Lubrication is a basic and relatively effective way to reduce friction in sheet metal forming operations. The drive to eliminate synthetic and mineral oils, which are difficult to recycle, from the manufacturing process has opened up opportunities for the use of vegetable-based bio-lubricants. This article presents a comparison of the lubrication performance of two non-edible oils (karanja and moringa) with the most frequently tested edible oils (sunflower and rape-seed). Deep drawing quality low-carbon steel sheets DC04, commonly used in the automotive industry, were used as the test material. Friction tests were carried out under various lubricants and normal pressures in the range between 3 and 12 MPa using the strip drawing test. Furthermore, a study was also made of the effect of a change in the surface topography and the mechanical properties of the sheet metal due to plastic deformation resulting from friction. It was found that under the most favorable lubrication conditions (sample pre-strain 21%, nominal pressure 6 MPa), karanja oil reduced the coefficient of friction by approximately 33%. Both non-edible lubricants provided the best lubrication when testing samples pre-strained at 7% under the whole range of nominal pressures. It was also revealed that in the case of the smallest pre-straining of the specimens (7%), karanja oil was the most effective within nominal pressures of 3–6 MPa, while at higher pressures (9–12 MPa), the moringa oil lowered the value of the coefficient of friction to a greater extent.
Friction is one of the most important technological phenomena and has a large influence on the flow characteristics of a deformed material. A strip drawing friction test was used to evaluate the friction characteristics of 0.8 mm thick DC04 steel sheets in a sheet forming operation. Friction tests were carried out using a specially designed friction simulator and uniaxial tensile tests were carried out to determine the mechanical properties of the specimens. In addition, measurements of the sheet surface topography were carried out to identify the tribological properties of the specimens. The friction tests were conducted under different pressure and lubrication conditions. A comparative analysis of the results of the friction tests revealed different changes in the surface topography of the test sheets which can be associated with specific friction mechanisms. It was found that the effectiveness of lubrication depends on the lubricant viscosity and nominal pressure. Increasing the nominal pressure intensifies the phenomenon of asperity flattening and reduces the volume of closed pockets of lubricant.
The purpose of this article is to determine the coefficient of friction of a DC04 steel sheet using a specially designed flat-die strip drawing test. Four different bio-based lubricants, edible (sunflower and rape-seed) and non-edible (karanja and moringa) were used in the study. The experiments were carried out for different contact pressure values. The as‐received specimens were pre‐strained with strains of 7, 14, and 21%. The values of the coefficient of friction as a ratio of the friction force to the normal force were determined. The influence of the viscosity of the lubricant and the contact pressure on the value of the coefficient of friction has been investigated using ANOVA. A tendency to a decrease in the coefficient of friction with increasing contact pressure was observed. Significance results obtained after the ANOVA analysis confirmed the influence of normal pressure and oil viscosity on the value of the coefficient of friction. At the same time, the hypothesis about the influence of the sheet pre-straining on the value of the coefficient of friction was not confirmed by the significant interactions.
This article presents the use of a specially designed flat strip drawing tester in order to assess the change in surface topography of DC04 steel sheets. The flat strip drawing test simulates friction conditions in the sheet metal-blankholder interface during deep drawing processes. Experimental tests were carried out at various nominal pressures and in dry friction and lubricated conditions. Two widely available gear and engine oils were used in the study. It was found that, in the range of pressures investigated between 3 and 12 MPa, 80W-90 gear oil provided a greater reduction in the value of the coefficient of friction (COF) than 5W-30 engine oil. Gear oil reduced the COF by an average of about 13.4 [%]. The lubrication efficiency depends on the pressure values; the greater the pressure, the lower the lubrication efficiency. A lowering of the value of the main amplitude surface roughness parameters Sa and Sq was generally observed. SEM analysis showed that even under lubrication conditions there was intense flattening of the roughness asperities of the sheet metal.
Accelerated wear of the moulds' inner surface used in forming loose masses contributes to its frequentreplacement or regeneration. This wear is indirectly influenced by the high pressure accompanying thecompaction process, but the main cause of accelerated wear is the friction that occurs between the die and thecompacted medium. Knowing that the value of the internal pressure in the moulded medium changes withthe change of the distance from the punch, in order to properly understand the phenomena accompanying thefriction that occurs in the mould during the pressing process, its characteristics must be determined. The paperanalyses the distribution of forming pressure inside the mould during the compaction of high-silica sand. Thedeformation on the die surface was measured using strain gauges, and x-ray tomography was used to visualisethe compaction of high-silica sand during the compaction process. The usefulness of an indirect method formeasuring the friction coefficient based on the analysis of die deformation has been demonstrated.
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