Week 3

Objective: Clean up the geometry and mesh the hood pertaining to the given quality criteria using ANSA preprocessor. 

The quality criteria to be followed:

Procedure:

1) After importing the step file, the inner and outer panels of the hood can be identified. These two components are separated using the NOT function and the views are locked so that they can be operated on separately. 

Fig: Inner panel 

Fig: Outer panel

2) Geometry cleanup is performed by using the Geometry check option from checks manager. Various geometrical errors are checked for, including: unchecked faces, needle faces, overlapping faces, cracks, intersections etc. 

Auto fix is done at first for some of the geometrical errors. Further errors are removed by opting for methods like, deleting the unwanted cons and generating faces wherever required. 

Fig: Component after performing geometry cleanup. 

3) Extracting midsurface: Midsurface can be extracted by using two methods: offsetting the faces by inputting values and using the mid-surface feature which automatically generates the mid surface. 

For extracting the mid surface from inner panel, manual offset is done. The thickness of the inner pannel is 0.75mm. So the offset value is taken as 0.375.

Fig: Mid surface extraction from the inner panel

For the outer panel, auto midsurface feature is used, while the offset value is maintained as 0.375mm. 

Fig: Mid surface extraction from the outer panel

The inner pannel has symmetry which can be confirmed by using the Rm.Dbl tool, which compares similar faces. Default node tolerance value as 0.05 and giving the similarity factor as 100%, we obtain the following figure, depicting the symmetry in the component. 

Fig: Areas devoid of symmetry are not highlighted as blue/green.

Hemming: Hemming is a technology used in the automotive industry to join inner and outer closure panels together (hoods, doors, tailgates, etc.). It is the process of bending/folding the flange of the outer panel over the inner one. The accuracy of the operation significantly affects the appearance of the car’s outer surfaces and is therefore a critical factor in the final quality of a finished vehicle.

Since the inner panel is inserted between the outer panels, overlapping of the faces will occur causing geometrical errors. 

Thickness is assigned to the hod hemming. That is, the summation of thickness of inner panel and (thickness of outer panel*2). 

Fig: Assigned thickness to the various PIDs related to our geometry. 

4) After extracting the mid surfaces, we proceed to meshing the components. As per the quality critera specified, the values are entered.

Since, the target or the average length to be taken as 5, values are to be entered in mesh parameters as well

Best mesh featured is used initially and the mesh quality is checked under the defined quality criteria. Then the quality of the mesh is improved wherever needed by using tools such as perimeter: num +/- ( used whereever the cons exceeded max length criteria or failed to meet the min length criteria), reconstruct( which reconstructs the mesh with any available meshing algorithm considering the mesh parameters) etc.

Conclusion:  Using the tools provided in the ANSA preprocessor, geometry cleanup was performed on the hood component and mid surfaces of the outer and inner panels were extracted using manual offset method as well the auto midsurface method(skin). The geometry was meshed according to the specified quality criteria and mesh parameters, improving the quality of the mesh using various features and methods. Hemming process was also performed as deemed necessary.