INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 11, No. 3, pp. 453-459 JUNE 2010 / 453 DOI: 10.1007/s12541-010-0052-x NOMENCLATURE a = undeformed chip thickness t = deformed chip thickness r = tool edge radius v = cutting speed γ = tool rake angle µ = coefficient of friction τ f = frictional stress k f = shear flow stress θ c = clearance angle δ s = stagnation point angle L c = contact length γ eff = effective rake angle 1. Introduction The contact phenomenon is the major thermomechanical activity in the cycle of chip formation, which has great economical effects in production. Predictions of cutting force, thermal aspects, cutting zone geometry, tool wear, tool strength are possible if the conditions of contact stress, contact length and stick-slide behavior are known. However, excellent previous work on contact stress distributions 1-4 and tool-chip contact length 5-7 in conventional machining is not entirely applicable in tool-based micromachining (TBM) due to the edge radius effect. The influence of such effect is reflected from material flow and piling-up ahead of the tool 8 during material separations at the stagnation point. 9 Thus, the contact behavior varies along the rake face, cutting edge and clearance face of the tool under different combinations of tool-workpiece, tool geometries and cutting conditions. At present, many salient features of the contact phenomenon are still remained unclear. In this paper, the study of contact behavior in TBM is attempted through an advanced finite element method (FEM) approach (Section 2.1) and a unique experimental approach (Section 2.2). Three major aspects are discussed: a) shear contact and material separations; b) stick-slide behavior and contact force; and c) contact length analysis that is discussed in Section 3.1-3.3 respectively. The numerical model is developed using the arbitrary Lagrangian- Eulerian (ALE) method to avoid mesh distortions without the incorporations of unrealistic chip separation criteria. A high-speed and low field-of-view photography technique is proposed for the contact length analysis. Numerical and Experimental Study of Contact Behavior in the Tool-based Micromachining of Steel Keng-Soon Woon 1,2 , Mustafizur Rahman 1,# and Kui Liu 2 1 Department of Mechanical Engineering, National University of Singapore, Singapore, 10 Kent Ridge Crescent, Singapore, 119260 2 Machining Technology Group, Singapore Institute of Manufacturing Technology, 71, Nanyang Drive, Singapore, 638075 # Corresponding Author / E-mail: mpemusta@nus.edu.sg, TEL: +65-6516-2168, FAX: +65-6779-1459 KEYWORDS: Micromachining, Contact phenomenon, Finite element method The contact mechanics is an important aspect in tool-based micromachining but a complete solution is not yet available. In this paper, a novel finite element analysis using arbitrary Lagrangian-Eulerian method and a special experimental setup using a high-speed and low field-of-view photography technique are used for the study of the contact problem. Discussions are emphasized on the interrelationship between shear contacts and material separation, the effect of contact pressure on the stick-slide behavior and the analysis of tool-chip contact length. The results revealed that material separation correlates to the stagnation phenomenon which is reflected from the shear contact vector while sticking and sliding is highly influenced by the distributions of contact pressure. Moreover, a non-dimensional solution for the contact length of micromachining is proposed based on the numerical and experimental results. Manuscript received: October 25, 2007 / Accepted: January 12, 2010 © KSPE and Springer 2010