Study on finishing inner wall of Co[sbnd]Cr alloy cardiovascular stent tube via novel atomized CBN/metal spherical magnetic abrasive powders

Abstract

In this study, in order to solve the problem that the inner wall of the cardiovascular stent is difficult to polish, the magnetic abrasive finishing (MAF) method is used to finish the inner wall of the CoCr alloy tube that is used for the manufacture of the cardiovascular stent. The surface defects such as wrinkles, cracks and pits generated in the production process are removed, and the internal surface roughness is decreased to obtain better surface quality. Firstly, aiming at the problem of poor performance of traditional magnetic abrasive powders (MAPs), “gas-solid two-phase double-stage atomization and rapid solidification” is proposed and a novel atomized CBN/metal spherical MAPs with different sizes are successfully prepared. This MAP is used for MAF of the inner wall of CoCr alloy cardiovascular stent. Secondly, the slotted magnetic pole is designed according to the numerical simulation, and the MAF setup for the inner wall of ultra-fine and ultra-long tubes is developed. Finally, the orthogonal experiment is carried out with surface roughness as the evaluation index. Through the analysis of range theory, the order of the apparent degree of each process parameter on surface roughness is as follows: tube rotational speed > feed speed of magnetic pole > MAPs filling quantity > MAP particle size. According to the result, a model of surface roughness prediction based on whale optimization algorithm (WOA) and least squares support vector machine (LSSVM) is constructed. The interaction between tube rotational speed and other process parameters is analyzed based on the model fitting results, and the process parameters are optimized. The result show that MAF technology can effectively remove the defects of the inner wall of the CoCr alloy cardiovascular stent tube and accurately predict the surface roughness. After MAF under the optimized process parameters, the surface roughness Ra decreases from 0.485 μm to 0.092 μm.