How to solve the sticking slag when laser cutting aluminum plate

Laser cutting aluminum slag (also known as hanging slag, slag) is a common problem, mainly by the high thermal conductivity of aluminum, low melting point, easy oxidation and molten state viscosity and other characteristics. In order to solve the problem systematically, it is necessary to optimize the gas, parameters, materials, equipment and process 5. The following provides a comprehensive set of solutions:

Core key: auxiliary gas selection and optimization (this is the most important part)

1. High purity nitrogen is preferred

• Principle: Nitrogen as an inert gas can effectively prevent the oxidation of aluminum melt and reduce the formation of aluminum oxide (Al₂O₃) sticky residue. At the same time, the high-pressure nitrogen can blow the molten aluminum liquid downward from the slit, rather than side-to-side accumulation.
• Purity requirement: ≥ 99.99%(99.995% or higher recommended). Lack of purity is one of the main causes of slag sticking.
• Pressure requirements: according to the plate thickness adjustment, usually higher (such as cutting 3mm aluminum plate to 1.5-2.0MPa). Insufficient pressure does not effectively blow away the melt.

2. High quality compressed air (economic alternative)

• Applicable scenarios: the lower surface quality requirements are not high, or thin aluminum plate (such as ≤ 3mm) rough machining.
• Necessary conditions:
• Must be equipped with high-efficiency refrigerated dryers and precision filters to ensure that the air is water-free and oil-free. Moisture and oil will aggravate aluminum oxidation and slag sticking.
• The pressure should be stable enough.

3. Oxygen (special purpose)

• Principle: Use the oxidation reaction to provide additional heat and increase the cutting speed. However, a large amount of rough and hard alumina slag will inevitably be produced, which is usually not recommended for cutting requiring no slag sticking, but only for occasions requiring very low surface requirements or subsequent processing.

cutting parameter optimization

Parameters shall be matched with gas for system debugging.

1. Power and speed balance:

• The power is too high/the speed is too slow: excess energy causes excessive melting of aluminum, the molten pool becomes larger, the gas is difficult to blow, and the bottom spherical slag is formed.
• Power is too low/too fast: insufficient energy, material is not cut through or the bottom is cooled too fast, the melt will solidify on the edge before it can be blown away.
• Debugging method: on the basis of the recommended parameters, the speed ladder test is carried out to find the “sweet spot” that just cuts through and hangs the least slag “.

2. Frequency and duty cycle:

• Reducing the frequency and adjusting the duty cycle sometimes helps to control the heat input and reduce the bottom overheating. For thin plates, higher frequencies may be used.

3. Focus position:

• Try to reduce the focus slightly (negative defocus) so that the energy is more concentrated in the lower half of the plate, which is conducive to blowing the melt out from the bottom. This is an effective means to improve the bottom hanging slag. It needs to be fine-tuned according to the actual situation.

Equipment and Consumables Status

1. Nozzle inspection and selection:

• Status: Ensure that the nozzle is free of wear, deformation and center-to-center. A worn nozzle will cause the airflow to be turbulent and the slag blowing is weak.
• Diameter: usually use a larger diameter nozzle (such as φ2.0mm or above) with high-pressure nitrogen, can form a stronger, wider coverage of the air flow barrier.

2. Beam quality:

• Ensure that the laser head lens (focusing mirror, protective mirror) is clean and pollution-free, and ensure that the beam energy distribution is uniform and concentrated.

Material and process preparation

1. Surface and material of aluminum plate:

• Cleaning: Remove the oil, dust and oxide layer on the surface of the aluminum plate before cutting. Special aluminum alloy cleaning agent can be used.
• Alloy grade: different aluminum alloy performance is different. Usually 5 series (such as 5052) than 6 series (such as 6061) better cutting, less sticky slag. Silicon, magnesium and other elements of high alloy viscosity greater.
• Oxide layer: if there is a thick oxide skin on the surface of the plate, it can be slightly polished or pickled.

2. Working distance:

• Ensure that the distance from the nozzle to the plate is constant and appropriate (usually 0.5-1.5mm). Too high will weaken the gas pressure.

3. Perforation and lead:

• Optimize perforation parameters to prevent spatter from accumulating on the surface during perforation.
• Use outer leads or arc leads to avoid slag accumulation at the beginning of the workpiece contour.

Treatment after cutting (remedial action)

If there is still slight slag hanging, the following measures can be taken:

1. Physical removal: Use a scraper, stainless steel brush or scouring pad to remove manually. For heavy plate hard slag, a small angle grinder with a special nylon wheel may be required.

2. chemical cleaning: the use of special aluminum cleaning liquid or diluted alkaline solution immersion wipe, can dissolve part of the sticky slag. Remember to avoid the use of strong acids and alkalis, and after treatment must be thoroughly rinsed with water and dried.

3. Sandblasting: For batch parts or requiring uniform matte surface, fine sand (such as glass beads) can be used for sandblasting.

Through the above systematic investigation and optimization, the slag sticking problem of laser cutting aluminum plate can be effectively controlled to achieve high-quality cutting. The key is to understand that “effective purging of high purity gas” is the core, and all other parameters are coordinated around this 1 core.