A new measuring method for friction factor by using ring with inner boss compression test

To overcome the disadvantage of the bulging effect due to non-uniform deformation in dimension measurement of the conventional ring compression test (RCT), a new measuring method for the friction factor called ring compression test with inner boss (RCT-IB) was proposed. The compression behavior of the ring with an inner boss was investigated and results showed that the change of inner boss was sensitive to friction. The non-concave profile of inner boss allows the dimensional changes to be easily and precisely measured. The calibration curves of RCT-IB were constructed and compared with those of RCT showing similar level of sensitivities at most friction conditions. The RCT-IB method was successfully used to measure the friction factors under four different lubricating conditions

Friction Reduction in Powertrain Materials: Role of Tribolayers

This study aims at understanding the micromechanisms responsible for reduction in friction and wear in the engine cylinder bore/liner materials when tested under lubricated and unlubricated conditions. The tribolayers formed in-situ during sliding contact are unique to each tribosystem and a detailed study of these tribolayers will shed light on the friction reduction mechanisms in powertrain materials. Boundary lubricated tribological performance of grey cast iron (CI) tested against non-hydrogenated diamond-like carbon coating (NH-DLC) resulted in 21% lower coefficient of friction (COF) and an order of magnitude lower volumetric wear compared to CI and steel counterfaces. Dilution of the engine oil by ethanol containing E85 biofuel, consisting of 85% ethanol and 15% gasoline, was beneficial as COF and volumetric wear losses were further reduced. TEM/EELS studies of the NH-DLC counterface provided evidence for OH adsorption of the dangling carbon bonds at the coating surface leading to low friction. Advantage of E85/engine oil blend was also evident during boundary lubricated sliding of eutectic Al-12.6% Si alloy against AISI 52100 steel. The oil residue layer (ORL) formed during boundary lubricated sliding incorporated nanocrystalline regions of Al, Si, ZnS, AlPO4 and ZnO surrounded by amorphous carbon regions. Higher proportions of Zn, S, and P antiwear compounds formed in the ORL when tested using the E85/oil (1:1) blend compared to the unmixed engine oil as the hydroxyl groups in ethanol molecules facilitated ZDDP degradation. Mico-Raman spectroscopy indicated two types of tribolayers formed during unlubricated sliding of thermally sprayed low carbon steel 1010 coating deposited on linerless Al 380 cylinder bore: i) Fe2O3 layer transformed from FeO during dry sliding and ii) Fe2O3 layer with a top amorphous carbon transfer layer when run against H-DLC coated TCR with COF of 0.18. The NH- and H-DLC coatings, that provide low friction under room temperature conditions, fail at temperatures \u3e 200 °C. It was shown that W containing DLC (W-DLC) coatings offered low and stable COF of 0.07 at 400 °C while a Ti incorporated multilayer MoS2 (Ti-MoS2) coating maintained COF between 0.11 at 25 °C to 0.13 at 350 °C. The low friction provided by these coatings was attributed to formation of high temperature lubricious oxides: tungsten trioxide (WO3) in case of W-DLC and MoO3 in case of MoS2, as revealed by Raman analyses of the tribolayers formed on counterface surfaces. Tribolayer formation during sliding friction of multuilayered graphene (MLG), a potential lubricant, depended on the material transfer and relative humidity (RH). Sliding friction tests performed on MLG in air (10- 45% RH) and under a dry N2 atmosphere showed that progressively lower friction values were observed when the RH was increased, with maximum COF of 0.52 in dry N2 and lowest COF of about 0.10 at 45% RH. Microstructural studies including cross-sectional FIB/HR-TEM determined that sliding induced defects which comprised of edge fracture, fragmented/bent graphene stacks compared to pristine graphene and disordered regions between them. In summary, this work shows that delineating the micromechanisms responsible for reduction in friction and wear is critical for development of appropriate materials and coatings for powertrain components

A novel approach towards a lubricant-free deep drawing process via macro-structured tools

In today’s industry, the sustainable use of raw materials and the development of new green technology in mass production, with the aim of saving resources, energy and production costs, is a significant challenge. Deep drawing as a widely used industrial sheet metal forming process for the production of automotive parts belongs to one of the most energy-efficient production techniques. However, one disadvantage of deep drawing regarding the realisation of green technology is the use of lubricants in this process. Therefore, a novel approach for modifying the conventional deep drawing process to achieve a lubricant-free deep drawing process is introduced within this thesis. In order to decrease the amount of frictional force for a given friction coefficient, the integral of the contact pressure over the contact area has to be reduced. To achieve that, the flange area of the tool is macro-structured, which has only line contacts. To avoid the wrinkling, the geometrical moment of inertia of the sheet should be increased by the alternating bending mechanism of the material in the flange area through immersing the blankholder slightly into the drawing die

Interactive mechanism and friction modelling of transient tribological phenomena in metal forming processes: A review

The accurate representation of tribological boundary conditions at the tool-workpiece interface is crucial for analysis and optimization of formability, material flow, and surface quality of components during metal forming processes. It has been found that these tribological conditions vary spatially and historically with process parameters and contact conditions. These time-dependent tribological behaviours are also known as transient tribological phenomena, which are widely observed during forming processes and many other manufacturing application scenarios. However, constant friction values are usually assigned to represent complex and dynamic interfacial conditions, which would introduce deviations in the relevant predictions. In this paper, transient tribological phenomena and the contemporary understanding of the interaction between friction and wear are reviewed, and it has been found that these phenomena are induced by the transitions of friction mechanisms and highly dependent on complex loading conditions at the interface. Friction modelling techniques for transient behaviours for metal forming applications are also reviewed. To accurately describe the evolutionary friction values and corresponding wear during forming, the advanced interactive friction modelling has been established for different application scenarios, including lubricated condition, dry sliding condition (metal-on-metal contact), and coated system

The benefits of thermal management to reduce friction losses in engines

The research reported in the thesis addresses questions of how engine fuel consumption and carbon dioxide emissions are can be reduced through improvements in thermal management, lubricant design, and energy recovery. The investigations are based on simulation studies using computational models and sub-models developed or revised during the work, and results provided by complementary experimental studies carried out by collaborating investigators. The brake thermal efficiency of the internal combustion engines (ICE) used in cars and light duty commercial vehicles is reduced by frictional losses. These losses vary with engine design, lubricant formulation and thermal state. They are most significant when the engine is running cold or partially warm. Over the New European Drive Cycle (NEDC), engine friction losses raise vehicle fuel consumption by several percentage points. A version of the computational model, PROMETS, has been developed and applied in studies of thermal behaviour, friction and engine lubricant to investigate the performance of a 2.0l, I4 GTDI spark ignition engine and in particular, how these influence fuel consumption over the NEDC. Core parts of PROMETS include a physics-based, empirically calibrated friction model, a cycle averaged description of gas-to-structure heat transfer and a lumped capacity description of thermal behaviour of the engine block and cylinder head. In the thesis, revisions to the description of friction and interactions between friction, local thermal conditions and lubricant are reported. It is shown that the bulk temperature of coolant rather than oil has the stronger influence on friction at the piston-liner interface, whilst bulk oil temperature more strongly influences friction in crankshaft bearings and other lower engine components. However, local oil film temperatures have a direct influence on local friction contribution. To account for this, local values of oil temperature and viscosity are used in describing local friction contributions. Implementation required an oil system model to be developed; an iterative model of the frictional dissipation within the main bearings, and a prediction of piston cooling jet heat transfer coefficients have been added to the oil circuit. Simulations of a range of scenarios and design changes are presented and analysed in the thesis. The size of the fuel savings that could potentially be made through improved thermal management has been demonstrated to be 4.5% for the engine being simulated. Model results show that of the friction contributing surfaces, the piston group is responsible for the highest levels of friction, and also exhibits the largest absolute reduction in friction as the temperature of the engine rises. The relatively low warm-up rate of the lower engine structure gives a correspondingly slow reduction in friction in crankshaft bearings from their cold start values. Measures to accelerate this reduction by raising oil temperature have limited effect unless the strong thermal links between the oil and the surrounding metal are broken. When additional heating is applied to the engine oil, only around 30% is retained to raise the oil temperature due to these thermal links

Process analysis and design in micro deep drawing utilizing a flexible die

As a result of the remarkable demands on electronic and other portable compact devices, the need to produce various miniaturized parts, particularly those made from metallic sheet is growing. In other words, in order for manufacturing companies to stay in competition, they are required to develop new and innovative fabricating processes to produce micro components with more complex features and a high standard of quality and functionality. Microforming is a micro fabrication process that can be employed efficiently for mass production with the advantages of greatly minimizing material waste and producing highly accurate product geometry. However, since the clearance between the rigid tools, i.e. punch and die, utilized in microforming techniques is relatively very small, there is a high risk of damaging the tools during the forming operations. Therefore, the use of forming tools made of flexible materials in sheet metal forming processes at micro scale has powerful potential advantages. The main advantages include a reduction in the production cost, eliminating the alignment and mismatch difficulties, and also the creation of parts with different geometrical shapes using the same flexible tool. As the workpiece is in contact with a flexible surface, this process can significantly improve the quality of the obtained products. Despite these clear advantages, micro flexible forming techniques are currently only utilized in very limited industrial applications. One reason for this is that the deformation behaviour and failure mode of sheet metals formed at micro scale are not yet well understood. Additionally, the experience-based knowledge of the micro-forming process parameters is not sufficient, particularly when flexible tools are used. Hence, to advance this technology and to improve the production quality of formed micro parts, more investigation of the key process parameters related to the material deformation are needed. The main contribution of this work is the development of a novel technique for achieving micro deep drawing of stainless steel 304 sheets using a flexible die and where an initial gap (positive or negative) is adopted between the blank holder plate and an adjustment ring utilized in the size-scaled forming systems developed for this purpose. The interesting point here is that this study presents the first attempt of employing flexible material as a forming die tool in the micro deep drawing technology to produce micro metallic cups at different scaling levels. Polyurethane rubber materials are employed in this study for the forming flexible die with various Shore A hardness. Also, the stainless steel 304 sheets utilized for the workpieces have different initial thicknesses. Various parameters that have a significant influence on the sheet formability at micro scale are carefully considered, these include initial gap value, rubber material properties, initial blank thickness, initial blank diameter, friction coefficients at various contact interfaces, diameter and height of the rubber die and process scaling factor. The size effect category of process dimension was also taken into account using similarity theory. Three size-scaled micro deep drawing systems were developed correspondingly to three different scaling factors. In each case, finite element simulations for the intended micro drawing systems are performed with the aim of identifying optimum conditions for the novel forming methodology presented in this thesis. The numerical models are built using the known commercial code Abaqus/Standard. To verify the microforming methodology adopted for the proposal technique as well as to validate the predictions obtained from simulations, an appropriate number of micro deep drawing experiments are conducted. This is achieved using a special experimental set up, designed and manufactured to fulfil the various requirements of the micro-forming process design procedure. The new knowledge provided by this work provides, for the first time, a predictive capability for micro deep drawing using flexible tools that in turn could lead to a commercially viable production scale process