Laser engraving is a process that uses lasers to create designs by precisely removing material from an object’s surface. This technique contrasts with other marking methods by eliminating the need for inks or physical tool bits that wear out, offering a durable and low-maintenance solution.
Distinction from Laser Marking:
It’s important to distinguish laser engraving from laser marking. While both use lasers, laser marking encompasses a broader range of techniques, including color changes through chemical alteration, charring, foaming, melting, and ablation. The term “laser marking” is also sometimes used as a general term for various surface treatments, such as printing, hot-branding, and laser bonding. Although the same machines can often perform both engraving and marking, the processes differ significantly.
Laser marking has found particular success with specially designed “laserable” materials and paints, including laser-sensitive polymers and novel metal alloys.
Laser Engraving Mechanisms:
Laser engraving achieves its effects by selectively removing microscopic layers of material, creating visible marks. The laser’s interaction with the material varies depending on its properties. On hard surfaces, ablation is the primary mechanism, where the focused laser beam dislodges particles. Engraving can achieve depths of 100μm or more, while laser marking is typically shallower.
The choice of laser is crucial for mark quality. Short bursts of high-quality laser pulses are preferred, as they deliver energy without excessive heating and melting. For example, femtosecond lasers provide high precision and resolution by emitting extremely short pulses, minimizing thermal effects on materials like metals, plastics, and sensitive electronics.
Laser Engraving Machines:
A laser engraving machine consists of a laser, a controller, and a work surface. The laser acts as a drawing tool, while the controller dictates the beam’s direction, intensity, speed, and spread. The work surface is selected based on the material being engraved.
The laser beam’s focal point, where it interacts with the surface, is typically very small. The laser’s energy alters the material at this point, either by vaporizing it or causing it to fracture. Vaporization necessitates ventilation to remove fumes and debris.
Laser beams are highly efficient at converting light energy into heat, enabling precise material removal. This efficiency, however, requires cooling systems or pulsed lasers to prevent overheating.
The controller guides the laser beam along a programmed path to create specific patterns. Consistent material removal is achieved by regulating the beam’s speed and intensity. Unlike older engraving methods, laser engraving doesn’t require resistive masks.
A common industrial application is production line marking, where lasers mark products with dates, codes, and numbers. This has largely replaced older technologies like hot stamping and pad printing.
Precision Engraving Techniques:
For detailed engravings, laser tables (X-Y tables) are used. These tables utilize movable mirrors to direct the laser beam across the work surface, allowing for intricate patterns. The laser beam is focused through a lens at the engraving surface.
Dynamic autofocus systems are used for surfaces with varying heights, adjusting the laser parameters in real time using ultrasound, infrared, or visible light.
Laser engraving machines operate in vector and raster modes. Vector engraving follows the lines and curves of a design, while raster engraving scans the laser across the surface in a back-and-forth pattern, similar to an inkjet printer. Raster engraving is well-suited for filling large areas and engraving photographs.
Materials for Laser Engraving:
- Natural Materials: Wood, paper, leather, and certain rubber compounds can be engraved. Organic materials are marked by carbonization, creating high-contrast marks.
- Plastics: Acrylic, laser-marked plastics, and some engineering plastics are suitable for engraving. Other plastics like styrene and thermoforming plastics may melt. Plastics containing chlorine should be avoided due to corrosive fumes.
- Metals: Metals are more challenging to engrave due to their thermal conductivity. Pulsed lasers are preferred. Coated metals, such as anodized aluminum and enamel-coated plates, are commonly laser-engraved. Spray coatings and pre-coated metals are also available.
- Stone and Glass: Laser engraving fractures stone and glass surfaces. Recent UV laser technology allows for clearer and more consistent engraving of glass.
- Jewelry: Laser engraving allows for precise and intricate designs on jewelry, including inside rings and on watch backs.
- Fine Art: Laser engraving is used to create fine art by revealing lower surface levels or creating grooves for inks and glazes.
- Trophies, Plaques, and Awards: Laser engraving is a cost-effective method for personalizing trophies and awards.
- Laser Etched Mirrors: Lasers can etch the glass surface or pulsate through the reflective silver layer on the rear of the mirror.
Industrial Applications:
- Flexographic Printing: Direct laser engraving is used for flexographic plates and cylinders, offering a digital workflow.
- Anilox Rolls: Laser engraving creates precise cell patterns on anilox rolls for flexographic printing.
- Sub-Surface Laser Engraving (SSLE): SSLE creates 3D images within transparent materials like glass and crystal.