1.What is the core reason?
The essence of slag buildup is that the molten metal produced during the cutting process is not completely blown away by the auxiliary gas and re-solidifies at the bottom of the cut. For cold-rolled coils, especially galvanized sheets, the zinc layer on the surface (boiling point of about 906°C, far lower than the melting point of iron of 1538°C) will vaporize first, bringing additional gas interference.
2.What are the effects of material factors?
Surface Condition: Oil film, dust, or uneven zinc coating on the surface of cold-rolled coils can affect laser absorption and the stability of initial perforation.
Solution: Clean the material surface before cutting. For sheets with excessively thick oil films, wipe them gently.
Note: Zinc vapor from galvanized sheets can interfere with cutting; stronger gas purging is required.
3.What are the effects of the auxiliary gas?
Gas Type and Purity:
Carbon Steel/Cold-Rolled Sheet: High-purity oxygen (≥99.95%) must be used. Insufficient oxygen purity is one of the most common causes of slag buildup. Oxygen not only blows away molten slag but also participates in the exothermic reaction, providing additional heat.
Stainless Steel/Aluminum: High-purity nitrogen (≥99.999%) is used for high-pressure cooling cutting. Insufficient purity will lead to oxidation and slag buildup at the cut.
Gas Pressure:
Insufficient oxygen pressure: Insufficient blowing force, unable to effectively remove molten slag, resulting in slag buildup at the bottom.
Insufficient oxygen pressure: Over-cools the cut, lowering the cutting temperature, making the cutting process unstable, and wasting gas.
Solution: Precisely adjust the pressure according to the sheet thickness and cutting speed. Generally, the thicker the sheet, the higher the required pressure, but the optimal point must be found. For example, cutting a 3mm cold-rolled sheet may require an oxygen pressure of around 0.3-0.5 Bar, while a 10mm sheet may require 0.8-1.2 Bar (refer to the equipment manufacturer's parameter table for specific details).
Gas Flow and Nozzle:
Check if the nozzle is damaged and if the orifice diameter is suitable (generally, the thicker the board, the larger the nozzle orifice diameter).
Ensure the nozzle is at the correct distance from the board surface (usually 0.5-1.5mm). Improper distance will cause airflow turbulence.
4.What impact do process parameters have?
Laser Power:
Insufficient Power: Inability to completely melt the material, resulting in incomplete cuts and slag buildup at the bottom.
Excessive Power: May cause over-melting, resulting in a rough cut and even burning the material.
Solution: Match the power to the material thickness. Modern laser cutting machines allow separate settings for piercing and cutting power; optimizing the piercing process can reduce initial slag buildup.
Cutting Speed:
Excessive Speed: Insufficient heat input, incomplete material cut, and incomplete slag removal, resulting in continuous slag buildup at the bottom.
Excessive Speed: Over-burning, resulting in a wide, rough cut, and the potential formation of large molten beads at the lower edge.
Solution: Find the "optimal speed point." Gradually increase the speed at a fixed power until slag buildup suddenly increases, then reduce the speed slightly; this is the optimal speed for that power level.
5.What special treatments are needed for cold-rolled coils (especially galvanized sheets)?
Using the "Galvanized Sheet Cutting Parameter Library": Many laser cutting machines have dedicated galvanized sheet cutting parameters that take into account the interference of zinc vapor and typically optimize piercing methods (such as using progressive piercing to avoid burst holes) and gas parameters.
Adjusting Piercing Height and Delay: Appropriately increasing the piercing height and setting a short delay after piercing to allow the initial zinc vapor to dissipate fully before cutting can improve the cutting quality at the starting point.
Consider using air or nitrogen to cut thin galvanized sheets: For thinner galvanized sheets (e.g., 1-3mm), sometimes using dry, clean compressed air or nitrogen for cutting can yield edges without oxidation and with less slag, but the speed will be slower than oxygen cutting.