Laser beams have an impressive ability to cut through metal, plastic, wood and even glass. But how is this possible? The answer lies in the unique properties of laser light.
Laser light is not just a beam of light, but a coherent beam of light. This means that photons of light have the same wavelength and phase and travel in the same direction. This coherence gives laser light its high energy density, which allows it to cut.
When a laser beam is focused on a material, the energy of the photons is transferred to the atoms of the material. This leads to a rise in temperature, which can cause the material to melt or evaporate. The exact way of cutting depends on the type of material and the parameters of the laser.
Cutting mechanisms for laser cutting
In laser cutting, metal sheets are cut by three main mechanisms: melting, evaporation and sublimation. The type of cutting mechanism depends on the type of material, the laser parameters (e.g. power, wavelength, focal point size) and the cutting conditions (e.g. type of assist gas and flow rate).
Melting:
This is the most common cutting mechanism and is most suitable for cutting thicker metal sheets (e.g. steel, stainless steel). The energy of the laser beam locally heats the metal above the melting point, creating a molten metal bath. The circulation of cutting gas (e.g. oxygen, nitrogen) in the cutting zone removes the molten metal and helps prevent slag formation. The cutting speed depends on the laser power and the thickness of the metal sheets.
Pros:
- High cutting speed
- Suitable for cutting thicker sheet metal
- Relatively low cost
Cons:
- Minimum Heat Affected Zone (HAZ)
- Slag formation possible
- Not suitable for all metals
Evaporation:
Evaporation is the cutting mechanism when the laser energy is sufficient to evaporate the metal in the cutting zone. This mechanism is suitable for cutting thinner sheets of metal (e.g. aluminium, copper) and results in a more precise cut than melting. The cutting speed depends on the laser power and the thickness of the metal sheets.
Pros:
- Precise cutting
- Minimum HAZ
- Smooth cutting surface
- Reduced slag formation
Cons:
- Lower cutting speed
- Suitable for cutting thinner sheet metal
- Higher cost
Sublimation:
Certain materials, such as wood and plastics, are directly sublimated, i.e. transformed from solid to vapour, when cut by laser. This cutting mechanism results in a precise and clean cut with minimal thermal impact. The cutting speed depends on the laser power and the type of material.
Pros:
- Precise and clean cut
- Minimum HAZ
- No slagging
Cons:
- Limited choice of materials
- Lower cutting speed
The influence of cutting parameters:
The quality and efficiency of laser cutting is affected by a number of parameters, including:
- Laser power: Laser power affects cutting speed, depth of cut and cut quality.
- Wavelength: the wavelength of the laser affects the interaction with the material and the cutting efficiency.
- Focal point size: the size of the focal point affects the width of the cutting gap and the thermal effect zone.
- Cutting speed: The cutting speed affects the cut quality and cutting costs.
- Type and flow rate of assist gas: The type and flow rate of assist gas affects melt removal, cut quality and cutting costs.
Optimising the laser cutting parameters for the material and the desired cut quality is essential.
In summary
The laser beam cuts by increasing temperature: melting thicker metal (melting), vaporising thinner metal (vaporisation) and sublimating plastic. The cutting method depends on the material and the laser setting. Laser cutting is a precise, versatile and automated process that is essential in many industries.
Sources:
https://mellowpine.com/laser/co2-laser-cutters-how-do-they-work/
https://engineeringproductdesign.com/knowledge-base/laser-cutting/
