Integrated laser based pre‐tempering at laser welding of AISI 1045 steel by using 3D‐scanner optics

Laser-based pre-heating of laser beam welding with a 3D scanning optics, applied to AISI 1045 steel, is studied. Laser heat-treatable steel challenging due martensitic hardening in combination defects. Pre-tempering aims the reduction cooling rates and microstructure within weld seam. An oscillating defocused was guided over surface for by means scanner optics. During pre-heating, power, speed number cycles were varied. Welding 4000 W 2 m/min focused executed. Thus resulting temperature profile behind ongoing time T8|5 between 800 °C–500 °C significantly extended. Two parameter combinations (15 cycles|600 W|50 mm/s(2) 10 cycles|800 mm/s2) succeeded bainite martensite. By extending 3.11 s(2) 4.17 s2. Thus, average hardness based pre-tempering 487 HV 0.5(2) 455 0.52 achieved. As reference, global at 400 using heating plate can reduce zone from 729 0.5 room 304 5.63 s. Es wird das laserbasierte Vorwärmen des Laserstrahlschweißens mit einer 3D-Scan-Optik, angewandt auf Stahl, untersucht. Das Laserstrahlschweißen von Vergütungsstahl ist aufgrund der martensitischen Härtung Kombination Defekten eine Herausforderung. zielt die Reduzierung Abkühlungsraten und Gefüges innerhalb Schweißnaht. Zum wurde ein oszillierender, defokussierter Laserstrahl mittels 3D-Scanner-Optik über Oberfläche geführt. Während Vorwärmens wurden Laserleistung, Scangeschwindigkeit Anzahl Zyklen variiert. bei fokussiertem geschweißt. Dadurch resultierende Temperaturprofil hinter dem laufenden Abkühlzeit zwischen deutlich verlängert. Zwei Parameterkombinationen Zyklen|600 Zyklen|800 führten zu einem Gefüge aus Bainit Martensit. Durch Verlängerung 3,11 4,17 s2 mittlere Härte für Vorwärmung 0,5(2) 0,52 erreicht. Als Referenz dient globale Heizplatte. Die Schweißzone 0,5 Raumtemperatur 5,63 s reduziert. The (C45) belongs group steels frequently used grade machine automotive industry. strength strongly dependents on technical treatment high carbon content 1. rate has strong influence steels. heat treatment, be controlled obtain desired properties such as improved ductility elimination residual stresses 2-4. process, very local temperatures are reached through energy input 5.This results gradients subsequent quenching. If cannot prevented, this leads melting thus brittle seam 6. Therefore limited ability requires suitable joining processes increase their use industry 7. Tempering specimen before or after delay cooling, change microstructure, prevent failure lack 8, 9. material major weld. It influences that occurs without tempering. In (20 °C) tempering, cracks avoided. yield highly hardened causes thermal exceed 10. > 0.2 %, it favourable perform avoid embrittlement possible cold cracking 11. For necessary tempering during different types high-strength fine-grained (S690QL), high-ductility (S500MC), boron-alloyed (22MnB5) 12-14. an inductor been found common solution. This type annealing implemented fixed position. Another possibility inductive pre- post-tempering. this, position source varies relation beam. All variations have prevented increasing extended time. result, fully not produced optimum case, quenched tempered combined post-annealing austenitic could reduced base 14. study, avoided induction 682 7 consists pearlite, microhardness range 300 0.05 flexible tool well reducing resistance shrinkage mild (S355 J2+N), stainless (X8CrMnNi19-6-3), fine grain structural (S690) already used. processing robot-guided optics 15. welded joints low-alloy ultra-high laser-based fiber shown produce microstructural heat-affected zone. uniform distribution. Specifically, also realized moving spot back forth along path (without material) 16. To sum up, several post-tempering methods sources arc kind investigated achieve significant affected Local one external dynamic still open field investigation. publication deals investigation 1045, power solid state disc laser. First, pre-tempering, plate, process specific distribution behaviour investigated. Afterwards linear carried out, fast under varying changing velocity oscillation movements. pre-heated start welding, cycle depending analysed. study structured two experimental test series. homogenously done, order investigate (static temperature) (dynamic geometry micro structure. second series done area, which directly identical minimize loss pre-tempered few milliseconds essential. optical setup used, offers first deflection homogenous opportunity extremely adapt cross section therefore intensity welding. Hereto At enhanced per brought reaching large defocussed diameter.The defocusing Z- direction aid Z-axis robot. purpose, positioned 50 mm above work piece robot regarding coordinate system. Additionally, further moved higher internal z-axis Figure 1 (left). measured diameter 4.5 mm. focus peace get intensity. z-shifter set −50 mm, 782 μm, (right). Scanning strategy, caustic while preheating (left), Scanstrategie, Position gemessene Laserstrahlkaustik beim Defokussieren zum (links), Schweißen (rechts). examinations out 40 seam, 2a. pendulum movement x-direction. defined cycles, vs Ptemp. overheating reversal points, ramped down 70 % Ptemp length Pweld 30 distance 3 starting point end defects, 2b (below). Schematic representation sequence area (orange) (red). Schematische Darstellung Prozessablaufs Bearbeitungsbereich Schweißens (rot). experiments performed TruDisk 4002 Yb-disk company TRUMPF. system maximum 4 kW wavelength 1030 nm, product 8 mrad. glass core 200 μm. 3D-scanning I-PFO TRUMPF focal 600 760 Rayleigh 17.8 divergence angle 42.7 exhibits elliptical view dimension 320×190 mm2. axis shift ±90 profiles Focus Monitor FM+(Primes) 500 W, 3. Measured W. Gemessenes Strahlintensitätsprofil Laserleistung specimens precise Harry Gestigkeit table below 4a. mounted 6 axes Kuka KR 60 HA. all investigations stationary vertically top parts sufficient adjustment way 4b. Experimental Setup a) control via b) pre-tempering. Versuchsaufbau Versuchsreihe globalen Temperaturregelung Heizplatte laserbasierten Vorwärmung. recorded automated triggered thermographic camera Image IR 8340 Infratec. infrared active cooled InSb detector resolution 640 pixels×512 pixels specified measuring −10 1700 measurement accuracy ±1 K filters. constant parameters speed, respectively m/min. Specimens made dimensions 100×50×6 mm3 Table samples cut blanked flats grinded afterwards. C Si Mn P S Cr Mo Ni Cu Al Cr+Mo+Ni 0.446 0.232 0.663 0.010 0.014 0.08 0.044 0.169 0.295 0.33 0.293 analyzation divided into defect detection structure hardness. impact, heat-affected-zone recorded. Therefore, frame Hz 4. temperature-time-characteristics, mainly gradient, analysed °C–1000 °C, decisive formation microstructure. additional 150 °C–300 validate difference achieved including entire repeated each twice imaging camera. run °C. geometries are: Point P1 P2 middle path, P3 line L1 horizontally centre 5a. evaluation rate, P2. profile, data points Definition positions analysis section, lines section. Festlegung Messpositionen thermografischen Analyse Lage Querschliffs, linearen Mikrohärtemesslinien am Querschliff. determine emissivity initial calibration sample integrated thermocouple plate. Due oxidation amounts Weld creating length, P2, separated, embedded prepared. assessment, polished etched Nital 20 Microscopic images complete created 50-fold magnification Axio Zoom.V16 (Zeiss). microscopic 500-fold Imager.Z2 Vario (Zeiss) electron microscope 10.000 fold Sigma VP created. taken 0.4 “Microscope image area”, 5b. hardness, according Vickers DIN EN ISO 6507–1 0.5, three 0.1 vertical horizontal surface, 2/3 depth, tester Durascan G5 (Struers/ Emcotest). high-temperature placed monitored thermocouple, ensuring addition (RT) switched-off pre-temperature varied steps basic just martensite 345 (calculated 17). expansion zone, sections TP, remelting given depth width, slightly material. While 4.4 increases up 5.0 width 1.7 2.3 aspect ratio (depth/ width) 1.54–2.77. A larger effect seen heat-affected-zone. When considering 2.8 TP = factor 66.4 4.2 function Schweißnahttiefe, Schweißnahtbreite, Wärmeeinflusszonentiefe -breite globaler Abhängigkeit Vorwärmtemperatur den Schweißparametern rate. analyse gradients, evaluated. cool dwell austenite formation. curves, interval decreases steadily curves decreasing temperature, With gradient decreases. looking time, 0.39 s, whereas increased 14.1. Cooling unter als Funktion gemessen Schweißnahtmitte. direction, (P1), (P2) (P3) evaluated, Figures Thermographic center beginning c) 2. Temperature (measurement L1). Thermografieaufnahmen im Messbereich 1000 Schweißnahtmitte Beginn Schweißung, Mitte Schweißung Ende Schweißung. Schweißnahtrichtung (Messlinie differences recognized, 1b, c. cause widespread exists. Temperature-distance diagrams more accurate quantitative comparison preliminary L1), ensure direct comparability, actual zero. (b P2) observed. (room 17.4 (P1) 673 getting pronounced. less high, reduced, 2c. So kept hole length. decreased sections, midline crack 9 Pre-heating this. 250 small imperfections wider, magnification, Mikroskopische Aufnahmen Querschnitte Schweißnahtlänge 50-facher Vergrößerung, Mittellinienriss Raumtemperatur, kleine Defekte Vorwärmung, Unterschiede Wärmeeinflusszone. surrounding cross-sections. exclusively develops pearlite matrix. existing corresponding 10.000-fold show ferrite (light, raised) islands perlite (grey, lamellar) surrounded dashed) traces shows refinement Microstructure detail 1) zone: Base matrix 2) Heat-affected-zone: Ferrite 3) (lamellar) dashed), 4) raised), martensite, 500x 10.000x magnification. Detail globales Vortemperieren Schweißzone: Grundmatrix Martensit Wärmeeinflusszone: Ferrit (hell, erhaben) (grau, gestrichelt) erhaben), Inseln Perlit (gestreift), Martensit.4) (gestreift) Martensit, 500-facher Vergrößerung 10.000-facher Vergrößerung. base, 11a. Inside almost constant. Beyond 5.5 values 273 0.5. Increasing same observed when curve 11b. box plot 11c. 670 approaches samples. corresponds relative 58 %. Micro (Laser m/min) Box-plot diagram TP. Mikrohärte nach (Laserleistung vertikaler Richtung durch Abstand zur horizontaler 0,1 Box-Plot-Diagramm Härteverteilung Schmelzzone Pl, N selected lower W–800 remain point. mm/s numbers (5, 15), tB 24 Thereby E changes 0.8 kJ 5 cycles|400 W|200 14.4 15 mm/s. n