1. Material Reflectivity to Laser
Aluminum/Copper: With reflectivity as high as 80%–95% (aluminum ~82%, copper ~95%), most laser energy is reflected and lost. Higher power (e.g., ≥6000W) or special processes (e.g., preheating) are required to enhance absorption. Insufficient power may lead to "failure to initiate cutting" or "inadequate penetration."
Stainless Steel: Reflectivity is ~30%–40% (without an oxide layer), allowing efficient energy absorption. Even low-power systems (e.g., 1500W) can stably cut thin sheets (≤8mm).
2. Material Thermal Conductivity
Aluminum/Copper: High thermal conductivity (aluminum ~237W/m·K, copper ~401W/m·K) causes rapid heat diffusion, making it hard to concentrate energy along the cutting path. Solutions include increasing power (to compensate for heat loss) or accelerating cutting speed (to reduce heat diffusion time). For example, cutting 2mm aluminum with a 6000W system achieves speeds up to 5m/min, while the same thickness of stainless steel only requires 3m/min.
Stainless Steel: Low thermal conductivity (~16–20W/m·K) keeps heat localized, stabilizing the molten pool. This makes it suitable for medium-to-thick plate cutting (≤12mm) with moderate power (e.g., 3000W).
3. Material Melting and Boiling Points
Aluminum: Melts at ~660°C (low) but boils at ~2467°C (high). Cutting primarily involves melting (not vaporization), requiring assist gas (e.g., nitrogen) to blow away molten slag. Insufficient gas pressure may cause slag adhesion and burrs.
Copper: Melts at ~1085°C (higher) and boils at ~2562°C (high). Higher power (≥6000W) is needed to melt it, and the viscous molten pool often leads to "dross sticking" defects.
Stainless Steel: Melts at ~1500°C (high) but boils at ~2750°C (much higher). Cutting primarily involves melting. Using oxygen as assist gas releases oxidation heat (contributing 30%–50% of cutting energy), reducing required laser power (e.g., 3000W oxygen cutting of 10mm stainless steel is more efficient than 6000W nitrogen cutting).
4. Material Oxidation Tendency
Stainless Steel: Reacts with oxygen to form iron oxide (Fe₃O₄), releasing heat that boosts cutting speed (e.g., 3000W oxygen cutting of 8mm stainless steel is twice as fast as nitrogen cutting). However, oxidation may slightly discolor the cut edge (requiring post-polishing).
Aluminum/Copper: High-temperature oxidation forms refractory oxide films (e.g., Al₂O₃ with a melting point of 2050°C, CuO with a melting point of 1326°C), which block laser energy absorption. Inert gases (nitrogen/argon) are thus required to prevent oxide formation and blow away molten slag.
5. Compatibility with Assist Gases
6. Typical Cutting Performance Comparison (6000W Fiber Laser)
Summary
High-reflectivity aluminum/copper requires high power + inert gas + high-pressure slag removal;
Stainless steel can leverage oxygen oxidation for energy efficiency or nitrogen for oxide-free precision cuts.