Instrucciones para la preparación de los trabajos a presentar en el XV congreso Nacional de Ingeniería Mecánica
Laser cutting process parameters
Download 0.65 Mb. Pdf ko'rish
|
CuttingParametersforthereductionofthematerialdegradationinlasercuttingofAHSSrev2
1.1 Laser cutting process parameters
Laser cutting is a thermal process. The material is heated to its melting or vaporisation temperature . Heating is achieved by concentrating the energy in a very small spot. This allows the cutting of almost all types of materials with thicknesses of up to 20 mm in the case of steel sheets without the need for very high levels of energy [10]. There are different laser generators depending on the type of medium being used. Each type of laser creates a different laser beam at a given wavelength. The CO 2 generators are the most used for cutting with a wavelength 10.6 µm, whilst the Nd:YAG lasers generate a beam with a wavelength of 1.06 µm. In general, the Nd:YAG lasers wavelength is better absorbed by most of materials (copper, aluminium, precious metals...). Steel, however, has acceptable absorption levels for the beam generated by CO 2 . This, added to the fact that the CO 2 generators are more powerful and cheaper, explains why their use in industry is much more widespread. Once the beam has been generated, a lens system focuses the beam on a point with diameters of around 0.2 mm. The focusing of the beam results in high energy density at the irradiated spot surface, a typical value being in the order of 1.4·10 10 W/m 2 . The high power density concentrated on the spot vaporises almost all types of material (as long as enough beam energy being absorbed) [11]. A gas jet is injected coaxially with the laser beam during cutting. The assisting gas jet has two effects, depending on the material that is being cut: • Inert gas is usually used in the case of composites to protect the heated area from the oxidations reactions and to sweep away the vaporised material from the back of the cutting surface. • On the other hand, oxygen is used to cut steel. This gas generates exothermal reactions that favour cutting as well as sweeping away the material that has been cut away. Figure 1 shows a diagram of a typical cutting head. 3/15 Cutting direction Evacuated material (Dross) Cutting head Gas inlet Lens Laser beam Figure 1. Experimental set-up used and diagram of a laser cutting head. Material cutting is achieved by the translation of the spot along the desired cutting path. The most common method is the use of 3 axes machines, which move the steel sheet underneath the laser beam. There are also machines capable of interpolating up to 5 axes simultaneously. These type machines are designed for cutting complex forms and their programming is much more complex than the 2D case, although there are no differences as far as the cutting process is concerned. The main parameters defining the process are [12, 13]: Properties and thickness of the material Power of the beam emitted by the generator. Cutting speed: speed of the spot movement along the steel sheet Pressure, flow rate and properties of the cutting assisting gas. Distance between laser head and sheet. A correct choice of parameters requires the minimum quantity of heat contribution in the part during the cutting. In this way, the part will be cut with the minimum amount of thermal damage. As the contribution of heat depends on the cutting power and the speed, the cutting speed should be maximised and the power minimised in order to minimise the thermal damage. Download 0.65 Mb. Do'stlaringiz bilan baham: |
Ma'lumotlar bazasi mualliflik huquqi bilan himoyalangan ©fayllar.org 2024
ma'muriyatiga murojaat qiling
ma'muriyatiga murojaat qiling