Challenge

Week 12 - Project-1

SSakthi Sridhar20 Nov 2020

MESHING OF PLASTIC COMPONENT SIDE DOOR

AIM

To extract midsurface of Side Door Plastic Component and to mesh the midsurface by adhering to the quality criteria as given below

Sl.No	Quality Criteria	Value
1	Aspect Ratio	5
2	Skewness	45
3	Warping	15
4	Taper	0.5
5	Min.Length	2mm
6	Max.Length	6mm
7	Min angle Quad	45
8	Max angle Quad	135
9	Min angle Tria	20
10	Max angle Tria	120
11	Tria%	10

INTRODUCTION:

PLASTICS COMPONENTS:

There are several plastics used in the automotive industry. These are the three types of plastic which makes up the total plastics used -

1) Polypropylene

2) Polyurethane

3) PVC

1) Polypropylene

Polypropylene is used in a wide variety of applications such as bumpers, chemical tanks, cable insulation, gas cans & carpet fibers.

2) Polyurethane

This type of plastic is found in flexible foam seating, foam insulation panels, suspension bushings, cushions, hard plastic parts, electrical potting compounds.

3) PVC

They are used in instrument panels, sheathing of electrical cables, doors. PVC has good flexibility, flame retardant, has good thermal stability, and low lead content.

OTHER PLASTICS USED IN AUTOMOBLE INDUSTRY ARE:

1) Acrylonitrile Butadiene Styrene (ABS):

Acrylonitrile Butadiene Styrene is a copolymer made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. The styrene gives the plastic a shiny, impervious surface. The butadiene, a rubbery substance, provides resilience even at low temperatures. A variety of modifications can be made to improve impact resistance, toughness, and heat resistance.

Application: automotive body parts, dashboards, wheel covers.

2) Polyamide (PA, Nylon 6/6, Nylon 6):

Nylon 6/6 is a general-purpose nylon that can be both moulded and extruded. Nylon 6/6 has good mechanical properties and wear resistance. It is frequently used when a low cost, high mechanical strength, rigid and stable material is required. Nylon is highly water absorbent and will swell in watery environments.

Application: gears, bushes, cams, bearings, weather proof coatings.

3) Polystyrene (PS):

Naturally clear, polystyrene exhibits excellent chemical and electrical resistance. Special high gloss and high impact grades are widely available. This easy to manufacture plastic has poor resistance to UV light.

Application: equipment housings, buttons, car fittings, display bases.

4) Polyethylene (PE):

Polyethylene has high impact resistant, low density, and exhibits good toughness. It can be used in a wide variety of thermoplastics processing methods and is particularly useful where moisture resistance and low cost are required.

Application: car bodies (glass reinforced), electrical insulation.

5) POM (polyoxymethylene):

POM has excellent stiffness, rigidity, and yield strength. These properties are stable in low temperatures. POM also is highly chemical and fuel resistant.

Application: interior and exterior trims, fuel systems, small gears.

6) Polycarbonate (PC):

Amorphous polycarbonate polymer offers a unique combination of stiffness, hardness and toughness. It exhibits excellent weathering, creep, impact, optical, electrical and thermal properties. Because of its extraordinary impact strength, it is the material for car bumpers, helmets of all kinds and bullet-proof glass substitutes.

Application: bumpers, headlamp lenses.

7) Acrylic (PMMA):

A transparent thermoplastic, PMMA is often used as a lightweight or shatter-resistant alternative to glass. It’s cheaper than PC but is also more prone to scratching and shattering.

Application: windows, displays, screens.

8) PBT (polybutylene terephthalate):

The thermoplastic PBT is used as an insulator in the electrical and electronics industries. It is highly chemical and heat resistant. Flame-retardant grades are available.

Application: door handles, bumpers, carburetor components.

9) Polyethylene Teraphthalate (PET):

PET is mostly used to create synthetic fibers and plastic bottles. We can recognize it on clothing labels under the name “polyester.”

Application: wiper arm and gear housings, headlamp retainer, engine cover, connector housings.

10) ASA (acrylonitrile styrene acrylate):

Similar to ABS, ASA has great toughness and rigidity, good chemical resistance and thermal stability, outstanding resistance to weather, aging and yellowing, and high gloss. Be careful while burning this material, It will cause a toxic smoke.

Application: housings, profiles, interior parts and outdoor applications

SIGNIFICANCE OF PLASTICS IN AUTOMOBILES:

Plastics are known to reduce costs and boost efficiency in different industries, with their countless applications and advantages. One of the industries that continues to be aided by the use of plastics—and by the consistent innovations—is the auto industry.

The plastics that are used to make cars have contributed to more energy efficiency, mainly due to weight reduction, along with corrosion resistance, design flexibility, durability, and higher performance at lower costs. This all leads to better cars at lower prices, and higher sales.

Plastics have actually been used in cars since the 1950s, but it’s the latest innovations that are really changing the industry for the better. Engineered polymers and plastics are continuing to replace aluminium and other metals in automobiles, with the average car interior now being made up of over 50% plastics. Different car parts are now made of plastics, and these plastics can be moulded together to replace the need for multiple parts, keeping manufacturing efficient and weight down.

In the car’s exterior, plastics are used right from the body panels to the bumpers, reducing the overall weight without affecting the safety or performance of the vehicle. Additionally, new technology has created ultra-lightweight wheel trims and other components that reduce weight and not only keep costs down, but also lowering the centre of gravity, enhance safety and improve performance.

MIDSURFACE

The Surface between upper and lower surface is called Midsurface or simply middle surface.

FIG 1. MIDDLE SURFACE REPRESENTATION

NECCESSITY:

Every model which we are handling is a 3D representative. Meshing the same with 3D elements like Hexa or Tetra will result in enormous number of elements & nodes. To avoid increase in number of nodes & elements which in turn consumes huge space in storage & processing time, so 3D model is converted into 2D replica (Shell elememts) by means of creating midsurface.

PLASTIC & SHEET METAL:

For Plastic components like side door, dashboard etc, the method of extracting midsurface is mannual midsurfacing where as for sheet metal components, auto midsurface option can be used for extracing midsurface.

Since plastic components have varying thickness, mannual midsurfacing is preferred over auto midsurface and sheet metal has uniform thickness, auto midsurface can be utilised for midsurface extraction.

TYPES OF EDGES:

The perimeter of a surface is defined by edges. There are four types of surface edges:

•Free edges:

Free edges are colored in red and they appear between two adjacent surfaces which means, the gap between two surfaces need to be fixed.

•Shared edges:

Shared edges appear in green color. When the edge between two surfaces is a shared edge, there is no gap or overlap between the two surfaces, means they are continuous.

•Suppressed edges:

Suppressed edges are colored blue. Like a shared edge, a suppressed edge indicates geometric continuity between two surfaces.

•Non-manifold edges:

Non-manifold edges are colored yellow and they basically occur at "T" intersections between surfaces or when 2 or more duplicate surfaces exist.

QUALITY CRITERIA:

WRAP ANGLE:

Warpage is the amount by which an element (or in the case of solid elements, an element face) deviates from being planar. Since three points define a plane, this check only applies to quads. The quad is divided into two trias along its diagonal, and the angle between the trias’ normals is measured.

FIG 28. WARP ANGLE REPRESENTATION

ASPECT RATIO:

The aspect ratio of 2D element is defined as the ratio of its shortest edge length to its longest edge length. A square has the aspect ratio of 1 since its sides have the same length. Aspect ratio < 5 is highly recommended.

Aspect ratio = Max edge length/Min edge length.

FIG 29. ASPECT RATIO IN QUAD FIG 30. ASPECT RATIO IN TRIA

SKEWNESS:

It defines how element deviate from the ideal element shape. The skew angle represents the absolute value of the difference between the angle and 90 degree. Skewness< 45 degree is highly recommended.

Skewness=90 degree-smallest angle.

NOTE: In skewness smallest angle causes the largest skewness.

FIG 31. SKEWNESS IN TRIA FIG 32. SKEWNESS IN QUAD

JACOBIAN:

The Jacobian ratio is found by the ratio of the maximum and minimum determinant value. The Jacobian calculation is done at the integration points of elements commonly known as Gauss Point. At each intergration point, Jacobian Determinant is calculated. It just coordinates the transformation. For 3D cube, Jacobian is 1. If we disort the cube by applying pressure at one of the vertex, Jacobian < 1. Jacobian is recommended to be > 0.6.

PROCEDURE:

MIDSURFACE EXTRACTION:

STEP 1) Import the model, open the side door model from your library & select import button at the bottom.

FIG 2. IMPORTING MODEL

STEP 2) Before starting mannual midsurface extraction, it is necessary to check each surface thickness to get the exact midsurface.

2.A) Reach Geom>distance option, and change to two points option to know the thichness of the surface.

FIG 3. THICKNESS CHECK REPRESENTATION

2.B) We can also use review thickness option from Geom>midsurface & select review thickness option by clicking the drop down list on right top corner (highlighted in blue square) to review the surface thickness.

FIG 3.1. THICKNESS CHECK REPRESENTATION

2.C) Select the surface which have to tested for thickness, as soon as selecting we will see the points (highlighted) on the edges & the thichness can be inferred from the average thickness.

FIG 3.2.REVIEW THICKNESS OPTION

STEP 3) Select OFFSET option from Geom>surface edit panel.

3.A) Make sure you select the disjoint effect option.

FIG 3.3. OFFSET OPTION

3.B) Select the surface which has to be offsetted, right click on the surface button & select duplicate option (highlighted).

FIG 3.4. DUPLICATE SELECTION

3.C) Select the current comp option.

FIG 3.5. CURRENT COMP SELECTION

3.D) Select the Vector normal option to see the direction of the surface (arrow pointing upwards direction) about to move.

FIG 3.6. VECTOR NORMAL REPRESENTATION

3.E) Reverse normal enables the surface to move downwards. Once the direction is verifed simply click offset button to generate midsurface. Make sure you give the exact offset value in the panel.

FIG 3.7. REVERSE NORMAL REPRESENTATION

3.F) Below images depicts Midsurface generated.

FIG 3.8. MIDSURFACE GENERATION

TOPOOGY CLEANING (or) GEOMETRY CLEAN UP:

After extracting midsurface of the side door the next process is to clean the geometry for a perfect mesh.

NECESSITY:

While creating midsurfaces in hypermesh, sometimes for complex geometry there may be geometric errors and discontiunity in surface connection, to fix the continuity issue of the created model & to get proper mesh flow, Geometry clean up is highly necessary. With the geometry cleanup we normally clear only the free and non manifold edges to make them shared edges, that is geometrically continuous.

TOOLS UTILIZED:

1) Edge fillets

2) split surf-node

3) split surf-line

4) toggle edge

5) unplit surf

6) add/remove points

7) release points

8) trim with surfs/plane

9) trim with lines

10) Drag

EDGE FILLETS:

STEP 1) Select the edge fillet option from geom>edge edit panel.

STEP 2) Select the surface from which fillets have to be removed.

STEP 3) Select the fillets on the surface and input the min & max radius value and hit find button. After that, Fillet wil be identified in the surface as representated below.

FIG.4. EDGE FILLETS

STEP 4) Simply select remove button to remove the fillet.

FIG.4.1. EDGE FILLETS

SPLIT SURF-NODE:

STEP 1) Select the node 1 & node 2 of the surface to be seperated.

FIG 5. SPLIT SURF-NODE REPRESENTATION

SPLIT SURF-LINE:

STEP 1) Select the node & line of the surface to get seperated.

FIG 6. SPLIT SURF-LINE REPRESENTATION

TOGGLE EGDE & UNSPLIT SURF:

STEP 1) Select the line to toggle which disturbs the path for proper mesh flow as shown below.

STEP 2) Also by giving the tolerance value to 0.5 or 1, we can stritch the free edge to shared edge.

FIG 7. TOGGLE EDGE & UNSPLIT SURF REPRESENTATION

STEP 3) Unslpit surf is used to untrim the seperated surfaces.

ADD/REMOVE POINTS, RELEASE POINTS & REPLACE POINT:

STEP 1) add/remove points is used to add points if we left click on the surface & release points is used to remove the points added if we right click in the mouse.

STEP 2) Replace point is used to replace a particular point.

FIG 8. BEFORE USING REPLACE OPTION FIG 9. AFTER USING REPLACE OPTION

STEP 3) Select the points highlighted first and retain point second to replace the point.

FIG 10. REPLACE POINT OPTION

The below two figure shows the application of replace points in stritching the surfaces.

FIG 11. APPLICATION OF REPLACE POINT

FIG 12. APPLICATION OF REPLACE POINT

DRAG

STEP 1) During some circumstances, midsurface generated may not be satisfied as below case. During that time Drag along vector option plays a very important role.

FIG 13. INCOMPLETE RIB FORMATION

STEP 2) Select the line to be extended from the lines option & choose direction for extension as mentioned as N1, N2.

FIG 14. DRAG ALONG VECTOR OPTION REPRESENTATION

STEP 3) Mention the distance required and hit drag + option.

RIB FORMATION:

STEP 1) Select the final edit tools option from Geom>midsurface panel.

FIG 15. FINAL EDIT TOOL OPTION

STEP 2) Select the surface on side1 & side 2 respectively and simply select extract button or click middle mouse button.

FIG 16. FINAL EDIT TOOLS REPRESENTATION

NOTE: The above method will be useful only when the two surfaces selected are symmetric.

MESHING:

The next process is to start with meshing of geometry cleaned midsurface with 4 mm of element size.

TOOLS UTILIZED:

1) Automesh

2) Rotate

3) Qulity index

4) Smooth

5) Replace

6) Edit element

7) mesh edit

STEP 1) Go to preference>Criteria file settings

FIG 17. CRITERIA FILE SETTING

STEP 2) Uncheck the checkbox encircled below, input the qulaity criteria & click apply Ok button.

FIG 18. QUALITY CRITERIA

2.1) Change the colour mode to "BY Topo" and change the surface visibility to "wireframe Geometry" for the easeness of meshing the surface.

FIG 19. BY TOPO MODE REPRESENTATION

FIG 20. WIREFRAME MODE REPRESENTATION

STEP 3) Start meshing the extracted midsurface surface by surface so that we can maintain proper mesh flow sequence. Use automesh option from 2D panel.

3.1) Make sure you change the mesh type to mixed so that we can avoid rotational quad, which is not advisible.

3.2) To ensure proper mesh flow, tick the align & size.

3.3) Select the surface to be meshed and simply hit the mesh button.

FIG 21. AUTOMESH PANEL REPRESENTATION

STEP 4) The below image represents the meshing of side door surface by surface.

FIG 22. MESHING OF SIDE DOOR

ROTATE:

Rotate option is used to make the proper mesh flow, in the surface where circle of certain radius is punched.

STEP 1) For using rotate option first we have create center node via distance option.

1.1) Go to Geom>distance and select two node option.

1.2) Select the two nodes (encircled below) of the circle and select nodes between option and center node for the circle will appear.

FIG 23. DISTANCE OPTION REPRESENTATION

STEP 2) Select Tool>rotate

2.1) Select the nodes of the circle as circled

2.2) Select N1, N2, N3 and Base node as highlighted below.

2.3) Give the specific angle value.

2.4) Select rotate+ to rotate the elements.

2.5) Finally remesh them for proper mesh flow.

2.6) Similarly the same way is followed to mesh other similar surfaces also.

FIG 24. ROTATE OPTION REPRESENTATION

EDIT ELEMENT & REPLACE:

CREATE:

This option is used to create quads or tria elements.

FIG 25. CREATE PANEL REPRESENTATION

COMBINE:

This option is used to combine two tria elements into a quad element.

FIG 26. COMBINE PANEL REPRESENTATION

SPLIT:

This option is used to split a quad element into two tria elements.

FIG 27. SPLIT PANEL REPRESENTATION

REPLACE:

It is used to combine two trias if trias is considered (as per below image) or also used to create two trias if a quad element is considered. Make sure you tick both equivalence & at mid-point option so that the combined element will be at center.

FIG 28. REPLACE PANEL REPRESENTATION

MESH EDIT:

STEP 1) Go to 2D> mesh edit.

1.1) Make sure source & destination are node list & elems respectively.

1.2) Select the nodes as highlighted, for the node list option.

1.3) Select the elements as selected for elems option.

1.4) Set the number of layers as 1. If we want as per requirement, increase the number of layers.

1.5) Finally hit create button.

1.6) This option makes the direction of the elements of the rib and underneath elements are perpendicular to each other.

FIG 29. MESH EDIT REPRESENTATION

1.7) In this way similarly every surface is meshed with the same element size of 4mm.

QUALITY CHECK:

Quality check in the mesh is made to decide for good or bad elements. Good elemnents gives the way for smooth and accurate results in the analysis. Mesh with bad elements (elements failing for quality), gives lower accurate results and takes long run time. Hence it is necessary to have a compulsary quality check for the meshed elements.

TRANSLATE:

Translate is ued to fix the warpage of an element.

STEP 1) Go to Tool>check elems or use F10 shortcut key.

1.1) Check the warpage of an element which is failing by left clicking the same element.

1.2) Go to Tool>Translate option.

1.3) Select the node (as circled below) of an element for which warpage has to be fixed, select N1, N2, N3 to define the plane & give magintude value of 0.5.

1.4) Finally use translate+ or translate - button to fix the issue. The issue can be confirmed that it is cleared by repeating STEP 1.

FIG 30. TRANSLATE TOOL REPRESENTATION

MIN ELEM LENGTH:

This issue can be fixed manually by using distance option or using F4 shortcut option.

OPTIMIZATION:

Optimization is used to optimize the element on free edge for a better finish.

SMOOTH:

After working on trias to reduce them, smooth can be used to get regular and proper mesh flow. Trias can be reduced by remeshing the concerned elements.

CHECK FOR FREE EDGE & GAP:

Finally after checking for quality and once it gets passed for every criteria, use Tool>edges or Shift+F3 shortcut to predict the free edges and to eliminate the gap between elements if any.

STEP 1) Select the bunch of elements for which gap presence have to be checked.

1.2) Increase the tolerance value to 0.5 or 1 and simply hit preview equiv.

1.3) If any gap is available it will be highlighted in the elements & click equivalence button.

1.4) Select the entire mesh, by right clicking on the elements and use displaced option

1.5) Select find edges option, & the free edge will be highlighted in red color across its boundary if any.

FIG 31. FREE EDGE REPRESENTATION FIG 32. GAP REPRESENTATION

1.6) If free edge is available, then check for equivalence.

FIG 33. CHECK ELEMS REPRESENTATION

THICKNESS ASSIGNATION:

To represent the 2D elements into 3D we have to assign the elements their thickness, taken from the parent geometry.

STEP 1) Right click on the tool bar and create component and property collector for their respective thickness.

FIG 33.1. THICKNESS ASSIGNATION REPRESENTATION

STEP 2) For the respective thickeness give the thickness value as highlighted below and right click the collector named Thickness 4 and assign the thickness 4 property.