Structural Analysis & Weight Optimization : Wheel Loader Front Axle Casings

Abstract: The purpose of this thesis work was to establish methodologies for performing structural analysis and weight optimization of wheel loader front axle casings at Volvo Construction Equipment AB (Volvo CE). A methodology for creating extensive finite element models to analyze durability with respect to both static failure and fatigue life was to be created in the software ANSYS 18.0 and a methodology for creating efficient finite element models to evaluate design changes in the software CATIA V5. The possibility to utilize topology optimization to generate design suggestions for axle casing was also to be investigated. These methodologies should be based on the front axle casing for L350 wheel loader model to analyze its current durability and investigate the possibility to reduce weight with maintained durability as a consequence of design changes. The methodology for creating extensive finite element models in ANSYS was created by investigating different contact conditions, mesh convergence, bolt pre-tensions and loads. The final case study model consisted of 105 components including frame, spindle, centre gear housing and bolted joints. Between all main components friction conditions were set and all bolts were pre-tensioned. The loads were retrieved from the internal Volvo CE program Redikomp and resulted in 11 different maximum/minimum and fatigue loading cases. Results from the model gave a maximum von Mises stress below the material yield limit and fatigue stresses below the pre-defined Volvo CE failure rate criterion. The methodology for creating efficient finite element models in CATIA was created by investigating the casing’s surrounding components and how these would impact the model, such as spindle, frame and centre gear casing. Results were then compared with the model created in ANSYS. The modeling approach which had the combination of generating accurate results with low pre-processing- and simulation time was selected. This model consisted of a joined centre gear housing to the axle casing, the spindle approximated with a rigid virtual part and the frame approximated with a smooth spring virtual part. Topology optimization methodology is an iterative process which involves several steps to generate an optimized structure given certain conditions. The process generates a structure which is based on the best utilization of material within a design space. The optimized casing was set to be optimized with the highest stiffness possible and a reduced weight. The model contained the same surrounding parts as in the FE-simulation in ANSYS but without the screw joints. The work on the L350 front axle casing started with generation of a CAD-model through reverse engineering based on an optical scan. This model served as a base for the FE-analysis performed with the methodology created in ANSYS where durability of the casing was analysed. A requirement specification for the new design was created and design changes was performed and evaluated with the FE-model in CATIA. When a design which fulfilled all requirements according to the CATIA model was found, it was confirmed by performing a final simulation with the model created in ANSYS. A weight reduction of 4% was achieved with manual design changes and using the FE-model created in CATIA, which is a quite insignificant amount in the context. However it still indicated that the developed methodology can be used to optimize axle casings. The design changes could be evaluated efficiently with a simple CATIA model and the final design fulfilled all criterions according to the ANSYS model. If the methodology would have been applied on a more robust casing or used earlier in a design stage, its utility would have been better. From the topology optimization a weight reduction of 12% was achieved. The optimized casing satisfied the maximum strength criterions and almost the entire failure rate criterion. This optimization routine can be used as a guide when designing new casing and gives an understanding on where material should be placed in order to create a casing with the most optimal material distribution.