Laser Machining And Surface Performance Analysis Of Nitinol Cardiovascular Stent

Nitinol stent has been used in the treatment of cardiovascular diseases because of its excellent biosolubility,weak magnetism and shape memory.Because of high cutting precision,good cutting quality,green and other advantages of fiber laser cutting’s,it has become the main way on cardiovascular stent processing.For this reason,this paper takes TLS-HT100 fiber laser cutting machine as the experimental equipment,selecting different process parameters for the laser cutting experiment,analyzing the change rule and distribution range of heat affected zone;rescast layer;surface morphology;roughness and dross,using variance and correlation degree analysis to optimize the process parameters.The majority research contents are as follows:(1)According to analyse the mechanism of spot energy transfer rate and total spot energy transfer value in radial and axial directions,the key technological parameters are determined.(2)The raw materials of Nitinol cardiovascular stent;laser cutting equipment and testing equipment were introduced briefly.The experimental scheme and detection scheme of stents performance indicators were designed.(3)The formation causes of different region of stents kerf were analyzed.The variation rule and distribution range of different region thickness and surface roughness were determined.The regularity of kerf surface roughness was obtained under different process parameters.(4)Variation rules of recasting layer,heat affected zone and dross were summarized under different process parameters,and the influence mechanism of each process parameter on recasting layer and heat affected zone was analyzed deeply.(5)All performance indicators on stents surface were summarized and analyzed.The influence of process parameters on each performance indicators was divided into very significant,significant and insignificant by means of one-way variance analysis and correlation degree analysis.And the parameters were optimized through analysising results.The experimental results showed that the key process parameters affecting Nitinol cardiovascular stents laser cutting were pulse width,laser power,pulse frequency and cutting speed.The variation rules and distribution range of the performance indicators of stents were also different under different process parameters.Pulse frequency is the mostimportant process parameter on stents surface performance,pulse width and cutting speed are the next,laser power is the least important.A group of optimized process parameters were obtained by single factor variance and correlation analysis.Under this parameter,the surface performance have been improved greatly.The stents kerf was stable without dross and recasting layer distribution.The kerf surface roughness is reduced to 650 nm.The heat affected zone is reduced to 1.8μm.And inner dross thickness is as low as 62.9 μm.