1.What is the core reason for the black edges?
Laser cutting uses a high-energy-density laser beam to melt or vaporize the material, while relying on auxiliary gases (such as oxygen, nitrogen, and compressed air) to blow away the slag. The essence of black edges is that the edge of the material is oxidized, carbonized, or slag remains at high temperatures.
2.How does material type affect black borders?
Carbon steel/low alloy steel: When cutting with oxygen, the black edge is more obvious (caused by scale); cutting with nitrogen can reduce oxidation, but the cost is higher.
Stainless steel/aluminum alloy: Usually cut with inert gases such as nitrogen, there is less oxidation and the black edge is relatively slight, but if the parameters are not appropriate (such as too high energy), there may still be slag residue and blackening.
Color-coated plate: The surface coating (such as polyester, fluorocarbon) is easy to carbonize at high temperature, which may aggravate the black edge (especially when the coating is thick).
3.What effect do laser parameter settings have on black edges?
Power: Too high power will lead to excessive melting, increasing the risk of oxidation and carbonization; too low power will result in incomplete cutting and more slag residue.
Speed: Too slow speed will cause the material to be heated for a long time and the edge will be blackened; too fast speed may cause slag accumulation due to insufficient cutting.
Focus position: Focus offset will lead to uneven energy distribution, overheating of the edge or poor cutting, exacerbating the black edge.
4.What impact do devices and environments have on black edges?
Nozzle status: Nozzle wear, blockage or mismatched models will lead to uneven gas injection and incomplete slag removal.
Environmental dust: Too much dust in the workshop may be burned by the high temperature of the laser and attached to the incision, forming black impurities.
5.What are the measures to reduce or avoid black borders?
Optimize process parameters
Adjust laser power, cutting speed and focus position according to material thickness and type (e.g. high speed and low power for thin materials, and appropriate increase of power and matching speed for thick materials).
Preferentially use inert gas (e.g. nitrogen) to cut materials with high surface requirements (e.g. stainless steel, color-coated plates) to reduce oxidation.
Ensure auxiliary gas quality
Use high-purity gas (nitrogen purity ≥ 99.99%) and ensure stable gas pressure (adjust according to material thickness, usually 5~15bar).
Clean the nozzle regularly to avoid blockage and ensure uniform gas injection.
Subsequent processing
For workpieces with obvious black edges, oxide scale and residues can be removed by grinding, pickling (carbon steel), polishing, etc.