Laser Cutting

Table of Contents

How do Lasers work?

LASER - meaning Light Amplification by Stimulated Emission of Radiation, uses spontaneous and stimulated emission to generate beams of light. A solid, liquid or gas medium is excited using an external energy source, and this triggers electrons in the medium to release photons (spontaneous emission). The energy absorbed by the atoms results in electrons jumping up to a higher energy state and dropping back down, releasing a photon during this. The gas medium and the emitted photons travel through a mirrored tube which allows for photons to freely reflect, thus further exciting the gas medium and releasing more photons (stimulated emission). A focusing lens concentrates the beam to a small point, further increasing its intensity, and this beam cuts through material [1].

Laser beams can either be fixed in position with a moving cutting bed, or move in x-y directions on top of a stationary bed that can move in the z direction (up and down). The focal distance between the surface of the material and the laser's lens must be maintained so adjustments in the z direction are critical for clean cuts [2]. It is also important to consider the limitations of the specific laser used, as thickness ranges can vary, as well as the type of material the laser is suited for. Some materials release toxic fumes (ex: polycarbonate releases chlorine gas when laser cut) so ensuring that the cutter is equipped for these hazards is necessary. 

Laser cutting creates quick, clean, and precise cuts with minimal damage to the material. Clean edges, curves and corners can be achieved with minimal dimensional tolerance (+/- 0.5mm on CO2 Laser Cutters) [3].

Types of Laser Cutting

Laser cutting machines are categorized by the medium used to generate the laser. CO₂ lasers are gas-medium lasers that are widely used for cutting a large variety of materials. Another common laser medium is neodymium-doped yttrium aluminum garnet (Nd:YAG) used in solid-state laser cutters. Depending on the material, the cutting process varies: [1]

• Fusion

Laser melts material to cut it. This method is suitable for cutting metal and thermoplastics.

• Chemical Degradation

Laser burns material to cut it. This is used on polymers and organic material such as wood and fibreboard.

• Evaporation

Laser's heat evaporates material as it cuts. This is used on materials like acrylic.

• Scribing/Engraving

Rather than a full cut, lasers can make partial depth cuts on the surface of the material to engrave designs or text.

• Oxidation

Similar to fusion cutting, except oxygen is used as an assist gas. It reacts with the material to oxidize its' cut edges, thus providing a cleaner cut.

Design Guidelines

• Laser cut parts are cut with high precision and are good for cutting flat components with holes or complex geometry
• Multiple laser cut parts can be joined together to form enclosures
• Laser cut parts can be joined together in various ways:
  • Press-fitting parts into slots
  • Creating slots and tabs for pieces to interlock with
  • Using an adhesive
• If the material is thick or the laser's speed is low, more material at the surface burns off and can create a slight slant in the edge
• Having a consistent datum or reference point will help in organizing parts on the laser bed
• Laser cutters typically accept a variety of file formats such as .dxf, .dwg, .svg, .pdf, and sometimes .jpeg and .png

Laser Cutting Materials

• Wood
• Acrylic
• Various Plastics
• Various sheet metals
• Fiberboard

References

[1] R. Ronquillo, A Guide to Laser Cutting and the CNC Laser Cutting Machine. [Online]. Available: https://www.thomasnet.com/articles/custom-manufacturing-fabricating/laser-cutting-technology/

[2] ESAB, “How does Laser Cutting Work?,” ESAB Knowledge Center. [Online]. Available: https://www.esabna.com/us/en/education/blog/how-does-laser-cutting-work.cfm

[3] “Laser Cutting Tolerances,” A-Laser Precision Laser Cutting. [Online]. Available: https://a-laser.com/laser-cutting-tolerances/