Which of the following is a disadvantage of FDM?

The correct answer highlights a notable limitation of Fused Deposition Modelling (FDM). The process tolerance of up to 0.2mm indicates that the precision of the parts produced may not meet the requirements for applications needing high accuracy. This level of tolerance can lead to challenges in achieving a good fit for interlocking parts or for assemblies where dimensional accuracy is critical.

In contrast, the other options present favorable aspects or misconceptions about the FDM process. For example, thicker layers can often produce a better surface finish due to fewer printing layers and quicker build times; however, they can also result in a rougher texture in some cases. Low operating costs are often touted as an advantage of FDM, making it an accessible technology for prototyping. Lastly, while the orientation of printed parts can vary, FDM printers typically do not print parts upside down; they build layer-by-layer from the bottom up, which is generally a more standard and effective approach in additive manufacturing.