Vacuum Brazing of Ultrasonic Cutting Tools

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With the continuous development of new structural materials, the ultrasonic cutting method is increasingly showing its important role. For example, high-quality cutting of C/C composite incisions without any burrs can be achieved by using the ultrasonic cutting method. In ultrasonic cutting equipment, the cutting tool is a very important component, which directly affects the quality of cutting. According to the basic principle of ultrasonic cutting, the cutting tool must meet its special energy transmission requirements, so the combination structure of titanium alloy as the tool bar and high-speed steel as the blade is generally used in the design of the tool. The connection between the arbor and the blade belongs to the connection of dissimilar materials. In order to ensure the quality of the connection, the vacuum brazing process is generally used in production. Practice has proved that this connection process is effective and can well meet the requirements of ultrasonic cutting.

Tool structure
The illustration is a typical structure of an ultrasonic cutting tool. Among them, the blade material is high-speed steel, and the blade material is titanium alloy. The entire tool adopts a mosaic structure, especially the root of the blade is closely connected with the bottom of the groove of the tool shank, which effectively reduces the stress exerted by the load on the brazing seam during the cutting process. Before brazing, there is a transition fit between the blade and the side face of the groove of the shank, so as to facilitate the placement of the sheet brazing filler metal. After brazing, the blade and the shank are connected together through the two brazing seams in the groove of the shank and the bottom brazing seam, thereby forming a complete cutting tool.

Brazing process and solder:
The brazing of the blade and the shank is actually the brazing between the high-speed steel and the titanium alloy. Due to the strong activity of titanium alloys, it is easy to react with oxygen, nitrogen and hydrogen and other gases to cause embrittlement, so it must be brazed with inert gas protection or vacuum environment. Since inert gas shielded brazing has high requirements on the purity of the gas, it is advisable to use the vacuum brazing method in practical applications.

Considering the brazing of high-speed steel, in order to reduce the influence of brazing heating on the microstructure and properties of high-speed steel, copper-based solder or silver-based solder can be used.

In conventional copper-based solder, copper-zinc solder is usually used for brazing, but this solder is not suitable for vacuum brazing because zinc has strong volatility in vacuum. The silver-based solder is mainly silver-copper solder. Due to its low melting point, the thermal stress generated by the brazed joint is small, which is beneficial to reduce the cracking tendency of the joint.
Based on the above considerations, the final decision to use silver-copper eutectic solder and vacuum brazing methods. The specific form of the brazing filler metal is foil-like, and its thickness is 50 μm. Vacuum brazing adopts radiation heating, and the vacuum degree can reach 10-3Pa.

Brazing process flow:
First, clean the surface of the processed high-speed steel blade and the groove of the titanium alloy shank with acetone, and place the two pieces of brazing filler metal with a slightly larger area than the groove on both sides of the groove, and then carefully place the blade. It is inserted between the two solder pieces, and it positions itself by means of a slightly tight fit. Follow this step to assemble all the blades and shanks into the cutting tool assembly to be welded.

Next, place all assembled components in sequence vertically on a brazing stand with multiple countertops in the furnace. Among them, the blade of each component is on the top, and the shank is on the bottom. There is a certain gap between the components on each countertop to allow the components to heat evenly.

Finally, vacuum brazing is carried out according to the process curve shown in the figure. When the vacuum degree in the furnace reaches 7×10-3Pa, the brazing heating can be carried out. Due to the radiant heating method, the heat received by the components on different platforms during the heating process will be different, so a slower heating rate should be used to minimize the temperature difference between the components. On the brazing process curve, a holding section is set before the brazing temperature is reached, and the purpose is to try to make all components have the same or a small temperature difference before the brazing filler metal is about to melt. After the holding time at the brazing temperature is reached, cooling is performed at a slower rate to reduce thermal stress between the insert and the shank due to the difference in thermal expansion coefficients.

Using Ag-Cu eutectic solder and vacuum brazing method, the reliable connection between the high-speed steel blade of the ultrasonic cutting tool and the titanium alloy shank was achieved under the brazing condition of 830 ℃ for 10 min. High production efficiency and good joint quality meet the performance requirements of automatic ultrasonic cutting equipment for cutting tools.
Equipment selection: The RHVB series vacuum brazing furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment of tooling and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum brazing process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.