Improving machinability of additively manufactured components with selectively weakened material

Abstract

Part design and the possibilities of production are disrupted by the increased usage of additive manufacturing (AM). Featuring excellent creative freedom due to the layer-by-layer buildup of components, AM leads to profound changes in future part design and enables previously impossible geometries. Laser powder bed fusion (LPBF) technology already allows to manufacture small quantities of parts with high productivity and material efficiency. Due to the specific process characteristics, the resulting surface finish of these parts is insufficient for a wide range of applications, and post-processing is usually unavoidable. Specifically for functional surfaces, this post-processing is often done by machining processes, which can pose challenges for intricate and complex AM parts due to excessive machining forces. In the present paper, the influence and the possibilities of the LPBF process parameters on the subtractive post-processing are shown. A novel weakened structure is developed to selectively reduce the strength of the material and improve the cutting conditions. Chip formation, cutting forces and vibrations during drilling as well as cutting forces during an orthogonal cut are examined. To quantify the differences, a comparison of the machinability between bulk material, standard support structures and the weakened structure is carried out.

The Additive-Subtractive Process Chain - a Review

“…Taking into account the correlations with regard to heat input and heat distribution in the component, this results in further specific requirements for the track planning. Special track planning methods were developed for the production of AM components with intentionally generated porosity [119,120] (Fig. 9).…”

“…Grain boundaries in relation to the cutting process [193] Accordingly, the conditions of mechanical machining should be taken into account in the design of the support structures. Support structures and allowances made of specifically porous material areas can contribute to a homogenisation of the machining forces and considerably improved surface qualities [120]. In Fig.…”

“…21. Influence of heat treatment and intentionally generated porosity on cutting forces [120] With regard to the removal of inhomogeneous surface layers on AM components, the compensation of component distortion resulting from AM processes as well as the renewed deformation of the components during mechanical post-processing due to residual stress effects, stock allowances on AM components must be provided from which the desired component geometry can be precisely worked out [195]. However, since the causal chain of effects is not fully understood and describable, oversized stock allowances are usually implemented.…”

Influence of the support structure on the bandsawing process when separating LPBF components from the building platform

“…The disadvantageous effects of the support structures on the machining process were shown here as well. Based on these findings, Maucher et al proposed adapted support structure geometries [13] as well as adapted process parameters to selectively weaken the material in order to improve the machining process [14].…”