Measurement in Machining and Tribology by J. Paulo Davim

Author:J. Paulo Davim
Language: eng
Format: epub, pdf
ISBN: 9783030038229
Publisher: Springer International Publishing

The above discussion was extended to the easy-to-anneal materials of the present investigation. Figure 2.19 shows the correlation between the friction values of annealed condition and strained condition. AISI 1045 was included for reference. Two different results can be observed: (i) material hardness presents significant influence on friction coefficient or (ii) no influence has been found and friction remains almost constant (points on the symmetry line, red dashed line). Engineering materials (AISI 1045, AA 1085 and AA 1050) seem to exhibit a significant sensitivity to material hardness, while friction coefficient value of pure metals remains almost constant. These tests have been verified under different metal cutting conditions with similar conclusions. These results are not per se an evident conclusion, but this may indicate that adhesion is the dominant contribution for the very soft pure material, while mechanical asperities interaction (penetration of the hard asperities on the soft material) depends most on the work material strength. These competing contributions make it difficult to understand the influence of the hardening mechanism on the coefficient of friction. This conclusion is in agreement with the low correlation that is generally observed between the numerical modelling and the experimentation of the ring test used to quantify friction in metal forming. Some solutions have been published showing the way in which hard asperities deform the surface of a softer metal in the presence of interfacial adhesion and these provide a very promising beginning for interfacial plasticity solution. However, since they do not take into account the work hardening produced by the process itself, the numerical results are of limited applicability [7].

Fig. 2.19Comparison of friction coefficient values obtained from annealed and strain hardened conditions for different materials (Al, Cu, Zn, AA 1085, AA 1050 and AISI 1045). Cutting tests have been carried out under different tribological conditions (surrounding medium: argon, oxygen and room ambient). Other test conditions: WC–Co tool, Ra = 0.01 µm polished tool, α = 0°, σ = 7°, rc < 1 µm, t0 = 0.025 mm, w = 2 mm, Vc = 500 mm/min

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