week 7 challenge

MID SURFACE EXTRACTION FOR SHEEL METAL COMPONENT USING SKIN, CASTING, OFFSET METHOD AND MESHING IT USING BATCH AND MANUAL MESH

(WEEK 7 CHALLENGE ANSA)

OBJECTIVE:

• Importing the sheet metal component into ANSA.
• Clean up the geometry until no topological error is found.
• Generate mid surface using skin option, casting option and offset method.
• Mesh the component using batch mesh, manual mesh with given quality criteria.
• Comparing the mesh flow which is formed as a result of casting, batch, and manual mesh.

QUALITY CRITERIA USED:

ABSRTACT:

In this challenge ANSA pre processor is used to generate mid surface using various options such as skin, casting, manual mid surfacing and mesh the sheet metal component using batch mesh and manual mesh (best mesh, spot mesh). The main objective is to compare and find out which option is best suitable for sheet metal component.

METHODOLOGY:

• Import CAD geometry into ANSA
• Do geometry check up and clear all the errors
• Generate mid surface and assign different PIDs for parent geometry and mid surface
• Setup Quality criteria and mesh parameters
• Meshing and improvement of the mesh

INTRODUCTION:

Sheetmetal generally comes in three forms — mild steel, aluminium, and stainless steel. Of these, aluminium and mild steel are by far the most used in automotive industry. Sheet metal is available in flat pieces or coiled strips. The coils are formed by running a continuous sheet of metal through a roll slitter. Metal foil is especially common with aluminium, often referred to as tinfoil. The thickness of foil is usually up to 0.2 mm. The thickness of sheet metal starts from 0.5 mm and goes up to 6 mm. Anything above that is a metal plate.

Sheet metal component

Sheet metal component

PROCEDURE:

MID SURFACE GENERATION USING SKIN AND MESHING WITH BATCH MESH OPTION

Step 1: Import the CAD geometry and do Faces --> Topo to stitch the surfaces.

Imported sheet metal component

Step 2: Clear all the geometrical errors and assign length (Mesh deck --> perimeters --> length) for the whole geometry to 3mm as the target length given in the quality criteria is 3.

Checks manager dialog box

Step 3: Extract mid surface using skin option. This option automatically selects one surface with red colour, bottom surface with green colour and thickness with blue colour.

Selecting sheet metal using skin option

• Carefully check all the areas whether ANSA detects these surfaces correctly. By using skin option ANSA automatically deletes the parent geometry after creating mid surface. You can check in the PID manager as the parent geometry is deleted.

Mid surface generated using skin option

Step 4: Mesh generation using Batch mesh option. The 1^st step is to create a new part in the model browser and assign the mid surface to that new part. Then open the batch mesh and create a new meshing scenario.

Selecting mid surface for batch mesh generation

• Update the content i.e. the mid surface and the required mesh parameters and quality criteria. Then click on RUN to generate batch mesh.

Generated mesh scenario

• The updated mesh will be showed under status as completed. The “!” mark is shown because there are some quality issues which are needed to be fixed.

Batch mesh generated for sheet metal component

• Batch mesh gave good results. Only 2 off elements are generated and all the holes are captured perfectly. But the mesh flow at some areas are not good.

Generated Batch mesh

MESH GENERATION USING CASTING OPTION

Step 1: The main advantage of casting is that mid surface and meshing is done in one shot. Select topo module à mid surface à casting. Assign minimum thickness, target element length and run on visible.

Assigning values in casting option

• The mesh generated by casting option has lot of off elements. The mesh flow at some regions is also not good.

Mesh generated as a result of casting

Step 2: Some features like holes and surfaces with different heights are not properly captured by ANSA using casting option.

Improper hole capturing during casting

Improper hole capturing during casting

• However, I have rectified these errors in some areas by deleting the elements and creating some elements. But this process is not advised.

Deleting element

• I have cleared all the off elements using reconstruct and smooth options. But the mesh flow and the hole capturing at some regions is not good.

Mesh after clearing all off elements generated by casting

MID SURFACE GENERATION USING OFFSET AND MESHING MANUALLY USING SPOT MESH BY SEPARATING REGION BY REGION.

Step 1: By using offset we can easily generate mid surface for parent geometry. As this sheet metal has thickness of 1mm we can offset this with 0.5mm for mid surface. Always enable cross-hatches and use feature area for easy selection.

Offsetting the parent geometry

Step 2: Mid surface formed using offset gives the exact features which the parent geometry consists. Isolate the mid surface and give separate PID for the mid surface.

Mid generated using offset

All features are properly captured using offset

Step 3: Make sure all the holes are numbered even. Use Number option or number +/- option.

Changing number of nodes to even

Step 3: Now, slide all the holes parallel to the edge using Slide option which is under perimeters in mesh module. This is done to get better mesh flow.

Hole before using slide option

Hole after using slide option

Step 4: Before meshing use mark option (mesh module --> hot points --> Mark/Unmark) to mark all the holes so that they are not disturbed while mesh generation.

Holes are marked before meshing

Step 5: After numbering, sliding, marking all the required holes then start meshing. Manual meshing basically means meshing and clearing all the off elements region by region in order to get the best mesh flow possible. Divide the region using macros --> cut option. Use spot or best options for mesh generation and use reconstruct for better mesh flow. Also use commands like paste, split, swap to eliminate the trias.

Dividing and meshing

Better mesh flow as a result of manual meshing

• After all the mesh is done manually, Use macros --> join to delete the user cuts which you have made while manual meshing.

Manual meshing done for whole sheet metal component

COMPARISON OF MESH FORMED BY CASTING, SKIN AND MANUAL MESHING

By comparing all the mesh types generated I can say that:

• Casting took very less time as it gives both mid surface and mesh in one click. But casting has not produced the desired result for mid surface generation as well as mesh generation.
• By using skin, the mid surface is perfectly generated and by batch meshing it I generated mesh for the whole component in one shot. The mesh generated is better than the mesh generated by casting. Although there are some areas with bad mesh flow and rotating quads.
• Manual offsetting gave me perfect mid surface and by manual meshing, I got perfect mesh flow. But it took lot more time than casting and batch mesh. In the picture below I have compared all the 3 mesh generations, brown indicates casting, turquoise blue indicates batch meshing and blue indicate manual meshing.

Comparing mesh generated by casting, batch meshing and manual meshing

LEARNING OUTCOME:

1. Understood various tools and tricks of ANSA to generate mid surface.
2. Aware of all the quality criterias and mesh parameters during mesh generation.
3. Implemented batch mesh, casting and manual mesh.
4. Compared all the three mesh types generated.
5. Learned how to improve mesh flow and remove trias to achieve better mesh flow.

CONCLUSION:

In this challenge I have successfully imported sheet metal component into ANSA and Cleaned the geometry until no topological error is found. Generated mid surface using skin option, casting option and offset method. Meshed the component using batch mesh, manual mesh with given quality criteria. Successfully compared the mesh flow which is formed as a result of casting, batch, and manual mesh.

Model of ANSA file links:

• Manual mesh model: https://drive.google.com/file/d/1-bvSWWs6nVhKns1ATtOEz4PtCugh9mK3/view?usp=sharing

• Skin and batch mesh model: https://drive.google.com/file/d/11o0iCfl6wFDKX1uE0gr64DMRPUbf5Vda/view?usp=sharing

• Casting model: https://drive.google.com/file/d/1BiuwKnwx7mBKUb2dQh9_xA059CI1dxEG/view?usp=sharing