Method for producing coaxial cables having a thin-walled, radially closed outer conductor

Abstract

A method for the continuous production of coaxial cables (224) having a thin-walled, radially closed outer conductor of nonferrous metal comprises supplying a flat strip of the nonferrous metal to a shaping apparatus (212), wherein the thickness of the strip corresponds to the wall thickness of the coaxial cable. The shaping apparatus is configured to continuously shape the supplied flat strip into a form corresponding to the outer conductor of the coaxial cable and around a cable core supplied before the outer conductor is closed. After the shaping, two opposite edges of the flat strip lie flush against one another in a contact region and are continuously welded to one another by a welding apparatus (216) by means of a laser, which radiates light having a wavelength smaller than 600 nm. The laser heats a point in a welding region that has a diameter smaller than 20% of the cross-sectional dimension of the coaxial cable. The welded coaxial cable is drawn off from the welding region and, after introducing a parallel or helical corrugation, is received in a receiving device (226).

Claims

1. A method for the continuous production of coaxial cables having a radially closed outer conductor of nonferrous metal that has a wall thickness of less than 0.15 mm, comprising: supplying a flat strip of the nonferrous metal at a first supply rate to a shaping apparatus, wherein the thickness of the strip corresponds to the wall thickness of the hollow profile to be produced, supplying an inner conductor encased with a dielectric, continuously shaping the supplied flat strip into a form corresponding to the outer conductor of the coaxial cable, wherein after the shaping operation two opposite edges of the flat strip lie flush against one another in a contact region extending in the longitudinal direction of the hollow profile, and wherein before the closing of the hollow profile forming the outer conductor, the inner conductor encased by a dielectric is supplied, with the result that the inner conductor encased by the dielectric lies in the hollow profile, continuously welding the edges that lie flush against one another in the contact region without prior treatment to reduce optical reflections, wherein the edges to be welded are guided at the first supply rate past a welding region that is stationary in relation to an apparatus which implements the method, and wherein a point in the welding region is heated by means of a laser which radiates light having a wavelength smaller than 600 nm, and wherein the heated point has a diameter which is less than 20% of the cross-sectional dimension of the hollow profile, drawing off the welded coaxial cable from the welding region, introducing a helical or parallel corrugation into the outer conductor of the coaxial cable without reducing the cross-sectional dimensions and/or the wall thickness beforehand by a drawing process that follows the welding, and receiving the coaxial cable in a receiving device.

2. The method as claimed in claim 1, wherein at least the welding region is flowed around or covered by an inert shielding gas during the heating.

3. The method as claimed in claim 1, further comprising: trimming one or two edges of the flat strip of nonferrous metal before the shaping operation.

4. The method as claimed in claim 3, further comprising: measuring the width of the trimmed strip of nonferrous metal prior to the welding and/or measuring at least one dimension of the coaxial cable after the welding, and controlling the cutting width in closed-loop fashion and/or controlling an apparatus for the purpose of shaping in a manner dependent on the measurement result and a specification value.

5. The method as claimed in claim 1, further comprising: measuring the temperature profile transversely with respect to the weld seam and controlling the energy introduced into the welding region in open-loop fashion in a manner dependent on a comparison of the temperature profile with a specification profile.

6. The method as claimed in claim 1, further comprising: inspecting the weld seam by means of ultrasound, eddy current measurement and/or x-rays.

7. The method as claimed in claim 1, further comprising: determining the tensile force on the flat strip of the nonferrous metal and/or the welded coaxial cable, and controlling, in closed-loop fashion, drives that supply the flat strip and/or the welded coaxial cable to the shaping operation, the welding operation, the corrugating operation and/or the receiving operation in a receiving apparatus.

8. An apparatus for the continuous production of coaxial cables having a thin-walled, radially closed, outer conductor of nonferrous metal, comprising: a supply device configured to supply a flat strip of the nonferrous metal, a supply apparatus configured to supply an inner conductor encased with a dielectric, a shaping apparatus, which shapes the flat strip of nonferrous metal into the profile of the outer conductor of the coaxial cable and around the supplied inner conductor such that the opposite edges of the flat strip of the nonferrous metal abut flush against one another in a butt-jointed manner, two guide means, which are spaced apart from one another and between which the edges are held lying flush against one another, a welding apparatus which welds the edges lying flush against one another between the guide means, wherein the welding apparatus comprises a laser which radiates light having a wavelength smaller than 600 nm with energy which causes local melting of the nonferrous metal to both sides of the abutting edges, a feed device, which conveys the welded coaxial cable further, a corrugator for introducing a helical or parallel corrugation into the outer conductor of the coaxial cable, and a receiving device, which receives the coaxial cable.

9. The apparatus as claimed in claim 8, further comprising: a measuring apparatus, which is arranged upstream of the shaping device and serves for ascertaining the tensile force acting on the supplied strip, wherein the ascertained tensile force is supplied for the purpose of open-loop control of drives of the apparatus.

10. The apparatus as claimed in claim 8, further comprising: a measuring and/or closed-loop control device, which is arranged downstream of the welding apparatus and which measures the tensile force acting on the welded coaxial cable, wherein the measured tensile force is supplied to a drive of the feed device for the purpose of closed-loop control.

11. The apparatus as claimed in claim 8, further comprising: a cutting device, which is arranged upstream of the shaping device and by means of which one or both edges of the supplied flat strip of nonferrous metal are trimmed, wherein the width of the trimmed strip corresponds to the circumference along the neutral fiber of the outer conductor of the coaxial cable.

12. The apparatus as claimed in claim 11, further comprising: an apparatus for receiving cutting remains.

13. The apparatus as claimed in claim 11, further comprising: a measuring device, which is arranged downstream of the cutting device and serves for measuring the width of the cut-to-size flat strip of nonferrous metal.

14. The apparatus as claimed in claim 8, further comprising: a measuring device for determining a temperature profile transversely with respect to the weld seam, wherein the measured temperature profile is supplied to the welding apparatus for the purpose of open-loop control of the energy discharged and/or to the supply device and/or to the feed device for the purpose of open-loop control of the supply rate.

15. The apparatus as claimed in claim 8, further comprising: a measuring device for measuring at least one dimension of the coaxial cable after the welding.

16. The apparatus as claimed in claim 8, further-comprising: a measuring device for inspecting the weld seam and/or checking for material defects or inhomogeneities of the material.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0040] The invention will be explained in more detail below by way of example on the basis of an embodiment with reference to the accompanying figures. All figures are purely schematic and not to scale. In the figures:

[0041] FIG. 1 shows an example of the method according to the invention for the continuous production of thin-walled, radially closed hollow profiles,

[0042] FIG. 2 shows an example of an apparatus according to the invention for the continuous production of thin-walled, radially closed hollow profiles,

[0043] FIG. 3 shows images of a weld seam of a hollow profile produced by the method according to the invention, and

[0044] FIG. 4 shows two exemplary coaxial cables having a helical and a parallel corrugation, respectively.

[0045] Identical or similar elements are provided with the same or similar reference signs in the figures.

EXEMPLARY EMBODIMENT

[0046] FIG. 1 shows steps of a method 100 for producing coaxial cables having a thin-walled, radially closed outer conductor according to one aspect of the invention. In step 102 of the method, a flat strip of nonferrous metal is supplied at a first supply rate to a shaping apparatus. For example, a flat copper strip is unwound from a coil. In the shaping apparatus, the supplied flat strip is shaped in step 108 into a form corresponding to the desired hollow profile of the outer conductor. The shaping may be effected by means of a roll forming tool, for example.

[0047] During the shaping, before the hollow profile forming the outer conductor is completely closed, a cable core which comprises an inner conductor encased by a dielectric and, if appropriate, further layers is supplied. The cable core may for example be supplied already in step 107 immediately before the first shaping stage.

[0048] Prior to the shaping, an optional step 104, in which one or both edges of the strip of nonferrous metal are trimmed or prepared in some other way, may be performed in a cutting device. In this way, even in the case of poor edge quality of the strip of nonferrous metal, the width of the strip can be uniformly and precisely set, and the edges can if appropriate be prepared for the subsequent welding operation. The cutting device may be supplied with measured values from a measuring apparatus which detects the width of the nonferrous metal strip after the trimming operation. The cutting remains may be received in a corresponding receiving apparatus.

[0049] During the shaping, the edges of the strip are guided by means of guide elements such that twisting prior to the welding is prevented, and the edges lying flush against one another are guided in a defined position and with a defined spacing past a welding apparatus. The guide elements may for example comprise one or more fin-type washers or guide blades and one or more guide bushings adapted to the geometry of the hollow profile and adapted to the hollow geometry to be manufactured. The geometry may be closed for example by means of drawing dies, closing rings or side-roller stages.

[0050] After the shaping, two opposite edges of the flat strip lie flush against one another in a contact region. In step 110, the edges which lie flush against one another in the contact region are continuously welded to one another. The welding is effected by means of a laser that radiates light having a wavelength smaller than 600 nm. If appropriate, the weld seam may be covered by means of shielding gas in a manner adapted to the required quality of the weld seam.

[0051] After the welding, the coaxial cable having the now radially closed outer conductor is drawn off from the welding region, step 114, and in step 119 a helical or parallel corrugation is introduced into the outer conductor before the now corrugated coaxial cable is supplied to a receiving device for receiving purposes in step 122. The drawing off is effected by means of a feed device, for example by means of a draw-off collet, draw-off cleat or draw-off belt. The feed device may be arranged upstream or downstream of the corrugator; it is also possible to provide two feed devices, one upstream and one downstream of the corrugator.

[0052] For the monitoring of the quality of the weld seam, it is possible in an optional step 112 for the temperature profile transversely with respect to the weld seam to be determined. The ascertained temperature profile may be supplied to a controller of the laser and to other elements of an apparatus which implements the method, in particular also to one or more drives which perform closed-loop control of the supply rate of the strip of nonferrous metal or the rate at which the welded coaxial cable is drawn off from the welding region.

[0053] The method may optionally also comprise an ascertainment of the tensile force on the strip prior to the shaping, step 106, and/or on the coaxial cable after the welding, step 120. The ascertained tensile force may likewise be supplied to one or more drives as a measured variable for the closed-loop control.

[0054] The method may furthermore comprise an optional step 116 in which one or more dimensions of the welded coaxial cable are determined. The ascertained dimensions may be supplied especially as input variables for the closed-loop control of the shaping process and of the cutting process for setting the width of the strip.

[0055] The method may furthermore comprise an optional step 118 in which the quality of the weld seam and/or the welding material are inspected non-destructively for material defects, for example by means of eddy current inspection, ultrasound or x-rays.

[0056] Not illustrated in the figure are subsequent processes by means of which the hollow profile is cut into pieces, the coaxial cable is encased with an insulating layer, or cables are assembled with plugs.

[0057] FIG. 2 shows an example of an apparatus according to the invention for the continuous production of coaxial cables having a thin-walled, radially closed outer conductor. A thin strip 204 of nonferrous metal, for example a copper strip, is unwound from a reel or unwinder 202. The strip 204 is supplied to a roll forming tool 212, by means of which it is brought into the form of the desired hollow profile of the outer conductor, for example is formed into a longitudinally slotted round tube. Between the reel or unwinder 202 and the roll forming tool 212 there may be provided a cutting apparatus 208, which cuts the strip 204 to a required width or cuts one or both edges of the strip 204 in order to obtain clean and smooth edges. A receiving device 205 may be provided for receiving cut-off parts of the strip 204. The width of the cut-to-size strip 204 may be inspected in a strip width measuring apparatus 210. The measurement results may be supplied to the cutting device 208 for the purposes of closed-loop control. Furthermore, between the coil or unwinder 202 and the roll forming tool 212 there may be arranged a measuring device 206 for ascertaining the tensile force, the measured values of which can be used for example for the closed-loop control of drives of the device. Before the closing of the hollow profile forming the outer conductor, from a supplying apparatus 207 there is supplied a cable core 209, which is received in the hollow profile after the flat strip of nonferrous metal has been shaped. Those edges of the strip that lie against one another after the hollow profile forming the outer conductor has been shaped can be guided in front of the laser welding apparatus 216 by one or more guide elements 214 such that twisting of the hollow profile prior to the welding is prevented, and the spacing with which it passes through below an optical system of the laser welding apparatus 216 is maintained. The guide elements may comprise one or more fin-type washers or guide blades and one or more guide bushings adapted to the hollow profile forming the outer conductor. The geometry of the hollow profile to be welded is closed by means of drawing dies, closing rings, side-roller stages or guide bushings 218, with the result that the edges of the strip 204 that have been shaped to form the hollow profile lie against one another in the region of the laser welding apparatus 216. The laser welding apparatus 216 radiates high-energy light at a wavelength smaller than 600 nm, preferably in a range between 550 and 450 nm. According to the invention, use may also advantageously be made of wavelengths in a range below 450 nm. The welding region may be covered with a shielding gas, for example argon, by means of a shielding-gas apparatus, not illustrated in the figure, in order to prevent reactions of the welding material with the atmosphere. The welded coaxial cable 224 is supplied by means of a feed device 219. The feed device 219 may for example comprise one or more draw-off collets, draw-off cleats, draw-off capstans or draw-off belts, or combinations of these. Before the welded coaxial cable 224 is wound up on a winder 226, one or more dimensions of the coaxial cable 224 may be detected, preferably contactlessly, by means of a measuring unit 220, and a helical or parallel corrugation may be introduced into the coaxial cable by means of a corrugator 223. In order to detect the tensile forces acting on the coaxial cable 224, a further tensile-force measuring apparatus 222 may be provided upstream of the winder 226.

[0058] FIG. 3 shows images of a weld seam of a hollow profile produced by the method according to the invention. The hollow profile is a copper tube having a wall thickness of 0.1 mm, which at a feed rate of 6 m/min was continuously shaped from a copper strip and welded. In this context, the welding point was covered with argon. FIG. 3 a) shows the weld seam, which has a width of between 140 and 150 m, on the outer side of the hollow profile. FIG. 3 b) shows a photograph of the inner side, on which the weld seam has a width of about 242 m, of the hollow profile. It can also clearly be seen that the weld seams are very uniform both on the inside and on the outside, with the result that reworking should not be necessary for most usage situations.

[0059] FIG. 4 shows two exemplary coaxial cables 500, 502 having a helical corrugation and a parallel corrugation, respectively. The coaxial cables 500, 502 are otherwise of conventional construction, having an inner conductor 504, surrounded by a dielectric 506, and outer conductors 508 and 510 which have helical corrugations and parallel corrugations, respectively. The outer conductors 508, 510 are surrounded by an outer insulating layer 512.

TABLE-US-00001 List of reference signs 1 Tube 2 Form 3 Plug 100 Method 102 Supplying the strip 104 Determining the tensile force 106 Trimming the edges 107 Supplying cable core 108 Forming the hollow profile 110 Welding operation 112 Determining the temperature profile 114 Drawing off the hollow profile 116 Determining the dimensions 118 Determining the quality 119 Corrugations 120 Determining the tensile force 122 Supplying to the receiving device 200 Apparatus 202 Winder/unwinder 204 Strip of nonferrous metal 205 Receiving apparatus for offcuts 206 Tensile force measuring apparatus 207 Supplying apparatus 208 Cutting device 209 Cable core 210 Strip width measuring apparatus 212 Roll forming tool 214 Guide element 216 Laser welding apparatus 218 Drawing die/guide bushings 219 Feed device 220 Measuring unit 222 Tensile force measuring apparatus 223 Corrugator 224 Coaxial cable 226 Winder 500 Coaxial cable (helical corrugation) 502 Coaxial cable (parallel corrugation) 504 Inner conductor 506 Dielectric 508 Outer conductor 510 Outer conductor 512 Insulating layer