Luoyang Judian Metal Hot Processing Equipment Co., LTD is mainly engaged in the manufacture of complete sets of equipment in the metal thermal processing industry and the integration of the entire production line.
High-frequency induction heating operates on a mechanism completely different from conventional resistance welding. In this process, an induction coil is placed a short distance ahead of the pressure rolls, surrounding the tube. The alternating magnetic field induces an electric current within the steel strip, flowing along the outer surface and completing its circuit through the edges of the “V” shaped opening, where the metal begins to make contact. This closed loop of induced current is the key to achieving proper heat concentration before the tube enters the welding rolls.
How High-Frequency Current Flows During Welding
High-frequency current naturally follows the path of least resistance, flowing through the point where the strip edges start to touch. When the inner sides of the strip edges make contact prematurely, most of the current flows through this narrow region. This can result in excessive localized heating, leading to casting-like structures, oxide inclusions, porosity, and an uneven internal weld seam. As a result, more input power is consumed, the heat-affected zone becomes wider, and the welding speed decreases.
Achieving Optimal Weld Quality
The best welding results are achieved when the contact zone of the steel strip edges is parallel before they enter the pressure rolls. Under this condition, the current distributes evenly across the cross-section of the material, allowing for ideal “forge welding.” The resulting weld joint exhibits maximum strength and minimal internal defects. However, maintaining perfect parallel alignment of the edges is technically challenging, as the tube tends to open slightly due to residual stresses on the strip surface during forming.
Forming Techniques for Better Edge Contact
Modern forming technologies have been successfully developed to produce parallel welding edges. Before the strip reaches the pressure rolls, it is pre-shaped into an almost circular tube cross-section, with the top portion slightly flattened. This geometry is achieved by using smaller roll passes that intentionally over-form the strip edges. Although this technique is not yet widely adopted—since many tube manufacturers still rely on traditional resistance welding rolls to minimize costs—it provides significant process advantages when used with high-frequency induction welding.
Edge Preparation and Beveling
For thicker tube sections, additional edge-trimming systems can be employed. These use cutting tools to bevel the strip edges at a specific angle to ensure that the edges become parallel just before the pressure zone. This technique helps produce a cleaner appearance, stronger welds, and improved consistency in the weld seam.
Conclusion: Maximizing the Potential of High-Frequency Welding
To fully exploit the advantages of high-frequency induction welding—such as higher speed, improved uniformity, and superior weld quality—special attention must be given to forming technology and tube cross-section design. The precision of edge alignment and pre-forming has a decisive impact on the mechanical strength and surface appearance of the final product. When properly implemented, HF induction welding offers one of the most efficient and reliable solutions in modern tube manufacturing.
