THE LASER TECHNOLOGY

Introduction
In this section are described the main characteristics of this technology. The term LASER is an acronym of Light Amplification by Stimulated Emission of Radiation. It indicates a device that is capable of emitting a concentrated rectilinear beam with a high rank caliber.

It can have numerous applications and by taking advantage of the above mentioned characteristics it can have diverse use: in the medical field, in industrial manufacturing, in precision measurements, in illumination systems, in network data transmission. The laser is also utilized to cut different types of materials. Accordingly to the structure and the power, it is possible to cut metals, plastic, fabrics, wood and paper.

The type of laser that we are going to describe is the CO2.
The beam is generated internally of a cylinder containing some type of a gas (nitrogen, helium, oxygen, carbon dioxide), a charge spans through the tube forcing the beam to dash out through a nozzle towards the first mirror (standing mirror), which adequately calibrated, reflects the beam on a second mirror (Y mirror) mounted on a guide which due to its motion, perpendicular to the cylinder, it gets closer or further from the first mirror.

From the second mirror, the beam continues its path reflecting itself towards the third mirror (X mirror) mounted on the horizontal trolley parallel to the laser cylinder. The third mirror slides from right to left. Unlike the other two, its position allows the beam to reflect towards the bottom. Thus, by going through a convexo-plane lens, it becomes further concentrated so that when it comes out of the nozzle it is able to cut or etch in a dotting manner. The laser beam functions as the light: it travels rectilinear, but, as it gets further from the source it tends to enlarge. This is the reason why the further is from the source the exit point of the laser, the more inaccurate will be the cut. This is a nominal difference to be considered when undertaking a cutting cycle.

MANUFACTURING WITH THE LASER TECHNOLOGY
The laser cuts materials by fusion or combustion: each material reacts in a different manner. This is due to the difference in the stoutness, the chemical composition, the finished surface, the mirror image aptitude and, obviously, the substance. This is the reason why not all the plastic materials can be cut with the laser. Some become warped, others turn yellow at the cutting point, others char or melt. One material that reacts better to the cutting and etching process is the PMMA (Polymethyl Methacrylate), better known with the commercial term of Plexiglass or Perspex.

It is important to underline that in the cutting phase, the beam “enters” the material casting it in a dotting manner and causing a slight overheating of the surface. If we inspect the cut on the microscope it can be noticed that the cut is not perfectly perpendicular, but slightly enlarged at the bottom. This is not due on an approximate calibration of the laser, but rather to a heating disparity between the top and the bottom of the material used. The thicker is the material, the greater is the possibility that this enlargement will be more evident. The problem becomes somehow reduced when working with a very powerful laser. In this case, the beam cuts more quickly and as a result “lingers” less. The thickness of the cut varies accordingly to the thickness of the material. Therefore, this gap must be considered when the cutting process involves two common pieces in order for the pieces to have the same exact measurements.

The engraving process is referred to the prospect of marking a surface with a micro fusion, a combustion or subtraction of material. The difference depends on its chemical composition and on its reaction to heat. The materials in plastic generally undergo a micro fusion; wood and paper a light combustion; stone and ceramics undergo a subtraction. Some materials cannot be engraved, but it is possible to undergo a marking. The surface is treated with products that at the transition of the laser become permanently impressed. This method consents to mark metals, mirrored surfaces, polycarbonate glass, etc..

At this point it is important to make a distinction between the raster and the vector engraving. The first one is obtained from a vector or bitmap file. The laser engraves in a horizontal direction, “by levels”. That is to say, it works as an ink-jet printer until it completes the defined graphic. This type of engraving has a high level quality of the details and consents nuances. This is the reason why it is, above all, used to reproduce photographs. As for the vector engraving, the file must thus be in the vector format: the laser, set at a low rating, follows the outline, creating a not very deep incision on the surface. The advantages of this procedure is the speed of the process and as a consequence, the drastic reduction of the machine labour cost. The disadvantages are that the quality is surely inferior and that its use is limited to few products.