting contours K.sub.ACTUAL on the tube R, the laser beam being guided by the cutting nozzle 4.1 along a desired cutting contour K.sub.DESIRED elated to the tolerance envelope H. The method can be performed using a laser beam because the execution of the cut does not require mechanical contact between a cutting tool and a workpiece and thus a defined position of the machining surface, as is the case with mechanical machining. In laser cutting, the machining surface can assume a different spatial position, at least within the focus range.

[0054] The method according to the invention makes it possible to produce the actual cutting contours K.sub.ACTUAL on the only roughly tolerated tubes R, to which other tubes R can be attached and welded. By modifying the actual cutting contours K.sub.ACTUAL, the rough tolerance of the tubes R is included only to a lesser extent, if at all, in the tolerance chain for the complete welding of the tubes R to a tubular frame. The method also enables the gripping arm 2.1 to automatically pick up the merely pre-oriented tubes R and feed them to the laser cutting device 4.

LIST OF REFERENCE NUMERALS

[0055] R tube

[0056] S interface

[0057] S.sub.ACTUAL actual interface

[0058] S.sub.DESIRED desired interface

[0059] K.sub.ACTUAL actual cutting contour

[0060] K.sub.DESIRED desired cutting contour

[0061] V joining surface

[0062] H tolerance envelope

[0063] 1 feed surface

[0064] 2 feeding means

[0065] 2.1 gripping arm

[0066] 3 optical measuring device

[0067] 4 laser cutting device

[0068] 4.1 cutting nozzle

[0069] 5 further optical measuring device

[0070] 6 control and storage unit