INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 14, No. 10, pp. 1677-1685 OCTOBER 2013 / 1677 © KSPE and Springer 2013 Thermo-mechanical Coupled Analysis of Laser-assisted Mechanical Micromilling of Difficult-to-machine Metal Alloys Used for Bio-implant Ninggang Shen 1 and Hongtao Ding 1,# 1 Department of Mechanical & Industrial Engineering, University of Iowa, Iowa City, IA 52242, USA # Corresponding Author / E-mail: hongtao-ding@uiowa.edu, TEL: 1-319-335-5674 KEYWORDS: Laser-assisted mechanical micromilling, Biomedical implant materials, Coupled thermo-mechanical analysis This study is focused on a numerical modeling analysis of laser-assisted mechanical micromilling (LAMM) for difficult-to-machine biomedical implant alloys, such as Ti6Al4V and stainless steels. Multiple LAMM tests are performed on these materials with 100 µm diameter endmills at various laser powers. A 3D thermal model is used to quantitatively analyze the material temperature increase due to laser heating during the LAMM process. Finite element (FE) models are developed using ABAQUS to simulate the continuous chip formation, and strain gradient constitutive material models are implemented to model the size effect. The quasi steady-state workpiece temperature after multiple milling cycles is analyzed with a heat transfer analysis based on the chip formation analysis and thermal model simulations. The modeling results in temperature, force and cutting stress are discussed and compared with the experimental results. Manuscript received: February 22, 2013 / Accepted: July 15, 2013 1. Introduction Stainless steels and titanium alloys are employed extensively as implant materials for a range of medical applications including orthopedic and dental implants. 1 In the field of orthopedics, for instance, more than 500,000 total hip and knee replacement surgeries with titanium implants are performed in the United States every year. 2 As the demands for the manufacture of biomedical parts with complex micro-scale features increase, it is critical to develop technologies for processing these materials with good precisions. Due to its great process flexibility, mechanical milling using micro-size endmills has been implemented as an alternative technology to generate accurate, three dimensional (3D) micro-scale features. However, during the micromilling process, the cutting edge radius (r e ) of the micro tools is usually comparable to the undeformed chip thickness (h), and in some occasions less than the size of the workpiece material grain size. Such a size effect often causes the material specific cutting force at the micro-scale much higher than at the macro-scale, which makes micromachining of difficult-to-machine materials even more difficult. 3-5 The high specific cutting force cannot be sustained by micro-sized tools, which usually results in a catastrophic failure of the tool and poor finished surface. Laser-assisted mechanical micromilling (LAMM) is a promising technology offering desired capability of producing complex 3D and high aspect ratio micro features. Softening the workpiece material using a controlled laser ahead of the cutting position reduces the cutting forces and size effect, and has the potential for extending the practical applications of the process. 6-8 To successfully design the mechanical micromilling process with optimized laser parameters, the key is to have an accurate thermal model to predict the workpiece temperature field undergoing intensive laser heating. Several finite element (FE) models have been attempted to model the workpiece temperature field undergoing the LAM process. 9-12 However, the material removal by the micro tool has been rarely considered in these studies, and the simulated material peak temperature under the laser spot was often much higher than the melting point. Tian et al. 13 developed a transient, 3D finite volume method (FVM) model for laser-assisted mechanical milling at a macro-scale, and has been adapted for LAMM process of micro side cutting configuration. 14 The size effect and elevated workpiece temperature due to laser heating contribute to a complicated material removal mechanism undergoing LAMM, which shows fundamental difference from DOI: 10.1007/s12541-013-0227-3