Laser welding is the process of using a high-energy laser beam to merge metal components. The process involves directing a laser beam onto the surfaces of materials. It melts them at the welding spot and then allows them to solidify into a joint. It is widely applied across industries due to its ability to create strong, precise welds with minimal distortion.

When selecting a laser for welding applications, several key parameters are carefully considered to ensure optimal performance and desired results. These parameters collectively shape the detailed process of laser welding and deliver excellent results in diverse industrial applications.

• Pulse Repetition Rate (or Pulse Frequency) - The repetition rate, often measured in Hertz (Hz), represents the number of laser pulses that are emitted per second. It determines the speed at which the laser can perform the welding process. In laser welding, a higher repetition rate can increase the speed and throughput of the welding process. This is particularly important in industrial applications where high production rates are required. The parameter governs the degree of overlap between adjacent spot welds. Higher pulse frequencies result in increased overlap rates, enhancing the welding quality.
• Shielding Gas - Shielding gases are used to protect the weld area from atmospheric contamination. These gases dissipate the vapor and plasma formed, allowing the laser beam to reach its intended target. They create a shielding atmosphere for the weld pool, safeguarding it during the welding process, and preserve the integrity of the focusing lens by shielding it from contaminants and debris. Argon (Ar), Helium (He), Nitrogen (N₂), Carbon dioxide (CO₂), Oxygen (O₂), etc. are different types of shielding gases being used. The choice of shielding gas depends on the material being welded and the specific requirements of the welding process.
• Beam Power and Traverse Speed - The reduction in traverse speed leads to a nearly exponential decrease in penetration depth for a specific power setting. Conversely, the depth-to-width ratio experiences a moderate increase with higher traverse speeds, reaching a stable point afterward. When the power input is increased at a constant speed, the penetration depth proportionally increases. It's crucial to note that findings derived from low-power laser welding (below 5 kW) are not directly applicable to high-power welding scenarios (around 20 kW). This difference arises due to plasma shielding effects resulting from either high power densities or elevated evaporation rates, both of which enhance plasma formation and significantly impact welding outcomes.
• Wavelength - Determines the absorption characteristics of the laser beam in the material. Materials have specific absorption bands where they absorb laser energy most efficiently. Choosing an appropriate laser wavelength ensures optimal absorption, leading to efficient and stable welding. For example, CO₂ lasers have a wavelength of around 10.6 micrometers and are well-absorbed by materials like metals and plastics.
• Laser Energy (or Pulse Energy) - Pulse energy, typically measured in joules (J) or millijoules (mJ), refers to the energy carried by each laser pulse. It affects the penetration depth. Higher pulse energy can lead to deeper weld penetration. The pulse energy needs to be adjusted based on the thickness and type of material being welded. Thicker materials may require higher pulse energies to achieve sufficient penetration, while thinner materials may require lower pulse energies to avoid excessive heat input.
• Pulse Width (or Pulse Duration) - Pulse width, often measured in nanoseconds (ns) or picoseconds (ps), represents the duration of each laser pulse. It impacts the heat-affected zone and the overall quality of the weld. The pulse width should be optimized to balance the desire for a narrow heat-affected zone with the need for proper material bonding. Shorter pulse widths are generally used for precision welding, while longer pulse widths may be suitable for thicker materials or when a more substantial weld bead is desired.

Materials Suitable for Laser Welding

Laser welding techniques exhibit versatility and can be applied to a wide range of materials. Here are some of the typical materials compatible with laser welding:

Metals:

• Different grades of aluminium alloys
• Copper alloys including bronze and brass
• Steel variants such as high-strength alloys, carbon steel, and stainless steel
• Titanium alloys, commonly used in medical and aerospace applications
• Nickel and its alloys, utilized in power generation and aerospace sectors

Plastics:

Specific types of plastics such as thermoplastics can be melted and solidified repeatedly using laser welding processes. Examples include:

• Acrylic (PMMA): Used in displays, signage, and medical equipment
• Polyvinyl Chloride (PVC): Commonly found in medical applications, construction materials, and pipes
• Polycarbonate (PC): Widely used for automotive components, safety equipment, and electrical enclosures

Composites:

Laser welding can join composites with diverse constituents, such as:

• Glass fiber-reinforced polymers (GFRP)
• Carbon fiber-reinforced polymers (CFRP)

Laser welding is capable of bonding diverse materials, including dissimilar metals. It can successfully weld dissimilar metal pairs like copper-nickel, nickel-titanium, copper-titanium, titanium-molybdenum, brass-copper, and low-carbon steel-copper, given specific conditions.

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