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Complete set of welding process methods for stainless steel pipes

The improvement in data processing has brought unique opportunities to the field of stainless steel pipe production. Typical applications include exhaust pipes, fuel pipes, fuel injectors, and other components.

When producing stainless steel pipes, flat steel strips are first formed, and then their shape is made into circular tubes. Once formed, the joints of the pipes must be welded together. This weld seam greatly affects the formability of the parts. Therefore, in order to obtain welding shapes that can meet the strict testing requirements of the manufacturing industry, selecting appropriate welding skills is extremely important. Undoubtedly, tungsten gas shielded arc welding (GTAW), high-frequency (HF) welding, and laser welding have been successfully used in the production of stainless steel pipes.

High frequency induction welding

In high-frequency touch welding and high-frequency induction welding, the equipment that supplies current and the equipment that supplies kneading force are independent of each other. In addition, both methods can use magnetic rods, which are soft magnetic components placed inside the tube body and help to gather welding flow at the edge of the steel strip.

In both cases, the steel strip is cut and organized, rolled up, and then sent to the welding point. Additionally, coolant was used to cool the induction coil used in the heating process. Finally, some coolant will be used for the kneading process. Here, a great deal of force is applied to the kneading pulley to avoid porosity in the welding area; However, the use of greater kneading force will result in an increase in burrs (perhaps welding beads). Therefore, specially designed cutting tools are used to remove burrs inside and outside the pipes.

One of the primary advantages of high-frequency welding process is that it can perform high-speed machining on steel pipes. However, a typical situation in most solid-state forging processes is that high-frequency welded joints are not easily subjected to reliable testing using traditional non-destructive techniques (NDT). Welding cracks may arise in the flat and thin areas of low strength connections, which cannot be detected using traditional methods, and therefore may lack robustness in some demanding automotive applications.

Gas Tungsten Arc Welding (GTAW)

Traditionally, steel pipe manufacturers have chosen to complete the welding process by gas tungsten arc welding (GTAW). GTAW undergoes an electric welding arc between two non consumable tungsten electrodes. Together, introduce lazy maintenance gas from the spray gun to shield the electrode, ionize the plasma flow, and maintain the molten weld pool. This is a process that has been established and understood by people, and it will be able to repeatedly complete high-quality welding processes.

The advantage of this process lies in its repeatability, no spatter during the welding process, and the elimination of porosity. GTAW is considered an electrically conductive process, so the process is relatively slow.

High frequency arc pulse

In recent years, GTAW welding power supplies, also known as high-speed switches, have enabled arc pulses to exceed 10000Hz. The customers of steel pipe processing plants first benefit from this new skill, as high-frequency arc pulses cause the downward pressure of the arc to be five times greater than that of traditional GTAW. Representative improvement features brought about include: increased explosive strength, faster welding line speed, and reduced waste.

Customers from steel pipe manufacturers quickly realized that the demand for welding shapes obtained by this welding process was reduced. In addition, the welding speed is still relatively slow.

Laser welding

In all steel pipe welding applications, the edges of the steel strip are melted, and when the steel pipe edges are kneaded together using a clamping bracket, the edges solidify. However, for laser welding, a unique property is its high energy beam density. The laser beam not only melted the surface of the data, but also created a keyhole, resulting in a very narrow weld shape.

If the power density is lower than 1MW/cm2, such as in GTAW skills, the energy density required to generate keyholes cannot be met. In this way, the keyless process results in a wide and shallow welding shape. The high precision of laser welding brings higher power penetration, which in turn reduces grain growth and brings better metallographic quality; On the other hand, the higher thermal input and slower cooling process of GTAW result in a rough welding structure.

Generally speaking, people believe that laser welding processes are faster than GTAW, as they have the same scrap rate, while the former brings better metallographic properties, which leads to higher explosive strength and formability. When compared with high-frequency welding, the laser processing data process does not undergo oxidation, which leads to lower scrap rate and higher formability.

The influence of spot size: In the welding of stainless steel pipe factories, the welding depth is determined by the thickness of the steel pipe. In this way, the production strategy is to improve formability by reducing the welding width and achieving higher speeds together. When selecting the most suitable laser, one must not only consider the beam quality, but also the correctness of the rolling mill. In addition, it was necessary to first consider the limitations of reducing the light spot when the scale error of the pipe rolling mill played a role.

There are many unique scale titles in steel pipe welding, but the primary factor affecting welding is the seam on the welding box (more specifically, the welding coil). Once the steel strip is prepared for welding through forming processing, the characteristics of the weld seam include: steel strip gaps, severe/slight welding misalignment, and changes in the centerline of the weld seam. The gap determines how much data needs to be used to form the welding pool. Excessive pressure will result in excess information on the top or inner diameter of the steel pipe. On the other hand, severe or slight welding misalignment can lead to poor welding shape.

In addition, after welding the box, the steel pipe will be further trimmed. This includes adjustments to scale and shape. On the other hand, rated operations can remove some severe/slight welding defects, but may not be able to completely eliminate them. Of course, we hope to achieve zero defects. Generally speaking, the rule of thumb is that welding defects should not exceed 5% of the thickness of the data. Exceeding this value will affect the strength of the welded product.

Ultimately, the presence of the welding centerline is crucial for the production of high-quality stainless steel pipes. With the increasing emphasis on formability in the automotive market, it is directly related to the demand for smaller heat affected zones (HAZs) and the reduction of welding shapes. On the contrary, this promotes the development of laser technology, which involves advancing beam quality to reduce spot size. As the scale of the light spot continues to decrease, we need to pay more attention to the accuracy of scanning the centerline of the seam. Generally speaking, steel pipe manufacturers will try to minimize this error as much as possible, but in reality, it is difficult to achieve an error of 0.2mm (0.008 inches).

This has brought about the need to use a seam tracking system. The two most common tracking skills are mechanical scanning and laser scanning. On the one hand, the mechanical system uses probes to touch the joints upstream of the welding pool, which can become dusty, worn, and vibrated. The accuracy of these systems is 0.25mm (0.01 inches), which is not accurate for high beam quality laser welding.

On the other hand, laser seam tracking can achieve the required accuracy. Generally speaking, laser light may be projected onto the surface of the weld seam, and the resulting image is fed back to a CMOS camera, which uses algorithms to confirm the orientation of the weld seam, faulty joint, and gap.

Of course, imaging speed is important, but when providing the necessary closed-loop control to directly move the laser focusing head on the seam, the laser seam tracker must have a fast controller to accurately compile the direction of the seam. Therefore, the accuracy of the weld seam marking is crucial, and the response time is equally important.

Overall, welding seam tracking skills have been fully developed, and steel pipe manufacturers can also be allowed to use higher quality laser beams to produce stainless steel pipes with better formability.

Therefore, laser welding has found its place of use, as it is used to reduce the porosity of welding, reduce the welding shape, and together maintain or advance the welding speed. Laser systems, such as dispersion cooled Flat noodles lasers, have improved beam quality and formability by reducing the welding width. This development has led to the need for stricter scale control and laser seam tracking in steel pipe factories.

Article source: Kaiping stainless steel faucet http://www.yishangshijue.cn/