Surface integrity in abrasive flow machining (AFM) of internal channels created by selective laser melting (SLM) in different building directions

Abstract

Selective laser melting (SLM) can produce a conformal cooling channel that is widely used in the mold industry. However, SLM inherent rough surface can cause stress concentration, reducing the fatigue life of the mold. In addition to the surface roughness, residual stress can affect fatigue life. Therefore, it is necessary to improve surface integrity, such as surface roughness and residual stress, of the internal channels created by SLM. The internal channels (ø3 mm) are created by SLM in horizontal and vertical directions. As a counterpart of the SLM process, the internal channel (ø3 mm) is also made by the conventional process, such as electrical discharge machining (EDM) in a wrought bar. After internal channels are finished by abrasive flow machining (AFM), the evolution of the internal channel’s surface integrity, such as surface roughness and residual stress, is investigated. The surface roughness of the horizontally and vertically SLM built as well as EDM generated channels are measured with a stylus. The initial surface topography of the SLM built channels differs significantly depending on the SLM building direction. The stylus measurement reveals significant improvement (< 1 µm Ra) in surface roughness of all internal channels after AFM. The residual stress on the internal surface channel is measured with X-ray diffraction (XRD). After AFM finish, the compressive residual stress in the AFM flow direction is found to be induced on the SLM built and EDM generated channels. Thus, AFM finish can be considered to be beneficial to the surface integrity of the internal channel created by SLM and EDM.