Structural Optimization Design Of Backhoe Hydraulic Excavator’s Boom Based On Extreme Digging Force

Backhoe hydraulic excavator is composed of two parts, the mainframe and working attachment. The working attachment is the executive mechanism of the excavator, which is made up of the boom, the arm and the bucket. The structural design of the working attachment influences the working performance and working efficiency directly. The boom, as the important component of the working attachment, often bears big loads, which consists of the impulse loads and the alternating loads caused by the arm digging and bucket digging. Also, the boom need lift and unload materials frequently, which may lead to fatigue failure and even fracture failure. Nowadays, the structural design of the working attachment is based on the theoretical digging force, and then selects the dangerous working conditions to optimize. However, on the one side, the digging force theory, which is widely used now, neglects the effect caused by the moment of resistance, on the other side, the dangerous working conditions selected according to the value of the theoretical digging force may not the most dangerous working conditions. Therefore, it has great practical significance to study the digging force theory and select the most dangerous working conditions.This paper is studied on a certain 36.5T backhoe hydraulic excavator, which takes use of the extreme digging force theory to get the pivot points forces on traditional conditions and tested conditions. And then make strength analysis of the boom. Finally select the most dangerous working condition to optimize the structure. The specific research work in this paper mainly includes the following aspects:(1) Analyze and summarize the characteristics of the mechanism and structure of the backhoe hydraulic excavator, and then set up the kinematics model. Different with the traditional digging force theory, this paper sets up the mechanics model based on the extreme digging force theory which takes the moment of resistance into consideration. Thus, it provides theoretical basis for the pivots coordinates and pivots forces of the working attachment.(2) By comparing the mechanism performance and structural performance based on the different digging force theory, this paper verifies the accuracy and superiority of the extreme digging force theory. Then select the most dangerous working condition according to the value of the stress applied on the boom. The dangerous working condition is that the boom lies on the horizontal position, the arm is vertical to the boom and these three points, that is the bucket tooth, the pivot point of bucket and arm, the pivot point of arm and boom, locate in a straight line.(3) Establish the parametric finite element model by ANSYS, and then compile APDL in order to be invoked and solved easily and conveniently.(4) Take advantage of MATLAB to compile the genetic algorithm, and then call the APDL to finish the finite element solution in order to optimize the boom structure, finally get the convergent result which has better strength and lighter weight. By compared to the model before optimization, it is proved that the optimization method in this paper has great practical significance to improve the structural strength of the boom and reduce the weight of the boom.