磁极开槽对磁粒研磨加工镍钛合金血管支架管材内壁表面质量的影响

目的提高镍钛合金血管支架管材内壁的表面质量及磁粒研磨加工效率,研究开槽与不开槽磁极对磁粒研磨加工镍钛合金血管支架管材内壁表面质量的影响。方法建立了有限元仿真模型,分别模拟了开槽磁极与不开槽磁极的磁感应强度分布情况。结合仿真结果,使用搭建的镍钛合金血管支架管材内壁磁粒研磨加工设备,分别采用开槽磁极和不开槽磁极进行镍钛合金血管支架管材内壁磁粒研磨加工实验。使用超景深3D显微镜对研磨前后表面粗糙度进行测量,使用扫描电子显微镜对内壁表面微观形貌进行对比分析。结果在工艺参数组合为管材旋转速度100 r/min、磁极进给速度5 mm/min、磨料填充量0.1 g、磨料粒径100.00μm、往复加工1次的参数条件下,使用不开槽磁极进行加工,管材内壁表面粗糙度Ra由加工前的0.5μm降至0.24μm,下降52%;使用开槽磁极进行加工,管材内壁表面粗糙度Ra由加工前的0.5μm降至0.11μm,下降78%。结论磁极开槽后,在改善磁感应强度分布的同时,避免了因磁极所产生的磁驱动力不足以克服磁粒刷与管材工件间的摩擦力而产生的磁性磨粒的滞后现象。同时加工2个工作行程,使用开槽磁极对镍钛合金血管支架管材内壁进行磁粒研磨加工,内壁原始缺陷层的去除效果更好,加工后管材内壁表面质量更优。根据表面粗糙度值的变化趋势,开槽磁极研磨加工效率更高。

Study on Surface Quality of Inner Wall of Ni-Ti Alloy Cardiovascular Stents by Magnetic Abrasive Finishing by Magnetic Pole Slotting

In order to improve the surface quality of the inner wall of Ni-Ti alloy cardiovascular stents pipe and the efficiency of magnetic abrasive finishing,and to study the effect of slotted and non slotted magnetic poles on the surface quality of Ni-Ti alloy cardiovascular stents pipe.The finite element simulation model is established to simulate the magnetic induction intensity distribution of slotted magnetic pole and non-slotted magnetic pole.Combined with the simulation results,the magnetic abrasive finishing equipment for the inner wall of the Ni-Ti alloy cardiovascular stents pipe was used,and the magnetic abrasive finishing experiments for the inner wall of the Ni-Ti alloy cardiovascular stents pipe were carried out with slotted magnetic pole and without slotted magnetic pole.Super depth of field 3D microscope was used to measure the surface roughness before and after grinding,and scanning electron microscope was used to analyze the microstructure of inner wall surface.Under the conditions of the process parameters combination of pipe rotation speed 100 r/min,feed velocity of magnetic poles 5 mm/min,magnetic abrasive filling quantity 0.1 g and size of diamond MAPs 100μm and one-time reciprocating machining,the surface roughness Ra of the inner wall of the pipe decreased from 0.5μm before machining to 0.24μm,which decreased by 52%;the surface roughness Ra of the inner wall of the pipe decreased from 0.5μm to 0.11μm,which decreased by 78%.Pole magnetic field distribution is greatly improved after grooving,after notching the tooth part of the magnetic induction intensity produced several poles“tip”,because“tip”magnetic induction intensity is relatively uniform,processing of magnetic abrasive will be gathered in a multiple pole tooth position of the uniform,avoid most of the magnetic abrasive gathered near the pole ends phenomenon,The grinding pressure of magnetic abrasive particles on inner wall of pipe is increased.After the pole is slotted,the magnetic induction intensity of the pole has a more complex gradient change,which solves the problem of weak magnetic induction intensity in the middle region of the magnetic pole surface,and is more conducive to magnetic particle grinding.At the same time,the hysteresis phenomenon of magnetic abrasive particles caused by the magnetic driving force generated by the magnetic poles is not enough to overcome the friction between the magnetic brush and the pipe workpiece is avoided.When the magnetic driving force can drive the magnetic particle brush to move,the hysteresis phenomenon will inevitably appear,and reducing the hysteresis becomes the key.The hysteresis is related to the magnetic induction intensity,the greater the magnetic induction intensity,the smaller the hysteresis,the smaller the magnetic induction intensity,the greater the hysteresis;The hysteresis is also related to the inner wall quality of the processed workpiece.The greater the friction coefficient,the greater the hysteresis of“magnetic particle brush”and magnetic pole,and vice versa.In addition,the hysteresis is related to the axial size of the magnetic pole and is approximately 1/3~1/2 of the axial size.At the same time,two working strokes are processed,and the magnetic particles on the inner wall of Ni-Ti alloy cardiovascular stents pipe are carried out by slot magnetic pole.