AutoCAD Mechanical toolset automatically creates hidden lines when you specify which objects overlap the others.
The overlapped areas of the objects that lie behind (referred to as the background) are drawn as hidden lines. Objects overlapping each other this manner are said to be involved in a “hide situation”.
Any closed contour on a contour layer or a non-mechanical layer can be selected as a foreground object. AutoCAD Mechanical toolset's automatic property management mechanism intelligently ignores objects that are not appropriate for a hide situation; for example, centerlines and hatches.
AutoCAD Mechanical toolset supports two commands for creation of hide situations, AMSHIDE and AM2DHIDE. AMSHIDE command was originally designed for mechanical structure drawings while AM2DHIDE was meant for non-mechanical structure drawings. However, we subsequently enhanced the AMSHIDE command to support non-mechanical structure workflows. AMSHIDE provides greater functionality than AM2DHIDE. Hence, we recommend AMSHIDE over AM2DHIDE.