EP1315255B1 - Method of producing sliding micro contacts - Google Patents

Description

The invention relates to a method for producing micro-grinding contacts according to the preamble of claim 1.

Micro-grinding contacts are used for contacting printed conductors or surfaces, with a relative movement often taking place between the micro-grinding contacts and the printed conductor or surface. In order to achieve a reliable contact, the micro-grinding contacts consist of a plurality of contact springs, which are arranged as close to each other as possible. The contact springs may be formed, for example, as spring tongues, which are punched out of Federblechbändern. A denser arrangement of contact springs, d. H. a larger number of contact springs per surface can be obtained by using round wires as contact springs.

In addition to the electrical conductivity is a corrosion resistance for the contact spring and abrasive sliding contacts an abrasion resistance important. It is known to produce the contact springs of spring bronze or steel. These materials are inexpensive and useful in terms of their electrical conductivity, spring properties and abrasion resistance. However, the corrosion resistance of these materials is not sufficient for all applications. It is therefore also known to produce the contact springs of a precious metal alloy. Such contact spring are well suited in their mechanical and electrical properties and have a high abrasion resistance and corrosion resistance. The disadvantage, however, are the relatively high material costs. As a compromise is known to produce contact springs as sheet metal stampings from a low-priced spring metal and apply by Stirnkanten- or roll clad precious metal parts in the areas of the contact spring, in which the contact surfaces are. In this manufacturing process, although only a smaller amount of the precious metal is needed, so that the material costs However, plating is an additional costly operation, which makes the advantage of reducing the cost of materials largely destroyed.

From JP 06275356 A a Mitschleifkontakt with a plurality of contact springs is known, which have contact-making contact surfaces, wherein the contact springs are provided with a noble metal coating.

US 2001/024735 A1 describes different brush contacts and methods for their surface treatment

The invention is therefore based on the object to provide a method with which micro-grinding contacts high quality can be produced inexpensively.

This object is achieved according to the invention by a method having the features of claim 1.

Advantageous embodiments of the method are specified in the subclaims.

According to the invention, the contact springs of the micro-grinding contact are produced from an alloy of at least one base metal. The contact surfaces are coated by build-up welding with an alloy containing at least one precious metal. This makes it possible to produce the contact spring from a low-cost material. The high wear resistance and corrosion resistance, which are necessary only for the contact surfaces, are achieved by coating these contact surfaces with a noble metal-containing alloy. The coating is carried out by build-up welding. This makes it possible to apply a very thin layer of the noble metal alloy, so that only the smallest possible amount of expensive precious metal alloy is needed. The build-up welding is simple in terms of production, so that this process step only reduces the production costs in one Compared to the saved material costs small dimensions fulfilled.

For cladding, the noble metal-containing alloy is preferably applied as a powder to the contact surface, for example, inflated by means of powder conveyors. The powder accumulated on the contact surface is then preferably melted by means of a laser beam. Cladding is expediently carried out under protective gas.

The application of the coating to the contact surface by fusion welding has the additional advantage that the edges of the contact springs in the region of the contact surface are also melted and rounded. An additional deburring of the contact springs is therefore not necessary.

The layer thickness of the noble metal alloy applied by the buildup welding can be very small and preferably only about 20 to 50 μ. Such a small layer thickness is sufficient to ensure the corrosion resistance and abrasion resistance. On the other hand, this small layer thickness means little need for the expensive noble metal alloy.

The inventive method for coating the contact surfaces can be used both in contact springs, which are formed as sheet metal stamped parts, as well as contact springs, which consist of round wires. The application of the noble metal alloy as metal powder has the advantage that the metal powder can be applied in a simple manner to the horizontally arranged contact surfaces. The powder that does not hit the contact surfaces can be collected below the contact springs and collected for further processing. Likewise, excess powder slips off the contact surfaces laterally and is also collected for further processing. After the powder has accumulated on the contact surface this is acted upon by a laser beam pulse, which melts the metal powder and preferably the surface of the contact spring, forming a liquid mirror of the noble metal alloy, which ensures a uniform formation of the contact surface after solidification.

If the contact spring is formed as a stamped part, the result is inevitably a gap between the individual spring tongues of the contact spring by punching. Through this gap, excess powder falls down when applied. Even with contact springs, which are formed from round wires, the excess powder falls between the contact springs down when the round wires are arranged at a distance. If round wires are arranged in the densest packing so that they touch each other in order to obtain the largest possible number of contacts per surface, the metal powder may not completely fall down between the individual contact surfaces of the round wires in certain circumstances. In this case, it may be expedient to guide the contact spring formed by the round wires over a rising ramp, so that the contact surfaces of the round wires are each raised individually. On the respective raised contact surface, the powder can now be applied and melted by means of Laserstrahlspülses.

When using round wires, it is also possible to use for the contact springs sheath wires, which have a core of a base metal and with a. Noble metal alloy, for example, are galvanically coated. As a result, the corrosion resistance is ensured even in the non-contact surface serving as lateral surface. When melting, the coating of the contact surface at the periphery connects to the shell of the round wire, so that there is a closed corrosion-resistant coating.

• Fig. 1: in perspektivischer vergrösserter Darstellung einen Mikroschleifkontakt,
• Fig. 2: eine Draufsicht auf den Mikroschleifkontakt,
• Fig. 3: eine Seiteansicht des Mikroschleifkontaktes,
• Fig. 4: vergrössert die Einzelheit A der Fig. 3 in einer Ausführung nach dem Stand der Technik,
• Fig. 5: eine Fig. 4 entsprechende Darstellung der Einzelheit A gemäß der Erfindung,
• Fig. 6: ein stark vergrößertes Foto der Einzelheit A nach dem Stand der Technik,
• Fig. 7: ein entsprechendes Foto der Einzelheit A gemäß der Erfindung,
• Fig. 8: in einer Seitendarstellung eine Erläuterung des Herstellungsverfahrens und
• Fig 9: eine Draufsicht auf Fig. 8.

In the following the invention will be explained in more detail with reference to an embodiment shown in the drawing. Show it

• 1 is a perspective enlarged view of a micro-grinding contact,
• 2 shows a plan view of the micro-grinding contact,
• 3: a side view of the micro-grinding contact,
• 4: enlarges the detail A of FIG. 3 in a version according to the prior art,
• 5 shows a representation corresponding to FIG. 4 of the detail A according to the invention,
• 6 is a greatly enlarged photograph of the detail A according to the prior art,
• 7 shows a corresponding photo of the detail A according to the invention,
• Fig. 8: in a side view an explanation of the manufacturing process and
• FIG. 9 is a plan view of FIG. 8.

FIGS. 1 to 3 show an example of a micro-grinding contact in which the production method according to the invention can be used.

A U-shaped stamped part 10 made of sheet metal, for example of steel or a copper-beryllium alloy, is inserted into a carrier block 12. On the free legs of the U-shaped stamped part 10 contact spring are welded, which are formed in the example shown as round wires 14. The Round wires 14 are welded with their rear ends on stamping lips 16 of the stamped part 10. The free ends of the round wires 14 are bent at right angles, so that the end faces of the round wires 14 form contact surfaces 18, with which the round wires 14 sit on tracks, not shown. In this way, the micro-grinding contact via the contact surfaces 18, the round wires 14 and the U-shaped stamped part 10 conductively connect two interconnects.

In the illustrated embodiment, a plurality of round wires 14, for example, fifteen round wires 14 with a diameter of about 0.1 mm are arranged side by side and touching each other. In this way, a large number of contact points on a relatively small width, for example, two millimeters are arranged side by side. It is obvious that, instead of the round wires 14, spring tongues punched out of the sheet metal of the stamped part 10 can also be used as contact springs. By punching the spring tongues remains between them each have a gap, so that the number of juxtaposed to a predetermined width contact springs in such an embodiment is lower.

Since the contact surfaces 18 have to bring about a contact contact with the respective conductor track, there is a risk that the contact resistance of this contact contact due to corrosion increases undesirably. If there is a relative movement between the contact surfaces 18 and the respective conductor surfaces with which they are in contact, the problem of abrasion and wear of the contact surfaces 18 also occurs.

According to the state of the art, it is known for these reasons to produce the round wires 14 from an alloy containing at least one precious metal. Such an alloy can be, for example, platinum, palladium, gold, silver and copper or contain a selection of these elements. In order to minimize the need for the expensive precious metal alloy, the U-shaped stamped part 10 is made of a low-cost material and only for the round wires 14 welded onto the stamped part 10 as a contact spring, the expensive precious metal alloy is used. Due to the precious metal used, the contact surfaces 18 of the round wires 14 are wear-resistant and corrosion-resistant. Figures 4 and 6 show the free ends of the round wires 14 with the contact surfaces 18 of a micro-grinding contact according to this prior art.

According to the invention, however, also for the contact springs, d. H. used in the illustrated embodiment, an inexpensive material for the round wires 14, which has the appropriate electrical conductivity and suitable spring properties, for example a spring bronze and in particular a copper-beryllium alloy. Since this material does not have the required high abrasion resistance and corrosion resistance, a coating 20 is applied according to the invention on the contact surfaces 18, which consists of an alloy containing at least one noble metal. The coating 20 thus forms the contact surface with which the round wires 14 resiliently come into contact with the conductor track. Figures 5 and 7 show the free ends of the round wires 14 with the coating 20 in a representation which corresponds to the representation of the prior art in Fig. 4 and 6.

To produce the coating 20, the precious metal-containing alloy is applied as a metal powder on the contact surfaces 18 of the free ends of the round wires 14 directed vertically upwards. Subsequently, the contact surfaces 18 are acted upon by the metal powder piled thereon under protective gas by means of a laser beam, preferably a pulsed laser beam. As a result, the metal powder and the surface of the contact surfaces 18 of the round wires 14 are melted so that they can connect. In this way For example, the coating 20 of the noble metal-containing alloy is applied by laser cladding.

In order to apply the metal powder containing the noble metal-containing alloy on the contact surfaces 18, the metal powder is preferably inflated by means of known powder conveyor on the contact surfaces 18 and piled. Due to the horizontal arrangement of the contact surfaces 18, a sufficient amount of the metal powder is deposited on these contact surfaces 18. By melting the metal powder by means of the laser beam, a mirror of the liquid noble metal alloy is produced which, after solidification, leads to a uniform, smooth coating 20 which has optimum contact properties. This coating 20 can be seen most clearly in FIG. 7.

If the contact springs are formed by stamped-out spring tongues or round wires 14 are used, which in contrast to the illustrated embodiment are spaced from each other, the metal powder and excess metal powder not striking the contact surface 18 fall laterally from the contact surfaces 18 laterally against the contact springs. The metal powder can be collected there and fed again.

If close-fitting round wires 14 are used, as shown in the illustrated embodiment, there is a risk that the powder applied to the contact surfaces 18 of the noble metal alloy bridges the contact surfaces 18 of abutting round wires 14 and when melting one of the adjacent round wires 14 connecting coating produced that obstructs the required mutual mobility of the individual round wires 14.

To avoid this, the method is modified in the manner shown in FIGS. 8 and 9. At the Laser cladding of the coating 20, the row of adjacent round wires 14 is moved over a ramp 22. The direction of movement is indicated in Fig. 8 by an arrow. When the round wires 14 are moved across the ramp 22 transversely to their axis, the round wires 14 are raised one at a time sequentially opposite the adjacent round wires 14, as shown in FIG. The powder of the noble metal alloy is in each case welded to the contact surface 18 by means of the pulsed laser beam on the upwardly raised round wire 14. Since the contact surface 18 of each raised round wire 14 is vertically separated from the contact surfaces 18 of the adjacent round wires 14, the application of the metal powder and the welding of the coating 20 without the above bridge formation can be carried out in the same manner as is possible with separate contact springs ,

In micro-grinding contacts, as they are often used in practice, the round wires 14 have a diameter of, for example, 0.1 mm. The material thickness of the coating 20 marked X in FIG. 5 is smaller than the wire diameter. Preferably, the thickness X of the coating 20 is 10% to 50% of the wire diameter. This results in a thickness X of the coating 20, which is in most cases about 20 to 50 μ. In the production, this thickness of the coating 20 generally already results from the fact that only a corresponding amount of the powder of the noble metal alloy can be piled up on the contact surfaces 18 of the round wires 14.

In an embodiment, not shown, the round wires 14 may be formed as a sheath wires. These have a core of the low-priced material, for example spring bronze, which is coated with a jacket made of a stainless steel alloy, for example. The jacket has a correspondingly small wall thickness. When surfacing the Coating 20 combines the molten metal powder on the contact surface 18 at the outer edge of the contact surface 18 with the material of the shell, so that a completely closed coating and sheathing of the round wires 14 is obtained with a noble metal-containing alloy.

LIST OF REFERENCE NUMBERS

10

U-shaped stamped part

12

carrier block

14

round wires

16

embossing ribs

18

contact surfaces

20

coating

22

ramp

Claims (7)

1. Method for producing microsliding contacts which comprise a number of contact springs with contact-providing contact surfaces, wherein the contact springs (14) are made from an alloy of at least one base metal and that a coating (20) of an alloy containing at least one noble metal is applied to the contact surfaces (18) of the contact springs (14), characterized in that the alloy containing at least one noble metal is blown onto the contact surface (18) as a metal powder by means of a powder conveyor and is applied by fusion-welding by means of a laser.
2. Method according to Claim 1, characterized in that the deposition welding is carried out under a protective gas.
3. Method according to one of the preceding claims, characterized in that the contact springs (14) are made of spring bronze, in particular beryllium bronze.
4. Method according to one of the preceding claims, characterized in that the alloy for the coating (20) contains one or more of the metals platinum, palladium, gold and silver.
5. Method according to Claim 4, characterized in that the alloy of the noble metals contains copper.
6. Method according to one of the preceding claims, wherein the contact springs are formed by round wires, characterized in that the round wires (14) are sheathed wires which comprise a core of the alloy of at least one base metal and a sheath of an alloy containing at least one noble metal.
7. Method according to one of the preceding claims, wherein the contact springs are mutually touching round wires, characterized in that the individual round wires (14) successively have their contact surface (18) raised above the contact surfaces (18) of the adjacent round wires (14), and in that the deposition welding of the coating (20) takes place on the raised round wire (14) in each case.

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