The method described above makes it possible to produce coaxial cables with outer conductors having a wall thickness of 0.10 mm at welding rates greater than 6 m/m in without a drawing process that follows the welding, it being possible to keep the quality of the weld seam constant for several hours, with the result that coaxial cables having large lengths can be produced.

The smaller wall thickness of the outer conductor of the coaxial cable results in saving in terms of copper and other alloy elements and thus in the conservation of valuable resources. A decrease in the wall thickness reduces the laser power required for the welding, this in turn being accompanied by energy savings or alternatively allowing the process rate to be increased while maintaining the same laser power.

With regard to the finished product, the thinner wall thickness of the outer conductor likewise proves to be advantageous, as it results in a lower weight per unit of length, which facilitates transport and installation.

The thinner wall thickness furthermore allows for smaller diameters when the outer conductor is being formed. This allows the outer diameter of the cable to be reduced while maintaining the same design. Apart from the further weight reduction, this leads to smaller minimum bending radii and thus to more flexibility in terms of the laying.

BRIEF DESCRIPTION OF THE DRAWING

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:

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

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

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

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

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

DETAILED DESCRIPTION

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.