Spray welding is a new process in which welding technology is applied to the surface treatment of metal parts. It is suitable for preventive protection of metal surfaces and repair of worn and corroded surfaces.
Spray welding is a process in which a self-fluxing alloy powder (such as a nickel-based, iron-based, or cobalt-based series) having a melting point of 950 to 1200 Â° C is sprayed onto the surface of a part using an oxy-acetylene flame. Solder layer and substrate (parts)

It is metallurgically bonded and has high strength, strong wear resistance, corrosion resistance, heat resistance and oxidation resistance.

1 Cutting of welding materials

Spray welding materials are one of the hard-to-cut materials, and their characteristics can be summarized as follows:

High hardness The surface hardness of the spray-welded layer is generally 30 to 40 HRC. When the content of Ni and Cr in the powder increases, the hardness of the spray-welded layer can reach above HRC60, and the cutting difficulty is very large. Conventional tools are difficult to perform. Even with superhard materials as the tool, the wear is still very fast.
The heat-dissipating slow- spraying layer has high strength and high toughness. When cutting, the tool is crushed and deformed on the surface to be cut, so the energy consumption is large and the heat is generated. The chip is broken and the contact area with the tool is small, which is not conducive to heat dissipation. , thus accelerating tool wear.
Although the spalling spray weld layer is metallurgically bonded, the hardness is higher than that of the base due to the thinner weld layer, and the structure is not dense enough. When the cutting force is large or the friction angle is increased due to the small back angle, the spray weld layer The surface is prone to spalling.
Easy to induce vibration The surface of the spray-welded layer will shrink. There must be tiny pores, and intermittent cutting occurs during the cutting process, which is easy to induce vibration.

2 Requirements for tool materials

Requirements for tool materials when cutting spray-welded material:

High wear resistance Due to chip breakage, the rake face does not cause crescent wear, the tool mainly wears abrasive wear on the flank face, and has a small amount of bonding and diffusion wear. Therefore, the tool material has high hardness and uniform distribution. Hard wear points.
High red hardness Because of the heat generated during the cutting process, the heat dissipation is slow, and the cutting heat is concentrated on the tool. Therefore, the red hardness of the tool is required to be high to reduce tool wear caused by high temperature.
Good thermal conductivity to facilitate the transfer of heat from the tool and reduce the cutting temperature.
High strength Because there are tiny pores on the surface of the spray-welded layer, vibration is easy to occur during cutting. Therefore, the tool should have sufficient strength and certain impact resistance and vibration resistance.

3 Reasonable selection of geometric parameters of the tool

The choice of tool geometry parameters should be considered based on the characteristics of the spray welding material, the shape of the surface to be sprayed, and the rigidity of the machine tool.

Leading angle The main declination of the conventional tool is changed to 10Â° to 30Â°, and the machining of the blind hole type workpiece is greater than 90Â°. Small values â€‹â€‹should be taken during finishing. The main deflection angle after grinding is equivalent to the excessive edge of the tool. Due to the small depth of cut, the fact that the excessive cutting edge replaces the main cutting edge takes over the main cutting work.
The rake angle can be 0Â°-10Â° when machining a spray-welded layer with a carbide insert. In order to make the blade sharp, it can be more than 12Â° during finishing. If the spray welding layer is processed by a combination ceramic tool, the negative rake angle should be selected, and it can be -30Â°.
The back angle takes a larger back angle to reduce the contact area between the tool and the cutting surface, resulting in a slower increase in tool wear length. Generally take 100-120, it can be bigger when finishing.
Since the cutting edge inclination spray layer depth is small, good chip breaking, and is therefore preferably between 0 Â° ~ 5 Â°, increase the radial force over the General Assembly during cutting.

4 cutting amount

The choice of cutting amount should be based on the full potential of the tool and machine tool.

Cutting depth The general principle is that the higher the hardness of the workpiece, the smaller the depth of cut. Excessive depth of cut can cause the weld to peel off.
Feed rate Due to the small depth of cut, a proper increase in feed rate is a good way to improve cutting efficiency. By appropriately increasing the feed amount, inverted chips can be formed. There are three advantages to using a larger feed rate: it can shorten the cutting path of the tool and reduce the tool wear; the secondary cutting edge can undertake the main cutting work, thereby deflecting the chip outflow direction; cutting the spray welding layer with a large feed can make The machined surface does not cause pitting and spalling.
Cutting speed Due to the high surface hardness of the spray-welded layer, various alloying elements form more wear-resistant carbides. Therefore, the cutting speed is related to the alloy composition of the base material, the tool material, the geometric parameters of the tool, and other cutting amounts. In general, a low hardness of the spray-welded layer may result in a higher cutting speed, and a higher hardness may take a lower cutting speed.

5 Conclusion

As the market demands continue to change, this new process plays a vital role in improving the surface quality of the product, the multiple repairs and use of the wearable parts, and the reduction of the cost of use, and also meets the needs of users. Mastering and applying this technology is very important for improving market competitiveness.

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