The laser beam is a column of very high intensity light, of a single wavelength, or color. In the case of a typical CO2 laser, that wavelength is in the Infra-Red part of the light spectrum, so it is invisible to the human eye. The beam is only about 3/4 of an inch in diameter as it travels from the laser resonator, which creates the beam, through the machine’s beam path. It may be bounced in different directions by a number of mirrors, or “beam benders”, before it is finally focused onto the plate. The focused laser beam goes through the bore of a nozzle right before it hits the plate. Also flowing through that nozzle bore is a compressed gas, such as Oxygen or Nitrogen.

Focusing the laser beam can be done by a special lens, or by a curved mirror, and this takes place in the laser cutting head. The beam has to be precisely focused so that the shape of the focus spot and the density of the energy in that spot are perfectly round and consistent, and centered in the nozzle. By focusing the large beam down to a single pinpoint, the heat density at that spot is extreme. Think about using a magnifying glass to focus the sun’s rays onto a leaf, and how that can start a fire. Now think about focusing 6 KWatts of energy into a single spot, and you can imagine how hot that spot will get.

How Does the Lens Used Affect the Thickness of the Cut?

The laser cutting process involves focusing a laser beam, usually with a lens (sometimes with a concave mirror), to a small spot which has sufficient power density to produce a laser cut.

The lens is defined by its focal length, which is the distance from the lens to the focused spot. The critical factors which govern the efficiency of the process are the focused spot diameter (d) and the depth of focus (L).

The depth of focus is the effective distance over which satisfactory cutting can be achieved. It can be defined as the distance over which the area of the focused spot does not increase beyond 50%.

The laser focal spot diameter and the depth of focus is dependent on the raw laser beam diameter on the lens and the focal length of the lens. For a constant raw laser beam diameter, decrease in the focal length lens of the focusing lens results in a smaller focal spot diameter and depth of focus. For a constant focus length lens, increase in the raw beam diameter also reduces both the spot diameter and the depth of focus.

To allow comparison between lasers with different beam diameters we therefore use a factor called the focus f-number, which is the focal length, F, divided by the incoming raw beam diameter, D.

The requirements for cutting are as follows:

a) high power density and therefore small focused spot size

b) long depth of focus to process thicker materials with a reasonable tolerance to focus position variation.

Because these two requirements are in conflict with each other, a compromise must be made. The only other consideration is that the shorter the focal length, the closer the lens is to the workpiece, and therefore more likely to get damaged by spatter from the cutting process.

In fact, it would be possible to optimise focal length for each material thickness, but this would involve additional set-up time when changing from one job to another, which would have to be balanced against the increased speed. In reality, changing the lens is avoided and a compromised cutting speed used, unless a specific job has special requirements.

There are many, many other parameters that affect cut quality as well, but when all are controlled properly, laser cutting is a stable, reliable, and very accurate cutting process.

10 years professional laser manufacturing experience and professional research team will help the in-depth development of laser machines. We constantly improve our products making sure our worldwide network of customers receive the best laser cutting and engraving solution possible.

As a company with a "century enterprise" vision, SHANGHAI KASU LASER will continue to pursue providing excellent global laser intelligent solution and insist on innovation to make China's national enterprise shine brightly in the world.

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