FI114401B - Method for Coating Copper and Copper Alloys - Google Patents

Description

, 114401

The present invention relates to a method for coating a copper or copper alloy surface by a laser plating device according to the preamble of claim 1.

Products are often finished with a coating. The uses of the coatings are different and can be grouped as follows: change of mechanical properties, change of corrosion resistance, change of sliding or adhesion properties of the surface, formation of a coating layer on the surface and other properties such as change of thermal or electrical conductivity of the surface. Often, a plating modifies several of the above properties simultaneously. Coatings of metals are often grouped according to the manufacturing technique into electrochemical coatings, reaction coatings, thermally formed coatings, melt deposition coatings, and diffusion coatings.

Thermal plating methods include conventional overhead welding (MIG / MAG, TIG, powder arc and needle welding) as well as newer physical gas phase plating; methods such as PVD (Physical Vapor Deposition), CVD (Chemical Vapor: 20 Deposition), HVOF (High Velocity Oxy-Fuel) and Plasma Injection. One thermal coating method is laser coating, in which * typically, powdered coating material is melted onto the substrate surface by laser beam. The coating material may also be yarn, chips or even a sheet. During coating, the laser beam melts a thin layer on the surface of the substrate and the coating 25 is fed to the molten to form a melt bond between the coating and the substrate. Pin-. during witchcraft, the melt is protected by a shielding gas. As the melt solidifies on the base material 't, a coating layer is formed. Laser coating has been described, for example, by chips. · · ·. in EP 293945 and EP 176942.

114401 2

The advantage of laser coating for other thermal coating methods is that, due to the high power density of the laser beam, the total heat input to the object being coated is small and controlled. This reduces the need for preheating and post-heat treatment. In addition, the structure and properties of the base material and the deformation of the body as well as the elongation and deformation are minor. A strong metallurgical bond is formed between the coating and the substrate. Laser coating is suitable for most additive and substrate combinations. However, there is a requirement for their metallurgical compatibility, which can be improved by the correct choice of additive or by changing the coating composition. Laser coating is useful especially when coating properties are required which are clearly different from those of the base material.

Although laser plating is suitable for most basic materials, laser plating of copper and copper alloys has previously been extremely difficult or even impossible. This is because the copper is highly reflective, whereby the laser beam that hits the surface of the object to be coated is reflected and the surface is not sufficiently heated. Typically, pieces of copper and copper alloy are coated by injection techniques and by dipping the item to be coated into the coating.

An object of the present invention is to provide a novel laser coating method for coating copper and copper alloys.

The invention is based on the fact that the laser beam is directed at an oblique angle to the curtain surface of the surface to be coated. Laser beam coverage •: Preferably, a metal coating powder is applied to the surface simultaneously with the laser beam. In addition, in the process of the invention, copper or copper; '*: The surface to be coated on the rise is matte for better light absorption.

If necessary, the surface to be coated can be compacted to the desired roughness before coating to improve light absorption. If necessary, the object to be coated may also be preheated prior to application.

The invention provides considerable advantages.

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By the method of the invention, copper or copper alloys can be coated with a laser coating device, which has previously been difficult. In addition, the method according to the invention requires little special action, but can be carried out by adjusting the parameters of the coating apparatus to the correct type.

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The invention will now be described in more detail with reference to the accompanying drawing, which shows a laser coating device and a body to be coated.

The CO 2 laser deposition device illustrated in the drawing comprises a coaxial plating-15 head 1, from which a laser beam 2 is applied to a copper or copper alloy body 3 to be coated. Copper alloys are those alloys which contain, in addition to copper, one or more alloys of at least 2.5%. Copper alloys include, for example, \ v 20 - copper-zinc alloys or brass • * - copper-tin alloys (tin bronzes) ,; * - copper-nickel-zinc alloys or nickel-silver t '' ', - copper-nickel alloys or nickel-copper * *, · - ·. - copper-aluminum alloys or aluminum bronzes 25 - special copper alloys.

The piece 3, in turn, can be, for example, rotationally symmetrical or planar.

: ': Preferably, the powder coating material is fed from the coating head 1 by means of a shielding tape to the surface of the body 3 in the area heated by the laser beam 2. Coating: "· 30 material is fed coaxially to laser beam 2, i.e., the flow of coating material and coating gas is surrounded by laser beam 2. The protective gas is carbon dioxide or argon. Due to its high power density, the laser beam 2 melts the surface layer of the article 3 and the coating material applied to the surface of the article 3, whereby a molten joint is formed between them. The coating surface 5 of the body 3 is moved relative to the laser beam 2 and / or the laser beam is moved relative to the coating surface of the body 3. Rotation symmetrical pieces can be attached to lathes, for example.

Preferably, the velocity of movement between the laser beam 2 and the surface to be coated on the body 3 is 100-1000 mm / min, preferably 230-270 mm / min. Since the heat supplied by the laser beam is mainly due to the body 3, the molten coating solidifies rapidly as the process progresses. The molten coating is protected by a shielding gas. The width of the coating applied in one run depends on the distance between the focal point of the laser beam and the surface to be coated. Typically, the width of the coating layer formed when moving the coating head 1 and / or the surface to be coated is 2-3 mm, preferably 2.4-2.6 mm.

The coating material shall be metallurgically compatible with the base material. Compatibility can be improved by the right choice of coating material additive or by changing the doping. The coating material is generally heat and / or; 'Wear-resistant material. The properties obtained with the coating depend on the application, the substrate, the coating agent and the process parameters used. Typically, the '' 'formed by the coating process of the invention. the coating layer has a thickness of 0.1 to 4 mm. If necessary, several layers of coating may be superimposed.

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...: In the method of the invention, the central axis of the laser beam 2 is angled at an angle to the curtain surface of the surface to be coated. Inclined angle pin

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'...: the laser beam directed at the witch surface is scattered, so that it is not reflected back to the surface »! '·' 30 to the kneading head 1. This prevents the coating head 1 from overheating. Typically, the angle α between the center axis of the laser beam * 5114401 2 and the normal curtain surface of the body to be coated is preferably 10-50 °, preferably 30-38 °. By curtain surface is meant here the dominant surface of the ideal shape of the piece, from which its actual shape may deviate, for example due to manufacturing tolerance, wear or other damage 5.

The surface to be coated on body 3 is darkened to mat prior to coating. The matte surface is substantially opaque and non-polished, which effectively absorbs light. The matte surface absorbs 2 light of the laser beam more than the shiny surface of that copper or 10 alloy. The surface can be darkened, for example, by spraying with a light absorption enhancer such as graphite.

Light absorption can be improved by machining the surface to be coated with a • coarser surface. ·. paid before darkening. The surface can be roughened, for example, by milling Ra • ·: 1. '. 15 to a roughness of preferably 2 to 3.5 µm, most preferably 2.5 to 3 µm.

«• ,,, · 'The coating body 3 can be preheated before coating, if necessary,': 1 1: whereby the coating and substrate can be thawed using a lower power in the laser beam. The temperature of the surface to be coated on part 3 is raised to preheat. . Preferably, 200 to 500 ° C, preferably 250 to 350 ° C.

The coating method according to the invention is very suitable, for example, for coating copper castings. Copper has good thermal conductivity, which allows the heat released from the cast member or profile to be obtained! '! 25 removed shells quickly. However, the problem is the softness of the copper, which causes the die to wear out quickly. Wear can be reduced by coating the chill surface with a wear-resistant coating. The following is an example of the coating parameters used to coat a copper casting die:

- laser beam power: about 6 kW

30 - distance of coating nozzle from surface to be coated: approx. 18 mm 6 114401 - distance of focal point of laser beam from coating nozzle: approx. 38 mm - normal angle between center of laser beam and surface to be coated: approx. 250 at 5 mm / min

The surface of the object to be coated was first machined by milling Ra to a roughness of about 2.6 m, after which the surface to be coated was cleaned with acetone. Thereafter, a graphite spray was sprayed onto the surface of the body to improve light absorption.

Further, the body was preheated to about 300 ° C prior to coating. The coating was formed on an area of 120 mm x 30 mm. The laser beam was displaced laterally about 2.5 mm at a time. Two coating layers were formed on top of each other. The feed powder feed rate was about 13 g / min. Carbon dioxide was used as the shielding gas. The coating used was Höganäs HMSP 153840 powder having the following chemical composition: - Carbon, C: 0.05% - Silicon, Si: 3.0% - Boron, B: 2.2% - Iron, Fe: 0.4 %: 20 - Nickel, Ni: rest; The invention also has embodiments different from those described above.

The coating material can be fed to the surface of the body 3 instead of the coating head 1 from 25 separate feeders. The coating material may also be applied to the surface to be • coated prior to coating.

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Claims (8)

7 114401 A method of coating a surface of copper or copper alloy with a laser coating device, comprising: - directing a laser beam (2) to the surface to be coated, - moving the laser beam (2) relative to the surface to be coated and / or on the surface to be coated, within the range of the laser beam (2), characterized in that: v. 15 · · - the surface to be coated is a matte surface, and t «· *: - the laser beam (2) is angled at an angle to the surface of the surface to be coated. 20 Method according to Claim 1, characterized in that the angle α between the normal curtain surface of the surface of the body to be coated and the central axis of the laser beam (2) is preferably 10-5 °, preferably 30-38 °. ! ' ! Method according to claim 1 or 2, characterized in that the surface to be coated has a roughness Ra of preferably 2 to 3.5 µm, preferably 2.5 to 3 µm. Method according to one of the preceding claims, characterized in that the laser beam (2) is moved with respect to the surface to be coated and / or the surface to be coated with the laser beam (2) at a speed of 100-1000 mm / min, preferably 230-270 mm. / min. Method according to one of the preceding claims, characterized in that the surface to be coated is pre-heated prior to coating. Method according to one of the preceding claims, characterized in that a CO 2 laser deposition device is used. 10 Method according to one of the preceding claims, characterized in that a plurality of coating layers are formed on one another. Method according to one of the preceding claims, characterized in that the coating layer has a thickness of 0.1 to 4 mm. 114401