class a surfaces

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Subject: Class-A Surface Guidelines

Contents1) Phases of Class-A surface creation 3

2) Class-A surface Definition 4

3) Mathematical Requirements 73.1 Positional Continuity OR 0 - Order continuity 7

3.2 Tangent Continuity OR 1 - Order continuity 9

3.3 Curvature Continuity OR 2 - Order continuity 12

4) Curve Creation 174.1 Curve order 17

4.2 Case study for curve creation 18

4.3 Curve Redistribution 19

4.4 Creation of Symmetry Curves 20

4.5 Boundary curve creation 21

5) Surface Creation 235.1 Criteria for surface creation 23

5.2 Patch/Surface Parameterization 24

5.3 Patch/Face Plan 25

5.4 ISO-Curve distribution 26

5.5 Patch/Face over building and trimming of Patch/Face 27

5.6 Minimum Descriptive profile for surface creation 27

5.7 Symmetry Criteria 28

5.8 Transition Surface 29

5.9 Surface Completeness 31

5.10 Fillets 32

6) Class-A surface verification 336.1 Patch properties 33

6.2 Connectivity Analysis / G0 - Continuity 33

6.3 Tangency Analysis / G1-Continuity 35

6.4 Curvature Analysis 35

6.5 Reflection Analysis 36

6.6 Dynamic Highlight Analysis 36

6.7 Absolute Curvature Analysis 37

6.8 Mean Curvature Analysis 37

6.9 Maximum and Minimum Curvature Analysis 38

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6.10 Guassian surface Analysis 38

7) Curvature Analysis – A case study 39

8) Summary of Class-A Surface Standards 418.1 Classification of components and Applicable Class-A standards 41

8.2 Class-A Standard-I 42

8.3 Class-A Standard-II 42

8.4 Class-A Standard-III 43

9) Manufacturing Criteria’s – Case studies 449.1 Tips for manufacturability of hood 44

9.2 Tips for manufacturability of fender 46

9.3 Tips for manufacturability of Rear quarter panel 48

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1) Phases of Class-A surface creation

Figure 3.1-1

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2) Class-A surface DefinitionClass-A surfaces and their requirements have a close relationship with the aesthetics of a product. The reflection of light plays a major role in surface appearance. If a surface does not posses certain described characteristics, Visual appearance of the product will get affected.

Characteristics of Class-A surface can be classified into three major categories

Visual Characteristicsa) Aesthetic requirements

b) Reflection, smoothness

c) Style features as intended by Designer/Stylist

Mathematical Requirementsd) 0 order continuity (Positional Continuity / G0 Continuity)

e) 1 order continuity (Tangent Continuity / G1 Continuity)

f) 2 order continuity (Curvature Continuity/ G2 Continuity)

g) 3 order continuity (Constant rate of change of curvature/ G3 Continuity)

Manufacturing requirementsh) Panels should retain their shape - proper stretching requirement should be taken care,

i) Styled features should retain intended shapes,

j) Feature lines like shoulder line or waist line on body side panel, feature lines on hood panel should retain their place (skidding),

k) Bulge effect on flange lines should be avoided,

l) Manufacturability of shapes (Forming of sheet metal, Moulded components) etc.

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Defects which do not qualify for Class-A surface requirements

Common visual defects, which can be attributed to the bad appearance of the surfacesm) Broken reflection lines - which will affect the homogeneous looks of the car body,

n) Unintended highlights ( Unequal/Non parallel)

o) Non-uniform transition highlights,

p) Underflush and Overflush conditions

q) Local dark spots in the middle of smooth surface - which may result in visual mismatch of colour,

r) Effect of transparent surfaces like windshield, window glasses and long lenses on surface

Curvatures,

s) Local bright -unintended highlights, spots etc.

Common Mathematical defects found in surfacest) Connectivity problems like gap and overlapping along common edge,

u) Tangency problem between two adjacent surfaces along common edge,

v) Curvature discontinuities between surfaces,

w) Bad parameterization,

x) Bad distribution of ISO-parametric curves,

y) Topological problems,

z) Twisted patches,

aa) Local depressions and bumps,

bb) Triangular patches, etc.

Common Manufacturing defects found in surfaces For sheet metal panelscc) Flat surface – inadequate lensings,

dd) Possibility of skid marks,

ee) Bulge at flange lines,

ff) Sharp, acute trim lines and shut lines,

gg) Draw depth and corner radii mismatch,

hh) Under flush and Over flush co-ordination,

ii) Local depressions and bumps etc.

For Plastic componentsjj) Shrinkage marks,

kk) Molding direction,

ll) Undercuts,

mm) Seen parting lines,

nn) Insufficient draft angle for given textures,

oo) Inadequate lensing,

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pp) Warping etc.

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3) Mathematical Requirements3.1 Positional Continuity OR 0 - Order continuitySurface are said to be having Positional Continuity, when they posses the following characteristics

Adjacent faces/surfaces are sharing a common edge,

Gap between them is less or equal to the recommended tolerance limit along the common edge

They are curvature continuous within

Refer images for more information

Surfaces are smoothNote:

1) Observe the smooth variation in reflection of light.2) Observe the presence of sharp reflection line in the middle of the surface

Image 3.1-1

Sharing Common edge

Image 3.1-2

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Curvature Continuous within Share a common edge Gap between them along the edge is within

tolerance limitNote:Angle between the Normals to the surface or curve on a point laying on the common edge is not within the set tolerance limit.

Image 3.1-3

Dynamic reflection highlights Analysis ResultNote the broken Highlights at Common edge

Image 3.1-4

Mean Curvature Analysis result

Image 3.1-5

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Refer images below for allowable errors for acceptance of surface for Positional continuity

Image 3.1-6

Industry Standard Examples

DCX GM FORD BERTONE TTL

Value 0.02 0.025 0.02 0.01 0.01

Note: Some values given here are based on the inputs from un-official source

Image 3.1-7

3.2 Tangent Continuity OR 1 - Order continuity Surface are said to be having Tangent Continuity, when they posses the following

characteristics. Adjacent faces/surfaces are sharing a common edge.

Gap between them is less or equal to the recommended value along the common edge.

Angle between the normals at any common point on common edge is within in the set tolerance value.

They are curvature continuous within.

Refer below images for more information

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1) Observe the smooth variation in reflection of light.

2) Observe the absence of sharp reflection line in the middle of the surface in comparison with Figure for G0 continuity.

Image 3.2-8

Sharing Common edge

Image 3.2-9

Curvature Continuous within Gap between them is within the

recommended tolerance limit Share a common edge

Note:

Angle between the normals to the surface or curve at a point laying on the common edge is within in the set tolerance value..

Observe the sudden change in curvature value between the normals to the surface or curve at a point laying on the common edge.

Image 3.2-10

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Dynamic reflection highlights Analysis ResultNote the abrupt deviation in highlights at Common edge.

Image 3.2-11


Image 3.2-12Refer image below for allowable errors for acceptance of surface for Tangent continuity



Value 0.05 0.05 0.07 0.1 0.05


Image 3.2-13

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3.3 Curvature Continuity OR 2 - Order continuitySurface are said to be having Curvature Continuity, when they posses the following characteristics.

qq) Adjacent faces/surfaces are sharing a common edge.

rr) Gap between them is less or equal to the recommended value along the common edge.

ss) Angle between the normals at any common point on common edge is within in the set tolerance value.

tt) Variation in curvature value at two points on same curve on surface is within specified value.

uu) They are curvature continuous within.



1) Observe the smooth variation in reflection of light.

2) Observe the uniform dispersion of light in the reflection zone in the middle of the surface in comparison with Figure for G1 continuity.

Image 3.3-14

Sharing Common edge

Image 3.3-15

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1) Curvature Continuous within2) Gap between them is within in the

tolerance limit 3) Share a common edge

Note: Angle between the normals to the surface or curve at a point laying on the common edge is within the set tolerance value.

Image 3.3-16

Dynamic reflection highlights Analysis Result

Note the smooth deviation in highlights at Common edge

Image 3.3-17


Image 3.3-18

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Refer image below for allowable errors for acceptance of surface for curvature continuity



Value 0.001 0.001 0.005 0.01 0.001


Image 3.3-19Constant Rate of Change of Curvature Continuity OR 3 - Order continuitySurface are said to be having Constant rate of change of curvature Continuity, when they posses the following characteristics Adjacent faces/surfaces are sharing a common edge,

Gap between them is less or equal to the recommended value along the common edge

Angle between the normals at any common point on common edge is within in the set tolerance value.

Variation in curvature value at two points on same curve on surface is within specified value.

Distant between two points on curves for which the change of curvature occurs has to be same for all point on the curves.



1) Observe the smooth variation in reflection of light.2) Observe the further improvement in uniform

dispersion of light in the reflection zone in the middle of the surface in comparison with Figure for G2 continuity.

Image 3.3-20

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Sharing Common edge

Image 3.3-21

Curvature Continuous within Gap between them is within the set tolerance

value Share a common edge

Note:Distance between points on curve on the surface For which curvature changes is constant

Image 3.3-22

Dynamic reflection highlights Analysis ResultNote the smooth deviation in highlights at Common edge

Image 3.3-23

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Image 3.3-24

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4) Curve CreationCreation of a curve plays a very important role in the process of Class-A surface creation. The quality of the curve dictates the quality of the surface.

Criteria for curve creation Curves should be of minimum required order as far as possible (preferred order-3 maximum

order is based on the software being used)

Curves should support or facilitate the adjacent curve nature

Avoid curve with inflection unless they are a must

Split the curve as far as possible to avoid unnecessary tension

Give a close look to curve descriptors while creating curves

4.1 Curve orderEvery curve has a degree - a mathematical concept referring to the degree of the polynomial that defines the curve. The degree is generally one less than the number of points in the curve descriptor. For this reason, you cannot have a curve with lesser points than the degree of the curve.

A higher degree curve is stiffer, in the sense that you have to move its poles a long way to produce any appreciable change in the shape of the curve. Lower degree curves are more pliable, and tend to follow their poles much more closely. However, it is recommended to use curves of degree 3.

Higher degree curves are more likely to contain undesirable oscillations. You should use lower degree curves whenever possible (3, 4, and 5). Use the default degree of three (3) unless you have some good reason for doing otherwise. The degree of a single segment curve is dependent on the number of its specified points.


Curve of Degree 3, and Class 4

Note:

Curves of this type are easier to handle; for any change made to the curve by moving its pole, the change in shape will be monotonic in nature across the curve.

Image 4.1-25

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Note:

Curves of this type are not easier to handle; for any change made to the curve by moving its pole, the change in shape may not be monotonic in nature across the curve because of high parameterisation of the curve.

Shape of the curve is exactly similar in shape and size to the curve shown in the image.

Image 4.1-26


Note:

Shape of the curve is exactly similar in shape and size to the curve shown in Image 4.1-25 and Image 4.1-26 on page No. 17

Observe the bad parameterisation of the curve, which is not desirable for Class-A surface creation.

Image 4.1-27

4.2 Case study for curve creationWhile creating a curve from digitised points, it is essential to give a close look to the parameter distribution of the curve.

In the given example, even though curves are exactly similar in shape, size and position they are not identical in their mathematical properties.

Curve Degree 7, Class 8Note:

Observe the curve parameter distribution, which is erratic.

Curve is of very high degree and class, which is not recommended.

Observe the adulations in curvature variation as seen from the curvature normals.

Image 4.2-28

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Curve Degree 3, Class 4

Note:

Smooth variation in curve parameter distribution.

Desired shape is achieved by a curve of lower degree and class, which is highly recommended.

Observe the curvature variation as seen from the curvature normals. The variation in this case is smooth as compared to the earlier case.

Image 4.2-29

4.3 Curve Redistribution

Curve of Degree 9 and Class 10

Note:

Observe highly haphazard distribution of curve parameters.

Curve created by software tool from digitized data.

Image 4.3-30

Curve of Degree 9 and Class 10

Note:

Observe smooth and monotonic variation in distribution of curve parameters

Curve created by using optimization and smoothing technique.

Image 4.3-31

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Curvature analysis of the Curve

Image 4.3-32

4.4 Creation of Symmetry CurvesFor curves, which are to be used in creating surfaces for panels like Hood, Windshield, Roof, Trunk lid and Front and rear bumpers, special care has to be taken while creating the curves and surfaces.

While creating symmetry curves check the following properties in the curve

2) Curvature continuity value at the plane of symmetry should be “Zero”

3) Tangency continuity at plane of symmetry should be “ Zero”

4) Positional continuity at plane of symmetry should be “ Zero”

5) It is recommended to have curves of Degree 3,5 and Class 4,6

6) It is not recommended to have a curve node at plane of symmetry.

Symmetry Curve

Note:

Observe the absence of curve node at plane of symmetry, most of the times this condition automatically ensures G0, G1 and G2 continuity.

Figure 4.4-2

4.5 Boundary curve creationWhile creating end boundary curve for patches, check for the following characteristics in the curves. Both curves should be of

Same class and degree

Similar nature in mathematical parameterisation.

Change in curve parameter distribution should be monotonic in nature. In the absence of above characteristics, chances of internal surface distortions are very high.

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End boundary curves

Note:

Observe polynomial distribution of the curves.

Image 4.5-33

End boundary curves

Note:

Observe the change in the polynomial distribution of the curves and the change in the curve position due to this.

Image 4.5-34

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5) Surface CreationAs explained in the earlier chapter, quality of the surface plays major role in aesthetics of the product, it is very important we take a lot of care while creating a surface. Apart from basic requirements like positional continuity, tangent continuity and curvature continuity, following criteria’s has to be given due consideration.

5.1 Criteria for surface creation Patch/Surface parameterisationPolynomial representation of a surface is defined by a network of lines and points, These control points or poles are distributed over sections.

Patch/Face PlanDivision or splitting of patches to create features in surfaces

ISO-curve distributionSurface over-building and trimming of surfaceCreation of extra surface beyond the required area for component design

Minimum descriptive profiles for surface creationUse minimum required number of end boundaries and internal support profiles to define a patch or surface.

Symmetry criteriaGuidelines for creation of symmetric surfaces.

Transition surface creationJoining of two main surfaces with another surface.

Surface or face tensionHigh concentration of patch descriptors in a local area of a patch/face, because of maximum curvature.

Surface completenessCompletely defined surface in all respects, by mathematical definitions.

Fillets

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5.2 Patch/Surface ParameterizationPatch or surface is said to be of good quality when it has the following characteristics

a) Good distribution of patch descriptors or vertices

b) Patch should not possess any kinks in the descriptors pattern.

c) Minimum number of descriptors

d) Uniform variation in descriptor pattern

Refer Images for more information

Good patch/face descriptors

Note:

Minimum number of patch descriptors.

Smooth variation in light reflection on the shape.

Image 5.2-35

Bad patch/Face descriptors

Note :

High number of patch descriptors.

Kink in one of the descriptors.

Image 5.2-36

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Patch/Face Plan

Important aspect of good surface creation is patch plan. It is important for the surface creator

to plan the patch/face split to achieve good quality in surfaces. Good patch/face plan goes a long way in helping creation of good merging of main surfaces, creation of features, termination of features, corners, transition surfaces, bends etc. only experience can help in deciding patch/face plan

Refer Images for more information

Shaded image of fender

Image 5.2-37

Patch/Face plan of fender

Image 5.2-38

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5.3 ISO-Parametric Curve distributionDistribution of ISO-curves is the primary indication of a good quality patch.

Bad ISO-curve distribution

Note:

Distribution of ISO-Parametric curves is not homogeneous

May have local surface tension.

Smooth variation is not there. Curves are bent and Curves are straight.

Image 5.3-39

Good ISO-curve distribution

Note:

Smooth variation in ISO-Parametric curve distribution

Image 5.3-40

Difference between good and bad ISO-curve distribution of patch/face

Note:Path with Bad ISO-parametric curve distribution is shown in dotted lines.Observe the difference in shorter boundary condition between two patches

Image 5.3-41

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5.4 Patch/Face over building and trimming of Patch/Face5.5 Minimum Descriptive profile for surface creationWhile creating a patch, use minimum required number of end boundaries and internal support profiles to define a face or patch. Try to create the main patches bigger than required area, Later trim them to a desired shape using trimming profiles.

Note:

e) Use of high number of profile to define the patch may result in bad quality.

f) Patch with minimum number of constraints posses characteristics like, good distribution of ISO-parametric curves, Better parameterization.

Refer image for more information

Patch over building

Image 5.5-42

Defining profiles

Trimming profiles

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5.6 Symmetry CriteriaWhile creating surface for Hood panel, Roof, Trunk lid , windshield, Rear window and tailgate, normal practice is to create one side of the panel, for other side surface is reflected.

While doing so, following criteria should be fulfilled at plane of symmetry (XOZ-Plane,Y=0)g) Positional Continuity h) Tangency and curvature continuityi) Curvature variation j) No directional variation

Curvature of good symmetry patch

Note:

In this case Positional, Tangency, and curvature continuities are fulfilled.

Observe the length and shape variation of curvature normal in the marked area.

Image 5.6-43

Curvature of bad symmetry patch

Note:

In this case only Positional and Tangency continuities are fulfilled.

Observe the length and shape variation of curvature normal in the marked area.

Image 5.6-44

Symmetry Plane

Symmetry Plane

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5.7 Transition SurfaceCase study for the use of transition surface and its advantages

Front fascia with transition surface Front fascia without transition surface

Figure 5.7-3

ObserveTwo main surfaces marked “M” are joined by using transition surface marked “C”Two main corner surfaces marked “C” are joined by using transition surface marked “T”

ObserveConcept of using transition surfaces is not applied while creating the surface

Figure 5.7-4

UniformISO-curve distribution

Irregular

MC M

T

C

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ObserveUniform distribution of ISO-curves between main surface and transition surfaces.This is the result of using a transition surface, which gives more control over creating corner and joining surfaces.

ObserveIrregular distribution of ISO-curves in main surface.

Figure 5.7-5

ObserveUniform variation in ISO-curve shapes.Synergy in variation of gaps between ISO-curves distribution.

ObserveIrregular variation in ISO-curve shapes.Irregular variation of gaps between ISO-curves distribution.

Figure 5.7-6

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5.8 Surface CompletenessSurface should be complete in all respects.

Check for the following imperfections like incomplete filleting operation, untrimmed patches, undefined corners, etc.

Refer images for further reference:

Observe untrimmed bottom patch

Figure 5.8-7

Observe marked area

Figure 5.8-8

Untrimmed patch

Incomplete corner and Fillet

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5.9 FilletsWhile creating fillets for joining two surfaces/patches, avoid using circular / cylindrical fillets.

This kind of fillets, will not guarantee a good reflection effect because of the sudden change in curvature at the joining lines.

To improve the aesthetic effects, it is suggested to use conical blending, which is available in software’s like CATIA and EUCLID-3.

Limit the use of mechanical blending to following areas

1) Unseen areas like corners, Flange line blending, Joggles on flanges etc.

2) Less important areas, like where fillet radius required R is < 5.

Mechanical Filleting

Image 5.9-45

Conical Filleting

Image 5.9-46

R

Conical Filleting

R

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6) Class-A surface verification 6.1 Patch properties

ISO-parametric Curve distribution/Patch parameterization

Polynomial representation of a surface, defined by a network of lines and points, called control points or poles. These points are distributed over sections.

Image 6.1-47

6.2 Connectivity Analysis / G0 - Continuity

Global connectivity analysis

This method is used for finding out the gaps in surface topology connections.

Connectivity analysis result for hood surface is shown in following images.

Image 6.2-48

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Wire frame model of the hood surface, shown before submitting for connectivity analysis

Note:

Observe green lines in surface

Image 6.2-49


Result of connectivity analysis

Gaps more than 0.05 are shown in “red” colour

Gaps less than 0.05 and free edges are still shown in “green” colour.

Note:

1) Threshold value for connectivity analysis used in this case is 0.05.

2) Method of result display is software dependent.

Image 6.2-50

6.3 Tangency Analysis / G1-Continuity

Global Tangency Analysis

This method is used for finding angle between two adjacent patch along a common edge.

Note:

1) Threshold value for connectivity analysis used in this case is 0.05.

2) Observe magenta coloured lines in surface.

3) Method of result display is software dependent.

Image 6.3-51

Green lines

Green linesRed lines

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6.4 Curvature AnalysisSurface/Patch curvature analysis of a curve

Laying on a surface for uniform variation in curvature

Note:

Curvature analysis of roof is shown.

Image 6.4-52

6.5 Reflection Analysis

Display of the reflection lines created on a patch by a line of light of infinite length

Image 6.5-53

6.6 Dynamic Highlight AnalysisThis action is used to detect local flaws on supporting surfaces and to check that surfaces are smooth. Highlights are similar to reflection lines with the difference that highlights do not depend on the user's view point. It is a simplified reflection model. As with reflection lines, highlights magnify discontinuities on a supporting surface.Tangent plane discontinuity between two patches in a surface is shown up as discontinuous highlights. Discontinuous highlight tangents shows curvature discontinuity between two patches (sharp angle where the contours join). Highlights have a lower order of continuity than the surfaces they are traced on.

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Display of the Dynamic Highlights created on a roof surface

Image 6.6-54

6.7 Absolute Curvature Analysis

It is used to detect the surface areas where the surface is locally almost flat, that is when the

absolute curvature is almost null.

Image 6.7-55

6.8 Mean Curvature Analysis

The utmost values appear where the surface is the most warped. Mean is largely used to detect

irregularities on the surface. A minimal surface is characterized by a null mean

curvature.

Image 6.8-56

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6.9 Maximum and Minimum Curvature Analysis

The geometric construction of main curvatures is the following: let be a plane containing the normal to the surface in a given point. This plane cuts the

surface along a curve that has a given curvature in this point. If this plane rotates around the normal, the curvatures of the curves of intersection with the surface will vary between two

utmost values. These two values are the main curvatures

Image 6.9-57

6.10 Guassian surface AnalysisIt describes the local shape of a surface in one point:

If it is positive, the point is elliptic, i.e. the surface has locally the shape of an ellipsoid around the point. If it is negative, the surface is hyperbolic in this point, i.e. the local shape is a horse saddle. If it is null, the surface is parabolic in this point, i.e. one of the two main curvatures is null in this point.

Ps: The cone and the cylinder are two surfaces where all points are parabolic.

Local depression on a roof surface Shown using Guassian surface analysis

Image 6.10-58

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7) Curvature Analysis – A case study

Good roof surface ObserveSmoothness of surfaceUniform Dispersion of light in reflection zone

Defective roof surfaceObserveSmoothness of surfaceUniform Dispersion of light in reflection zone

Image 6.10-59

Good roof surface ObserveSmoothness of Dynamic highlightsUniform variation in dynamic highlight line shapesUniform Gap between dynamic highlight lines

Defective roof surfaceObserveSmoothness of Dynamic highlightsUniform variation in dynamic highlight line shapesNon-uniform Gap between dynamic highlight lines

Image 6.10-60

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Good roof surface Mean curvature analysis result

Defective roof surfaceMean curvature analysis result

Image 6.10-61

Good roof surface Observe absence of local depression inGuassian curvature analysis result

Defective roof surfaceObserve presence of local depression in Guassian curvature analysis result

Image 6.10-62

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8) Summary of Class-A Surface Standards8.1 Classification of components and Applicable Class-A standards

SHEET METAL PANELS

External Panels Internal Panel

External Seen External Unseen Internal Seen Internal Unseen

Class A Standard I Class A Standard II Class A Standard II Class A Standard III

SHEET METAL PANELS


External Seen External Unseen Internal Seen Internal Unseen


Figure 8.1-9

Plastic Trims


Painted/Textured Seen Painted/Textured Unseen Painted/Textured Seen PaintedTextured Unseen


Plastic Trims


Painted/Textured Seen Painted/Textured Unseen Painted/Textured Seen PaintedTextured Unseen


Figure 8.1-10

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8.2 Class-A Standard-IApplicable For Characteristics Standards

1) External seen Sheet metal panels

2) Exterior seen painted plastic trims

G0 – Positional Continuity 0.01

G1 – Tangency Continuity 0.05

G2 – Curvature Continuity 0.001

G3 – Constant rate of changes of curvature ---

Patch descriptors Refer Section 5.2

ISO-curve distribution Refer Section 5.4

Fillets Mechanical Fillets for < 5R *Manufacturability criteria’s Refer Section 9

Dynamic highlights Refer Section 6.6

Table 8-1

8.3 Class-A Standard-IIApplicable For Characteristics Standards

1) Exterior seen plastic textured trims

2) Interior seen plastic textured trims

3) Interior seen plastic textured trims

4) Interior seen sheet metal panels








Table 8-2

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8.4 Class-A Standard-IIIApplicable For Characteristics Standards

1) External unseen areas of Sheet metal panelsExample: Areas of Body side panel hidden after door closer, Lamp pockets, Mirror pockets on door frame, Etc.

2) Unseen painted and textured plastic trims








Note:3) Take care for not changing “styling intent” shapes and features in all above cases.

4) Seen means - areas which are coming in lines of direct visual angle of a person standing next to the car, and sitting inside the car.

5) Unseen means - areas which are not coming in lines of direct visual angle of a person standing next to the car, and sitting inside the car.

6) * In case of fillet values take care for minimum exterior and interior projection regulations.

7) Decide the maximum allowed deviation for Class-A surface creation from Digitised data for each model.

8) Take the approval from Styling department in case of deviation from digitized data.

9) Observe for regulatory requirements during the creation of Class-A surfaces.

Example: Minimum external and internal projection regulations.

10) At the stage of design verification, changes done on styled surface with respect to the Styling-freeze should be documented and agreed upon.

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9) Manufacturing Criteria’s – Case studiesObjective of this section is to lead stylist or product engineers through the manufacturing process for sheet metal. Cases listed in this section of the documents are only for reference and knowledge of the stylist and product engineers. The cases explained here are not to be considered as guidelines.

While designing the panels for manufacturability, proper attention needs to be given for following aspects of sheet metal components.

Panels should retain their shape after stamping process, for the same proper stretching requirement should be taken care, Styled features should retain intended shapes, For example, Feature lines like shoulder line or waist line on body side panel, Feature lines on hood panel should retain their place. Bulge effect on flange lines should be avoided.

In the same way, while designing plastic trims, care should be taken care to avoid warping of panels at free ends, shrinkage effect on the areas where internal ribs are provided for strength purpose.

9.1 Tips for manufacturability of hood

Shaded image of hood panel

Image 9.1-63

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Figure 9.1-11

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9.2 Tips for manufacturability of fender

Shaded Image of Front fender LeftImage 9.2-64

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In depth “D” is not constant, give constant offset depth “d” to avoid bulge effect along flange line

Dd

Indicator Lamp depression depth to be kept within 2-3 mm

50R – Minimum Radius to be kept

Feature line near wheel arch, high risk of skidding, if the panel is stretched to the maximum limit

Incase of radical under sweeping at rear of wheel arch, Reduce the flange with to minimum possible

In depth “D” is not constant, give constant offset depth “d” to avoid bulge effect along flange line

Dd

Indicator Lamp depression depth to be kept within 2-3 mm

50R – Minimum Radius to be kept

Feature line near wheel arch, high risk of skidding, if the panel is stretched to the maximum limit

Incase of radical under sweeping at rear of wheel arch, Reduce the flange with to minimum possible

Figure 9.2-12

9.3 Tips for manufacturability of Rear quarter panelKeep the feature line away from flange line by minimum 25mm, to avoid skidding effect.

Do not leave the feature line sharp for avoiding local stretching, on the fillet. Complete them by using conical filleting option with maximum possible ratio

Flange Line

Minimum angle suggested between thetwo surfaces creating this kind of feature is 20

Keep the feature line away from flange line by minimum 25mm, to avoid skidding effect.

Do not leave the feature line sharp for avoiding local stretching, on the fillet. Complete them by using conical filleting option with maximum possible ratio

Flange Line

Minimum angle suggested between thetwo surfaces creating this kind of feature is 20

Figure 9.3-13

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Figure 9.3-14

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Figure 9.3-15

class a surfaces

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