Yancong Liu

Research on variation and stress status of graphite in laser cladding process of grey cast iron

Abstract Grey cast iron codenamed HT250 was processed by laser cladding with Fe based alloy to investigate the graphite variation in laser cladding process. To study the phenomenon that microcracks appeared at some graphite tips in the bonding zone, the macro laser cladding model and micro graphite model were established. Thermal–mechanical characteristics of the area around graphite were investigated using the models. The results showed that graphite in the bonding zone had complicated variation and microcracks appeared on a portion of graphite tips. Tensile stress concentration emerged at graphite tips in the cooling period which was a hazardous area of microcracks initiation. Microcracks were caused by coactions of microstructure characteristics of graphite area and stress concentration at graphite tips. The tensile stress was closely related to graphite dimensions. Graphite with large radius and length caused larger tensile stress which resulted in microcracks more easily.

Forming accuracy analysis of plate in multi-scanning laser bending process

Laser bending is realized by local plastic deformation based on non-uniform thermal stress resulting from laser beam radiation. The aim of laser bending is to achieve bending deformation of a plate; however, the bending angle varies along the scanning line greatly affecting assembly accuracy in real industry applications. To control the forming accuracy in multi-scanning laser bending, several heating methods are proposed in this article. It is evident that the heating methods have a significant influence on the forming accuracy. The experimental results show that the bending angle variation can be reduced using the proper heating methods.

Numerical investigation of temperature field of different mechanisms in laser forming

In laser forming, deformation of a plate is different when different mechanisms play dominant roles. A deformation field depends on a temperature field that is related to process parameters, material properties and plate size. Numerical investigations of temperature distribution with different process parameters were carried out when different mechanisms were active. A critical temperature for generating plastic deformation was investigated. Four temperature feature parameters were defined based on the temperature distribution characteristics of the high-temperature zone. The numerical results show that the temperature gradient is obviously different under different mechanism conditions. The temperature distribution features for the different mechanisms have a larger difference, which is helpful for the discrimination of different mechanisms according to the temperature field in real industrial applications.

Modeling of High-Frequency Induction Heating Surface Cladding Process: Numerical Simulation, Experimental Measurement and Validation

A study of experimental measurement and numerical simulation was carried out with respect to 45 steel shaft work piece in the high-frequency induction heating cladding process. Firstly, the model domain boundaries were divided in according to material characteristics. Secondly, the electromagnetic model and the thermal model were built with temperature-dependent material properties and coupled electromagnetic-thermal problem were solved by mean of magneto-quasi-static iteration between electromagnetic and thermal model. Thirdly, the three-dimensional geometry accurate model with regard to high-frequency induction heating cladding process was employed. Lastly, the experimental results of temperature distributions are in agreement with the results calculated using numerical simulation FEM and the maximal relative error was limited in a reasonable range.