An Off-line Methodology to Determine Limits of Lubrication in Sheet Metal Forming

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Abstract

In order to sustain in the competitive market in manufacturing, high-quality products with good surface finish and tight tolerances is a nec-essary but not sufficient condition. To keep pace with the high growth rate of the developing industry and the economy, it is also required to reduce the resources and increase the productivity. In order to ensure an efficient manufacturing line, the practice is to use environmentally haz-ardous chlorinated paraffin oils. By using these oils, not only the lubri-cant film breakdown, leading to scratching of the surfaces of the metal sheets, but otherwise required repolishing of the tools can be avoided, too. Thereby, financial and material resources can be reduced. At the same time, as a result of the growing awareness of environmental as-pects and increasing legislations, some companies are substituting these oils with more environmentally friendly lubricants and/or tribo-systems. However, these attempts have been only partially successful, because the change in the tribo-system often results in a shift in the active lubrication mechanism. It is therefore the aim of this project to propose an off-line methodology on how to replace environmentally hazardous oils with en-vironmentally friendly tribo-systems. While doing so, attention is also paid to numerical simulation of the lubrication in sheet metal forming operations by means of a newly proposed approach based on full cou-pling of fluid flow and metal flow.
In this project, an industrial case from the production line of Grundfos A/S was selected. The process concerns manufacturing of a stainless steel cup and includes thirteen stages consisting of multiple drawings and a final collar drawing and ironing operation. Lubricant breakdown occurs due to large reduction of wall thickness during the ironing op-eration. To start with, the production platform was analysed and the tribological parameters were identified. The methodology during the detailed analysis of the production includes experimental work in pro-duction, thermo-mechanical numerical calculations and validation of the results. The Strip Reduction Test (SRT) was selected as a suitable labo-ratory test to emulate the ironing operation in the production. A new SRT tool emulating both forward and backward strokes of the ironing opera-tion has been designed and manufactured. The testing and the analyses of the entire SRT at room temperature as well as at elevated tempera-ture were performed. After ensuring similar process conditions in the laboratory, selected tribo-systems were investigated. Additionally, en-hancements for improving the current design were suggested and tested.
The proposed off-line methodology for industrial ironing operations was followed by a more fundamental research. The final part of the thesis fo-cuses on understanding the behaviour of the fluids as pressure carriers in metal forming processes. For that, the finite element flow formula-tion, enabling strong coupling between metals and fluids, was adapted. Finally, the developed model was applied to thickness reduction testing of a sheet with mesoscopic surface pockets in order to investigate the mechanisms causing the escape of lubricants from the pockets.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages215
ISBN (Electronic)978-87-7475-544-9
Publication statusPublished - 2018

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