Research On Upsetting Of Cylindrical H62 In Micro-scale At Elevated Temperature

Microforming as one of microfabrication technologies is becoming more and more important since1990s, and the development is very fast.In microforming, the specimens are small size and high accuracy.Due to the size effects, the know-how of conventional forming cannot be simply transferred to microforming. Firstly, four geometrically similar upsetting test of different absolute size are performed with decreasing H62 brass specimens from 4 to 0.5mm in diameter (height / diameter =1.5:1) at the room temperature and 250 Centigrade. The experimental results show decrease in flow stress and increase in hardness with decreasing specimen size at the same temperature, and with increasing temperature the material flow tends to homogenize.Then, research on the size effects can advance strain gradient theories, which are theories that combine size effects based on the continuum mechanics. In the present paper, strain gradient theories and their advances are reviewed, and meso-scale model is discussed, which is described in terms of the grain elements and grain boundary elements, and the grain elements and grain boundary elements formulations can be obtained,thus the finite element analysis is well prepared in the future.There are many unjustly conceptions and ambiguous appellations in microforming research,accordingly, the size effects are newly defined from the view of microforming, which are classified as material attributive size effects and technical condition size effects. The quantifying methods are demonstrated, which act on positive function in evaluating size effects by using known data.At last the friction and lubrication in microforming are introduced, polytetrafluoroethylene (PTFE) thin film is used to be lubricant and the regular of friction is interpreted by open/close lubricate pockets.