Methodology of using PAAW and the Underlying Support Network of an L-PBF Part to Facilitate Machining

The Laser- Powder Bed Fusion (L-PBF) process is currently used to print geometrically complex, thin walled, metallic parts. Critical features on these parts must be machined. Unfortunately, the parts are difficult to fixture without clamping distortion, and are susceptible to machining chatter. This paper describes a methodology in which the underlying support network that is used to facilitate printing is used to mitigate these machining problems. For the first machining operation, the support network is adhered to a Photo-Activated Adhesive Workholding (PAAW) fixture to achieve five-sided cutting tool access and minimum cutting tool overhangs. Subsequently all of the critical geometry above the network is machined. In the second operation, the support network is machined away to create new geometry at the former support-solid metal interfaces. Tool paths are chosen to take advantage of the stiffness imparted by the network. The potential advantages of this approach are that it simplifies the machining sequence and reduces the total number of required operations and fixtures to two. The holding complexity of the first operation is simplified to the extent that it may be done using a general purpose, modular PAAW fixture. It does not require the printing of extra metal. In addition, it takes advantage of the inherent stiffness that the support network imparts to the main geometry of the part, thus making it easier to machine critical geometry without inducing chatter or excessive distortion. The results of a feasibility study indicate that this methodology is effective at mitigating chatter and creating geometrically accurate surfaces with a fine texture. Unfortunately, this study also reveals that stress relaxation distortion degrades the accuracy of these surfaces once the part is released from the fixture after the 2nd operation. In addition, the machining of the network deposits a small quantity of difficult-to-clean powder sludge in the machining center. (C) 2019 The Authors. Published by Elsevier B.V.