The continuous development of hot forming tool steels has resulted in steels with improved mechanical properties. A change in alloying composition, primarily a decreased silicon content, makes them tougher and more wear resistant at elevated temperatures. However, it is at the expense of their machinability. The aim of this study is to explain the mechanisms behind this negative side effect. Hot work tool steels of H13 type with different Si content were characterised mechanically, and evaluated analytically and by dedicated machining tests. Machining tests verified that materials with low Si content displayed reduced machinability due to their stronger tendency to adhere to the cutting edge. Three hypotheses were tested. The first hypothesis, that the improved toughness of the low Si steels is the reason behind their relatively poor machinability, was rejected after machining tests with one low Si steel heat treated to the same relatively low toughness as conventional hot work tool steels. The second hypothesis, that a change in oxidation properties, also associated with the change in Si composition, lies behind the reduced machinability was investigated by dedicated tests and evaluations. It was found that the oxide thickness increased with reduced Si content and that there was an enrichment of Cr at the oxide/steel interface. The differences in oxide thickness and the possible differences in oxidation properties may influence the machinability of the materials through their different abilities to adhere to the cutting edge. The third hypothesis, that a high enough temperature to initiate phase transformation from ferrite to austenite is generated during machining of the tool steels, was also investigated. This may lead to a reduced machinability because higher austenite content is directly related to higher compressive stresses and higher cutting forces. This causes accelerated tool wear. This hypothesis was verified by ThermoCalc calculation of austenite content in the steels, which showed a good agreement with Gleeble compression tests and cutting force measurements. This thesis confirms that a reduced Si content in conventional H13 steel improves the toughness, reduces the oxidation resistance and lowers the ferrite-to-austenite transformation temperature. The reduction in austenite temperature is probably the most important factor behind the reduced machinability.

Abstract This thesis work is about finding out which coating should be used for which hardened tool steel and this was done by testing different coated cutting tools in different kinds of tool steels. The thesis work is performed at Uddeholms AB together with Uddeholms AB in the department of R&D at machinability cooperating with eifeler-Vacotec GmbH. The thesis work is going on from the end of January to the start of June and is a part of the education as mechanical engineer at Karlstad University and includes a total of 22,5 hp. The objective after finished thesis work is to be able to leave a recommendation to Uddeholms AB which coating is most suitable for each tool steel. To be able to leave that recommendation cutting tests are performed in four different hardened steel grades from Uddeholms AB combined with seven different coatings from eifeler-Vacotec GmbH. Steel grades tested are NIMAX®, DIEVAR®, VANADIS® 10 and ORVAR® SUPREME and coatings tested are CROSAL®, EXXTRAL® and SISTRAL® in different compounds. ORVAR® SUPREME gave such a long cutting tool-life that it was left for further investigation due to time limits that the thesis work had. In the other three tool steels it was possible to get a recommendation out of the four coatings tested in each tool steel. The coating that is recommended for each tool steel is only based on the cutting tool lasting the longest in each tool steel. That is not how a recommendation usually is formed, however for this thesis work there is no time for checking all the aspects that is vital for a proper recommendation. In order to get a proper recommendation, further more aspects that are checked are for example: Different cutting parameters (cutting speed, feed, etc.) Different geometries on the cutting tool Smoothness of the cutting tool and the coating In table 1 there is a compilation of which coating that was recommended for which tool steel. Table 1. This is a compilation of which coating that was recommended for which tool steel. NIMAX®               CROSAL® V1 DIEVAR®             SISTRAL® Ultrafine VANADIS® 10    SISTRAL® S

SWISS STEEL, filiale du groupe SCHMOLZ + BICKENBACH, finance des travaux de thèse menés au Centre de Recherches d’UGITECH, en collaboration avec le laboratoire SIMaP de Grenoble. Le but de ce programme est de trouver des alternatives au plomb (Pb) dans les aciers bas carbone de décolletage. Les objectifs sont de conserver le niveau d’usinabilité des aciers de décolletage au plomb, sans leurs défauts (toxicité, recyclage des aciers au plomb). La production d’acier au plomb est stratégique pour SWISS STEEL, puisqu’elle représente environ 30% de son activité. Parmi les différentes alternatives signalées dans la littérature, l’addition d’étain, et la graphitisation des aciers, sont les concepts les plus intéressants. En effet, il est suggéré que l’étain présente un comportement similaire à celui du plomb lors de l’usinage. Par ailleurs, Le graphite est connu pour être un lubrifiant utilisé dans des applications industrielles, ce qui peut améliorer l’usinabilité. Une caractérisation complète d’aciers industriels au plomb, et sans plomb, en provenance de SWISS STEEL (11SMn30 et 11SMnPb30), a été menée : analyse chimique, observations métallographiques et microscopiques (MEB), propriétés mécaniques, etc. Ensuite, nous avons essayé de comprendre les mécanismes par lesquels le plomb améliore l’usinabilité des aciers de décolletage aux basses vitesses de coupes (Vc < 100 m/min), grâce à des essais d’usinage spécifiques. Des calculs thermodynamiques ont été menés sur le procédé de graphitisation, et des analyses d’aciers ont été déterminées. Ce qui nous a conduits à élaborer des aciers à l’étain et des aciers graphitiques à l’échelle du laboratoire. La caractérisation de ces coulées de laboratoire, avec la même procédure que celle utilisée par les aciers industriels, a permis de vérifier la fiabilité de ces concepts, et leur bienfaits sur l’usinabilité. Des résultats encourageants ont été enregistrés. Pour une étude plus approfondie, il a été proposé de produire, à l’échelle industrielle, une analyse d’acier particulière, susceptible de remplacer le plomb dans les aciers de décolletage au plomb. / SWISS STEEL, a steel company part of SCHMOLZ + BICKENBACH group, has supported a PhD program, lead in UGITECH’s Research Center, in collaboration with the SIMaP laboratory of Grenoble. The aim of this program is to find some alternatives to lead (Pb) in low carbon free-cutting steels. The objectives are to keep the machinability level of leaded free-cutting grades without their drawbacks (toxicity, recycling of Pb steels). The production of leaded free-cutting steels is strategic for SWISS STEEL, since it represents about 30% of its activity. Among the different alternatives pointed out by the bibliography, tin addition, and graphitisation of steels, were the most interesting concepts. Indeed, it is suggested that tin presents a similar behaviour to that of lead during machining. Moreover, graphite is a well known lubricant in industrial applications, which could improve machinability. A complete characterisation on leaded, and non-leaded, grades form SWISS STEEL has been carried out (11SMn30 and 11SMnPb30): chemical analysis, metallographic and SEM observations, mechanical properties, etc. Then we tried to understand, thanks to specific machining tests, the mechanisms by which lead improves the machinability of free-cutting steel, at low cutting speed (Vc < 100 m/min). Thermodynamic calculations have been performed to study the graphitisation process, and conducted to the determination of steels analyses. This lead us to develop tin-added-, and graphitic steels at the laboratory scale. The characterisation of these laboratory grades, with the same procedure, than that of industrial steels, allowed to check the reliability of these concepts, and their benefits on machinability. Promising results have been recorded. For deeper exploration, it has been proposed to produce, at the industrial scale, a particular steel analysis, which could replace leaded free-cutting steels.

It is a well established fact that all materials have a difference in chemical composition and show different physical properties. Long experience with the machining of materials had shown this investigator that in many respects the machining of each material differed slightly from the machining of any other material. This led to the idea that perhaps the one factor which had been overlooked by other investigators in the field of machinability was the factor of time. The question was, “Could a machine be built which was capable of measuring the differences in materials in terms of the variation in the times required to remove metal under a given set of conditions?” The first step in the program to answer this question was to build a machine which would be rugged enough to make heavy cuts possible, and still be sensitive enough to measure what might turn out to be very small variations in time. This machine has now been built. While it still has a long way to go to become perfected the results are encouraging enough to create the desire to continue with the work along this line. The second step in the program was to design tests which would not only serve to test the functioning of the machine, but would serve to indicate along what lines the future work should follow. The one hundred and twenty-five tests made have proved two facts quite conclusively. The first fact is that the idea on which the testing machine was designed is fundamentally sound. Time variations can be used to measure machining characteristics of different materials. The second fact proved by these tests is that the machine is not only capable of measuring the differences existing between various materials, but that it can be used to test such factors as the proper tool angles to use in machining a given material, the force required to remove a given volume in a given time, and the best speeds to use to give the smallest time per unit volume. It was evident during these tests that several minor changes could be made to improve the performance to the point where it would be even more capable of showing the time variations which occur. These changes have been incorporated in the following section of the thesis. / Master of Science

The vision of this thesis is to study how it is possible to obtain optimised workpieces during metal cutting processes in industry. Specifically, the work is aimed to increase the understanding between the steel characteristics and their link to the chip breaking and tool wear during metal cutting. The emphasis is on the influence of the cleanliness and the characteristics of non-metallic inclusions in the workpiece on the machinability of carburising steel grades. The machinability of a case hardening steel is improved by a M-treatment (additions of Ca). Also, the improved machinability of the M-steels offers an attractive potential to save money which makes it possible to reduce the tooling costs with up to 50%. The improved machinability of Ca-treated steels is correlated to the formation of lubricating slag layers consisting of Ca-enriched sulfide inclusions and oxy-sulfide inclusions, which are formed on the rake face during the machining operation. It is proposed that the formations of slag layers from the workpiece constituents are essential to minimise the chemical degradation of the tool edge due to a contact with the chip. During this process, sulfur minimises the material transfer from the chip flow, whilst Ca-treated impurities have a stabilising effect on the protective deposits made of slag layers. Since there is a remaining industrial need to increase the production rate, whilst maintaining a high quality of the finished parts, the future production will continue to require extreme demands on the quality of workpieces. If the emphasis is focused on the workpiece, it should be possible to obtain a robust manufacturing process. Therefore, the challenge for future steel metallurgists is to develop high performance grades with optimised combined properties. / Syftet med denna avhandling är att studera hur det är möjligt att framställa optimala ämnen för skärande bearbetning i industriell skala. Målsättningen med arbetet är att öka förståelsen för ståls egenskaper och dess inverkan på spånbrytning och slitage av verktyg vid skärande bearbetning. Avhandlingen fokuserar på kopplingen mellan arbetsstyckets renhet och inneslutningskarakteristik och dess inverkan på skärbarhet hos sätthärdningsstål. Skärbarheten hos vanligt sätthärdningsstål kan förbättras markant genom en Ca-behandling, dvs. en så kallad M-behandling. Den förbättrade skärbarheten hos M-stål möjliggör stora kostnadsbesparingar, som uppskattas kunna reducera verktygskostnader med upp till 50%. Den förbättrade skärbarheten hos M-stål beror på bildningen utav tribologiska skikt som är anrikade med (Mn,Ca)S- och (CaO)x-Al2O3-S-slagg. Dessa tribologiska skikt bildas på skärverktygets spånsida under ingrepp vid skärande bearbetning och består utav vissa atomer som överförts från det bearbetade ämnet till skäret. Bildandet av ett skyddande skikt anses nödvändigt för att undvika att verktygets skäregg utsätts för ett kemiskt angrepp i kontaktytan med spånflödet. Svavel anses minimera att rent arbetsmaterial överförs till skärverktyget medans kalcium-berikade inneslutningar hjälper till att bilda ett stabilt och skyddande tribologiskt skikt. Det eviga behovet att öka produktionstakten, utan att för dess skull riskera slutproduktens kvalité ställer stora krav på framtidens material. Med utgångspunkt från arbetsstycken så ska det vara möjligt att uppnå en robust industriell produktion. Utmaningen är därför att utveckla högpresterande stål med en förhöjd kombinerad funktionsegenskap.

OBJECTIVE: The purpose of this in vitro study was to evaluate the cutting performance and accuracy of CAD/CAM diamond burs in different chemo-mechanical conditions when machining yttria-stabilized zirconia (YTZ), lithium-disilicate, feldspathic porcelain, and double network hybrid ceramic material. The study also examined bur wear mechanisms. MATERIALS AND METHODS: Two experiments were performed. Experiment 1: 45 samples of each material were milled, and four criteria were tested: milling time; surface roughness; change in bur weight after machining, and total cement space. Experiment 2: Four different coolant liquids were used while machining 15 samples of lithium-disilicate, feldspathic porcelain, and double network hybrid ceramic material. The four criteria in Experiment 1, plus marginal adaptation, were measured. Burs and ceramic materials used were examined with SEM before and after machining. RESULTS: Experiment 1: All burs milled 15 crowns of each material successfully, with a general increase in milling time and decrease in weight. Four wear patterns were identified: grit cracks, micro-fractures, dislodgement, and matrix abrasion. Sequential milling time increased for all of the ceramic materials. Surface roughness (Ra) decreased in general for all materials used in the study except YTZ, which showed an increase in Ra by the end of the machining series. Experiment 2: Additives used in this study had no significant effect on IPS e.max CAD milling efficiency or Ra. Boric acid reduced Vita MarkII machining time significantly and Ra. CONCLUSIONS: The cutting rate of diamond burs differed when machining different ceramic materials. In sequential machining, every consecutive milling demonstrated lower cutting efficacy. The surface roughness of consecutive machined samples differed. Some cooling liquids affected the quality of the machined surface. The bur wear mechanism was the same when different ceramic materials were machined, and their microstructure affected their machinability. / 2019-09-26T00:00:00Z

Este trabalho visou estudar o efeito dos parâmetros microestruturais da liga de latão 60/40 isenta de chumbo, com enfoque na observação da influência de 4 diferentes frações volumétricas e morfologias da fase &#946 nos aspectos de usinabilidade. Os resultados foram comparados com duas referências comerciais de ligas de latão, sendo uma de corte livre com adição de chumbo, e outra de latão 70/30 isenta de fase &#946. Esta comparação foi feita por meio dos ensaios de caracterização microestrutural, ensaios mecânicos de dureza Vickers, tração uniaxial e ensaios de usinabilidade. Na avaliação da usinabilidade foram estudadas as morfologias macro e microestrutural dos cavacos, rugosidade final das peças usinadas, medição das forças de corte e análise da vida útil da ferramenta. Esta comparação de desempenho em usinabilidade busca viabilizar a gradativa substituição das ligas de latão com chumbo por ligas isentas de metais pesados, preenchendo uma demanda crescente de mercado por este tipo de produto. A fase &#946 exerce uma importante influência na redução das forças de corte e rugosidade, além do fato de que o efeito térmico cumpre um papel importante no comportamento em usinagem dos latões, evidenciado pela alteração das frações volumétricas das fases µ e &#946 no cavaco analisado, a qual é associada a uma transformação de ordem-desordem. / This work presents a study of microstructural features of lead-free 60/40 brasses on their machinability, which was focused on the observation of four different volumetric fractions and morphologies of &#946 phase. Two commercial brasses were used as base materials: a free cutting brass with lead and a 70/30 brass without &#946 phase, respectively. These materials were manufactured through hot extruded, cold worked and heat treated rods of these three different alloys, and submitted a microstructure analysis, and mechanical characterization by Vickers hardness and a uniaxial tensile test. Machinability tests were conducted to evaluate the morphology and microstructure of the chips and the final roughness of the workpieces, cutting forces and tool wear test. The results help to evaluate the feasibility of substitution of the leaded brasses for brasses without heavy metals, filling a growing demand for this product in the industry. The &#946 phase has a strong influence on cutting forces and roughness reduction as well as the thermal effect plays an important role in the volume fraction of µ and &#946 phases of the analyzed chip, which was related to the presence of &#946 phase and an order-disorder transformation.

Over the last two decades or so, metal matrix composites (MMCs) have been drawing the attention of the industry due to their potentials in fulfilling demands for high performance industrial materials, products and advanced engineering applications. On the other hand, the high precision machining is becoming one of the most effective methods for enabling these difficult-to-machine composites to be applied particularly in precision engineering. Therefore, in-depth scientific understanding of MMC precision machining is essential and much needed so as to fulfil the gap between fundamental issues in precision machining of MMCs and their industrial scale applications. This thesis focuses on development of a multiscale multiphysics based approach to investigating the machinability of particulate MMCs and the machining process optimisation. In order to investigate the surface generation in relation to the process variables, this PhD study covers the key fundamental issues including chip formation process, dynamic cutting force, cutting temperature partition and tool wear by means of combining modelling, simulation and experimental study. The chip formation mechanisms and the minimum chip thickness in precision machining of SiCp/Al and B4Cp/Al MMCs by using PCD tools are investigated through a holistic approach. Minimum chip thickness (MCT) value is firstly identified based on the modified mathematical model. The certain threshold of the uncut chip thickness, i.e. chips starting to form at this chip thickness point, is then established. The chip formation process including the matrix material breakage, particles fracture, debonding, sliding or removal and their interfacial interactions are further simulated using finite element analysis (FEA). The minimum chip thickness and chip formation simulations are evaluated and validated via well-designed experimental trials on a diamond turning machine. The chips and surface profiles formed under varied process variables in periodic material removals are inspected and measured in order to obtain a better understanding on MMC chip formation mechanisms. The improved dynamic cutting force model is developed based on the micro cutting mechanics involving the size effect, undeformed chip thickness effects and the influence of cutting parameters in the micro scale. Cutting process variables, particle form, size and volume fraction at different scales are taken into account in the modelling. The cutting force multiscale modelling is proposed to have a better understanding on the MMCs cutting mechanics and to predict the cutting force accurately. The cutting forces are modelled and analysed in three cutting regimes: elastic recovery zone, ploughing zone and shearing zone. A novel instantaneous chip thickness algorithm including real chip thickness and real tool trajectory is developed by taking account of the tool runout. Well-designed cutting trials are carried out under varied process variables to evaluate and validate the force model. In order to obtain the actual cutting forces accurately, transfer function technique is employed to compensate the measured cutting forces. The cutting force model is further applied to correlate the cutting tool wear and the prediction of the machined surface generation. Multiphysics coupled thermal-mechanical-tribological model and FE analysis are developed to investigate the cutting stress, cutting temperature, tool wear and their intrinsic relationships in MMCs precision machining process. Heat generation, heat transfer and cutting temperature partition in workpiece, chips and cutting tool are simulated. A modified tool wear rate model is proposed, tool wear characteristics, wear mechanisms and dominate tool wear are further investigated against the real machining process. Cutting tool wear is monitored and assessed offline after machining experiments. The experimental study on the machined surface generation is presented covering cutting force, tool wear, tool life, surface roughness and machining efficiency. Process optimisation is explored by considering the variation of cutting parameters, cutting tool conditions and workpiece materials in order to achieve the desired outcomes and machinability.

Precisão dimensional e qualidade de superfície usinada são fundamentais em componentes de aplicações mecânicas. Dentre as variáveis que exercem influência sobre estes fatores, está a grande quantidade de calor gerado na usinagem, que deve ser reduzida, minimizando seus efeitos na ferramenta e na estrutura superficial e sub-superficial da peça. Reduzir este calor e seus efeitos é uma das funções da lubri-refrigeração, porém, intensificamse as pesquisas com o objetivo de restringir ao máximo o uso destes fluídos. Neste trabalho, analisou-se a eficiência da lubri-refrigeração na qualidade da superfície usinada, no desvio dimensional e na variação microestrutural de amostras do aço AISI 4140 com diferentes microestruturas, usinado pelo processo de torneamento longitudinal. Observou-se que a lubri-refrigeração não teve efeito considerável sobre a qualidade da superfície usinada, não apresentando uma melhora significativa na rugosidade. Na questão dimensional observou-se que, em mais de 60% dos ensaios realizados, os resultados com e sem a presença da lubri-refrigeração mantiveram-se dentro da faixa de tolerância préespecificada, e na avaliação microestrutural, avaliando a deformação plástica, observou-se que houve uma queda na dureza da borda do material, em comparação com regiões mais próximas do centro do corpo-de-prova. / Submitted by Ana Guimarães Pereira (agpereir@ucs.br) on 2015-10-07T13:50:18Z No. of bitstreams: 1 Dissertacao Marcelo Evandro Tedesco.pdf: 2625254 bytes, checksum: b06979aea49156d0b72bf7d6ea7b3961 (MD5) / Made available in DSpace on 2015-10-07T13:50:18Z (GMT). No. of bitstreams: 1 Dissertacao Marcelo Evandro Tedesco.pdf: 2625254 bytes, checksum: b06979aea49156d0b72bf7d6ea7b3961 (MD5) / Dimensional deviation and surface quality are fundamental components for mechanical applications. The variables that influence these factors, the quantity of heat generated must be reduced in order to minimize their effects on tool and on the superficial and sub-superficial structure of the piece. Reducing this heat and its effects is one of the cooling functions; however, the researches trying to restrict the use of those fluids. In this work, the cooling efficiency was analyzed on the surface quality, dimensional deviation and microstructural variation of AISI 4140 steel samples machined with different microstructure by longitudinal turning process. As a result, it was found that the cooling is not a significant effect on surface quality, not improving the roughness. In regard to dimensional, it was noticed in more than 60% of tests that the results with and without the presence of cooling kept between the pre-specified tolerance ranges. In the microstructural analysis, analyzing the plastic deformation, it as noticed that the hardness decrease in the edge of the sample, comparing with the center.

Este trabalho visou estudar o efeito dos parâmetros microestruturais da liga de latão 60/40 isenta de chumbo, com enfoque na observação da influência de 4 diferentes frações volumétricas e morfologias da fase &#946 nos aspectos de usinabilidade. Os resultados foram comparados com duas referências comerciais de ligas de latão, sendo uma de corte livre com adição de chumbo, e outra de latão 70/30 isenta de fase &#946. Esta comparação foi feita por meio dos ensaios de caracterização microestrutural, ensaios mecânicos de dureza Vickers, tração uniaxial e ensaios de usinabilidade. Na avaliação da usinabilidade foram estudadas as morfologias macro e microestrutural dos cavacos, rugosidade final das peças usinadas, medição das forças de corte e análise da vida útil da ferramenta. Esta comparação de desempenho em usinabilidade busca viabilizar a gradativa substituição das ligas de latão com chumbo por ligas isentas de metais pesados, preenchendo uma demanda crescente de mercado por este tipo de produto. A fase &#946 exerce uma importante influência na redução das forças de corte e rugosidade, além do fato de que o efeito térmico cumpre um papel importante no comportamento em usinagem dos latões, evidenciado pela alteração das frações volumétricas das fases µ e &#946 no cavaco analisado, a qual é associada a uma transformação de ordem-desordem. / This work presents a study of microstructural features of lead-free 60/40 brasses on their machinability, which was focused on the observation of four different volumetric fractions and morphologies of &#946 phase. Two commercial brasses were used as base materials: a free cutting brass with lead and a 70/30 brass without &#946 phase, respectively. These materials were manufactured through hot extruded, cold worked and heat treated rods of these three different alloys, and submitted a microstructure analysis, and mechanical characterization by Vickers hardness and a uniaxial tensile test. Machinability tests were conducted to evaluate the morphology and microstructure of the chips and the final roughness of the workpieces, cutting forces and tool wear test. The results help to evaluate the feasibility of substitution of the leaded brasses for brasses without heavy metals, filling a growing demand for this product in the industry. The &#946 phase has a strong influence on cutting forces and roughness reduction as well as the thermal effect plays an important role in the volume fraction of µ and &#946 phases of the analyzed chip, which was related to the presence of &#946 phase and an order-disorder transformation.