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Fiber laser metal cutter – how does it work?

A fiber laser metal cutter effortlessly cuts through iron as if it were nothing. Here we explain how a fiber laser works.

What is a laser?

The laser is a type of amplified light that is obtained by stimulated radiation.

Basic laser characteristics

  • High intensity and brightness
  • Small wavelength range
  • Monochrome light
  • Good coherence and long coherence length
  • Nice parallel bunder with good directionality
Fiber laser metal cutter

High energy coherent laser light

Coherent laser light versus normal light

Process of continuous metal melting

When the laser beam is irradiated on the surface of the workpiece, the light energy is absorbed and converted into heat energy, so that the temperature at the irradiation site is rapidly raised, melted and evaporated to form a small pit. The metal around the spots melts through thermal diffusion. The metal vapor in the small well expands rapidly, causing a micro-explosion. The molten material is ejected at high speed, creating a hole with a large top and a small bottom in the workpiece.

fiber laser metal cutting

Fiber Laser Metal Cutter Definition

Fiber laser cutting is a hot cutting method that uses the focused high power density laser beam as the main heat source. The laser beam ensures that where the workpiece is hit by the beam, the material quickly melts and evaporates. At the same time, molten material is blown away with the help of a fast air flow. By doing this continuously, the workpiece is cut.

In recent years, laser sources and fiber optic technologies have been improved and become more affordable so that they can be used on an increasingly large scale. The scope of work is still expanding due to the large amount of research and development in this industry.

The world's first laser cutting machine originated in the 70's. In the past 40 years, with the continuous expansion of application and continuous improvement of laser cutting machine, many enterprises have been engaged in the production of various kinds of laser cutting machine to meet the market demand comply. There are now special machines for cutting 2D sheet material, 3D laser cutting machine and pipe laser cutting machines.

Fiber laser source operation

Laser cutting of metal plates

In the field of thin sheet cutting, the traditional CO2 laser and YAG laser is gradually adopted by fiber laser metal cutters, mainly for the following reasons:

  • Low costs. The photoelectric conversion efficiency of a fiber laser is about 30%. The photoelectric conversion efficiency of CO2 laser is 6 ~ 10%, and the photoelectric conversion efficiency of YAG lasers is only 3%. In addition, the fiber laser source has no vulnerable parts and maintenance costs are typically low.
  • Optical fiber lasers have a small volume, lightweight, movable and flexible head so that they can be easily deployed for a wide variety of applications.
  • By using optical glass fibers for the light guide, the optical light beam length is always constant. As a result, the cut quality is always constant. With CO2 lasers, the light path is not constant, which means more frequent adjustments and the cut quality depends somewhat on the location on the workbed where cutting is done. With fiber laser, the cutting quality or the entire work bed is constant. This also makes it possible to realize large format laser machines without loss of quality when cutting.
  • The light beam is transmitted through the optical fiber without external reflection mirrors in the optical light path. This saves costs, no fine adjustment of the optical light path is required, no light path contamination can occur and fewer moving parts are subject to wear.
  • The wavelength of the optical fiber laser (1.06 m) is more easily absorbed by the metal material compared to the wavelength of CO2 (10.6 m). This is especially beneficial for cutting sheet material.

The cutting speed of it is 2 to 4 times higher than with CO2 lasers. At the same time, a fiber laser has a better cutting result for highly reflective material such as aluminum alloy, copper and various copper alloys.

Fiber laser metal cutter process

Fiber laser cutting process
  1. Lens A. Empty height
  2. Laser beam B. Puncture Height
  3. Air flow C. Cutting height
  4. Cutting line T. Sheet thickness
  5. Molten material
  6. Cutting plane
  7. Nozzle / mouthpiece
  8. Cutting direction

Influencing factors

  • Machine
  • Cutting speed
  • Focus position
  • Lens
  • Nozzle
  • Cut gas
  • Laser quality
  • Material
  • Lightpad

Maximum sheet thickness for fiber laser metal cutters

Fiber laser metal cutter machines with a 1.5kW source can cut 3-4mm stainless steel without burr and up to ~10mm thick carbon steel when oxygen is added. However, when oxygen is used, a thin oxide film is formed on the cutting surface. The maximum cutting thickness can be increased, but with greater cutting tolerances. With laser powers up to 20kW, up to 40mm of stainless steel can be cut.

Hardly any post-processing

The investment in a fiber laser metal cutter has decreased significantly in recent years, but is still significant. The advantage is often that little post-processing is required in subsequent steps, which leads to lower costs.

Flexible and also for small batches

Because there are no further tool costs, the laser cutting equipment is also suitable for making small batches of parts.

Importing CAD designs

Fiber laser metal cutting machines use an automated digital CNC control technology. After the device is turned on, the cutting data can be sent from a design CAD workstation.

Laser cutting process

Fiber laser cutting head

On the right is a rough view of a fiber laser cutting head. During cutting, this cutting head is approximately 1 mm above the sheet material. The focus height varies depending on the material thickness and material type and has a major influence on the final cut quality of the edge and surface of the material.

For example, when cutting carbon steel, the focus is on the top surface of the plate. When cutting stainless steel, the focus is on about half the thickness of the plate. When cutting an aluminum alloy, the focal length is close to the bottom surface of the plate.

Fiber laser cutting head

Automatic focus height correction

During the cutting process, due to irregularities in the surface of the material, the focal length of the laser changes, which affects the cut quality.

To overcome this phenomenon, a capacitive sensor has been placed on the laser head. It measures the distance between the laser head and the workpiece extremely accurately and in real time. This information is passed on to the laser controller.

According to this information, it is used to adjust the height of the cutting head in real time by means of a very precise actuator. This creates a closed-loop control that continuously and in real-time adjusts the cutting head height to the material so that it is always perfectly set at the correct focus height.

Fiber laser focus height

Laser cutting speed and laser power of a fiber laser metal cutter

The laser power has a major influence on the cutting thickness, cutting speed, cutting width and cutting quality. In general, the higher the laser power, the greater the cutting depth and the higher the cutting speed.

For different materials and thicknesses there is an optimal setting for cutting speed and laser power. The roughness of the cut surface is smallest at these settings. Outside the optimal operating range, the surface roughness of the workpiece increases. In addition, the cutting efficiency is lower, which leads to higher costs. If you work even further outside these settings, both too high and too low power will result in fire or slag formation.

When the laser power and the pressure of the auxiliary gases are kept constant, there is a non-linear inverse relationship between the cutting speed and the gap width:

  • As the cutting speed increases, the gap width decreases.
  • As the cutting speed decreases, the gap width increases.

The cutting speed has a parabolic relationship with the surface roughness of the cut.

As the cutting speed increases from zero, the surface roughness of the section gradually decreases. When the optimum cutting speed is reached, the surface roughness of cut is minimal. As the cutting speed continues to increase, the surface roughness will decrease further until there is not enough power to cut all the way through the bottom of the plate.

Optimization of cutting speed and laser power

In the laser program, the cutting power and cutting speed can be optimized per design or subsection. For example, the cutting speed is usually slower when a small circle or sharp corner is cut. In the program the cutting power can be reduced locally by adjusting the cutting speed so that the cutting precision and quality are perfect everywhere.

Use of auxiliary gases in the laser cutting of metal

Choosing the right auxiliary gases and optimizing the right amount is a difficult job and essential for a good end result.

Optimizing this takes time and experience, which is typically built up by experimenting a lot with different materials, powers, gas pressures and cutting speeds. We try to help you on your way here, we try to answer questions such as:

  • How to choose the right auxiliary gas?
  • Which aspects of cut quality are affected by different gases?
  • Which auxiliary gas should be used for different materials?
  • What pressure of the auxiliary gas should be used?
  • How pure should the gas be?

Different functions of auxiliary gases

Auxiliary gases have a number of functions:

  • Use the assist gas to blow the slag away in the coaxial cut
  • Cool the surface of the workpiece to reduce the effects of the extreme local heat
  • Cool and prevent contamination of the laser lens so that it does not overheat
  • Some cutting gases help to protect the base metal.

Different materials require the use of matching auxiliary gases.

Oxygen is generally used for laser cutting of low-carbon steel sheet. The role of oxygen in the carbon steel cutting process is to fuel and blow off the molten material.

Types of auxiliary gases and characteristics

The auxiliary gases commonly used in laser cutting are:

  • nitrogen
  • oxygen
  • sky

Auxiliary gas pressure and flow requirements are different for materials of different thicknesses and different materials.

Auxiliary gas purity

Impurities in the auxiliary gas can damage the lens, causing fluctuations in cutting power. In addition, inconsistencies can arise at the top or bottom of the plate material.

Oxygen

The purity of oxygen is generally higher than 99.5%. The higher the purity, the brighter the cutting surface. It is important to note that the oxygen contains impurities, such as water, which can seriously affect the cut quality of the plate surface. If the oxygen purity is not high and the processed parts have higher demands on the surface quality, it is necessary to add oxygen drying equipment and other devices to improve the oxygen purity.

Nitrogen

Nitrogen is mostly used for cutting stainless steel and aluminum alloy materials. The role of nitrogen in the stainless steel cutting process is to eliminate oxidation and blow off the melt. The thicker the plate, the higher the nitrogen pressure required. When cutting stainless steel, the required nitrogen purity is typically higher than 99.999%. Low purity nitrogen can cause yellowing of the cut surface and decrease clarity.

Pressure of auxiliary gases

The amount of air pressure that can be used for different types of auxiliary gases is different.

The optimum settings are determined on the basis of the properties of the gas, such as flammability and combustion, and experimentation.

If the auxiliary gas is used to prevent dross formation or to protect the lens, it is roughly the case that the greater the gas pressure, the more metal vapor can be blown away. As a result, it can be cut at a higher speed. This is the function of the use of nitrogen in thin sheet cutting.

This is different for thick sheet material. MetaQuip can help you find the optimal settings for your materials.

Auxiliary gases for fiber laser

Oxygen

Mainly used for cutting carbon steel.

While the oxygen heat of reaction is used to increase the cutting efficiency, the resulting oxide film increases the spectral absorption factor of the reflective material beam. The end of the cut is black or dark yellow.

Oxygen is mainly used for rolled steel for welding construction, carbon steel for mechanical construction, tool plate, stainless steel, galvanized steel plate, copper, copper alloy, etc. The purity requirement is generally 99,95% or higher. Its main function is to burn and blow away the cut melt.

The pressure and flow are different, which is inextricably linked to the size of the nozzle and the thickness of the material.

In general, the pressure required is 0.3-1 MPa and the flow varies depending on the thickness of the material. For example, if you are cutting 22mm mild steel, the flow rate should be 10m3 / h.

Nitrogen

Nitrogen prevents an oxide film from depositing on the cutting surface when cutting with oxygen. The advantage is that the material can be welded immediately afterwards. The cut is whitish.

The main materials are stainless steel, galvanized steel, brass, aluminum, aluminum alloy, etc. Its role is to prevent oxidation and blow off the melt.

The purity of the nitrogen is very important. Especially with stainless steel of 8 mm or more, a purity of 99.999% is usually required with a (relatively high) pressure of approximately 1.5 MPa.

If you want to cut stainless steel 12 mm or thicker, the pressure must be 2 Mpa or higher.

The flow varies depending on the nozzle type, but is generally large. For example, cutting 12mm stainless steel requires 150m3 / h, while cutting 3mm requires only 50m3 / h.

Sky

Air can be supplied directly from an air compressor, so very cheap compared to the other gases.

Although air contains approximately 20% oxygen, the cutting efficiency is much less than that of oxygen, and the cutting power is more comparable to that of nitrogen.

The main applicable materials are aluminum, stainless copper, brass, galvanized steel sheet and so on.

When the quality requirements of the cut product are high, such as with aluminum, aluminum alloy, stainless steel, etc., the use of air is not recommended, as air oxidizes the base material. The choice of which auxiliary gas is also partly a cost consideration.

If the quality requirements are not that high and post-processing (such as painting) is going to take place anyway, working with air can be a good option. If the cut part is the final product and there are no further process steps, it is necessary to use oxygen or nitrogen as an auxiliary gas.

From design to part with a fiber laser metal cutter

Features fiber laser metal cutter

Compared to other thermal cutting methods, laser cutting is characterized by high cutting speed and high quality, as summarized below:

Good cutting quality

Laser cutting can achieve a very high cutting quality thanks to the small laser spot, high energy density and high cutting speed. The laser beam focuses to a small light point, resulting in a high power density in the focal point. The material is quickly heated to evaporation. With the relative linear movement of the laser head with respect to the material, the hole is continuously formed into a narrow laser cut. The cutting edge of the laser cut is minimally affected by the applied heat and there is no deformation of the workpiece. In the cutting process, auxiliary gases are added that are suitable for the cut material.

Materials with a high reflection, such as gold, silver, copper and aluminum, are good heat conductors, which makes laser cutting more difficult or sometimes impossible in some cases. Laser cutting with fiber laser can be burr-free with higher precision than plasma cutting, for example.

No molds and punches - fast and cheap

The advantage of laser technology is that no punches and molds are required. Although the processing speed is still slower than with a mold, no investment in molds and mold maintenance is required, which saves time and costs. 

Narrow laser cut 

The laser cut is narrow, the slits are parallel and perpendicular to the surface, and the dimensional accuracy of the cutting can reach ± 0.05mm.

No post-processing 

The cutting surface is smooth and beautiful, the surface roughness is only a few tens of micrometers and laser cutting can even be used as the final process step. No further post-processing is required and the parts can be used immediately.

No deformation

After laser cutting, the width of the heat affected zone is small. As a result, the material is virtually untouched, even in the vicinity of the laser cut, without distortions.

High cutting efficiency

You can organize the laser file in such a way that maximum efficient use is made of the available material. If the design needs to be adjusted, this can usually be adjusted quickly and easily.

Furthermore, the material does not need to be clamped or fixed during laser cutting, which saves time for clamping or loading and unloading.

High cutting speed

By cutting a 2mm low carbon steel plate with a fiber laser cutting machine with a laser power of 1500W, the cutting speed can reach 600cm / min.

Non-contact cutting

The laser beam is a non-contact cutting tool and does not exert any force on the workpiece, which means:

  • No mechanical deformation of the workpiece;
  • No tool wear, no problem with tool changes;
  • The laser cutting ability is not affected by the hardness of the cutting material. Any hardness material can be cut.

Easy to adjust and flexible

The laser beam is easy to control, adjust and flexible, so:

  • Fiber laser machines are easy to combine with automation equipment and the cutting process is easy to automate.
  • A design can be copied indefinitely.
  • In combination with the computer, the whole plate can be arranged to save material.
  • A large number of different metals can be cut with these types of machines.

Metal types for laser cutting

Structural steel

The material will get better results when cut with oxygen.

When oxygen is used as an auxiliary gas, the cutting edge is slightly oxidized. For plates up to 4 mm thick, nitrogen can be used as a gas for cutting. In this case, the cutting edge is not oxidized. On plates with a thickness of more than 10 mm, oil can be applied to the surface of the workpiece to obtain a better cut quality.

Stainless steel

Oxygen can be used when oxidation of the cutting edge is acceptable. Use nitrogen to get a non-oxidized edge without burrs.

Titanium

Titanium plates are cut with argon and nitrogen as process gases. 

Aluminum

Despite its high reflectivity and thermal conductivity, aluminum can be cut to a thickness of 6 mm, depending on the alloy type and laser power.

When cutting with oxygen, the cutting surface is rough and hard. The cut surface is smooth when using nitrogen.

Pure aluminum is very difficult to cut because of its high purity. The laser system must be equipped with a “reflective absorption” device for cutting aluminum, otherwise the optical components will be damaged by reflection.

Copper and brass

Both materials have a high reflectivity and a very good thermal conductivity.

Brass with a thickness of 1 mm can be cut with nitrogen. Copper with a thickness of less than 2mm can be cut with oxygen.

Copper and brass are cut only if the laser system is equipped with a “reflective absorption” device, otherwise the optical components will be damaged by reflection.

Cut quality of a fiber laser

Laser cutting machine is a kind of device that can partially replace the traditional metal cutting methods. It has a fast cutting speed and high cutting quality.

In recent years, fiber laser metal cutters have been widely used to make metal laser cutting easier and more efficient.

But how can we judge a laser cutter is good? The cutting quality of the laser cutting machine is an important measure for assessing whether the cutting machine is qualified. 

Read more about assessing the cut quality of a fiber laser here ...

How to Improve Cutting Quality

Hardware factors

  • Is the lens clean?
  • Is the laser beam in the center of the nozzle?
  • Does the actual position of the focal length correspond to the position of the focal length on the scale

Parameter factors

  • Focus distance
  • Cutting speed
  • Cutting pressure of the auxiliary gases
  • Laser power
Assess cut quality fiber laser

Applications of fiber laser metal cutter machines

In the automotive industry, the cutting technology of space curves such as car skylights is widely used. Volkswagen AG uses a 500W laser to cut complex body sheets and various curved parts.

In the aerospace industry, laser cutting technology is mainly used for cutting special aerospace materials, such as titanium alloy, aluminum alloy, nickel alloy, chrome alloy, stainless steel, ceria, composite materials, plastics, ceramics and quartz.

Aerospace components realized by laser cutting include engine flame tube, thin wall titanium alloy machine, aircraft frame, titanium alloy skin, long stern wing, tail plating, helicopter main rotor, space shuttle ceramic heat insulation tile etc.

The products suitable for laser cutting can generally be divided into a number of categories.

Flexible processing of sheet material

Sheet metal work that is not suitable for making the mold from a technical or economic point of view, especially workpieces with a complicated contour shape and small batches. Saves costs and time for mold making.

Examples of products: automatic elevator construction parts, elevator panels, machine tools and food machinery covers, various electrical gas cabinets, switchgear, textile machine parts, construction machinery structural parts, large motor silicon steel sheet, etc.

Stainless steel for decorative applications

Stainless steel (thicknesses up to 3 mm) used for decoration, advertising, service industry or logos, marketing and lettering. Such as logos of companies, government institutions, hotels, retail chains, and so on.

Special parts that need to be cut evenly

Typical parts are punch plates used in the packaging and printing industry. 

New applications and customization

New applications are added every day. Think of a 3D laser cutting system or industrial robots to laser cut 3D curves or special cutting systems with integrated material transport systems and technical systems to improve production efficiency. New applications in machine building and shipbuilding.

Fiber laser metal laser cutter

MetaQuip has a portfolio of small to very large fiber laser metal cutters for both sheet material and tube material. If you are looking for a machine for a special application, MetaQuip can also realize custom solutions. View our fiber metal laser cutter portfolio.