How to identify and prevent incomplete penetration and incomplete fusion?

The direct harm of incomplete penetration to welded structures is to reduce the load-bearing cross-sectional area and reduce the mechanical properties of welded joints. The stress concentration caused by incomplete penetration is far more harmful than the decrease in strength. Welding structures that withstand alternating loads, impact loads, stress corrosion, or work at low temperatures often result in brittle fracture.

Lack of fusion not only reduces the effective thickness of the welded structure, but also during the use of the workpiece, stress concentration is prone to occur at the edges of the lack of fusion, which can expand outward to form cracks, leading to cracking of the entire weld seam.

1. Incomplete penetration is the phenomenon of incomplete penetration at the root of a welded joint

The morphological characteristics of incomplete penetration in the weld seam are shown in Figures 1-10.

1) Reasons for incomplete penetration defects:

Improper selection of welding parameters, such as low welding current, fast running speed, improper electrode angle, arc blowing, small butt gap, and improper groove angle, etc., lack of penetration is not closely related to welding metallurgical factors;

Operational errors, such as center deviation during double-sided submerged arc welding without groove opening;

Poor groove processing, such as thick blunt edges, thick on one side and thin on the other, and low welding current.

2) Preventive measures for incomplete penetration defects:

Using a high current for welding is the basic method to prevent incomplete penetration defects. For fillet welds, using AC instead of DC can prevent magnetic bias blowing.

In addition, reasonable design of the groove and keeping it clean, as well as measures such as short arc welding, can effectively prevent the occurrence of incomplete penetration defects.

2. The part that is not fully fused and bonded between the weld metal and the base metal or between the weld bead metal and the weld bead metal

Lack of fusion often occurs on the sidewall of the groove, between layers of multi-layer welding, and at the root of the weld. Lack of fusion has a large time gap and is difficult to distinguish from slag;

Sometimes, although tightly bonded but not welded, micro cracks often occur at the end of the unfused zone.

1) Reasons for lack of fusion defects:

The welding surface is not cleaned thoroughly, with oil stains or rust; Unreasonable groove shape with dead corners; Welding current is too low; Welding gun not fully swinging: the welder increases the current without authorization to accelerate the welding speed, etc.

2) Preventive measures for incomplete fusion defects:

Use a high welding current, perform welding operations correctly, and keep the groove clean.

Summary

In an environment where mechanized production is gradually replacing manual production, talent is also a major cost that enterprises are vying to invest in. According to different solder materials, the welding limit temperature also varies. Automated machinery can control the welding temperature more intelligently and accurately, resulting in higher efficiency. As long as the automatic welding equipment is adjusted properly, there is no probability of efficiency and quality curve, and there is no gap between beginners and skilled workers, etc. The product quality and efficiency of wire welding are stable and can work continuously.