Friction and wear of a low-speed PTFE/Ti-6Al-4V joint for a precise space mechanism

Polytetrafluoroethylene (PTFE) and titanium alloys are widely used in precision space mechanisms, where reliable dry-contact performance is essential for long-term operation. This study investigates the friction and wear of a PTFE/Ti-6Al-4V joint in the guiding system of the Grabbing, Positioning, and Release Mechanism, a key subsystem of the Laser Interferometer Space Antenna (LISA) mission. Friction forces are crucial in ensuring the desired precision of motion for this mechanism. It features a Ti-6Al-4V linear runner, which is laterally constrained by a preloaded roller pair and two opposing PTFE pads. In a dedicated test campaign, we estimate friction from load cell data and quantify wear with a 0.01mg resolution balance. To assess the influence of sliding speed, two sets of pads are tested at 200μm/s and 500μm/s, each covering a total sliding distance of about 28 m . Experimental results show that both friction and wear increase with speed; specifically, the mean friction coefficient increases by 29%, while the total wear mass increases by 13%. We propose a novel exponential law of the sliding distance to describe the whole transient dynamics of the friction coefficient (reaching R 2 > 0.99 ). We verify that the established PTFE wear power law remains valid within a sub-millimeter speed regime previously unexplored in the literature. We introduce a numerical procedure based on Fourier Transform and Otsu’s method to estimate the actual PTFE pad area affected by wear with a localized spatial precision of 0.12mm. In a wider framework with respect to LISA, these findings bridge a literature gap by providing data for PTFE/Ti-6Al-4V joints at sub-millimeter speeds typical of piezoelectric-driven mechanisms.