EP1048375B1 - Method for forming a copper blank by cold extrusion - Google Patents

Description

Method according to the preamble of claim 1 for forming a copper blank by cold extrusion.

The invention is in the field of prefabrication for gas-filled surge and is in the design of the course of a cold extrusion process and in the design of the associated press tool a single-stage double pressure apply, with which a blank copper is formed by cold extrusion in an end electrode for a gas-filled surge. Commonly used gas-filled surge arresters in the simplest version consist of a hollow-cylindrical ceramic insulator and two end electrodes inserted into the open ends of the insulator. These end electrodes are made of either an iron-nickel-cobalt alloy or copper and are cup-shaped, so that they have a pronounced Lötflansch. Well-shaped electrodes are most easily produced by flow-pressing or embossing processes ( DE 28 28 650 . DE 31 00 924 . U.S. 3,876,894 ).

Machines for the production of finished parts by cold extrusion usually carry out several pressing steps for forming a blank. Previously, the blank is obtained by cutting off a usually round bar stock, which is then automatically inserted into the actual pressing tool. The cutting process, for which the so-called cold gene exchange is widely used (Drahtwelt 2-1979, page 54ff), is integrated in the working steps of the press ( DE 36 35 677 A1 ). The length of the blank is determined by means of a feeder, which feeds the wire to the cutting tool, wherein the catchment length and thus the length of the blank is adjustable by means of a sliding block. The cutting tool is assigned a stop against which the wire end can be moved. - The Kaltgenauscheren is also used for the recovery of blanks made of copper; the minimum length of such blanks may be 0.2 d for rod material with a diameter d of 6 to 35 mm, if the rod material to be separated is previously brought to the yield point by compression in the space pressure stress state. - (Drahtwelt 1979). For very small compacts, such as end electrodes of gas-filled surge arresters, the blanks may need to be cut from a copper wire about 4.5 mm in diameter.

In the conversion of blanks to finished parts in two pressing steps so-called single-stage double pressure presses are often used, in which the pressing tool from a first, arranged in a fixed support molding, ie a single die, and arranged from two other of these die arranged in movable holders Moldings, ie stamping, namely a so-called pre-sampler and a so-called finished maker exists. If more than two pressing steps are required for forming the blank, so-called multi-stage presses are used, in which each forming step is assigned its own die and its own punch, wherein the blank to be formed is transported from forming stage to forming stage ( Manual "upsetting and pressing", Karl Hansa-Verlag Munich, 1973 ).

In the case of drop forging, which work with a closed die, it is necessary and customary to dimension the blank in the same volume as the finished part ( DE 38 05 628 A1 ).

For the production of nickel-iron-cobalt alloy end electrodes for gas-filled surge, it is also known to make the Kaltfließpreßvorgang so that the final electrode with finished molded Lötflansch - one in terms of compliance with its dimensions particularly critical area - the press leaves; this requires a prefabricated blank of the same size (sampling of the patent applicant with end electrodes by Biegelow, USA, in March 1994).

In the production of cup-like, i. With a conical dome provided end electrodes made of copper by means of a single-stage double pressure press, it has not been possible to work with a finished part to the same volume blank. The soldering flange was rather made with oversize and cut this soldering flange in a separate operation to finished size. - Such a cutting process would basically be integrated into a multi-stage press. However, the tool of a multi-stage press can also be configured such that a blank which is equal in volume to the finished part can be processed (presses supplied to the patent applicant by Schumag, DE, tool of the company K. Sieber GmbH & Co. KG, DE).

In the mentioned preparation of cup-like electrodes made of copper with a single-stage double printing press, the die has a provided with a waffle counter punch and is provided with an insert which serves to form the actual electrode body and the outer wall of the dome (similar to presses for the production of Collar sleeves, see reference book " Cold extrusion of steel and non-ferrous metals ", picture part, page 161, Springer-Verlag, 1983 such as " Cold Forming Guide II, pages 189/214, Michael Trilsch-Verlag, DRAHT-WELT, Dusseldorf, 1962 ). Furthermore, the pre-aspirator an Vorstauchernadel for preforming the electrode body and a filling piece for Hubbegrenzung the Vorstauchernadel and the Fertigmacher an insert with a pin for forming the calotte and with a pin adjacent to the plane annular surface for forming the Lötflansches on. At the same time, the pre-sampler and the use of the finishing machine maintain a distance to the die at the front dead center.

1. 1.: Zum Zwecke der Volumengleichheit zwischen Rohling und fertiggepreßter Endelektrode weist der Kulissenstein eine solche Länge auf, daß die Länge des abgeschnittenen Drahtstückes kleiner als der Durchmesser des Runddrahtes ist.
2. 2.: Die Vorstauchernadel weist eine abgerundete Kante auf und das Füllstück der Vorstauchernadel ist derart bemessen, daß die Vorstauchernadel im eingefahrenen Zustand des Vorstauchers aus der Vorstaucherbuchse heraus- und um etwa 0,5 mm in die Matrize hineinragt.
3. 3.: Der Matrizeneinsatz weist eine zylindrische Bohrung auf, die den Außendurchmesser des Lötflansches festlegt und in die zur Formung des eigentlichen Elektrodenkörpers und der Außenwand der Kalotte eine Einsatzbüchse eingesetzt ist; dabei weist zur Formung des Lötflansches die Stirnfläche der Einsatzbüchse von der Stirnfläche der Matrize einen Abstand auf, der etwa 5 % kleiner als die Dicke des herzustellenden Lötflansches ist.

Based on a method having the features of the preamble of claim 1, the invention has for its object to make the transformation of the copper blank to a terminal electrode rational. To solve this problem is provided with respect to the method that a copper blank is cut off, the volume of which corresponds to the volume of the final electrode to be produced and that is given its final shape with the second pressing step of the end electrode to be produced; With regard to a pressing tool for carrying out this method, the following measures are provided:

1. 1: For the purpose of equal volume between the blank and finished end electrode pressed the sliding block to such a length that the length of the cut piece of wire is smaller than the diameter of the round wire.
2. 2 .: The pre-plunger needle has a rounded edge and the filler of the pre-plunger needle is dimensioned such that the pre-plunger needle protrudes in the retracted state of the pre-sampler from the Vorstaucherbuchse and protrudes by about 0.5 mm into the die.
3. 3: The die insert has a cylindrical bore which defines the outer diameter of the Lötflansches and in which an insert bushing is used for forming the actual electrode body and the outer wall of the dome; In this case, for the formation of the Lötflansches the end face of the insert sleeve from the end face of the die at a distance which is about 5% smaller than the thickness of the Lötflansches to be produced.

This embodiment of the forming process and the tools required for carrying out the forming process leads to a discontinuation of the previous operation "edge trimming" with the known advantage of lower material consumption. This is possible because the length of the blank determined solely by the length of the sliding block is and that in the first pressing step by the design of the pre-dipper, the dome of the electrode is preformed.

Figur 1

die Matrize des Preßwerkzeuges mit zugeordnetem Fertigmacher,

Figur 2

den Einsatz und die Einsatzbüchse der Matrize,

Figur 3

den der Matrize im ersten Preßschritt zugeordneten Vorstaucher,

Figur 4

den der Matrize im zweiten Preßschritt zugeordneten Fertigmacher und

Figur 5

eine mit dem Preßwerkzeug hergestellte Endelektrode.

An embodiment of essential parts of a molding tool according to the invention is in the FIGS. 1 to 5 shown. It shows

FIG. 1

the die of the pressing tool with associated finished maker,

FIG. 2

the insert and the liner of the die,

FIG. 3

the pre-sampler associated with the die in the first pressing step,

FIG. 4

the die associated with the die in the second pressing step and

FIG. 5

an end electrode made with the pressing tool.

According to FIG. 5 End electrodes 1 are to be produced, which consist essentially of the actual electrode body 2 and a Lötflansch 3, wherein the soldering flange and electrode body are connected to each other via a hollow cone-like wall 4, which forms a conical dome 5. In this cap protrudes a welding nozzle 6 for welding a lead wire to the electrode 1 into it.

To produce such a terminal electrode is a pressing tool, according to the FIGS. 1 and 3 consists essentially of a stationarily arranged die 10 and two dies associated with this die 20 and 30, wherein it is the punch 20 is a preassembler and the punch 30 is a finished maker.

The die 10 has a continuous, stepped bore into which initially a filler 17 and an insert 11 are inserted. In the bore of the tubular insert 11, an insert sleeve 14 is inserted, the end face 15 within the bore 12 of the insert 11 relative to the end face 13 of the insert 11 is reset by a distance a is. This distance corresponds in principle to the thickness of the electrode flange 3 in order to form the electrode flange in this area; however, it is smaller by about 5% than the thickness of the soldering flange to be produced.

According to FIG. 1 The finished maker 30 includes an insert 31, which forms the forming part of the finished maker 30 and according to FIG. 4 is provided with a pin 33 for the final forming of the dome 5 of the end electrode and is further provided adjacent to the pin with a flat annular surface 32 for forming the Lötflansches 3. The finished maker 30 is guided in the associated Kaltfließpreßmaschine so that it maintains a distance b from the end face 15 of the insert 11 of the die 10 at the front dead center with its annular surface 32, which is about 5% of the thickness of the produced Lötflansches 3. For example, with a thickness of the solder flange of 0.48 mm, the distance b is about 2/100 mm.

To form the electrode 1, a counter punch 16 is inserted into the die 10, which is supported by a holder 18.

According to FIG. 3 the die 10 is associated in a first pressing step of the pre-upshot 20, which, inter alia, has a bush 21 for guiding the pre-plunger needle 22 and whose pre-plunger needle 22 is slightly rounded in the edge region 23. In the rear space 24 of the pre-sampler a spring, not shown, and a filler not shown in detail for determining the penetration depth of the pre-plunger needle 22 are arranged in the die 10. The filler is dimensioned so that the pre-plunger needle 22 protrudes in the retracted state of the pre-dipper in the die by about 0.5 mm, thereby preforming the dome of the end electrode.

Claims (1)

1. Method for deforming a copper blank by cold extrusion to form a terminal electrode (1), equipped with a conical dome (5) and a soldering flange (3), for a gas-filled overvoltage arrester,
   in which method it is firstly the case in a first manufacturing step that the copper blank is cut off from a round wire with a diameter of approximately 4.5 millimetres, and in which method it is subsequently the case that the copper blank is inserted between a first mould part, which is arranged in a static holder, and two further mould parts, which are arranged in movable holders, and the two further mould parts are moved against the copper blank successively in two pressing steps,
   characterized
   in that a copper blank is cut off whose volume corresponds to the volume of the terminal electrode (1) to be produced, and in that the terminal electrode (1) to be produced has its final shape imparted to it by means of the second pressing step.

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