Which method is best for sheet steel cutting?
There are many ways to cut sheet steel, some of which are suitable for automation, others are not. Some are suitable for thinner sheet metal, others for thicker. Some are fast, some are slow. Some are cheap, some are expensive. And some are accurate, some are not. This article takes a brief look at the four main processes used on CNC shape cutting machines, compares the strengths and weaknesses of each, and then provides some criteria to help you decide which process is best for your application.
- Oxyfuel
- Plasma
- Laser
- Water jet
Oxyfuel cutting - Flame cutting
Autogenic Flame cutting is by far the oldest cutting process that can be applied to steel. It is generally regarded as a simple process and the equipment and consumables are relatively inexpensive. A Oxy-fuel torch can handle very thick sheets This is primarily limited by the amount of oxygen that can be supplied. It is not unusual to be able to cut through 20 cm of steel with an oxy-fuel torch. However, when cutting sheet steel to shape, it is mainly thinner sheets that are processed.
When set correctly, an oxy-fuel torch produces a smooth, square cut surface. There is very little slag on the bottom edge and the top edge is only slightly rounded due to the preheating flames. This surface is ideal for many applications without further treatment.
Oxy-fuel cutting is ideal for sheets with a thickness of more than 2 to 3 cm, but can also be used with some difficulty up to a sheet thickness of around half a cm. It is a relatively slow process, finishing at around 40 cm per minute for 3 cm thick material. Another advantage of oxyfuel cutting is that you can easily cut with several torches at the same time, which multiplies your productivity.
Plasma cutting
Plasma cutting is a great process for cutting sheet steel, offering much higher speeds than oxy-fuel cutting but sacrificing edge quality. This is where plasma cutting is tricky. The edge quality has a sweet spot that generally lies between 0.5 cm and 4 cm, depending on the cutting current. The squareness of the edge suffers when the sheet becomes very thin or very thick (outside the range just mentioned), even though the edge smoothness and dross performance can still be quite good.
Plasma equipment can be expensive compared to oxyfuel torches, as a complete system requires a power supply, water cooler (for systems over 100 amps), gas control, torch lines, connecting hoses and cables, and the torch itself. But the higher productivity of plasma compared to oxyfuel makes up for the cost of the system in no time.
You can plasma cut with multiple torches simultaneously, but the added cost factor usually limits this to two torches. Some customers, however, opt for up to three or four plasma systems on one machine, but these are usually high-end manufacturers cutting a large quantity of the same parts to support a production line.
Laser cutting
The Laser cutting is suitable for cutting steel with a thickness of up to around 3 cm. Beyond the 2.5 cm limit, everything has to be right for it to work reliably, including the material (laser steel), the gas purity, the nozzle properties and the beam quality.
The Laser is not a very fast procedureThis is because steel is basically just a burning process that uses the extreme heat of a focussed laser beam instead of a preheating flame. The speed is therefore limited by the speed of the chemical reaction between iron and oxygen. However, the laser is a very precise process. It produces a very narrow kerf and can therefore cut very precise contours and accurate small holes. The edge quality is usually very, very good, with extremely small serrations and delay lines, very square edges and little to no dross.
Another advantage of the laser process is its reliability. The service life of the consumables is very long and the machine automation is very good, so that many laser cutting jobs can be carried out.
Due to the complexity of the beam guidance, CO2 lasers are not suitable for cutting with multiple heads on the same machine. With fibre lasers, however, cutting with multiple heads is possible.
Water jet cutting
Waterjet cutting is also very suitable for cutting steel, achieving a smooth and extremely precise cut. The accuracy of waterjet cutting can exceed that of laser cutting as the edge smoothness can be better and there is no heat distortion. In addition, waterjet cutting is not limited in thickness like laser and plasma cutting. The practical limit of waterjet cutting is around 15 to 20 cm, as cutting this thickness takes a lot of time and the waterjet tends to warp.
The disadvantage of waterjet cutting is the operating costs. The acquisition costs are generally somewhat higher than for plasma cutting, which is due to the high cost of an amplifier pump, but not as high as for laser cutting. However, the cost per hour of operation for waterjet cutting is significantly higher, primarily due to the cost of the garnet abrasive used for the cut.
Waterjet cutting is also suitable for cutting with multiple cutting heads, and this can even be done with a single intensifier pump. However, each additional cutting head requires additional water flow, which requires either a larger pump or a smaller opening.
Criteria for the decision
So how do you make the best decision for a particular procedure?
1. start with the thickness.
Think about the thicknesses you want to work with.
2 Consider the requirements for accuracy and edge quality:
Can you accept the edge quality of the plasma? Most sheet steel workpieces can be welded well with a plasma cut.
Can you accept the heat-affected zone of oxyfuel, plasma or laser? If not, use water jet.
3. think about what is more important: productivity or costs?
If the production rate is most important, you should stay away from the water jet.
If low initial investment and low operating costs are most important, you should opt for oxyfuel.
4. decisive: tolerance for secondary operations
Can you tolerate the occasional dross on the underside of the board? If not, use a water jet or laser.
Do secondary operations require perfectly round holes? If so, use water jet or laser.
5. use of multiple tools
Are the parts suitable for cutting with 2, 4 or more torches? Then oxyfuel cutting is superior to plasma or laser cutting. Cutting with multiple plasma torches is possible, but will be expensive when you consider the initial investment for all the equipment. With waterjet cutting, multiple waterjet nozzles can be operated with a single booster pump if you purchase a pump with a high enough flow rate to support multiple cutting heads. Laser cutting is traditionally limited to a single cutting head, although the fibre laser opens up the possibility of cutting with multiple cutting heads simultaneously.
6. combined use
Another consideration that throws a spanner in the works of any calculation is the idea of multi-process cutting - the application of two of these cutting processes to one and the same part. The most logical combination of processes is waterjet and plasma or waterjet and oxyfuel. With the new fibre laser technology, it is now possible to combine laser and plasma or laser and oxyfuel. The advantage of multi-process cutting is the ability to use the slower, more precise process for some contours and switch to the faster and more cost-effective process for other contours. The result is the production of parts with the required accuracy, but at a much lower cost than if you were to cut the entire part using the high-precision process.
Summary
The overlapping thickness ranges and capabilities of these four processes make it difficult to decide which process to use for a particular structural steel part. Fabricators or steel service centres that need to cut a wide range of materials therefore often have machines equipped with two or more cutting processes. Sometimes the only way to find out which process is best for a particular part is to try it out in different ways and see which process works best.
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7 responses
Water jet cutting seems to be the best method in my case. I will proceed with that. Hopefully I'll manage to finish my project soon.
I am pleased to hear that you have decided in favour of waterjet cutting. This method is indeed very precise and versatile, especially when it comes to complex cuts or avoiding the influence of heat. I wish you every success with your project and hope that you can achieve the desired results quickly and efficiently. If you have any questions or experiences to share during the process, I would love to hear from you.
The good thing about waterjet cutting is that no high temperatures are generated. This is particularly important for materials that are sensitive to heat. I have also worked with waterjet cutting myself.
You are absolutely right, one of the biggest advantages of waterjet cutting is the cool cutting method that does not generate high temperatures. This is particularly advantageous for heat-sensitive materials, as it does not cause any thermal distortion or changes to the material properties. It is good to hear that you have already gained experience with this technique. Perhaps you have some tips or interesting findings from your practice that you would like to share with other readers? The exchange of practical experience can be very enriching for everyone involved.
Cutting with plasma was an absolutely fascinating experience. The precision and speed with which the plasma jet glides through metal is impressive. It's amazing to see how this technology can cut through even thicker materials.
I am pleased to hear that you found plasma cutting to be a fascinating experience. The combination of precision and speed is indeed one of the most impressive features of this technique. In particular, the ability of the plasma beam to cut through even thicker materials with relative ease is a remarkable achievement of modern manufacturing technology. Her enthusiasm for plasma cutting is infectious and highlights the many possibilities of this method. Perhaps you have realised a special project or have special tips you would like to share from your experience with plasma cutting? Such insights are very valuable for other readers considering similar techniques.
I have now purchased a water cutting system for my company. The higher accuracy was particularly important to us. Laser cutting had too much of a negative impact, especially with the thermal deformations. perndorfer.at/wss-anlagen/