Surface texturing of metals and alloys has recently been identified as an environmentally friendly alternative to the use of high-performance lubricants with complex formulations.
Adding micro-scale ...textures to one or both sliding surfaces of mechanical components can reduce friction and wear compared to conventional/untextured surfaces.
This study investigates the effect of laser textured surfaces on the tribological behavior of titanium Ti6Al4V. Multiple texture types were created by varying the energy density of pulse and scanning speed of the laser. These variations modify the outer layers of the alloy, rising the generation of specific topographies and changing the initial properties by means of microstructural modifications and oxidation processes.
The performance of these surfaces was evaluated using a ceramic ball in a ball-on-flat reciprocating tribometer under lubricated conditions. Wettability of the tribological system was examined by measuring the contact angle of the oil used on textured and conventional surfaces.
Tribological performance of textured surfaces was found to strongly depend on the laser patterning parameters. Replacing conventional surfaces with textured surfaces reduced friction up to 62% and wear up to two orders of magnitude. Wear mechanisms are discussed from optical microscopy and SEM/EDS observation of wear tracks on titanium disks and ceramic balls.
Dry machining of aluminum parts has been the most eco-friendly method in an attempt to reduce the use of mineral-based lubricants and other working fluids. The drawbacks of dry machining include an ...increase of contact temperatures and stresses leading to high values of tool wear and a decrease of the tool life. For this reason, more sustainable lubricants are needed as a middle point between waste generation and tool life.
Since 2001, Ionic Liquids (ILs) have attracted interest as high-performance lubricants and lubricant additives. In this work, the lubricating ability of one halogen-containing and two halogen-free ILs used as additives in water has been investigated and compared to a halogen-containing cutting fluid (CF). Tests were performed using a pin-on-disk tribometer for aluminum-tungsten carbide pair. The worn surfaces of the disks and balls were analyzed by optical and scanning electron microscopies, non-contact 3D profilometry and energy dispersive X-ray spectroscopy. It was found that the addition of 1 wt% of one of the halogen-free ILs reduces friction and wear of both aluminum disks and ceramic balls with respect to dry or water-lubricated conditions. In addition, no wear was detected on the ball surface, therefore increasing the tool life compared to the CF.
•Ionic liquids as additives in water are efficient sustainable lubricants.•Results showed friction reductions of more than 70% and negligible wear.•The use of ionic liquids also improved the surface finish inside the wear track.•Water-based cutting fluids using ionic liquids showed potential of extending the tool life.
Abstract
Surface texturing has demonstrated to be a useful technique for improving the tribological performance of surfaces in contact. In particular, in this research it has been applied to the ...Ti6Al4V titanium alloy, with poor tribological behaviour, by creating different texturing densities with pyramidal geometries. Additionally, these geometries have been obtained through sinking electro-discharge machining processes, scarcely addressed in the scientific literature. In dry sliding conditions, the results obtained show an improvement of about 65% in the coefficient of friction, while in lubricated contact, the improvement in the lubricant retention capacity results in the formation of an abrasive paste formed by the lubricant and the wear debris, which worsens tribological behaviour.
Abstract
Weight reduction is a constant improvement point for the aerospace sector. The joining of difficult to weld materials such as 2xxx and 7xxx aluminium series alloys has attracted the ...attention to Friction Stir Welding (FSW) in this field. This solid state welding process has already been presented as an environmentally friendly alternative for riveted joints and conventional welding operation in the automobile sector. Unfortunately, its application on the aeronautical sector is not completely studied at the moment and concerns about its quality and in-service behaviour have delayed its implementation. This paper stablished a methodology to study the effect of the welding parameter and applied it to a structural aluminium AA2024-T3, covering the design of the testing bench, the tool, the process monitoring and the analysis of the quality and main mechanical properties of the joint. The results showed the impact of the welding parameters on the quality of the joint. The burr and the roughness were optimised for 850 rpm and the forces were reduced up to 30% for this rotational speed. Similarly, the mechanical properties were reduced by up to 61.5% and 45% compared to the base material for the UTS and microhardness respectively.
Abstract
The customisation or redesign of parts for Additive Manufacturing (AM) to meet the design requirements is an increasing trend. In this context, numerous studies related to the improvement of ...the mechanical properties of Additive Manufacturing parts used for static applications are emerging. However, the use of these parts in dynamic applications or in relative movement situations has not been deeply developed. Some studies have been focused on the fatigue properties of AM parts while few authors have analysed the sliding behaviour of these parts. This paper presents a characterisation of the wear behaviour of Fused Deposition Modelling (FDM) parts using Pin-on-Disc techniques with the aim of studying their possible implementation in dynamic applications.
Manufacturing Engineering Processes Knowledge Area has developed an innovative teaching experience in order to give, only in one session, a complete view of a basic subject, Manufacturing ...Engineering. This experience has been developed on the basis of making a cube constructed in card by groups of students. Starting from this, the different steps of a manufacturing process have been identified, as well as the necessity of establishing a quality control for any of them. Moreover, the different material processing technology types have been distinguished, the concept of process performance has been introduced and the different possibilities for sequential and/or parallel processing have been analyzed. On the basis of this, the students have built the topics program of the subject, justifying its competences distribution. In the same way, the students have defined the related basic concepts. At the end of the course, a questionnaire containing the basic cognitive concepts was answered by them, 100% successfully.
Laser Surface Texturing (LST) is widely used to modify hard material surfaces improving their physic-chemical and mechanical properties. This technology is particularly relevant for tungsten ...carbides, a material that requires high complexity methods when other micro-machining processes are used. LST allows innovative cutting tool designs that improve the machining behavior and enlarge the cutting tool lifetime.
This research analyses the influence of LST parameters on the track dimensions, roughness, microstructure, hardness, and lubricant retention ability of the modified surfaces. Twelve combinations of energy density of pulse and scanning speed created different geometrical patterns on WC-Co surfaces. LST parameters were related to specific shape and dimensions of the linear grooves. Energy density was proven as the most influential parameter for dimensional characteristics and roughness values. Specific channel morphologies increased the lubricant expansion area up to 50%, leading the lubricant to a linear track direction. Low scanning speed and high energy density also increased the surface hardness up to 20%. The surface composition was also modified. The thermal effect of the laser treatments and the non-protective atmosphere increased the oxygen on the surface and modified the WC-Co microstructure. However, the thermal affected zone is considerably low compared to other texturing processes.
•Laser parameters affect the micro-groove geometry of WC-Co.•Aggressive laser parameters increase hardness of WC-Co surface.•Microgroove geometry modifies the lubricant retention ability.•Laser Surface texture influences WC-Co surface oxidation.
We determined the contribution of common carotid intima-media thickness (IMT) in the prediction of future coronary heart disease and cerebrovascular disease when added to established risk factors.
We ...used data from a nested case-control study comprising 374 subjects with either an incident stroke or a myocardial infarction and 1496 controls. All subjects were aged 55 years and older and participated in the Rotterdam Study. Mean follow-up was 4.2 years (range, 0.1 to 6.5 years). We evaluated which correlates of coronary heart disease and cerebrovascular disease contribute to the prediction of either a new incident myocardial infarction or a stroke. Logistic regression modeling and the area under the receiver operating characteristic curve (ROC area) were used to quantify the predictive value of the established risk factors and the added value of IMT.
The ROC area of a model with age and sex only was 0.65 (95% CI, 0.62 to 0.69). Independent risk factors were previous myocardial infarction and stroke, diabetes mellitus, smoking, systolic blood pressure, diastolic blood pressure, and total and HDL cholesterol levels. These risk factors increased the ROC area from 0.65 to 0.72 (95% CI, 0.69 to 0.75). This model correctly predicted 17% of all subjects with coronary heart disease and cerebrovascular disease. When common carotid IMT was added to the previous model, the ROC area increased to 0.75 (95% CI, 0.72 to 0.78). When only the IMT measurement was used, the ROC area was 0.71 (95% CI, 0.68 to 0.74), and 14% of all subjects were correctly predicted. There was no difference in ROC area when different measurement sites were used.
Adding IMT to a risk function for coronary heart disease and cerebrovascular disease does not result in a substantial increase in the predictive value when used as a screening tool.
Additive Manufacturing (AM) is one of the Key Enabling Technologies (KET’s) in Industry 4.0. One of the most worldwide used technologies is Fussed Deposition Modelling (FDM), a technology commonly ...used for domestic purposes. However, it could become a profitable option for industrial applications such as protections parts, flexible clamping systems or large volume parts. One of the issues that keeps this technology away from the mainstream industry is the lack of dimensional accuracy and the appearance of layer deposition defects that are produced as a consequence of the nature of the process. Those defects are usually reduced using chemicals post treatments. However, this option considerably increases the cost of the part as well as it environmental impact for big size parts. This work studied machining procedures as sustainable post-operation in order to reduce FDM dimensional and superficial defects. For this purpose, Acrylonitrile-Butadiene-Styrene (ABS) parts produced by FDM were machined using different machining strategies. Parts were perimetral milled using up milling and down milling strategies and finally a face milling operation was performed. The relationship between the layer height and the directionality of the layers in machining results was analyzed, in terms of surface quality (Ra, Rz, Rsm) and dimensional accuracy. Rz and Rsm results had been analyzed to verify that the grooves produced in FDM process disappeared. Ra values were reduced by up to ten times after milling process. Dimensional accuracy is increased by up to 50% while the removed rate was kept in a maximum of 7%. Additionally, removed material can be reused by means of proper chip extraction system, favoring the performance of the resources.
Machining process usually involves relevant wear effects on the cutting tool, producing undesirable surface features on the work-pieces. Lubricants and cooling fluids are used with the aim to ...minimize the wear phenomena as well as high temperatures produced during the cutting processes. However, the use of these fluids may have an adverse environmental impact. For this reason, the reduction of quantity of cutting fluids used in the machining process is a requirement in order to improve the performance and sustainability of the process. For this purpose, this work proposes an increase of the lubricant retention ability for cutting tools based on surface modification. In this research, micro-geometrical features of Carbide (WC-Co) surfaces have been modified by laser texturing techniques. A wide range of roughness topographies had been developed by changing the laser irradiation parameters of energy density of pulse (Ed) and scanning speed of the beam (Vs). Different geometries of the textured tracks (single spots, linear tracks, circular tracks) also were studied. Moreover, through specific roughness features conducted by texturing process, the retention ability of cutting fluids was modified. It was evaluated by the contact angle between liquid and solid phases. This modification allowed to increase the self-lubricant effect of the WC-Co surface. This methodology has been validated on carbide tools under lubricated machining processes. Wear effects on the cutting tool were reduced and the surface finish of the machined parts was remained at least in the same ranges as non-modified tools.
PDF
