1. Field of the Invention
The invention relates to a method and a device for manufacturing a noble metal armored electrode for a spark plug.
2. Description of Related Art
European Patent Application EP 0 418 281 B1 and corresponding U.S. Pat. No. 4,810,220 disclose a method for manufacturing a noble metal armored electrode for a spark plug through a large number of different working steps which include the transport of intermediate products to several finishing stations, which means that the production process is generally expensive and associated with considerable production tolerances.
A primary object of the present invention is to provide a method and device of the type already mentioned, wit which series production of noble metal armored electrodes of improved quality is possible.
This object is achieved according to the invention by a method and device by which a noble metal piece is placed on a front end of a base electrode element and is pressed into the base electrode element while controlling displacement.
In the method and device according to the invention an electrode base element is positioned in a work station and fixed there, and a piece of noble metal is then positioned by means of a feeding means on the tip of the base electrode element. After the base electrode element and the piece of noble metal arranged on it are heated, the noble metal piece is pressed into the base element. After cooling, the piece of noble metal is pressed flat by further pressing. In this process, the working steps of manufacturing the noble metal armored electrode take place either in a single work station or, in parallel, in several identical work stations, which shortens the cycle times. This guarantees better dimensional stability since the pressing-in of the piece of noble metal is not determined by the pressure but by displacement.
If, in addition, laser welding of the piece of noble metal is provided on the base electrode element, a longer service may be achieved.
A particularly preferred embodiment of the method and device according to the invention is described in greater detail in the following with reference to the accompanying drawings.
The device for manufacturing a noble metal armored electrode shown in
As shown in
The device shown in
The device described above operates according to the following process:
In a first process step, shown in
In the next process step, shown in
During this current supply, or immediately after the electric current is switched off, the noble metal piece 3 is then pressed into the tip of electrode blank 1, as shown in
During subsequent pressing, the pressing path is also limited to achieve high dimensional accuracy. As also shown in
On the interface between both components 1, 3, an alloy weld layer 8′ has been formed by laser welding on the circumference, which layer represents a mixture of the noble metal in noble metal piece 3 and the material of electrode blank 1. This alloy weld layer 8′ serves not only for secure fastening, but also as a transitional zone of the coefficient of thermal expansion. This transitional zone reduces the stresses between the two materials under thermal load due to the different coefficients of thermal expansion that could lead to detachment of noble metal piece 3 after long-term use.
It is particularly advantageous for alloy layer to extend throughout the cross-section or at least over most of the cross-section of the noble metal armored electrode formed.
The electrode formed by the method described above may be further machined, e.g., by mold reduction on the electrode tip.
In the above, the method of the invention was described by taking the example of manufacturing the central electrode of a spark plug. It is understood that the method according to the invention can also be used to manufacture a mass electrode in different molds.
The shape of noble metal piece 3, which is fed to the tip of electrode blank 1 in the first process step, is not limited to the spherical shape described above and provided in preference. Noble metal piece 3 may be a small plate, a pipe section, a cylinder, a ring or a composite material formed of a noble metal and a non-noble metal.
The method according to the invention and the device according to the invention enable several working processes to be combined in one work station.
It is also possible to manufacture, e.g., machine the electrode in all positions, e.g., even horizontally.
Number | Date | Country | Kind |
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10 2005 015 413.1 | Apr 2005 | DE | national |