Differences Between Excavator Boom and Arm

The excavators boom and arm form an interconnected lever system in terms of function, but their responsibilities are distinct. The boom, also known as the main boom, is hinged to the excavators upper frame and serves as the basic skeleton of the entire working device. Its core function is to achieve large-scale lifting and luffing, and to transmit the huge thrust from the lifting cylinder to the front end, while bearing the main excavation reaction force and bending moment transmitted back from the arm and bucket. Therefore, the booms structure focuses more on overall bending and torsional strength, and its box-shaped structure is usually larger and more robust.

In contrast, the arm (or dipper stick) is hinged between the front end of the boom and the bucket, and its function is more specific and refined. It mainly adjusts the working radius through its own extension and retraction movements on the basis of the support established by the boom, and precisely controls the excavation trajectory and cutting angle of the bucket. The arm directly drives the bucket to perform cutting and material gathering actions, so the part of its front end connected to the bucket is subject to frequent impacts and severe wear.

This difference in function and stress characteristics directly leads to different focuses in processing technology. For the boom, the core of the manufacturing process lies in ensuring the integrity and stability of the overall structure as a foundation. High-penetration, high-quality welding processes and comprehensive stress relief annealing after welding are crucial, aiming to eliminate internal stresses and ensure that it does not deform or crack under heavy loads. For the arm, in addition to the need for a solid welded structure, the focus of its process is more on dealing with local wear and fatigue. The hinge hole walls at its front end, which connect to the bucket, usually require special strengthening treatments, such as welding wear-resistant bushings or local surface quenching, to significantly improve their wear resistance and impact resistance, and extend their service life.