A burr, a rough edge, an uneven edge, melt-through, jagged edges, or excessive bevel after cutting are indicators that help assess whether the metal-cutting process is proceeding correctly. They do not always indicate a serious problem, but it is always worth knowing how to interpret them correctly.
The quality of the cut edges affects the time required for further processing, weld preparation, assembly, the aesthetic appearance of the components, and production repeatability. Problems can arise with any thermal cutting technology— plasma, laser, or gas cutting—and each has its own characteristics. Therefore, troubleshooting should not involve randomly changing parameters, but rather analyzing the symptoms, the cutting technology, the material, the CNC program, and the machine’s condition.
Cutting marks, burrs, and edge quality—what should you evaluate after cutting?
In manufacturing terminology, “slag” most often refers to molten and solidified material remaining along the bottom edge of a workpiece. Depending on the technology, parameters, and thickness, it can take the form of a delicate coating, residue that is easy to remove, or a hard, firmly adhered burr. Not every residue indicates a process error—a delicate film that comes off when wiped away is usually not a real problem. What matters is whether the cutting residue affects further processing, cleaning time, fit, welding, or the appearance of the finished product.
When assessing edge quality, it’s a good idea to check:
- the number of trails or gratu,
- Are the residues easy to remove,
- Is the edge even and consistent,
- Is there a bevel on the edge,
- Is teething visible,
- Does the problem occur throughout the entire part, or only in certain areas?
- Does the quality vary at holes, corners, perforations, or short sections,
- Does the edge require additional grinding before welding, assembly, or painting?
Only by considering all these factors together can we determine whether we are dealing with a natural consequence of the technology or with a problem that requires a process adjustment.
The most common causes of scoring and edge quality deterioration
Edge quality issues most often result from an improper balance between process energy, cutting speed, cutting torch height, process gas, and the method of removing molten material from the cut. The most common causes include:
- cutting speed that is too low or too high,
- incorrect torch height of the plasma torch, oxy-fuel torch, or laser cutting head,
- incorrectly selected cutting current, laser source power, or gas parameters,
- a worn nozzle, electrode, shield, lens, or other consumable parts,
- incorrect gas pressure or flow,
- contaminated material: scale, rust, oil, paint, primer, or moisture,
- incorrect piercing of the material,
- a poorly written CNC program,
- radii that are too small, sharp corners, or complex part geometry,
- unstable handling of the machine,
- mismatch between the technology and the type and thickness of the material.
The mere fact that “a streak has appeared” is not enough to make a diagnosis. What matters is where it appears, how much of it there is, whether it can be easily removed, and whether the problem recurs on subsequent parts.
Troubleshooting Post-Cutting Issues — Where to Start?
The best approach is to analyze the symptoms step by step. In mass production, a random change in several parameters at once makes it difficult to identify the cause—it is better to check the process in a logical order: starting with the appearance of the edges, then moving on to the parameters, material, and consumables, and finally checking the CNC program and the condition of the machine.
1. Check where the slag or burr appears
A burn mark on the lower edge usually indicates the cutting speed, cutting torch height, gas selection, or improper removal of molten material. If the problem occurs only at corners, small holes, perforations, or at the ends of the contour, check the cutting strategy, piercing, approach passes, speed reductions, and program geometry. In laser cutting, localized burrs tend to appear precisely where the machine slows down or changes direction.
2. Determine whether the residue is easy to remove
A light film that comes off when rubbed or lightly tapped is usually within an acceptable range. If the slag is hard, thick, firmly adhered, and requires intensive grinding, the process should be adjusted. In practice, what matters is whether the residue increases the cost and production time of the part.
3. Check the cutting speed
A feed rate that is too slow causes excessive heating, more molten metal, and a poorer bottom edge. A feed rate that is too fast leads to undercutting, a hard burr, and an unstable edge. It’s important to evaluate the speed not only on straight sections, but also in corners, near small holes, along short contours, and at perforations.
4. Check the torch height or burner head height
An incorrect working height compromises cut quality in all cutting technologies: in plasma cutting, it affects arc stability, kerf width, bevel, and slag volume; in laser cutting, the nozzle distance, focal point position, and assist gas flow are critical; in gas cutting—flame stability and material preheating. Check not only the initial settings but also how the height control performs during operation (sheet warping, thermal deformation, unstable support).
5. Assess the condition of the wear parts
Worn parts reduce quality even when operating parameters remain unchanged. In a CNC plasma cutting machine, the nozzle, electrode, and shield are critical; in fiber laser cutting machines, the condition of the nozzle, the cleanliness of the optics, and the quality of the gas are key; and in gas cutting machines, the nozzle and flame stability are crucial. If quality deteriorates gradually, inspecting the components should be one of the first steps.
6. Review the material
Rust, mill scale, paint, oil, moisture, an uneven surface, or variations between batches affect cutting stability. If the problem affects only one batch or sheet, compare it with another batch of the same grade and thickness—this test helps distinguish between a processing issue and a material issue.
Plasma cutting — kerf, bevel, and edge quality
In plasma cutting, the slag and edge bevel are among the most commonly analyzed characteristics. Their extent depends on the parameters, the class of the plasma system, the material thickness, the type of gas, the cutting speed, the torch height, and the condition of the consumables. A slight bevel on the edges is typical for plasma cutting—it is not always a problem, especially for components used in steel structure welding. However, if the bevel is large, irregular, or differs on opposite sides of the workpiece, check the cutting torch height, the condition of the nozzle, the cutting direction, and the stability of the cut.
The system class is very important. Standard (air) plasma systems typically generate more spatter and a more visible edge structure than high-quality systems. In HQC or HD narrow-beam plasma, there is usually less slag, and if it does appear, it is easier to knock off or clean—which reduces the time needed for weld preparation and assembly. When diagnosing plasma cutting issues, it is worth checking:
- cutting speed,
- torch height,
- condition of the nozzle and electrode,
- arc stability,
- gas quality and pressure,
- piercing the material,
- cutting direction,
- material quality,
- CNC program settings.
Laser cutting — burrs, oxidation, and localized deterioration in quality
In laser cutting, the classic slag line appears much less frequently than in plasma cutting. A fiber laser cutter typically produces a very clean, repeatable edge—especially when the parameters are correct, the material is of good quality, and the assist gas system is functioning properly. However, this does not mean that problems never occur. The following issues may arise:
- a slight burr on the bottom edge,
- air raid,
- overflow,
- discoloration,
- edge deterioration on small holes,
- local problems with perforations or complex geometry,
- undercutting due to incorrectly selected parameters.
It is worth paying special attention to areas where the machine slows down, changes direction, or makes many short movements. If the residue is minimal and easy to remove, it may be acceptable. If they affect the subsequent process, check the speed, laser source power, focal position, nozzle condition, gas pressure, material quality, and cutting strategy.
Gas Cutting — Flame Quality and Process Stability
In gas cutting, the quality of the cut edges depends on proper preheating of the material, nozzle selection, gas pressure, cutting speed, torch height, and stability of the cut. With thicker materials, the edge structure tends to be more visible than with laser cutting, but it should be consistent and predictable.
Problems may manifest as excessive slag, an uneven edge, difficulty piercing the material, overheating of the material, or an unstable cutting path. When troubleshooting, it is important to check the condition of the nozzle, the quality of the flame, the settings of the cutting torch, the speed, the purity of the oxygen, and the preparation of the material surface.
CNC Programs and Part Geometry — An Often Overlooked Source of Problems
Burrs, rough edges, and poor edge quality are not always caused by the technology or the machine—often the source is the CNC program or the part’s geometry. This is especially true for small holes, sharp corners, short sections, perforations, densely spaced features, and areas where the machine frequently decelerates and accelerates. When troubleshooting, it’s worth checking:
- breakpoint,
- how to enter the contour,
- the length and direction of the approach,
- a strategy of cutting corners,
- the order in which the parts are cut,
- distances between elements,
- cutting gap compensation,
- parameters for small holes,
- perforation settings,
- stability of the material support after cutting out adjacent elements.
A well-prepared CNC program minimizes local quality issues, improves part repeatability, and reduces the amount of post-cutting rework.
How can I reduce the number of scratches and improve the quality of the edges?
Improving edge quality requires a comprehensive view of the process—changing a single parameter is rarely enough. Most often, you need to examine the relationship between speed, cutting torch height, gas, operating conditions, material, and the CNC program. To minimize the amount of slag, burrs, and rework, it’s important to ensure the following:
- the proper selection of technology based on the material and thickness,
- consistent cutting parameters,
- regular inspection of wear-and-tear parts,
- the correct torch height or head height,
- adequate gas quality and flow,
- inspection of the material before cutting,
- a refined CNC program,
- the right strategy for holes, corners, and perforations,
- routine procedures for operators,
- periodic assessment of the quality of parts after cutting.
The goal does not always have to be the complete elimination of every trace of the cut. It is more important to achieve a quality appropriate for the part’s application and to minimize those effects that actually increase production costs, prolong the cleaning process, or hinder further processing. When a part is to be welded, it also helps to perform weld preparation directly on the machine—for example, using a 3D bevel cutting head and bevel cutting.
The Role of CNC Machines in Ensuring Consistent Edge Quality
Process stability depends not only on the parameters, but also on the machine’s design, the CNC control system, the quality of the feed mechanism, height control, and the software. Even well-selected parameters will not produce repeatable results if the machine cannot maintain stable motion, the correct distance from the material, or handle the dynamics required for complex contours. Therefore, when selecting a machine, it is important to evaluate not only the maximum cutting thickness and power of the cutting source, but also the quality of the construction, the control capabilities, and the height control system.
STIGAL designs and implements CNC metal-cutting machines built for reliable operation in industrial environments. Depending on your needs, these can include fiber laser cutting machines, CNC plasma and oxy-fuel cutting machines, solutions for cutting steel plates, tubes, profiles, and structural sections, large-format machines, and systems with 3D bevel cutting heads and edge beveling capabilities. Properly selected machines, technology, and configurations help minimize edge quality issues right at the cutting stage, rather than passing them on to subsequent workstations.
Summary
Beading, burrs, bevels, serration, and uneven edges are important diagnostic indicators—they help assess whether the plasma, laser, or gas cutting process is stable and whether the machine is operating properly. Not every slight surface defect indicates a problem: some effects are inherent to the technology and may be acceptable if they do not interfere with welding, assembly, or further processing.
However, if the residue is large, hard, difficult to remove, irregular, or affects production time, it is worth conducting a diagnostic analysis covering parameters, speed, cutting torch or head height, operating condition, gas quality, material, CNC program, and workpiece geometry. This approach reduces the need for additional machining, improves repeatability, and increases the stability of the entire production process. If you’re unsure which technology to choose, you may also find the guide “Laser or Plasma—How to Choose a Cutting Technology” helpful.
Are you having trouble with edge quality or excess traces?
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Frequently Asked Questions — Grain and Edge Quality
Szlaka pojawia się wtedy, gdy stopiony materiał nie zostaje prawidłowo usunięty ze szczeliny cięcia i zastyga przy krawędzi detalu. Przyczyną może być prędkość cięcia, wysokość palnika, parametry gazu, zużyte elementy eksploatacyjne, jakość materiału albo geometria detalu.
Nie każda. Delikatny nalot lub cienka warstwa, która schodzi po przetarciu albo lekkim zbiciu, często nie stanowi istotnego problemu. Problemem jest przede wszystkim szlaka gruba, twarda, nieregularna, trudna do usunięcia lub wpływająca na dalszą obróbkę.
Warto sprawdzić prędkość cięcia, wysokość palnika, stan dyszy i elektrody, dobór prądu, jakość gazu, przebicie materiału, kierunek cięcia oraz program CNC. Znaczenie ma również klasa systemu plazmowego.
Zwykle tak. Plazma HQC lub HD wąskostrumieniowa najczęściej pozwala uzyskać mniejszą ilość szlaki niż plazma standardowa, często określana jako powietrzna. Jeżeli szlaka się pojawia, zwykle jest łatwiejsza do zbicia lub oczyszczenia.
Przy cięciu laserowym szlaki jest zwykle znacznie mniej niż przy plazmie albo nie występuje ona w klasycznym rozumieniu. Może pojawić się delikatny grat, nalot lub lokalne pogorszenie krawędzi, szczególnie przy małych otworach, perforacjach, skomplikowanych konturach lub zwolnieniach prędkości.
Nie zawsze. Drobne ząbkowanie często nie stanowi problemu przy spawaniu konstrukcji stalowych. Może jednak mieć znaczenie przy elementach widocznych, wymagających wysokiej estetyki, dokładnego pasowania albo ograniczenia dodatkowej obróbki.
Parametry warto zweryfikować, gdy szlaka jest trudna do usunięcia, pojawiają się niedocięcia, jakość krawędzi jest niestabilna, ukos jest zbyt duży albo detal wymaga zbyt dużej ilości pracy po cięciu.
