Deep resolution laser surface treatment technology

Laser surface treatment is a technology that changes the surface properties of materials by heating, melting and freezing the surface of materials through laser beam. It can be processed in atmosphere, vacuum and other environments, and has the advantages of non-contact processing and minimal workpiece deformation.

According to the different purpose of surface treatment, laser surface treatment can be divided into surface modification treatment and removal treatment. Among them, the surface modification treatment includes laser glazing, laser remelting, laser alloying, laser coating, etc. Removal treatment mainly refers to laser cleaning.

Laser surface treatment technology is widely used in automotive, aerospace, electronics, machinery and other industries. For example, in automotive manufacturing, laser surface treatment can be used to improve the wear and corrosion resistance of engine components; In the aerospace sector, laser surface treatment can be used to improve the surface properties of aircraft components, increasing their fatigue life and reliability.

Laser surface treatment is a method that uses the laser beam to quickly and locally heat the workpiece to achieve local urgent heating or cooling, so as to change the surface properties of the material. According to the different purpose of surface treatment, laser surface treatment can be divided into surface modification treatment and removal treatment.

Laser surface modification treatment is to improve the surface performance of the workpiece through the change of the organizational structure of the material itself or the introduction of other materials during the laser scanning process, the technology can selectively treat the surface of the workpiece, which is conducive to maintaining sufficient toughness and strength of the workpiece as a whole, and the surface to obtain high and specific performance, such as wear resistance, corrosion resistance and fatigue resistance, oxidation resistance. Common laser surface modification techniques include laser glazing, laser remelting, laser alloying and laser coating.

Laser removal treatment mainly refers to laser cleaning, which uses the laser beam to be absorbed by the contaminated layer on the surface to be treated, and the absorption of large energy forms a rapidly expanding plasma, generating a shock wave, under the action of the shock wave, the pollutants become fragments and are removed. Compared with the traditional cleaning methods, laser cleaning has the advantages of non-contact, high efficiency, reducing environmental pollution and so on.

The treatment effect of laser surface treatment technology is mainly affected by the following factors:

1.Laser parameters

• Laser power: The power size directly affects the energy input, the higher the power, the more intense the heating effect, which may lead to deeper processing depth and more significant tissue changes.
• Laser wavelength: The absorption and penetration capacity of different wavelengths of laser in the material is different, which affects the treatment effect.
• Pulse width and frequency: Short pulse widths enable finer processing, while high frequencies increase processing efficiency.

2.Scanning speed

The scanning speed determines the time of action of the laser at each position, too fast speed may lead to inadequate processing, too slow speed may cause excessive heating and heat affected zone expansion.

3.Spot size

Spot size affects the concentration of energy distribution, and smaller spots enable more accurate local processing.

4.Material characteristics

• Material composition: The content and type of different elements will affect the absorption and reaction of the material to the laser.
• The original microstructure state, such as grain size and phase composition, will affect the phase transition and microstructure evolution after treatment.

5.Treatment environment

including atmosphere (such as vacuum, inert gas, oxidizing gas, etc.) and temperature, which will affect the oxidation, nitriding and other chemical reactions during the treatment process.

6.Overlap rate

In multiple scanning processing, the degree of overlap between adjacent scanning tracks will affect the uniformity and continuity of processing.

7.Auxiliary process

such as adding blow gas in the treatment process, applying magnetic field or electric field and other auxiliary means, will also affect the treatment effect.

The following are some ways to optimize the treatment effect of laser surface treatment technology:

1. Precise control of laser parameters

• Perform extensive experiments and simulations to determine parameters such as optimal laser power, wavelength, pulse width, frequency, and scan speed for specific materials and processing requirements.
• The use of advanced laser equipment for finer parameter adjustment and stability.

2. Optimize spot quality and shape

• The use of high-quality optical components to ensure spot uniformity and focusing accuracy.
• According to the processing requirements, select the appropriate spot shape, such as round, rectangular or other specific shape.

3. Improve the scan policy

• Adopt reasonable scanning path planning, such as spiral scanning, parallel scanning, etc., to achieve uniform processing effect.
• Adjust the bonding rate to ensure continuity and consistency in the processing area.

4. Material pretreatment

• Clean the material, remove the oxide layer and other pretreatment, improve the laser absorption rate of the material surface and the uniformity of treatment.

5. Control the processing environment

• Depending on the purpose of the treatment, the appropriate atmosphere environment is selected, such as vacuum, inert gas protection or specific reactive gases.
• Control the temperature during the treatment process, either by cooling device or preheating means.

6. Incorporate auxiliary processes

• The introduction of blow gases, such as nitrogen, argon, etc. helps to remove slag and control chemical reactions.
• Apply magnetic or electric fields to affect the interaction process between the laser and the material.

7. Real-time monitoring and feedback

• Using online monitoring technology, such as infrared temperature measurement, optical imaging, etc., real-time monitoring of temperature, morphology and other parameters in the processing process.
• According to the monitoring results, timely adjust the laser parameters and processes to achieve closed-loop control.

8. Multi-process combination

• Combine laser surface treatment with other surface treatment technologies, such as electroplating, chemical heat treatment, etc., to play their respective advantages and obtain better performance.

9. Material development and selection

• Develop and select new materials with good laser processing adaptability, or optimize the composition and organizational structure of existing materials.

10. Process simulation and simulation

• Use computer simulation and simulation software to predict and optimize the laser surface treatment process, reduce the number of experiments and reduce costs.

Evaluating the treatment effect of laser surface treatment technology can be carried out from the following aspects:

1. Surface morphology and roughness

• Use optical microscope and scanning electron microscope (SEM) to observe the microscopic morphology of the surface to check whether it is flat, whether there are cracks, pores and other defects.
• Measure the surface roughness with a roughness meter to evaluate the smoothness of the treated surface.

2. Hardness and strength

• Using hardness testing methods, such as Rockwell hardness, Vickers hardness, etc., to measure the hardness value of the treated surface to determine the degree of hardness improvement.
• Perform tensile, compression and other mechanical properties tests to evaluate the strength change of the material.

3. Wear resistance

• Wear test was carried out using friction and wear testing machine to compare the wear resistance of the material before and after treatment.

4. Corrosion resistance

• Evaluate the corrosion resistance of materials after surface treatment by means of salt spray test, electrochemical corrosion test, etc.

5. Residual stress

• Measure residual stress distribution on the surface and inside using X-ray diffraction techniques, etc., to understand the effect of treatment on the stress state of the material.

6. Coating bonding strength

• For processes such as laser coating, the bonding strength of the coating to the substrate is tested, e.g. scratch testing.

7. Microstructure analysis

• Using metallographic microscopy, electron backscatter diffraction (EBSD) and other means to analyze the microstructure after treatment, such as grain size, phase composition and other changes.

8. Chemical composition

• Use energy dispersive analysis (EDS), X-ray photoelectron spectroscopy (XPS) and other methods to determine the composition and distribution of surface elements.

The evaluation of the above aspects can comprehensively and accurately judge the treatment effect of laser surface treatment technology, and provide a basis for further optimization of the process.

The following materials are suitable for laser surface treatment technology:

1. Metal materials:

Steel: including carbon steel, alloy steel, etc., often used to improve its hardness, wear resistance and corrosion resistance.

• Aluminum and aluminum alloy: can improve the surface hardness, wear resistance and corrosion resistance.
• Titanium and titanium alloys: enhance their surface strength and corrosion resistance, suitable for aerospace and other fields.
• Copper and copper alloys: such as improving electrical conductivity, wear resistance, etc.

2. Ceramic materials: such as alumina, zirconia, etc., improve their toughness and surface quality through laser treatment.

3. Polymer materials: such as polycarbonate, polyethylene, etc., can enhance its surface hardness, wear resistance and bonding properties.

4. Composite materials: such as carbon fiber reinforced composite materials (CFRP), can improve the surface bonding properties and wear resistance.

5. Cemented carbide: often used in tool and mold manufacturing, laser treatment can extend its service life.

6. Die steel: such as Cr12MoV, etc., after laser surface treatment to improve the surface quality and service life of the die.

The following are some ways to improve the processing efficiency of laser surface treatment technology:

1. Optimize laser equipment

• Choose a laser source with high power and high repetition frequency to increase the energy output per unit time.
• Upgrade the optical system to improve the quality and transmission efficiency of the laser beam.

2. Multi-beam technology

• Simultaneous processing with multiple laser beams can significantly increase the processing area and speed.

3. Improve the scanning system

• Use high-speed scanning galvanometer or more advanced scanning devices to improve scanning speed and accuracy.

4. Plan the scan path properly

• Design the optimal scan path to reduce invalid travel and overlapping areas and improve processing efficiency.

5. Automation and intelligent control

• Combine robotics to automate clamping, positioning and handling, reducing manual intervention time.
• Use an intelligent control system to adjust laser parameters in real time according to material characteristics and handling requirements.

6. Parallel processing

• For mass-produced workpieces, multiple workpieces can be processed simultaneously.

7. Preheat treatment

• The workpiece is properly preheated to reduce energy consumption and time during laser processing.

8. Optimization of process parameters

• Through extensive experiments and simulations, determine the best combination of laser power, scanning speed, pulse frequency and other process parameters to achieve the highest processing efficiency.

9. Material pretreatment

• Pre-treatment of the material such as surface cleaning and oxidation layer removal in advance to improve the absorption efficiency and treatment effect of the laser.

10. Cooling system optimization

• Ensures an efficient cooling system that prevents the workpiece from overheating, thereby increasing the processing speed.

11. Develop new treatment processes

• Research and application of more efficient laser surface treatment processes, such as ultrafast laser treatment.

1. Automotive industry 

Laser hardening technology has been successfully applied to the surface strengthening of vulnerable parts in the automotive industry, such as gears, shaft surfaces, guides, jaws, molds, etc. By laser quenching, the surface hardness and wear resistance of these parts are improved, the service life is significantly extended, and the deformation of the workpiece before and after quenching is almost negligible, especially suitable for parts with high precision requirements.

2. Mold industry

In mold manufacturing, the use of laser surface treatment technology can improve the surface performance of the mold. For example, laser cladding technology can be used to repair worn molds, improving their surface hardness and durability; Laser quenching can enhance the hardness and fatigue resistance of the mold surface, and reduce the wear and deformation of the mold during use.

3. Aerospace field

Laser shock strengthening technology is often used to improve the fatigue resistance, wear resistance and corrosion resistance of aerospace parts. The technology uses plasma shock waves generated by strong laser beams to create deep compressive stresses on the surface of components, thereby extending their service life. At the same time, laser annealing technology can be used to adjust the matrix structure of the material, reduce the hardness, refine the grain, eliminate the internal stress, etc., in semiconductor processing can improve the integration of integrated circuits.

4. Cultural relics protection

Laser cleaning technology has a good application effect in cultural relics cleaning. It can remove dirt, rust, coating, etc., on the surface of cultural relics, while not causing damage to the cultural relics. For example, some ancient metal relics, stone carvings, murals, etc., can be restored to their original appearance by laser cleaning.

5. Flat wire motor manufacturing

Laser removing flat copper wire oxide layer technology by precisely controlling the energy of the laser beam, can quickly and efficiently remove the flat copper wire surface oxide layer, and almost no damage to the copper wire itself. This technology not only restores and improves the electrical conductivity of the motor, but also improves production efficiency and reduces environmental pollution and material waste. In the fields of new energy vehicles and industrial automation, the flat wire motor treated with this technology has better electrical conductivity and thermal stability, and its reliability and life are also improved.

6. Bone Implants

Nanosecond laser surface treatment technology developed by the Korea Advanced Institute of Science and Technology can be used to induce the formation of artificial bone coatings. The technology eliminates the need to separately synthesize raw materials for the artificial bone coating, and the coating can be created using nanosecond lasers, and the resulting hydroxyapatite coating has a high coating strength. For example, when applied to titania-based bone fixation devices, it can enhance bone conduction properties, improve the biocompatibility, osteogenic ability and bone conductivity of the coating, and the new method can form a coating bond three times that of traditional coating materials, and can form a coating on the surface of not only metal but also polymer materials.

7. Titanium surface treatment

Korea Electric Research Institute uses femtosecond laser surface treatment of titanium, which can not only improve the inherent properties of titanium, but also create a functional surface. The hydrophilic titanium material after femtosecond laser treatment can be prepared into dental implants, which has high affinity with human body and can achieve stable fusion with human bone, thus greatly shortening the treatment cycle of patients. The titanium material after hydrophobic treatment can be prepared into medical devices for transplantation in vivo, which helps to reduce the foreign body reaction in the patient.

Laser surface treatment technology is an advanced technology to change the surface properties of materials by laser beam, which has many advantages such as high precision, local treatment and small deformation. The processing effect is affected by laser parameters, scanning speed, spot size, material properties, processing environment and other factors. In order to optimize the treatment effect, it can be started from many aspects, such as precise control of laser parameters, improvement of spot and scanning strategy, combination of auxiliary technology and real-time monitoring feedback. The technology is suitable for metal, ceramics, polymers, composite materials and other materials. The treatment effect can be evaluated from many angles such as surface morphology, hardness, wear resistance and corrosion resistance. Methods to improve processing efficiency include optimizing laser equipment, using multi-beam and advanced scanning systems, planning scanning paths, and realizing automatic control. There are successful application cases in many fields such as automobiles, molds, aerospace, and cultural relics protection, which have played an important role in improving product performance and quality. In the future, laser surface treatment technology is expected to continue to develop in precision, efficiency, intelligence and other aspects, and expand a wider range of application fields.

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