Laser Cutting Applications in Sheet Metal Industry

Sheet metal processing in traditional workshops often involves processes such as shearing, punching, and bending.

The punching process is known for its low or non-cutting process and requires a significant number of dies. This results in high production costs, as hundreds of sets of molds may be required for a single product.

The use of so many dies increases the cost of the product, resulting in excessive spending.

To address this issue and modernize sheet metal processing, laser processing technology was introduced. This has reduced production costs and improved processing technology.

The implementation of laser cutting machines has greatly advanced sheet metal processing technology and revolutionized the way sheet metal is fabricated and processed.

Laser cutting technology and equipment are becoming increasingly popular and widely accepted among sheet metal processing enterprises. This is due to its numerous advantages, such as high processing efficiency, accuracy, and good cutting quality, as well as its ability to perform three-dimensional cutting. As a result, laser cutting technology is gradually replacing traditional sheet metal cutting equipment, such as CNC equipment, shears, punches, flame cutting, plasma cutting, and high-pressure water cutting.

Laser cutting technology plays a crucial role in the development of sheet metal processing, as it enhances labor productivity and advances the field. With its high degree of flexibility, a laser cutting machine can significantly shorten the processing cycle, increase cutting speed, and improve processing accuracy, contributing to faster product development. These benefits are attracting attention from many manufacturing companies.

A laser cutter operates by emitting a laser beam that is focused by an optical path system into a high-power density beam. The laser beam is directed onto the surface of the workpiece, causing it to reach its melting or boiling point. At the same time, a high-pressure gas stream blows away the molten or vaporized metal. As the laser beam moves across the workpiece, it cuts the material to form a slit.

The laser cutting process is a modern and advanced method for cutting metal, which utilizes an invisible laser beam instead of a traditional mechanical knife. This process is characterized by its high precision, fast cutting speed, and ability to automatically nest cuts to conserve material. The laser cutting process also results in a smooth kerf and lower processing costs, making it a more efficient alternative to traditional metal cutting methods.

One of the key benefits of the laser cutting process is that the mechanical part of the laser cutter never comes into contact with the workpiece, eliminating the risk of scratches or other surface damage. The laser cutting process is also fast and produces a smooth, even kerf, which often eliminates the need for further processing. The heat-affected zone is small, leading to minimal plate deformation and narrow cuts (0.1 to 0.3mm), and the incision is free of mechanical stress and shearing burrs.

Laser cutting is also highly repeatable, with no damage to the surface of the material. It can be easily programmed with CNC software to process any design, making it an economical choice for cutting large-format sheets without the need for molds. Carbon steel plates up to 12mm thick and stainless steel plates up to 10mm thick are typically recommended for laser cutting.

In addition to its high precision, the laser cutting process is also highly adaptable, as it exerts no cutting force and generates no tool wear. This makes it suitable for cutting a wide range of materials, including simple or complex parts. With automatic nesting capabilities, laser cutting also offers economic benefits by optimizing material utilization.

Types of laser cutting machine

The current market for laser cutting machines is broadly divided into three types based on the type of laser generator used: CO2 laser cutting machine, YAG (solid-state) laser cutting machine, and fiber laser cutting machine.

CO2 laser cutting machine

CO₂ laser cutting machines are capable of cutting carbon steel up to 20mm thick, stainless steel up to 10mm thick, and aluminum alloy up to 8mm thick. The wavelength of the CO₂ laser is 10.6μm, which is easily absorbed by non-metal materials such as wood, acrylic, PP, and plexiglass, allowing for high-quality cutting of these materials. However, the photoelectric conversion rate of CO₂ lasers is relatively low, at around 10%.

To increase cutting speed and ensure smooth cuts, CO₂ laser cutting machines are equipped with a nozzle that blows oxygen, compressed air, or inert gas N2 at the beam exit. To improve the stability and lifespan of the power supply, the CO₂ gas laser must address the discharge stability of high-power lasers.

In accordance with international safety standards, laser hazard levels are divided into 4 levels, with CO₂ lasers falling into the least hazardous category.

Related reading: Laser Product Safety Levels

The main advantage of CO₂ laser cutting machines is their high power, with a general power range of 2000 to 4000W. This allows them to quickly cut full-size stainless steel and carbon steel up to 25mm thick, aluminum up to 4mm thick, acrylic boards up to 60mm thick, wood material boards, PVC boards, and cutting sheets, among others.

Another advantage of CO₂ lasers is that they output a continuous laser beam, which results in the smoothest cutting cross-section among the three types of laser cutting machines.

Main Market Focus: Cutting of medium and heavy plates with a thickness ranging from 6-25mm, primarily serving large and medium-sized enterprises and some purely foreign laser cutting companies.

However, due to factors such as high maintenance costs for lasers and high energy consumption of the main engine, the market has been shrinking significantly in recent years due to the massive impact of fiber laser cutting machines.

YAG (solid-state) laser cutting machine

The YAG solid-state laser cutting machine is known for its low cost and stability, but its energy efficiency is typically less than 3%. The majority of its products have an output power of below 800W, which limits its use mainly to punching, spot welding, and cutting thin plates.

Its green laser beam can be used in both pulsed and continuous wave modes, with a short wavelength and good condensation properties. This makes it suitable for precise machining, especially in the case of pulsed hole processing, but also for cutting, welding, and lithography.

However, the YAG solid-state laser has a wavelength that is not easily absorbed by non-metallic materials, making it unsuitable for cutting non-metallic materials. Improving its power stability and longevity is crucial for its development.

To achieve this, the use of a large-capacity, long-life optical pump excitation light source is necessary. The use of semiconductor optical pumps can significantly increase its energy efficiency.

The Main Advantages: This machine has the ability to cut aluminum, copper, and most non-ferrous metal materials, which other laser cutting machines are unable to cut.

In terms of cost and maintenance, the machine is relatively inexpensive to purchase and requires simple maintenance. Many of the key technologies have been successfully developed by domestic enterprises.

Additionally, the cost of accessories and maintenance is low, making operation and maintenance of the machine straightforward, even for those with limited technical expertise.

Main Market Focus: Cutting materials with a thickness of 8mm or less.

This machine is primarily used by small enterprises for self-use, as well as medium-sized enterprises and the majority of users in industries such as sheet metal manufacturing, home appliance manufacturing, kitchenware manufacturing, decoration, advertising, and others with low processing demands.

In the future, it may gradually replace traditional processing equipment like wire cutting, CNC punching, water cutting, and low-power plasma.

Optical fiber laser cutting machine

The optical fiber laser cutting machine offers a highly flexible transmission of the laser through optical fibers, resulting in fewer points of failure, easy maintenance, and fast speed, making it highly advantageous for cutting thin plates within 4mm. However, its quality when cutting thick plates is inferior due to the influence of solid laser wavelengths.

The wavelength of the optical fiber laser cutting machine is 1.06μm, which is not easily absorbed by non-metallic materials, making it unsuitable for cutting non-metallic materials. Its photoelectric conversion rate is as high as 25%.

In terms of electricity consumption and cooling system parameters, the optical fiber laser has clear advantages. However, due to its short wavelength, it poses the greatest danger to the eyes according to international safety standards, and as a result, optical fiber laser processing must be carried out in a fully enclosed environment for safety reasons.

Despite being an emerging laser technology, the optical fiber laser cutting machine is not as widely used as the CO₂ laser cutting machine.

The Main Advantages: The fiber laser cutting machine has a high photoelectric conversion rate, low power consumption, and the ability to cut stainless steel plates within 12mm, as well as carbon steel plates. It is the laser cutting machine with the fastest cutting speed among the three machines.

Additionally, it is suitable for fine cutting due to its fine slit and good spot quality.

Main Market Focus: Cutting materials with a thickness of 12mm or less, particularly the high precision processing of thin plates.

This machine is designed for manufacturers with extremely high processing accuracy and efficiency requirements.

It is predicted that with the advent of lasers with output powers of 5000W or more, fiber laser cutting machines will eventually replace most of the market for CO2 high-power laser cutting machines.

Laser cutting method

Figure 1 shows the three methods of laser cutting.

Fig. 1: Laser cutting method

Laser melting cutting

(1) In laser melting cutting, a high-purity inert cutting gas is used in conjunction with a laser beam to partially melt the workpiece. The molten material is then expelled by an air stream. This process is referred to as laser melting cutting because the transfer of the material occurs only in its liquid state.

(2) The cutting gas promotes the melted material away from the slit, but it does not actively participate in the cutting process.

(3) Compared to vaporizing cutting, laser melting cutting allows for higher cutting speeds because the energy required to melt the material is usually less than the energy required to vaporize it. The laser beam is only partially absorbed during the process.

(4) The maximum cutting speed is influenced by various factors, including laser power, plate thickness, material melting temperature, air pressure at the cutting kerf, and the thermal conductivity of the material. At a given laser power, these factors determine the limiting conditions.

(5) Laser melting cutting produces oxidation-free cuts for ferrous materials and titanium, and a laser power density of 104 W/cm² to 105 W/cm² for steel materials. This power density melts the material without causing it to vaporize.

Laser flame cutting

Laser flame cutting is different from laser fusion cutting in that it uses oxygen as the cutting gas, leading to a chemical reaction between the oxygen and the heated metal, which further heats the material. This method results in a higher cutting rate for the same thickness of structural steel compared to fusion cutting.

However, the quality of the kerf is not as good as that produced by melt cutting, as wider kerfs, significant roughness, a larger heat affected zone, and poor edge quality are produced.

(1) When working with precision models and sharp corners, laser flame cutting may not be the best option, as there is a risk of burning off sharp corners. To minimize the heat-affected zone, pulsed mode lasers can be used.

(2) The cutting speed is determined by the laser power used. The limiting factors at a given laser power are the availability of oxygen and the thermal conductivity of the material.

Laser vaporization cutting

Laser vaporization cutting involves the vaporization of the material at the cutting edge, which requires a high laser power. To prevent the material vapor from condensing on the slit wall, the material thickness must not exceed the diameter of the laser beam significantly. This process is only suitable for the limited use of iron-based alloys and cannot be used on materials such as wood and ceramics, which typically result in thicker kerfs.

(1) The optimal beam focus in laser vaporization cutting depends on factors such as material thickness and beam quality.

(2) The optimal focus position is affected by laser power and heat of vaporization.

(3) For certain plate thickness, the maximum cutting speed is inversely proportional to the material vaporization temperature.

(4) The required laser power density can be greater than 108 W/cm2, depending on the material, cutting depth, and beam focus position.

(5) For a certain plate thickness, the maximum cutting speed is limited by the speed of the gas jet, assuming sufficient laser power.

Laser cutting process

The process refers to the interaction between a laser beam, a process gas, and the workpiece being treated.

Figure 2 shows the processing parameters.

Fig.2 Processing parameters

Cutting process

Before cutting, the laser heats the workpiece to the temperature required for melting and vaporizing the material. The cutting plane consists of a nearly vertical plane that absorbs laser radiation to heat and melt the material.

In laser flame cutting, a stream of oxygen is introduced into the slit, further heating the melting zone to a temperature close to boiling. The resulting vaporization removes the material, while the liquefied material is expelled from the lower part of the workpiece with the help of the heated gas.

In laser melting cutting, the liquefied material is expelled with the gas, which protects the slit from oxidation. The continuous melting zone moves gradually in the direction of the cut, creating a continuous slit.

Many key aspects of the laser cutting process occur in this zone, and analyzing these activities provides important information about laser cutting. This information allows for the calculation of cutting speed and helps explain the formation of draw line characteristics.

Material Properties

The results of cutting on the workpiece can vary, ranging from a clean cut to rough edges or overburning. The quality of the cut is influenced by several factors, including:

(1) Alloy composition: The composition of the alloy affects its strength, specific gravity, weldability, oxidation resistance, and acidity to some extent. Some of the important elements in ferrous alloy materials are carbon, chromium, nickel, magnesium, and zinc. The higher the carbon content, the more difficult it is to cut the material (the critical value is considered to be a carbon content of 0.8%). Carbon steels such as St 37-2, StW 22, and DIN 1.203 can be well-cut with lasers.

(2) Microstructure of the material: In general, the finer the particles that make up the material, the better the quality of the cut.

(3) Surface quality and roughness: If the surface has areas of rust or oxidation, the cut profile will be irregular and have many breakage points. To cut corrugated board, select the maximum thickness cutting parameter.

(4) Surface treatment: The most common surface treatments are galvanizing, painting, anodizing, or covering with a plastic film. Sheets treated with zinc tend to have sluggish edges. The quality of the cut depends on the composition of the painted product. Plates coated with plastic film are very suitable for laser cutting. The layered edge must always be on the upper part of the cutting workpiece for trouble-free capacitive detection and optimal adhesion of the coated layer.

(5) Beam reflection: The way the light beam is reflected on the surface of the workpiece depends on the base material, surface roughness, and treatment mode. Some aluminum alloys, copper, brass, and stainless steel have high reflectivity characteristics. Special care should be taken to adjust the focus position when cutting these materials.

(6) Thermal conductivity: Materials with low thermal conductivity require less power than materials with high thermal conductivity when welding. For example, chrome-nickel alloy steel requires less power than structural steel, and less heat is absorbed during processing. Materials such as copper, aluminum, and brass conduct heat away from the target point of the beam, making it more difficult to melt the material in the heat-affected zone.

(7) Heat-affected zone: Laser flame cutting and laser melting cutting cause material variation in the edge area of the cut material. The range of the heat-affected zone is related to the thickness of the basic material.

Table 1 lists some reference values.

Table 1 Relationship between material thickness and the heat-affected zone

The table shows that:

(1) When processing low-carbon steel or oxygen-free steel, the quenching effect in the heat-affected zone is reduced.

(2) High-carbon steel, such as Ck60, will harden the edge area.

(3) The heat-affected zone of a hard-rolled aluminum alloy will be slightly softer than the rest of the material.

Laser cutting incision evaluation analysis

Processability of different materials

(1) Structural steel

Oxygen cutting can be utilized, however, the cutting edge may be slightly oxidized.

For plates with a thickness of 4mm, nitrogen gas is appropriate for high-pressure cutting.

When handling complex contours and small holes (with a diameter less than the material thickness), the pulse mode should be employed to prevent cutting of sharp corners.

Structural steel: cut with O₂

Defect	Possible cause	Solution
No burr, consistent traction line	Right power Suitable feed rate
The pull line at the bottom is greatly offset, and the cut at the bottom is wider	Feed rate is too high Laser power is too low Air pressure is too low Focus is too high	Reduce the feed rate Increase laser power Increase air pressure Lower focus
The burrs on the bottom surface are similar to slag, drip-shaped and easy to remove	Feed rate is too high Air pressure is too low Focus is too high	Reduce the feed rate Increase air pressure Lower focus
Metal burrs connected together can be removed as a whole piece	Focus is too high	Lower focus
Metal burrs on the bottom surface are difficult to remove	Feed rate is too high Air pressure is too low Impure gas Focus is too high	Reduce the feed rate Increase air pressure Use purer gas Lower focus
Only one side has burrs	Incorrect nozzle alignment Defective nozzle	Centering nozzle Change nozzle

When cutting structural steel, the following should be considered:

• The higher the carbon content, the more prone the cutting edges are to quenching and overburning of corners.
• Sheets with a higher alloy content are more challenging to cut compared to those with a lower content.
• A surface that has been oxidized or sandblasted will result in poor cutting quality.
• The residual heat on the plate surface can negatively impact the cutting outcome.
• For plates thicker than 10mm, better results can be achieved by using special laser electrodes and oiling the workpiece surface during the process.
• To relieve tension, it is recommended to only cut steel plates after secondary treatment.
• To obtain a clean-cut surface on structural steel, the following guidelines should be followed:

Si ≤ 0.04%: laser processing is preferred.

Si < 0.25%: poor cut quality may occur in some cases.

Si > 0.25%: not suitable for laser cutting.

Defect	Possible cause	Solution
Material is discharged from above	Power is too low Feed rate is too high	Increase power Reduce the feed rate
Inclined surface cuts well on both sides, but poor on both sides	The polarizing mirror is not suitable, the installation is incorrect or defective The polarizing mirror is installed at the position of the deflection mirror	Check the polarizing mirror Check the deflection mirror
Blue plasma, the workpiece is not cut through	Processing gas error (N2) Feed rate is too high Power is too low	Use oxygen as the processing gas Reduce the feed rate Increase power
The cut surface is not precise	Air pressure is too high The nozzle is damaged The nozzle diameter is too large Bad material	Reduce air pressure Replace nozzle Install the right nozzle Use a smooth surface Homogeneous material
No burrs, the inclined incision of the traction line becomes narrower at the bottom	Feed rate is too high	Reduce the feed rate
Crater	Air pressure is too high Feed rate is too low Focus is too high Rust on the surface of the sheet Overheated workpiece Impure material	Reduce air pressure Increase the feed rate Lower focus Use better quality material
The very rough cut surface	Focus is too high Air pressure is too high Feed rate is too low Material is too hot	Lower focus Reduce air pressure Increase the feed rate Cooling material

 Several key parameters affecting the process

N1 gas parameters

• Gas type: nitrogen, oxygen and compressed air
• Gas purity: Generally between 99.99% and 99.999% of air pressure.
• The maximum air pressure during low-pressure cutting is 5 bar, and the maximum air pressure during high-pressure cutting is 20 bar between the nozzle and the plate;
• The distance between the nozzle opening and the workpiece surface must be as small as possible.
• The smaller the distance, the greater the actual airflow into the incision.
• The gap is usually between 0.5 and 1.5 mm.

(2) Stainless steel

• Oxygen cutting is utilized when there is minimal edge oxidation.
• By combining high power and high-pressure nitrogen, a cutting speed equivalent to or faster than that of oxygen cutting can be achieved.
• When using nitrogen to process stainless steel thicker than 4mm, it is necessary to reset the focus position and decrease the speed to minimize the formation of burrs.
• For plates thicker than 5mm, oxygen cutting is suitable; however, it is necessary to decrease the feed speed and employ the laser pulse mode.
• The same nozzle height should be used for piercing and cutting. For cutting stainless steel, the recommended method is high-pressure nitrogen.

Defect	Possible cause	Solution
Produces tiny regular burrs	Focus is too low Feed rate is too high	Raise focus Reduce the feed rate
Long irregular filament-like burrs are produced on both sides, and the surface of the large plate is discolored	Feed rate is too low Focus is too high Air pressure is too low Material is too hot	Increase the feed rate Lower focus Increase air pressure Cooling material
Only produce long, irregular burrs on one side of the cutting edge	The nozzle is not centered Focus is too high Air pressure is too low Speed​is too low	Centering nozzle Lower focus Increase air pressure Accelerate
Yellow cutting edges	Nitrogen contains oxygen impurities	Use good quality nitrogen
Plasma is generated on a straight section	Feed rate is too high Power is too low Focus is too low	Reduce the feed rate Increase power Raise focus
Beam divergence	Feed rate is too high Power is too low Focus is too low	Reduce the feed rate Increase power Raise focus
Plasma at the corner	Angle tolerance is too high Modulation too high Acceleration too high	Reduce angle tolerance Reduce modulation or acceleration
The beam diverges at the beginning	Acceleration too high Focus is too low The molten material failed to discharge	Decrease acceleration Raise focus Pierced hole
Rough cut	The nozzle is damaged The lens is dirty	Replace the nozzle to clean the lens, replace if necessary
Material is discharged from above	Power is too low Feed rate is too large Air pressure is too high	Increase power Reduce the feed rate Reduce air pressure

(3) Aluminum

Aluminum and its alloys are more suitable for cutting in continuous mode.

N2 laser power

There is a choice between continuous or pulsed mode, with continuous mode being typically used for fast, routine cutting operations.

Pulsed mode is employed for high-precision cutting operations that have strict requirements for the end face, and it operates significantly slower than the continuous mode.

• When cutting with oxygen, the cutting surface is rough and hard, resulting in a small, difficult-to-eliminate flame.
• When cutting with nitrogen gas, the cutting surface is smooth. Additionally, when processing plates less than 3mm, optimal adjustments can result in incisions with virtually no burrs. However, for thicker plates, burrs that are difficult to remove may occur.
• Pure aluminum is challenging to cut due to its high purity.
• The higher the alloy content, the easier the material is to cut.

Note: Before cutting aluminum, a “reflective absorption” device must be installed on the system, otherwise the optical components will be damaged.

Aluminum alloy: cutting with N₂ high pressure

Defect	Possible cause	Solution
Both sides have long irregular filamentous burrs, which are difficult to remove	Focus is too high Air pressure is too low Feed rate is too low	Lower focus Increase air pressure Increase the feed rate
Long irregular burrs on both sides Can be removed manually	Feed rate is too low	Increase the feed rate
Rough cut	The nozzle diameter is too large The nozzle is damaged Air pressure is too high	Install the right nozzle Replace nozzle Reduce air pressure
Produces fine and regular burrs, which are difficult to remove	Focus is too low Feed rate is too high	Raise focus Reduce the feed rate
Plasma is generated on a straight section	Feed rate is too high Focus is too low	Reduce the feed rate Raise focus
Beam divergence	Feed rate is too high	Reduce the feed rate
Plasma at the corner	Angle tolerance is too high Modulation too high Acceleration too high	Reduce angle tolerance Reduce modulation or acceleration
The beam diverges at the beginning	Approach speed is too high Focus is too low	Reduce approach speed Raise focus
Rough cut	The nozzle is damaged	Replace nozzle
Material is discharged from above	Power is too low Feed rate is too large	Increase power Reduce the feed rate

(4) Titanium

Titanium plates are cut using argon and nitrogen as the process gases. Further parameters can be found in nickel-chromium steel.

(5) Copper and brass

• Both copper and brass have high reflectivity and excellent thermal conductivity.
• Brass with a thickness up to 1mm can be cut using nitrogen gas.
• For copper processing with a thickness less than 2mm, oxygen gas must be utilized.

Note: Cutting copper and brass is only possible if a “reflection absorption” device is installed on the system, otherwise the optical components will be damaged.

(6) Synthetic materials

Cutting speed

The cutting speed of a sheet depends on its thickness, with thinner sheets allowing for faster cutting.

When straight contours are being processed, the cutting speed can reach its maximum set value.

However, when processing arc contours or corners, the cutting speed will be automatically reduced to ensure high-quality processing.

Laser power is also a factor in the processing speed, with a higher laser power resulting in faster processing.

It is important to consider the potential hazards of cutting synthetic materials and the emission of harmful substances when using a laser cutter.

Synthetic materials that can be processed include thermoplastics, thermosetting materials, and artificial rubber.

However, it is not recommended to use a laser cutter to process PVC or polyethylene due to the toxic gases they release. Water cutting is a safer alternative for these two materials.

Acrylic glass can be cut with a laser, and nitrogen is used as the processing gas. The pressure must be kept below 0.5 bar to achieve a smooth cutting surface.

(7) Organics

Acrylic glass can be cut using a laser with nitrogen as the processing gas. To achieve a smooth cutting surface, the air pressure must be below 0.5 bar.

There is a fire hazard associated with cutting organic materials, whether using nitrogen or compressed air as the processing gas.

Materials such as wood, leather, cardboard, and paper can be laser cut, resulting in burnt (brown) edges. The faster the feed rate, the less carbonization will occur.

When cutting plywood, clean cuts cannot be guaranteed due to the varying composition of each layer of glue.