Many automotive components are made of Al-Si coated ultra-high strength boron steel (UHSS) and are produced by hot stamping process. In this process, the workpiece is heated to an austenitizing temperature and is then formed and quenched simultaneously between the tools to achieve the desired shape and high strength. During hot stamping process, friction and wear occur which affect formability and maintenance intervals for tool replacement and repair. To repair worn tools, metal is deposited by fusion welding technique. The tribological behaviour of repair welded tool steel sliding against Al-Si coated UHSS has not been studied in detail and there is a need to investigate if the modified tool surface will affect friction and wear. Hot stamping, similar to many manufacturing processes, is affected by the global mega trend of digitalization and Industry 4.0. To monitor the process and optimize the control and operation are the main aims. In view of this, tribological condition monitoring is a promising approach that can allow measurement of physical properties such as vibrations, temperatures, and acoustic emission to be coupled to the tribological response of the system. The aim is to monitor the hot stamping process and enable early detection of changes in friction and wear which can be used for e.g. optimized maintenance and minimized scrap. The aim of this M.Sc. thesis was to improve the robustness of hot forming processes by studying the tribological behaviour of repair welded tool steel sliding against Al-Si coated UHSS under conditions relevant for hot stamping. Another aim was to obtain more predictable tool maintenance by the implementation of acoustic emission measurement system on a hot-strip tribometer and correlating condition monitoring signals to friction and wear phenomena. The tribological tests were carried out using a hot-strip tribometer in conditions representative of a hot stamping process of automotive components. Acoustic emission during sliding between hot work tool steel and different automotive component material surfaces was measured at room temperature in the same strip drawing tribometer and correlated to friction and wear of the surfaces to get more predictable maintenance intervals. Tool steel specimens were welded with the same material as the base material QRO90. Before conducting the tribological test, the repair welded tool steel pin cross-section was polished, etched, and observed under optical microscope and SEM to analyze the effect of Tungsten Inert Gas (TIG) welding process on the microstructure. The analysis was completed with EDS to study the elements in the microstructure. Microhardness was measured to obtain the microhardness profile from the repair welded tool steel pin surface to the bulk in order to study the effect of different microstructures on the mechanical properties. The weight and surface roughness of the pins were measured before the tribological test. After the test was finished, the weight of the pins was measured to calculate the weight difference. The sliding surface of the pins and the strips were photographed. The sliding surface of the pins was also observed and analyzed using SEM and EDS after the test to study wear characteristic of the repair welded tool steel at high temperatures. Acoustic emission signal from the sliding was studied using Toolox44 pins with surface roughness 300-400 nm and with lay direction parallel and perpendicular to sliding direction. Toolox44 pins were sliding against uncoated UHSS, as-delivered Al-Si coated UHSS, and heat-treated Al-Si coated UHSS strips. Acoustic emission was measured during the sliding at the same time as COF measurement. Weight of the pins was measured before and after the test and the wear damage on both surfaces was photographed. COF, AE signals in the time and frequency domain, and wear damage were compared and analyzed. It is found that repair welded tool steel has similar COF compared to the original hot work tool steel with the largest weight gain from the test at 700 ⁰C due to compaction galling mechanism with slower lump formation and the presence of wear particles, transfer layer, and formation of lumps. The weight gain is smaller from the test at 750 ⁰C due to faster lump formation. The weight loss from the test at 600 ⁰C is due to abrasive wear mechanism. SEM micrographs revealed that the repair welded tool steel surface and transfer layers can be found beneath a transfer layer. Wear particles adhered on the repair welded tool steel surface come from broken transfer layer or directly from Al-Si coated UHSS. A change in wear mechanism is indicated by acoustic emission burst signals or gradual amplitude change in the time domain. Frequency analysis of AE signals revealed a change in wear mechanism due to the formation of transferred material in the form of a lump causes AE signals with peaks at higher frequencies above 0.3 MHz to shorten.

Os projetos de carrocerias veiculares atuais procuram desenvolver estruturas leves, seja para reduzir o consumo de combustível, no caso dos motores de combustão interna, seja para maior autonomia de bateria, no caso dos veículos elétricos e híbridos. Redução no consumo de combustível significa redução na emissão de poluentes. As estruturas precisam ser leves, mas cada vez mais resistentes e rígidas a fim de proporcionar máximo conforto e segurança aos ocupantes. Estas premissas têm levado ao contínuo desenvolvimento dos materiais. No caso dos aços, um dos processos que tem permitido a melhora significativa das propriedades mecânicas é a estampagem a quente. Nos últimos anos, as peças estampadas a quente têm ocupado lugar de destaque na estrutura das carrocerias veiculares por estarem em sintonia com as demandas mencionadas. Há muitas pesquisas em curso para esta tecnologia, seja nos materiais, nos meios de produção, nos revestimentos e em aplicações. O aço mais utilizado neste processo, 22MnB5, também apresenta o chamado efeito bake hardening; a tensão de escoamento é aumentada após tratamento térmico realizado em temperaturas próximas a 200 °C. Neste trabalho, visando à melhoria nas propriedades mecânicas, amostras foram tratadas termicamente na faixa de temperatura supracitada. Após isso, dados obtidos de ensaios mecânicos foram inseridos em programas de simulação de impacto lateral cujo resultado foi a redução na intrusão na célula de sobrevivência. O efeito bake hardening também propiciou um aumento na absorção da energia de impacto em teste estático feito com barras de proteção lateral. O mecanismo metalúrgico envolvido no fenômeno, devido à difusão de intersticiais foi evidenciado no ensaio de atrito interno. / The current auto body projects seek to build light structures whose immediate impact is in the reduction in fuel consumption of internal combustion engines or in longer battery life for electric and hybrid vehicles. Reduction in fuel consumption means reduced emissions. The structures need to be lightweight, but increasingly resistant to provide maximum comfort and safety to the occupants. These demands led to the continuous development of new materials. In the case of the steels hot stamping has allowed significant improvement in the mechanical properties. In recent years, hot stamped parts took prominent place in the structure of auto bodies to be in line with the mentioned demands. There are a lot of researches lines for this technology: materials, modes of production, coatings and applications. The most commonly used steel in this process, 22MnB5, also exhibits the bake hardening effect: its yield strength is increased after thermal treatment at temperatures close to 200 °C. To verify this improvement in the mechanical properties, samples were thermally treated. After that, data obtained from mechanical tests were inserted into side-crash simulation programs that resulted in a reduction in intrusion in the passengers compartment. The bake hardening effect also provided an increase in the absorption of the impact energy in a static test done with door beam. The metallurgical mechanism involved in the phenomenon, due to the movement of interstitial was evidenced in the internal friction test.

O processo de estampagem é influenciado por diferentes variáveis, tais como, propriedades mecânicas e rugosidade da chapa, lubrificação do blank, coeficiente de atrito entre o blank e a ferramenta, parâmetros da prensa (força relativamente constante e velocidade), bem como variações nas ferramentas de conformação (deformação elástica). Este trabalho se dedica a investigação da influência do atrito entre a ferramenta e o blank. Em particular, será investigado o desenvolvimento de padrões artificiais de rugosidade de chapas metálicas (textura de superfície). O foco do presente trabalho é o estudo, em condições industriais, da inter-relação entre topografia superficial caracterizada pelos parâmetros de rugosidade 2D e 3D e estampabilidade de chapas de aço para painéis automotivos. Diferentes texturas superficiais de chapas de aço foram analisadas em termos de estampabilidade (medido pelo deslocamento do blank durante a estampagem) e tentativamente relacionadas com os parâmetros de rugosidades (2D e 3D) obtidos na chapa antes de estampar. Algumas tendências relevantes foram estabelecidas entre estes parâmetros. Os resultados aqui apresentados estão em concordância com publicações recentes mostrando uma clara relação entre estes parâmetros e que trabalhos futuros são necessários. / The stamping process is influenced by several variables such as sheet mechanical properties and roughness, blank lubrication, friction coefficient, press parameters (press force and speed), as well as variations in the forming tools (elastic strain). This work is dedicated to study the influence of friction between the tool and the blank. In this sense, it is necessary to study the development of artificial roughness patterns of sheet metals (surface textures). The aim of this research work is to study the inter-relationship, using the surface topography characterized by 2D and 3D roughness parameters and the formability of steel sheets for automotive panels. Different surface textures of sheet metal have been evaluated in terms of formability (measured by material flow during the process stamping) and tentatively related to roughness parameters (2D and 3D) obtained in the sheet metal prior to stamping. Some relevant tendencies have been established amongst these parameters. The results presented here are in accordance with other recently published research work showing that there is a clear relationship between these parameters, and that further detailed studies are needed.

A demanda por produtos mais econômicos, eficientes e menos poluentes faz com que a indústria automobilística invista em novos e melhores materiais e processos de produção. Assim, surgiu o processo de estampagem à quente chamado Press Hardening e seus produtos, os Press Hardened Steels. Esta classe de aços é capaz de produzir uma microestrutura totalmente martensítica durante o rápido resfriamento em prensa. Com o aumento da produção de peças por Press Hardening, evidenciou-se um grave problema: a suscetibilidade à fragilização por hidrogênio dos aços submetidos a esse processo. A ocorrência das chamadas fraturas retardadas induzidas por hidrogênio é relatada na literatura e uma pesquisa indica que microadições de nióbio ao aço 22MnB5 poderiam aumentar a resistência à fratura induzida por hidrogênio. Para estudar os efeitos do hidrogênio no aço 22MnB5, foram utilizadas seis diferentes composições A, C, CP, Ec, Ep e N (contém nióbio) em dois ensaios principais: ensaio de permeabilidade de hidrogênio e trincamento induzido por hidrogênio. A técnica de microdureza Vickers foi posteriormente utilizada para verificar possíveis efeitos do ensaio de permeabilidade de hidrogênio. Quatro das seis ligas receberam inicialmente o tratamento de press hardening e todas as seis apresentavam estruturas martensíticas nos ensaios de permeabilidade e trincamento. Por meio do método tlag, os parâmetros de difusão dos ensaios de permeabilidade foram calculados e comparados à literatura. As ligas CP e N apresentam os maiores valores de difusividade aparente de hidrogênio, menores valores de concentração máxima de hidrogênio e menores densidades de sítios de aprisionamento, sendo assim menos suscetíveis à fragilização por hidrogênio. Os ensaios de trincamento revelaram que as composições A, C e Ec apresentam trincas maiores do que as demais ligas, corroborando os resultados obtidos nos ensaios de permeabilidade (melhor resistência à fragilização por hidrogênio das ligas CP e N que contém Nb). Os ensaios de microdureza Vickers mostraram que não há redução na dureza após o ensaio de permeabilidade. Palavras-chave: A demanda por produtos mais econômicos, eficientes e menos poluentes faz com que a indústria automobilística invista em novos e melhores materiais e processos de produção. Assim, surgiu o processo de estampagem à quente chamado Press Hardening e seus produtos, os Press Hardened Steels. Esta classe de aços é capaz de produzir uma microestrutura totalmente martensítica durante o rápido resfriamento em prensa. Com o aumento da produção de peças por Press Hardening, evidenciou-se um grave problema: a suscetibilidade à fragilização por hidrogênio dos aços submetidos a esse processo. A ocorrência das chamadas fraturas retardadas induzidas por hidrogênio é relatada na literatura e uma pesquisa indica que microadições de nióbio ao aço 22MnB5 poderiam aumentar a resistência à fratura induzida por hidrogênio. Para estudar os efeitos do hidrogênio no aço 22MnB5, foram utilizadas seis diferentes composições A, C, CP, Ec, Ep e N (contém nióbio) em dois ensaios principais: ensaio de permeabilidade de hidrogênio e trincamento induzido por hidrogênio. A técnica de microdureza Vickers foi posteriormente utilizada para verificar possíveis efeitos do ensaio de permeabilidade de hidrogênio. Quatro das seis ligas receberam inicialmente o tratamento de press hardening e todas as seis apresentavam estruturas martensíticas nos ensaios de permeabilidade e trincamento. Por meio do método tlag, os parâmetros de difusão dos ensaios de permeabilidade foram calculados e comparados à literatura. As ligas CP e N apresentam os maiores valores de difusividade aparente de hidrogênio, menores valores de concentração máxima de hidrogênio e menores densidades de sítios de aprisionamento, sendo assim menos suscetíveis à fragilização por hidrogênio. Os ensaios de trincamento revelaram que as composições A, C e Ec apresentam trincas maiores do que as demais ligas, corroborando os resultados obtidos nos ensaios de permeabilidade (melhor resistência à fragilização por hidrogênio das ligas CP e N que contém Nb). Os ensaios de microdureza Vickers mostraram que não há redução na dureza após o ensaio de permeabilidade. / The demand for more economical, efficient and less polluting products makes the automobile industry invest in new and better materials and production processes. In this way, arose the hot stamping process called Press Hardening and its products, the Press Hardened Steels. This class of steels is capable of producing a fully martensitic microstructure during rapid cooling in the press. With the increase of the production of pieces by Press Hardening, a serious problem was evidenced: the susceptibility to the hydrogen embrittlement of the steels made by this process. The occurrence of the so-called hydrogen-induced delayed fractures is reported in the literature and a research indicates that micro-alloying of niobium to 22MnB5 steel may increase hydrogen-induced fracture resistance. In order to study the hydrogen effects on the 22MnB5 steel, were used six different compositions A, C, CP, Ec, Ep and N (which contains niobium) in two main tests: hydrogen permeation test and hydrogen induced cracking. The Vickers micro hardness technique was later used to verify possible effects of the hydrogen permeation test. Four of the six alloys received the press hardening processing and all six had martensitic structures in the permeability and induced cracking tests. By means of the tlag method, the diffusion parameters of the permeability tests were calculated and compared to the literature. The CP and N alloys present the highest values of hydrogen apparent diffusivity, lower values of maximum hydrogen concentration and lower densities of trapping sites, thus being less susceptible to hydrogen embrittlement. The induced cracking tests showed that compositions A, C and Ec present higher cracks than the other alloys, corroborating the results obtained in the permeability tests (better resistance to hydrogen embrittlement of the alloys CP and N containing Nb). The Vickers microhardness tests showed that there is no reduction in hardness after the permeability test.

No description available.

Objets très communs dans l’aire de culture tibétaine, les tsha tsha, fabriqués à l’aide de moules, sont des images en argile figurant des stūpa, des divinités bouddhiques, des personnages historiques, ainsi que des inscriptions. Leur fabrication est avant tout considérée comme une pratique religieuse visant à générer des mérites mais aussi à purifier les actions négatives. Réalisés en masse, ils constituent des témoignages fidèles et mésestimés des développements iconographiques et stylistiques qui ont marqués l’art bouddhique tibétain au fil des siècles. En l’absence d’études antérieures, un travail de recensement systématique des matériaux relatifs aux tsha tsha a fait apparaître une richesse documentaire insoupçonnée susceptible d’éclairer non seulement l’histoire de l’art tibétain, mais également certains aspects relevant de l’anthropologie religieuse, de la philologie, ou encore de la paléographie. Dans le cadre de notre thèse, nous avons privilégié une démarche globalisante prenant en considération l’ensemble des données disponibles en procédant conjointement à l’étude d’un très large corpus de pièces sélectionnées, à celle de la littérature afférente, et aux observations de terrain. Dans cette perspective, nous avons envisagé l’étude des tsha tsha sous divers angles: l’origine et l’histoire de la diffusion de cette pratique au Tibet, la terminologie relative à ces objets, les techniques de fabrication, les usages, l’iconographie, les styles et enfin les inscriptions présentes à leur surface ou introduites. Cette approche nous a permis de révéler finement l’ampleur et les développements que cette pratique bouddhique d’origine indienne a connu dans le monde tibétain. / Very commonplace in the Tibetan world, tsha tshas are clay impressions produced from a mould depicting, either in relief or moulded in the round, stūpas, Buddhist deities, historical figures and inscriptions. Making them is essentially considered to be a religious practice intended to generate and accumulate merit but also to purify negative deeds and obscurations. Produced in mass and generally preserved inside sealed edifices, tsha tshas are true yet underrated evidence of the iconographic and stylistic developments that have marked Tibetan Buddhist art over the centuries. In the absence of any previous studies, the task of establishing a systematic inventory of sources related to tsha tshas revealed an unsuspected wealth of material for elucidating not only the history of Tibetan art, but also some aspects of religious anthropology, philology, or paleography. In this doctoral research, we favored a globalizing approach that takes into account all the available data by studying a very large corpus of selected pieces, of the literature related to the tsha tshas, as well as field observations. In this context, we considered the study of tsha tshas from different angles: the origin and history of how this practice spread through Tibet, the terminology for these objects, the techniques for making them, their uses, iconography, styles and finally the inscriptions that are found on their surface or inside them. This approach has allowed us to explain more accurately the true extent of this Buddhist practice of Indian origin and the developments it has undergone in the Tibetan world since its introduction in about the 8th-9th centuries to the present day.

O processo de estampagem é influenciado por diferentes variáveis, tais como, propriedades mecânicas e rugosidade da chapa, lubrificação do blank, coeficiente de atrito entre o blank e a ferramenta, parâmetros da prensa (força relativamente constante e velocidade), bem como variações nas ferramentas de conformação (deformação elástica). Este trabalho se dedica a investigação da influência do atrito entre a ferramenta e o blank. Em particular, será investigado o desenvolvimento de padrões artificiais de rugosidade de chapas metálicas (textura de superfície). O foco do presente trabalho é o estudo, em condições industriais, da inter-relação entre topografia superficial caracterizada pelos parâmetros de rugosidade 2D e 3D e estampabilidade de chapas de aço para painéis automotivos. Diferentes texturas superficiais de chapas de aço foram analisadas em termos de estampabilidade (medido pelo deslocamento do blank durante a estampagem) e tentativamente relacionadas com os parâmetros de rugosidades (2D e 3D) obtidos na chapa antes de estampar. Algumas tendências relevantes foram estabelecidas entre estes parâmetros. Os resultados aqui apresentados estão em concordância com publicações recentes mostrando uma clara relação entre estes parâmetros e que trabalhos futuros são necessários. / The stamping process is influenced by several variables such as sheet mechanical properties and roughness, blank lubrication, friction coefficient, press parameters (press force and speed), as well as variations in the forming tools (elastic strain). This work is dedicated to study the influence of friction between the tool and the blank. In this sense, it is necessary to study the development of artificial roughness patterns of sheet metals (surface textures). The aim of this research work is to study the inter-relationship, using the surface topography characterized by 2D and 3D roughness parameters and the formability of steel sheets for automotive panels. Different surface textures of sheet metal have been evaluated in terms of formability (measured by material flow during the process stamping) and tentatively related to roughness parameters (2D and 3D) obtained in the sheet metal prior to stamping. Some relevant tendencies have been established amongst these parameters. The results presented here are in accordance with other recently published research work showing that there is a clear relationship between these parameters, and that further detailed studies are needed.

Os projetos de carrocerias veiculares atuais procuram desenvolver estruturas leves, seja para reduzir o consumo de combustível, no caso dos motores de combustão interna, seja para maior autonomia de bateria, no caso dos veículos elétricos e híbridos. Redução no consumo de combustível significa redução na emissão de poluentes. As estruturas precisam ser leves, mas cada vez mais resistentes e rígidas a fim de proporcionar máximo conforto e segurança aos ocupantes. Estas premissas têm levado ao contínuo desenvolvimento dos materiais. No caso dos aços, um dos processos que tem permitido a melhora significativa das propriedades mecânicas é a estampagem a quente. Nos últimos anos, as peças estampadas a quente têm ocupado lugar de destaque na estrutura das carrocerias veiculares por estarem em sintonia com as demandas mencionadas. Há muitas pesquisas em curso para esta tecnologia, seja nos materiais, nos meios de produção, nos revestimentos e em aplicações. O aço mais utilizado neste processo, 22MnB5, também apresenta o chamado efeito bake hardening; a tensão de escoamento é aumentada após tratamento térmico realizado em temperaturas próximas a 200 °C. Neste trabalho, visando à melhoria nas propriedades mecânicas, amostras foram tratadas termicamente na faixa de temperatura supracitada. Após isso, dados obtidos de ensaios mecânicos foram inseridos em programas de simulação de impacto lateral cujo resultado foi a redução na intrusão na célula de sobrevivência. O efeito bake hardening também propiciou um aumento na absorção da energia de impacto em teste estático feito com barras de proteção lateral. O mecanismo metalúrgico envolvido no fenômeno, devido à difusão de intersticiais foi evidenciado no ensaio de atrito interno. / The current auto body projects seek to build light structures whose immediate impact is in the reduction in fuel consumption of internal combustion engines or in longer battery life for electric and hybrid vehicles. Reduction in fuel consumption means reduced emissions. The structures need to be lightweight, but increasingly resistant to provide maximum comfort and safety to the occupants. These demands led to the continuous development of new materials. In the case of the steels hot stamping has allowed significant improvement in the mechanical properties. In recent years, hot stamped parts took prominent place in the structure of auto bodies to be in line with the mentioned demands. There are a lot of researches lines for this technology: materials, modes of production, coatings and applications. The most commonly used steel in this process, 22MnB5, also exhibits the bake hardening effect: its yield strength is increased after thermal treatment at temperatures close to 200 °C. To verify this improvement in the mechanical properties, samples were thermally treated. After that, data obtained from mechanical tests were inserted into side-crash simulation programs that resulted in a reduction in intrusion in the passengers compartment. The bake hardening effect also provided an increase in the absorption of the impact energy in a static test done with door beam. The metallurgical mechanism involved in the phenomenon, due to the movement of interstitial was evidenced in the internal friction test.

The aim of diploma thesis is to design technology components production orders. For a given part of the technology will be used non conventional deep drawing Wheelon method. For manufacturing lengthwise recesses and consequent cutting of shaped holes using a plasma cutting. The suitability of technological applications will be tested using the cost functions.

This project submits a proposal for manufacturing technology of casement and frame window hardware base, made of 11343.23 steel 2,5 mm in thickness and with 15000 pieces annual production volume. The components form an integral part of a window hardware arrest mechanism. From potential variants of manufacturing, the technology of stamping and bending, with the use of a combined tool, was chosen. A bibliographic search examining these technologies was made and the machine LE 250 with nominal forming force 2 500kN was selected. The project comprises structural and technological calculations, including the combined tool design. In the economical part of the project, the product prices were quoted and the break-even point was determined. The break-even point is broken as soon as 13 046 pieces are manufactured.