| Due to the aging society and the improvement of living standards,the domestic use of medical alloy materials is increasing rapidly,but most of my country’s high-end medical devices are still imported.The main problem is that the current processing methods would inevitably cause medical alloy materials damage,for example traditional mechanical polishing will cause deformation,residual stress,hardened layer and other problems on the surface of medical alloy materials,which will affect the service life,for example the surface quality after electrolytic polishing is uneven and the residual chemical substances can not meet the medical standards.Research on the non-damage smooth surface processing method of medical alloy materials is the key issue that needs to be solved urgently.In this paper,a polishing method,cluster magnetorheological finishing with dynamic magnetic fields,is proposed to process medical alloys.Under the premise of protecting the purity of the chemical composition of the material itself,it can achieve high-efficiency and ultra-smooth processing of the surface of medical alloy materials.The main research contents of this paper are as follows:First of all,the cluster magnetorheological finishing with dynamic magnetic fields of medical alloy materials was studied by finite element simulation software COMSOL,and it was found that compared with traditional magnetorheological finishing,the eccentric rotation of the permanent magnet can increase the effective polishing area and avoid the uneven radial distribution of the magnetic field.At the same time,the size and position of the magnetic field generated change from time to time,which can help the renewal of abrasives and the real-time shaping of polishing pads,and provide theoretical support for realizing high-efficiency and ultra-smooth processing of medical alloy materials.Secondly,cluster magnetorheological finishing with dynamic magnetic fields was used to carry out systematic polishing experiments on two typical medical alloy materials(medical TC4 titanium alloy and Zr-based bulk metallic glass).The effects of the parameters of the magnetorheological polishing fluid and technological parameters on the polishing effect of medical alloy materials were studied by single factor experiment and orthogonal experiment,and the optimal process parameters of different materials were obtained.Using 5μm alumina abrasive,the medical TC4 titanium alloy was polished for 4 hours under the process of machining gap 1 mm and polishing disk rotation speed 25 r/min,and a smooth surface with surface roughness Ra of 2.87 nm were obtained.Under the conditions of 3 μm silicon abrasive with mass fraction of 7 wt.%,iron powder with mass fraction of 20 wt.%,the machining gap of 1mm,polishing plate rotation speed of 35 r/min,magnetic pole speed of 30 r/min,workpiece speed of 350 r/min,the medical Zr-based bulk metallic glass was polished for 1 hour.The surface roughness Ra can be reduced to 4.93 nm.Finally,the effect of cluster magnetorheological finishing with dynamic magnetic fields on the surface properties of medical alloy materials were studied.Scanning electron microscopy(SEM)was used to detect the surface composition of medical TC4 workpieces.The elemental content did not change significantly before and after polishing,and there was no iron adhesion and oxidation reaction in the whole polishing process.The polishing process has little effect on the microhardness,but it can change the surface of the workpiece from hydrophobic to hydrophilic,and improve the biocompatibility of medical alloy materials.The corrosion resistance of medical alloys was studied by medium immersion method.After the polished workpiece was soaked in Hank’s artificial body fluid for 90 days,the added value of surface roughness was smaller and there was no crystallized substance on the surface.The friction and wear properties of medical alloys in Hank’s artificial body fluid were tested by a friction and wear instrument,after magnetorheological polishing,the friction coefficient was reduced,the width of the wear mark was narrower,and the wear resistance was further improved.In conclusion,the properties of medical alloy materials after cluster Magnetorheological finishing with dynamic magnetic fields were improved to a certain extent. |
