Patent Publication Number: US-2021178527-A1

Title: Welding method for manufacturing a heat sink structure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Chinese Patent Application No. 201911288382.1 filed Dec. 13, 2019, the disclosure of which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of manufacturing a heat sink component, especially to a manufacturing method via welding to combine several components as a heat sink component. 
     2. Description of the Prior Art 
     A heat sink component comprises several tiny structures, so making a heat sink component from a single workpiece is a hard task. For example, a heat sink component may comprise a fin assembly and the fin assembly includes multiple fins spaced apart at intervals. If such heat sink component is manufactured from a single metal block, the fin assembly may be shaped via cutting or drilling, which is hard to carry out. Besides, the fins made from such process may weaken the rigidity and strength. As a result, in the current manufacture method, a base and fins are made respectively from multiple workpieces and then the fins are welded on the base. However, some heat sink components are made of aluminum alloy but aluminum alloy cannot be welded easily, such that the welded aluminum alloy workpieces are easy to be separated by an external force. 
     To overcome the shortcomings, the present invention provides a welding method for manufacturing a heat sink structure to mitigate or obviate the aforementioned problems. 
     SUMMARY OF THE INVENTION 
     The main objective of the present invention is to provide a welding method for manufacturing a heat sink structure that can produce a heat sink component with high strength so that the heat sink component cannot be destroyed easily. 
     The welding method includes the following steps in sequence: (1) removing rust from a first surface of a first workpiece and a second surface of a second workpiece, and degreasing the first surface and the second surface; (2) increasing surface roughness of both the first surface and the second surface; (3) performing a supersonic cold spray process of copper grains to the first surface and the second surface; (4) combining the first surface and the second surface via welding. 
     Thus, with the copper supersonic cold spray step and the surface treatment steps before the copper supersonic cold spray step (i.e. rust removal, degreasing, and roughness increasing), the solder can be attached to the workpiece tightly during the combining via welding step. Thus, the welded workpieces are combined firmly and cannot be separated easily. If a heat sink component is made through welding workpieces in the aforesaid welding method, the heat sink component has higher strength and cannot be destroyed easily. 
     Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow chart of a welding method in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , a welding method for manufacturing a heat sink structure in accordance with the present invention is provided. The welding method is configured to weld two workpieces and said workpieces are part of a heat sink structure. With more workpieces welded, those workpieces will be combined as a heat sink component. For example, the heat sink component may be a fin assembly including a base and multiple fins. 
     Hereinafter the welding method of the present invention is described with a first workpiece and a second workpiece. Precisely, a first workpiece may have multiple surfaces and one of said surfaces is a first surface. Similarly, a second workpiece may have multiple surfaces and one of said surfaces is a second surface. The first workpiece may be made from aluminum, copper, or an alloy thereof and the second workpiece may be made from aluminum, copper, steel, or an alloy thereof. In other words, the welding method of the present invention can be adopted to weld aluminum and aluminum, aluminum and copper, aluminum and steel, etc. The welding method of the present invention may include the following steps in sequence: a rust removal and degreasing step, a surface roughness increasing step, a supersonic cold spray process of copper grains (hereinafter referred as “copper supersonic cold spray step”), and a combination via welding step. 
     The rust removal and degreasing step is to remove rust from the first surface and the second surface and degrease the first surface and the second surface and thereby dyne values of both the first surface and the second surface are larger than or equal to 36 dyn. In a preferred embodiment, the dyne value should be larger than or equal to 38 dyn. Precisely, after the rust removal and degreasing step, to check the dyne values of the first surface or the second surface, a mark may be painted on the first surface and the second surface via a 38 dyne test pen. If an ink of the dyne test pen is stable or spreads outward, the dyne value of the first surface or the second surface is equal to or larger than 38 dyn, and the workpiece is suitable for subsequent manufactures. However, if the ink of the dyne test pen concentrates to drops, the dyne value of the first surface or the second surface is less than 38 dyn and rust removal and surface degreasing should be performed again until the dyne value is equal to or larger than 38 dyn. 
     In the surface roughness increasing step, 80-grit sandpapers or 120-grit sandpapers may be adopted. The first surface and the second surface should be ground until the surface roughness thereof is increased to 10 μm to 35 μm. In a preferred embodiment, the surface roughness is increased to 15 μm to 25 μm. 
     In the copper supersonic cold spray step, a copper spray device sprays the air with copper grains in high pressure toward the first workpiece and the second workpiece, so that the copper grains are embedded on the first surface and the second surface. The aforesaid rust removal and degreasing step and the surface roughness increasing step are configured to facilitate the copper grains to be embedded on the first workpiece and the second workpiece, i.e. embedding the copper grains via lower air pressure or lower temperature. In this embodiment, the pressure of air sprayed from the copper spray device is 0.4 MPa to 1.0 MPa, a size of each copper grain is 10 μm to 50 μm, and surface porosity of each copper grain is less than or equal to 10%. Meanwhile, the temperature of the first surface and the second surface is lower than 180° C. In a preferred embodiment, the pressure of sprayed air is 0.5 MPa to 0.8 MPa, the size of each copper grain is 15 μm to 40 μm, the surface porosity of each copper grain is less than or equal to 5%, and the temperature of the first surface and the second surface temperature is lower than 150° C. 
     Finally, in the combination via welding step, the first surface and the second surface undergoing aforesaid surface treatments step are welded together. In this embodiment, before welding, the first workpiece and the second workpiece are heated until higher or equal to 260° C. Thus, the first workpiece and the second workpiece are combined tightly. 
     The welding method of the present invention can be carried out to a portion of the first surface and a portion of the second surface. In other words, a specific portion of the first surface and a specific portion of the second surface undergo the rust removal and degreasing step, the surface roughness increasing step, and the copper supersonic cold spray step, and then the specific portion of the first surface and the specific portion of the second surface are combined via welding. Therefore, not the entire first surface and the entire second surface undergo the surface treatments and welding, which reduces manufacturing time and saves manpower. 
     With the welding method of the present invention, the strength between two combined workpieces is increased significantly. In a pulling force test, the welding surface with a 48 mm by 51 mm rectangular shape can endure a 70 kgw pulling force. Therefore, the heat sink component made via the welding method of the present invention has higher strength and cannot be destroyed easily. 
     Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and features of the invention, the disclosure is illustrative only. Changes may be made in the details, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.