Multi-cycle Numerical Analysis On The Local Cooling Capacity Of Mould During Casting Solidification Process

It's easy to form hot spot during casting solidification process. Many factors contribute to this, such as the structure and wall thickness of casting, thickness of mould, materials and so on. Series of problems result from casting hot spot, which is due to inefficient heat diffusion of local mould, such as the unbalance of casting temperature field, disordered solidifying and casting defects. In addition, hot spot also disorders mould temperature field and contributes to both thermal fatigue and short life of mould. The eliminating of hot spot plays an important role in technological designing of casting process; it is also one of the premises to get high quality casting and extend mould life. In this thesis, multi-cycle numerical analyses during casting solidification process were carried out, and hot spot which resulted from the differences in wall thickness of casting was studied. For solving the problem, thermal solution of ANSYS software was used. Criterion, which was the difference between maximum temperature of casting and the temperature at casting center, was established. Under given hot spot wall thickness circumstances, influences of mould wall thickness, cooling conditions and thickness of dopes on temperature field and local cooling capacity of mould were researched. Quantitative relations between criterion and factors mentioned above were obtained. Measures of removing hot spot can be achieved according to the research results. Based on above consideration, these conclusions were drawn from the simulation analysis:①During single casting, within the range of mould wall thickness(10~25mm), under the condition of natural cooling, influences of mould wall thickness on local cooling capacity of mould were not visible; Under the condition of enhancing heat transfer, local cooling capacity of mould declined while mould wall thickness increased.②Temperature differences changed with the increase of casting times; Steady temperature gradient was founded inside casting mould in four to six casting cycles, temperature differences changed less than 0.05℃between adjacent two cycles and inclined to stabilization then.③Within the range of mould wall thickness(10~25mm) and hot spot wall thickness(3~6mm), temperature differences after six casting cycles, which were defined as"balanced temperature difference", increased while mould wall thickness increased, and local cooling capacity of mould declined. ④Under the condition of natural cooling, regression equation between balanced temperature difference(?T), mould wall thickness(w) and hot spot wall thickness(h) was obtained:ΔT = 0.4272Ln(w) + 33.1743Ln(h)– 36.4713 The equation manifested that hot pot wall thickness affects temperature differences more remarkably compared with mould wall thickness.⑤Under the condition of natural cooling, after thickness of dope reduced, temperature differences decreased observably, and local cooling capacity of mould also improved remarkably. The results show that the method to improve local cooling capacity of mould through adjusting thickness of dope was feasible.⑥Under the condition of enhancing heat transfer, temperature differences decreased observably, and local cooling capacity of mould improved evidently. In addition, the positive influence of enhancing heat transfer on local cooling capacity of mould became more apparent with the increase of casting times.⑦Convection heat transfer was strengthened after velocity of cooling water increased, under this circumstances, local cooling capacity of mould improved farther.⑧Influences of mould wall thickness on local cooling capacity of mould strengthened while local cooling capacity of mould improved, which can be observed by comparing coefficients of mould wall thickness in regression equations under different researching conditions with each other.