Metal Additive manufacturing (AM) can produce mechanical parts of complex structures such as lattice structures and hollow structures that are difficult to fabricate by subtractive processing. The main AM methods using metal materials are powder bed fusion (PBF), directed energy deposition (DED), and material extrusion (ME). The ME method is acknowledged as being inexpensive and convenient for manufacturing parts. However, the ME method using metal material requires a sintering process using a furnace after the AM process. Sintering generates shape errors in parts with a hollow structure, which is a characteristic of AM. Various factors cause shape errors, including the temperature control parameters in sintering. In this study, we investigated the effect of tool paths on shape errors caused in sintering and proposed a tool path that suppresses shape error. Experiments on the effect of the infill structure on shape error revealed that a smooth contact between the contour path and infill path can suppress shape errors in sintering. It was also determined that the overlap of infill paths decreases shape errors in sintering. These results demonstrate that the dominant factor causing shape errors is the tool path, rather than the kind of the infill structure. Based on this result, another experiment was conducted to investigate the effect of tool paths on shape errors in sintering. Among the tool path features, we focused on the material amount instability caused by retraction and excessive self-overlapping at the contact points between the contour and infill paths. The results demonstrated that the unstable feeding of material at the contact points owing to retraction and excessive self-overlapping caused a non-uniform filling rate and thickness variations in the specimens. This, in turn, affected the shape error in sintering.

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