Influences of temperature and grain size on the material deformability in microforming process

Abstract

This paper investigated the influences of temperature and grain size on the deformability of pure copper in micro compression process. Based on the dislocation theory, a constitutive model was proposed taking into account the influences of forming temperature, Hall-Petch relationship and surface layer model. Vacuum heat treatment was employed to obtain various grain sizes of cylindrical workpieces, and then laser heating method was applied to heat workpieces during microforming process. Finite element (FE) simulation was also performed, with simulated values agreed well with the experimental results in terms of metal flow stress. Both the FE simulated and experimental results indicate that forming temperature and grain size have a significant influence on the accuracy of the produced product shape and metal flow behaviour in microforming due to the inhomogeneity within the deformed material. The mechanical behaviour of the material is found to be more sensitive to forming temperature when the workpieces are constituted of fine grains. experimental results indicate that forming temperature and grain size have a significant influence on the accuracy of the produced product shape and metal flow behaviour in microforming due to the inhomogeneity within the deformed material. The mechanical behaviour of the material is found to be more sensitive to forming temperature when the workpieces are constituted of fine grains.

Influence of temperature on deformation behavior of copper during microextrusion process

“…It is well understood that in order to facilitate more extensive use of micro forming, better understanding about the mechanism behind size effects is desirable, as it results in the inaccuracy of final product due to the increase in the scatter of the process parameters. 1,2 This is due to the fact that only few grains directly participate in the forming process. Further, each grain characterized by its individual size, orientation, position, and randomly distributed characteristics lead to inhomogeneous material behavior.…”

Microstructure and mechanical properties of thin varying thickness strips with different transition zones produced by micro flexible rolling

“…With the ongoing trend towards miniaturisation of systems and devices, 21 micro flexible rolling technology has been developed and applied to produce ultrathin strips with varying longitudinal thickness in microscale 22 but when the thickness of the workpiece to be flexibly rolled is scaled down to the submillimetre range, the so-called size effects that characterise the micro world will have a significant influence on the forming process. 23,24 Qu et al 25 developed a 3D Voronoi tessellation model to analyse the springback behaviour in relation to material heterogeneity and found that springback is expanded in the thickness direction, owing to the decrease in grain quantity with the decrease in initial specimen thickness.…”

Analysis of Springback Behaviour in Micro Flexible Rolling of Crystalline Materials

“…For instance, Lu et al [38] established a microscale constitutive model on the basis of grain size, shape, deformability, and specimen dimension to discuss the deformation behaviours of polycrystalline copper grain with different grain and feature sizes in microforming processes, like microcompression and microcross wedge rolling. According to the dislocation theory, Jiang et al [39] proposed a constitutive model with consideration of forming temperature, Hall-Petch relationship and surface layer model to investigate the influences of temperature and grain size on the deformability of pure copper in microcompression process, where both factors were found to significantly affect the shape accuracy of the produced product, as well as the metal flow behaviour due to material heterogeneity. Liu et al [40] developed a novel constitutive model to characterise the effects of grain size and boundary and geometry size on the flow stress of pure copper foils as well as on the microextrusion of CuZn30 alloy billets.…”