Anna Unt

Effect of welding parameters and the heat input on weld bead profile of laser welded T-joint in structural steel

The high power fiber laser has become one of the most efficient energy sources for deep penetration welding processes used in heavy manufacturing and marine industries. Combinations of cost-efficient, easily automatable process together with fairly mobile and flexible welding equipment have raised high expectations for improved quality and economic feasibility. In this study, the fillet welding of a low alloyed structural steel was studied using a 10 kW fiber laser. Plates of 8 mm thick AH36 were welded as a T-joint configuration in flat (1F) and horizontal (2F) positions using either an autogenous laser welding or a hybrid laser arc welding process. The effect of heat input on the weld bead geometry was investigated using one variable at a time approach. The impact of single process parameter such as laser power of 4.5–6 kW, welding speed of 0.5–2.5 m/min, beam inclination angle of 6°–15°, focal point position of −2 to +2 mm, and welding positions of 1F and 2F were studied. All welds were visually evaluated for weld imperfections described in EN ISO 13919-1 standard. Penetration depth, geometries of the fusion and heat affected zones, and hardness profiles were measured. Produced joints have a high depth to width ratio and a small heat affected zone; full penetration welds with acceptable weld quality on both sides of the joint were produced. The parameter configurations for optimizing the welding processes are proposed.

Effect of gas shielding and heat input on autogenous welding of duplex stainless steel

Stainless steel is increasingly being used in various applications where the laser process may be the perfect tool for welding autogenously. Use of the keyhole welding mode typically assures high weld quality and productivity. Heat tint and discoloration on the surface may decrease the corrosion resistance and have to be removed or minimized. With laser welding, it is possible to limit the weld bead and root oxidization and thereby decrease the need for post-weld cleaning. The main drawback of using a keyhole when welding duplex stainless steels is the high cooling rate, which can cause unfavorable phase balance in weld metal. Thus addition of over-alloyed filler metal or even post-weld annealing is required. Another solution is to use laser hybrid welding to increase the heat input and add filler metal. This is, however, not an attractive choice for welding thin materials and in continuous production. The excellent beam quality of modern high-brightness lasers can, together with high power provide a great opportunity to shorten the total welding time, but the difficulty in obtaining suitable phase balance remains or is even enhanced. This study concentrates on testing the effect of dynamic beam forming on the laser beam absorptivity and resulting weld microstructure in order to define the usability of this technique for welding of thin duplex stainless steel sheets. The differences between various focal spot configurations were analyzed together with the effect of gas shielding technique. The focal spot size and shape had a significant effect on the absorption and heat input and thus affected the weld metal microstructure.Stainless steel is increasingly being used in various applications where the laser process may be the perfect tool for welding autogenously. Use of the keyhole welding mode typically assures high weld quality and productivity. Heat tint and discoloration on the surface may decrease the corrosion resistance and have to be removed or minimized. With laser welding, it is possible to limit the weld bead and root oxidization and thereby decrease the need for post-weld cleaning. The main drawback of using a keyhole when welding duplex stainless steels is the high cooling rate, which can cause unfavorable phase balance in weld metal. Thus addition of over-alloyed filler metal or even post-weld annealing is required. Another solution is to use laser hybrid welding to increase the heat input and add filler metal. This is, however, not an attractive choice for welding thin materials and in continuous production. The excellent beam quality of modern high-brightness lasers can, together with high power provide a grea...

Laser scribing of stainless steel with and without work media

The advantages such as tight restrictions for heat and mass transfer make micro-/milli scale devices of mixing and droplet formation viable to become widely used in specialty chemical industry. Small dimensions and simple geometry ensure laminar flow and mixing through diffusion, ensuring well-defined behavior of mixing and short reaction times. Combining dry etching by laser beam with wet chemical etching is expected to reduce the production costs of these novel devices.In this study the manufacturing of grooves in stainless steel SS 316L by means of laser micro-/milli processing was investigated. Deep and narrow channels with depth to width ratio of 1:1 at least are preferable, width is allowed to vary from 10-500 micrometer. Lasers used for this study were: 5 kW IPG YLR-5000 S, 200 W IPG YLS-200-SM-WC, 1 kW IPG YLR-1000-SM fiber lasers, 400 W Powerlase diode pumped Nd:YAG laser and 14 W diode pumped Nd:YVO4 laser. Chemical assisted laser scribing is also included in this study.Preliminary results show possibility to obtain channels with desired parameters in pulsed mode laser machining. However, investment cost for CW (continuous wave) lasers per kilowatt are in order of magnitude smaller than for pulsed lasers, that’s why the study was essentially focusing on lasers operating in CW mode. Optimal scribing parameters were defined by adjusting laser power, number of repetitions and speed. Preliminary experiments done without any media resulted in low quality grooves with moderate depth and burned edges. It was concluded in this study that finding a suitable chemical to improve to scribing process is a key moment of getting channels with acceptable quality.The advantages such as tight restrictions for heat and mass transfer make micro-/milli scale devices of mixing and droplet formation viable to become widely used in specialty chemical industry. Small dimensions and simple geometry ensure laminar flow and mixing through diffusion, ensuring well-defined behavior of mixing and short reaction times. Combining dry etching by laser beam with wet chemical etching is expected to reduce the production costs of these novel devices.In this study the manufacturing of grooves in stainless steel SS 316L by means of laser micro-/milli processing was investigated. Deep and narrow channels with depth to width ratio of 1:1 at least are preferable, width is allowed to vary from 10-500 micrometer. Lasers used for this study were: 5 kW IPG YLR-5000 S, 200 W IPG YLS-200-SM-WC, 1 kW IPG YLR-1000-SM fiber lasers, 400 W Powerlase diode pumped Nd:YAG laser and 14 W diode pumped Nd:YVO4 laser. Chemical assisted laser scribing is also included in this study.Preliminary results show ...