Recent trends in sustainable mobility are posing new challenges to automotive manufacturers of sheet metal stamped parts, further increasing the complexity of stamping tools and control systems. In this context, proper controlling of the material flow by segmented blank-holders or springs is mandatory to avoid tearing and wrinkling phenomena. As an alternative, the possibility of using ferrofluid-based lubricants to control point-by-point the blank flow during forming may allow the use of simpler dies and, at the same time, improved stamping performances. However, the tribology of ferrofluids under magnetic field is still little investigated for both friction and wear behaviour. The paper presents a new laboratory machine for testing ferrofluids lubrication performances under reciprocating sliding. The reciprocating sliding contact between the dies and metal sheet is performed under the application of a magnetic field to vary the lubricant viscosity and the frictional conditions at the tribo-pairs interface. Saddle-shape magnetic coils, optimized by numerical tools to have uniform magnetic flux density on a wide contact surface between the tool and blank, are embedded on a moving carriage that is made to slide against a fixed die, manufactured as the stamping dies. The mechanical and thermal conditions are monitored and adjusted in real-time during testing. Experiments were conducted with sliding speeds in the range 5–20 mm/s and contact pressures up to 5 MPa, by superposing different values of electro-magnetic fields. Mono-directional sliding tests were carried out to determine the frictional conditions, while cyclic tests were used to investigate the wear behaviour at the interfaces. The surface topography at the wear onset was investigated by means of 3D optical profiler and scanning electron microscopy. Results allowed to correlate the magnetic field intensity to both the frictional and wear behaviour in the case of steel stamping.
A new machine for testing ferrofluids lubrication performances by reciprocating sliding wear
Simonetto E.
;Ghiotti A.;Brun M.;Bruschi S.
2023
Abstract
Recent trends in sustainable mobility are posing new challenges to automotive manufacturers of sheet metal stamped parts, further increasing the complexity of stamping tools and control systems. In this context, proper controlling of the material flow by segmented blank-holders or springs is mandatory to avoid tearing and wrinkling phenomena. As an alternative, the possibility of using ferrofluid-based lubricants to control point-by-point the blank flow during forming may allow the use of simpler dies and, at the same time, improved stamping performances. However, the tribology of ferrofluids under magnetic field is still little investigated for both friction and wear behaviour. The paper presents a new laboratory machine for testing ferrofluids lubrication performances under reciprocating sliding. The reciprocating sliding contact between the dies and metal sheet is performed under the application of a magnetic field to vary the lubricant viscosity and the frictional conditions at the tribo-pairs interface. Saddle-shape magnetic coils, optimized by numerical tools to have uniform magnetic flux density on a wide contact surface between the tool and blank, are embedded on a moving carriage that is made to slide against a fixed die, manufactured as the stamping dies. The mechanical and thermal conditions are monitored and adjusted in real-time during testing. Experiments were conducted with sliding speeds in the range 5–20 mm/s and contact pressures up to 5 MPa, by superposing different values of electro-magnetic fields. Mono-directional sliding tests were carried out to determine the frictional conditions, while cyclic tests were used to investigate the wear behaviour at the interfaces. The surface topography at the wear onset was investigated by means of 3D optical profiler and scanning electron microscopy. Results allowed to correlate the magnetic field intensity to both the frictional and wear behaviour in the case of steel stamping.
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