| 1. |
- Nybacka, Mikael, et al.
(författare)
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Project: CASTT - Centre for Automotive Systems Technologies and Testing
- 2007
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Annan publikation (populärvet., debatt m.m.)abstract
- Through the Centre for Automotive Systems Technologies and Testing, Luleå University of Technology aims to first of all support automotive winter testing in Northern Sweden. This means to support the local automotive test entrepreneurs and through them their customers: the car manufacturers and their suppliers. To succeed in this task, the center relies on the university's areas of leading research and most importantly on the cooperation between those areas.
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| 2. |
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| 3. |
- Pieringer, Astrid, 1979, et al.
(författare)
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Investigation of railway curve squeal using a combination of frequency- and time-domain models
- 2016
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Ingår i: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16. ; , s. 444 - 451
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Konferensbidrag (refereegranskat)abstract
- Railway curve squeal arises from self-excited vibrations during curving. In this paper, a frequency- and a timedomainapproach for curve squeal are compared. In particular, the capability of the frequency-domain model topredict the onset of squeal and the squeal frequencies is studied. In the frequency-domain model, linear stabilityis investigated through complex eigenvalue analysis. The time-domain model is based on a Green's functionsapproach and uses a convolution procedure to obtain the system response. To ensure comparability, the samesubmodels are implemented in both squeal models. The structural flexibility of a rotating wheel is modelled byadopting Eulerian coordinates. To account for the moving wheel‒rail contact load, the so-called moving elementmethod is used to model the track. The local friction characteristics in the contact zone is modelled inaccordance with Coulomb's law with a constant friction coefficient. The frictional instability arises due togeometrical coupling. In the time-domain model, Kalker's non-linear, non-steady state rolling contact modelincluding the algorithms NORM and TANG for normal and tangential contact, respectively, is solved in eachtime step. In the frequency-domain model, the normal wheel/rail contact is modelled by a linearization of theforce-displacement relation obtained with NORM around the quasi-static state and full-slip conditions areconsidered in tangential direction. Conditions similar to those of a curve on the Stockholm metro exposed tosevere curve squeal are studied with both squeal models. The influence of the wheel-rail friction coefficient andthe direction of the resulting creep force on the occurrence of squeal is investigated for vanishing train speed. Results from both models are similar in terms of the instability range in the parameter space and the predictedsqueal frequencies.
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| 4. |
- Bayani, Mohsen, 1981
(författare)
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Squeak and Rattle Prediction for Robust Product Development in the automotive industry
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Squeak and rattle are nonstationary, irregular, and impulsive sounds that are audible inside the car cabin. For decades, customer complaints about squeak and rattle have been, and still are, among the top quality issues in the automotive industry. These annoying sounds are perceived as quality defect indications and burden warranty costs to the car manufacturers. Today, the quality improvements regarding the persistent type of sounds in the car, as well as the increasing popularity of electric engines, as green and quiet propulsion solutions, stress the necessity for attenuating annoying sounds like squeak and rattle more than in the past. The economical and robust solutions to this problem are to be sought in the pre-design-freeze phases of the product development and by employing design-concept-related practices. To achieve this goal, prediction and evaluation tools and methods are required to deal with the squeak and rattle quality issues upfront in the product development process. The available tools and methods for the prediction of squeak and rattle sounds in the pre-design-freeze phases of a car development process are not yet sufficiently mature. The complexity of the squeak and rattle events, the existing knowledge gap about the mechanisms behind the squeak and rattle sounds, the lack of accurate simulation and post-processing methods, as well as the computational cost of complex simulations are some of the significant hurdles in this immaturity. This research addresses this problem by identifying a framework for the prediction of squeak and rattle sounds based on a cause-and-effect diagram. The main domains and the elements and the sub-contributors to the problem in each domain within this framework are determined through literature studies, field explorations and descriptive studies conducted on the subject. Further, improvement suggestions for the squeak and rattle evaluation and prediction methods are proposed through prescriptive studies. The applications of some of the proposed methods in the automotive industry are demonstrated and examined in industrial problems. The outcome of this study enhances the understanding of some of the parameters engaged in the squeak and rattle generation. Simulation methods are proposed to actively involve the contributing factors studied in this work for squeak and rattle risk evaluation. To enhance the efficiency and accuracy of the risk evaluation process, methods were investigated and proposed for the system excitation efficiency, modelling accuracy and efficiency and quantification of the response in the time and frequency domains. The demonstrated simulation methods besides the improved understanding of the mechanisms behind the phenomenon can facilitate a more accurate and robust prediction of squeak and rattle risk during the pre-design-freeze stages of the car development.
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| 5. |
- Li, Xiaojian, 1991, et al.
(författare)
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A new method for performance map prediction of automotive turbocharger compressors with both vaneless and vaned diffusers
- 2021
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 235:6, s. 1734-1747
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Tidskriftsartikel (refereegranskat)abstract
- A new approach to predict the performance maps of automotive turbocharger compressors is presented. Firstly, a polynomial equation is applied to fit the experimental data of flow coefficient ratios for the centrifugal compressors with both vaneless and vaned diffusers. Based on this equation, the choke and surge flow coefficients under different machine Mach numbers can be quickly predicted. Secondly, a physically based piecewise elliptic equation is used to define compressors’ characteristic curves in terms of efficiency ratio. By introducing the flow coefficient ratio into the efficiency correlation, the empirical coefficients in the piecewise elliptic equation are uniquely calibrated by the experimental data, forming a unified algebraic equation to match the efficiency maps of the compressors with both vaneless and vaned diffusers. Then, a new universal equation, which connects the work coefficient, the impeller outlet flow coefficient and the non-dimensional equivalent impeller outlet width, is derived by using classical aerothermodynamic method. The off-design pressure ratio is predicted based on the equivalent impeller outlet width with less knowledge of the compressor geometry and no empirical coefficients. Finally, three state-of-the-art turbocharger compressors (one with vaneless diffuser, two with vaned diffusers) are chosen to validate the proposed method, and the results show a satisfactory accuracy for the performance map prediction. This method can be used for the preliminary design of turbocharger compressors with both vaneless and vaned diffusers, or to assess the design feasibility and challenges of the given design specifications.
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| 6. |
- Vernersson, Tore V, 1968, et al.
(författare)
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Wear of Railway brake block materials at elevated temperatures : pin-on-disc experiments
- 2012
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Ingår i: Proceedings of Eurobrake 2012. - FISITA.
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Konferensbidrag (refereegranskat)abstract
- An experimental study on a pin-on-disc rig is presented where the wear of some brake block materials at controlled elevated disc temperatures are reported. It is found for the three studied organic composite materials that the (specific) wear rate increases radically at a temperature of about 500 oC. For temperatures below 500 oC, the wear rate is found to increase with temperature. The cast iron material shows an increase of the wear rate up to 500 oC, after which a transition in the wear mechanism occurs and the wear rate is decreasing with increasing temperature. The studied sinter material shows a weak dependence of the wear rate with temperature.
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| 7. |
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| 8. |
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| 9. |
- Lundberg, Oskar, 1980-
(författare)
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On the influence of surface roughness on rolling contact forces
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Road vehicle tyres, railway wheels and ball bearings all generate rolling contact forces which are transferred within a finite area of contact between the rolling element and the substrate. Either it is visible or not for the human eye, a certain degree of roughness is always present on the contacting surfaces and it influences the generation of both vertical and lateral contactforces. The purpose of this investigation is to enhance the understanding and modelling of the influence from small-scale surface roughness on the generation of rolling contact forces. To this end, a computationally efficient method to include roughness-induced contact nonlinearities in the dynamic modelling of rolling contacts is proposed. The method is implemented in a time domain model for vertical wheel–track interaction to model rolling-induced rail vibrations, showing good agreement with measurements. Furthermore, a test rig is developed and used for the investigation of tyre–road rolling contact forces. Detailed studies are performed on the influence of substrate roughness on the resulting contact forces for a tyre tread block which is rolling at different operating conditions. The choice of substrate as well as the rolling velocity and the slip ratio is observed to have significant influence on the resulting friction coefficient. For high slip ratios, stick–slip oscillations appear, exhibiting frequency content which is largely dependent on the choice of substrate. The outcomes of this study can potentially be used to improve future tyre–road contacts with respect to wear, traction and noise generation.
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| 10. |
- Torstensson, Peter, 1981, et al.
(författare)
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Hybrid model for prediction of impact noise generated at railway crossings
- 2016
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Ingår i: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16 (2016). ; , s. 539 - 545
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Konferensbidrag (refereegranskat)abstract
- A hybrid model for the prediction of impact noise at railway crossings is presented. The hybrid model combines the simulation of vertical wheel‒rail contact force in the time domain and the prediction of sound pressure level using a linear frequency-domain model. The time-domain model uses moving Green’s functions for the vehicle and track models (accounting for wheel flexibility and a discretely supported rail with space-variant beam properties) and a non-Hertzian wheel‒rail contact model. The time-domain and frequency-domain models are coupled based on the concept of an equivalent roughness spectrum. The model is demonstrated by investigating the influence of axle load, vehicle speed and wheel profile on generated impact noise levels. A negligible influence on impact noise is observed for axle loads in the interval 15 – 25 tonnes. On the other hand, increasing vehicle speed from 80 km/h to 150 km/h, or comparing a nominal S1002 wheel profile with a severely hollow worn profile, result in substantially higher levels of impact noise; for the given wheel and track conditions the differences are in the order of 10 dB(A).
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| 11. |
- Winroth, Julia, 1981, et al.
(författare)
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Contact stiffness considerations when simulating tyre/road noise
- 2017
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 409, s. 274-286
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Tidskriftsartikel (refereegranskat)abstract
- Tyre/road simulation tools that can capture tyre vibrations, rolling resistance and noise generation are useful for understanding the complex processes that are involved and thereby promoting further development and optimisation. The most detailed tyre/road contact models use a spatial discretisation of the contact and assume an interfacial stiffness to account for the small-scale roughness within the elements. This interfacial stiffness has been found to have a significant impact on the simulated noise emissions but no thorough investigations of this sensitivity have been conducted. Three mechanisms are thought to be involved: The horn effect, the modal composition of the vibrational field of the tyre and the contact forces exciting the tyre vibrations. This study used a numerical tyre/road noise simulation tool based on physical relations to investigate these aspects. The model includes a detailed time-domain contact model with linear or non-linear contact springs that accounts for the effect of local tread deformation on smaller length scales. Results confirm that an increase in contact spring stiffness causes a significant increase of the simulated tyre/road noise. This is primarily caused by a corresponding increase in the contact forces, resulting in larger vibrational amplitudes. The horn effect and the modal composition are relatively unaffected and have minor effects on the radiated noise. A more detailed non-linear contact spring formulation with lower stiffness at small indentations results in a reduced high-frequency content in the contact forces and the simulated noise.
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| 12. |
- Gomez-Gallegos, A. A., 1983-, et al.
(författare)
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A comparative study assessing the wear behaviour of different ceramic die materials during superplastic forming
- 2017
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Ingår i: Materialwissenschaft und Werkstofftechnik. - : Wiley-VCH Verlagsgesellschaft. - 0933-5137 .- 1521-4052. ; 48:10, s. 983-992
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Tidskriftsartikel (refereegranskat)abstract
- Superplastic forming is an advanced manufacturing process where metallic sheets are heated to their superplastic region to be then blow formed within a die set. The process allows for the forming of complex parts but it is typically restricted to low volume production and high value pieces. Despite their brittle nature, ceramic dies are a developing technology for superplastic forming as they offer lower production costs and shorter lead times than conventional metallic dies, thus reducing process costs. This work presents a method to assess ceramic die wear by means of a novel test rig developed a at the Advance Forming Research Centre of the University of Strathclyde, Scotland, UK where the superplastic forming die-part interaction can be replicated at laboratory scale. Controllable normal load tests at standard superplastic forming conditions on three different reinforced ceramic materials are carried out with a view to understanding their wear mechanisms and to ultimately identify methods to improve their wear resistance.
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| 13. |
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| 14. |
- Kumar, Mayank, 1991-
(författare)
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Friction in threaded fasteners : Influence of materials and tooling
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Threaded fasteners represent the most common type of machine element, with a unique function that facilitates ease of assembly and disassembly. This ease of disassembly allows machine parts to be reused, refurbished, and recycled. Easy as these components are to assemble, several factors must be considered to achieve the desired clamp force and to utilize the fastener to its full load capacity. The research presented in the thesis compares different tightening strategies and assembly tools to show that the clamp force and it´s scatter are influenced by the variation in the coefficient of friction (CoF) to a much larger extent than by the accuracy of an assembly tool. The research therefore focus on understanding the frictional response in a threaded fastener joint during tightening.A range of design and assembly factors are considered to identify how to increase reliability of the threaded fastener joints. These factors include tightening speed, coating, surface topography, fastener storage conditions, cutting fluid residue and joint material. A torque-controlled, two-step tightening method was mainly used in the studies as it is widely practiced across the production floor of the motor vehicle and general industries to tighten threaded fastener joints. A state-of-the-art friction test rig (FTR) was built to quantify variations in the CoF in the thread and under-head contacts during tightening. Coatings and contact surfaces are also characterized using SEM, FIB, indenters, and optical microscopes to gain an insight to find the likely reasons behind CoF variation. Fasteners with different Zn-based coatings were tightened on plates with surface topographies similar to those found in the motor vehicle industry. The samples were not cleaned before the testing but used "as-received" from the supplier. The degree of damage to the joint surface and fastener thread from the tightening depends on the hardness of the coating. The hardest coating (Zn-Ni) remained relatively unchanged but gave twice as high CoF in the under-head contact compared to the softest coating (Zn-flake). The under-head friction often dominates the tightening process and may be significantly affected by the joint surface topography and the level of cleanliness. In the automotive industry, many parts to be assembled are not thoroughly cleaned, increasing the risk of cutting fluid residue on the joint surface. Different types of cutting fluids were compared in a study with fasteners tightened against “as-received" and cleaned plates. It was shown that CoF might drastically decrease depending on the coating and cutting fluid types. An ester-based fluid performed best, providing the lowest CoF in the under-head contact due to its higher viscosity and polarity. A water-based fluid showed a significantly larger scatter. Water can also influence friction due differences in humidity and temperature. Sometimes fasteners are stored outside a factory which could lead to water diffusion in the coating in hot-humid climate or condensation of water on the fastener surface when it is brought from the outside storage at sub-zero temperatures into the production hall. Water on the coating and inside of it could lead to low CoF, with overtightening and fastener failure as a result. Four Zn-based coatings were compared and showed different response depending on the coating structure and topcoat. Another way to reduce CoF is to use variable speed tightening. It will also increase productivity, as it is faster. It will also improve operator ergonomics, as it gives much lower reaction torque. Much higher CoF was found for EPZ coating when tightened at a constant and very low speed, 5 rpm, due to cohesion that resulted in material transfer, compared to CoF during high, variable speed tightening. At the same time, speed had negligible influence on the CoF when using soft Zn-flake coating as the coating easily sheared off, acting as a solid lubricant.A soft coating is also practical when used in contact with parts made using additive manufacturing (AM). The AM parts are often rough, but a soft coating can mitigate an increase in the under-head CoF. An interesting finding was that the cheapest solution of using an uncoated fastener works very well. An anti-corrosion oil on the plain fastener helped in achieving low CoF. When the AM plate was machined, the CoF and surface damage significantly increased due to the lay of the surface topography created by machining. The findings presented in the thesis increase understanding of how various design and assembly factors govern friction in the thread and under-head contacts. The under-head contact dominates friction response. A proper selection and adjustment of these factors will help design engineers to optimize joint designs and achieve high fastener strength utilization.
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| 15. |
- Cervantes, Michel, et al.
(författare)
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Porjus U9A full-scale hydropower research facility
- 2008
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Ingår i: Hydro technology and the evironment for the new century. - Foz do Iguassu.
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Konferensbidrag (refereegranskat)abstract
- Hydropower still faces complex scientific and technical challenges in order to secure the availability and reliability of the power plants despite more than a century of development. The main challenge is due to new market constrains such as electrical market deregulation and introduction of renewable sources of energy. The major problem is related to the dynamic of the rotor involving several fields: hydraulics, power engineering and mechanics. On the other side, the large and growing hydropower world market represents an opportunity for technically advanced companies offering better efficiency. The difficulty to scale rigorously any technical advance makes full-scale experiment a necessity. World unique facilities are available at Porjus, Sweden, for this purpose. The Porjus Hydropower Centre is composed of a Francis (U8) and a Kaplan (U9) turbine of 10 MW, each exclusively dedicated to education, research and development. In order to further investigate specific issues related to availability and reliability, a project was initiated in 2006. The main objective is to make U9 a full-scale hydropower laboratory able firstly to furnish the necessary data for the development of rotor-dynamic models but also turbines and bearings. To this purposes more than 200 sensors have been installed to measure displacements, forces, pressure, film thickness, strains... The work presents an overview of the newly upgrade facility as well as some of the problems faced during the instrumentation of the machine.
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| 16. |
- Karlsson, Stefan, 1984-, et al.
(författare)
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Non-destructive strength testing of microindented float glass by a nonlinear acoustic method
- 2023
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Ingår i: Construction and Building Materials. - 0950-0618 .- 1879-0526. ; 391
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Tidskriftsartikel (refereegranskat)abstract
- The present paper describes a method for non-destructive testing of the glass strength. Square 10 × 10 cm2 samples of annealed float glass was inflicted with a controlled defect in the centre of the atmospheric side using Vickers microindentation-induced cracking with a force of 2 N, 5 N and 10 N and compared to an un-indented reference. The samples were non-destructively tested using a nonlinear acoustic wave method resulting in defect values. The average of the defect values was found to linearly correlate to the indentation force in a log–log relationship. The samples were subsequently tested in a ring-on-ring setup that allows for an equibiaxial stress state. The indentation-induced cracking gave practically realistic strength values in the range of 45 to 110 MPa. The individual sample values for failure stress as a function of normalized defect value show linear trends with approximately half of the data within 95% confidence limit. In summary, this study provides an initial proof-of-concept for a non-destructive testing of the strength of glass.
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| 17. |
- Mill, O., et al.
(författare)
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Analysis and development of hydro power research : synthesis within Swedish Hydro Power Centre
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The market for hydropower re-investments in Sweden is approx 2.5 billion SEK/yr the coming decade. Large investments will also be carried out in Swedish tailing dams. This will result in challenging projects and need of experts. A crucial factor for a successful management of these challenges is the supply of engineers and researchers with hydro power and dam skills and knowledge. Swedish Hydro Power Centre (Svenskt vattenkraftcentrum, SVC) is a competence centre for university education and research environments within hydro power and mining dams. SVC comprises of two knowledge areas: Hydraulic Engineering and Hydro Turbines and Generators, respectively. SVC builds high-quality and long term sustainable knowledge at selected universities...
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| 18. |
- Persson, Erik, et al.
(författare)
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Clamp Force Accuracy in Threaded Fastener Joints Using Different Torque Control Tightening Strategies
- 2021
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Ingår i: SAE technical paper series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; :2021
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Tidskriftsartikel (refereegranskat)abstract
- The assembly of threaded fasteners may seem straightforward. However, there are many factors to consider to achieve quality tightened joints, including the joint material, threaded fastener, and coatings. Additionally, there are many assembly tool types and torque application strategies to choose from. This investigation studies the tightening speed dynamics when using torque as a control method. The clamp force obtained in the joint changes when tightening at high speed or when the speed varies greatly during tightening. This type of tightening is called highly dynamic. Highly dynamic torque control tightening strategies are studied, such as impact, pulse, and inertia-controlled methods, and compared with the continuous drive strategy, which is a standard dynamic torque tightening method. The clamp force and its scatter caused by the torque accuracy in the assembly tool type are investigated for the abovementioned torque application strategies. The study also focuses on the different results obtained from the International Organization for Standardization’s (ISO) 16047:2005 (Fasteners-Torque/clamp force testing) standard compared to a production-like setup.
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| 19. |
- Silva-Magalhães, Ana, et al.
(författare)
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In-situ temperature measurement in friction stir welding of thick section aluminium alloys
- 2019
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Ingår i: Journal of Manufacturing processes. - : Elsevier. - 1526-6125 .- 2212-4616. ; 39, s. 12-17
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Tidskriftsartikel (refereegranskat)abstract
- Friction stir welding (FSW) is a reliable joining technology with a wide industrial uptake. However, several fundamentals of the process such as the temperature inside the stirred zone of the weld and its influence on mechanical properties, are not yet fully understood. This paper shows a method for accurate temperature measurements in multiple locations around the tool, to identify the location of the peak temperature, the temperature variations between the advancing and the retreating side of the tool and its relation to the tool geometry. Both standardised thermocouples in the FSW tool and the novel “tool-workpiece thermocouple” method were used to record temperatures.Bead-on-plate welds in 20 mm thickness AA6082-T6 were produced while the temperatures were measured in three locations on the FSW tool: at the shoulder outer diameter, at the transition from shoulder to probe and at the probe tip. It was found that the hottest point in the stirred zone was 607 °C and was located at the transition between the shoulder and probe, on the retreating-trailing side of the tool. The lowest temperature was found at the probe tip on the retreating-leading side of the tool.The results offer a better understanding of the temperature distribution around a FSW tool. The method presented can be applied to verification of thermal simulation models, tool design optimization, quality assurance and temperature feedback control.
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| 20. |
- Casanueva, Carlos, 1981-, et al.
(författare)
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Comparison of wear prediction models for different contact conditions
- 2016
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Ingår i: Proceedings of the 24th Symposium of the International Association for Vehicle System Dynamics (IAVSD 2015), Graz, Austria, 17-21 August 2015. - : CRC Press. - 9781138028852 - 9781498777025 ; , s. 871-878
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Konferensbidrag (refereegranskat)abstract
- Simulation of wheel and rail wear allows to predict long term profile evolution and thus, study the consequences of wheel damage in the dynamic behaviour of the vehicle, or study future maintenance requirements. Several models have been developed which try to solve the wear issue by relating the energy dissipated in the wheel-rail contact to the worn out material, from which two can be highlighted (Tg/A and Archard) which have significant differences on contact level. Even though, the prediction of long term wheel profile evolution has been validated with these two models, which means that for regular applications they seem to have an equivalent behaviour. In this work similarities and differences between the long term wear prediction methodologies are analysed, discussing their actual limitations. Then, these differences are exploited in specific operational cases to compare their wear prediction performance.
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| 21. |
- Gåård, Anders, 1977-, et al.
(författare)
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Nano-scale friction of multi-phase powder metallurgy tool steels
- 2015
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Ingår i: Advanced Materials Research. - : Trans Tech Publications. - 1022-6680 .- 1662-8985. ; 1119, s. 70-74
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Tidskriftsartikel (refereegranskat)abstract
- Friction is a fundamental phenomenon in tribology involving complex mechanisms between thecontacting surfaces. Measurements of friction are often made using devices with substantially largercontact area than dimensions corresponding to microstructural features of the materials. Hence, for multi-phase materials,influence of particular microstructural constituents is not resolved. In the present work, a tribometerwith a contact area in the nano-scale range was used to map friction for different types of tool steelswith different chemical- and phase composition. Owing to the small tip radius, frictionalcharacteristics of primary carbides and the steel matrix were measured and compared. Dependingon chemical composition, a difference was observed where the coefficient of friction wasapproximately twice higher for the steel possessing highest coefficient of friction, including bothcarbides and the steel matrix.
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| 22. |
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| 23. |
- Karlsson, Patrik, 1973-, et al.
(författare)
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Galling resistance and wear mechanisms for cold-work tool steels in lubricated sliding against high strength stainless steel sheets
- 2012
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Ingår i: Wear. - Amsterdam : Elsevier. - 0043-1648 .- 1873-2577. ; 286-287, s. 92-97
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Tidskriftsartikel (refereegranskat)abstract
- Tool damage in sheet metal forming of stainless steel is of high concern for the forming industry. In the present work, ingot cast AISI D2 and advanced powder metallurgy tool steel (PM) cold-work tool steels were evaluated and ranked regarding wear mechanisms and galling resistance. Wear tests were performed using a slider-on-flat-surface (SOFS) tribometer in sliding against austenitic–ferritic (duplex) stainless steel sheets at different contact pressures in lubricated conditions. The best galling resistance was observed for the nitrogen alloyed PM tool steels. Abrasive scratching of the tool surfaces and transfer of sheet material due to adhesive wear were the main metal forming tool surface damage mechanisms. By increasing the hardness of one PM sheet metal forming tool grade, the galling resistance was enhanced.
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| 24. |
- Karlsson, Patrik, 1973-, et al.
(författare)
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Galling resistance evaluation of tool steels by two different laboratory test methods for sheet metal forming
- 2012
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Ingår i: Lubrication Science. - : John Wiley & Sons. - 0954-0075 .- 1557-6833. ; 24:6, s. 263-272
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Tidskriftsartikel (refereegranskat)abstract
- Adhesive accumulation of work material on the tool surface is today a major problem in many sheet metal-forming applications. Different laboratory test methods are used to investigate galling with respect to different tool materials, lubricants and process conditions. In the present study, the galling resistance of a modern nitrogen-alloyed powder metallurgy tool steel and an conventional ingot cast D2 type tool steel was evaluated under lubricated sliding against ferritic stainless steel sheets using a commercial pin-on-disc (POD) and an in-house made slider-on-flat-surface (SOFS) tribotester. The investigated tool steels ranked similarly in terms of galling resistanc in both test methods. However, sliding distances to galling were longer for the SOFS equipment due to continuous sliding on new lubricated sheet surface. Best performance was demonstrated by the powder metallurgy tool steel treated to 65 HRC. Differences in friction behaviour and galling initiation were analysed on the basis of the two different working conditions, i.e. open (SOFS) and closed (POD) tribosystems. Copyright © 2012 John Wiley & Sons, Ltd.
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| 25. |
- Karlsson, Patrik, 1973-, et al.
(författare)
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Influence of tool steel hard phase orientation and shape on galling
- 2014
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Ingår i: Advanced Materials Research. - : Trans Tech Publications. - 1022-6680 .- 1662-8985. ; 966-96, s. 249-258
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Tidskriftsartikel (refereegranskat)abstract
- Conventionally manufactured cold work tool steel is often used in sheet metal forming as die material. Due to the forging process, the as-cast network structure of carbides is broken into elongated particles. Depending on the tool cross-section, the orientation and shape of carbides in the active tool surface is different. In the present research, the influence of tool steel hard phase orientation and shape on galling was investigated. D2 type tool steel was cut in three different orientations and tested in lubricated sliding conditions against AISI 304 austenitic stainless steel. Tests were performed using a Slider-On-Flat-Surface and galling was detected by changes in friction and post-test microscopy. The lubricant was Castrol FST8 using 5 g/m2 sheet material. Results showed a strong correlation between sliding distance to galling and tool steel hard phase orientation and shape at low loads, whereas high load contact resulted in early galling in all cases. Material transfer was observed mainly to the tool steel matrix. The worst performance was observed for specimens cut so that the tool steel hard phase, M7C3 carbides in the D2 steel, were oriented along the sliding direction, which resulted in longer open tool matrix areas contacting the sheet material.
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