In the mid-20th century, laser technology emerged. Over the years, due to the hard work and dedication of generations of scientists and technicians, laser technology has evolved and been refined. From its early stages of development to its practical application in various fields, laser technology has seen significant growth and success.
In the 21st century, laser technology, particularly laser processing technology applied in the industrial field, has gained great popularity and has had a substantial economic and social impact. It has been fundamental in driving the advancement of natural sciences and technology and the progression of the social economy.
Principle of Laser Machining
Laser processing technology, as shown in Figure 1, creates a laser beam with high energy density by focusing light energy through a lens. This technology utilizes the unique properties of the laser beam and material interaction for a variety of purposes, including cutting, welding, surface treatment, punching and micromachining in metallic and non-metallic materials.
Fig.1 Schematic diagram of laser processing
As a state-of-the-art manufacturing technology, laser processing technology is widely used in industries such as automotive, electronics, aviation, metallurgy and machine manufacturing. It plays a crucial role in improving product quality, increasing labor productivity, promoting automation and reducing pollution and resource consumption.
Among the various applications, laser cutting, laser marking and laser welding are the most used.
Application of Laser Technology
Laser cut
Traditional cutting techniques such as gas cutting, machining cutting, blanking cutting and plasma cutting have their limitations. Despite offering fast cutting speeds and the ability to cut thicker materials, cut size accuracy is often poor. This results in higher cutting costs and additional processing expenses.
Machining cutting provides high precision, but its slow cutting speed limits its ability to cut complex curves. Furthermore, significant material loss occurs during cutting.
Blind cutting is more efficient and economical, but its processing quality is limited and its scope of application is narrow. The cutting quality is poor, especially when processing thick sheets and complex curved shapes.
Although plasma cutting is more efficient, it produces a better cutting section than other methods, but its cutting accuracy is limited to the millimeter level. As such, it is only suitable for rough and semi-finishing machining.
Fig.2 Laser cutting
Compared with traditional cutting technology, the advantages of laser cutting technology (figure 2) are obvious:
- Fast cutting speed
- High efficiency
- Wide machining range
- In machining, the incision is smooth because it replaces the traditional tool or flame with a beam of light. There is no need for additional processing.
- The area affected by cutting heat is small.
- Small sheet deformation
- Small cutting seam (high utilization rate)
- There is no mechanical stress on the incision
- No shear burrs
- High machining precision
- Good repeatability
- Do not damage the board surface
- CNC Programming
- No need to open the mold
- Savings and time savings
The advantages of laser cutting are especially visible when machining curves. Compared with blanking cutting, the surface produced by laser cutting is smooth and does not show obvious blade marks on curved parts. Additionally, because the plate remains stationary during processing, it eliminates the risk of scratches caused by movement.
Laser cutting works by directing a focused, high-power-density laser beam at the workpiece, causing the material to quickly melt, vaporize, extinguish, or ignite. The workpiece is then cut by blowing the molten material using a high-velocity airflow along the same axis as the beam.
Laser cutting is considered one of the thermal cutting methods.
Laser cutting can be divided into four categories:
- laser vaporization cutting
- laser fusion cutting
- laser oxygen cutting
- laser engraving and tear control
(1) Laser vaporization cutting
Laser vaporization is a process where the part is heated by a laser beam with high energy density. The temperature of the material increases rapidly and reaches the boiling point in a short period of time, causing the material to vaporize and form vapor. The steam is quickly expelled, resulting in an incision in the material. This method is mainly used to cut extremely thin metals and non-metallic materials.
(2) Laser fusion cutting
In laser fusion cutting, metal material is melted by laser heating. A non-oxidizing gas, such as Ar, He or N2, is then sprayed from the nozzle along the same beam axis. The liquid metal is expelled by the powerful gas pressure, creating an incision. This method requires only 1/10th the energy required for vaporization, as the metal does not need to be completely vaporized. It is mainly used to cut non-oxidizable or active metals such as stainless steel, titanium, aluminum and alloys.
(3) Oxygen laser cutting
Oxygen laser cutting operates on a similar principle to oxyacetylene cutting. The laser is used as a preheating source, and oxygen or other active gases are used as the cutting gas. The gas produced by the jet reacts with oxidation, generating a large amount of heat. Molten oxide and molten material are expelled from the reaction area, resulting in an incision in the metal. Oxygen laser cutting requires only half the energy required for fusion cutting, but has a much faster cutting speed. It is mainly used for cutting carbon steel, titanium steel, heat treatment steel and other easily oxidized metal materials.
(4) Laser engraving and burst control
In laser engraving, the high-energy density laser scans the surface of fragile materials, heating the material in a small groove. Applying pressure causes the brittle material to crack along the groove. Among the first three cutting methods mentioned, laser tracing and burst control are least commonly used.
Currently, laser cutting is most effective for cutting black metal, with high cutting speed and the ability to cut up to a thickness of 20 mm or more. However, due to the reflection effect of the molecular structure of non-ferrous metals in the laser beam, the cutting effect on these materials is slightly weaker. The machine must be equipped with a reflector.
According to statistics, the maximum thickness that can be cut in aluminum alloys is no more than half of that of black metal, and the cutting effect in copper alloys, especially copper, is even worse.
The core of laser cutting technology is the laser generator, which comes in two forms: CO2 laser and fiber laser generator.
CO2 Laser Generator: The CO2 laser generator is generated by discharging a mixture of CO2, He and N2 into the laser cavity under high pressure. This process excites the atoms in the mixture to release energy, which is then emitted in the form of photons or electrons to create the laser. The laser emitted by the CO2 laser is visible light, which can cause slight damage to the retina and skin. Therefore, it is advised that operators wear protective glasses during use.
Fiber Laser Generator: A fiber laser generator uses a glass fiber doped with rare earth elements as a gain medium. Under the action of pump light, a high power density can be easily formed within the optical fiber, which causes the laser energy level of the working substance to reverse the number of particles. A positive feedback loop is added to form the output of the laser oscillator. The output is not visible light, which may cause serious damage to the retina and skin, so the operator must wear special protective glasses during operation.
The CO2 laser has a more complex optical path structure and higher optical lens loss, with higher environmental requirements (less dust). The machine must be isolated from seismic sources and kept in a dry environment with a constant temperature. Fiber laser, on the other hand, has a simple optical path structure with lower environmental requirements (high tolerance to dust, vibration, shock, temperature and humidity). The fiber laser is faster in cutting thin sheets, while the CO2 laser is stronger in cutting thick sheets. The CO2 laser cannot cut highly reflective metal plates, but a fiber laser can cut thin copper plates.
laser welding
Laser welding (figure 3) is an important field of laser technology.
Fig.3 Laser welding
Laser welding is a new type of welding that uses high-energy laser pulses to heat small areas of material. The energy of laser radiation diffuses through heat conduction in the material, causing it to melt and form a specific molten pool. This method is mainly used for welding thin-walled materials and precision parts, and can be used for various types of welding such as spot welding, butt welding, stack welding and seal welding.
Key features include:
- High depth wide aspect ratio
- Small weld width
- Small heat affected area
- Small deformation
- Fast welding speed
- The smooth and beautiful welding seam
- No need to process or simply process after welding
- High quality of welding seam
- No gas hole
- Precise control
- Small focus light
- High positioning accuracy
- Easy automation implementation
Laser welding is widely used in various areas, especially in the manufacture of high-speed railways and automobiles, due to its numerous benefits. These benefits include:
(1) Minimum thermal input, with small metallographic variation in the area of thermal effect and minimum deformation caused by heat conduction.
(2) The ability to confirm and reduce the time required to weld thick sheets, even eliminating the need for filler metal.
(3) No need for electrodes, no worries about contamination or damage. Furthermore, it does not belong to the contact welding process, minimizing losses and deformations of the fixation.
(4) The laser beam can be easily focused, aligned and guided by optical instruments, with the ability to place it at an appropriate distance from the workpiece and redirect it around obstacles.
(5) The ability to place the workpiece in enclosed spaces controlled by a vacuum or internal gas environment.
(6) The laser beam can be focused on small areas, making it ideal for welding small, closely spaced parts.
(7) Capable of welding a wide range of materials and sewing various heterogeneous materials.
(8) Easy to weld quickly and automatically, or controlled by digital or computer technology.
(9) When welding thin material or thin diameter wire, it will not be as easy as arc welding.
(10) It is not affected by magnetic fields and is capable of accurately aligning welded parts.
(11) The ability to weld two metals with different properties, such as different strengths.
(12) The ability to achieve a weld depth ratio of 10:1 in perforated welding.
(13) The ability to transfer the laser beam to multiple workstations.
Due to the above characteristics of laser welding, laser welding is widely used in the field of civil vehicle manufacturing.
Laser welding is the main welding process in the manufacture of high-speed railways and automobiles.
Despite its benefits, laser welding also has several disadvantages that must be considered. These disadvantages include:
(1) The need for precise positioning of the welded parts within the focusing range of the laser beam.
(2) The need for clamps that ensure that the final position of the weld is aligned with the welding point that will be impacted by the laser beam.
(3) Limited maximum weldable thickness, with laser welding being unsuitable for materials with a penetration thickness greater than 19 mm.
(4) The impact of laser welding on the properties of high reflectance and high thermal conductivity materials such as aluminum, copper and alloys.
(5) The use of a plasma controller to remove ionized gas around the molten pool when using high-energy laser beam welding.
(6) Low energy conversion efficiency, generally less than 10%.
(7) Rapid solidification of the weld bead which can lead to porosity and embrittlement.
(8) High cost.
The high cost of laser welding equipment is a significant limitation and restricts its widespread use.
Laser engraving
Laser engraving involves using a high-energy density laser beam controlled by a computer to instantly melt or vaporize the surface of a product, creating the desired text or logo, as shown in Figure 4.
Fig.4 Laser letters
Laser engraving is also called laser marking.
Features of laser marking:
- Steady constantly
- Beautifully designed
- High speed and efficiency
- Contactless mode
- High repeat accuracy
- No need to make the format
- No pollution
- Easy to achieve synchronous flight printing with the production line.
Material that can be marked with laser engraving includes numbers, letters, Chinese characters, graphics, barcodes and more.
Laser engraving is an advanced and widely used marking method suitable for modern, high-speed production.
As shown in Table 1, a comparison of various marking techniques reveals that the advantages of laser marking technology are clear.
Table 1. Comparison of various marking techniques
| Marking technology | Performance | Effect and Accuracy | Marking color | Chart changes | Consumables |
|---|---|---|---|---|---|
| Laser marking | Good | High precision and good effect | Determined by material | Make yourself comfortable | No |
| Chemical Etching | Good | Low accuracy | Material color | Difficult | Yes |
| Ink printing | Worse | High precision | Any color | Easy | Yes |
| Mechanical engraving | To improve | Low accuracy | Material color | Make yourself comfortable | Yes |
| Mechanical press | Worse | Poor accuracy | Material color | Difficult | Yes |
Laser rapid prototyping technology
Laser rapid prototyping (as shown in Figure 5) represents a significant shift in modern manufacturing technology.
It represents an expansion of laser technology in industrial applications.
Fig.5 Laser rapid prototyping technology
Competition in the manufacturing industry has intensified with the acceleration of the global market integration process, and the speed of product development has become the main competitive contradiction. To meet the ever-changing needs of users, the manufacturing industry requires technology that is more flexible, allowing the production of small batches or even single parts without increasing the cost of the product.
Rapid prototyping (RP) technology is a manufacturing method that builds material layer by layer, or more broadly, computer-designed 3D graphics. The high temperature produced by the laser is used to sinter metal powder into 3D graphics, resulting in metallic components. Prototypes can be made directly from solid 3D CAD models in just a few hours or dozens of hours.
Rapid prototyping provides a more comprehensive and intuitive representation than drawings and computer screens, especially during the product development phase, allowing for comprehensive consideration of multiple factors. This leads to shorter development cycles, better product quality, reduced costs and reduced investment risks.
When combined with precision casting in the foundry, laser rapid prototyping technology allows the foundry to quickly produce all types of wax molds used for precision casting of large and complex structures, reducing outsourcing costs. Meanwhile, the production of single or small batches of precision castings can be carried out without a mold, saving tooling costs and significantly shortening the production cycle.
The development and production of new products saves valuable time and reduces production costs, and the precision casting level of foundries has been improved, laying a solid foundation for successful precision casting production in future products.
It is clear that the use of laser rapid prototyping technology will become more widespread in the future.
Laser heat treatment
Laser Heat Treatment (as shown in Figure 6) is a technology that involves using a laser to heat the surface of metallic materials for the purpose of surface heat treatment.
Fig.6 Laser heat treatment
This process can be used for a variety of metal surface modification treatments, including hardening (also known as surface quenching, surface amorphization, remelting and surface quenching), surface alloying and other modifications.
The result of laser treatment leads to changes in surface composition, structure and performance that are not possible with conventional surface hardening. After laser treatment, the surface hardness of cast iron can reach 60HRC, while carbon steel with medium to high carbon levels can reach up to 70HRC.
This improvement in surface hardness leads to an increase in wear resistance, fatigue resistance, corrosion resistance, oxidation resistance and extends the overall service life of the metal.
Conclusion
Due to its numerous advantages, laser processing technology is highly valued in the industrial manufacturing sector, with low costs, high efficiency and vast application potential. This has led to intense competition between the world's major industrialized nations.
Laser technology is expanding into new fields and its development continues at an astonishing rate. In major manufacturing industries such as automobiles, electronics, machinery, aviation and steel, some countries have completely transitioned from traditional processing methods to laser processing and entered the “age of light”.
