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Abstract
□ Residual stress is one of the critical characteristics for assessing the qualities and functionalities of machined products in light of its direct effect on endurance limit, distortion, and corrosion resistance. Primary factors responsible for residual stresses distribution include mechanical effects, thermal effects, microstructure evolutions, and a combination of these mechanisms. This study investigates the effects of minimum quantity lubrication (MQL) on machining force, temperature and residual stress through a physics-based modeling method. Both the lubrication and cooling effects caused by MQL air-oil mixture contribute to changes in friction due to boundary lubrication as well as variations in the thermal stress due to heat loss. The modified Oxley's model is employed to predict the cutting force and temperature directly from cutting conditions. The predicted cutting force and temperature are then coupled into a thermal-mechanical model which incorporates the kinematic hardening and strain compatibility to predict the machining-induced residual stress under lubricated conditions. The proposed analytical method is experimentally verified by orthogonal cutting tests for AISI 4130 alloy steel in the context of forces, temperatures, and residual stresses.
NOMENCLATURE
| as | = | Approach of two surfaces |
| D | = | Inclination of distribution function |
| E | = | Elastic modulus of workpiece material |
| G | = | Elastic shear modulus |
| Hmax | = | Distribution height of asperities |
| h | = | Plastic modulus of workpiece |
| = | Average heat transfer coefficient | |
| = | Effective heat transfer coefficient for the air-oil mixture flow in the tool flank face | |
| kair | = | Thermal conductivity of the air |
| Leff | = | Effective lubricated length |
| N | = | Normal load under dry condition |
| n0 | = | Total asperity number |
| nij | = | Direction of plastic strain rate |
| Pr | = | Prandtl number |
| pm | = | Yield pressure of the metallic contact area |
| qhl | = | Heat intensity of the heat loss due to the air-oil mixture flow |
| R | = | Radius of asperity tip |
| Re | = | Reynolds number |
| Tflank | = | Average tool flank face temperature |
| T0 | = | Ambient temperature |
| tb | = | Effective adsorbed lubricant film thickness |
| α | = | Coefficient of thermal strain |
| λ | = | Coefficient of calculating the effective heat transfer coefficient |
| μs | = | Friction coefficient in boundary lubrication condition |
| = | Stress rate in elastic Hertzian solution | |
| = | Stress rate in plastic solution | |
| = | Strain rate in X, Y direction | |
| Ψ | = | Blending function |
| κ | = | An algorithm constant in blending function |