Experimental study of static and dynamic rigidities of flexible particulate bed fixtures under external vertical and torque loads

Abstract

Abstract Rigidity of particulate bed fixtures under vertical (extraction and downward) loads, both static and dynamic, was investigated experimentally using a slender rod to represent a workpiece. Rigidity under external static and dynamic torque loads was also studied experimentally. Results of rigidity are represented as a function of submergence depth, compaction pressure, and workpiece cross section. Dynamic loads were of two types—step and impact. Loads applied to the workpiece represented typical loads encountered in manufacturing operations, such as in machining, milling, drilling, routing, inspection, welding, and painting. Results show that compaction pressure and rod depth have signifacant effects on bed fixture performance. Fixture rigidity exhibits different trends with load types. Fixture rigidity is reliable and repeatable under static vertical loading; it is also somewhat linear. Under torque loads, rigidity is highly nonlinear. Fixture rigidity is highly nonlinear in the case of dynamic loads as well. Under the loading conditions outlined above, displacement of the workpiece can be maintained within acceptable tolerances even for close tolerance machining operations and tight indexing applications such as surface inspection. Results of rigidity are conservative because the type of workpiece used in the study represents the worst possible geometry for fixturing.