Research Advances of Rehbinder Effect in Material Removal Process

The Rehbinder effect on the surface characteristics of the workpiece can be utilized to enable better control of the surface quality of the parts in precision machining processes. The microscopic manifestation of the Rehbinder effect varies among different engineering materials, but the macroscopic result is the reduction of the surface hardness of the workpiece, making the material removal process easier to proceed. A systematic review of the conceptualization and development process of the Rehbinder effect is presented, and its expressions and applications are elaborated, which can provide a way for the material removal method during processing and have a guiding significance for the formation of material surface integrity. The relevant findings of researchers on the Rehbinder effect in recent years are listed, both brittle materials and plastic materials, can be removed easily in machining process by utilizing the Rehbinder effect. However, the expressions of the Rehbinder effect are different for different materials. For polycrystalline hard and brittle materials such as rocks, surface active additives adsorbed on the surface of the workpiece enter the micro -cracks and continue to penetrate when there are micro -cracks on the material surface. Surface active additives can promote the expansion of micro -cracks to accelerate the mechanical damage of the structure. For single crystal hard and brittle materials such as silicon carbide and sapphire, surface active additives adsorbed on the material surface undergo a chemical reaction with the workpiece. The lower hardness of the reaction products makes the material easier to machine. For plastic materials such as metals, the role of the Rehbinder effect is also related to the grain size and dislocation density of the material. The mechanism of the Rehbinder effect can be demonstrated in the macroscopic and microscopic performance in the machining process. The factors that affect the Rehbinder effect such as the adsorption activity of polar molecules and the grain size of the workpiece material are summarized. The Rehbinder effect occurs on the premise that polar molecules adsorb on the surface of the workpiece. The diffusion, dislocation, and interstitial mechanisms generated by the Rehbinder effect reduce the surface strength of the workpiece further. Related mechanisms of the Rehbinder effect evaluated by numerical simulation methods are reviewed. The discrete element method can be used to analyze the mechanical processes in rocks, but there are limitations in the analysis of the Rehbinder effect. The finite element method is an important tool for simulating the deformation and removal processes of plastic materials. Some scholars have investigated the Rehbinder effect through the finite element method by modifying the fracture energy, elastic modulus or yield stress of different phases/grains in the ink -affected layer, and finding changes in the chip morphology. Because of the difficulty in modeling the adsorption of the surface active additives on the surface of materials and the diffusion in cracks, most of the current studies have simulated the adsorption by the surface modification of the material and have not involved penetration and diffusion. Molecular dynamics simulations can be adopted to evaluate the mechanism of the Rehbinder effect at smaller scales. The results show that the water molecule can improve the surface quality in precision and ultra -precision machining with a small amount of material removal as a kind of polar molecule, which is a manifestation of the Rehbinder effect. The combination of the experimental phenomena and simulation results can be effectively explained for the mechanism of the Rehbinder effect. The Rehbinder effect can be regarded as a modification mechanism for the machined surface. The study of the matching mechanism between surfactant and machined surface under the action of Rehbinder effect is the key to improving the material surface integrity, which is significant for promoting the development of precision manufacturing process.