Abstract
Ensuring adequate lubrication is a key task in the sheet metal forming process. The replacement of commonly used synthetic lubricants in metal forming operations by eco-friendly equivalents is a way to introduce sustainable manufacturing. In this paper, six kinds of vegetable oils (linseed, palm, sunflower, cotton seed, soybean and coconut) were used to study the effect of lubricant type on the value of the coefficient of friction (COF) in sheet metal forming. The strip drawing test was used to simulate the friction conditions. The tests were carried out for various lubrication conditions and pressures. The polynomial quadratic regression model was used to determine the relationship between the input variables (test conditions) and the COF. For the range of the nominal pressures considered (2–12 MPa), the following oils provided the highest lubrication efficiency: palm, sunflower and cotton seed. These oils decreased the value of the COF by about 11–16% depending on the nominal pressure. Linseed oil had the most unfavourable properties, reducing the COF by about 7–12%. For the whole range of pressures considered, the increase in the viscosity of the oil caused a reduction in the value of the COF. The effect of oil density on the COF value was similar. The most unfavourable friction conditions occurred when there was low density and low viscosity of the oil at the same time.
Highlights
Sheet metal forming (SMF) is a common method of obtaining products with a complex shape, primarily in the automotive industry [1,2]
In sheet metal forming, the lubrication efficiency depends on the lubricating properties of the oil, the range of the values of the forces acting on the lubricated friction couple and the properties of the surface layer, especially the roughness of the surfaces in contact with each other
To determine the effectiveness of the lubricants used to reduce the frictional resistance, let us introduce the concept of the lubrication efficiency coefficient λl: λl μd − μd μl where μd is the coefficient of friction determined in dry friction conditions and μl is the COF determined in lubricated conditions
Summary
Sheet metal forming (SMF) is a common method of obtaining products with a complex shape, primarily in the automotive industry [1,2]. During this process, the sheet is deformed with metallic dies of a shape corresponding to the shape of the product. Friction in SMF processes is a complex function of the process parameters, the surface topography of the sheet to be formed and the tools, and the contact conditions that are constantly evolving in various regions of the drawpiece [6]. One of the methods for effectively reducing the friction during SMF is lubricating the surface of the sheet formed with greases [7,8]
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