Week 3 - 2D meshing for Sheet metal

OBJECTIVE

To mesh the given hood component after proper geometry cleanup and mid-surface generation using the ANSA preprocessing software. Also, to ensure the generated mesh follows the given quality criteria and the corresponding thickness of each surface is assigned to the mesh.

QUALITY CRITERIA

S.No	Quality Criteria	Value
1	Target/Average length	5
2	Minimum Length	2
3	Maximum Length	7
4	Aspect	3
5	Warpage	15
6	Skewness	45
7	Jacobian	0.7
8	Minimum Quad Angle	45
9	Maximum Quad Angle	135
10	Minimum Tria Angle	30
11	Maximum Tria Angle	120
10	Tria Percentage%	15

THE COMPONENT

PROCEDURE

• They are as follows: Inner Panel - 0.75mm, Outer Panel - 0.75mm, Hinge Reinforcement - 1.2mm and Latch Reinforcement - 1.2mm.

• Initially, the part will not have a proper resolution so to ensure proper detailing and viewing, we can use the length option which can be accessed through the Mesh module. This tool works in creating a finer representation of the model based on how finely the length of the feature lines is broken up. All the surfaces need to be selected to use this tool.

• Before anything else is carried out, a geometry check and cleanup need to be carried out and ANSA has a tool that takes care of that. The checks tool can be accessed from the upper toolbar. Checks > Geometry. With all components visible, the checks can be 'executed'. The geometric discrepancies will be highlighted by the tool and they can all be selected, right clicked, and fixed by clicking 'fix' as shown in the screenshot.

Chick Manager

• After cleaning up and reorienting the faces of the part - using the orient tool, we can assign properties and property ID to accommodate the mid surfaces that will be created. Doing this will also make it easier for viewing components separately. To create a property, go to properties from the upper toolbar and right-click the list. Then go to New-PSHELL-PSHELL to create a new property ID. This opens a new window where we have the option to edit many of the particular property's attributes. In this case, we are to assign a thickness. We can go ahead and assign one of the two thicknesses. The process will be repeated for each of the components' mid surfaces. We can do the same and assign properties for the main components. The intention is to view the mid surfaces and their mesh and parent surfaces separately.

• Now, we shall generate the mid-surface of each surface. This can be done using the mid-surface tool in the faces menu or using the offset tool from the Topo module. The mid-surface tool would be ideal here as the components have a constant thickness. The offset tool would be more effective in cases of varying thicknesses. For practice purposes, I went with the offset tool. After selecting the offset tool, it will ask us to select the surfaces to offset. We can select the surfaces on one side of the component. After that, we can assign the offset value of (0.75/2)=0.375.

The offset tool will show the direction of the offset in the form of an arrow. If it is in the opposite direction of the required offset, the offset value needs to be negative, as shown in the screenshot. If we proceed, the surface will be offset and we will have the option of keeping the parent surfaces. The midsurface tool also requires surface selection but you would need to select all the surfaces of the particular parent component. Furthermore, there will be an option to not delete the parent surfaces on the bottom right panel. The offset can then be assigned their respective property, through the 'apply' option discussed in the previous step.

• After the mid-surface is generated for each of the components, we can go ahead and prepare to mesh the mid-surfaces. To start off, we can assign the quality parameters as per the challenge. We need to access the mesh parameters and quality criteria options from the top toolbar. And then we can assign the values as per the table. Use the F11 key and minimum and maximum lengths would be 2mm and 7mm respectively. And then give the given value.

• After that, we can go ahead and assign the target length. This is done by accessing the length tool again from the Perimeters section under the Mesh module. We need to select the entire mid-surface and assign the target length which would be 5mm.
• To facilitate better mesh flow and ensure good mesh quality, the mid-surface needs further preparation with regard to proper surface cuts. This can help prevent tria formation.

• Cuts can be made using the Cut tool from the Mesh module under macros. We can go ahead and try our best to split up the surfaces into rectangular regions to ensure the least number of tries. Existing feature lines that may hinder this can also be suppressed. This is done by right-clicking the lines using the same cut tool.

Before flow

After Flow

Inner extract panel

There are 1242 trias out of 38938 total. It means the trias percentage is 3.19%.

LEARNING OUTCOMES

1. Application of several versatile tools that are part of the ANSA ensemble.

2. Understanding of the more automated geometry cleanup process and other geometric tools used to facilitate the meshing process in the TOPO module.

3. Understanding of midsurface generation options available in ANSA.

4. Understanding of meshing techniques, property creation, and application, quality criteria, and mesh cleanup procedures.

CONCLUSION

The given hood part was meshed as per the required quality criteria, after having carried out topology cleanup and generated mid-surfaces for each of its components, and thickness was assigned to each of them.