Friction welding originated over a century ago and after more than half a century of research and development, friction welding technology matured and entered the stage of widespread application. Since the 1950s, when qualified weld joints were first successfully achieved by friction welding, it has garnered attention from all industrialized nations due to its high quality, efficiency, low consumption, and environmental benefits.

The friction welding process for DTH drill rods uses the heat generated by the friction at the contact surfaces of the workpieces, which under pressure causes plastic deformation, thus facilitating the welding.

1. Principle of Friction Welding

The principle of friction welding involves using the relative motion between the welding contact surfaces to generate friction heat and plastic deformation, raising the temperature around the contact area to near melting point. At this temperature, the material becomes more pliable and its resistance to deformation decreases. With this plastic deformation, the rod and joint under pressure join through interface recrystallization and molecular diffusion.

2. Friction Welding Process

Prepare DTH drill rod joint and body and align them to ensure co-axial alignment during welding. Start the friction welding machine to rotate the joint at a specific speed while applying axial pressure to the DTH drill rod body to begin friction heating. When the friction surfaces of the joint and rod body reach the welding temperature, stop rotation. Simultaneously with the cessation of rotation, apply greater axial pressure to perform forge press. Maintain this forge pressure for a period, then let the joint cool naturally to room temperature. After a period of cooling, the material in the weld joint re-solidifies to form a robust connection. After friction welding, the welded area of the DTH drill rod and joint often experiences defects such as poor mechanical properties and unstable microstructure. Therefore, it is necessary to carry out heat treatment of the weld area, specifically quenching followed by high-temperature tempering, to achieve a uniform and stable weld structure with good overall mechanical properties.

3.  Advantages of Friction Welding

1.  Short welding construction time and high production efficiency.

2.  High weld quality, typically free from weld spatter, with high post-weld dimensional accuracy.

3.  Welding does not produce smoke, arc light, or harmful gases, thereby avoiding pollution.

4.  High degree of mechanization and automation, consistent welding quality.

During drilling operations, DTH drill rods are subjected to various complex loads such as bending, twisting, compression, and tension, making safety paramount. Friction welded DTH drill rods exhibit strong bending resistance, good flexibility, and wear resistance, which contributes to their widespread application.