Plasma, Oxy-Fuel, Laser, or Waterjet: Which One to Choose?

Choosing the Right Metal Cutting Machine Plasma, Oxy-Fuel, Laser, or Waterjet

In metal processing applications, users often struggle with choosing the most suitable metal cutting machine. The mainstream metal cutting processes available today have unique characteristics related to cutting thickness, accuracy, metallurgical performance, and productivity.

While this article cannot delve into all the details of these features, we can provide an overview that will help you better understand and make the best choice.

Before discussing the technology and capabilities of each process, we must first define the most important needs of users in the metalworking industry.

Choosing the Right Metal Cutting Machine Plasma, Oxy-Fuel, Laser, or Waterjet

Equipment purchase cost

Different cutting methods require various CNC machines, dust removal equipment, CAD/CAM software, among other things.

For instance, laser cutting demands higher speed and precision on thin sheets, as opposed to the slower cutting speed of waterjet and flame methods. These requirements can result in a significant disparity in equipment costs.

Cutting cost per unit part or unit length

The cost mentioned above includes gas, nozzles, electrodes, electricity, and water. In certain situations, equipment acquisition costs and labor costs, such as loading and unloading, are also shared. It is crucial to understand the scope of these costs when making comparisons.

When determining the cost of a project, it is recommended to consider the cost per part or unit length, which takes into account the cutting speed and productivity, as it provides a more accurate reference point than the cost per time.

Ease of use

This requirement is primarily related to software, especially CAM, and CNC.

Nowadays, learning times are being reduced and the reliance on experience is being diminished by integrating built-in professional experience.

For instance, Hypertherm, the industry leader in plasma cutting, has incorporated the full set of Hypertherm plasma process parameters into its own nesting software and CNC control, enabling new users to quickly learn and maintain the same cut quality and productivity as experienced veterans.

Although this need is difficult to quantify, it should never be disregarded for practical production.

Productivity

Cutting speed, also known as production capacity, is often the decisive factor that determines the output capacity.

Accuracy of cut parts

Measuring the accuracy of a metal part can be done in various ways. Typically, the outer contour requires lower tolerances compared to the inner bore.

As a result, several metal cutting suppliers are now introducing processes that allow for cutting higher quality bores. Furthermore, users often only measure the top surface during their measurements, even though the dimensions of the bottom surface can differ significantly due to the slope of the cut.

For the sake of simplicity in this article, it is recommended to use the positive and negative tolerance values measured for the top surface and then factor in the cut slope for each process.

Edge quality, metallurgical properties

All the above processes have different effects on metal machinability, forming properties and weldability.

Maintenance requirements

When considering the long-term cost of ownership, it is important to factor in the maintenance requirements and ease of maintenance for each of these different processes.

To provide a brief overview of these processes, the following are included: flame cutting, fine plasma, 3 kW fiber laser, and waterjet.

For comparison purposes, the purchase cost of a complete system that includes an industrial CNC machine (not entry-level or maximum configuration), CAD/CAM software, and a cutting area of approximately 5′ x 10′ (1.5 x 3 m) will be used.

1. Oxy-fuel (Flame) cutting

Oxy-fuel (Flame) cutting

The oxy-fuel cutting process is the simplest among all the cutting techniques that we are discussing here. The principle behind this process is to first heat the steel using a combustible gas to the “ignition point” temperature, which is approximately 1800F. Once this temperature is reached through preheating, pure oxygen is injected to create an exothermic reaction with the hot steel, rapidly eroding it.

This technique can only cut carbon steel, mostly in thicknesses ranging from 1/4″ (about 6.35mm) to 6″ (about 150mm). For thicknesses over 2″ (approx. 50 mm), the cutting speed is faster than other processes.

It is easy and inexpensive to install multiple flame torches on a CNC oxy-cutting machine simultaneously, doubling its capacity.

5′ x 10′ flame cutting machine Cost:

RMB 80,000 – 120,000 (relatively simple type machine with low speed)

Cost of cutting per unit part or per unit length:

The cutting speed is slow, and it consumes a significant amount of gas.

Cutting costs become more favorable compared to plasma as the thickness of the steel plate increases.

Usually, the cost per foot of cutting is higher than plasma, but it is relatively lower for thicknesses over 2″ (~50mm).

Ease of use:

In order to achieve the fastest cutting speed and the best cut quality, operating Flame CNC cutting machines requires an experienced operator. Additionally, the cutting process typically demands continuous monitoring.

Productivity:

Oxy-fuel cutting has low productivity due to long preheating time and slow cutting speed.

Cut part accuracy:

A good operator with the most appropriate speed, height, gas, and nozzle will cut parts with an approximate dimensional tolerance of ±0. 030″ (approximately 0.76mm) and less than 1 degree of slope.

Edge quality, metallurgical properties:

The heat-affected zone of flame cutting is large.

The section is rough and has hanging slag.

Maintenance requirements:

Maintenance of the flame cutting bed is relatively simple and can be mastered by the user himself.

2. Fine Plasma

Fine Plasma

Fine plasma technology utilizes high-temperature ionized gas to generate a high-energy density cutting arc, allowing it to cut through all conductive materials.

The latest advancements in technology have eliminated the need for operators to have prior experience.

Fine plasma is most effective in cutting carbon steel ranging from 26 gauge (approx. 0.45mm) to 2″ (approx. 50mm) thick, as well as stainless steel and aluminum up to 6¼” (approx. 160mm) thick.

5′ x 10′ plasma cutting machine cost:

150,000 – 250,000 RMB (faster, equipped with height adjustment and dust removal)

Cutting cost per unit part or unit length:

On carbon steel from ¼” (approx. 6.35mm) to 2″ (approx. 50mm) thick, plasma cutting costs are the lowest relative to other processes.

Ease of use:

When equipped with the latest CNC and software, plasma is very easy to learn and use.

Since professional process parameters are already built into the nesting software, there is no experience required of the operator.

Productivity:

Plasma cutting is faster than laser for thicknesses greater than ¼” (~6.35mm), and it cuts faster than flame at thicknesses less than 2″ (~50mm). In fact, plasma is the fastest and most efficient cutting process of them all.

Cut part accuracy:

The dimensional tolerances for cut pieces of carbon steel are approximately between ±0.015″ (approx. 0.38mm) and 0.020″ (approx. 0.5mm).

For thin plates that are less than 3/8″ (approx. 9.5mm) thick, the tolerance slope is 2-3 degrees.

For boards thicker than 1/2″ (approx. 12.7mm), the tolerance slope is within 1 degree.

Edge quality, metallurgical properties:

The heat affected zone is typically very small, usually less than 0.010″ (about 0.25mm). Additionally, the section has good weldability, and appears smooth with no hanging slag.

Maintenance requirements:

Maintenance is relatively simple and can be mastered by the user himself, or only requires telephone support from the manufacturer.

3. Fiber laser

Fiber laser

Fiber laser is the latest laser technology available.

It utilizes a solid-state laser generator that is more efficient than the traditional CO2 laser. The wavelength of the fiber laser is also appropriate for conduction in the thin, flexible fiber, making it more pliable and easier to maintain than the CO2 laser, which can only be conducted through mirror reflection.

The high-energy laser focuses on melting the material being cut, and an auxiliary gas (usually oxygen when cutting carbon steel) blows off the molten metal.

A 3 kW fiber laser has the same cutting power and speed as a 4 to 5 kW CO2 laser. Its cutting capacity is typically up to ¾” (approximately 19mm) thick carbon steel.

5′ x 10′ fiber laser cutting machine cost:

300,000 – 500,000 RMB (laser cutting bed requires higher motion accuracy and shade protection)

Cost per unit part or unit length cut:

The most cost-effective use of laser cutting is for thicknesses less than ¼” (approximately 6.35mm). However, as the thickness of the material being cut increases, the cutting speed significantly decreases, and the cost becomes higher than that of plasma cutting. Nevertheless, laser cutting offers exceptional quality and accuracy in the resulting cut.

Ease of use:

Like the latest plasma systems, laser cutting machines can also be equipped with the latest CNC and software, making them easy to learn and use because all settings are automated.

Productivity:

Highest productivity on thin sheets, equal to plasma as thickness increases to ¼” (~6.35mm).

Cut part accuracy:

The highest quality fiber laser cut parts have dimensional tolerances of approximately ±0.01″ (or 0.25mm), which is superior to plasma cutting and comparable to waterjet cutting.

Additionally, the slope of the cuts is within 1 degree.

Edge quality, metallurgical properties:

The heat affected zone is slightly smaller than the plasma.

Maintenance requirements:

In comparison to the previous CO2 laser, the fiber laser is significantly easier to maintain and can typically be managed by the user with remote assistance from the manufacturer.

4. Waterjet

Waterjet

Waterjet technology has been in use for several decades and has been applied to a wide range of materials, from soft cakes to hard granite.

Pure water can be used to cut soft materials, with a high-pressure stream of water (ranging from 40,000 to 60,000 psi) compressed by a nozzle, which increases the flow rate and energy density.

Sand can also be added to the water stream, acting like the teeth of a saw, to cut through the material with the impetus of the water stream.

Today’s state-of-the-art waterjet pumps can achieve pressures of up to 100,000 psi, leading to faster cutting speeds, but they require regular maintenance as the pump seals need to be replaced frequently.

Waterjet technology offers two major advantages over other cutting processes, including the lack of a heat-affected zone and the ability to cut virtually any material. Additionally, the accuracy of waterjet cutting is very high.

However, the main disadvantage of waterjets is their slow cutting speed.

The cost of a 5′ x 10′ waterjet cutting machine can range from 200,000 to 350,000 RMB. Due to the slower speed, the cost is lower than a laser bed, but slightly more expensive than a plasma cutter.

Cutting cost per unit part or unit length:

Since waterjet cutting is so slow, the cost per part cut is the highest compared to other processes.

See also:

Ease of use:

Similar to the latest plasma systems, when equipped with the latest CNC and software, waterjet cutting machines are just as easy to learn and use. Very little experience is required of the operator.

Productivity:

Very slow on carbon steel and stainless steel, cutting aluminum will be faster.

Cut part accuracy:

The accuracy of the waterjet is the best of all cutting processes, with dimensional tolerances of cut pieces within approximately ±0. 005″ (approximately 0.13mm).

The slope is within 1 degree.

Edge quality, metallurgical properties:

No influence on the metallurgical properties of the material to be cut.

Smooth section, cutting quality is related to the grit and cutting speed (the slower it is, the smoother it is).

Maintenance requirements:

Maintenance is relatively simple and can be mastered by the user himself.

Conclusion

After clarifying your needs and practical applications, and taking into account the various process characteristics described in this article, I believe that you will be able to choose the most suitable metal cutting process and equipment.

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Shane
Author

Shane

Founder of MachineMFG

As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.

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