In laser cutting, how can piercing and blowholes be addressed?

Piercing and blowholes are very common issues in laser cutting, representing key challenges that affect cut quality, processing efficiency, and operational safety. First, let’s clarify two concepts:

Piercing: Refers to the process of using a laser to create an initial hole in the material before cutting begins. The problems typically manifest as long piercing times, low efficiency, and incomplete piercing.

Keyholing: A runaway condition during the piercing process characterized by violent spattering of molten metal, abundant sparks and burrs, and potential damage to the nozzle and lenses. It typically occurs when cutting thicker plates (especially with an oxygen flame) or special materials such as galvanized steel.

Core solution approach: Balance energy input.

Whether it’s perforation or blowout, the underlying cause is an imbalance in the transient interaction among laser energy, gas, and the material. The key to solving this problem lies in “control” rather than “forceful attack”—that is, allowing the energy to penetrate the material smoothly and gradually, instead of causing an instantaneous “blowout.”

Conventional methods to address inefficient/unstable perforation

1. Optimization of perforation parameters (most basic and direct)

• Reduce perforation power: Use power lower than cutting power in the initial stage to avoid excessive heat accumulation.
• Improve the pulse frequency: use high-frequency pulse perforation, the continuous energy is dispersed into a number of small energy packets, so that the material layer by layer melting, rather than a one-time gasification explosion.
• Adjust the duty cycle: Reduce the duty cycle (the proportion of time the laser is “on”) to further control the average power.
• Increase the perforation time: give enough time for the slag to be blown away and gradually penetrate.

2. Adopt advanced perforation process

Step perforation/progressive perforation: Modern laser cutting machines have this function.

• First low and then high: first use low power and high frequency to preheat and make a small hole, then gradually increase the power or switch the parameters to expand and penetrate.
• Layered perforation: For thick plates, set multiple perforation heights, and the laser focus stays at different depths to penetrate layer by layer.

Blast perforation. Progressive Perforation:

• Explosion perforation: for thin plate, the use of nitrogen cutting stainless steel is often used, fast.
• Progressive perforation: It must be used for thick plates, carbon steel or special materials with oxygen, which can effectively prevent bursting.

3. Control gas

• The perforation pressure is lower than the cutting pressure: lower pressure is used for perforation (for example, when cutting with oxygen, the perforation pressure is set to 50-70% of the cutting pressure) to prevent bursting caused by violent combustion of high-pressure oxygen. After the perforation is successful, switch to high cutting pressure.
• Advance air supply and delay air shut-off:

4. Auxiliary process

• Spraying puncture liquid: spraying special explosion-proof hole liquid (or common marker ink) at the perforation point can inhibit splashing and the effect is remarkable.
• Use film/sticker: for mirror stainless steel, aluminum plate, etc., paste the protective film and then cut, can reduce the reflection and improve the stability of perforation.
• Cutting from the edge of the plate: if the process allows, try to introduce cutting from the edge of the plate to avoid perforation completely.

Focus on solving the problem of “bursting holes”

Puncturing is an extreme manifestation of uncontrolled perforation and requires a more targeted strategy.

1. Fine adjustment of parameters (for blasting holes)

• Further reduce the puncturing power: This is the most effective first step.
• Greatly increase the pulse frequency: make the laser action more “soft”.
• Significantly increase perforation time: give sufficient time for energy dissipation and slag removal.
• Try to raise the focus: set the perforation focus position 0.5-2mm above the surface of the material (the specific value needs to be tested), so that the beam diameter is slightly larger, the energy density is reduced, and a little “blasting” is avoided “.

2. Gas strategy optimization

• Check to ensure that the perforation air pressure has decreased.
• For galvanized and coated plates: consider using nitrogen or air for perforation, and switch to oxygen cutting (if necessary) after the perforation is completed. Because oxygen will react violently with the zinc layer, resulting in a burst hole.
• Ensure gas purity: oxygen purity needs to be above 99.95%, impurities will interfere with the process.

3. Material and process adaptation

• Galvanized plate/coated plate treatment: This is the hardest hit area for blasting holes. In addition to the above gas methods, you can also:
• When programming, the perforation point is set in an area with no coating or a shallow coating (e. g. the edge of the sheet, the area where the coating is cut off first).
• If conditions permit, pre-treat the perforation points (e. g., lightly sand the coating off).
• Thick plate oxygen cutting: must use progressive perforation, and use the combination of “low power-long time.

Systematic Inspection and Prevention Checklist

When problems occur, troubleshoot in this order:

Final Safety Tips

In case of serious bursting, stop the operation immediately and check:

1. Protect the lens: Is it contaminated or damaged? This is the most common loss.

2. Nozzle: Is it blocked or damaged by slag? To be replaced

3. Inside the cutting head: Is there any sputtering residue? Professional cleaning is required.

To sum up, the essence of solving the problem of perforation is: for different materials (especially galvanized sheet), give up the “one size fits all” perforation, adopt the “gradual” mild perforation strategy, and independently set the lower perforation pressure. Starting from the standard process library of the equipment, the “golden parameters” of the most suitable current materials can be found by small-step, targeted parameter testing and optimization “.