脉冲电磁场辅助平面磁粒研磨加工试验

目的在传统的平面磁粒研磨加工中添加脉冲辅助磁场,增大加工区域中磁感应强度和加工时磁感应强度动态变化,丰富磨料粒子在加工时的运动形式,使研磨轨迹复杂化,降低工件表面粗糙度,获得更好的工件表面形貌。方法通过分析磨料粒子在有无辅助磁场时各自的受力情况,探究辅助磁场对磨料在加工时运动状态的影响,研究脉冲辅助磁场下磨料的运动行为机理。利用Ansoft Maxwell软件对电磁铁不同形状的磁极头产生的磁场进行模拟对比,确定理论上最优的磁极头形状。同时模拟对比脉冲电流在不同时刻加工区域内磁感线的分布情况,以及恒定磁场和脉冲磁场下磨料的运动轨迹。通过试验对比无辅助磁场、恒定辅助磁场和脉冲辅助磁场下磁粒研磨加工SUS304不锈钢的表面形貌和表面粗糙度。结果在磁粒研磨加工中,磁性磨料分布受磁感线的影响,在脉冲辅助磁场的作用下加工区域内的磁性磨料会随磁感线的变化而做周期性的往复运动,加工时会有更为复杂的研磨轨迹。模拟3种不同形状的磁极头在加工区域产生的磁感应强度曲线,平面、圆锥面和半球面在中点处的磁感应强度峰值分别为655、636、702 mT。以SUS304不锈钢板作为试验对象,原始表面粗糙度为0.46μm,采用半球形的电磁铁磁极头,在研磨间隙为2 mm、永磁极转速为800 r/min、进给速度为5 mm/s的试验条件下,对比电磁铁不通电、通入0.8 A直流电流、通入1 Hz,占空比50%,峰值电流0.8 A的单向脉冲电流3种辅助磁场分别对工件研磨30 min后的工件表面形貌,无辅助磁场时工件表面仍残留一些原始纹理;恒定辅助磁场下工件表面原始纹理被去除,但表面存在明显圆弧形研磨痕迹;脉冲辅助磁场下工件表面形貌更为光整、平滑。研磨后工件表面粗糙度分别降至0.28、0.13、0.06μm。结论脉冲磁场辅助磁粒研磨在提高加工区域磁感应强度的同时,可使磁性磨料在加工时做周期性运动,研磨轨迹复杂化,促进了磨料的更新,相比传统磁粒研磨和恒定辅助磁场磁粒研磨工艺,脉冲磁场辅助磁粒研磨加工后的工件表面形貌更加平滑,表面粗糙度更低。

Experimental Study on Pulsed Electromagnetic Field Assisted Planar Magnetic Abrasive Finishing

The work aims to add pulse assisted magnetic field in the traditional plane magnetic abrasive finishing process to increase the magnetic induction intensity in the processing area and the dynamic change of magnetic induction intensity during processing,enrich the movement form of abrasive particles during processing,complicate the grinding path,reduce the surface roughness of workpiece,and obtain better surface topography of workpiece.The effects of the assisted magnetic field on the motion state of the abrasive in processing were studied by analyzing the forces of the abrasive particles with or without the assisted magnetic field,and the motion mechanism of the abrasive under the pulse assisted magnetic field was studied.The magnetic field generated by the different shape of the pole head of the electromagnet was simulated and compared with Ansoft Maxwell,and the optimal pole head shape was determined.At the same time,the distribution of magnetic induction lines in the processing area was compared when the electromagnet was on and off,and the trajectories of abrasive under constant magnetic field and pulsed magnetic field were compared.The surface morphology and specific surface roughness of SUS304 stainless steel without assisted magnetic field,with constant assisted magnetic field and pulse assisted magnetic field were compared by experiments.The distribution of magnetic abrasive was affected by magnetic induction line in the magnetic abrasive finishing process.Under the action of pulse assisted magnetic field,the magnetic abrasive in the processing area made periodic reciprocating motion with the change of magnetic induction line,and there was a more complex grinding track in the processing.The magnetic induction intensity curves generated by three different shapes of magnetic poles in the processing area were simulated.The peak values of magnetic induction intensity at the midpoint of horizontal plane,conical surface and hemispheric surface were 655,636 and 702 mT,respectively.The SUS304 stainless steel plate with the original surface roughness of 0.46μm was taken as the test object.A hemispherical electromagnet pole head was used when the processing clearance was 2 mm,the speed of the permanent magnet pole was 800 r/min,and the feed speed was 5 mm/s.The following methods were used to grind the workpiece for 30 min respectively:the electromagnet was not energized,the electromagnet was energized with 0.8 A DC current,and the electromagnet was energized with 1 Hz,duty cycle was 50%,and the current amplitude was 0.8 A unidirectional pulse current.After finishing the machining,the surface morphology of the three kinds of workpiece was compared.The results showed that there were still some original textures on the workpiece surface without the assisted magnetic field.Under constant assisted magnetic field,the original texture of the workpiece surface was removed,but there were obvious arc-shaped grinding traces on the surface.The surface morphology of the workpiece was smoother under the pulse assisted magnetic field.After grinding,the surface roughness of the workpiece was reduced to 0.28,0.13 and 0.06μm,respectively.Pulsed magnetic field assisted magnetic abrasive finishing in improving processing area of magnetic induction intensity at the same time,can make the magnetic abrasive have periodic motion when processing,complicate the grinding trajectory,and promote the renewal of the abrasive.Compared with the traditional magnetic abrasive finishing and constant magnetic field assisted magnetic abrasive finishing process,the surface morphology of workpiece processed by pulsed magnetic field assisted magnetic abrasive finishing is more smooth,and has lower surface roughness.