Iefrosinin D. The technological support of the accuracy and roughness of the surface of the head of the hip joint endoprosthesis from titanium

The work is devoted to the determination of the regularity of the mechanical finishing treatment of the surface of the head of the endoprosthesis of the hip joint of the Grade 2 grade titanium with subsequent thermodiffusion nitriding (TDN). The materials of the development of an adaptive tool for precision machining of the spherical surface of the titanium head of the hip joint prosthesis are presented. Adaptation occurs due to changes in the height of the projection of the grains in contact with the processed material. For the tool design, it is necessary to determine the boundaries of change in the surface stiffness of the bunch K when interacting with other material. The approximation of the theoretically necessary values of bond stiffness for uniform material removal were calculated in the following grains ranging z = 200/160 – 20/14. The theoretically calculating of the maximum stiffness value K = 51 – 1113 of the eight bond specimens were sintered. This should correspond to this values. At the Institute for Strength Problems of G. S. Pysarenko of the NAS of Ukraine (Kyiv) was tested the stiffness of the bonding specimens by squeezing them on an Instron 8802 destructive machine. The stiffness K varied from near zero to about 2200 N / mm. The verification of the received bond to adaptability and the absence of adhesive bonding confirmed the possibility of its use for machining titanium. The processing a titanium component on a lathe according of the technological scheme of free grinding for the new tool the operating conditions were determined. These are two main parameters that are affect to the processing of the workpiece: the pressing force to the tool P = 50 – 200 N and the frequency of the rotation of the workpiece n = 1000 rpm. The cutting speed at the same time at the different points has the following range Vp = 0.2 – 1 m / s. Increasing or decreasing the frequency of the rotation of the workpiece will result to tearing into parts of the workpiece, or breakage of the tool, this result automatically to brack the parts. The work of the tool in the range grains of Z = 200/160 – 28/20 were tested. The grain size of the tool below Z = 28/20 has a very poor performance efficiency the tool. The results of increasing the clamping force is to leading of the tearing on the workpiece. It is experimentally established that such lapping results in a surface roughness of Ra 0.25 and a deviation from non-circularity of less than 10 μm when using a tool with a grain size of Z = 200/160; 63/50; 28/20. Finishing mechanical polishing of a spherical surface on titanium of Grade 2 to the roughness of Ra < 0.05 when measured at a track length of 0.08 mm according the international standard ISO 7206-2:2011 was conducted using the developed polishing paste, that has an intensive the mechanical and chemical action to the surface of the workpiece. The best result of the polishing the head of the hip joint endoprosthesis from titanium was obtained by using cotton non-stitched circles with a diameter of 150 mm and the specially designed of the polishing paste. The spead of rotation on the periphery of the circle was V = 3.75 m / s. The head of the hip joint endoprosthesis from titanium of Grade 2 followed by TDN were tested on a simulator in friction pair with chirulene. It was proved that the developed the technology of manufacturing this head contributes to the improvement of the tribotechnical properties of 3,3 times in the metal-polymer friction pair. The results were tested in the terms of industrial enterprises «UkrBudAvtomatyka» Ltd.