Transient Analysis of Worm Gear Assembly

OBJECTIVE

The objective of this project is to perform transient analysis on a worm gear assembly and compare the results of equivalent stress, equivalent elastic strain, and total deformation.

CAD Geometry/Assembly considered for simulation (front view shown below):

The nomenclature considered for ease in identification based on component, i.e. gear, and worm.

Material and their respective properties considered for simulation (tabulated below):

	Young’s Modulus	Poisson’s Ratio	Yield Strength	Ultimate Strength	Density
Structural Steel	200 GPa	0.30	250 MPa	460 MPa	7850 kg.m-3

Both the worm gear and spur gear are considered to be of structural steel for the simulation.

Contact sets were setup between worm and spur gear based on their respective behaviour or interaction, i.e., frictionless shown below in figure.

Joints were setup for both worm and spur gear based on their behaviour with respect to ground as shown below in figure. Consideration of connection type as body-ground and type as revolute for joint definition.

Meshing of complete assembly was carried automatic resulting in discretization of model using tetrahedron element. Considered adaptive sizing for better element size based on contact with quality smoothing as high. As the simulation was carried out in academic version, the overall count for elements/nodes were always kept below 32,000 by adjusting the element size (fine up to maximum extent).

Analysis Settings for successful simulation run:

Step Controls

Number of Steps – 15

Auto Time Stepping – ON

Define By – Time

Carry over Time Step – ON

Initial Time Step – 0.05 s

Minimum Time Step – 0.05 s

Maximum Time Step – 0.5 s

Time Integration – ON

Solver Controls

Weak Springs – Program Controlled

Large Deflection – ON

Boundary Conditions

To simulate worm gear assembly, worm gear joint is provided with rotation of 3000^o in 15 steps (i.e., increment of 200^o) at worm gear revolute joint (setup earlier) as shown below:

Total Deformation Results

Equivalent Stress Results

Equivalent Elastic Strain Results

Above results shows that the worm gear assembly has been successfully simulated for rotation of spur gear up to almost end of half spur gear.

To avoid the convergence issue as worm gear joint rotation is increased by 4 times, i.e. from 750^o to 3000^o, it is recommended to reduce the time step by 4 times (i.e. from 0.2 to 0.05).

Else, we could also increase the number of steps to reach 3000^o rotation of worm gear with the same time step considered for 750^o rotation (i.e. 0.2).

This gives the insight that step size should be considered in such a way that stress shockwave doesn’t skip any of the element while computation. Skipping of any element leads to non-convergence or inaccurate results.