DESIGN OF DETACHABLE PRECISION FIXTURES WHICH UTILIZE HARD AND LUBRICANT COATINGS TO MITIGATE WEAR AND REDUCE FRICTION HYSTERESIS

摘要

Detachable precision fixtures have reached a performance barrier defined by tribological phenomena driven by friction and wear. Although detachable fixtures with nanometer-level precision have been made using exotic and expensive materials, a low-cost means of achieving the same level of performance remains elusive. The goal of this paper is to introduce experimental results that indicate low to moderate cost hard coating of balls and grooves can improve the repeatability of detachable fixtures. Coatings such as TiN have long been used to reduce friction and wear of high-performance tooling. These coatings can easily be adapted to do the same for the interfaces of detachable fixtures. Increasing the hardness of contacting surfaces, increases the energy required to change the surface (i.e. wear). Lower-friction coatings minimize the energy stored at the contacting interfaces, thereby reducing friction hysteresis and reducing the energy available to promote surface wear. This is important given the high energy density and energy density gradients near-the point contacts of balls and grooves in kinematic couplings. Based upon the preceding knowledge, a "first generation" experiment was run to indicate whether the hypothesis that hard coatings improve repeatability may be true. The experiments and results are discussed in the following paper. These efforts form the basis for a more detailed, "second generation" of experiments which will be used to create deterministic models that link coating characteristics and properties to coupling repeatability.