A novel procedure for establishing clinching parameters for high strength steel sheet

The building industry has a particular interest in using clinching as a joining method for frame constructions of light-frame housing. Normally many clinch joints are required in joining of frames.In order to maximise the strength of the complete assembly, each clinch joint must be as sound as possible. Experimental testing is the main means of optimising a particular clinch joint. This includes shear strength testing and visual observation of joint cross-sections. The manufacturers of clinching equipment normally perform such experimental trials. Finite element analysis can also be used to optimise the tool geometry and the process parameter, X, which represents the thickness of the base of the joint. However, such procedures require dedicated software, a skilled operator, and test specimens in order to verify the finite element model. In addition, when using current technology several hours' computing time may be necessary. The objective of the study was to develop a simple calculation procedure for rapidly establishing an optimum value for the parameter X for a given tool combination. It should be possible to use the procedure on a daily basis, without stringent demands on the skill of the operator or the equipment. It is also desirable that the procedure would significantly decrease thenumber of shear strength tests required for verification. The experimental workinvolved tests in order to obtain an understanding of the behaviour of the sheets during clinching. The most notable observation concerned the stage of the process in which the upper sheet was initially bent, after which the deformation mechanism changed to shearing and elongation. The amount of deformation was measured relative to the original location of the upper sheet, and characterised as the C-measure. By understanding in detail the behaviour of the upper sheet, it waspossible to estimate a bending line function for the surface of the upper sheet. A procedure was developed, which makes it possible to estimate the process parameter X for each tool combination with a fixed die. The procedure is based on equating the volume of material on the punch side with the volume of the die. Detailed information concerning the behaviour of material on the punch side is required, assuming that the volume of die does not change during the process. The procedure was applied to shear strength testing of a sample material. The sample material was continuously hot-dip zinc-coated high-strength constructional steel,with a nominal thickness of 1.0 mm. The minimum Rp0.2 proof stress was 637 N/mm2. Such material has not yet been used extensively in light-frame housing, and little has been published on clinching of the material. The performance of the material is therefore of particular interest. Companies that use clinching on a daily basis stand to gain the greatest benefit from the procedure. By understanding the behaviour of sheets in different cases, it is possible to use data at an early stage for adjusting and optimising the process. In particular, the functionality of common tools can be increased since it is possible to characterise the complete range of existing tools. The study increases and broadens the amount ofbasic information concerning the clinching process. New approaches and points of view are presented and used for generating new knowledge.

Electromagnetic Design of a Solid Steel Rotor Motor for Demanding Operation Environments

The solid-rotor induction motor provides a mechanically and thermally reliable solution for demanding environments where other rotor solutions are prohibited or questionable. Solid rotors, which are manufactured of single pieces of ferromagnetic material, are commonly used in motors in which the rotationspeeds exceed substantially the conventional speeds of laminated rotors with squirrel-cage. During the operation of a solid-rotor electrical machine, the rotor core forms a conductor for both the magnetic flux and the electrical current. This causes an increase in the rotor resistance and rotor leakage inductance, which essentially decreases the power factor and the efficiency of the machine. The electromagnetic problems related to the solid-rotor induction motor are mostly associated with the low performance of the rotor. Therefore, the main emphasis in this thesis is put on the solid steel rotor designs. The rotor designs studied in thisthesis are based on the fact that the rotor construction should be extremely robust and reliable to withstand the high mechanical stresses caused by the rotational velocity of the rotor. In addition, the demanding operation environment sets requirements for the applied materials because of the high temperatures and oxidizing acids, which may be present in the cooling fluid. Therefore, the solid rotors analyzed in this thesis are made of a single piece of ferromagnetic material without any additional parts, such as copper end-rings or a squirrel-cage. A pure solid rotor construction is rigid and able to keep its balance over a large speed range. It also may tolerate other environmental stresses such as corroding substances or abrasive particles. In this thesis, the main target is to improve the performance of an induction motor equipped with a solid steel rotor by traditional methods: by axial slitting of the rotor, by selecting a proper rotor core material and by coating the rotor with a high-resistive stainless ferromagnetic material. In the solid steel rotor calculation, the rotor end-effects have a significant effect on the rotor characteristics. Thus, the emphasis is also put on the comparison of different rotor endfactors. In addition, a corrective slip-dependent end-factor is proposed. The rotor designs covered in this thesis are the smooth solid rotor, the axially slitted solid rotor and the slitted rotor having a uniform ferromagnetic coating cylinder. The thesis aims at design rules for multi-megawatt machines. Typically, mega-watt-size solidrotor machines find their applications mainly in the field of electric-motor-gas-compression systems, in steam-turbine applications, and in various types of largepower pump applications, where high operational speeds are required. In this thesis, a 120 kW, 10 000 rpm solid-rotor induction motor is usedas a small-scale model for such megawatt-range solid-rotor machines. The performance of the 120 kW solid-rotor induction motors is determined by experimental measurements and finite element calculations.

Automated formulation of optimisation models for steel beam structures

Over 70% of the total costs of an end product are consequences of decisions that are made during the design process. A search for optimal cross-sections will often have only a marginal effect on the amount of material used if the geometry of a structure is fixed and if the cross-sectional characteristics of its elements are property designed by conventional methods. In recent years, optimalgeometry has become a central area of research in the automated design of structures. It is generally accepted that no single optimisation algorithm is suitable for all engineering design problems. An appropriate algorithm, therefore, mustbe selected individually for each optimisation situation. Modelling is the mosttime consuming phase in the optimisation of steel and metal structures. In thisresearch, the goal was to develop a method and computer program, which reduces the modelling and optimisation time for structural design. The program needed anoptimisation algorithm that is suitable for various engineering design problems. Because Finite Element modelling is commonly used in the design of steel and metal structures, the interaction between a finite element tool and optimisation tool needed a practical solution. The developed method and computer programs were tested with standard optimisation tests and practical design optimisation cases. Three generations of computer programs are developed. The programs combine anoptimisation problem modelling tool and FE-modelling program using three alternate methdos. The modelling and optimisation was demonstrated in the design of a new boom construction and steel structures of flat and ridge roofs. This thesis demonstrates that the most time consuming modelling time is significantly reduced. Modelling errors are reduced and the results are more reliable. A new selection rule for the evolution algorithm, which eliminates the need for constraint weight factors is tested with optimisation cases of the steel structures that include hundreds of constraints. It is seen that the tested algorithm can be used nearly as a black box without parameter settings and penalty factors of the constraints.

A novel approachfor assessing the fatigue strength of ultrasonic impact treated welded structures.

It is commonly observed that complex fabricated structures subject tofatigue loading fail at the welded joints. Some problems can be corrected by proper detail design but fatigue performance can also be improved using post-weld improvement methods. In general, improvement methods can be divided into two main groups: weld geometry modification methods and residual stress modification methods. The former remove weld toe defects and/or reduce the stress concentrationwhile the latter introduce compressive stress fields in the area where fatigue cracks are likely to initiate. Ultrasonic impact treatment (UIT) is a novel post-weld treatment method that influences both the residual stress distribution andimproves the local geometry of the weld. The structural fatigue strength of non-load carrying attachments in the as-welded condition has been experimentally compared to the structural fatigue strength of ultrasonic impact treated welds. Longitudinal attachment specimens made of two thicknesses of steel S355 J0 have been tested for determining the efficiency of ultrasonic impacttreatment. Treated welds were found to have about 50% greater structural fatigue strength, when the slope of the S-N-curve is three. High mean stress fatigue testing based on the Ohta-method decreased the degree of weld improvement only 19%. This indicated that the method could be also applied for large fabricated structures operating under high reactive residual stresses equilibrated within the volume of the structure. The thickness of specimens has no significant effect tothe structural fatigue strength. The fatigue class difference between 5 mm and 8 mm specimen was only 8%. It was hypothesized that the UIT method added a significant crack initiation period to the total fatigue life of the welded joints. Crack initiation life was estimated by a local strain approach. Material parameters were defined using a modified Uniform Material Law developed in Germany. Finite element analysis and X-ray diffraction were used to define, respectively, the stress concentration and mean stress. The theoretical fatigue life was found to have good accuracy comparing to experimental fatigue tests.The predictive behaviour of the local strain approach combined with the uniformmaterial law was excellent for the joint types and conditions studied in this work.

Welding time models for cost calculations in the early stages of the design process

It is generally accepted that between 70 and 80% of manufacturing costs can be attributed to design. Nevertheless, it is difficult for the designer to estimate manufacturing costs accurately, especially when alternative constructions are compared at the conceptual design phase, because of the lack of cost information and appropriate tools. In general, previous reports concerning optimisation of a welded structure have used the mass of the product as the basis for the cost comparison. However, it can easily be shown using a simple example that the use of product mass as the sole manufacturing cost estimator is unsatisfactory. This study describes a method of formulating welding time models for cost calculation, and presents the results of the models for particular sections, based on typical costs in Finland. This was achieved by collecting information concerning welded products from different companies. The data included 71 different welded assemblies taken from the mechanical engineering and construction industries. The welded assemblies contained in total 1 589 welded parts, 4 257 separate welds, and a total welded length of 3 188 metres. The data were modelled for statistical calculations, and models of welding time were derived by using linear regression analysis. Themodels were tested by using appropriate statistical methods, and were found to be accurate. General welding time models have been developed, valid for welding in Finland, as well as specific, more accurate models for particular companies. The models are presented in such a form that they can be used easily by a designer, enabling the cost calculation to be automated.

Analytical Study on the Influence of Geometrical Parameters on the Fatigue Strength of Welds with Undercuts

The purpose of this study is to analyze the influence of geometric parameters on the fatigue strength of the welded joint. The thesis includes the analytical study pertaining to variation of undercut and the weld toe radius. The theoretical part includes the concepts of fracture mechanics, different stages of the crack propagation and finally the results. The numerical results are obtained from FRANC2D/L. The results show that the fatigue strength of the welded structure depends on the parameters of the welds such as the weld toe radius, weld angle, height of the undercut and plate thickness. The results show that the fatigue life can be improved by having the undercut as minimum as possible. However there has been significant variation on the fatigue life of the structure when the weld toe radius is increased.

Tandem-GMA Welding of Low Alloy Structural Steel

The Tandem-GMAW method is the latest development as the consequences of improvements in the welding methods. The twin-wire and then the Tandem-method with the separate power sources has got a remarkable place in the welding of many types of materials with different joint types. The biggest advantage of Tandem welding method is the flexibility of choosing both the electrodes of different types from each other according to the type of the parent material. This is possible because of the feasibility of setting the separate welding parameters for both the wires. In this thesis work the effect of the variation in three parameters on the weld bead in Tandem-GMA welding method is studied. Theses three parameters are the wire feed rate in the slave wire, the wire feed rate in the master wire and the voltage difference in both the wires. The results are then compared to study the behaviour of the weld bead with the change in these parameters.

Hitsauksen laadunvarmistus teräsrakentamisessa

Suomessa on tapahtunut 2000-luvulla neljä kappaletta ns. suuronnettomuuden vaaratilanteiksi luokiteltavaa teräsrakenteiden vaurioitumisesta aiheutunutta onnettomuutta, joista yksi johti ihmishengen menetykseen. Onnettomuuden syynä oli huonolaatuisten pienahitsien pettäminen kuormituksen alaisena, joka puolestaan oli seurausta puutteellisesta hitsauksen laadunvarmistuksesta. Teräsrakenteiden valmistus ja hitsaus eivät ole yhtä tarkan viranomaisvalvonnan alaista kuten esimerkiksi painelaitteiden valmistus, vaikka teräsrakenteiden vaurioitumisesta aiheutuvat riskit ovat erittäin merkittäviä. Työn tavoitteena oli tutustua onnettomuustapauksiin, teräsrakenteista annettuihin viranomaismääräyksiin sekä ohjeisiin ja esittää laadunvarmistustoimenpiteitä, joiden avulla voidaan varmistua hitsaustyön riittävästä laadusta teräsrakentamisessa. Näitä laadunvarmistustoimenpiteitä ovat mm. hitsaushenkilöstön pätevöinti, hitsausohjeiden käyttäminen, ainetta rikkomattomat tarkastukset ja rakennesuunnitelmien tarkastukset. Toisena tavoitteena oli kartoittaa rakenteiden valmistajien ja pääurakoitsijoiden nykyistä tilannetta laadunvarmistuksen osalta sekä selvittää kiinnostusta kolmannen osapuolen tarjoamiin laadunvarmistuspalveluihin. Kyselyiden perusteella laadunvarmistuspalveluille on olemassa kysyntää tietyin kustannuksiin liittyvin varauksin. Palveluista eniten kiinnostusta herättivät ainetta rikkomattomat tarkastukset ja rakennesuunnitelmien tarkastukset.

Assessing intellectual capital in a research institute environment in steel industry

Diplomityön tavoitteena oli tutkia aineettoman pääoman hallintaa terästeollisuuden tutkimuslaitosympäristössä, sekä luoda mittaristo kuvaamaan sen tilaa ja kehitystä. Työn rajausten mukaan aineeton pääoma jaettiin Annie Brookingin jaottelun mukaan, ja tarkasteluun valittiin teollisoikeudet sekä henkilöstövoimavarat. Empiirinen osa työstä perustui pääasiassa haastatteluihin sekä Case –yrityksen sisäisiin julkaisuihin. Näitä pyrittiin tulkitsemaan kvalitatiivisten tutkimusmenetelmien oppien mukaan. Tutkimustulosten perusteella voidaan todeta teollisoikeuksien hyödyntämisen olevan suhteellisen vähäistä terästeollisuuden parissa. Syitä tähän on työssä käsitelty melko laajasti. Henkilöstön kehittäminen pitkällä tähtäimellä sekä tiedonkulun tehostaminen henkilöstön keskuudessa ovat puolestaan asioita, joihin kiinnitetään kyseisellä teollisuudenalalla kiitettävässä määrin huomiota. Työn loppupuolella esitelty aineettoman pääoman mittaristo tarjoaa yritykselle työkalun, jonka avulla voidaan monipuolisesti arvioida tätä yrityksille nykyisin elintärkeää asiaa. Lopullista ratkaisumallia se ei aineettoman pääoman mittaamiseen tarjoa, mutta luo kuitenkin tärkeän ensiaskeleen kohti tulevaisuuden yhä kehittyneempiä mittausmenetelmiä.

Suojakaasuseoksen koostumuksen vaikutus CO2-laser-MAG-hybridihitsauksessa

Hitsaavassa teollisuudessa kilpailukyvyn säilyttäminen edellyttää hitsauksen tehokkuuden nostoa. Niinpä metalliteollisuus etsii kuumeisesti uusia yhä tehokkaampia hitsausmenetelmiä. CO2-laserin ja MAG:in yhdistelmän muodostamalla hybridihitsauksella saadaan aikaan syvä tunkeuma kuten laserhitsauksessa, mutta sallitaan laserhitsausta väljemmät railotoleranssit. Samalla muodonmuutokset vähenevät huomattavasti verrattuna perinteiseen kaarihitsaukseen. Kaariavusteisessa laserhitsauksessa yhdistetään laserhitsaukseen perinteinen kaarihitsaus eli MIG/MAG-, TIG- tai plasmahitsaus. Menetelmää voidaan kutsua myös hybridihitsaukseksi ja sillä hyödynnetään molempien prosessien edut välttyen yksittäisten prosessien haitoilta. Prosessin haittapuolena on parametrien suuri määrä, joka on rajoittanut menetelmän käyttöönottoa. Diplomityössä tutkittiin suojakaasuseoksen koostumuksen vaikutusta rakenneteräksen CO2-laser-MAG-hybridihitsauksessa. Laserhitsauksen ja MAG-hitsauksen suojakaasuvirtaukset yhdistettiin siten, että heliumseosteinen suojakaasu tuotiin MAG-polttimen kaasukuvun kautta. Suojakaasun heliumpitoisuus nostettiin niin korkeaksi, että estettiin laserhitsauksen muodostaman plasman syntyminen. Samalla hitsauskokeissa opittiin paremmin ymmärtämään prosessia ja sen parametrien riippuvuutta toisiinsa. Tutkitut suojakaasuseokset koostuivat heliumista, argonista ja hiilidioksidista. Hitsauskokeiden perusteella havaittiin, että suojakaasuseoksen optimaalinen heliumpitoisuus on 40-50 %. Tällöin laserin tunkeumaa häiritsevää plasmapilveä ei synny ja prosessi on stabiili. Päittäisliitosten hitsauksessa suojakaasuseoksen 2 %:n CO2-pitoisuudella saadaan aikaan hyvin vähän huokosia sisältävä hitsi, jonka tunkeumaprofiilin muoto ja liittymä perusaineeseen on juoheva. Pienaliitoksilla 7 %:n CO2-pitoisuudella prosessi pysyy stabiilina ja vähäroiskeisena. Tunkeuma hieman levenee hitsin keskeltä ja hitsin liittyminen perusaineeseen on juoheva.CO2-laser-MAG-hybridihitsauksella aikaansaadaan laadukkaita hitsejä taloudellisesti, mikäli käytetyt parametrit ovat oikein valittuja. Parametrit on sovitettava jokaiseen hitsaustapaukseen erikseen, eikä niitä välttämättä voida suoraan käyttää toisessa tapauksessa.

Roolit, vuorovaikutus ja päätöksenteko johtoryhmätyöskentelyssä, case Imatra Steel Imatran terästehdas

Tutkimus on luonteeltaan laadullinen ja sen tavoitteena on tarkastella johtoryhmätyöskentelyä ja päätöksentekoa roolien ja vuorovaikutuksen kautta. Roolit perustuvat havainnointitutkimukselle Imatra Steelin Imatran terästehtaan johtoryhmässä. Tutkimuksessa on lisäksi hyödynnetty teemahaastatteluja ja yrityksen dokumentteja, ja näin ollen aineistotriangulaatiota. Tutkimuksen painotus on empiirisellä osalla. Tutkimuksen avulla todetaan, että johtoryhmätyöskentely kohdeyrityksessä on perinteitä noudattelevaa ja keskittynyt informaation jakamiseen sekä toiminnan koordinointiin. Strateginen päätöksenteko ja dynaaminen johtoryhmätyöskentely ovat vähemmän painottuneita. Päätökset johtoryhmän kokouksissa syntyvät keskustelujen tuloksena puheenjohtajan tehdessä lopullisen ratkaisun.

Lujien terästen hitsauksen kehittäminen

Työn teoriaosuudessa käsitellään lujia hitsattavia teräksiä sekä niiden hitsauksessa huomioitavia erityispiirteitä. Työssä esitellään hitsattavuuden arviointiin kehitettyjä teoreettisia menetelmiä sekä otetaan kantaa hitsauksen suoritustekniikkaan ja lisäainevalintaan. Myös lujien terästen hitsauksessa tyypilliset hitsausvirheet on käsitelty tässä työssä. Työn kokeellisessa osassa selvitettiin metsäteknologian tuotteita valmistavan metalliyrityksen käyttämien lujien terästen hitsattavuus ja hitsauksen esivalmistelujen tarpeellisuus. Kokeelliseen osioon kuului myös sopivan lisäainelangan valinta sekä tarkempaan tarkasteluun valitun esimerkkituotteen hitsien laadun selvittäminen. Tutkimuksissa käytettyjä menetelmiä olivat makro- ja mikrohietutkimus, hitsausliitoksen poikittainen vetokoe, Vickersin kovuuskoe ja murtokoe. Tarkasteluissa peilautuu myös hitsauksen automatisoinnin vaikutukset lujien terästen hitsaukseen. Kokeellisessa osiossa huomattiin nuorrutettujen terästen pehmeneminen liian suurella lämmöntuonnilla. Termomekaanisesti valssatut teräkset ovat paremmin hitsattavissa kuin nuorrutetut ja karkaistut teräkset. Kyseessä olevassa yrityksessä hitsattavien materiaalien paksuudet ovat pääsääntöisesti niin ohuita, ettei korotettua työlämpötilaa tarvita. Alilujat lisäaineet soveltuvat hitsauslisäaineeksi tuotantokäyttöön muutamia tuotekohtaisia poikkeuksia lukuun ottamatta.

Determining risk potential through accidents and near-accidents: an empirical study in a steel factory

Fatal and permanently disabling accidents form only one per I cent of all occupational accidents but in many branches of industry they account for more than half the accident costs. Furthermore the human suffering of the victim and his family is greater in severe accidents than in slight ones. For both human and economic reasons the severe accident risks should be identified befor injuries occur. It is for this purpose that different safety analysis methods have been developed . This study shows two new possible approaches to the problem.. The first is the hypothesis that it is possible to estimate the potential severity of accidents independent of the actual severity. The second is the hypothesis that when workers are also asked to report near accidents, they are particularly prone to report potentially severe near accidents on the basis of their own subjective risk assessment. A field study was carried out in a steel factory. The results supported both the hypotheses. The reliability and the validity of post incident estimates of an accident's potential severity were reasonable. About 10 % of accidents were estimated to be potentially critical; they could have led to death or very severe permanent disability. Reported near accidents were significantly more severe, about 60 $ of them were estimated to be critical. Furthermore the validity of workers subjective risk assessment, manifested in the near accident reports, proved to be reasonable. The studied new methods require further development and testing. They could be used both in routine usage in work places and in research for identifying and setting the priorities of accident risks.

The effects of real time control of welding parameters on weld quality in plasma arc keyhole welding

Joints intended for welding frequently show variations in geometry and position, for which it is unfortunately not possible to apply a single set of operating parameters to ensure constant quality. The cause of this difficulty lies in a number of factors, including inaccurate joint preparation and joint fit up, tack welds, as well as thermal distortion of the workpiece. In plasma arc keyhole welding of butt joints, deviations in the gap width may cause weld defects such as an incomplete weld bead, excessive penetration and burn through. Manual adjustment of welding parameters to compensate for variations in the gap width is very difficult, and unsatisfactory weld quality is often obtained. In this study a control system for plasma arc keyhole welding has been developed and used to study the effects of the real time control of welding parameters on gap tolerance during welding of austenitic stainless steel AISI 304L. The welding tests demonstrated the beneficial effect of real time control on weld quality. Compared with welding using constant parameters, the maximum tolerable gap width with an acceptable weld quality was 47% higher when using the real time controlled parameters for a plate thickness of 5 mm. In addition, burn through occurred with significantly larger gap widths when parameters were controlled in real time. Increased gap tolerance enables joints to be prepared and fit up less accurately, saving time and preparation costs for welding. In addition to the control system, a novel technique for back face monitoring is described in this study. The test results showed that the technique could be successfully applied for penetration monitoring when welding non magnetic materials. The results also imply that it is possible to measure the dimensions of the plasma efflux or weld root, and use this information in a feedback control system and, thus, maintain the required weld quality.

Commodity Price Driven Risk Management from Viewpoint of High Grade Steel Alloys

The study of price risk management concerning high grade steel alloys and their components was conducted. This study was focused in metal commodities, of which nickel, chrome and molybdenum were in a central role. Also possible hedging instruments and strategies for referred metals were studied. In the literature part main themes are price formation of Ni, Cr and Mo, the functioning of metal exchanges and main hedging instruments for metal commodities. This section also covers how micro and macro variables may affect metal prices from the viewpoint of short as well as longer time period. The experimental part consists of three sections. In the first part, multiple regression model with seven explanatory variables was constructed to describe price behavior of nickel. Results were compared after this with information created with comparable simple regression model. Additionally, long time mean price reversion of nickel was studied. In the second part, theoretical price of CF8M alloy was studied by using nickel, ferro-chrome and ferro-molybdenum as explanatory variables. In the last section, cross hedging possibilities for illiquid FeCr -metal was studied with five LME futures. Also this section covers new information concerning possible forthcoming molybdenum future contracts as well. The results of this study confirm, that linear regression models which are based on the assumption of market rationality, are not able to reliably describe price development of metals at issue. Models fulfilling assumptions for linear regression may though include useful information of statistical significant variables which have effect on metal prices. According to the experimental part, short futures were found to incorporate the most accurate information concerning the price movements in the future. However, not even 3M futures were able to predict turning point in the market before the faced slump. Cross hedging seemed to be very doubtful risk management strategy for illiquid metals, because correlations coefficients were found to be very sensitive for the chosen time span.