Boom structure of construction machine and manufacturing method thereof

摘要

This invention provides with a boom structure comprising a first straight portion, a curvilinear portion positioned contiguously to the first straight portion, and a second straight portion positioned contiguously to the curvilinear portion in a direction of the boom, characterized in that a tubular member forms one or more of corners of a generally rectangular cross-section in the curvilinear portion, wherein the tubular member has a closed cross-section, whereby capable of improving the fatigue strength of the boom and attain a reduction of its weight.