class a document

8/13/2019 Class a Document

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Subject: Class-A Surface Guidelines

Contents

1) Phases of Class-A surface creation 3

2) Class-A surface Definition 4

3) Mathematical Requirements 6

3.1 Positional Continuity OR 0 - Order continuity 6

3.2 Tangent Continuity OR 1 - Order continuity 8

3.3 Curvature Continuity OR 2 - Order continuity 11

4) Curve Creation 16

4.1 Curve order 164.2 Case study for curve creation 17

4.3 Curve Redistribution 18

4.4 Creation of Symmetry Curves 19

4.5 Boundary curve creation 19

5) Surface Creation 21

5.1 Criteria for surface creation 21

5.2 Patch/Surface Parameterization 22

5.3 Patch/Face Plan 235.4 ISO-Curve distribution 24

5.5 Patch/Face over building and trimming of Patch/Face 25

5.6 Minimum Descriptive profile for surface creation 25

5.7 Symmetry Criteria 26

5.8 Transition Surface 27

5.9 Surface Completeness 29

5.10 Fillets 30

6) Class-A surface verification 316.1 Patch properties 31

6.2 Connectivity Analysis / G0 - Continuity 31

6.3 Tangency Analysis / G1-Continuity 32

6.4 Curvature Analysis 33

6.5 Reflection Analysis 33

6.6 Dynamic Highlight Analysis 33

6.7 Absolute Curvature Analysis 34

6.8 Mean Curvature Analysis 34

6.9 Maximum and Minimum Curvature Analysis 35

6.10 Guassian surface Analysis 35


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7) Curvature Analysis A case study 35

8) Summary of Class-A Surface Standards 388.1 Classification of components and Applicable Class-A standards 38

8.2 Class-A Standard-I 39

8.3 Class-A Standard-II 39

8.4 Class-A Standard-III 40

9) Manufacturing Criterias Case studies 41

9.1 Tips for manufacturability of hood 41

9.2 Tips for manufacturability of fender 43

9.3

Tips for manufacturability of Rear quarter panel 44


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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 certaindescribed characteristics, Visual appearance of the product will get affected.

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

Visual Characteristics

a) 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 requirements

h) 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 hoodpanel 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, w hich can be attributed to the bad appearance of the surfaces

m) 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 ofcolour,

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 surfaces

t) 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 panels

cc) 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 components

jj) Shrinkage marks,

kk) Molding direction,

ll) Undercuts,

mm) Seen parting lines,

nn) Insufficient draft angle for given textures,

oo) Inadequate lensing,

pp) Warping etc.


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3) Mathematical Requirements3.1 Positional Continuity OR 0 - Order cont inuity

Surface are said to be having Positional Continuity, when they posses the followingcharacteristics

Adjacent faces/surfaces are sharing a common edge,

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

They are curvature continuous within

Refer images for more information

Surfaces are smooth

Note:

1) Observe the smooth variation in reflection of light.

2) Observe the presence of sharp reflection line in themiddle 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 withintolerance limit

Note:

Angle between the Normals to the surface orcurve on a point laying on the common edgeis not within the set tolerance limit.

Image 3.1-3

Dynamic reflection highli ghts Analysis Result

Note 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 inputsfrom un-official source

Image 3.1-7

3.2 Tangent Continuity OR 1 - Order cont inui ty

Surface are said to be having Tangent Continuity, when they posses the followingcharacteristics.

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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Surfaces are smoothNote:

1) Observe the smooth variation inreflection of light.

2) Observe the absence of sharp reflectionline in the middle of the surface incomparison with Figure for G0continuity.

Image 3.2-1

Sharing Common edge

Image 3.2-2

Curvature Continuous within

Gap between them is within therecommended tolerance limit

Share a common edge

Note:

Angle between the normals to the surface orcurve at a point laying on the common edge iswithin in the set tolerance value..

Observe the sudden change in curvaturevalue

between the normals to the surface or curve at apoint laying on the common edge.

Image 3.2-3


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Dynamic reflection hi ghlights Analysis Result

Note the abrupt deviation in highlights atCommon edge.

Image 3.2-4


Image 3.2-5

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



Value 0.05 0.05 0.07 0.1 0.05


Image 3.2-6


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3.3 Curvature Continuity OR 2 - Order cont inui ty

Surface 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 settolerance value.

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

uu) They are curvature continuous within.


Surfaces are smooth

Note:

1) Observe the smooth variation inreflection of light.

2) Observe the uniform dispersion of lightin the reflection zone in the middle of thesurface in comparison with Figure for G1continuity.

Image 3.3-1

Sharing Common edge

Image 3.3-2


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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 orcurve at a point laying on the common edgeis within the set tolerance value.

Image 3.3-3

Dynamic reflection highli ghts Analysis Result

Note the smooth deviation in highlights at Commonedge

Image 3.3-4


Image 3.3-5


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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 3.3-6

Constant Rate of Change of Curvature Continu ity OR 3 - Order continuity

Surface are said to be having Constant rate of change of curvature Continuity, when they posses thefollowing 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 tolerancevalue.

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 samefor all point on the curves.


Surfaces are smooth

Note:

1) Observe the smooth variation in reflection of light.

2) Observe the further improvement in uniformdispersion of light in the reflection zone in themiddle of the surface in comparison with Figure

for G2 continuity.

Image 3.3-7


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Sharing Common edge

Image 3.3-8

Curvature Continuous within

Gap between them is within the set tolerancevalue

Share a common edge

Note:

Distance between points on curve on the surface Forwhich curvature changes is constant

Image 3.3-9

Dynamic reflection highl ights Analysis Result

Note the smooth deviation in highlights atCommon edge

Image 3.3-10


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Image 3.3-11


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4) Curve CreationCreation of a curve plays a very important role in the process of Class-A surface creation. The qualityof 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 maximumorder 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 curves4.1 Curve order

Every curve has a degree - a mathematical concept referring to the degree of the polynomial thatdefines 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 produceany appreciable change in the shape of the curve. Lower degree curves are more pliable, and tend tofollow 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 degreecurves whenever possible (3, 4, and 5). Use the default degree of three (3) unless you have somegood 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 anychange made to the curve by moving its pole, thechange in shape will be monotonic in nature acrossthe curve.

Image 4.1-1


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Note:

Curves of this type are not easier to handle; for anychange made to the curve by moving its pole, thechange in shape may not be monotonic in natureacross the curve because of high parameterisation ofthe curve.

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

Image 4.1-2


Note:

Shape of the curve is exactly similar in shapeand size to the curve shown in Image 4.1-1 andImage 4.1-2 on page No. 16

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

Image 4.1-3

4.2 Case study for curve creation

While creating a curve from digitised points, it is essential to give a close look to the parameterdistribution of the curve.

In the given example, even though curves are exactly similar in shape, size and position they are notidentical in their mathematical properties.

Curve Degree 7, Class 8

Note:Observe the curve parameter distribution, whichis erratic.

Curve is of very high degree and class, which isnot recommended.

Observe the adulations in curvature variation asseen from the curvature normals.

Image 4.2-1


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Curve Degree 3, Class 4

Note:

Smooth variation in curve parameter distribution.

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

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

Image 4.2-2

4.3 Curve Redist ribution

Curve of Degree 9 and Class 10

Note:

Observe highly haphazard distribution of curveparameters.

Curve created by software tool from digitizeddata.

Image 4.3-1

Curve of Degree 9 and Class 10

Note:

Observe smooth and monotonic variation indistribution of curve parameters

Curve created by using optimization and

smoothing technique.

Image 4.3-2


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Curvature analysis of the Curve

Image 4.3-3

4.4 Creation of Symmetry Curves

For 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 curvesand 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 ofsymmetry, most of the times this conditionautomatically ensures G0, G1 and G2 continuity.

Figure 4.4-1

4.5 Boundary curve creation

While 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 4.5-1

End boundary curves

Note:

Observe the change in the polynomialdistribution of the curves and the change in thecurve position due to this.

Image 4.5-2


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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 likepositional continuity, tangent continuity and curvature continuity, following criterias has to be givendue consideration.

5.1 Criteria for surface creation

Patch/Surface parameterisation

Polynomial representation of a surface is defined by a network of lines and points, Thesecontrol points or poles are distributed over sections.

Patch/Face Plan

Division or splitting of patches to create features in surfaces

ISO-curve distribution

Surface over-building and trimming of surface

Creation of extra surface beyond the required area for component design

Minimum descriptive profi les for surface creation

Use minimum required number of end boundaries and internal support profiles to define a patchor surface.

Symmetry criteria

Guidelines for creation of symmetric surfaces.

Transition surface creation

Joining of two main surfaces with another surface.

Surface or face tension

High concentration of patch descriptors in a local area of a patch/face, because of maximumcurvature.

Surface completeness

Completely defined surface in all respects, by mathematical definitions.

Fillets


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5.2 Patch/Surface Parameterization

Patch 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 descriptorsNote:

Minimum number of patchdescriptors.

Smooth variation in light reflectionon the shape.

Image 5.2-1

Bad patch/Face descriptors

Note :

High number of patch descriptors.

Kink in one of the descriptors.

Image 5.2-2


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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 along way in helping creation of good merging of main surfaces, creation of features, terminationof features, corners, transition surfaces, bends etc. only experience can help in decidingpatch/face plan

Refer Images for more information

Shaded image of fender

Image 5.2-3

Patch/Face plan of fender

Image 5.2-4


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5.3 ISO-Parametric Curve dist ribution

Distribution of ISO-curves is the primary indication of a good quality patch.

Bad ISO-curve distribution

Note:

Distribution of ISO-Parametric curves is nothomogeneous

May have local surface tension.

Smooth variation is not there. Curves are bentand Curves are straight.

Image 5.3-1

Good ISO-curve distributio n

Note:

Smooth variation in ISO-Parametric curvedistribution

Image 5.3-2

Difference between good and bad ISO-curvedistribution of patch/face

Note:

Path with Bad ISO-parametric curve distribution is shownin dotted lines.

Observe the difference in shorter boundary conditionbetween two patches

Image 5.3-3


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5.4 Patch/Face over building and trimming of Patch/Face

5.5 Minimum Descriptive profile for surface creationWhile creating a patch, use minimum required number of end boundaries and internal supportprofiles 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 distributionof ISO-parametric curves, Better parameterization.

Refer image for more information

Patch overbuilding

Trimming profiles

Defining profiles

Image 5.5-1


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5.6 Symmetry Criteria

While 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 continuity

i) Curvature variation

j) No directional variation

Curvature of good symmetry patchNote:

In this case Positional, Tangency, andcurvature continuities are fulfilled.

Observe the length and shape variation ofcurvature normal in the marked area.

Image 5.6-1

Curvature of bad symmetry patch

Note:

In this case only Positional and Tangencycontinuities are fulfilled.

Observe the length and shape variation ofcurvature normal in the marked area.

Symmetry Plane

Symmetry Plane

Image 5.6-2


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Observe

Uniform distribution of ISO-curves between main surface

and transition surfaces.

This is the result of using a transition surface, which givesmore control over creating corner and joining surfaces.

Observe

Irregular distribution of ISO-curves in main surface.

Figure 5.7-3

Observe

Uniform variation in ISO-curve shapes.

Synergy in variation of gaps between ISO-curvesdistribution.

Observe

Irregular variation in ISO-curve shapes.

Irregular variation of gaps between ISO-curves distribution.

Figure 5.7-4


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5.8 Surface Completeness

Surface should be complete in all respects.

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

Refer images for further reference:

Observe untrimmed bottom patch

Figure 5.8-1

Observe marked area

Untrimmed patch

Incomplete corner and Fillet

Figure 5.8-2


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5.9 Fillets

While 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 incurvature at the joining lines.

To improve the aesthetic effects, it is suggested to use conical blending, which is available insoftwares 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 5.9-1

Conical Filleting

Conical Filleting

Image 5.9-2


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6) Class-A surface verification

6.1 Patch properties

ISO-parametric Curve distribution/Patchparameterization

Polynomial representation of asurface, defined by a network oflines and points, called controlpoints or poles. These points aredistributed over sections.

Image 6.1-1

6.2 Connectivi ty Analysis / G0 - Continuity

Global connectivity analysis

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

Connectivity analysis result for hood surface isshown in following images.

Image 6.2-1


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

Note:

Observe green lines in surface

Image 6.2-2


Result of connectivity analysis

Gaps more than 0.05 are shown inred colour

Gaps less than 0.05 and free edgesare still shown in green colour.

Note:

1) Threshold value for connectivityanalysis used in this case is

0.05.

2) Method of result display issoftware dependent.

Green lines

Red lines

Green lines

Image 6.2-3

6.3 Tangency Analysis / G1-Continuity

Global Tangency Analysis

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

Note:

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

2) Observe magenta coloured lines in surface.

3) Method of result display is softwaredependent.

Image 6.3-1


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6.4 Curvature Analysis

Surface/Patch curvature analysis of a curveLaying on a surface for uniform variation incurvature

Note:

Curvature analysis of roof is shown.

Image 6.4-1

6.5 Reflection Analysis

Display of the reflection lines created on a patch bya line of light of infi nite length

Image 6.5-1

6.6 Dynamic Highlight Analysis

This 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'sview point. It is a simplified reflection model. As with reflection lines, highlights magnify discontinuitieson a supporting surface.Tangent plane discontinuity between two patches in a surface is shown up asdiscontinuous highlights. Discontinuous highlight tangents shows curvature discontinuity between two

patches (sharp angle where the contours join). Highlights have a lower order of continuity than thesurfaces they are traced on.


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Display of the Dynamic Highlights created on a roofsurface

Image 6.6-1

6.7 Absolute Curvature Analysis

It is used to detect the surface areas where thesurface is locally almost flat, that is wh en the

absolute curvature is almost null.

Image 6.7-1

6.8 Mean Curvature Analysis

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

irregularities on the surface. A minimal surface ischaracterized by a null meancurvature.

Image 6.8-1


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6.9 Maximum and Minimum Curvature Analysis

The geometric construct ion of main curvatures isthe following: let be a plane containing the normalto the surface in a given point. This plane cuts the

surface along a curve that hasa given curvature in this point . If this plane rotatesaround the normal, the curvatures of the curves ofintersection with the surface will vary between two

utmos t values. These two values are the maincurvatures

Image 6.9-1

6.10 Guassian surface Analysis

It 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 thepoint. If it is negative, the surface is hyperbolic in this point, i.e. the local shape is a horse saddle. If itis 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 usingGuassian surface analysis

Image 6.10-1

7) Curvature Analysis A case study


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Good roof su rface

Observe

Smoothness of surface

Uniform Dispersion of light in reflection zone

Defective roof surface

Observe

Smoothness of surface

Uniform Dispersion of light in reflection zone

Image 6.10-1

Good roof su rface

Observe

Smoothness of Dynamic highlights

Uniform variation in dynamic highlight line shapes

Uniform Gap between dynamic highlight lines


Observe

Smoothness of Dynamic highlights

Uniform variation in dynamic highlight line shapes

Non-uniform Gap between dynamic highlight lines

Image 6.10-2

Good roof su rface

Mean curvature analysis result


Mean curvature analysis result

Image 6.10-3


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Good roof sur face

Observe absence of local depression in

Guassian curvature analysis result


Observe presence of local depression in

Guassian curvature analysis result

Image 6.10-4


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8.2 Class-A Standard-I

Appl icable For Characterist ics Standards

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 criterias Refer Section 9

1) External seen Sheetmetal panels

2) Exterior seen paintedplastic trims

Dynamic highlights Refer Section 6.6

Table 8-1

8.3 Class-A Standard-II

Appl icable For Characterist ics Standards








1) Exterior seen plastictextured trims

2) Interior seen plastic

textured trims3) Interior seen plastic

textured trims

4) Interior seen sheet metalpanels


Table 8-2


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8.4 Class-A Standard-IIIAppl icable For Characterist ics Standards








1) External unseen areas ofSheet metal panels

Example: Areas of Bodyside panel hidden afterdoor closer, Lamppockets, Mirror pocketson door frame, Etc.

2) Unseen painted andtextured 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 nextto the car, and sitting inside the car.

5) Unseen means - areas which are not coming in lines of direct visual angle of a person standingnext 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 eachmodel.

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 Criterias Case studiesObjective of this section is to lead stylist or product engineers through the manufacturing process forsheet metal. Cases listed in this section of the documents are only for reference and knowledge of thestylist 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 followingaspects of sheet metal components.

Panels should retain their shape after stamping process, for the same proper stretching requirementshould be taken care, Styled features should retain intended shapes, For example, Feature lines likeshoulder 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 9.1-1


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Figure 9.1-1


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9.2 Tips for manufacturability of fender

Shaded Image of Front fender Left

Image 9.2-1


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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 9.2-1

9.3 Tips for manufacturabil ity of Rear quarter panel

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 the

two 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 the

two surfaces creating this kind of feature is 20

Figure 9.3-1


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Page 45 of 45


Figure 9.3-2


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Page 46 of 46


Figure 9.3-3

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