Impact microactuators rely on repeated collisions to generate gross displacements of a microelectromechanical machine element without the need for large applied forces. Their design and control relies on an understanding of the critical transition between non-impacting and impacting long-term system dynamics and the associated changes in system behavior, known as grazing bifurcations. Here, a theoretical normal-form analysis is presented that predicts the character of such transitions from a set of conditions that are computable in terms of system properties at grazing. The analysis also suggests opportunities for using passive design or active control to regulate the system response near grazing. The theoretical analysis is validated against numerical simulations of an experimentally realized impact microactuator.