Impact of wire and arc additively manufactured workpiece geometry on the milling process

Abstract

In recent years, the wire and arc additive manufacturing (WAAM) process has been given attention as a possibility to save material during the production of large-scale parts. Drawbacks of the WAAM process are the relatively low surface quality and the low form accuracies, which require post-processing of all functional surfaces. The milling process is researched as a post-processing option, especially to achieve high form accuracies. While several authors presented successful applications of the milling process, the difficulties of machining wire and arc manufactured parts (WAAM-parts) due to the part geometry have not yet been researched. In the present research, the impact of the WAAM-part geometry on the milling process was analyzed by machining three sets of samples, and guidelines for a milling strategy were developed. The results show that the geometry leads to modulated cutting forces, whose frequency, in turn, has to be considered for the milling setup. Additionally, the modulated cutting force leads to a periodically changing deflection resulting in a form deviation on the final workpiece.

Machining Strategy Determination for Single- and Multi-Material Wire and Arc Additive Manufactured Thin-Walled Parts

“…Surface waviness is directly related to the WAAM parameters. Optimization studies have confirmed that WAAM parameters significantly affect the machinability; for example, a higher heat input increases the surface irregularity [8,9]. Moreover, higher heat input and lower cooling rates increase the surface waviness of parts and decrease the hardness [2,8,10].…”

“…High surface irregularity has a negative impact on machining. Generally, the initial surface state influences the final roughness [8] and can cause unstable cutting conditions, leading to unwanted conditions such as forced vibration [8,9]. High surface irregularity causes variation in the depth of the cut in the cut direction.…”

“…However, in contrast to the semi-finished and finished cuts for cast and forged geometries, a constant depth of cut cannot be determined. To determine the depth of cut, WAAMed parts are usually 3D scanned, and the machining allowances are calculated by fitting the scanned models to the target model [8,9]. Some studies removed the specified machining allowances in a single pass [8] or pre-machined high-waviness surfaces and then machined the subsurfaces in multiple passes [9,12].…”

“…To determine the depth of cut, WAAMed parts are usually 3D scanned, and the machining allowances are calculated by fitting the scanned models to the target model [8,9]. Some studies removed the specified machining allowances in a single pass [8] or pre-machined high-waviness surfaces and then machined the subsurfaces in multiple passes [9,12]. The cutting forces are unstable in the first pass due to the surface irregularity for the multipass strategy.…”

“…The cutting forces are unstable in the first pass due to the surface irregularity for the multipass strategy. In subsequent passes, because the surface waviness has been removed, the processing is conducted under stable conditions, as is the case for casting and forging parts [9].…”