Qualidade da costura de solda a laser: Tipos de juntas e fatores de influência

Laser welding is steadily replacing other types of welding technologies. This is hardly surprising—the quality of weld seams improves significantly due to the precise focusing of the laser beam, eliminating the need for additional processing. The high density and strength of the material at the joint increase the structure’s service life, enhance reliability and enable resistance to mechanical loads.

Due to these properties, laser welding has almost become a universal technology. It is widely used in the production of high-precision parts and instruments, construction, jewelry industry, aerospace, shipbuilding, and other industrial sectors. Essentially, it is suitable wherever high weld quality is required. Today, we will discuss the factors that affect weld seam quality, the types of welding joints, and how to select laser equipment.

Types of Welding Joints

Welding joints are classified based on two criteria: penetration depth and the contact surface area of the connected parts. In terms of penetration depth, there are three levels:

1. Micro Welding – No more than 0.1 mm. They are used for connecting thin film elements, fine wires, and other small components requiring high precision and weld quality.
2. Mini Welding – From 0.1 to 1 mm. Suitable for connecting thin metal sheets, such as aluminum, welding wires to a larger base, and other similar technical operations.
3. Macro Welding – Over 1 mm. They were commonly used for connecting metal sheets, profiles, and complex-shaped parts up to 12-13 mm thick, depending on the alloy grade and equipment power.

Regarding the contact surface area, there are two types of joints: seam joints and spot welds. Let’s first discuss seam joints, as they are the most common.

Seam Joints

This method is used for welding parts that need to withstand significant loads or require tightly sealed joints. Examples include water, oil, and gas pipelines, metal containers for liquids and bulk products, construction structures, and protective facilities. Laser equipment can also seal critical component housings, such as quartz resonators in high-precision instruments. Thanks to the precise focus of the laser beam, the defect rate can be reduced by nearly 35%.

The main advantages of seam laser welding include:

– High weld strength
– Sealing capability
– Resistance to impact and vibration loads

Seam joints do not have any particularly noticeable disadvantages. The only issue is that this type of welding may not be feasible or practical in all cases. In such scenarios, spot welding is used.

Spot Welding

This method is used for welding small components that are not subjected to high loads and cannot be fastened using other types of connectors due to their small size. Such products include fine wires, thin film elements, thermocouple ends, and complex-designed jewelry. Laser spot welding is also suitable for welding dissimilar metals: nickel-chromium, platinum-palladium, copper-aluminum, and so on.

Due to these characteristics, this technology is widely used in the production of printed circuit boards, semiconductors, and high-precision instruments. Laser spot welding is ideal for manufacturing integrated circuits, particularly for connecting wires to film elements. The latter are made of precious and rare-earth metals with thicknesses ranging from 0.3 to 1 micrometer, and the wires’ diameters do not exceed 80 micrometers.

Such tiny components cannot be connected using soldering. Or rather, they can, but this would result in up to 80% of the products being rejected. Therefore, only laser equipment is used in micro welding to save the materials and time required to process defective products.

However, micro and mini welding are not the only applications for spot welding. It is also used for fixing large metal structures before final assembly. Afterward, these products can be welded using seam methods or fixed by other means such as bolting. Thanks to welding fixation, the displacement of structural elements is prevented, and the exact dimensions of gaps and slots are maintained.

Advantages of spot welding include:

– Suitable for connecting micro-components
– High precision and excellent weld quality—can be used to manufacture critical structural elements and complex electronic instruments
– Fast welding speed

Disadvantages include the lack of joint sealing and slightly lower strength compared to seam methods. Therefore, this method is used only when these conditions are not required.

What Influences Weld Seam Quality?

The first thing that comes to mind is the skill level of the welder. This is partially true—their skills significantly impact many aspects, but not everything. There are also several critical parameters, such as metal weldability, equipment selection and welding mode, workpiece thickness, and weld cooling speed. Let’s start with the first characteristic.

Weldability

The weldability of a metal depends on the amount of carbon—high-carbon steels (with more than 0.35% carbon) require special welding modes. Additionally, alloy additives and impurities affect this parameter, potentially improving or worsening it. For instance, nickel and titanium enhance weldability, while high concentrations of chromium, silicon, and manganese reduce it. To improve the weld quality of poorly weldable alloys, special measures can be taken, such as preheating the workpiece, using protective gases, and subsequent heat treatment.

Metal Cooling

During welding, liquid metal forms at the joint, which begins to crystallize as it cools. If the material cools too quickly, various defects such as cracks or workpiece deformation may occur. Therefore, experienced welders often aim for natural cooling of the metal.

When welding cast iron, the workpiece should be preheated to 600-650°C, both before starting and during the beginning and end of the work. This ensures a strong weld that won’t shatter from accidental impacts and can withstand high pressure. Slow cooling also prevents the deformation of part walls and avoids the white cast iron phenomenon.

However, the risk of defects is partially reduced when using a laser welding machine. This is because the heating area in laser welding is very small, and heat hardly extends beyond the melt pool. Therefore, lasers can be used for welding heat-sensitive metals and alloys. Despite this, all recommendations regarding preheating and cooling the workpiece remain valid.

By understanding these factors, you can ensure high-quality weld seams and choose the appropriate laser equipment for your needs.