Abstract
Finding effective and environmentally friendly lubrication to use in sheet metal forming operations presents a substantial environmental and economic challenge to the automotive industry. This paper examines the effectiveness of different lubricants in the reduction of the coefficient of friction (COF) in the process of sheet metal forming of the low carbon steel sheets. These lubricants are based on a combination of boric acid (H3BO3) and edible vegetable oils, both of which are natural and environmentally friendly. To evaluate the friction characteristics of the lubricants in a forming operation, a strip drawing friction test is used. This test consisted in drawing a specimen in the form of a sheet metal strip between two non-rotating counter-samples with radii of 200 and 10 mm. The effectiveness of environmentally friendly lubricants in reducing the COF was compared to the traditional petroleum-based lubricants which are used in sheet metal-forming operations. The effect of lubricant conditions and tool surface roughness on the value of COFs is studied. It was found that palm oil in both configurations of countersample radius, both as pure oil and with the addition of 5 wt.% of H3BO3, was the most effective in lowering the coefficient of friction. In most of the conditions analysed, the addition of boric acid into vegetable oils leads to an increase in the lubrication efficiency by up to 15% compared to pure oils. The effectiveness of lubrication by olive and rapeseed oils in decreasing the frictional resistances clearly depends on the nominal pressure applied.
Highlights
The friction occurring between a deformed sheet and the tool surface has a significant impact on the course of plastic deformation, tool life and product performance
It can be stated that the effects of interaction of friction forces in the sheet metal forming processes are almost always unfavourable
The friction modifiers from the cashew nut shells were tested on a four-ball tribometer and the results show that they act as effective extreme-pressure additives at higher loads
Summary
The friction occurring between a deformed sheet and the tool surface has a significant impact on the course of plastic deformation, tool life and product performance. In sheet metal forming (SMF), friction forces decide on both the value and state of stress in the surface layer of the material being deformed. It can be stated that the effects of interaction of friction forces in the sheet metal forming processes are almost always unfavourable. The unit pressures occurring on the contact surface are very large and can significantly exceed the value of yield stress of one workpiece material [4,5]. As a result of high pressures, the friction conditions change significantly because of decreases in lubrication efficiency, causing a break in the lubricating film and leading to direct contact of the asperities of rough surfaces
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