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Application and implementation
Center of Engineering Research & Develoment
Laser Application Centre

LASER HARDENING

laserové kalení

During laser hardening, in comparison with conventional methods, the laser beam intensively heats only the surface layers of material under the melting temperature, while the surrounding material is maintained at the ambient temperature. Using the laser beam you can quickly and efficiently heat-treat the surface of material to a depth of 2.5 mm. For laser hardening there are used CO2 lasers, Nd:YAG lasers, fibre lasers, but above all high performance diode lasers. Powerful diode lasers work with a relatively short wave lengths. The absorption of supplied energy by work-piece material is considerably greater in comparison with other types of lasers, the efficiency of these lasers is approximately 35 % - their operation is thus more economical. This technology finds its application mainly in the field of processing metallic materials. Laser hardening is applied in simple and more complex shapes, more difficult areas to reach, various openings or grooves where the emphasis is placed on maximum accuracy and minimal deformation. Therefore laser hardening is also carried out using modern robotic systems that are accurate and reliable at the same time.


  • PRINCIPLE OF LASER HARDENING

Laser hardening denotes a heat treatment in which there is a rapid heating, temperature maintenance and rapid cooling. The structure of material being processed is affected by several parameters, such as laser beam performance and its mode, ability to absorb the laser radiation, specific material properties, as well as its micro-structure. During surface hardening by high performance diode lasers the maintenance at the temperature is approximately 10-3 to 10 seconds. So as regards steel at the heating stage the austenitization occurs and during subsequent cooling a desired fine grain martensitic structure is formed. Dissipation of heat, i.e. cooling of material, takes place directly through the work-piece material. Hardening is primarily carried out without coolant supply, i.e. directly under the atmospheric conditions. To prevent the oxidation of surface, hardening can be carried out under the protective atmosphere of assistance gas.


  • POSSIBILITIES

Laser can be applied for the surface hardening of ordinary structural and tool steels, grey cast iron, cast iron with lamellar graphite, as well as ball graphite. The condition for material hardenability is the carbon content. The hardened material must have a minimum of 0.22 % of carbon. In addition, high performance diode lasers can be also used for hardening the steels with pre-carburized or pre-nitrated surface.  During laser hardening the rate of temperature increase is over 1000 [K∙s-1]. The temperature of heating is adjustable and monitorable by means of pyrometer or thermal imager.


ADVANTAGES OF LASER HARDENING

  • Local surface hardening in exactly desired points/places while maintaining toughness of the material not affected
  • Low temperature deformations
  • On-line control of process temperature
  • High process speed and efficiency
  • None or minimal need for subsequent treatment
  • No surface cracks arise
  • Low surface oxidation
  • Environmentally friendly process
  • Energetic efficiency
  • Easy process automation

 

MOST FREQUENT USE OF LASER HARDENING

  • Complex shape casting and pressing moulds
  • Shearing and bending tools
  • Bearing Bushings
  • Gear wheels and sprockets
  • Turbine blades
  • Piston rings

 

TECHNOLOGY OF LASER APPLICATION CENTRE

  • 6-Axis Robot KUKA KR60 HA
  • Rotary Tilting Positioner KUKA DKP-400
  • Table 1000 x 1500 mm with 3D Clamping System
  • Diode Laser Source Laserline LDF 4000-100
  • Hardening Laser head Laserline
  • IR Pyrometer
  • Connection of Working Gases - CO2, O2, N2, Ar, He
  • CAM KUKA.Sim Pro


TECHNICAL PARAMETERS

Robot KUKA KR60 HA
Maximum Reach                    2033 mm
Number of Axes                    6
Accuracy of Repeatability      <±0,05 mm
Control                                   KR C4

Positioner KUKA DKP400
Number of Axes                    2
Accuracy of Repeatability      ±0,1 mm
Load Capacity                        400 kg

Laser Source Laserline LDF 4000
Maximum Performance          4 kW cw
Extensibility                           10 kW
Wave Length                          1030-1060 nm


Process Optics Laserline LLK-B
Beam Quality                         20-150 mm.mrad
Focal Length                          250 mm
Spot                      ˜               Ø 0,2-30 mm, 4x4 mm, 4x8 mm, 4x16 mm


Demonstration of laser hardening can be found here.



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