Stress and Vibration Analysis of a MDOF Excavator Bucket

Abstract

Multi degrees of freedom (MDOF) excavator is a very popular machine in today’s mining industry and are also popularly used in roads and building constructions or demolition and for material handling. All these uses involve exposer of the bucket to high amount of linear and non-linear reaction forces which might sometimes cross the limit of endurable stress of the bucket, also because of the continuation of reaction forces noise and vibration is observed in the bucket which propagates to the whole excavator body. There have been very limited research works done till now on the engineering analysis of excavator or excavator bucket. Most of the works concentrated on the different attachments’ modified or optimized design, and almost no work has been done on the vibration analysis of the bucket particularly. The vibration due to input digging force and reaction force damage the bucket and its cutting teeth with the time being, so it is a common practice to change the bucket with a new one or replace the teeth which are no longer usable. Some companies use reinforced steel with the bucket as attachments to increase its strength and resist wear when mining. This research work is focused on different techniques of using rubber and other materials with the bucket as attachments to reduce vibration so that it can last longer and work under less disturbances. In this thesis work three dimensional (3D) MDOF (Multi Degrees of Freedom) bucket is modelled with the help of SOLIDWORKS software and analyzed in ANSYS 14 software. In ANSYS Software three different analysis platform is used on the 3D model namely Modal, Harmonic and Static Structure analysis. Firstly, the Modal analysis is done to understand the mode shapes and natural frequencies of the bucket. Secondly, Harmonic analysis is done to understand the vibration amplitudes in different natural frequencies. And lastly Static Structure analysis is performed to understand the equivalent von-misses stresses developed in the bucket. The simulation or numerical analysis has been performed on a standard bucket then several cases were developed. The use of rubber materials with the bucket as attachments to reduce vibration and to observe change in the mode shapes and natural frequencies is a major highlight of this thesis work. Also use of other materials and their effect is observed in this thesis work. Different techniques were studied to use rubber strips which will not increase the total weight of the bucket but will reduce vibration and stress developed in the system. The thesis also includes how the different vi aspects of using attachments such as how much thickness it should be or what are the effects of thickness of attachments. The numerical simulation is validated with published journal paper for the stress developed in the bucket and results found are in well agreement with the results of the paper. An experiment is also performed on a bucket model made locally with local materials and using common mechanical tools such as bending, rolling, scissor and welding. The experimental model is fixed on a fixture then vibration output was measured under different loads. Then rubber sheet and rubber strips also attached with this experimental model and experimentation was done. Similar model was developed in the SOLIDWORKS software and analyzed accordingly in ANSYS and validated with the experimentation. The experiment was only performed on the harmonic analysis of the bucket with and without rubber and the results found from the experiments are in similar pattern with the simulation results.