Mastering Laser Piercing: Technical Strategies for Thick Plate Cutting
(Summary): Piercing is the most critical stage of the fiber laser cutting process. Poor piercing leads to nozzle damage, protective lens failure, and slag buildup. This technical guide explores the differences between Blast Piercing and Stage Piercing, and how to optimize parameters for high-power fiber lasers.
1. What is Laser Piercing?
Every cut starts with a pierce. The laser beam must melt and blow through the entire thickness of the material before the cutting motion begins. For thin sheets, this happens instantly. However, for thick plates (over 10mm), piercing can take several seconds and involves a high risk of material "splash-back."
2. Blast Piercing vs. Stage Piercing (Pulse Piercing)
To handle different thicknesses and materials, engineers use two primary methods:
Blast Piercing:
Mechanism: The laser uses high power and constant pressure to force its way through the metal quickly.
Pros: Very fast.
Cons: Creates a large, messy hole and significant molten splash. It is generally avoided for high-precision parts or thick stainless steel.
Stage/Pulse Piercing:
Mechanism: The laser "pulses" the beam (turning it on and off rapidly) while gradually increasing the power or decreasing the focus.
Pros: Produces a very small, clean hole with minimal slag. This is the professional standard for thick plate processing.
Cons: Takes longer than blast piercing.
3. Critical Parameters for a Clean Pierce
To optimize your piercing process, you must fine-tune these four technical variables in your CNC system:
Duty Cycle: In pulse piercing, this is the ratio of "on" time to "off" time. A lower duty cycle reduces the heat buildup, preventing the metal from "boiling" over and splashing.
Frequency: High-frequency pulses help in creating a finer hole, while low frequency is better for thicker, stubborn materials.
Nozzle Height: For the piercing phase, the nozzle should be kept higher from the plate (e.g., 5.0mm - 10.0mm) than during the cutting phase (e.g., 0.5mm - 1.0mm) to protect the optics from sparks.
Oxygen Pressure: Using lower pressure during the initial stages of piercing helps contain the splash, increasing it as the hole deepens.
4. The "Oil Spray" Trick: Protecting Your Machine
When piercing thick carbon steel, the molten slag often sticks to the surface of the plate, which can cause the cutting头 to crash later.
Technical Tip: Many professional machines use an automated Oil Spray System. A small mist of oil is applied to the piercing point. The oil prevents the molten slag from sticking to the plate, allowing it to be easily blown away.
5. Recommended Piercing Time Reference (Example for 6kW)
| Material Thickness | Piercing Method | Estimated Time | Gas Used |
|---|---|---|---|
| 6mm Carbon Steel | Blast | <0.5 sec | Oxygen |
| 12mm Carbon Steel | Stage (2 Steps) | 1.5 - 2.0 sec | Oxygen |
| 20mm Carbon Steel | Stage (3 Steps) | 3.0 - 5.0 sec | Oxygen |
| 10mm Stainless Steel | Pulse | 1.0 - 1.5 sec | Nitrogen |
Conclusion: Efficient piercing is the bottleneck of thick plate productivity. By moving away from blast piercing toward controlled, multi-stage pulse piercing, you not only improve the quality of your parts but also significantly extend the life of your laser nozzles and protective lenses.