Study of Dimensional Repeatability and Fatigue Life for Deformation Machining Bending Mode

Deformation machining (DM) is a hybrid process which combines two emerging manufacturing processes, machining of thin structures and single-point incremental forming (SPIF). This hybrid process enables the creation of structures that have geometries that would be difficult or impossible to create using any either process alone. A comprehensive study of DM bending mode components has been carried out in this paper by studying their dimensional repeatability and fatigue life and comparing these with similar components fabricated with sheet metal. Experimental studies have been performed for part features created by the DM “bending mode” process, in which a thin vertical wall is machined on the part, and then incrementally bent with a single-point forming tool. The dimensional repeatability of DM components is compared with sheet metal components made by single-point incremental forming and conventional bending in a press brake [Agrawal et al., 2010, “Comparison of Dimensional Repeatability of Deformation Machined Components With Sheet Metal Components,” North American Manufacturing Research Conference, NAMRC 38, Transactions of NAMRI/SME, Vol. 38, pp. 571–576]. The results of this study indicate that the DM process is not capable of holding tolerances as tight as a standard milling process. This may be due to local variations in material properties that influence the yield strength and resulting springback. However, thin components created by DM are more repeatable than similar components created from sheet metal using SPIF, but less repeatable than components created by conventional bending of sheet metal. The second objective of the present work is to investigate whether components fabricated using the DM process can be considered for fatigue critical applications [Megahed et al., 1996, “Low-Cycle Fatigue in Rotating Cantilever Under Bending I: Theoretical Analysis,” Int. J. Fatigue, 18(6), pp. 401–412; Khalid et al., 2007, “Bending Fatigue Behavior of Hybrid Aluminum/Composite Drive Shafts,” Mater. Des., 28, pp. 329–334]. Studies were performed to experimentally compare the fatigue life of components fabricated by DM process with sheet metal components made by single-point incremental forming and conventional bending. Results of the study indicate that sheet metal SPIF components under the present loading conditions have significantly longer fatigue life of approximately 3900–5500 cycles, compared to DM and sheet metal conventionally bent components with approximately equal fatigue life of 2200–3900 cycles.