Kapearailotekniikan käyttö jauhekaarihitsauksessa

Diplomityössä tavoitteena oli tutkia kapearailojauhekaaritekniikan soveltuvuutta konepajakäyttöön ja sen vaikutusta hitsauksen tuottavuuteen sekä hitsin mekaanisiin ominaisuuksiin. Työ tehtiin vertailukokeilla, jossa koehitsaukset suoritettiin eri aineenpaksuuksille siten, että jokaiselle tutkimuksen kohteena olleelle materiaalille tehtiin yksi hitsaus käytössä olevalla jauhekaaritekniikalla, jolloin saatiin vertailukohde, johon uutta kapearailotekniikkaa verrattiin. Tulokset osoittivat, että kapearailotekniikalla 1 palko/palkokerros aineenpaksuudeltaan Pl. 60 mm koekappale saatiin hitsattua n. 39 % nopeammin verrattuna perinteiseen tandem -hitsaukseen. Kyseisellä aineenpaksuudella lisäainelangan kulutus oli n. 41 % ja jauheen kulutus n. 71 % pienempi verrattuna perinteiseen X- railohitsaukseen tandem -menetelmällä. Lisäksi tuli esille, että ”palkoa palonpäälle” -tekniikka on kapearailotekniikoista tehokkain, sillä 2 palkoa/palkokerros menetelmässä railon leveyttä jouduttiin leventämään, jolloin kapearailotekniikan pieni railotilavuus menetettiin. Lisäaineen kulutus tälläkin menetelmällä jäi pienemmäksi verrattuna X- railohitsaukseen. Ennalta pelättyä kuonan irtoamisongelmaa ei kapearailohitsauksessa havaittu, vaan kuona irtosi ongelmitta railon kyljistä. Lisäksi kapearailotekniikalla hitsattujen hitsien lujuudet olivat vertailukelpoiset tandem- ja yksilankamenetelmällä hitsattujen hitsien kanssa.

Welding development of crane main girder

Konecranes Corporation manufactures huge steel structures in 16 factories worldwide, in which the environment and quality varies. The company has a desire to achieve the same weld quality in each factory, regardless of the manufacturing place. The main subject of this master’s thesis was to develop the present box girder crane welding process, submerged arc welding and especially the fillet welding. Throughput time and manufacturing costs can be decreased by welding the full penetration fillet weld without a bevel, changing present groove types for more appropriate ones and by achieving the desired weld quality on the first time. Welding experiments of longitudinal fillet welding were made according to the present challenges, which the manufacturing process is facing. In longitudinal fillet welding tests the main focus was to achieve full penetration fillet weld for 6, 8 and 10 millimeters thick web plates with single and twin wire submerged arc welding. Full penetration was achieved with all the material thicknesses, both with single and twin wire submerged arc welding processes. The main problem concerning the weld was undercutting and shape of the weld bead. The question about insufficiency of presently used power sources with twin wire was risen up during testing, due to the thicknesses that require high welding current. Bigger power source is required when box girders are welded nonstop, if twin wire is used. For single wire process the penetration was achieved with significantly less amperage than with twin wire.

Sellutehtaan vedenkäytön vähentäminen

Työn tarkoituksena oli etsiä mahdollisia kohteita sellutehtaan veden käytön vähen-tämiseksi. Analyysien avulla selvitettiin voidaanko havaittujen kohteiden tällä hetkellä menetettyjä vesivirtoja käyttää uudelleen. Lopuksi arvioitiin miten kierrä-tettävät vedet vaikuttaisivat raakaveden laatuun, mikäli ne yhdistettäisiin tämän joukkoon. Veden käytön vähentämiskohteita etsittiin tutkimalla tehtaan prosessi-kaavioita osastokohtaisesti sekä selvittämällä näin havaittuja kohteita osastoilla. Työn kokeellinen osa koostui vesianalyyseistä. Vesianalyyseissä määritettiin seu-raavat arvot sellutehtaalle tulevasta vedestä: sameus (FTU), kiintoaine, sähkönjoh-tavuus, pH, CODCr, BOD7ATU, kokonaisfosfori P, Mn, Cl, K, Ca, Mg ja AOX. Nämä tehtiin valituista kohteista havaituista tällä hetkellä tehtaalta pois johdetuista mutta mahdollisesti kierrätettävistä vesistä. Työn tuloksien perusteella havaittiin, että seuraavissa tarkasteluun valituissa koh-teissa vedet olivat hyvin puhtaita ja talteen otettavia kierrätykseen. Näitä olivat savukaasupesurin vedet, sekundäärilauhdesäiliön vedet sekä tiivistevedet. Haih-duttamon lämminvesisäiliön sekä kuivauskone 4 kiertovesitornin vedet olivat hieman likaantuneet mutta hyvin kierrätettävissä. Koivulinjan D0-vaiheen, havu-linjan D1-vaiheen sekä kuivauskone 4 lajittamon vesivirtoja ei likaantumisen vuoksi kannattanut kerätä hyötykäyttöön.

Uittonippujen sidelangan valinta ja sitomiskonstruktion suunnittelu

Työssä suunniteltiin uittonippujen sidonnan koneellistamiseksi tarvittavan sidontalangan käsittelylaitteisto. Sen toiminnalliset pääkomponentit ovat langan ohjauskouru, syöttölaite sekä solminta- ja katkaisulaitteet. Lisäksi työssä tehtiin koneelliseen sidontaan sopivan sidontalangan määrityksiä.

Performance and scalability of isolated DC-DC converter topologies in low voltage, high current applications

Fuel cells are a promising alternative for clean and efficient energy production. A fuel cell is probably the most demanding of all distributed generation power sources. It resembles a solar cell in many ways, but sets strict limits to current ripple, common mode voltages and load variations. The typically low output voltage from the fuel cell stack needs to be boosted to a higher voltage level for grid interfacing. Due to the high electrical efficiency of the fuel cell, there is a need for high efficiency power converters, and in the case of low voltage, high current and galvanic isolation, the implementation of such converters is not a trivial task. This thesis presents galvanically isolated DC-DC converter topologies that have favorable characteristics for fuel cell usage and reviews the topologies from the viewpoint of electrical efficiency and cost efficiency. The focus is on evaluating the design issues when considering a single converter module having large current stresses. The dominating loss mechanism in low voltage, high current applications is conduction losses. In the case of MOSFETs, the conduction losses can be efficiently reduced by paralleling, but in the case of diodes, the effectiveness of paralleling depends strongly on the semiconductor material, diode parameters and output configuration. The transformer winding losses can be a major source of losses if the windings are not optimized according to the topology and the operating conditions. Transformer prototyping can be expensive and time consuming, and thus it is preferable to utilize various calculation methods during the design process in order to evaluate the performance of the transformer. This thesis reviews calculation methods for solid wire, litz wire and copper foil winding losses, and in order to evaluate the applicability of the methods, the calculations are compared against measurements and FEM simulations. By selecting a proper calculation method for each winding type, the winding losses can be predicted quite accurately before actually constructing the transformer. The transformer leakage inductance, the amount of which can also be calculated with reasonable accuracy, has a significant impact on the semiconductor switching losses. Therefore, the leakage inductance effects should also be taken into account when considering the overall efficiency of the converter. It is demonstrated in this thesis that although there are some distinctive differences in the loss distributions between the converter topologies, the differences in the overall efficiency can remain within a range of a few percentage points. However, the optimization effort required in order to achieve the high efficiencies is quite different in each topology. In the presence of practical constraints such as manufacturing complexity or cost, the question of topology selection can become crucial.

Novel Methods for Error Modeling and Parameter Identification of a Redundant Serial-Parallel Hybrid Robot

To obtain the desirable accuracy of a robot, there are two techniques available. The first option would be to make the robot match the nominal mathematic model. In other words, the manufacturing and assembling tolerances of every part would be extremely tight so that all of the various parameters would match the “design” or “nominal” values as closely as possible. This method can satisfy most of the accuracy requirements， but the cost would increase dramatically as the accuracy requirement increases. Alternatively, a more cost-effective solution is to build a manipulator with relaxed manufacturing and assembling tolerances. By modifying the mathematical model in the controller, the actual errors of the robot can be compensated. This is the essence of robot calibration. Simply put, robot calibration is the process of defining an appropriate error model and then identifying the various parameter errors that make the error model match the robot as closely as possible. This work focuses on kinematic calibration of a 10 degree-of-freedom (DOF) redundant serial-parallel hybrid robot. The robot consists of a 4-DOF serial mechanism and a 6-DOF hexapod parallel manipulator. The redundant 4-DOF serial structure is used to enlarge workspace and the 6-DOF hexapod manipulator is used to provide high load capabilities and stiffness for the whole structure. The main objective of the study is to develop a suitable calibration method to improve the accuracy of the redundant serial-parallel hybrid robot. To this end, a Denavit–Hartenberg (DH) hybrid error model and a Product-of-Exponential (POE) error model are developed for error modeling of the proposed robot. Furthermore, two kinds of global optimization methods, i.e. the differential-evolution (DE) algorithm and the Markov Chain Monte Carlo (MCMC) algorithm, are employed to identify the parameter errors of the derived error model. A measurement method based on a 3-2-1 wire-based pose estimation system is proposed and implemented in a Solidworks environment to simulate the real experimental validations. Numerical simulations and Solidworks prototype-model validations are carried out on the hybrid robot to verify the effectiveness, accuracy and robustness of the calibration algorithms.

Applications and Benefits of Adaptive Pulsed GMAW

In ship and offshore terminal construction, welded cross sections are thick and the number of welds very high. Consequently, there are two aspects of great importance; cost and heat input. Reduction in the welding operation time decreases the costs of the work force and avoids excessive heat, preventing distortion and other weld defects. The need to increase productivity while using a single wire in the GMAW process has led to the use of a high current and voltage to improve the melting rate. Unfortunately, this also increases the heat input. Innovative GMAW processes, mostly implemented for sheet plate sections, have shown significant reduction in heat input (Q), low distortion and increase in welding speed. The aim of this study is to investigate adaptive pulsed GMAW processes and assess relevant applications in the high power range, considering possible benefits when welding thicker sections and high yield strength steel. The study experimentally tests the usability of adaptive welding processes and evaluates their effects on weld properties, penetration and shapes of the weld bead.The study first briefly reviews adaptive GMAW to evaluate different approaches and their applications and to identify benefits in adaptive pulsed. Experiments are then performed using Synergic Pulsed GMAW, WiseFusionTM and Synergic GMAW processes to weld a T-joint in a horizontal position (PB). The air gap between the parts ranges from 0 to 2.5 mm. The base materials are structural steel grade S355MC and filler material G3Si1. The experiment investigates heat input, mechanical properties and microstructure of the welded joint. Analysis of the literature reveals that different approaches have been suggested using advanced digital power sources with accurate waveform, current, voltage, and feedback control. In addition, studies have clearly indicated the efficiency of lower energy welding processes. Interest in the high power range is growing and a number of different approaches have been suggested. The welding experiments in this study reveal a significant reduction of heat input and a weld microstructure with the presence of acicular ferrite (AF) beneficial for resistance to crack propagation. The WiseFusion bead had higher dilution, due to the weld bead shape, and low defects. Adaptive pulse GMAW processes can be a favoured choice when welding structures with many welded joints. The total heat reduction mitigates residual stresses and the bead shape allows a higher amperage limit. The stability of the arc during the process is virtually spatter free and allows an increase in welding speed.

Sähkögeneraattoriosien hitsauksen tuottavuuden kehittäminen

Hitsauksen tuottavuuteen vaikuttavat hitsausmäärä, käytetyt prosessit ja laatu. Työn teoriaosuudessa tutustutaan hitsauksen tuottavuuteen sekä suunnittelullisesta että valmistuksellisesta näkökulmasta. Hitsauksen laadulliset asiat, kuten laatustandardit ja vaatimukset käydään läpi keskittyen standardin SFS-EN ISO 3834 kattaviin laatuvaatimuksiin. Rikkomaton ja rikkova aineenkoetus ja yleisimmät hitsausvirheet esitetään yleisellä tasolla. Hitsausprosesseista esitetään MIG/MAG- ja MAG-täytelankahitsauksen sekä pulssihitsauksen perusteet. Tässä diplomityössä tutkitaan pulssihitsauksen soveltuvuutta sähkögeneraattorin staattoripaketin eripariliitoksen hitsaukseen ja kykyä parantaa sekä tuottavuutta että laatua. Tutkimus perustuu koehitsauksiin ja niiden perusteella tehtyihin johtopäätöksiin. Lisäksi pohditaan sisätuulettimien hitsauksen kehittämistä ja annetaan kehitysehdotus valmistusprosessista. Koehitsauksien perusteella pulssihitsaus on hyvä prosessiparannus staattoripakettien hitsaukseen. Kohdistettu valokaari ja alhaisempi lämmöntuonti verrattuna perinteiseen MAG-hitsaukseen sekä hitsauksen yksinkertaisuus tuovat etuja eripariliitoksen hitsauksen laatuun. Kustannuslaskelmien myötä hitsausprosessin muutoksen odotetaan tuovan kustannussäästöjä. Hitsauslaadun parantuessa ja jälkityöstön määrän vähentyessä hitsausprosessin muutos on kannattava.

Identification of Some Additional Loss Components in High-Power Low-Voltage Permanent Magnet Generators

Permanent magnet generators (PMG) represent the cutting edge technology in modern wind mills. The efficiency remains high (over 90%) at partial loads. To improve the machine efficiency even further, every aspect of machine losses has to be analyzed. Additional losses are often given as a certain percentage without providing any detailed information about the actual calculation process; meanwhile, there are many design-dependent losses that have an effect on the total amount of additional losses and that have to be taken into consideration. Additional losses are most often eddy current losses in different parts of the machine. These losses are usually difficult to calculate in the design process. In this doctoral thesis, some additional losses are identified and modeled. Further, suggestions on how to minimize the losses are given. Iron losses can differ significantly between the measured no-load values and the loss values under load. In addition, with embedded magnet rotors, the quadrature-axis armature reaction adds losses to the stator iron by manipulating the harmonic content of the flux. It was, therefore, re-evaluated that in salient pole machines, to minimize the losses and the loss difference between the no-load and load operation, the flux density has to be kept below 1.5 T in the stator yoke, which is the traditional guideline for machine designers. Eddy current losses may occur in the end-winding area and in the support structure of the machine, that is, in the finger plate and the clamping ring. With construction steel, these losses account for 0.08% of the input power of the machine. These losses can be reduced almost to zero by using nonmagnetic stainless steel. In addition, the machine housing may be subjected to eddy current losses if the flux density exceeds 1.5 T in the stator yoke. Winding losses can rise rapidly when high frequencies and 10–15 mm high conductors are used. In general, minimizing the winding losses is simple. For example, it can be done by dividing the conductor into transposed subconductors. However, this comes with the expense of an increase in the DC resistance. In the doctoral thesis, a new method is presented to minimize the winding losses by applying a litz wire with noninsulated strands. The construction is the same as in a normal litz wire but the insulation between the subconductors has been left out. The idea is that the connection is kept weak to prevent harmful eddy currents from flowing. Moreover, the analytical solution for calculating the AC resistance factor of the litz-wire is supplemented by including an end-winding resistance in the analytical solution. A simple measurement device is developed to measure the AC resistance in the windings. In the case of a litz-wire with originally noninsulated strands, vacuum pressure impregnation (VPI) is used to insulate the subconductors. In one of the two cases studied, the VPI affected the AC resistance factor, but in the other case, it did not have any effect. However, more research is needed to determine the effect of the VPI on litz-wire with noninsulated strands. An empirical model is developed to calculate the AC resistance factor of a single-layer formwound winding. The model includes the end-winding length and the number of strands and turns. The end winding includes the circulating current (eddy currents that are traveling through the whole winding between parallel strands) and the main current. The end-winding length also affects the total AC resistance factor.

Ohjelmistoradion hyödyntäminen tiedonsiirron tutkimisessa LVDC-verkossa

Työssä tutkitaan tiedonsiirtoa eri modulaatioilla, bittinopeuksilla ja amplitudin voimakkuuksilla ja tuloksia tarkastellaan Bit Error Ration avulla. Signaaleja siirrettiiin myös koodattuna ja vertailtiin koodauksen etuja ja haittoja verrattuna koodaamattomaan tietoon. Datavirta kulkee AXMK-kaapelissa, joko tasasähkön mukana, tai maadoituskaapelissa. Tuloksissa havaittiin, että suurempi bittinopeus ei kasvattanut häviöiden määrää. Koodauksen käyttö toisaalta vähenti bittivirheiden määrää.

Optimization of parameters for fiber laser-MAG hybrid welding in shipbuilding applications

The Arctic region becoming very active area of the industrial developments since it may contain approximately 15-25% of the hydrocarbon and other valuable natural resources which are in great demand nowadays. Harsh operation conditions make the Arctic region difficult to access due to low temperatures which can drop below -50 °C in winter and various additional loads. As a result, newer and modified metallic materials are implemented which can cause certain problems in welding them properly. Steel is still the most widely used material in the Arctic regions due to high mechanical properties, cheapness and manufacturability. Moreover, with recent steel manufacturing development it is possible to make up to 1100 MPa yield strength microalloyed high strength steel which can be operated at temperatures -60 °C possessing reasonable weldability, ductility and suitable impact toughness which is the most crucial property for the Arctic usability. For many years, the arc welding was the most dominant joining method of the metallic materials. Recently, other joining methods are successfully implemented into welding manufacturing due to growing industrial demands and one of them is the laser-arc hybrid welding. The laser-arc hybrid welding successfully combines the advantages and eliminates the disadvantages of the both joining methods therefore produce less distortions, reduce the need of edge preparation, generates narrower heat-affected zone, and increase welding speed or productivity significantly. Moreover, due to easy implementation of the filler wire, accordingly the mechanical properties of the joints can be manipulated in order to produce suitable quality. Moreover, with laser-arc hybrid welding it is possible to achieve matching weld metal compared to the base material even with the low alloying welding wires without excessive softening of the HAZ in the high strength steels. As a result, the laser-arc welding methods can be the most desired and dominating welding technology nowadays, and which is already operating in automotive and shipbuilding industries with a great success. However, in the future it can be extended to offshore, pipe-laying, and heavy equipment industries for arctic environment. CO2 and Nd:YAG laser sources in combination with gas metal arc source have been used widely in the past two decades. Recently, the fiber laser sources offered high power outputs with excellent beam quality, very high electrical efficiency, low maintenance expenses, and higher mobility due to fiber optics. As a result, fiber laser-arc hybrid process offers even more extended advantages and applications. However, the information about fiber or disk laser-arc hybrid welding is very limited. The objectives of the Master’s thesis are concentrated on the study of fiber laser-MAG hybrid welding parameters in order to understand resulting mechanical properties and quality of the welds. In this work only ferrous materials are reviewed. The qualitative methodological approach has been used to achieve the objectives. This study demonstrates that laser-arc hybrid welding is suitable for welding of many types, thicknesses and strength of steels with acceptable mechanical properties along very high productivity. New developments of the fiber laser-arc hybrid process offers extended capabilities over CO2 laser combined with the arc. This work can be used as guideline in hybrid welding technology with comprehensive study the effect of welding parameter on joint quality.

Hitsauslankojen kallistuskulmien vaikutus hitsausliitoksen ominaisuuksiin S355-rakenneteräksen tandem-MAG-pienahitsauksessa

Tämä kandidaatintyö on tutkimus hitsauslankojen kallistuskulmien vaikutuksesta hitsausliitoksen ominaisuuksiin tandem-MAG-pienahitsauksessa S355-rakenneteräkselle. Kokeellinen osuus suoritettiin Lappeenrannan teknillisen yliopiston hitsaustekniikan laboratoriossa jatkotutkimuksena Binbin Yanin diplomityölle ”Influence of wire configurations of welding S355 structural steel with tandem GMAW”. Tutkimuksen tavoitteena on määrittää tandem-MAG-hitsauksessa käytettyjen hitsauslankojen kallistuskulmien vaikutus hitsausliitoksen ominaisuuksiin. Teoriaosuuden tavoitteena on selvittää myös muiden hitsausparametrien vaikutus hitsausliitoksen ominaisuuksiin sekä perehtyä hitsisulan käyttäytymiseen terästen tandem-MAG-hitsauksessa.

Two-phase flow measurements with spacer grid in a rod bundle geometry

Heat transfer effectiveness in nuclear rod bundles is of great importance to nuclear reactor safety and economics. An important design parameter is the Critical Heat Flux (CHF), which limits the transferred heat from the fuel to the coolant. The CHF is determined by flow behaviour, especially the turbulence created inside the fuel rod bundle. Adiabatic experiments can be used to characterize the flow behaviour separately from the heat transfer phenomena in diabatic flow. To enhance the turbulence, mixing vanes are attached to spacer grids, which hold the rods in place. The vanes either make the flow swirl around a single sub-channel or induce cross-mixing between adjacent sub-channels. In adiabatic two-phase conditions an important phenomenon that can be investigated is the effect of the spacer on canceling the lift force, which collects the small bubbles to the rod surfaces leading to decreased CHF in diabatic conditions and thus limits the reactor power. Computational Fluid Dynamics (CFD) can be used to simulate the flow numerically and to test how different spacer configurations affect the flow. Experimental data is needed to validate and verify the used CFD models. Especially the modeling of turbulence is challenging even for single-phase flow inside the complex sub-channel geometry. In two-phase flow other factors such as bubble dynamics further complicate the modeling. To investigate the spacer grid effect on two-phase flow, and to provide further experimental data for CFD validation, a series of experiments was run on an adiabatic sub-channel flow loop using a duct-type spacer grid with different configurations. Utilizing the wire-mesh sensor technology, the facility gives high resolution experimental data in both time and space. The experimental results indicate that the duct-type spacer grid is less effective in canceling the lift force effect than the egg-crate type spacer tested earlier.