Session: 03-04-03: Advanced Machining and Finishing Processes

Paper Number: 113419

113419 - Study of the Effect of Toolpath and Machining Parameters on Sphericity, Surface Finish, and Dimensional Tolerance of Polymer Acetabular Cups 

At the present time, the demand for prostheses for hip arthroplasty is growing quickly, because they reduce pain, and improve mobility and quality of life of patients. Hip prostheses are composed of a femoral stem, femoral head, polyethylene insert (acetabular cup), and cup. Ultra-high molecular weight polyethylene (UHMWPE) is commonly used for the manufacture of the acetabular cup because of its notable mechanical, physical, and chemical properties. In manufacturing the acetabular cup, the surface finish plays an important role, since it controls the wear behavior of the joint elements. Therefore, the study of cutting parameters, machining strategies, characteristics of the cutting tool on precision, and final surface quality are vital to obtaining prosthetic elements that allow extending the useful life by delaying joint replacement. In this work, an experimental study of CNC milling machining of the internal diameter of 28 mm of an acetabular cup for hip prosthesis was carried out. A Fadal VMC 3016C vertical milling machine, a 2-flute flat-nose roughing mill, and a 4-flute ball-nose surface finishing mill, both 10mm diameter and suitable for cutting polymers, were used in this work. The investigation was carried out by means of a Taguchi L9 design, and the influence of 4 machining parameters with 3 levels and 2 replicates. The factors studied were the effect of the toolpath (vertical-horizontal parallel, spiral-radial, vertical-spiral parallel), depth of cut (0.5, 1.0, and 1.5 mm), spindle speed (1400, 1700, and 2000 rpm) and overlap (0.01, 0.07 and 0.15 mm) on average roughness, sphericity, nominal diameter tolerance and machining time. The results of average roughness, sphericity, and diameter precision obtained in all the experimental tests are in accordance with the international standard ISO 7206-2 for the analysis of surfaces of hip replacement components, whose tolerances for the insert must comply with sphericity ≤ 100μm, the nominal inside diameter of 28+0.3+0.1mm, and an average roughness Ra ≤ 2μm. The average roughness, sphericity, nominal diameter tolerance, and machining time range obtained in this study are in the range of 0.644 to 0.851 µm, 45 to 74 µm, 28.110 to 28.142 mm, and 27.1 to 92.0 minutes, respectively. The greatest mean roughness reduction (0.6436 µm) was obtained considering a vertical-spiral parallel strategy, a depth of cut of 0.5 mm, a spindle speed of 2000 rpm, and a cutting overlap of 0.07 mm. Our finding suggests that the cutting parameters proposed through the design of experiments of this work can help to obtain the desired surface finish in acetabular cup components in accordance to the international standard ISO 7206-2.

Presenting Author: Ernestina Becerra-Becerra Universidad de Guanajuato

Presenting Author Biography: Ernestina Becerra is a PhD Studen at the University of Guanajuato. She is working on the topic of surface finish through the CNC milling machining and burnishing processes. She has published JCR papers and she has participated in international conferences.

Authors:

Ernestina Becerra-Becerra Universidad de Guanajuato
Agustin Vidal-Lesso UNIVERSIDAD DE GUANAJUATO-DICIS
Alberto Saldaña-Robles Universidad de Guanajuato
Juan Francisco Reveles-Arredondo Universidad de Guanajuato