Week 8 Worm Gear Challenge

OBJECTIVE

To carry out a transient structural analysis on the given worm gear model and generate equivalent stress, equivalent strain and total deformation outputs of the model for the worm rotating the gear up till halfway through the gear (which is to be cut in half).

MODEL IMAGE

PROCEDURE

1. After opening ANSYS Workbench, we are met with the Project Schematic window. Here, we can select the 'Transient Structural' analysis system on the left. Doing so creates a new project. Here, we can rename the project and also change the material if needed. We will need to right-click 'Geometry' and select 'import'. The file provided for this project should be selected. 

Once imported, we can right-click 'geometry' and click 'edit'. This brings up the model in the SpaceClaim interface. Here, using the split tool, we can cut the gear in half as required. But before that, we can create a rectangle along the XZ plane. Then, we can go to the split body tool and select the gear body, along with the rectangle as the cutting plane. Since the origin is located at the centre of the gear, the rectangle on the XZ plane will cut it exactly in half. The other half can then be deleted (along with the rectangle).

Once we are done, we can simply exit out of SpaceClaim, right-click 'model' and select 'edit' to bring up the mechanical interface.

Model after splitting in half:
2. Once the model is opened in the mechanical interface, we can rename the parts and the generated contact as well. Since the simulation needs to run till the end of the gear half, we need to select more regions of contact on the gear teeth (for target surfaces) in addition to the ones selected as shown.

Also, the contact type needs to be made frictionless.

3. We can now work on the mesh. Since the challenge suggested using a finer mesh, we can introduce sizing for the points of contact. I went with a sizing measurement of 2mm. For general mesh settings, adaptive sizing was turned on and the smoothing was set at medium.

4. After that, two revolute joints were created via right-clicking connections > insert > joint. The type for both was body-ground. The inner surface of each gear and worm thread were selected as scope surfaces.

Care must be taken to ensure the axis of rotation is correct.

5. Moving on, the analysis settings were worked on. The number of steps would be 35. Selecting the first step alone, we can assign the following attributes:

For steps 2-35, the following attributes were assigned:

All the output controls were turned on except the 'contact miscellaneous' option.

6. Next, we need to right-click Transient > Insert > Joint Load. This is for the revolute joint created on the worm thread. The type would be rotation and we can assign tabular values as shown (in increments of 50 degrees till step 35):

7. Now we can generate the outputs. To do this, we can right-click Solution > Insert > Strain > Equivalent (Von-Mises) (for equivalent strain) and right-click Solution > Insert > Stress > Equivalent (Von-Mises) (for stress) and right-click Solution > Insert > Deformation > Total.

Now, all we need to do is right-click solution again and click 'Evaluate all results'. When the analysis is done, we can view the results by simply clicking each of these output entities we created, in the Outline menu.


OUTPUTS

EQUIVALENT STRESS

Maximum & Minimum stress

EQUIVALENT STRAIN

Maximum & Minimum strain

TOTAL DEFORMATION

Maximum & Minimum deformation

OBSERVATIONS

For the challenge, the number of steps had to be increased to ensure the worm thread reached as close as possible to the gear, which is why there are 35 steps compared to the video's 15. As for the values, one point of note is the maximum stress generated. It must be stated that the yield stress of the structural steel used in this analysis is 250 MPa. Therefore, the worm gear model will most likely fail, since stresses higher than that value were generated in both the worm and the gear. That means a different material might need to be used to manage the high amount of stress generated (more durable materials). If that is not an option, some design modifications may be required, probably to the tooth shape geometry or the size of the components.

RESULT

The transient structural analysis was carried out on the given worm gear model and the outputs of equivalent stress, strain and total deformation were generated. As per stress values, it was established that the model will fail due to the maximum stress generated being close to 10 times the yield strength of the structural steel material used for the components.