The cutting process
This page brings together practical guidance for achieving reliable, high‑precision results in oxy‑fuel, plasma, and laser cutting. From piercing and tight‑radius cutting to controlling edge quality, cut angles, dross, roughness, and nozzle performance, you’ll find clear explanations of the factors that shape cut quality — and how to optimize them. Use this collection as a quick, effective reference to improve consistency, reduce defects, and get the best possible results from your cutting process.
How to pierce steel with an oxy fuel torch?
Before starting an oxy-fuel cutting operation, it is essential to ensure that all equipment is in proper working condition. This includes checking There are two main ways to initiate an oxy-fuel cut: starting from the edge of the plate or piercing from the plate surface.
Starting from the edge of the plate
Edge-starting is relatively simple. Position the torch so that half of the nozzle is over the plate edge, and the other half extends over empty space. Begin heating until the steel reaches its ignition temperature—you’ll see the area beneath the nozzle turn bright red. At that point, release the cutting oxygen jet. This initiates the oxidation reaction and the torch can begin moving along the cutting path.
Starting from the edge is easier because the ignition temperature is reached more quickly, and there's space for slag and molten metal to escape cleanly from the cut zone.
Piercing from the surface of the plate
Piercing directly into the surface is more challenging, especially with thicker plates. It takes longer to heat the material to ignition temperature because heat dissipates more quickly into the surrounding metal.
The biggest issue during piercing is slag and molten metal buildup, which has nowhere to escape. This causes excessive splatter, leading to nozzle clogging and interruption of the piercing process. For this reason, oxy-fuel piercing is limited by plate thickness, and the maximum thickness depends on the specific equipment and manufacturer.
Piercing technique to prevent nozzle clogging
To successfully pierce steel with an oxy-fuel torch, follow these steps:
- Ignite the fuel gases and set the nozzle clearance according to the manufacturer's table.
- Heat the material until it reaches ignition temperature.
- Start the machine movement and gradually open the cutting oxygen valve so that the molten material does not damage the nozzle.
- For thicker plates, use a longer piercing oxygen time to ensure clean penetration without clogging.
Proper piercing technique improves cut quality, prolongs nozzle life, and ensures a stable cutting process—especially when working with demanding materials and thicker steel plates.
How to cut small radiuses or sharp corners?
SSAB steels are advanced high-strength steels. Compared to standard mild steel, these grades have a higher level of residual stresses that are evenly distributed throughout the plate.
When cutting—whether using thermal or cold cutting methods—it is important to be aware of stress concentrators. These are areas where residual stresses become localized and intensified, which can significantly increase the risk of hydrogen-induced cracking.
In summary, when cutting SSAB high-strength steels, always keep the following in mind:
- Avoid sharp inward-facing corners whenever possible
These shapes act as strong stress concentrators and increase the likelihood of crack initiation. - Use smooth and continuous geometries
Gentle transitions and flowing contours help distribute stress more evenly across the cut edge. - If sharp corners are unavoidable, add a circular loop around outward-facing corners
This technique reduces sudden changes in direction and helps relieve stress during the cutting process. - If the cutting process must be interrupted (e.g., overnight), finish with a clean cut
Removing any partially cut sections helps eliminate stress risers and prevents crack formation during the pause.
How to achieve high edge quality in oxy-fuel cutting of steel?
The photos below shows various scenarios of cutting edge quality along with corresponding improvement suggestions. These examples help identify optimal cutting conditions and highlight common issues encountered during cutting operations.
Optimal cutting edge quality
Too low oxygen cutting pressure
Too low heat input
Too high heat input
Nozzle to plate distance too close
Nozzle to plate distance too far
Too high cutting speed
Too low cutting speed
Low cutting speed combined with low cutting oxygen pressure, resulting in a wider kerf with potential slag inclusion.
Low cutting speed with insufficient cutting oxygen pressure, leading to an uneven cut surface and possibly increased dross.
Recommended cutting method
How to get high edge quality with plasma cutting of steel?
Improving the quality of plasma-cut parts is crucial and involves controlling the cut angle and addressing factors such as the edge's shape, smoothness, and the presence of unwanted cut edge roughness and dross. Key adjustments include aligning the torch correctly, selecting appropriate materials, and using the right cutting speed to achieve superior results.
Negative cut angle
A “negative” cut angle occurs when the top dimension of a cut part is larger than the bottom dimension. This can result from several factors:
- Misaligned torch
- Bent or warped material
- Worn or damaged consumables
- Low arc voltage
- Cutting speed too low
Negative cut angle
Positive cut angle
Positive cut angle
Conversely, a "positive" cut angle is when the top dimension is smaller than the bottom dimension. This is usually caused by:
- Misaligned torch
- Bent or warped material
- Worn or damaged consumables
- High arc voltage
- Cutting speed too high
- Improper amperage settings
Top and bottom rounded cut flatness
This issue typically arises when cutting materials thinner than 6 mm. It is most often caused by over-powering the material or using too much current (amperage) for the material thickness.
Top and bottom rounded cut flatness
Top edge undercut
Top edge undercut
Occurs when the sides of the cut face curve inward, likely from the torch being too close to the material and/or the arc voltage being too low.
Process induced roughness
If you see irregularities in the cut face that are consistent, and may only appear in one axis, it is probably induced by the process. Likely problems include:
- Worn or damaged consumables, and/or
- Gas flow too high.
Process Induced Roughness
Cut face machine induced roughness
When cut face irregularities are inconsistent, and often confined to one axis, then look for roughness induced by the machine motion.
This could be caused by:
- Dirty machine rails, wheels, rack, and/or pinion
- Rails out of alignment
- Wheels or bearings worn, damaged, or loose.
High Speed Dross
High speed dross
When the dross is small but appears welded or rolled over on the bottom surface of cut part, it is usually caused by cutting too fast. This type of dross is difficult to remove and may require grinding. It will often be accompanied by "S-shaped” lag lines, which also indicate that you are cutting too fast. Also, check if the arc voltage is too high.
Low speed dross
Low Speed Dross forms as larger globules on the bottom of the cut, but it usually pops off easily. Try speeding up and/or adjusting the arc voltage higher to increase the cutting height.
Low Speed Dross
Top Dross
Top dross
This appears as splatter on top of the parts and is usually easy to remove. It is most often associated with cutting too fast or cutting too high (high arc voltage).
How to get high edge quality with laser cutting of steel?
Each type of laser — CO2, fiber, and Nd:YAG — offers benefits tailored to specific cutting requirements.
Key considerations for high-quality laser cutting of steel
Material Considerations: Choosing the appropriate steel is essential. Thickness, alloy composition, and surface condition greatly affect the quality of the cut. Proper pre-treatment, including cleaning and surface preparation, ensuring the laser to interact with the steel as efficiently as possible, promoting clean cuts.
Laser cutting parameters
Regular maintenance and precise calibration of the laser cutter are mandatory for consistent, high-quality results, as well as preventing machine issues and maintaining accuracy.
During the Design Phase, clean, vector-based design files are crucial. Efficient part nesting reduces waste and improves cutting efficiency while avoiding complex patterns that can affect cut quality.
Troubleshooting common issues
Finally, always prioritize safety by using appropriate protective equipment, following safety protocols, and managing emissions and waste sustainably.
Good cut quality
Remedial Action: None.
Good cut quality
Nozzle misalignment
No action or issue indicated.
This is showing the correct setup and schematically depicts a good surface.
Correct Nozzle
Correct Aligned Laser
Dirty steel sheet
Remedial action: Remove dirt, rust or other surface contaminants that cause poor cut result.
Bad cut due to dirty steel sheet
Poor nozzle
Remedial action: Replace with a new nozzle.
Bad cut due to Poor Nozzle
Laser power too low
Remedial action: Increase laser power to its appropriate level for the given material.
Laser Power Too Low
Cutting speed too high
Remedial action: Change to correct cutting speed for the given material.
Cutting Speed Too High
Nozzle misalignment
Remedial Action: Correct nozzle set up. Make sure that the laser beam exits the nozzle orifice in the center.
Nozzle Misalignment
Too small nozzle diameter
Remedial Action: Change to correct nozzle diameter for the given material.
Nozzle Diameter Too Small
Too large nozzle diameter
Remedial Action: Change to correct nozzle diameter for the given material.
Bad edge quality due to the too large nozzle diameter
Too high oxygen pressure
Remedial Action: Decrease the oxygen pressure to its right setting for the given material.
Bad edge quality due to too high oxygen pressure
Cutting speed is too low
Remedial Action: Change to correct cutting speed for the given material.
Bad edge quality, the cutting speed is too low
FAQs about cutting
Manage deformations and thermal effects
Thermal effects and material movement can impact your final result. Learn how to control deformations and secure consistent cutting quality.
Take your cut to the final finish
Once the cutting is complete, the right finishing techniques ensure accuracy, durability, and a clean end result. Discover how to perfect the final steps.
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The information in this report is only applicable to SSAB’s products and should not be applied to any other products than original SSAB products.
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