This report covers the work and results of the thesis project in Mechanical Engineering from Luleå university of technology performed by Niklas Ydebäck. The objective of the thesis project is to research if it is possible, with general principles of fluid flow between components and the corresponding geometric constraints between them and just a few channels of data, to model the leakage of a radial piston hydraulic motor. The model is of the grey box kind which makes use of both numerical and statistical methods together with known physical properties of a system in order to model the system. The unknown parameters of this system that are estimated using the least squares method are the three different gap heights of the system as well as the two different eccentricities in the system. The model contains the physical properties of the system, stated in equations for the leakage in the relevant lubrication interfaces, but no relational properties for the dynamics and affects between the individual lubricating interfaces. The model developed is due to the model generality together with the data quality accessible not able to model the system with reliable quality. The model is however able to capture the general trend of the leakage in the system over the applied time series datasets. / Den här rapporten presenterar arbetsgången och resultatet av examensarbetet för en civilingenjörsexamen i Maskinteknik från Luleå tekniska universitet utförd av Niklas Ydebäck. Målet med examensarbetet är att utvärdera och undersöka om det är möjligt, med generella och vedertagna principer av fluidflöde mellan smorda komponenter tillsammans med de geometriska begränsningarna som hör dem till och några få kanaler av data, att modellera läckaget för en radialkolvsmotor. Modellen är en grålådemodell som med hjälp av numeriska och statistiska metoder och kända fysikaliska principer av ett system bildar en modell av systemet. De okända parametrarna av systemet som estimeras med hjälp av minsta kvadrat metoden är de tre olika typerna av spalthöjderna och de två olika eccentricitetstyperna som finns i systemets smorda kontakter. Modellen består av de fysikaliska egenskaperna i systemet, formerade i ekvationer för läckaget i de relevanta smorda kontakterna, men inga relationella egenskaper för dynamiken och effekterna mellan de olika smorda kontakterna. Den utvecklade modellen är på grund av den generella karaktären av modellen tillsammans med kvaliteten på den data som finns tillgänglig inte möjlig att modellera läckaget i systemet med tillräcklig noggrannhet. Modellen är trots detta kapabel att fånga de generella trender som återfinns i den uppmätta datan på läckaget för de applicerade dataseten.

With the increasing restrictions in emission legislations, the automotive industry aims to improve the efficiency of the lubricating system and to decrease fuel consumption. In the power cylinder unit (PCU), the piston rings are the major contributor to these consumptions. Hence, focus on the dynamic behaviour of the rings to reduce lube oil consumption (LOC) becomes a key factor in thriving towards sustainability. Several studies have been conducted on the piston ring-pack specifically using a 2D ring dynamics approach. This study focuses on developing a 3D ring dynamics model, in the software tool AVL EXCITE™ Piston&Rings, which is capable of observing the behaviour of the ring along the third dimension i.e. circumferential direction. A coordinated approach used in the methodology gives an insight into the parameters affecting the model behaviour. Within the PCU, wear on the cylinder liner surface and in the piston ring grooves can lead to accelerated LOC. This study further focuses on using the 3D model to analyse the friction and wear on the piston rings. Factors contributing towards LOC are individually studied and the results obtained are compared to the experimental engine test data. The outcome of the 3D numerical model developed shows promising results. The model can therefore be used to simulate different piston ring-packs and analyse the behaviour of the piston ring with a better prediction of friction, wear and LOC. Thus, the model will contribute to reducing the number of physical tests conducted, the expense involved in conducting those tests and would provide satisfactory products to the customer and would manage future emission requirements.

Over the last decade, the application of ultra-high strength steel as safety components and structural reinforcements in automobile applications has increased due to their favourable high-strength-to-weight ratio. The complex shaped components are widely produced using hot stamping. However, this process encounters problems such as galling and increased wear of the tools due to harsh operating conditions associated to the elevated temperatures. Moreover, quenching is a critical step that affects the hot formed components. Slow cooling rates results in inhomogeneous mechanical properties and increased cycle time. Therefore, fast and homogeneous quenching of the formed components in combination with reduction of wear rates during hot forming are important targets to ensure the quality and efficiency of the process. The use of additive manufacturing (AM) technologies opens up potential solutions for novel tooling concepts. The manufacturing of complex shape cooling channels and integration of high-performance alloys at the surface could benefit the tribological performance in the forming operation. However, the research into high temperature tribological behaviour of AM materials in hot forming applications is very limited. The aim of this work is to study the tribological performance of additively manufactured materials. Two steels were used – a maraging steel and modified H13 tool steel. The hot work tool steel H13 is commonly applied for dies in metal forming processes. In this thesis it was used to study additive manufacturing as the processing route instead of conventional casting. The choice of a maraging steel is motivated by a possible application of high-performance alloys as a top layer on dies. The materials were post-machined and studied in milled, ground and shot-blasted conditions. The different post-machining operations were applied to study the effect of surface finish on the tribological behaviour and also to evaluate different methods of post-machining an AM surface. As fabricated dies are usually manufactured with milled surface. During its use, the dies undergo refurbishment after certain number of cycles and the surface condition is changed to a ground surface. These surface finishes are commonly tested for hot forming applications. The shot blasted operation was chosen as alternative surface finish. The process allows to prepare large sized tools easily and the surface has beneficial compressive stresses. The tribological behaviour of AM steels was studied using a hot strip drawing tribometer during sliding against a conventional Al-Si coated 22MnB5 steel. The workpiece temperature during the tests was 600 and 700°C. The results of the tribological performance of AM materials were compared to conventionally cast tool steel QRO90.The results have shown that the friction behaviour of both maraging and H13 steels at 600°C was stable and similar whereas at 700°C the COF was more unstable and resulted in an earlier failure of the tests due to increased material transfer of Al-Si coating from the workpiece surface.The main wear mechanisms for AM materials were galling and abrasion at both temperatures. Abrasion is more severe for the AM steels in comparison to cast tool steel QRO90. The galling formation on milled and ground surfaces showed similar behaviour to cast steel and it increased with higher workpiece temperatures. The shot-blasted surfaces showed less build-up of transferred material on the surface but folding of asperities and entrapment of Al-Si particles within surface defects generated during shot-blasting.

Laserpåsvetsning och laserytimpregnering är additiva tillverkningsmetoder som kan användas för att förlängakomponenters livslängd och specialanpassa ytor med avseende på friktions-, slitage- och korrosionsegenskaper.Duroc Laser Coating i Luleå är störst i Sverige på laserytbehandlingar men saknar objektiv data på friktionsoch nötningsegenskaperna hos de laserpåsvetsade materialen vilket har varit det huvudsakliga målet med dettaarbete att ta fram.Tolv material, varav tre referensstål för jämförelse, har testats enligt en något modifierad ASTM G132 standard avseende tvåkroppsabrasion. Resultaten visade att det abrasiva nötningsmotståndet ökade med ökandehårdhet. Tre material med karbidpartiklar i ytskiktet uppvisade överlägset högst nötningsmotstånd. Ytornahar undersökts med svepelektronmikroskop och ytprofileringsmätningar efter testerna för att karakterisera debakomliggande nötningsmekanismerna.Materialens mikrostruktur, hårdhet och deformationshärdning närmast ytan efter abrasiv nötningsprovninghar undersökts. De mjukaste materialens mikrostruktur hade deformerats i glidriktningen medans resterandematerials mikrostruktur var opåverkad. Koboltlegeringarna uppvisade högst deformationshärdning.Åtta material, varav två referensstål, har testats enligt ASTM G99 i en pin-on-disk uppställning för att undersöka adhesivt nötningsmotstånd och friktionsegenskaper med lagerstål som mötande material. Resultatenvisade att de tre koboltbaserade legeringarna som testades hade lägst och stabilast friktion med minst materialöverföring, medans ett brons som testades hade högst friktion och materialöverföring. Ett rostfritt stål hadelägst nötning.Målen med arbetet har uppnåtts och den tribologiska prestandan har kartlagts för de material som ingått iarbetet. Metodiken som tagits fram under arbetets gång kan även användas för att göra ytterligare materialkarakterisering i framtiden.

This study aims to develop coatings which show wear resistant behaviour along with multiple functions such as improved ice adhesion, better freezing delay etc which help in improving the effectiveness of the wind turbine efficiency. The significance of anti-icing/de-icing solutions for wind turbines is emphasized since ice accretion can cause serious issues in generation of power and might lead to damage of blades. The use of active and passive anti-icing/de-icing technologies in wind turbine blade applications is reviewed. The discrepancy between passive anti-icing, which depends on surface treatment, coatings, de-icing fluids and active anti-icing, which uses heating devices, sensors such as actuators, transducers, is explored along with the current challenges in industry. In this study we’ve developed interesting methods for improving the anti-icing/de-icing capabilities of wind turbine blades by using gelcoat coatings in which are filler particles (boron nitride and graphene) and oils (vegetable and paraffin oil) are incorporated. Evaluating the impacts of type of fillers, oils, their concentrations on anti-icing efficacy, as well as the prospects for this technique to enhance wind energy production's reliability and productivity will be explored. In summary, this study aims to develop multi-functional polymer coatings for anti-icing/de-icing application in wind turbine blades. The coatings with boron-nitride and graphene showed an increase in the surface roughness and contact angles, while there’s no change in the chemical composition in comparison with pure gelcoat. The thermal conductivity of the coatings was increased with addition of fillers. For the wear test, the operating parameters chosen are a load of 5N and 1Hz frequency of slider, which is run for a duration of 10 min. The COF for both the coatings is lesser than baseline coatings whereas graphene provided better wear resistance. The hardness was increased for boron-nitride coatings and it remained almost same for graphene coatings. The ice adhesion strength, freezing delay and thermal analysis (TGA) for these coatings showed better performance than pure gelcoat. Whereas for coatings with vegetable and paraffin oils, the contact angles were increased and surface roughness was increased in case of paraffin oil coatings whereas it reduced for vegetable oil coatings. Both the coatings offered better wear resistance and reduced COF, whereas the hardness was reduced. The ice adhesion strength and freezing delay improved drastically and are much better than both pure gelcoat as well as coatings with boron-nitride and graphene. There is slight increase in the glass transition temperature than pure gelcoat coating.

Without lubrication, machines are not imaginable to perform over a long period of time and complete their designated operations. With its omnipresent availability, the air is capable of functioning as a lubricant in long operations very efficiently. Moreover, thrust bearings support axial loads and transmit power at the same time under heavy loads. Therefore, to provide separation under heavy loads in lubricated rotating devices such as thrust pad bearings keeping the power losses at a minimum, film thickness and pressure distribution are very important to investigate at the bearing interfaces. Thrust pad gas (air) bearings are being used in very high-speed rotating machines. Usages of these air bearings are increasing nowadays in industries. In this thesis project, simulations of lubricated contacts of a thrust pad air bearing are performed utilizing multiphysics phenomena and surface textures as mathematical functions. Structural mechanics and fluid mechanics physics are used to model multiphysics functionality. Ideal surface texture models defined by mathematical functions are utilized. More efficient techniques such as homogenization techniques to model the influences of surface roughness are introduced for multiscale study. The current work also presents the Reynolds equation for incompressible and iso-viscous Newtonian fluid flow and formulation for a stationary study. The air bearing with three pads is presented and a virtual twin of this model is built for simulation in COMSOL Multiphysics software. Simulation results are obtained using a single pad from the air bearing considering periodicity of the mathematical formulation. Numerical solutions for pressure build-up and film thickness distributions are achieved from a stationary study performed in COMSOL Multiphysics. MATLAB is used for rigid body solutions. Numerical verification is carried out between the rigid body solutions from MATLAB and fluid physics solutions from COMSOL Multiphysics only for the simulations with tilting pad configuration. Obtained rigid body solutions are also compared to the trends of thrust pad bearing design diagrams to verify the modelling approach and the results. A tilting pad lubricating configuration is used for the thrust pad bearing first. Then pocket geometries for optimization of the bearing pads are explored. For that purpose, separate digital models of the bearing pad are built in COMSOL and analysed for the best performances. Material properties of steel AISI 4340 and Polylactic Acid (PLA) material are used to model virtual bearing pads. To understand the performance of the bearing better, its performance parameters such as load carrying capacity (LCC), relative power loss, and coefficient of friction torque (COT) solutions from the simulations of lubricated contacts of the thrust pad air bearing are analysed. To characterize the performance of the bearing, dimensionless LCC, relative power loss, and COT are explicitly formulated and computed from the pressure and film thickness solutions obtained in the simulations. Relative power loss and COT are resulted from the development of shear stresses in the lubricating fluid due to motion. Parametric analysis is also performed for these parameters in COMSOL Multiphysics. Additionally, performances of several pocket geometry design configurations are also analysed for the best values reached such as the maximum LCC. Pockets with shallower depths are found to have provided higher LCC in general than deeper pocket geometries and plane pads with tilting pad lubricating configuration. Finally, a physical model of an air thrust pad bearing with 3D-printed bearing segments made of PLA material is tested. The physical bearing performed very well in achieving full film separation in the test.

The development of lightweight design for automotive applications has lasted for many years and is still increasing. Vehicles with light structures use less fuel, emit less CO2, and are better for the environment. The next generation of lightweight vehicle structures will be realized using materials with a high strength-to-weight ratio, corrosion resistance, and high bending stiffness such as high-strength aluminium alloys. Increased formability, lower spring-back, and the ability to incorporate age-hardening heat treatments into the process are all advantages of the hot forming of aluminium alloys. However, because aluminium is prone to adhesion even at low temperatures, it can be difficult to avoid its transfer onto the tool. When forming aluminium, lubrication is always required to lower the interfacial shear strength and avoid direct contact between the interacting surfaces, to promote low friction and wear. However, lubricants can fail and significant issues with material transfer arise. Because of this, interruptions are needed for tool refurbishing, this issue affects process efficiency. Developing new or improved lubrication technologies to prevent adhesion and high friction, surface engineering solutions, as well as effective testing platforms related to aluminium forming, are vital. A significant challenge when studying the interaction between lubricant, aluminium, and tools often result in poor reproducibility of tests and uncertainties regarding the effect of lubricant thickness/weight on the friction behavior. Problems associated with reproducibility also affect modelling and simulations of the forming operation, as there are many uncertainties in the experimental campaigns, thus affecting the validation stages. The current study aim is to optimize the tribology test methodology used in the hot strip drawing method, with emphasis on the lubricant application methodology, to improve the reproducibility of tribological tests. Lubricant application methodology was developed by using air-brush equipment, and a consistent amount of lubricant. Different lubricant weights were characterized using two different types of lubricants (graphite-based and polymer-based lubricants), and then the tribological response was evaluated after the tribological tests. Lubricants were applied on cast iron and tool steel (CrN coated) to take into consideration the effect of the surface material and topography on the reproducibility, and consistency of the lubricant application methodology. The hot strip drawing method was used to perform tests at 350°C temperature, 10MPa pressure and 100mm sliding distance. To simulate the forming conditions encountered in hot stamping of aluminium, solubilization of a 6XXX aluminium alloy at 540°C was done before testing. An optical microscope, 3D optical profilometry, and SEM were used for the characterization of specimens after the tribological tests. With the lubricant application method, good reproducibility was obtained and it was determined that, in the case of cast iron, as the amount of both lubricants (polymer-based, graphite-based) increases the effective sliding also increases, but tool steel (CrN coated) shows slightly good results only when lubricant amounts are highest.

Environmentally adaptable grease (EAG) lubricants are essential in applications with loss lubrication due to their biodegradable nature. This is because the lubricants could be expelled into the environment during usage in some applications e.g., marine and mining applications. However, although this type of grease is sustainable to use, it also needs to bridge the performance gap it has with the mineral-based grease counterpart.  In this thesis project, a tribological evaluation comparison between the performance of EAGs and traditional mineral-based greases in large open gears is carried out. A twin disc tribometer is used to mimic the contact mechanisms of the test gears while being lubricated automatically by the grease samples through a syringe pump. For the experiments, the material surface of all the discs in the tribometer setup is steel while the different grease samples are tested for each setup. Two of the grease samples; UPL 04123 (NLGI 1.5) and UPL 04124 (NLGI 0.5) are fully formulated EAGs, while the third is a popular commercial mineral-based grease currently used in large open gears in the mining industry. An investigation of the wear of the discs used in each grease test is carried out using optical interferometry and a Scanning electron microscope (SEM). The wear volumes and wear rates are then analysed and compared to evaluate the performance of the grease samples. The wear results from the tribological characterisation using the twin disc are validated with the ISO 14635-3 standard on the FZG back-to-back test rig. Also, chemical characterisation of the unused and used grease is carried out using the advanced ATR-FTIR method to evaluate additive depletion and lastly an SEM-EDS analysis to confirm the presence of tribofilm on the surfaces of the disc samples. In conclusion, it is found that there is a correlation between the consistency of the grease sample and wear prevention; where the commercial grease with the least consistency performs best, followed by the 0.5G and lastly the 1.5G. Also, there are clear indications in the wear rates of the actions of extreme pressure additives activation at high contact pressures between the discs. The inadequacies of the ATR-FTIR and SEM-EDS methods to evaluate additives and tribofilm respectively are also discussed.

Environmentally friendly lubricants are in demand in response to the rising concerns and restrictive legislation that surround the use of mineral oil lubricants. One area of importance is understanding the service life of the environmentally friendly base oils of these non-toxic, biodegradable and renewable alternatives. The service life of a lubricant is directly influenced by its degradation behavior, especially oxidation.  In this research, selected environmentally friendly base oils; Glycerol, Rapeseed oil, Polypropylene glycol, Polyethylene glycol, Bis(di-2-ethyl hexyl) sebacate, Squalene and reference mineral oil; paraffin,  were subjected to thermo-oxidative ageing at 150oC. The changes in the chemical structures of the samples were followed using Spectroscopic, chromatographic, rheological and corrosivity studies. Tribological tests were also carried out to quantify the changes in these lubricants. The results obtained showed that the thermal oxidation affected the physicochemical properties and the lubricating ability of the base oils. However, each base oil degraded distinctly to the accelerated ageing conditions.

Gears are machine elements essential for mechanical transmission. Wear of gear teeth can causechanges in their profile geometry, causing vibration, noise, and subsequent gear failure. In this thesisproject, a twin disc tribometer has been used to mimic the actual Alfa Laval separator screw gearsystems. An investigation of the wear of different material pairs has been done using a twin disctribometer machine. In the twin disc tribometer, the material surface for one disc was bronze and thematerial for the counter disc surface was varied with steel of different types. Each bronze-steel pair wastested against different loading, lubricating and surface roughness conditions. For the wear tests, twodifferent loads, 75 N and 150 N and two different types of lubricants, Polyalphaolefin (PAO) andPolyalkylene Glycol (PAG) were taken. Wear tests were also done with the Applied Nano Surfaces(ANS) triboconditioning (TCG) steel disc samples which are surface treated to obtain a lower surfaceroughness. To obtain the wear volume and wear rate values the disc pairs were further analysed usinglaboratory equipment and computer software such as the digital microscope, optical interferometer andMountainsLab premium 9. Analytical calculations for minimum film thickness and thermally correctedminimum film thickness between the disc surfaces were obtained using the Dowson-Hamrock equationand Gupta formula, respectively. It has been found that the wear on the bronze disc is minimum if thecounter steel discs are Applied Nano Surfaces (ANS) of TCG 1 type followed by counter disc as casehardened steel, all of it at 75 N and with Polyalphaolefin (PAO) lubricant oil.