Determination of Actual Friction Factors in Metal Forming under Heavy Loaded Regimes Combining Experimental and Numerical Analysis

Derivation of the Coefficients in the Coulomb Constant Shear Friction Law from Experimental Data on the Extrusion of a Material into V-Shaped Channels with Different Convergence Angles: New Method and Algorithm

The combined Coulomb constant shear friction law is widely used in commercial and research software for the finite-element analysis (FEA) of metalworking and is naturally more flexible and hence, more relevant to real-life manufacturing than the individual Coulomb and constant shear friction laws. In this work, a new mathematical model of coefficients in the Coulomb constant shear friction law for extruding a metal through narrow V-shaped channels with small convergence angles has been developed and evaluated and compared with laboratory measurements. The extrusion of the model material (lead) through narrow V-shaped channels with small convergence angles varying from 0 to 3.5 degrees has been studied. The Coulomb friction coefficient µ and the constant friction factor m appear to be independent of the dimension ratio and are influenced mostly by roughness and range from µ = 0.363 (with lubricant) to µ = 0.488 (without lubricant) and from m = 0.726 (with lubricant) to 0.99 (without lubricant). The relative length dominated by the Coulomb friction law is less than 1%, and the Coulomb’s coefficient of friction can be approximated as ½ the constant shear friction factor for all tested cases. The developed method and algorithm can be used in both FEA of manufacturing processes and efficiency tests for lubricants used in metalworking.

Tribological Performance of Environmentally Friendly Bio-Degradable Lubricants Based on a Combination of Boric Acid and Bio-Based Oils

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.

Understanding of plasticity size-effect governed mechanical response and incomplete die filling in a microscale double-punch molding configuration

Direct replication of microscale patterns onto metal surfaces by compression molding with patterned dies is used to fabricate metal-based structures for microsystem applications. Micron scale plasticity governs both the mechanical molding response and the geometric fidelity of replicated patterns. Microscale molding replication offers a technologically relevant example in which various plasticity size effects manifest themselves and control the effectiveness of the fabrication process. Microscale compression molding of a single-crystal Al specimen was studied by combining experimentation with conventional and strain gradient plasticity finite element simulations. In the single-punch molding configuration, single rectangular punches with different widths and lengths were used. In the double-punch configuration, two identically-dimensioned rectangular punches with a spacing in between were used. Under single-punch molding at the micron scale, both the absolute punch width as well as the length-to-width ratio affected the characteristic molding pressure. Under double-punch molding, both the measured characteristic molding pressure and the material flow to fill the gap between the two rectangular punches exhibited a significant dependence on the spacing to punch-width ratio and-when this ratio was fixed-on the absolute spacing between punches. The present study elucidates the impact of plasticity size effects on the efficacy of pattern replication by molding at the micron scale.