From the perspective of appearance quality
1. Beautiful weld shape
- The weld surface is flat and smooth, like a delicate silver ribbon tightly fitting on the welded parts. For example, in manual arc welding, a good weld shape should have a natural transition on both sides without obvious unevenness. The width of the weld is uniform, which reflects the proper control of parameters such as current, voltage and welding speed during welding. For example, when welding thin plates, the weld width can be accurately controlled within an appropriate range, neither too wide to cause the weld to be too high, nor too narrow to cause problems such as incomplete penetration.
- The weld excess height (the part of the weld surface that is higher than the parent material) is moderate. Appropriate excess height can ensure that the weld has sufficient bearing capacity, while not affecting the appearance and stress distribution of the structure due to excessive excess height. Generally speaking, for some important structural parts welding, it is ideal to control the excess height to about 0.5-3mm, which requires welders to have superb skills to accurately control the welding heat input and the amount of filler metal.
2. The weld is defect-free
- Carefully observe the appearance and there are no pores. Porosity is a cavity formed by gas remaining in the weld during welding, which will reduce the density and strength of the weld. Under a good welding process, the weld surface is smooth and no pores like small pinholes can be seen. For example, in carbon dioxide gas shielded welding, by reasonably controlling the gas flow, welding parameters and wire quality, the generation of pores can be effectively avoided.
- There is no slag inclusion. Slag inclusion refers to the phenomenon that slag remains in the weld metal. A good weld is clean inside and there is no trace of slag inclusion. This shows that the slag can be well separated and properly handled during the welding process. For example, in multi-layer and multi-pass welding, each layer of the weld can be well cleaned of slag before the next layer of welding is carried out to ensure the quality of the weld.
- There are no cracks in the weld. Cracks are very serious defects in welding, which will seriously affect the integrity and safety of the structure. A good welding process can effectively control welding stress and welding thermal cycle, so that there are no cracks on the surface and inside of the weld. For example, in the welding of some high-strength steels, cracks are prevented by preheating, controlling the welding sequence, and post-weld heat treatment.
From the perspective of internal quality (although the internal quality cannot be directly observed with the naked eye, it can be judged by some detection methods)
1. Good fusion
- The weld and the base metal are well fused. This means that the filler metal and the base metal can be fully fused during the welding process. From the microstructural point of view, there is no obvious unfused area in the transition zone between the weld metal and the base metal. For example, in butt welding, the weld metal can penetrate well into the molten pool of the base metal to form a complete and uniform weld joint. This allows the weld joint to work as a whole when subjected to load, rather than a weak link at the junction of the weld and the base metal.
2. Uniform metallographic structure
- The metallographic structure inside the weld is uniform. Under the appropriate welding process, the structure formed after the weld metal cools should be uniform. For example, in the welding of some low-carbon steels, fine ferrite and pearlite structures are mainly formed inside the weld. This uniform structure can ensure that the weld has good mechanical properties, such as appropriate strength and toughness. If the welding process is improper, coarse Widmanstatten structure and other undesirable structures may appear, resulting in reduced weld performance.
From the perspective of welding process stability
1. Stable control of welding parameters
- Parameters such as current, voltage and welding speed can always be kept within the appropriate range and have small fluctuations. For example, in the automatic welding process, these parameters can be accurately controlled through advanced welding control systems. Taking laser welding as an example, the stable control of laser power (equivalent to the current in traditional welding) and welding speed can ensure stable weld formation, and the size and shape of the weld will not be abnormal due to large fluctuations in parameters. Stable welding parameters also mean uniform heat input during welding, which is conducive to obtaining high-quality welds.
2. No abnormal interruption in the welding process
- The welding process can be carried out continuously without frequent arc extinction, wire breakage, etc. In gas shielded welding, the gas supply is stable and the welding wire can be continuously and evenly fed into the molten pool. This stable welding process not only ensures the continuity of the weld appearance, but also contributes to the uniformity of the internal quality of the weld. For example, when welding large structural parts, a continuous and stable welding process can avoid welding defects caused by interruptions, such as arc pits.
From the perspective of welding efficiency and adaptability
1. High welding efficiency
- It can complete the welding task at a faster speed while ensuring quality. For example, advanced welding methods such as laser welding have fast welding speed and small heat-affected zone. In some thin plate welding, the speed of laser welding can be several times or even dozens of times higher than that of traditional manual arc welding. This is due to the high concentration of laser welding energy, which can quickly melt the metal to form a weld. At the same time, the efficient welding process can also reduce welding deformation, because the welding time is short, the heat input is relatively small, and the thermal impact on the workpiece is small.
2. Good adaptability
- It can adapt to the welding of different materials, different thicknesses and different structural forms. For example, a good welding process can be used to weld metal foils as thin as paper to large steel structures as thick as tens of centimeters. For different materials, such as carbon steel, stainless steel, aluminum alloy, etc., the welding quality can be guaranteed by adjusting the welding method, welding materials and welding parameters. For example, in stainless steel welding, the use of suitable welding materials and shielding gas can prevent problems such as intergranular corrosion of stainless steel during welding, while ensuring the corrosion resistance and mechanical properties of the weld.