DE102019201185A1 - Process for producing a spark plug electrode, spark plug electrode and spark plug - Google Patents

Abstract

The invention relates to a method for producing a spark plug electrode (3) comprising an electrode base body (9) made of a first material and an ignition element (10) made of a second material, the method comprising the following steps: providing the electrode base body (9) and the Ignition element (10), performing a welding process for connecting the electrode base body (9) and the ignition element (10) to form a weld seam (11), wherein to carry out the welding process, a welding beam (5) of a pulsed laser is applied to a reflection means (6) Connection area between the electrode body (9) and the ignition element (10) is directed and the weld seam (11) is generated, and by tilting the reflection means (6) the welding beam (5) is guided over the connection area.

Description

State of the art

The present invention relates to a method for producing a spark plug electrode and a spark plug electrode with very good spark formation, high spark erosion resistance and service life. Furthermore, the present invention also relates to a spark plug which comprises the spark plug electrode according to the invention.

The lifespan of a spark plug is largely determined by the durability of its components. The spark plug electrodes represent a special limitation of durability because they are subject to high erosion rates due to the spark load. Here, permanent good spark formation is achieved through the use of noble metals for the ignition elements, the so-called electrode pins, which are connected to an electrode base body. The larger the surface of the ignition element, the better, more stable and more permanent ignition sparks can be formed. To connect an ignition element to an electrode base, strikes DE 10 103 045 A1 a laser welding method using a cw laser beam (continuouswave laser beam), in which the cw laser beam is directed statically onto the connection area between the electrode base and the ignition element. Due to the continuous heating due to the uninterrupted radiation, the connection area heats up strongly and the ignition element and the electrode base body melt strongly, which leads to the formation of a wide weld seam and is accompanied by a reduced, remaining pure material of the ignition element. The remaining height of the ignition element, viewed in the direction of the longitudinal axis of the spark plug electrode, is low, which prevents a stable and permanently good spark formation.

Disclosure of the invention

The method according to the invention enables the production of a spark plug electrode in which an electrode base body made of a first material and an ignition element made of a second material are connected by a weld seam with a small width, and by means of which melting and thus loss of pure material of the ignition element is reduced that a residual height of the ignition element in the direction of the longitudinal axis of the spark plug electrode, and thus also a surface of the ignition element, is maximized. The residual height of the ignition element is understood to mean the height of the pure material of the ignition element remaining in the direction of the longitudinal axis of the spark plug electrode, that is to say without including the weld seam formed between the electrode base body and the ignition element. The weld seam contains a mixture of the first material of the electrode base body and the second material of the ignition element. The longitudinal axis of the spark plug electrode coincides in particular with the longitudinal axis of the main electrode body and the longitudinal axis of the ignition element.

For this purpose, the method according to the invention initially provides a step of providing the electrode base body and the ignition element. These elements are then arranged in a desired arrangement to one another. A welding process is then carried out to connect the electrode base body and the ignition element, by means of which a weld seam is formed between the electrode base body and the ignition element. The welding process is carried out using a welding beam from a pulsed laser, the welding beam being directed via a reflection means onto a connection area between the electrode base body and the ignition element and producing the weld seam. By tilting the reflection means, the welding beam is guided over the connection area, that is, over the locations of the electrode base body and the ignition element to be connected, so that the electrode base body and the ignition element are connected to one another in a permanently stable manner, forming a weld seam. The tilting of the reflection means, which is in particular a periodic tilting, results in a local modulation of the welding beam on the surface areas of the spark plug electrode to be connected. The reflection means is, for example, a mirror or a so-called scanner.

According to the invention, a pulsed laser is used which emits an intermittent welding beam. This means that each laser pulse is accompanied by a heating phase of the materials to be connected, which is followed by a cooling phase until the next laser pulse hits the connection area. In particular, the heat input into the materials is modulated by the cooling phases, so that only an average heating in the material is shown, which has only a slight increase over the welding time. Since less first material and second material also melt, this significantly reduces the loss of pure material of the ignition element and the weld seam is formed with a narrow width, which also means that the remaining height of the ignition element remains at a maximum. Due to the large surface area of the ignition element with very good spark formation, this leads to a permanently stable and spark erosion-resistant spark plug electrode, which is characterized by a long service life. Error patterns, such as welding pores or notches, can be reduced. The weld seam formed by the method according to the invention with a small width also enables the use of ignition elements with a lower absolute height, since the loss of pure material on the second material of the ignition element is reduced and the residual height is also increased. By using ignition elements with a lower absolute height before the welding process, further material costs can be saved.

The method according to the invention is simple and inexpensive to use.

The subclaims show preferred developments of the invention.

The formation of a weld seam with a small width can further be promoted by the advantageous development in which the electrode base body and the ignition element are pressed against one another during the welding process with a force F in the direction of the longitudinal axis of the electrode base body and the ignition element. The longitudinal axes of the electrode base body and of the ignition element preferably coincide to form a longitudinal axis and can also be regarded as the longitudinal axis of the spark plug electrode. This also prevents the formation of defects in the weld seam. Since there is no significant heating of the materials to be welded due to the pulsed laser process to be used, pressing against one another is of particular advantage and also only possible through the cooling phases following the heating phases. It is not possible or only possible to a limited extent when using a cw laser method, since here the materials to be welded are continuously heated in the connection area, so that pressing against one another leads to mutual insertion of the first material of the electrode base body and the second material of the ignition element. This significantly increases the loss of second material. On the other hand, if the materials to be welded are not pressed against one another, the formation of defects in the weld seam can be increased. The force with which the materials to be welded are pressed against one another is preferably 5 to 15 N and further advantageously 10 to 12 N.

It is preferably provided that the welding beam is guided along a line on the surface of the spark plug electrode that is parallel to a longitudinal axis of the ignition element. This longitudinal axis advantageously extends through the connection area between the ignition element and the basic electrode body, that is to say also through the subsequent weld seam.

According to a further advantageous development, the electrode base body and the ignition element rotate at the same speed and in the same direction during the execution of the welding process. This leads to a uniform further movement of the welding beam and thus to a very good connection between the electrode base and the ignition element.

Furthermore, the reflection means is advantageously tilted at a frequency of at least 1000 Hz. For example, the reflection means is tilted at a frequency of 1200 Hz. The result of this is that the welding beam essentially executes a movement parallel to the longitudinal axis X of the ignition element and the electrode base body and slips over the same line or the same area several times.

This is also supported, for example, by the fact that the electrode base body and the ignition element are preferably rotated during the welding process, as described above, and the frequency of rotation of the electrode base body and the ignition element is lower than the frequency at which the reflection means is tilted. Due to the relatively rapid tilting of the reflection means in comparison to the rotation of the electrode base body and the ignition element, the welding beam practically performs a scanner movement on the surface of the materials to be connected.

The wavelength of the pulsed laser is preferably 1.03 to 1.07 μm, which can be achieved by using an Nd: YAG laser or Yb: YAG laser. Alternatively, the wavelength can also be in a range from 800 to 1030 nm or in a range from 1070 to 2000 nm.

• - mittlere Laserleistung: 1 W bis 2 kW
• - Pulsdauer τ: 1 bis 500 ns, insbesondere 120 bis 500 ns
• - Repetitionsrate des Lasers v_rep: 1 Hz bis 2 MHz
• - Fortbewegungsgeschwindigkeit des Reflexionsmittels: 1 mm/s bis 1 km/s (2D-Polygonscanner), insbesondere 1 mm/s bis 10 m/s (2D-Galvo-Scanner)
• - f_Wobble: mindestens 1 Hz, insbesondere 1 Hz bis 4 kHz.

In order to further reduce heating of the materials to be welded, the welding process is preferably carried out with the following parameters:

• - Average laser power: 1 W to 2 kW
• - Pulse duration τ: 1 to 500 ns, in particular 120 to 500 ns
• - Repetition rate of the laser v _rep : 1 Hz to 2 MHz
• - Movement speed of the reflection medium: 1 mm / s to 1 km / s (2D polygon scanner), in particular 1 mm / s to 10 m / s (2D galvo scanner)
• - f _wobble : at least 1 Hz, in particular 1 Hz to 4 kHz.

The wobble frequency f _wobble denotes the period of a cycloid resulting from the movement of a circular path.

• mit π = 3,14
• α = thermische Leitfähigkeit [m²/s]
• I₀ = Strahlintensität Laser [W/cm²] (Leistung pro Fokusfläche auf Bauteil)
• R = Reflexionsgrad des Materials (bestimmbar z.B. mit Ulbricht-Kugel, A+R+T=1)
• K = Wärmeleitfähigkeit des Materials [W/mK] (bestimmbar z.B. über k = α*ρ*Cp, mit Kombination aus z.B. Laserflash + Dilatometer + Differential Scanning Calorimetrie (DSC))
• t = Laserpulsdauer [s] (bestimmbar mittels z.B. Oszillation für kurze und mit AutoKorrelation für ultrakurze Pulse)
• v_rep = Repetitionsrate des Lasers (einstellbar durch z.B. Güteschaltung (Q-switch) bei Nanosekundenlaser)

The mean heating ΔT [K] as a result of a laser pulse of the materials to be bonded results from the following equation: $$\Delta \text{T}=\left(1-\text{R}\right)*\left(\mathrm{2nd}*{\text{I.}}_0/\text{K}\right)*{\text{v}}_{\text{rep}}*\mathrm{\tau }*{\left(\mathrm{\alpha }*\text{t}\right)}^{1/\mathrm{2nd}}*1/{\mathrm{\pi }}^{1/\mathrm{2nd}},$$

• with π = 3.14
• α = thermal conductivity [m ² / s]
• I ₀ = laser beam intensity [W / cm ² ] (power per focus area on component)
• R = reflectance of the material (determinable e.g. with Ulbricht sphere, A + R + T = 1)
• K = thermal conductivity of the material [W / mK] (can be determined e.g. via k = α * ρ * Cp, with a combination of e.g. laser flash + dilatometer + differential scanning calorimetry (DSC))
• t = laser pulse duration [s] (can be determined using, for example, oscillation for short and auto-correlation for ultra-short pulses)
• v _rep = repetition rate of the laser (can be set using, for example, Q-switch for nanosecond lasers)

A further advantageous development provides that the first material is nickel or a nickel alloy with nickel as the main constituent in mass%. A first material based on nickel has the advantage that it is easy to machine and has low material costs.

Alternatively or in addition to this, the second material is preferably a noble metal or a noble metal alloy, the noble metal in particular being at least one element from the group consisting of: Ir, Pt, Pd, Rh, Ru, Re, Ag, Au and Os. A second material based on a noble metal has the advantage that the ignition element made of it has a high corrosion resistance and erosion resistance. The method according to the invention is of particular advantage, in particular for precious metal-containing second materials, since, owing to the reduced width of the weld seam that is formed, only a small proportion of noble metal of the ignition element for spark formation is lost by forming the weld seam with a small width and the remaining height of the ignition element and thus also Surface of the ignition element is maximum.

The spark plug electrode is particularly advantageously a central electrode, since the method according to the invention can be used particularly well here.

Furthermore, according to the invention, a spark plug electrode is also described which is produced by the above method according to the invention. Due to the specific production, the spark plug electrode is characterized by a long service life with very good spark formation, is very resistant to corrosion and erosion and is inherently and therefore mechanically stable.

In addition, according to the invention, a spark plug electrode is also described which comprises an electrode base made of a first material and an ignition element made of a second material. The electrode base and the ignition element are connected to one another by a weld seam, a ratio of a residual height of the ignition element to a width of the weld seam, measured in each case along a longitudinal axis of the spark plug electrode, being 15: 1 to 10: 1. The spark plug electrode can be produced according to the method disclosed above using a pulsed laser welding method.

Furthermore, according to the invention, a spark plug is also described which contains a spark plug electrode as disclosed above, which is designed in particular as a center electrode. The spark plug according to the invention is also characterized by a high durability and long service life with reliable ignition spark formation.

Figure list

• 1 eine schematische Teilschnittansicht einer Zündkerze gemäß einer ersten Ausführungsform und
• 2 eine schematische Zeichnung, veranschaulichend ein Verfahren zur Herstellung einer Zündkerzenelektrode gemäß einer zweiten Ausführungsform.

Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawing. In the drawing is:

• 1 is a schematic partial sectional view of a spark plug according to a first embodiment and
• 2nd is a schematic drawing illustrating a method for producing a spark plug electrode according to a second embodiment.

Embodiments of the invention

In the figures, only the essential features of the invention are shown. All other features have been omitted for the sake of clarity. Furthermore, the same reference numerals denote the same components.

How out 1 can be seen, includes the spark plug 1 according to a first embodiment, a ground electrode 2nd and a center electrode 3rd . An isolator 4th is provided such that the center electrode 3rd in a known way something from the isolator 4th protrudes. The isolator 4th itself is partly from a housing 5 surround. The reference number 6 denotes an electrical connection nut.

From the electrical connection nut 6 is an electrically conductive connection via a connection bolt 7 and a spark plug resistance element 8th to the center electrode 3rd intended.

The center electrode 3rd is according to the in 2nd illustrated method.

In the 2nd The spark plug electrode shown corresponds to the center electrode 3rd out 1 and comprises an electrode base 9 , an ignition element 10th and a weld 11 with a width B that the electrode base 9 and the ignition element 10th cohesively connected. The ignition element 10th has a longitudinal axis Y that is perpendicular to the connection area between the ignition element 10th and the electrode base 9 , or also perpendicular to the weld 11 after the welding process. The longitudinal axis X of the spark plug electrode 10th coincides with the longitudinal axis Y of the electrode body 9 and the ignition element 10th together.

The ignition element 10th is for example in the form of a pin or a pin. The center electrode 3rd has a surface 14 going through the surface 15 of the ignition element 10th and the surface of the electrode base 9 is formed. The area of the surface 14 the center electrode 3rd around the connection area between the electrode base body 9 and ignition element 10th is also referred to as the welding area in which the materials to be welded are present. The welding process creates the weld in the connection area 11 .

The electrode base body is advantageously 9 and the ignition element 10th during the execution of the welding process with a force F in the direction of the longitudinal axis Y of the ignition element 10th and the electrode body 9 pressed against each other so that the weld seam 11 trains without defects.

About a reflection medium 13 , for example a mirror, the welding beam 12th , a laser beam from a pulsed laser, onto the connection area between the electrode base body 9 and the ignition element 10th directs and creates the weld there 11 .

Such a welding process is also a laser scanner welding process, for example, in which a laser beam is directed onto the objects to be welded via a scanner and produces a weld seam. By moving the scanner, the laser beam is guided to the desired position on the objects. According to the invention, a pulsed laser is used, since this results in only a slight heating and, after each heating by a laser pulse, the materials to be welded in the connection area are cooled again. This only leads to a slight melting of the materials to be welded, so that the width B of the weld seam 11 compared to a weld created by means of a cw laser, is significantly smaller.

The basic electrode body 9 and the ignition element 10th are rotated about the longitudinal axis Y in the same direction at the same speed. After rotation of the spark plug body 9 and the ignition element 10th The weld seam is formed around the longitudinal axis Y during the welding process 11 , which then extends over the entire diameter of the ignition element 10th extends.

During the irradiation of the welding beam 12th to the surface 14 the center electrode 3rd becomes the reflection medium 13 periodically tilted so that the welding beam 12th in a periodic movement along the surface 14 to be led. The movement is preferably parallel to the longitudinal axis Y of the ignition element 10th and the electrode body 9 . Through this local modulation of the irradiation of the welding beam 12th there will be a good connection between the ignition element 10th and the electrode base 9 promoted.

Typically the reflective 13 tilted at a frequency of at least 1000 Hz, here eg 1200 Hz. The rotation of the electrode body 9 and the ignition element 10th about the longitudinal axis Y of the ignition element 10th and the electrode body 9 has a much lower frequency.

• - mittlere Laserleistung: 1 W bis 2 kW
• - Pulsdauer τ: 1 bis 500 ns, insbesondere 120 bis 500 ns
• - Repetitionsrate des Lasers v_rep: 1 Hz bis 2 MHz
• - Fortbewegungsgeschwindigkeit des Reflexionsmittels: 1 mm/s bis 1 km/s (2D-Polygonscanner), insbesondere 1 mm/s bis 10 m/s (2D-Galvo-Scanner)
• - f_Wobble: mindestens 1 Hz, insbesondere 1 Hz bis 4 kHz.

In order to further reduce heating of the materials to be welded, the welding process is carried out in particular with the following parameters:

• - Average laser power: 1 W to 2 kW
• - Pulse duration τ: 1 to 500 ns, in particular 120 to 500 ns
• - Repetition rate of the laser v _rep : 1 Hz to 2 MHz
• - Movement speed of the reflection medium: 1 mm / s to 1 km / s (2D polygon scanner), in particular 1 mm / s to 10 m / s (2D galvo scanner)
• - f _wobble : at least 1 Hz, in particular 1 Hz to 4 kHz.

This in 2nd The method shown enables the production of a central electrode 3rd in which an electrode body 9 of a first material, which contains in particular nickel or an alloy with nickel as the main constituent in mass%, and an ignition element 10th from a second material, the is in particular a precious metal, through a weld 11 are connected with a small width B, and through which a melting and thus a loss of pure material of the ignition element 10th is reduced so that a residual height R of the ignition element 10th in the direction of the longitudinal axis of the center electrode 3rd , and thus also a surface available for spark formation 15 of the ignition element 10th is maximized. In particular, there is a ratio of the residual height R of the ignition element 10th to the width B of the weld 11 , each measured along a longitudinal axis X of the spark plug electrode 1 , 10: 1. In other words, this means that if the residual height R of the ignition element 10th 4 mm, the width B of the weld 11 Is 0.4 mm.

This enables the central electrode produced in this way 3rd with very good spark formation, permanent stability against corrosion and erosion, so that the center electrode 3rd characterized by a long service life. Error patterns, such as welding pores or notches, are reduced. For the center electrode 3rd can due to the weld seam that forms 11 with small width B ignition elements 10th with a reduced absolute height, which means that additional material costs can be saved.

QUOTES INCLUDE IN THE DESCRIPTION

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Patent literature cited

• DE 10103045 A1 [0002]

Claims (11)

Method for producing a spark plug electrode (3) comprising an electrode base body (9) made of a first material and an ignition element (10) made of a second material, the method comprising the following steps: - providing the electrode base body (9) and the ignition element (10), - performing a welding process for connecting the electrode base body (9) and the ignition element (10) to form a weld seam (11), - In order to carry out the welding process, a welding beam (12) of a pulsed laser is directed via a reflection means (13) onto a connection area between the electrode base body (9) and the ignition element (10) and generates the weld seam (11), and - By tilting the reflection means (13) the welding beam (12) is guided over the connection area. Procedure according to Claim 1 , wherein the electrode base body (9) and the ignition element (10) are pressed against one another during the execution of the welding process with a force (F) in the direction of the longitudinal axis (Y) of the electrode base body (9) and the ignition element (10). Procedure according to Claim 1 or 2nd , wherein the electrode base (9) and the ignition element (10) rotate during the welding process at the same speed and in the same direction. Method according to one of the preceding claims, wherein the reflection means (13) is tilted at a frequency of at least 1000 Hz. Method according to one of the preceding claims, wherein the wavelength of the pulsed laser is 1.03 to 1.07 µm, 800 to 1030 nm or 1070 to 2000 nm. Method according to one of the preceding claims, wherein the welding process is carried out with the following parameters: - average laser power: 1 W to 2 kW - pulse duration τ: 1 to 500 ns, in particular 120 to 500 ns - repetition rate of the laser v _rep : 1 Hz to 2 MHz - speed of travel of the laser beam (12): 1 mm / s to 1 km / s (2D polygon scanner), in particular 1 mm / s to 10 m / s (2D galvo scanner) - f _wobble : at least 1 Hz, in particular 1 Hz to 4 kHz. Method according to one of the preceding claims, wherein the first material is nickel or a nickel alloy with nickel as the main component and / or the second material is a noble metal or a noble metal alloy, in particular the noble metal at least one element from the group: Ir, Pt, Pd, Rh , Ru, Re, Ag, Au and Os is. Method according to one of the preceding claims, wherein the spark plug electrode is a central electrode (3). Spark plug electrode, produced by a method according to one of the Claims 1 to 7 . Spark plug electrode comprising an electrode base (9) made of a first material and an ignition element (10) made of a second material, the electrode base (9) and the ignition element (10) being connected to one another by a weld seam (11), a ratio of a residual height ( R) of the ignition element (10) to a width (B) of the weld seam (11), measured in each case along a longitudinal axis (X) of the spark plug electrode (1), is 15: 1 to 10: 1. Spark plug comprising a spark plug electrode after Claim 9 or 10th , wherein the spark plug electrode is in particular a center electrode.

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