Week 6-Meshing of Hood Challenge

CHALLENGE -5 : Meshing of Hood Challenge

AIM:

• To mesh the component given by following the quality criteria specified.
• To Assign property and thickness to the component.

OBJECTIVE:

• Meshing the model components seperately by creating sepearte mid-surface.
• Using the 'Mixed' (Not Quad) option to generate the mesh, because the model is preparing for the crash & safety simulations. The quad-only mesh is preferred for durability and structural simulations.
• Understand quality index and model check options available in HyperMesh.

THEORY:

Front cover (also called engine cover and engine hood) is the most eye-catching body component, is an important opening piece to body, which directly affects the overall performance of the body and the comfort. Front cover assembly not only plays a role in air guiding, but also protects the engine and surrounding pipeline accessories, meanwhile it can sufficiently avoid impact, corrosion, rainwater and electric interference. In design requirements of the front cover, modal or stiffness need meet the actual needs and lightest quality, otherwise easily the affects overall security and NVH performance of vehicle.

The following are the design consideration involved in the Design of Engine Hood.

• Pedestrian Safety :
  Pedestrian safety always a factor involved in the design of the hood. This is achieved by proper selection of material that can readily deform avoiding risk during impact, Providing embosses to inner panels, etc. This is one of the major factors for a vehicle to have better safety ratings.

• Vehicle Quality :
  This involves how best the hood can be designed to have better quality in terms of Torsional stiffness, dent resistance(Hailstone and stone chippings), Corrosion resistance better weight distribution, and noise attenuation.

• Occupant Safety :
  The design consideration must include the impact caused due to Frontal Crash Collapse. Such Scenario is expected that Hood maintains its Integrity with hinges and also retain any of loosed components from Engine Compartments.
  
  
• Styling :
  Better Surface quality (A-class Surface Finishing), Tight radii on hemmed panel edges & low strain between curved regions of the inner and outer panel.
  
  
• Manufacturability
  The design should be always considered for manufacturability e.g. Embossing on the inner Panel should have sufficient draft angles provided for the Punching tool to flow-in and flow-out. Any Design should be studied for Manufacturability in order to produce it.

Material Used

Material selection for automotive closures is influenced by different factors such as cost, weight and structural performance.

• Steel Sheets : Steel sheets of thickness 0.6 to 0.7mm are used for making inner and outer panels. In regions of the reinforced thickness of 1.5mm are implemented. Traditional steel sheets exhibiting low carbon content from (0.02% to 0.08% ), very low controlled quantity of phosphorus, sulfur, manganese, and potentially up to 0.3% of titanium improves the deep drawing capacity, elongation at break above 40% and limited thinning.
  
  
• Aluminum Sheets : The main advantage of aluminum over zinc-coated steel is the lower specific mass ti reduce parts overall weight since the yield strength of aluminum alloys is not so much lower than most steel grade available in use. Traditionally, the performance equivalence between steel sheets and aluminum sheets was rated in terms of the bending stiffness of plate. Since the plate bending stiffness is related to the third power of gauge, in order to obtain stiffness is related equivalence, the required increase of aluminum thickness should be the cubic root of 3 or approximately 1.43.

GIVEN CRITERIA:

S.N	Quality Criteria	Value
1	Aspect Ratio	5
2	Skewness	45
3	Warping	15
4	Taper	0.5
5	Min. Length	2 Units
6	Max. Length	8 Units
7	Min angle Quad	45
8	Max angle Quad	135
9	Min angle Tria	20
10	Max angle Tria	120
11	Tria %	10

PROCEDURE:

Step 1: Importing geometry and cleanup:

• To import the geometry, go to file → Import → Import geometry → Import.
  File name given: hood.stp
  
  Imported model
  
  
• After importing the geometry, the geometry is checked for any missing surfaces or triple cons. If there are no errors present in the geometry then the geometry is ready for the mid-surface extraction.

Step 2: Mid-surface generation:

• Remove the solid before midsurfacing, Delete → Solid → Select solid → delete entity. Then using By topo geometry color mode check the model for free lines and errors.
  
  
• After checking the model, we need to produce mid surface for meshing. There are 4 subcomponents present in the imported model, inner extract, outer extract, hinge reinforcement extract and latch reinforcement extract.
  
  
• The mid surface is created for each component seperately and they are named appropriately.
  
  Geom. → auto midsurface → select surface → extract.
  Selected extraction option: skin offset
  
  

Step 3: Auto cleanup:

• After midsurface generation, it is also checked for any freelines and errors. Then the criteria file is saved. Preferences → criteria file settings.
• Then the auto cleanup option is used to toggle the unwanted lines and small pinholes etc for better meshing.
  
  

Step 4: Surface trimming:

• We can see that the outer extract and inner extract is symmetric component. So to reduce the meshing time we split them into two. Then remove the other half and used for meshing. Also the 2 hinge parts are same. So only need to mesh one. Then we can reflect same mesh into other using reflect tool.
  
  Symmetric half part of inner extract
  
  
  
  Meshed symmetric half part of outer extract

Step 5: Meshing quality checking:

• As decided each part is meshed seperately using automesh with mixed element as specified.
  2D → automesh → select surface , element size =5, mesh type = mixed → mesh
  
  
• The rebuild mesh is used to create better mesh flow. 2D → rebuild mesh
  
  
• Then we need to check the quality of the mesh. open, 2D → qualityindex. It will show the elements failing the criteria. Then we need to rectify it using the cleanup tools available. We can also use rebuild tool.
  
  cleanup tools
  
  
• If needed we can split element using split option.
  2D → element edit → split (Split by dragging if needed)

Step 6: Completing the mesh using reflect tool:

• Use reflect tool to reflect the surface and element to the other half of inner and outer extract. This tool is also used to reflect the element into the hinge. Tool → reflect → select what we want to reflect and duplicate it → select base point and reflecting directon → reflect
  
  
  
  

Step 7: Assigning property and material:

• The materal is added and assigned for each component.Also by adding property, we assign the thickness also. Use the renumber tool to renumbering as per our input.
  
  
  

Step 8: Model check:

• Find edges of the model for perfection.
  Tools → edges → select element dispalyed → find edges,
  If no error noticed, delete edges . select element again → preview equivalent → return
  otherwise, you can click on equivalence and try to fill that.
  
  
• Element to surface edge check: To check how the element is captured the surface geometry.
  mesh → check → elements → comparison → click on element tab shown in source entity → Select element displayed → Proceeds → click surface tab in the target entity → select surface displayed → Tolerance = 0.2 → Run
  The yellow and pink color in mesh is okay. If there is defect, we used project tool to rectify it.
  
  
  
  Latch Reinforcement Extract
• Check for Normals: Tools → Normals → display → we can choose colordisplay or vector display.
  The defected element's normals are reversed using the same tool by selecting the element.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
• 
  
  
  
  
• Penetration & intersection check: Tools → penetration → select element displayed → check
  Penetration is defined as the overlap of the material thickness of shell elements, while intersection is defined as elements that actually pass completely through one another.
  
  

FINAL MODEL:

• Meshed components:
  
  Latch Reinforcement Extract
  
  
  
  
  
  Hinge Reinforcement Extract
  
  
  
  
  Inner Extract
  
  
  
  
  
  Outer Extract
  
  
  
  
  
  
  
• Quality Index Check Result:

Latch reinforcement extract:

Hinge reinforcement extract:





Inner Extract:

Outer Extract:

RESULT:

• Meshed the given component by following the quality criteria specified and tried to reduce maximum error.
  
  
• The property and thickness is assigned to the component. The mixed element (Both tria ansd quad) is used for meshing.