A Study on Parametric Appraisal of Drilling on Bio-compatible Materials

Abstract

Titanium alloy and stainless steel finds widespread applications in different fields such as bio-medical, aerospace and electronics due to their superior physical properties (high strength,toughness,corrosion resistance and durability and low density). Due to their bio-compatibility in nature,they are used in the field of bio-medical engineering such as artificial bone joints,
artificial knee joints and in dental fields. Drilling is one of the important machining processes involved in most of the application fields including bio-medical engineering. This study investigates the effect of drilling parameters on performance measures through development of numerical model using finite element approach.The numerical model is validated by experimental study. The parameters included for investigation are spindle speed, feed rate and drill diameter.The experimental plan is made using design of experiment approach, specifically a face centered central composite design of response surface methodology in order to reduce the experimental runs and reduce cost of experimentation. The output performance characteristics considered are burr height at entry, burr height at exit, surface roughness, circularity at entry and circularity at exit.In order to optimize multiple responses simultaneously,
the responses are converted into single response using superiority and inferiority ranking (SIR) method. Empirical model relating machining parameters with output responses have been developed using non-linear regression analysis. An improved version of latest evolutionary approach known as Harmony Search (HS) algorithm has been is used to find out best parametric condition subjected to constraints such as circularity at entry and circularity at exit.The study also investigates the effect of high speed laser drilling process of Ti6Al4V and AISI 316 stainless steel during laser drilling.Laser machining is carried out using assistant gas as nitrogen environment using a 2.5 kW CO2 laser.The experimental planning has been done using Taguchi L9 orthogonal design. The machining parameters used for investigation in the study are flushing pressure, laser power and pulse frequency.The output responses investigated are heat affected zone (HAZ), spatter area, circularity and taper of hole. Parametric study on drilling process helps in providing guidelines to the practitioners for securing the implant material in an adequate manner.