Laser Surface Treatment Technology

Laser Quenching

Laser quenching is one of the solutions for processing high-stress complex components. It can make components with high wear such as camshafts and bending tools bear higher stress and extend their life.

Its principle is to rearrange the carbon atoms in the metal lattice (austenite ), and then the laser beam steadily heats the surface along the feed direction. As the laser beam moves, the surrounding material cools rapidly, and the metal lattice cannot return to its original form, thus producing martensite, which significantly increases the hardness. The hardening depth of the outer layer of carbon steel achieved by laser hardening is usually 0.1-1.5mm, and can be 2.5mm or greater on some materials.

Compared with traditional quenching methods, its advantages are:
1. Targeted heat input is limited to local areas, so there is almost no component warping during processing. Rework costs are reduced or even eliminated entirely;
2. It can also be hardened on complex geometric surfaces and precision parts, and can achieve precise hardening of locally limited functional surfaces that cannot be quenched by traditional quenching methods;
3. No distortion. In conventional hardening processes deformations occur due to higher energy input and quenching, but in laser hardening processes the heat input can be precisely controlled thanks to laser technology and temperature control. Components remain almost in their original condition;
4. The hardness geometry of the part can be quickly changed "on the fly". This means no need to convert optics/entire system.

Laser Texturing

Laser texturing is one of the process methods for surface modification of metal materials. During the structuring process, the laser creates regularly arranged geometric shapes in layers or substrates in order to specifically modify technical properties and develop new functionalities. The process involves the use of laser radiation, usually short-pulse lasers, to produce regularly arranged geometric shapes on a surface in a repeatable manner. The laser beam melts the material in a controlled manner and solidifies into a defined structure with appropriate process management.

Laser Colorful Surface Treatment

Laser tempering is commonly used in laser colorful surface treatment, also known as laser color marking. The process principle is that when the laser heats the material, the metal is locally heated to slightly lower than its melting point. Under appropriate process parameters, the structure of the gate will change at this time; an oxide layer will be formed on the surface of the workpiece, and this film will be exposed to light. Under irradiation, the interference of incident light causes various tempering colors to appear at this time. The phantom marking layer generated on the surface changes with different viewing angles, and the marking patterns will also change into various different colors. color.

These colors are temperature stable up to approximately 200 °C. At higher temperatures, the gate returns to its original state-the marking disappears. Surface quality will be intact. It has a high degree of security and traceability in anti-counterfeiting applications. It has been used in medical technology for a long time and, in addition to new black marking with ultra-short pulse lasers, is also ideal for product marking and thus unique traceability according to UDI directives.

Laser Cladding

It is an additive manufacturing process suitable for metal and cermet hybrid materials. This allows you to create or modify 3D geometric shapes. Using this production method, the laser can also perform repairs or coatings. Therefore, in the aerospace industry, additive manufacturing is used to repair turbine blades. In tool and mold making, cracked or worn edges and functional surfaces can be repaired or even partially armored. To protect against wear and corrosion, bearing locations, rollers or hydraulic components are coated in the energy technology or petrochemical sectors. And additive manufacturing is also used in automobile manufacturing. A large number of components have been improved here. In conventional laser metal cladding, the laser beam first locally heats the workpiece and then forms a molten pool. Fine metal powder is then sprayed directly into the molten pool from the nozzle of the laser processing head. During high-speed laser metal cladding, the powder particles are heated almost to melting temperature just above the substrate surface. Therefore, less time is required to melt the powder particles. Effect: Significantly improve process speed. Due to the smaller thermal effects, very heat-sensitive materials such as aluminum alloys and cast iron alloys can also be coated by high-speed laser metal cladding. The HS-LMD process enables very high surface velocities of up to 1500 cm²/min to be produced on rotationally symmetric surfaces. At the same time, feed speeds of up to several hundred meters per minute are achieved. Repair expensive parts or molds quickly and easily with laser powder laser metal cladding. Damages large and small can be repaired quickly and virtually without leaving a trace. The design can also be changed. This saves time, energy and materials. Especially for expensive metals like nickel or titanium, it's quite worthwhile. Typical application examples are turbine blades, various pistons, valves, shafts or moulds.

Laser Heat Treatment

Thousands of tiny lasers (VCSELs) are mounted on a single chip. Each transmitter is equipped with 56 of these chips, and a module consists of several transmitters. A rectangular radiation zone can contain millions of tiny lasers and can output several kilowatts of infrared laser power. The VCSEL generates a near-infrared beam with a radiation intensity of 100 W/cm² via a large, directional rectangular beam cross-section. In principle, this technology is suitable for all industrial processes that require extremely precise surface and temperature control. The laser heat treatment module is particularly suitable for large-area heating applications that require stringent precision and flexibility. Compared with traditional heating methods, this new heating process has higher flexibility, accuracy and cost savings.

This technology can be used to seal pouch-type battery sheets to prevent aluminum foil from wrinkling, thus extending the life of the battery. It can also be used in applications such as drying aluminum foil for batteries, light-wetting solar panels, and precisely processing areas to be heated on specific materials such as steel and silicon wafers.

Laser Polishing

The mechanism of laser polishing technology is surface narrow melting and surface over-melting, which relies on surface remelting and re-solidification of the laser remelted layer. When a metal surface is irradiated by a sufficiently high-energy laser, its surface undergoes a certain degree of remelting, redistribution, and surface tensile stress and gravity, achieving a smooth surface before solidification. The entire thickness of the melted layer is less than the height from trough to crest, allowing the entire molten metal to fill the nearby troughs. The driving force for this filling is achieved through the capillary effect, while a thicker melted layer will promote liquid metal The driving force for flow outward from the center of the molten pool is the thermocapillary or Marconi effect, which redistributes it.

Laser Shot Peening / Laser Shock Strengthening

Laser shock peening, also called laser peening, irradiates the surface of metal parts with high-energy density, high-focus, short-pulse laser (λ=1053nm), and the surface metal (or absorption layer) is instantly formed under the action of high-power-density laser. Plasma explodes, and the explosion shock wave is transmitted to the inside of the metal part under the constraints of the constraint layer, causing the surface grains to undergo compressive plastic deformation, and obtaining surface strengthening effects such as residual compressive stress and grain refinement in the thicker surface of the part. Compared with traditional mechanical shot blasting, it has the following advantages:

1. Strong directionality: the laser acts on the metal surface at a controllable angle, with high energy conversion efficiency, while the impact angle of mechanical projectiles is random;
2. Large force: the instantaneous pressure generated by laser shot peening plasma blasting is as high as several GPa; high power density: the peak power density of laser shock reaches several to tens of GW/cm2;
3. Good surface integrity: Laser shock has almost no sputtering effect on the surface, while after mechanical shot peening, the surface morphology is damaged and stress concentration occurs. The maximum compressive stress value after laser impact is better, the surface residual compressive stress is increased by about 40% to 50%, and the fatigue life, high temperature resistance, bending forming and other related indicators of the workpiece are significantly improved. It has been used in aircraft surface treatment, aero-engine surface treatment and other fields.