Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/06—Surface hardening
  • C21D1/09—Surface hardening by direct application of electrical or wave energy; by particle radiation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K15/00—Electron-beam welding or cutting
  • B23K15/0006—Electron-beam welding or cutting specially adapted for particular articles

Definitions

• the invention relates to a method for changing the local microstructure on the surface of a material in the solid or liquid phase by means of high-energy radiation with the features of the type described in the preamble of patent claim 1.
• Methods for changing the local microstructure on the surface of a material, the surface of the processing location being heated to a defined temperature by means of high-energy radiation are known per se.
• Lasers such as CO 2 lasers and Nd-YAG high-performance lasers are used for irradiating the surface of the materials of components.
• a workpiece machining device for surface hardening of workpieces is known which works with a laser, specifically with a carbon dioxide laser.
• This processing device has a focusing device for focusing the laser beam onto the workpiece and a radiation detector assigned to this workpiece, which detects the heat radiation of the heated workpiece and in each case delivers an output signal which is dependent on the intensity of this radiation for power control of the laser.
• the laser In the beam path of the laser there is a mirror which is transparent to the radiation with the wavelength of the laser beam and which directs the heat radiation emitted by the workpiece separately to the radiation detector arranged outside the beam path.
• This detector delivers electrical output signal proportional to the strength of the heat radiation, which after amplification is fed as an actual value to a control circuit to which the laser is connected.
• the control loop then strives to maintain the laser power at a target value previously entered in the control loop. It is therefore possible to measure the temperatures directly in the area in which the workpiece is heated. The workpiece is always brought to the same temperature, regardless of the laser output power.
• a method for laser heat treatment which is used for laser hardening, laser soft annealing and laser recrystallization of components in the solid state.
• a radiation pyrometer which only detects the heat radiation of a certain wavelength or a certain wavelength range in isolation, measures the surface temperature along a processing area of the component. With the help of a PID controller, the power of a laser is regulated on-line so quickly that the temperature of the surface in the processing area is always kept constant in a predetermined temperature interval.
• CO 2 lasers and solid-state lasers e.g. Nd-YAG laser.
• metals can be hardened on the surface of components using a CO high-power laser.
• the invention is therefore based on the object of providing a simple and inexpensive method suitable for mass production and a corresponding device for this, which is used in the manufacture of materials or in the post-processing on the surface of the materials during the machining process by regulation
• Defined boundary conditions for the production of certain local microstructures on the surface are created, so that depending on the nature of the material, different local microstructures can be achieved on the surface to a large extent.
• the reproducibility of the machining results should always be achieved given is.
• the advantages of the invention consist in particular in that after the end of the heating phase of the material, the temperature-time profile during cooling is followed exactly, which is done by appropriate measurements on the surface of the processing location.
• This provides a further reference variable for controlling the machining process during the cooling phase, while at the same time online cooling speed control is now possible.
• the temperature-time profile during cooling can be controlled in a precisely defined manner in accordance with the material conditions and the desired or required structure on the surface of the material. This increases the quality of the processing by achieving precisely defined microstructures at the processing location. Due to the exact process monitoring and process control, the reproducibility of the different microstructures within the limits given by the properties of the material is now also possible at any time.
• FIG. 1 shows a schematic representation of the method according to the invention, the sensor being moved with the workpiece
• FIG. 2 temperature-time curve at any observation point during a machining process
• Figure 3 different variants of the processing device, wherein the beam splitting can be done either via prisms, dichroic mirrors or scraper mirrors.
• a laser source not shown in FIG. 1, emits an overall laser beam 1, which is split by a beam splitter 2 into a primary beam 3 and into one or more secondary beams 5, 6, etc.
• the deflection mirrors for the primary and secondary beams can be designed as scraper mirrors, folding mirrors or oblique mirrors.
• Primary and secondary beams therefore form a system coupled via one or more beam splitters.
• a primary high-energy radiation is carried out at the processing location by means of the primary beam 3, and the temperature arising there is selected by means of a temperature sensor 4. measured during the machining process. The measured actual value is correspondingly changed by means of a control unit (not shown here) by changing the emitted power density of the laser beam source in the direction of the required and thus predetermined target value.
• the primary jet 3 thus serves to heat the material.
• the temperature profile is measured continuously by the temperature sensor 4.
• This temperature sensor can be designed, for example, as a pyrometer, as a photodiode or as another temperature sensor which can measure such temperatures.
• the temperature-time profile during the cooling of the material is measured by means of the temperature sensor 4.
• the temperature of the material must be measured at least at two different times during the cooling at the machining site so that the course of the cooling curve can be determined. If the course of the temperature-time course deviates from the desired value, the determined temperature-time course is controlled during the cooling process by carrying out at least one or more further high-energy irradiations of the material at the processing location become.
• secondary beams 5 and 6 are branched off from the total beam 1 via the beam splitter.
• the beam splitter Of course, not only one, but also more than two such secondary beams can be coupled out.
• Corresponding coupling systems between the secondary beams are provided for this.
• the coupling systems are designed to be controllable with respect to the distribution of the radiation components of the total beam, so that any desired temperature-time profile can be achieved by means of the secondary beams in the cooling phase.
• the deviations from the predetermined target values in the form of the required resulting temperature-time profile can be regulated both by means of variable intensity components and also by means of the variable power of the partial beams, the corresponding control devices not being shown and described here in each case.
• a continuous control of the cooling rates is achieved by means of defined temperature-time profiles by means of the method according to the invention and the corresponding device. And in this way, those lines can be approached in a time-temperature diagram that correspond to the desired microstructure of the material in question during cooling.
• a predetermined hardness of the surface material can be achieved, for example, by converting the phases at a specific temperature. With such temperature-time profiles, however, the temperature gradients of the material can also be reduced, and thus a reduction in the thermally induced stresses of the material on the surface can be achieved.
• the coupling system for the primary and secondary beams and also the coupling systems between a plurality of secondary beams for further subdivision of the secondary beams can be designed as movable laser beam splitters.
• the coupling systems between primary beams and secondary beams and the coupling systems between several secondary beams are designed to be controllable with regard to the distribution of the radiation components of the overall beam.
• the distribution of the secondary beam components within the secondary beams is also designed to be changeable.
• temperature sensors 4 are assigned to both the primary radiation and the respective secondary radiation for measuring the temperature at the processing location.
• a beam splitter, a mirror to be imaged and a temperature sensor for a compact, modular beam guiding, Beam shaping and measuring unit combined, the beam guides and the beam shaping are not shown here.
• These modular units are controlled by a higher-level control unit in accordance with the required resultant temperature-time curve during cooling.
• the total laser radiation divided into the primary beam and one or more secondary beams acts and irradiates the surface of the workpiece at the processing location one after the other.
• the variable power of the partial beams and the variable intensity components of the partial beams are also available as controlled variables.
• the beams can be split using prisms, dichroic mirrors or scraper mirrors.
• FIG. 2 shows a temperature-time diagram in which the temperature-time profiles when the local microstructure changes on the surface of the material during high-energy radiation are shown by the device according to the invention or by the method according to the invention.
• the processing process proceeds as follows. At time t 2 , a fixed point of the workpiece enters the primary beam with its surface. This processing location passes through the primary beam 3 in the feed direction 8 with an adjusted and controllable feed speed. This represents the heating phase for the processing location on the surface of the material.
• the temperature sensor 4 checks the maximum temperature reached at the processing location. If this is not sufficiently high, the power share of the primary route is changed, for example, in accordance with the manipulated variables listed above.
• a second temperature sensor 4 detects any deviations between the desired temperature value and the actual temperature value at time t 3 .
• the control mechanisms provided change the manipulated variable of the travel path of the prism and / or the laser power until the deviation is eliminated. All other subcomponents of the secondary path function accordingly at times t 4 , etc.
• the temperature-time profile denoted by 9 represents the required curve during solidification to the desired structure, that is, it forms the target value.
• the temperature-time The curve represents the actual curve, i.e. the actual value, as it arises when the material surface is processed by irradiation with high energy.
• the corrections achieved by the method according to the invention and the associated device can be seen.
• the resulting temperature-time curve is within the permissible range without the required structural structure of the material being changed or impaired.
• an even better approximation to the required target curve can be achieved by additional measuring points or corresponding corrections.
• the usage properties of a material or a component on the surface can be changed in such a way that a desired structural structure of the material is produced which is adapted to the expected loads and can withstand the expected wear.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Laser Beam Processing (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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Cited By (1)

Citations (1)

• 1992
  • 1992-09-24 DE DE19924231956 patent/DE4231956C1/de not_active Expired - Fee Related
• 1993
  • 1993-09-18 WO PCT/DE1993/000896 patent/WO1994006596A1/de not_active Ceased

Patent Citations (1)

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