Abstract
The Reference Free Part Encapsulation (RFPE) is a workholding system which is designed to “free-up” the design space and greatly expand the possible range of the parts that can be designed and then machined. RFPE allows the machining of parts with thin spars and narrow cross-sections. Such parts are often difficult or impossible to hold with conventional vises or toe-clamps. Despite the increased capability of the RFPE technique, its influence on part warpage and part accuracy has not yet been sufficiently documented, and thus the experiments reported here have made a new contribution in this direction. 7075T6 aluminum (annealed) and ABS materials were machined with flat end mills, and deflections of the specimens were measured. The results were obtained in two categories i) without RFPE using conventional toe clamps ii) with RFPE. RFPE uses a bi-phase material (Rigidax™). In the conventional toe clamp set-up, the aluminum specimens showed increasing warpage with decreasing test-part dimension. When the molten fixturing material was applied, the warpage remained the same for the aluminum specimens. In the conventional toe clamp set-up, the ABS plastic showed almost no warpage after machining. However, warpage increased to a maximum of 0.04∼0.06 inch when the fixturing material was applied to the ABS specimens. The warpage is proposed to occur due to the relaxation of ABS’s anisotropic molecular chains during the heating and cooling process. In conclusion, warpage of thin aluminum parts was from machining-induced residual stress, but warpage of thin ABS parts was mainly from thermal residual stress developed during the RFPE process. Results presented in this paper indicate the amount of warpage that might be expected. These values could be used in CAD/CAM databases for DFM (Design For Manufacturing) checking.
