Experiment study on the corrosion resistance of the surface metamorphic layer of grinding

Workpiece will face corrosive problems during its application after the manufacturing process. As the common final process, grinding can generate special metamorphic layer on the surface of workpiece and change the initial corrosion resistance of workpiece. In order to study the corrosion resistance of workpiece after grinding process, the paper carries on combining experiment of grinding and electrochemical corrosion. The characteristic of corrosion resistance of grinding is revealed based on the association of grinding mechanism and electrochemical theory. The corrosion potential of workpiece after grinding is higher than matrix, which shows the grinding surface is difficult to begin to corrode. Electrochemical impedance spectroscopy (EIS) shows the grinding surface has large phase angle, impedance and capacitance characteristic because the metamorphic layer of grinding has good obstructive ability. They reveal that grinding improves the surface corrosion resistance of workpiece. Then the mechanism of the corrosion resistance of grinding is revealed. The special grain boundary formed in grinding with much C element, large clusters and complex shape prolongs the corrosion channel, which reduces the corrosive speed. While, the sensitive hardening structure generated in grinding hardening with much free energy is easy to form the corrosion cell, which will accelerate the corrosion.

A research on the mechanism and model of surface micro-damage in grinding hardening

Grinding hardening can obtain hardening effect besides fine machining effect on the surface of workpiece. A certain degree of surface micro-damage will be formed during grinding hardening process which mainly contains micro-crack, melting coating, decarburization, and surface scratch. In order to study the micro-damage of grinding hardening, the paper carries on a grinding hardening experiment and the characteristics of micro-damage are observed. The generation mechanism of micro-crack is revealed. It is formed by the accumulation of dislocation pile-up in the condition of grinding hardening process. When the grinding depth reaches a certain value, the surface micro-crack will be produced obviously and become more serious with the increasing of grinding depth. Other micro-damage containing surface melting coating, decarburization, and surface scratch are also studied and their relevance with micro-crack is revealed. Based on the grinding hardening theory and pile-up dislocation theory, a model for micro-crack of grinding hardening is established. The calculating result of the model accords with the experimental result in general.

Online Detection and Study of Cracks in Grinding Hardening

Grind-Hardening technology is a new technology for cutting that combines grinding theory with quenching theory, and the heat produced during the grinding process has a great effect on the surface quality of the parts. This paper take advantage of method of acoustic emission testing to test the grinding hardened parts by online or scene. The wavelet packet is used to denoise the signal, then the denoising signal is analyzed to judge those grinding cracks or defects that may appear on the surface of the parts, and besides, this method is easy to do.

Study of Grinding Hardening Force Based on the Influence of Grinding Arc Temperature and Workpiece Deformation

The grinding hardening workpiece deformation caused by high temperature leads to the variation of the grinding force. Grinding force of dynamic variation affects the grinding depth of hardened layer distribution. So it is necessary to study the variation rule of grinding hardening force. Through grinding arc temperature analysis and deformation analysis, the influence factor for grinding arc temperature and workpiece deformation on grinding force is analyzed. The analysis results are compared with the experimental results.

On the Profile and Microstructure Variations of Grinding-Induced Hardening Layer in A Cylindrical Workpiece

Grinding-hardening is a thermo-mechanical process capable of simultaneous material removal and surface enhancement. However, there are difficulties in dealing with cylindrical workpieces, because of the complex 3D-helical movement of the grinding-induced heat source. This paper investigates the effects of some key grinding parameters on the profile and microstructure variations of the hardened layer generated by a traverse cylindrical grinding, both experimentally and numerically. It was found that the ratio of the longitudinal wheel feed to the rotational speed of the workpiece R is most influential on the hardened layer profile. A larger R results in a thicker hardened layer but a more pronounced discontinuity of two adjacent hardening zones. Although a smaller R yields a relatively thinner hardened layer, the non-uniformity could be minimised by the overlapping of the grinding heating. The microstructure of the hardened layer can be altered by the tempering in subsequent grinding heating. A thermal analysis with the aid of the finite element method in conjunction with an experimental microstructural examination showed that the temperature distribution in the tempered region would lead to a variation of the precipitated carbide, and that a higher tempering temperature could result in a higher degree of the carbide precipitation and a more significant reduction of hardness.

An Investigation of the Grinding-Hardening Induced by Traverse Cylindrical Grinding

This study investigates the formation of the layer hardened on a cylindrical workpiece by grinding-hardening using the traverse grinding method. A finite element heat transfer model, that took into account the helical trajectory of the of the grinding heat source movement, was developed. The hardened layer was found featuring a wavy profile as a result of the heat conduction from an adiabatic plane crossing the middle of the trajectory pitch. The accumulation of the grinding heat within a small pitch can lead to the welding of the molten material with the base material. Enlarging the pitch by reducing the workpiece speed will increase the time of heating, allowing the heat to penetrate deeper and to expand wider in the workpiece, thus thickening the hardened layer.