Anna Unt
@lut.fi
Mechanical engineering
LUT University
RESEARCH INTERESTS
additive manufacturing of metals
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Patricia Nyamekye, Anna Unt, Antti Salminen, and Heidi Piili
MDPI AG
Laser based powder bed fusion (L-PBF) is used to manufacture parts layer by layer with the energy of laser beam. The use of L-PBF for building functional parts originates from the design freedom, flexibility, customizability, and energy efficiency of products applied in dynamic application fields such as aerospace and automotive. There are challenges and drawbacks that need to be defined and overcome before its adaptation next to rivaling traditional manufacturing methods. Factors such as high cost of L-PBF machines, metal powder, post-preprocessing, and low productivity may deter its acceptance as a mainstream manufacturing technique. Understanding the key cost drivers of L-PBF that influence productivity throughout the whole lifespan of products will facilitate the decision-making process. Functional and operational decisions can yield profitability and increase competitiveness among advanced manufacturing sectors. Identifying the relationships between the phases of the life cycle of products influences cost-effectiveness. The aim of the study is to investigate the life cycle cost (LCC) and the impact of design to it in additive manufacturing (AM) with L-PBF. The article provides a review of simulation driven design for additive manufacturing (simulation driven DfAM) and LCC for metallic L-PBF processes and examines the state of the art to outline the merits, demerits, design rules, and life cycle models of L-PBF. Practical case studies of L-PBF are discussed and analysis of the interrelating factors of the different life phases are presented. This study shows that simulation driven DfAM in the design phase increases the productivity throughout the whole production and life span of L-PBF parts. The LCC model covers the whole holistic lifecycle engineering of products and offers guidelines for decision making.
Heikki Saariluoma, Aki Piiroinen, Anna Unt, Jukka Hakanen, Tuomo Rautava, and Antti Salminen
MDPI AG
Ensuring the precision and repeatability of component assembly in the production of electric vehicle (EV) battery modules requires fast and accurate measuring methods. The durability of EV battery packs depends on the quality of welded connections, therefore exact positioning of the module components is critical for ensuring safety in exploitation. Laser welding is a non-contact process capable of welding dissimilar materials with high precision, for that reason it has become the preferred joining method in battery production. In high volume manufacturing, one of the main production challenges is reducing the time required for assessment of dimensional and geometrical accuracy prior to joining. This paper reviews the challenges of EV battery design and manufacturing and discusses commercially available scanner-based measurement systems suitable for fabrication of battery pack components. Versatility of novel metrological systems creates new opportunities for increasing the production speed, quality and safety of EV battery modules.
Y.A. Bistrova, E.A. Shirokina, R.V. Mendagaliev, M.O. Gushchina, and A. Unt
Trans Tech Publications, Ltd.
Review focuses on describing of mechanical properties of the components manufactured via direct laser depositionfrom cold resistant steel material. The results of tensile and impact testing are presented and microstructures of the fractures are shown. The process of laser deposition of cold-resistant steels, the formation of structures, as well as the mechanical properties of these samples are poorly understood. The results of tensile and impact tests are presented, and microstructures are shown. Mechanical tests for impact strength were carried out at a temperature of -40˚С, with different laser radiation powers. The results are given using the as-received powder, as well as used powder with a different mixing ratio, and the results are analyzed. As a result of the study, it was found that the fractional composition of the 09XH2MD alloy powder affects the mechanical characteristics of samples obtained by direct laser deposition. The effect of recycled powder on the mechanical properties of the obtained samples is given, the optimal laser deposition regimes are selected
R.V. Mendagaliyev, A.A. Voropaev, O.G. Klimova-Korsmik, N.V. Lebedeva, and A. Unt
Elsevier BV
Ilya Nikolaevich Udin, A.A. Voropaev, and A. Unt
Trans Tech Publications, Ltd.
Laser technologies deservedly take their place in modern mechanical engineering production. Using laser source for welding has already become common. However, the creation of critical welded constructions is impossible without extensive technological surveys, which can be greatly simplified by using a computational experiment. To achieve this goal, special programs are usually used. That can be unjustified difficult and thereby awkward for technological practice. The article describes an application built on the basis of a simplified model for calculating the temperature field for the cases of laser and laser-arc welding of internal fillet welds as well as single-sided T-joints and simultaneous double-sided welds. The results of calculations by the model and comparing them with experimental data have shown that it is sufficiently adequate for use in technological purposes. The developed application contemporaneously has a simple and intuitive interface, does not require significant computational resources and can be used for quick preliminary estimation of the result of welding for the selected type of weld.
Stefan Grünenwald, Anna Unt, and Antti Salminen
Elsevier BV
Anna Unt, Ilkka Poutiainen, Stefan Grünenwald, Mikhail Sokolov, and Antti Salminen
MDPI AG
Laser welding of thick plates in production environments is one of the main applications of high power lasers; however, the process has certain limitations. The small spot size of the focused beam produces welds with high depth-to-width aspect ratio but at times fails to provide sufficient reinforcement in certain applications because of poor gap bridging ability. The results of welding shipbuilding steel AH36 with thickness of 8 mm as a single-sided T-joint using a 10 kW fiber laser are presented and discussed in this research paper. Three optical setups with process fibers of 200 µm, 300 µm and 600 µm core diameters were used to study the possibilities and limitations set by the beam delivery system. The main parameters studied were beam inclination angle, beam offset from the joint plane and focal point position. Full penetration joints were produced and the geometry of the welds was examined. It was found that process fibers with smaller core diameter produce deeper penetration but suffer from sensitivity to beam positioning deviation. Larger fibers are less sensitive and produce wider welds but have, in turn, lower penetration at equivalent power levels.
Ivan Bunaziv, Odd M. Akselsen, Antti Salminen, and Anna Unt
Elsevier BV
Antti Salminen, Farhang Farrokhi, Anna Unt, and Ilkka Poutiainen
Laser Institute of America
The recently developed direct-quenched ultrahigh strength steels have a combination of high tensile strength and toughness properties at subzero temperatures down to −80 °C. The low carbon content of the material is beneficial for weldability. Modern high power lasers provide an excellent opportunity to modify the focal point diameter by changing the feeding fiber diameter, collimation and focal length, and thus modify the beam intensity and heat input in actual welding process. In this study, butt joints of Optim 960 QC direct-quenched ultrahigh strength steel with a thickness of 8 mm were welded with 10 kW fiber laser with various different optical setups in order to evaluate the characteristics of the joints within the range of low to high heat inputs possible for this welding process. The mechanical properties of the joints were studied by subjecting the specimens to a number of destructive tests of mechanical properties. The weld metal hardness and tensile strength was tested. It was found that high quality butt joints with superior tensile strength could be obtained. However, having a high level of all these properties in the joint narrows, the process parameters' window and the heat input needs to be strictly controlled.
Anna Unt and Antti Salminen
Laser Institute of America
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.
Anna Unt, Ilkka Poutiainen, and Antti Salminen
Elsevier BV
Anna Unt, Ilkka Poutiainen, and Antti Salminen
Elsevier BV
A. Unt, E. Lappalainen, and A. Salminen
Elsevier BV
Antti Salminen, Elin Westin, Esa Lappalainen, and Anna Unt
Laser Institute of America
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...
Anna Unt, Heidi Piili, Marika Hirvimäki, Matti Manninen, and Antti Salminen
Laser Institute of America
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 ...
S. Maryashin, A. Unt, and V. P. Gapontsev
SPIE
We have developed an all-fiber format 10-mJ energy and 200 W average power Yb-doped laser. Based on a seed that utilizes first relaxation peaks and 65-um multimode fiber amplifier, the laser produces 300 ns pulses at 1-50 kHz variable repetition frequencies. Wall plug efficiency of 25% and 10 m delivery output with isolated head are essential features for industrial applications.