Welding is the process of joining two materials (same or different) together using heat, pressure, or both, with or without a filler material, to bond the workpieces atomically, creating a permanent connection.

Stainless steel welded pipes are produced by rolling stainless steel sheets through multiple dies on a pipe forming machine. Due to the high strength of stainless steel and its face-centered cubic crystal structure, it is susceptible to work hardening. During pipe forming, the molds are subject to significant friction, which can lead to wear. Furthermore, the stainless steel sheets can easily adhere to the mold surface, causing strain on both the pipe and the mold surface. Therefore, a good stainless steel forming mold must possess extremely high wear resistance and anti-sticking (seizure) properties. Analysis of various advanced pipe welding molds by Tuofa CNC Machining indicates that these molds typically utilize a surface treatment with ultra-hard metal carbide or nitride coatings.

Key Technical Points of Stainless Steel Welding Processes

Compared to traditional fusion welding, laser welding and high-frequency welding offer advantages such as high welding speed, high energy density, and low heat input. This results in a narrow heat-affected zone, reduced grain length, minimal weld distortion, and excellent cold forming properties. They are easily automated, enabling single-pass penetration of thick plates. Their most significant advantage is that I-beam butt welds require no filler material.

Welding techniques are primarily applicable to metal base materials, with commonly used methods including arc welding, argon arc welding, CO2 shielded welding, oxyacetylene welding, laser welding, and electric melt pressure welding. Non-metallic materials such as plastics can also be welded. There are over 40 metal welding methods, primarily categorized as fusion welding, pressure welding, and brazing.

Fusion Welding

Fusion welding involves heating the interface between the workpieces to a molten state, completing the weld in the absence of pressure. During fusion welding, a heat source rapidly melts the interface between the two workpieces, forming a molten pool. The molten pool moves forward with the heat source and cools to form a continuous weld, joining the two workpieces.

During the fusion welding process, if the atmosphere comes into direct contact with the high-temperature molten pool, the oxygen in the atmosphere will oxidize the metal and various alloying elements. Atmospheric nitrogen and water vapor enter the molten pool, and during the subsequent cooling process, defects such as pores, slag inclusions, and cracks will form in the weld, deteriorating the weld quality and performance.

Pressure welding

Pressure welding is the atomic bonding of two workpieces in the solid state, also known as solid-phase welding. A common pressure welding process is resistance butt welding. When current passes through the connecting ends of the two workpieces, the high resistance causes the temperature to rise. Once heated to a plastic state, axial pressure is applied to form a single piece.

A common feature of various pressure welding methods is that they apply pressure during welding without the use of filler material. Most pressure welding methods, such as diffusion welding, high-frequency welding, and cold pressure welding, do not involve a melting process. Therefore, there is no risk of burning beneficial alloying elements, as with fusion welding, nor is there the risk of harmful elements entering the weld. This simplifies the welding process and improves welding safety and hygiene. At the same time, because the heating temperature is lower than that of fusion welding and the heating time is shorter, the heat affected zone is smaller. Many materials that are difficult to weld by fusion welding can often be welded into high-quality joints with the same strength as the parent material by pressure welding.