MSc. Thesis Defense: Toprak Pehlivan

APPLICATION OF PROCESS DAMPING IN STABILITY OF

VARIABLE PITCH TOOLS

Toprak Pehlivan
Manufacturing Engineering, MSc. Thesis, 2025

Thesis Jury

Prof. Dr. Erhan Budak (Thesis Advisor)

Assoc. Prof. Dr. Lütfi Taner Tunç

Asst. Prof. Dr. Faraz Tehranizadeh

Date & Time: 17th of July, 2025 – 12:30 PM

Place: FASS G049

Keywords : Process Damping, Chatter Stability, Variable Pitch Tools, Milling Dynamics, Semi-Discretization Method

Abstract

Chatter remains one of the most significant challenges in milling operations, limiting productivity, surface quality, and tool life. Stability lobe diagrams (SLDs) are widely used to select chatter-free cutting parameters, yet their accuracy diminishes at low cutting speeds, where process damping becomes increasingly influential. Variable pitch end mills have emerged as an effective solution to enhance machining stability by disrupting the regenerative effect responsible for chatter. However, the combined impact of process damping and variable pitch geometry on milling stability has not been thoroughly explored. This thesis investigates the application of process damping to the chatter stability of variable pitch end mills. The dynamic properties of a variable pitch carbide end mill were characterized through impact testing and modal analysis. Stability predictions were performed using the semi-discretization method (SDM), enabling accurate modeling of the multi-delay systems inherent in variable pitch geometries. The influence of process damping at low cutting speeds is incorporated into the model, drawing from literature-based approaches and measured tool geometry. Simulation results demonstrate that variable pitch tools significantly enlarge the stable cutting regions, and that process damping further increases the stability limit, particularly in low-speed regimes. Planned cutting experiments will validate the theoretical findings and quantify the practical benefits of these combined strategies. The outcomes of this research provide valuable insights for the design and application of chatter-resistant milling tools, enabling higher productivity and reliability in challenging machining operations.