Berndt Brenner

Precise hardening with high-power diode lasers using beam-shaping mirror optics

Heat Treatment is one of the most promising application of multi kilowatt high power diode lasers. Providing a sufficient beam quality HPDLs have the advantage of their high efficiency comparing to Nd:YAG-lasers. Application of scanning mirror optics for multi kilowatt lasers is well known at CO2- or Nd:YAG-lasers. Fraunhofer IWS has developed a special driver unit, which generates automatically an optimized scanning function to provide a stress adapted intensity profile. Know the application of this technology at multi kilowatt high power diode lasers has been implemented successfully. Using 2.5 kW diode laser power hardening tracks of 30 mm in width and a penetration of about 1 mm are possible. Applying the temperature guide laser power controller LompocPro additionally, stress adapted hardening of edges with varying cross sections became possible. Besides hardening this system allows heat treatment with a rectangular beam of 5 x 85 mm2. Some applications show the performance of this technology.

New developments in high power diode laser welding

Welding thin sheet metal with high power diode lasers closes the feed rate gap between conventional techniques like TIG- or plasma-welding and CO2- or Nd:YAG-laser welding. Because of its size a high power diode laser can be integrated in common mobile linear welding devices. The weld seams are narrower comparing to TIG-welding, even with filler wire. Deep penetration welding with filler wire is performed with a lower heat input if a high power diode laser is used. That minimizes distortion and refinishing. Some applications for mobile use of high power diode lasers are presented. Heat treatment of conventional or laser beam welded carbon steel or TRIP-steel sheets is used to avoid cracking. High power diode lasers are well suited for that task. Surface temperature controlled post heat treatment of crack sensitive welds is presented in the paper.Welding thin sheet metal with high power diode lasers closes the feed rate gap between conventional techniques like TIG- or plasma-welding and CO2- or Nd:YAG-laser welding. Because of its size a high power diode laser can be integrated in common mobile linear welding devices. The weld seams are narrower comparing to TIG-welding, even with filler wire. Deep penetration welding with filler wire is performed with a lower heat input if a high power diode laser is used. That minimizes distortion and refinishing. Some applications for mobile use of high power diode lasers are presented. Heat treatment of conventional or laser beam welded carbon steel or TRIP-steel sheets is used to avoid cracking. High power diode lasers are well suited for that task. Surface temperature controlled post heat treatment of crack sensitive welds is presented in the paper.

Innovations in heat treatment with high power diode lasers

Using high power diode lasers for steel hardening is the kick-off for laser beam hardening in lots of industrial applications. The very high efficiency, the compact size and the shorter wavelength are advantages of high power diode lasers which are available up to 6 kW laser power. A new laser hardening system was developed to meet the industrial demands for a reproducible, economy-priced, and flexible laser hardening tool. It includes a High power diode laser, a cost-effective CNC-machine, a fast surface temperature control unit, and a special CNC-postprocessor. The base is a standard four-axis-milling-machine. Different lasers can be used. For instance we adapted a 2.5 kW-system with a flexible beam shaping unit. The surface temperature control unit tunes the laser power for a temperature accuracy of ±5 K at a selectable point of the laser spot. On-line control and storage of process data are possible if necessary for industrial applications. The CNC-postprocessor reduces the time for CNC-programming of components without CAD-data and a complicated shape. The postprocessor has an integrated look-ahead-function to change the feed rate as a function of heat outflow at convex and concave shaped components. The performance of this system will be shown at some industrial applications.Using high power diode lasers for steel hardening is the kick-off for laser beam hardening in lots of industrial applications. The very high efficiency, the compact size and the shorter wavelength are advantages of high power diode lasers which are available up to 6 kW laser power. A new laser hardening system was developed to meet the industrial demands for a reproducible, economy-priced, and flexible laser hardening tool. It includes a High power diode laser, a cost-effective CNC-machine, a fast surface temperature control unit, and a special CNC-postprocessor. The base is a standard four-axis-milling-machine. Different lasers can be used. For instance we adapted a 2.5 kW-system with a flexible beam shaping unit. The surface temperature control unit tunes the laser power for a temperature accuracy of ±5 K at a selectable point of the laser spot. On-line control and storage of process data are possible if necessary for industrial applications. The CNC-postprocessor reduces the time for CNC-programming of...

Integrated heat treatment – Comparison of different machine concepts

Heat treatment of machine components or automotive parts traditionally is done at separate facilities or companies. Very effective manufacturing becomes possible if heat treatment processes can be integrated in line to avoid logistics and to save time and money. The need of qualified heat treatment experts prevents manufactures from applying heat treatment technologies so far. Laser heat treatment is very suitable for integration in production lines. And with a certain amount of hard- and software tools it becomes possible to decrease the barrier of applying heat treatment in production lines. A short overview over latest developments of these tools is given. In the framework of governmental supported and industrial projects a wide variety of solutions have been installed during the last years. A comparison gives answers which concept suites best for different conditions of for instance mass production and or single part manufacturing.Heat treatment of machine components or automotive parts traditionally is done at separate facilities or companies. Very effective manufacturing becomes possible if heat treatment processes can be integrated in line to avoid logistics and to save time and money. The need of qualified heat treatment experts prevents manufactures from applying heat treatment technologies so far. Laser heat treatment is very suitable for integration in production lines. And with a certain amount of hard- and software tools it becomes possible to decrease the barrier of applying heat treatment in production lines. A short overview over latest developments of these tools is given. In the framework of governmental supported and industrial projects a wide variety of solutions have been installed during the last years. A comparison gives answers which concept suites best for different conditions of for instance mass production and or single part manufacturing.

Induction assisted laser welding of advanced high strength steels to increase the formability of welded automotive body structures

Advanced high-strength multi phase steels are currently approaching to practical application in the automotive body industry. The outstanding mechanical properties of these materials, e.g. high strength and excellent formability, base on their multi phase structure. Due to high productivity and low heat input, laser welding is a profitable production procedure for joining these materials in semi-finished production and in body in white manufacturing. But the enhanced content of alloying elements of high strength multi phase steels causes an increased seam hardness which results in a reduced ductility within the weld metal and the HAZ and leads to a severely restricted formability of the welded structure. In order to improve the mechanical properties of the welded joint several strategies of induction assisted laser welding have been investigated. The optimized welding procedure realizes a hardness reduction and a significant increase of ductility. This makes the adjustment of the weld seam formability possible and improves the joint properties adapted to the functional requirements. The formability of laser-induction welded structures of various materials have been discovered by determination of forming limit curves. Different preformed material states have been investigated too, in order to determine the influence of work hardening effects. The results enable the assessment of the forming behavior of complex welded components as well as the estimation of the material performance in case of crash.Advanced high-strength multi phase steels are currently approaching to practical application in the automotive body industry. The outstanding mechanical properties of these materials, e.g. high strength and excellent formability, base on their multi phase structure. Due to high productivity and low heat input, laser welding is a profitable production procedure for joining these materials in semi-finished production and in body in white manufacturing. But the enhanced content of alloying elements of high strength multi phase steels causes an increased seam hardness which results in a reduced ductility within the weld metal and the HAZ and leads to a severely restricted formability of the welded structure. In order to improve the mechanical properties of the welded joint several strategies of induction assisted laser welding have been investigated. The optimized welding procedure realizes a hardness reduction and a significant increase of ductility. This makes the adjustment of the weld seam formability pos...

Fast and innovative determination of parameters for steel hardening with high-power diode lasers

Laser Beam Hardening with High Power Diode Lasers is presented as an excellent method for local heat treatment and minimum distortion. An overview is given about several strategies for local heat treatment and different industrial applications. Precise measuring and controlling of the surface temperature makes the process very reliable and is an essential tool for industrial users. To keep a constant penetration of the hardening zone at constant surface temperatures the feed rate can be adapted to local heat flow conditions. A former postprocessor of Fraunhofer IWS generates a CNC-program for the treatment and changes the feed rate in dependence of the surface shape. The new processor additionally considers local heat flow variations of a part caused by boreholes, grooves and changing local thickness. The processing is very fast and can be applied for solving daily problems of laser beam hardening. Some examples show the performance of the new postprocessor.

Computational process parameter optimization for laser beam transformation hardening

Laser beam transformation hardening is rapidly growing in popularity as a method to achieve high quality surface hardened zones. At the same time, the complexity of the parts and the requirements are increasing. Currently a direct calculation of the hardening parameters is only possible on very basic geometries, therefore an experimental approach is almost always used instead. But cost and time considerations, as well as rising demands on quality and process stability, make it unavoidable to explore new ways to determine the process parameters.This paper presents a new approach to find the parameters semi-automatically. The approach, a self-optimizing finite differences method (FDM) simulation, was pinpointed as the most promising method in a former investigation. To prove its applicability, a new software package was developed to calculate the feed rates for laser hardening on two-dimensional shaped parts. Several differently-shaped work pieces with complex geometries (complexity as seen from a hardening-process point of view) were used for testing. The results from the simulation were applied on real parts to evaluate the quality of the parameter prediction. The tests showed not only a good agreement of the simulation with reality, but also that the automatic parameter calculation was able to find suitable process parameters as required.Laser beam transformation hardening is rapidly growing in popularity as a method to achieve high quality surface hardened zones. At the same time, the complexity of the parts and the requirements are increasing. Currently a direct calculation of the hardening parameters is only possible on very basic geometries, therefore an experimental approach is almost always used instead. But cost and time considerations, as well as rising demands on quality and process stability, make it unavoidable to explore new ways to determine the process parameters.This paper presents a new approach to find the parameters semi-automatically. The approach, a self-optimizing finite differences method (FDM) simulation, was pinpointed as the most promising method in a former investigation. To prove its applicability, a new software package was developed to calculate the feed rates for laser hardening on two-dimensional shaped parts. Several differently-shaped work pieces with complex geometries (complexity as seen from a hardening...

Innovation in laser hybrid technology for aluminum welding

Innovative developments in the area of hybrid welding for aluminum integrate conventional shielded arc welding techniques, such as MIG, TIG and Plasma with CO2 or Nd:YAG lasers. The objective is to achieve a stable and reliable industrial process, which accommodates the requirements for joint fit-up and misalignment tolerances, and at the same time lower the demands for edge preparation and increase welding speed or penetration.The paper will compare the weld properties and mechanical behavior of the aluminum alloy 5754 in respect to the hybrid welding process. The welds are analyzed by comparing results from macroscopic analysis, tensile testing, and micro hardness measurements, as well as optical inspections. In the final part of the presentation different applications are introduced, such as a dashboard support and tailor welded blanks.Innovative developments in the area of hybrid welding for aluminum integrate conventional shielded arc welding techniques, such as MIG, TIG and Plasma with CO2 or Nd:YAG lasers. The objective is to achieve a stable and reliable industrial process, which accommodates the requirements for joint fit-up and misalignment tolerances, and at the same time lower the demands for edge preparation and increase welding speed or penetration.The paper will compare the weld properties and mechanical behavior of the aluminum alloy 5754 in respect to the hybrid welding process. The welds are analyzed by comparing results from macroscopic analysis, tensile testing, and micro hardness measurements, as well as optical inspections. In the final part of the presentation different applications are introduced, such as a dashboard support and tailor welded blanks.

Induction assisted laser-cladding a new and effective method for producing high wear resistant coatings on steel components

Despite better wear resistance two problems hinder the wide industrial application of laser-cladding: 1) low cladding speeds and deposition rates; and 2) crack formation (within the clad when using heat treatable steels as base material and within brittle hard-facing alloys). To avoid these disadvantages, an additional power source, which is suitable for the laser-cladding process, is needed. The purpose of this additional power source is to reduce the temperature gradient within the clad and base material while cooling and to deliver supplementary inexpensive energy. Induction heating is a smart, easily adjusted and adaptable technique to address this need.The combination of induction preheating followed by laser-cladding, for example, makes it possible to coat high carbon steels (AISI 1043) such as cold work tool steels (AISI O2) with hard, wear resistant alloys (Nicrobor 40, Deloro 60). Although cracks within the clad can be avoided in every case, induction assisted laser-cladding allows the simultaneous generation of martensitic layers within the base material. This opens the possibility for laser-cladding and induction heat treatment in one step. Furthermore the cladding speed and the deposition rate can be increased by ten times over conventional laserbeam-cladding. As a result, production cost can be reduced despite higher technological expenditure. Nevertheless, the typical advantage of laser-cladding (namely, low dilution of base material into the clad material) is maintained.Despite better wear resistance two problems hinder the wide industrial application of laser-cladding: 1) low cladding speeds and deposition rates; and 2) crack formation (within the clad when using heat treatable steels as base material and within brittle hard-facing alloys). To avoid these disadvantages, an additional power source, which is suitable for the laser-cladding process, is needed. The purpose of this additional power source is to reduce the temperature gradient within the clad and base material while cooling and to deliver supplementary inexpensive energy. Induction heating is a smart, easily adjusted and adaptable technique to address this need.The combination of induction preheating followed by laser-cladding, for example, makes it possible to coat high carbon steels (AISI 1043) such as cold work tool steels (AISI O2) with hard, wear resistant alloys (Nicrobor 40, Deloro 60). Although cracks within the clad can be avoided in every case, induction assisted laser-cladding allows the simultaneo...

Laser-multi-pass-welding of aluminiun and steel with sheet thickness above 50 mm

Thick-walled components made of steel or aluminum alloys are widely used for industrial applications.Welded steel components with sheet thicknesses of 50 mm and above are used for example in big mobile cranes, housings of turbines for power plants and for the base plate of servo-hydraulic presses for automotive body parts etc.Thick-walled welded aluminum components can be found in applications of the chemicals industry and for transportation of liquid natural gases such as LNG tanker.For both material types conventional arc welding technologies are state of the art, often manually performed. Caused by size of the welding torch and the limited penetration depth of multi-pass welding, grove angles of 45° or more are essential. This leads to a high volume weld metal and a high heat input into the base material as well as to a high consumption of filler material. Weld distortion and therefore straightening of the components are cost drivers, too.The paper will be present the latest developments at the Fraunhofer IWS for laser-multi-pass-welding (laser-MPNG) using brilliant solid state laser with laser power of approximately 3 kW for welding aluminum as well as high power diode laser with up to 10 kW for welding of steel.Brilliant laser sources (fiber, disk) with a beam parameter product of 0.4 mm mrad and laser power up to 3 kW are used for multi-pass-narrow-gap welding of aluminum for welding depth of 50 mm and above. Very low groove angles of less than 4° are used, which leads to seam width of max. 4 mm@50 mm welding depth. Using high power diode laser with laser power of up to 10kW the groove angle can be reduced to 12° by using an edge preparation by plasma cutting as known from conventional arc welding technologies.Summarized potential industrial application will be presented. A comparison of laser-multi-pass-narrow-gap welding with the state of the art conventional welding technologies will be given with respect to welding speed, energy input per unit length as well as filler material consumption.Thick-walled components made of steel or aluminum alloys are widely used for industrial applications.Welded steel components with sheet thicknesses of 50 mm and above are used for example in big mobile cranes, housings of turbines for power plants and for the base plate of servo-hydraulic presses for automotive body parts etc.Thick-walled welded aluminum components can be found in applications of the chemicals industry and for transportation of liquid natural gases such as LNG tanker.For both material types conventional arc welding technologies are state of the art, often manually performed. Caused by size of the welding torch and the limited penetration depth of multi-pass welding, grove angles of 45° or more are essential. This leads to a high volume weld metal and a high heat input into the base material as well as to a high consumption of filler material. Weld distortion and therefore straightening of the components are cost drivers, too.The paper will be present the latest developments at the Fraunho...