A fiber laser metal cutting machine is known for its precision, speed, and ability to cut through various metals. However, even when operating at the same power level, it exhibits different cutting speeds and efficiencies for different metals. This discrepancy arises due to several key scientific and technical factors, which we will explore in detail.
1. The Role of Material Properties in Cutting Speed
The rate at which a fiber laser metal cutting machine cuts through metal depends significantly on the intrinsic properties of the material. Here are the primary factors:
a. Thermal Conductivity
- Metals with higher thermal conductivity dissipate heat more quickly, reducing the amount of energy available for cutting.
- Example: Copper and aluminum have high thermal conductivity, meaning they require higher power or slower cutting speeds to achieve a clean cut.
- In contrast, stainless steel has lower thermal conductivity, allowing the laser to concentrate heat in a smaller area, leading to a faster cut.
b. Absorption Rate of Laser Wavelength
- Different metals absorb laser light differently, affecting how much energy is actually utilized in the cutting process.
- Fiber lasers typically operate at 1.06 µm (1064 nm), which is well absorbed by materials like stainless steel, carbon steel, and titanium.
- However, metals like aluminum and copper reflect a significant portion of the laser energy, making them harder to cut.
c. Melting Point
- A metal’s melting point influences the laser’s ability to cut efficiently.
- Lower melting point metals require less energy and can be cut faster.
- Example: Aluminum (660°C) has a lower melting point than stainless steel (1450°C), but due to its high reflectivity, it often requires more power and a slower speed.
2. Interaction Between Laser Beam and Metal Surface
When a fiber laser beam contacts a metal surface, several interactions occur:
a. Reflection and Absorption
- Highly reflective metals bounce the laser light instead of absorbing it, making the cutting process inefficient.
- Example: Brass and copper reflect more laser energy, requiring assistive gases or higher power levels.
b. Energy Distribution and Material Removal
- The laser needs to vaporize or melt the metal to create a cut.
- If a metal absorbs laser energy efficiently, it heats up quickly, melts, and is blown away, enabling a faster cut.
- If it doesn’t absorb well, the process slows down due to poor energy conversion.
3. Influence of Assist Gases on Cutting Performance
Assist gases play a crucial role in fiber laser cutting by enhancing material removal and controlling oxidation. Different metals require different gases:
a. Oxygen (O₂) Cutting
- Used for carbon steel because it creates an exothermic reaction that enhances cutting speed.
- However, this reaction is not beneficial for metals like aluminum or stainless steel, which do not oxidize in the same manner.
b. Nitrogen (N₂) Cutting
- Suitable for stainless steel, aluminum, and brass since it prevents oxidation and produces a cleaner cut.
- However, nitrogen cutting is slower than oxygen-assisted cutting.
c. Air Cutting
- A cost-effective alternative, often used for thin sheets of aluminum and stainless steel.
- However, air-assisted cutting results in rougher edges and may require post-processing.