Laser Welding: Line Scanners for Beam Shaping and Guiding Alfred G. Arlt Ingenieurbüro für Lasertechnik +Verschleißschutz (ILV) Sulzbacher Str. 4 65824 Schwalbach/Taunus aga@ilv-arlt.de lt
History of ILV: April 1988 Founded as one-men firm by the owner Alfred G. Arlt Process development Consulting and training Marketing of (own) technology patents January 1989 Expanding activities Conception, sales and set up of turnkey systems for Laser material processing (Together with ILV contractors) January 1993 Expanding activities Development, manufacturing and sales of own Laser optics and sensors Scanners for Surface Treatment Scanners for Welding Seam Finder Special Beam Delivery Systems June 2011 Expanding activities Founding of ILV-Anwendungstechnik with 5 low and medium power Laser systems for process development, research and job shop work (Marking, welding of plastics and metal, surface treatment)
Progress in Laser Development Lasers (cw) for material processing Type Industrially Beam Quality Focus Diameter Power up to available since (M 2 )* (mm)** (kw) Nd:YAG Lamp pumped 1970 75 0.810 5 CO 2 1984 17 1.7 0170 0.170 20 Fast axial flow CO 2 Diffusion cooled Nd:YAG Diode pumped Diode Fiber coupled 1994 1.1 0.110 8 1997 35 0.380 5 1997 20 0.400 6 Disc (Yb:YAG) 2003 1.3 0.014 16 Fiber (Yb-Glas) Multi mode Fiber (Yb-Glas) Single mode 2004 1.3 0.014 30 2005 1.05 0.011 10 *) Typical values for 2000 W Lasers **) f = 200 mm and 25 mm beam diameter on focusing optic
The table before shows the continuous improvement of beam quality, with shorter development cycles during the last 10 years. Today, focus diameters of 150 µm and less are state of the art for high-power lasers. In many cases these spots are too narrow for being suitable for welding parts with tolerances and gaps > 0,1 mm In order to solve this problem and also to cover a wide range of applications, flexible optical systems are required to adjust the beam shape on the material surface according to the needs of part geometry, tolerances and/or the type of processing. Typical Power Density for different Applications: Plastic Welding: 100 W/cm 2 Transformation Hardening 2.000 W/cm 2 Cladding: 50.000 W/cm 2 Head Conduction Welding: 400.000000 W/cm 2 Deep Penetration Welding: 1.000.000 W/cm 2
One way to achieve the required power density on the work piece in an area of suitable geometry, is to move a laser beam of sufficient power along one axis back and forth, fast enough*) to transfer the laser energy into the work piece quasi- simultaneously, instead of modifying the laser beam profile itself. For specific purposes a two-dimensional movement is also possible. The figure shows the principal i set up of a line scanner to be used with fiber-coupled high power lasers. With such a unit, frequencies of up to 1000 Hz and amplitudes of up to 20 mm (@ f=200 mm & frequency 150 Hz) are achievable. Advanced controllers (see picture) for this type of scanners also offer the possibility to deliver different levels of laser power along the scan line. With direct water cooled scan mirrors, the actual maximum cwpower possible is 30 kw. *) Experience from electron beam welding and heat ttreatment, t t as well as first tests with line scanners by ILV during the mid-1990s showed that typical scan frequencies must be set to 100 Hz
During dynamic beam shaping at given feed rate the weld seam width is no longer determined by the laser focus spot on the work piece but rather by the elongation amplitude perpendicular to the feed direction. The corresponding power density is then calculated from the laser power, the spot size, and the scan width. To achieve a continuous weld seam, the scanner frequency and the linear feed rate must be set in a way that sufficient overlap is generated. The net power density should be in the range of the power density, required for the chosen process.
Line scanners from ILV are available as add-on for standard welding optics or as stand-alone units with and without transmissive beam shaping components. Examples: Source: Precitec, Gaggenau Source: Trumpf Laser- und Systemtechnik, Ditzingen DCY-Scanner (Stand-alone unit)
Specifications of ILV DC- and DCY-Scanners Maximum laser power : 30 kw Maximum frequency : 1000 Hz Maximum amplitude : 20 mm (f = 200 mm), 150 Hz 3 mm (f = 200 mm), 250 Hz 0.7 mm (f = 200 mm), 600 Hz Controller Power supply : AC 230 V, 50 Hz (others on demand) Power consumption : 1500 W (max.) Mirror unit Maximum mirror diameter : 65 mm Type of mirrors : copper, coated copper, coated aluminum Cooling water flow : Minimum 5 liters per minute Cooling water pressure : Maximum 5 bar Mirror operating temperature : 15 to 60 C Laser Power Control : 32 fields along scan axis time base generated by scanner controller Diagrams of Power Control Settings
Examples for Beam Shaping
Beam Guiding Welding with Dynamic Power Control Line scan with variable power density Lap weld, scan width = 3.0 mm Laser Weld (shaft material X46Cr13) 4-sheet butt weld, scan width = 3.5 mm Dynamic power control: Welding high carbon steel without cold cracking
Application Example Tube to Tube Connection TIG Weld Laser Weld, scan width 1.8 mm Laser Weld, cross section
Production System with Optic for Dynamic Beam Shaping and Guiding Welding of parts for railway vehicles Source: Sondermaschinenbau Calvörde
DC- and DCY-Scanner used in Production of Automotive Parts (Selected) Drive shafts More than 5 Million parts welded since 2002 Exhaust silencer tubes More than 2 Million parts welded since 2004 Car door body More than 2 Million parts welded since 2005 EGR-Bypass Flaps with 14 different welds per part More than 1.6 Million parts welded since 2007