Materials Science Forum Vol. 1147

Abstract: Oil-in-water emulsions (O/W-emulsions) are generally used to lubricate the cold rolling process of low-carbon steel. Besides the obvious advantages of efficient lubrication and cooling of the process, there are also some disadvantages mainly related to emulsion bath maintenance, subsequent production steps and waste disposal. In some application areas, Oil Free Lubricants (OFL’s) have shown to be at least equally effective in decreasing friction and wear as conventional lubricants, while resulting in benefits related to waste disposal. In 2018 a project (acronym ‘RollOilFree’) was started with funding from the Research Fund for Coal and Steel (RFCS). The objective of this project was to develop an OFL as a lubricant for the cold rolling process of low-carbon steel and hot rolling of aluminium. A cold rolling lubricant can be evaluated based on many criteria; for some criteria the OFL even outperformed the oil-based emulsion, but it was found that for some rolling conditions the coefficient of friction with the OFL was still too high. In September 2023 a follow-up project, “Transfer of aqueous oil free lubricants into steel cold rolling practice” (acronym ‘RollOilFreeII’) has begun, also in the RFCS-framework. This article briefly recapitulates the findings in the RollOilFree-project and describes the objectives and benefits of the RollOilFreeII-project. Furthermore, the main activities in the project will be discussed.

Abstract: This research explores the feasibility of utilising supercritical carbon dioxide (scCO₂) as a coolant coupled with minimum quantity lubrication (MQL) as a lubricant, to replace conventional coolant and lubricating fluids (CLF’s) in small diameter deep hole drilling (DHD) of austenitic stainless steel (AISI 304L). The study investigates the impact of scCO₂+MQL on hole quality, surface roughness, and tool wear parameters in comparison to high-pressure soluble oil cutting fluid (HPC). The motivation stems from the need to supply sustainable and environmentally conscious CLF alternatives within the machining industry, specifically addressing the reduction of dependence on traditional HPC’s.ScCO₂+MQL offers significant advantages under specific conditions, particularly with mid-range feed rates and higher cutting speeds. On average, drilling under scCO₂+MQL conditions achieved a success rate 71% as effective as when drilling with HPC, however the difference can be attributed to the set of cutting conditions optimised primarily for HPC, not for scCO2. The results indicate the viability of scCO₂+MQL and its ability to produce results comparable to HPC. It also emphasises the complexities of transitioning from traditional CLFs to sustainable alternatives like scCO₂+MQL in DHD processes. The outcomes present an encouraging case for the environmental and cost benefits associated with scCO₂+MQL. However, it also highlights the need for further investigation and optimisation, particularly in tool design, to enhance performance and address the existing challenges.

Abstract: The manufacturing industry has a significant impact on the economy of a country. Therefore, carrying out necessary developments and modifications in manufacturing machine components is essential. Some materials, called superalloys, are challenging to machine, and they have a wide application in the turbine components of aerospace, submarines, oil, nuclear, steam, and other power generation industries. Due to the exceptional properties of these superalloys their machining becomes very difficult and time-consuming; They damage the cutting tool, and excessive use of lubricants eventually affect the material handling and cost. These problems lower down the sustainability and therefore an attempt has been made in the current research work to eliminate the use of cutting fluid by impinging solid lubricant on AlTiN coated tungsten carbide cutting tool by using pulsed direct current magnetron sputtering and cathodic arc physical vapour deposition techniques. The micro-texturing is first done on rake face of the milling insert such that graphite, which acts as a solid lubricant, can be then deposited in those micro-textures. The end milling of Nimonic 90, a superalloy, is done using the solid lubricant filled microtextured insert under compressed air environment, and the cutting forces, cutting temperature, tool wear, and surface roughness are analysed. It is found that there is a substantial decrease in the cutting forces and tool wear when compared with non-textured tool due to less friction and temperature at the machining zone. Sustainability of such solid lubricant based textured cutting tool has shown improvement when compared with non-textured cutting tool. The machinability of Nimonic 90 is increased by implementing the solid lubricant-based cutting tool, and therefore, it can be effectively utilised for the machining of superalloys soon.

Abstract: Cold forming is characterized by high dimensional and shape accuracy as well as energy and cost efficiency in the series production of highly stressed components. Cold forming is characterized by high tribological loads. Complex lubrication systems are necessary to ensure fault-free production despite the high tribological loads. In the course of increasing demands on environmental compatibility, the disadvantageous zinc-phosphate-based lubricant systems have been replaced by more environmentally friendly single-layer lubricant systems. However, their functionality is strongly dependent on temperature, so that exact knowledge of the prevailing temperatures in the forming zone is necessary for optimum design of the lubricants [1]. Due to the high tribological stress, established measuring methods based on thermocouples can only approach the forming zone up to 10 mm. Previous works of the authors have shown that sensory lubricants based on thermochromic indicators are in principle capable of measuring temperatures directly in the forming zone [2,3]. Their functionality is based on the irreversible color change as a function of temperature [4]. The aim of this study is to develop a standardized test methodology for calibrating the sensory lubricants, which enables an exact correlation between temperature and color value. In addition, suitable indicators are to be identified and their influence on the tribological system analyzed. The test methodology developed uses inductive heating to heat the samples coated with the sensory lubricant to as high as 500 °C within 1 s. The temperature of the surface is determined by the temperature of the lubricant. By determining the surface temperatures reached as well as the color values under diffuse illumination in an integrating sphere, defined temperature ranges can be assigned to the color values of the indicators. With three indicators, which were identified as suitable, it was possible to detect temperatures in the contact zone of a full forward extrusion process and in the contact zone of the sliding compression test that reflect the simulated temperatures. In addition, the sliding compression test showed that the indicators have no influence on the tribological system up to an indicator concentration of 4 %.

Abstract: During a machining operation, the tool tip is subjected to elevated interface temperatures and contact pressures. A considerable improvement can be achieved through an appropriate selection and application of a cutting fluid. Although many technologies attempt to reduce their use to move to a cleaner production, they are still widely employed in industry. Under such severe conditions, it is necessary to understand their exact contribution from a tribological point of view in order to optimize their use. The aim of this study is to evaluate the ability of a fluid to penetrate and remain at the tool-material interface.

Abstract: Improved understanding of friction during cold rolling is crucial to further optimize the rolling process, to accurate analyse cold rolling defects and to increase model accuracy enabling an improved mill setup during industrial operation. Classical slab rolling models make use of the Coulomb friction law, assuming a constant coefficient of friction in the roll bite. In the last decades, mixed-lubrication models have been developed that explicitly take the lubricant action into account. These models have greatly increased the understanding of factors that influence friction during cold rolling, but quantitatively the model results should still be further improved before such models can be used as an online tool for setting up the cold rolling mill. This article describes a mixed-lubrication model to simulate cold rolling of low-carbon steel. Especially the tribological core of the model is extended and improved compared to state-of-the-art models. Friction mechanisms now also include a viscous shear stress and ploughing friction. The quantification of viscous shear stress was reported in a previous work [1], this work focuses on the quantification of ploughing friction. Material Point Method (MPM) simulations were carried out to determine the work piece strain-hardening and strainrate-hardening under a ploughing indenter. These simulations result in an ‘Surface Ploughing Resistance’ and finally in a quantification of the contribution of ploughing friction to the overall friction in the roll bite. The description of the various friction mechanisms (ploughing, adhesive and viscous shear) is implemented in the mixed-lubrication model. This article concludes by presenting typical results of the developed model. One of the main conclusions is that the contribution of ploughing friction in a cold rolling process cannot a priori be neglected.