1
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

2
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

3
Deep laser welding
4
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
5
Deep laser welding

• When the laser fascicle touches the surface of
  the part, a part of it is reflected and 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) I0 e-az a
  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

6
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 I0 A?I,
  determines the absorption A

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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

8
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

9
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 6l/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

10
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 the4 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 LabVIEW VI Express
  program, realizes applications and measure the
  specific application parameters.

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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
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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 CO2, and
  wave length 10,6µm