DE102010024233A1 - Supplying a filler material during laser beam build-up welding, comprises placing the filler material either in the form of a foil or a filler material bound to the foil, in focused laser beam - Google Patents

Abstract

Supplying a filler material during laser beam build-up welding, comprises placing the filler material either in the form of a foil or a filler material bound to the foil, in focused laser beam. An independent claim is also included for a device for carrying out the above method, comprising the filler material bound to the foil.

Description

The invention relates to a method for feeding filler material in laser beam buildup welding, in particular in micro laser beam buildup welding.

State of the art

Welding means (according to EN 14610 and DIN 1910-100 ) the non-detachable joining of components using heat or pressure, with or without welding consumables. During fusion welding, the base materials are heated up to liquefaction and thus connected.

Laser beam welding is mainly used for welding components which have to be joined with high welding speed, narrow and slim weld seam shape and with low thermal distortion. The laser beam welding or laser welding is usually performed without feeding a filler material.

The laser radiation is focused by means of optics on the workpiece surface. The focal spot has typical diameters of a few tenths of a millimeter, resulting in very high energy concentrations when the laser used has the typical power of a few kilowatts of laser power. By absorbing the laser power on the workpiece surface, an extremely rapid rise in temperature beyond the melting temperature of metal, so that forms a melt. Due to the high cooling rate of the weld this becomes very hard depending on the material and usually loses toughness.

In laser deposition welding, an additional material, usually a powder or wire, is melted with the laser beam and fusion-metallurgically bonded to the base material. The main process features are u. a. The high-precision, automated application of layers with thicknesses of 0.1 millimeters to several centimeters, the metallurgical fusion of the layer with the workpiece, the absence of Einbrandkerben, a low heat input into the substrate, a large selection of similar and alien additional materials and the Possibility of machining almost all metallic alloys.

Thanks to the very good focusing properties of the laser beam, the method allows extremely thin walls of only a few tenths of a mm width to be built up. The welded layers are typically 0.2 to 0.5 mm thick. Typical area rates are several cm ² per minute for a layer thickness of about 1 mm. At the same time, layer thicknesses of 1/10 mm to several mm are possible with this method due to multi-layer technology.

Compared to other processes, such as plasma build-up welding, laser powder build-up welding impresses with minimum thermal stress on the component and extremely low distortion of the workpiece.

In particular, CO ₂ , Nd: YAG and diode lasers for pulsed and continuous operation as well as fiber lasers with laser powers of 100 W to several kW are used for laser deposition welding.

In the case of laser-beam build-up welding with powdered filler materials, powder feed into the molten bath is of decisive importance. The powder utilization rate, the oxidation by the surrounding atmosphere and the roughness of the layer are thereby significantly determined. At present, there are already several industrial-grade powder nozzles which are usually of modular construction and optionally also already allow integrated water cooling.

The additives can be supplied not only in powder form, but in principle also as a constituent of an ink in the ink-jet process (eg from Optomec) or in the form of a wire. For example, thin wires with diameters between 0.15 and 0.6 millimeters are preferred for manual buildup welding.

At the Fraunhofer Institute for Laser Technology ILT, an automated micro-laser build-up welding has been developed with which selectively damaged and worn areas of micro tools can be repaired or coated with wear protection layers.

By using laser beam diameters of less than 100 μm in conjunction with small laser powers, the thermal load on the substrate material is kept low, and the contour accuracy is increased even with very small structures compared to conventional repair methods.

Due to the precise application of the material, component surfaces of microcomponents can be repaired by similar material application or selectively modified by means of a foreign material application (coating, dispersion). To achieve the required structure sizes, continuous wave fiber lasers and pulsed Nd: YAG lasers are used. The powdered additional material is fed to the molten bath and melted via a nozzle specially developed for micro-laser build-up welding, resulting in a metallurgical bond.

Currently, the powder gas guide for the promotion of powdery filler materials with grain fractions smaller than 20 microns is being further developed. By adapting existing coaxial nozzles, the powder efficiency should be further increased. Suitable filler metals are powders based on iron, nickel and cobalt, as well as precious metals such as gold or silver.

When using powdered filler material has been found that often only a part of the powder gets into the focused laser beam, where it is melted. The unused rest must therefore be collected and, if necessary, recycled. Furthermore, it has been found to be disadvantageous that it takes a certain time for a necessary change in the position of the powder nozzle, until again sets a uniform powder jet.

Task and solution

The object of the invention is to provide a method for feeding filler material during laser deposition welding, in which the aforementioned disadvantages can be overcome.

The object of the invention is achieved by a method according to the main claim and by an additional material according to the independent claim. Advantageous embodiments of the method or of the additional material can be found in the respectively related claims.

Subject of the invention

In the context of the invention it has been found that it is advantageous, instead of using powder or wire, to use the filler material in the form of a film.

According to the invention, the filler itself is positioned as a foil or bound to a foil in a laser beam focused on the substrate (material). By the laser beam substrate and filler material are melted and bonded together.

In this case, all previously customary filler materials can be used as filler materials, provided that they themselves can be produced as a film, or can be bound to a film.

As an additional material that is itself produced as a film, in particular iron, nickel, cobalt or gold, silver, aluminum and metal alloys, eg. As iron, nickel or stainless steel alloys suitable. The film of filler usually has a layer thickness between 0.002 and 0.5 mm, preferably between 0.005 and 0.01 mm.

If the filler material is to be thinner, or if the filler material itself can not be produced as a foil, it is advisable to thinly bond the filler material to a corresponding foil. Suitable films are in particular plastic films, such as polyethylene or polypropylene, into consideration. Depending on the selected film, the laser beam penetrates the plastic and heats the substrate and the filler material, or first evaporates the film and then heats the substrate and the filler material.

As a filler, which can be advantageously bonded to a film, in particular iron, nickel, cobalt, gold, silver, aluminum or metal alloys, such as. As iron, nickel or stainless steel alloys suitable. The filler material bound to the film is generally present in the form of individual powder particles having a particle size between 2 and 100 μm. Advantageously, the powder particles have a particle size of between 5 and 50 .mu.m.

In the method according to the invention, the film comprising the filler material is first placed on the substrate. As usual, the laser beam is moved in a point-like manner or as a line over the workpiece, wherein the filler metal present in the focused laser beam is melted and forms a metallurgical bond with the substrate.

Since working without a powder jet, the otherwise usual waiting time for the method of the machining head is dispensed with in the method according to the invention. This advantageously reduces the processing time. The unused filler material remains after processing as a film and does not need to be collected as excess loose powder, as in the prior art. Depending on the applied geometry, a multiple use of the film is possible. Following a film can then be recycled to recover the filler regularly, z. B. be melted again.

• – Der Zusatzwerkstoff ist an eine Folie gebunden oder liegt selbst in Form einer Folie vor, woraus sich eine vereinfachte Handhabung des Zusatzwerkstoffes ergibt.
• – Bei häufigem Positionswechsel ergibt sich gegenüber dem bekannten Stand der Technik eine deutliche Zeitersparnis, da nicht mehr die Einstellung eines gleichförmigen Pulverstrahls abgewartet werden muss.
• – Da kein Zusatzwerkstoffverlust auftritt und keine Filtertechnik für die Zusatzwerkstoff-Rückgewinnung notwendig ist, ergibt sich auch eine Kosteneinsparung gegenüber dem bekannten Stand der Technik.
• – Die Rückgewinnung des nicht genutzten Zusatzwerkstoffs ist einfacher.
• – Die erfindungsgemäße Folie ist mehrfach verwendbar, das bedeutet die relative Position der Folie zum Werkstück wird jeweils nur geringfügig in x- und/oder y-Richtung versetzt, wobei die Oberfläche des Werkstückes, auf die der Zusatzwerkstoff aufgebracht wird, die x-y-Ebene aufspannt.
• – Da keine lungengängigen Pulverpartikel eingesetzt werden, ist auch die Gesundheitsgefährdung deutlich geringer, als bei den aus dem Stand der Technik bekannten Verfahren.

The advantages of the method according to the invention or the use of a filler in the form of a film can be summarized as follows:

• - The filler material is bound to a film or is itself in the form of a film, resulting in a simplified handling of the filler material.
• - With frequent position change over the known prior art results in a significant time savings, since no longer the setting of a uniform powder jet must be awaited.
• - Since no additional material loss occurs and no filter technology for the additional material recovery is necessary, there is also a cost savings over the prior art.
• - The recovery of the unused filler material is easier.
• - The film according to the invention is reusable, that is, the relative position of the film to the workpiece is only slightly offset in the x and / or y direction, the surface of the workpiece to which the filler material is applied, the xy plane spans ,
• - Since no respirable powder particles are used, the health hazard is much lower than in the known from the prior art method.

The method and the use of a film are particularly suitable for the application of the filler in the form of simple geometric patterns. Thus, for example, linear applications or point-like applications can be produced in a particularly advantageous manner because a film is used multiple times and the filler material can be optimally utilized on or in the film.

For longer, strip-like applications, difficulties may arise in that, after a first application, the film only consists of individual strips held together at the outer edge, whose positioning over the material for a second application may be possible in principle, but practically difficult.

Special description part

The invention will be explained in more detail below with reference to an example and some figures.

The type of feeding of the filler according to the invention is of interest, for example, in selective coating of bipolar plates for reducing the contact resistance in fuel cells. Gold dots with a diameter of 70 μm and a height of 30 μm are applied to the substrate material at a grid spacing of 2 mm.

In the following example, was shown in the 1 to 10 , first a foil coated with filler material ( 1 ) and then dried ( 2 ). The film used was a plastic film made of polyethylene or polypropylene with a layer thickness of 0.08 mm. On this, the filler gold was applied in the form of a dispersion comprising gold particles with a particle diameter of about 30 microns, and connected by adhesion to the film. The application was advantageously carried out using a customary coating method, screen printing. Drying was at room temperature for 1 hour.

The thus dried foil was placed with the gold side down ( 3 ) are arranged on a structured bipolar plate ( 4 ). The bipolar plate had on both sides outwardly open channels for the transmission of resources. As a substrate, a bipolar plate made of a stainless steel alloy was used.

The gold foil lay on the lands of these channels on the first side of the bipolar plate. In order to improve the contact of the gold foil with the surface of the bipolar plate, a slight vacuum could additionally have been applied to the channels of the bipolar plate, so that, for example, the gold foil engages closely against the webs of the bipolar plate ( 5 ). For this purpose, the bipolar plate could have been arranged, for example, on a vacuum table.

This was followed by the actual application step by laser deposition welding. For this purpose, the focused laser beam of a fiber laser was guided perpendicular to the gold foil surface along the webs of the bipolar plate ( 6 ). The gold from the gold foil was melted and formed a metallurgical bond with the top of the ridges of the bipolar plate.

Subsequently, the gold foil could be easily lifted from the bipolar plate, since only there was the film damaged where the filler material was transferred. The fused with the surface of the webs on one side of the bipolar plate remained gold. The film thus exhibited strips without gold after detachment ( 7 ).

For further application, the bipolar plate was rotated. Once again she had channels open at the top. The gold foil was placed again on the webs of the channels of this second side of the bipolar plate, but offset such that the webs each had contact with the gold of the film. In a particularly advantageous embodiment, then the strips without gold are each directly above the channels ( 8th ).

This was followed by the second step of laser buildup welding. For this purpose, the focused laser beam was again guided perpendicular to the gold foil surface along the webs of the second side of the bipolar plate ( 9 ). The gold from the gold foil was melted and formed a metallurgical bond with the top of the lands of the second side of the bipolar plate.

Subsequently, the gold foil could be easily lifted from the bipolar plate again. The fused with the surface of the webs on the second side of the bipolar plate remained gold. The film thus now had further stripes without gold ( 10 ).

Depending on the geometry to be applied, the film could advantageously be used twice or even several times. If the geometry, in combination with the amount of filler left on the film, no longer permits reuse of the film, it may then be subsequently recycled to recover the residual gold bound to the film.

In principle, nothing changes at the aforementioned process steps if, alternatively, a film produced directly from the filler material would be used.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• EN 14610 [0002]
• DIN 1910-100 [0002]

Claims (15)

Method for feeding a filler material during laser deposition welding, in which the filler material is introduced into the focused laser beam, either in the form of a foil or bonded to a foil. The method of claim 1, wherein iron, nickel, cobalt, gold, silver, aluminum or a metal alloy is used as filler material in the form of a film. Process according to Claim 2, in which a film having a layer thickness between 0.002 μm and 0.5 μm, in particular between 0.005 μm and 0.01 μm, is used. The method of any of claims 2 to 3, wherein the film is in direct contact with a substrate during laser deposition welding. A method according to claim 1, wherein a filler material bound to the film comprising iron, nickel, cobalt, gold, silver, aluminum or a metal alloy is used. The method of claim 5, wherein the filler is present bound with a particle size between 2 microns and 100 microns to the film, in particular with a particle size between 5 microns and 50 microns. The method of claim 5 to 6, wherein a film having a layer thickness between 0.002 mm and 0.5 mm, in particular between 0.005 mm and 0.01 mm, is used. A method according to claim 5 to 7, wherein the filler material is bonded to a plastic film, in particular to a plastic film made of polyethylene or polypropylene, is used. A method according to claim 5 to 8, wherein the filler material bound to a film is introduced into the focused laser beam in such a way that the filler has direct contact with a substrate during laser deposition welding. Use of an iron, nickel, cobalt, gold, silver or aluminum foil or a foil of a metal alloy as filler material in laser beam buildup welding. Apparatus for carrying out the method according to one of claims 1 to 10, comprising a filler material bound to a film. Apparatus according to claim 11, comprising iron, nickel, cobalt, gold, silver, aluminum or a metal alloy as the filler bound to the film. Apparatus according to claim 10 to 12, wherein the film has a layer thickness between 0.002 mm and 0.5 mm, in particular between 0.005 mm and 0.01. Apparatus according to claim 11 to 13, wherein the bound to the film filler material in a particle size between 2 microns and 100 microns, in particular between 5 microns and 50 microns, is present. Apparatus according to claim 11 to 14, with a film made of plastic, in particular polyethylene or polypropylene.

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