KEYHOLE PHENOMENON AND ITS APLICABILITY FOR WELDING WITH

“KEYHOLE” PHENOMENON AND ITS APLICABILITY FOR WELDING WITH LASER OF THE DIAMOND SEGMENTS/PARTS Ing. Cristina Marinescu Dr. ing. Paul Beca INCDMF- Bucharest, Romania Dr. Ing. Ioan Farcas INFLPR – Bucharest, Romania

Introduction presents the “keyhole” phenomenon applied to welding with high power laser of the diamonded segments on the disks surface with the apparition of the high power lasers were realized studies on “keyhole” – deep laser welding, characterized by narrow and deep fusion, limited by parallel surfaces

Deep laser welding

Deep laser welding electromagnetic radiation absorption study of the polarization status dependency in the case of oblique incidence and of the incidence angle Absorption variation with the incidence angle

Deep laser welding When the laser fascicle touches the surface of the part, a part of it is reflected another one is absorbed The absorbed power is transformed in heat: photons from the laser fascicle excite the electrons from the metal superficial layers on the superior energy levels The excited electrons come back to the initial status providing energy to the metal atomic net as heat This phenomenon is produced in an interval of about 10 -12 s The fascicle absorption in the part material is made according to Beer law I(z) = I 0 e-αz α is the absorption factor The absorption length in the material is defined as the distance towards which the intensity is reduced with a factor of 1/e the absorption length is very small and the laser fascicle is absorbed and transformed in heat in a very thin layer at the surface of the very surface

Deep laser welding The balance between the absorbed power and the incident power is named coupling factor and is expressed in percentages It depends of physical parameters such as: complex permittivity, electric resistance and the refraction index and by other parameters with practical value, such as: the nature of the part material and the level of the surface finish; the laser fascicle wave length; the part temperature depending on the fascicle power and its intensity In the welding with laser processes not all the incidental intensity I will be coupled within the processed part but only the fraction I 0 = A I, determines the absorption A

Characteristics of the welding with laser high energy density – keyhole welding high processing speed rapid switch on/off welding at atmosphere pressure X rays are not generated without additional material narrow welding reduced influenced thermal aria very precise welding good profile of the welding margin the fascicle is mot moving in the magnetic field small contamination or not contaminated small loose of volatile parts sometimes can be welded “not welded” materials

Experiments Macro laser Centre having the ROFIN SINAR RS 2000 equipment and needed to adapt the parts modules in order to achieve the optimal values of the process parameters ROFIN SINAR RS 2000 have been made tests for welding the diamonded parts on disks made by steel for constructions As a result of this tests were necessary adjustments, constructive and functional modifications of the substances entering in the MACROLASER Center structure

Experiments Laser fascicle supplying system – emits a high quality laser fascicle (spot) previously adjusted for the following parameters: absorbed power P- 17600 W argon flow – 6 l/min disc rotation 4, 17 rot/min for the mentioned parameters have been obtained at present the welding belt according to requests LASER FASCICLE TRANSPORT SYSTEM - realizes the laser fascicle orientation from the laser source being improved to: cables/wires for transport was realized by aluminum bar, telescopic fixed realizing the horizontal and vertical transport of the laser fascicle, parts for laser fascicle defluxion – changes the laser fascicle direction by the help of deflectors, supporting frame

Experiments ACTIVE SYSTEM FOR PROCESSING – realizes the laser fascicle motion over the processed materials Head for fascicle focalization – drives the fascicle in the active aria and passes it through the fascicle concentrate mirrors. MODULE FOR FASCICLE ADJUSTMENT – focalizes the fascicle energy by pressing the 4 max. aria intensity fascicle in the active aria. MODULE FOR PROTECTION GAZES – directions/drives the protection gaze in the working aria POSITIONING AND FIXING MODULE – drives the diamonded segment and the metallic disk towards the laser fascicle UNIT FOR ORDER AND CONTROL – orders the port components (segments/disk) module displacement and rotation by the specific SOFTWARE PROGRAM. The equipment uses “an using interface” choused from more options of the Lab. VIEW VI Express program, realizes applications and measure the specific application parameters.

Laser fascicle focalizing head The main characteristics: positions correctly the two components during processing positions the diamonded segments between two positioning stiffs and between two windows from the supporting plate, necessary for spot passing provides the segments pressing on the disk steel body displays the sub ensemble port components to the focalizing head “ready for welding” provides the speed of the rotating disk according to the welding regime choused

Results As results of the tests has been noted the necessity of doing some constructive modifications of the nozzle from the let out of the laser computer, for reorientation of the compressed air jet so that it stops the deposits penetration from the (scanteie) on the deflection prism Glass CEEX 1 project – “The national research facility with laser fascicle” high power MACROLASER Center – 2200 W, functioning with gas CO 2, and wave length: 10, 6µm