CLASS A

Page 1 of 45

Subject: Class-A Surface Guidelines

Contents 1) Phases of Class-A surface creation ................................................................................................................. ... ...3 3 2) Class-A surface Definition........................................................................................................ ................................................................................................................................ ........................ .. ..4 4 3) Mathematical Requirements................................................................................................................... ............................................................................................................................ ........... ..6 6

3.1 Positional Continuity OR 0 - Order continuity.............................................................................................. ..............................................................................................6 6 3.2 Tangent Continuity OR 1 - Order continuity........................................................................................... ...... ......8 8 3.3 Curvature Continuity OR 2 - Order continuity........................................................................................... ...........................................................................................11 11 4) Curve Creation..................................................................................................................... ................................................................................................................................................. ............................ .16

4.1 Curve order .............................................................................................................. ............................................................................................................................................ .............................. ...... ......16 16 4.2 Case study for curve creation ............................................................................................................... ....... .......17 17 4.3 Curve Redistribution ...................................................................................................................................18 ...................................................................................................................................18 4.4 Creation of Symmetry Curves .................................................................................................................. .... ....19 19 4.5 Boundary curve creation.......................................................................................................... .............................................................................................................................. ....................19 19 5) Surface Creation...................................................................................................... ................................................................................................................................ .......................... ........ ............... .......21 21

5.1 Criteria for surface creation .......................................................................................................................21 .......................................................................................................................21 5.2 Patch/Surface Parameterization.................................................................................................................. ..................................................................................................................22 22 5.3 ISO-Parametric Curve distribution................................................................................................. ......... ............ ...24 24 5.4 Patch/Face over building and trimming of Patch/Face............................................................................... ...............................................................................25 25 5.5 Minimum Descriptive profile for surface creation......................................................................... ......... ............. ....25 25 5.6 Symmetry Criteria....................................................................................................................... ................................................................................................................................. ................. .......26 26 5.7 Transition Surface............................................................................................................... ........................................................................................................................................ .........................27 27 5.8 Surface Completeness.............................................................................................................................. .... ....29 29 5.9 Fillets................................................................................................................ .......................................................................................................................................... .......................... ........ ................. .........30 30 6) Class-A surface verification ............................................................................................................................31 ............................................................................................................................31

6.1 Patch properties............................................................................................................ ........................................................................................................................................ ............................ ... ...31 31 6.2 Connectivity Analysis / G0 - Continuity ....................................................................................................... .......................................................................................................31 31 6.3 Tangency Analysis / G1-Continuity................................................................................................... ......... .........32 32 6.4 Curvature Analysis................................................................................................................... ....................................................................................................................................... ....................33 33 6.5 Reflection Analysis........................................................................................................ .................................................................................................................................... ............................ ... ...33 33 6.6 Dynamic Highlight Analysis................................................................................................................. ....... .......33 33 6.7 Absolute Curvature Analysis .................................................................................................... ........................................................................................................................ ....................34 34 6.8 Mean Curvature Analysis................................................................................................................... ............................................................................................................................. ..........34 34 6.9 Maximum and Minimum Curvature Analysis.................................................................................... ........ .......... ..34 34 6.10 Guassian surface Analysis..................................................................................................................... .... ....34 34

Page 2 of 45

Subject: Class-A Surface Guidelines 7) Curvature Analysis – A case study................................................................................................................ ................................................................................................................... ...35 35 8) Summary of Class-A Surface Standards......................................................................................................... .........................................................................................................37 37

8.1 Classification of components and Applicable Class-A standards ..............................................................37 ..............................................................37 8.2 Class-A Standard-I....................................................................................................................... ....................................................................................................................................... ................38 38 8.3 Class-A Standard-II .................................................................................................... ...................................................................................................................... .................. ......... ............... ......38 38 8.4 Class-A Standard-III .................................................................................................... .............................................................................................................................. .......................... ...... ......39 39 9) Manufacturing Criteria’s – Case studies........................................................................................................ ........................................................................................................40 40

9.1 Tips for manufacturability of hood ..................................................................................................... ........ ..........40 40 9.2 Tips for manufacturability of fender ......................................................................................................... ... ...42 42 9.3 Tips for manufacturability of Rear quarter panel ........................................................................................ ........................................................................................43 43

Page 3 of 45


1)

Phas Ph ases es of Cla Class ss-A -A su surf rfac ace e crea creati tion on

Figure 3.1-1

Page 4 of 45


2)

Cla lass ss-A -A su surf rfac ace e Defi Defini niti tio on

Class-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 Characteristics a)

Aesthetic requirements

b)

Reflectio tion, smoothness

c)

Styl Style e fea featu ture res s as as int inten ende ded d by by Des Desig igne ner/ r/St Styl ylis istt

Mathematical Requirements d)

0 order order conti continui nuity ty (Posit (Positio ional nal Conti Continu nuity ity / G0 Contin Continuit uity) y)

e)

1 ord order er con conti tinu nuit ity y (Tan (Tange gent nt Cont Contin inui uity ty / G1 G1 Con Conti tinu nuit ity) y)

f)

2 orde orderr con conti tinu nuit ity y (Cur (Curva vatu ture re Cont Contin inui uity ty// G2 G2 Cont Contin inui uity ty))

g)

3 orde orderr conti continui nuity ty (Const (Constant ant rate rate of of chan change ge of curvat curvature ure// G3 G3 Con Contin tinuit uity) y)

Manufacturing requirements h)

Panels Panels should should retain retain their their shape shape - proper proper stretch stretching ing requirem requirement ent should should be taken taken care, care,

i)

Styl Styled ed feat featur ures es sho shoul uld d reta retain in int inten ende ded d sha shapes, pes,

j) j)

Feat Featur ure e lines lines like like shou should lder er line line or wai waist st line line on body body side side pane panel, l, feat featur ure e lines lines on hood hood panel should retain their place (skidding),

k)

Bulg Bulge e eff effec ectt on on fla flang nge e lin lines es shou should ld be avoi avoide ded, d,

l)

Manu Manufac factur turabi abilit lity y of shape shapes s (Form (Forming ing of she sheet et meta metal, l, Moul Moulde ded d comp compone onents nts)) etc. etc.

Page 5 of 45

Subject: Class-A Surface Guidelines Defects which do not qualify for Class-A surface requirements Common visual defects, which can be attributed to the bad appearance of the surfaces m)

Broken Broken reflection reflection lines lines - which will affect affect the the homog homogeneo eneous us looks looks of the the car car body, body,

n)

Unin Uninte tend nded ed high highli ligh ghts ts ( Une Unequ qual al/N /Non on para parall llel el))

o)

NonNon-un unif ifor orm m tra trans nsit itio ion n hig highl hlig ight hts, s,

p)

Unde Underf rflu lush sh and and Ove Overf rflu lush sh cond condit itio ions ns

q)

Local Local dark dark spo spots ts in the the middle middle of of smooth smooth surf surface ace - whic which h may result result in in visual visual mism mismatc atch h of colour,

r)

Effect Effect of of transp transpare arent nt surfa surfaces ces like like wind windshi shield eld,, window window glas glasses ses and and lon long g lense lenses s on surf surface ace Curvatures,

s)

Loca Locall bri brigh ghtt -uni -unint nten ende ded d hig highl hlig ight hts, s, spot spots s etc etc..

Common Mathematical defects found in surfaces t)

Conn Connect ectivi ivity ty proble problems ms like like gap gap and and over overlap lappin ping g alon along g com commo mon n edg edge, e,

u)

Tang Tangenc ency y probl problem em betw betwee een n two two adjac adjacent ent surfac surfaces es alon along g comm common on edg edge, e,

v)

Curv Curvat atur ure e disc discon onti tinu nuit itie ies s betw betwee een n surf surfac aces es,,

w)

Bad parameterization,

x)

Bad Bad dist distri ribu buti tion on of of ISOISO-pa para rame metr tric ic cur curve ves, s,

y)

Topological pr problems,

z)

Twisted patches,

aa) aa)

Loca Locall depr depres essi sion ons s and and bump bumps, s,

bb) bb)

Tria Triang ngul ular ar patc patche hes, s, etc. etc.

Common Manufacturing defects found in surfaces For sheet metal panels cc) cc)

Flat Flat surf surfac ace e – ina inade dequ quat ate e len lensi sing ngs, s,

dd) dd)

Poss Possib ibil ilit ity y of of ski skid d mar marks ks,,

ee) ee)

Bulge lge at at fl flange line ines,

ff) ff)

Shar Sharp p, acu acute te trim trim line lines s and and shut shut line lines, s,

gg) gg)

Draw Draw dep depth th and and cor corne nerr radi radiii mism mismat atch ch,,

hh)

Under Under flush flush and and Over Over flush flush co-or co-ordin dinati ation, on,

ii) ii)

Loca ocal de depre pressio ssions ns and and bu bumps etc etc..

For Plastic components j j)

Shrinkage marks,

kk)

Molding dir direction,

l l)

Undercuts,

mm) mm) Seen Seen par parti ting ng line lines, s, nn)

Insuf Insuffic ficien ientt draf draftt angle angle for given given textu textures res,,

oo) oo)

Inade nadequ qua ate le lensi nsing, ng,

pp)

Warping et etc.

Page 6 of 45


3)

Mat athe hem mat atiica call Requ Requir irem emen ents ts 3.1 Pos Positi itiona onall Contin Continuit uity y OR 0 - Ord Order er cont continu inuity ity Surf Surfac ace e are are said said to be havi having ng Posi Positi tion onal al Cont Contin inui uity ty,, when when they they poss posses es the the foll follow owin ing g 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 smooth Note:

1) Observe the reflection of light.

smooth

variation

in

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

Page 7 of 45


•

Curvature Continuous within

•

Share a common edge

•

Gap between them along the edge is within tolerance limit

Note: 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 Result Note the broken Highlights at Common edge

Image 3.1-4

Mean Curvature Analysis result

Image 3.1-5

Page 8 of 45


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

Image 3.1-6

Industry Standard Examples DCX Value

0.02

GM 0.025

FORD

BERTONE

0.02

0.01

TTL 0.01

Note: Some values given here are based on the inputs from un-official source Image 3.1-7

3.2 Tan Tangen gentt Conti Continu nuity ity OR OR 1 - Ord Order er con contin tinuit uity y 

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



They are curvature continuous within.

Refer below images for more information

Page 9 of 45


Surfaces are smooth Note: 1) Observe Observe the smooth smooth variat variation ion in refle reflection ction of light. 2) Observe Observe the absence absence of sharp sharp reflect reflection ion 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

Page 10 of 45


Dynamic reflection highlights Analysis Result

Note the abrupt deviation in highlights at Common edge.

Image 3.2-11


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

Industry Standard Examples DCX Value

0.05

GM 0.05

FORD

BERTONE

0.07

0.1

TTL 0.05

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

Image 3.2-13

Page 11 of 45


3.3 Cu Curva rvatur ture e Con Contin tinuit uity y OR OR 2 - Orde Orderr con contin tinuit uity y Surface are said to be having Curvature Continuity, when they posses the following characteristics. qq)

Adjac Adjacent ent face faces/s s/surf urface aces s are shar sharing ing a commo common n edge edge..

rr)

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

ss)

Angle Angle betw betwee een n the norma normals ls at any any commo common n point point on comm common on edge edge is withi within n in the set set tolerance value.

tt)

Vari Variat atio ion n in curv curvat atur ure e value value at two poin points ts on same same curve curve on surfa surface ce is withi within n speci specifi fied ed value.

uu) uu)

They They are are cur curva vatu ture re con conti tinu nuou ous s with within in..

Refer images for more information

Surfaces are smooth Note: 1) Observe Observe the the smoo smooth th variat variation ion in reflec reflection tion 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

Page 12 of 45


1) Curvat Curvature ure Conti Continu nuous ous within within 2) Gap Gap betwe between en them them is with within in in in the the tolerance limit 3) Shar Share e a comm common on edge 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

Page 13 of 45


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

Industry Standard Examples

Value

DCX

GM

FORD

BERTONE

0.001

0.001

0.005

0.01

TTL 0.001

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

Image 3.3-19 Constant Rate of Change Change of Curvature Continuity Continuity OR 3 - Order continuity Surface 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.

Refer images for more information

Surfaces are smooth Note: 1) Observ Observe e the smo smooth oth vari variat ation ion in reflection of light. 2) Observ Observe e the furth further er impro improvem vement ent 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

Page 14 of 45


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 Result

Note the smooth deviation in highlights at Common edge

Image 3.3-23

Page 15 of 45



Image 3.3-24

Page 16 of 45


4)

Curve Cr Creation

Creation 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 unnecessary tension



Give a close look to curve descriptors while creating curves

4.1

Curve order

Every 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. Refer images for more information

Curve of Degree 3, and Class 4 Note: Curves Curves of this this type type are easier easier to handle handle;; for for any 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

Page 17 of 45


Curve of Degree 5, and Class 6 Note: Curves of this type are not easier to handle; for any change made to the curve by moving its pole, the chang change e in shape shape may may not not be monot monotoni onic c in natur nature e 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

Curve of Degree 6, and Class 7 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. 16 Observe the bad parameterisation of the curve, whic which h is not not desi desira rabl ble e for for Clas Class-A s-A surf surfac ace e creation.

Image 4.1-27

4.2 4. 2

Case Ca se st stud udy y for for cur curve ve cr crea eatio tion n

While 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 8 Note: 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

Page 18 of 45

Subject: Class-A Surface Guidelines 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 Observe the curvature curvature variation variation as seen seen from the curvature normals. The variation in this case is smooth as compared to the earlier case.

Image 4.2-29

4.3 4. 3

Curv Cu rve e Red Redis istr trib ibut utio ion n

Curve of Degree 9 and Class 10 Note: Observe highly haphazard distribution of curve parameters. Curve created created by software software tool from digitize digitized d data.

Image 4.3-30

Curve of Degree 9 and Class 10 Note: Observ Observe e smoot smooth h and and monoto monotonic nic varia variatio tion n in distribution of curve parameters parameters Curv Curve e crea create ted d by usin using g smoothing technique.

Image 4.3-31

opti optimi miza zati tion on

and and

Page 19 of 45


Curvature analysis of the Curve

Image 4.3-32

4.4 4. 4

Crea Cr eati tion on of Sy Symm mmet etry ry Cu Curv rves es

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 curves and surfaces. While creating symmetry curves check the following properties in the curve 2)

Curvat Curvature ure contin continuit uity y valu value e at the plan plane e of of symme symmetry try should should be “Ze “Zero” ro”

3)

Tange Tangency ncy contin continuit uity y at at pla plane ne of symmet symmetry ry should should be “ Zero Zero””

4)

Positi Positiona onall con contin tinuit uity y at at plan plane e of of symm symmetr etry y shou should ld be “ Zero Zero””

5)

It is is reco recomm mmen ended ded to have have curv curves es of Degree Degree 3,5 and and Clas Class s 4,6 4,6

6)

It is is not not recom recommen mende ded d to have have a curve curve node node at plane plane of symme symmetry try..

Symmetry Curve Note: Observe the absence of curve node at plane of symm symmet etry ry,, most most of the the time times s this this cond condit itio ion n automatically automatically ensures G0, G1 and G2 continuity.

Figure 4.4-2

4.5 4. 5

Boun Bo unda dary ry cur curve ve cre creat atio ion n

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 mathematical parameterisation.

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

Page 20 of 45


End boundary curves Note: Observe polynomial distribution of the curves.

Image 4.5-33

End boundary curves Note: Observe the the change in the polynomial distribution of the curves and the change in the curve position due to this.

Image 4.5-34

Page 21 of 45


5)

Surface Creation

As 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. consideration.

5.1 5. 1

Crit Cr iter eria ia for for sur surfa face ce cre creat atio ion n

Patch/Surface parameterisation Polynomial representation representation of a surface is defined by a network of lines and points, These control 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 profiles for surface creation Use minimum required number of end boundaries and internal support profiles to define a patch or 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 maximum curvature.

Surface completeness Completely defined surface in all respects, by mathematical definitions.

Fillets

Page 22 of 45


5.2 5. 2

Patc Pa tch/ h/Su Surf rfac ace e Pa Para rame mete teri riza zati tion on

Patch or surface is said to be of good quality when it has the following characteristics a)

Good Good dist distri ribu buti tion on of pat patch ch des descr crip ipto tors rs or or vert vertic ices es

b)

Patch Patch should should not not posse possess ss any any kin kinks ks in in the the descri descripto ptors rs pat patter tern. n.

c)

Minim inimu um num number ber of des descrip cripto tors rs

d)

Unif Unifor orm m var varia iati tion on in des descr crip ipto torr pat patte tern rn

Refer Images for more information

Good patch/face descriptors Note: Minimum number descriptors.

of

patch

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

Page 23 of 45

Subject: Class-A Surface Guidelines 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, features, corners, corners, transition transition surfaces, surfaces, bends bends etc. only experien experience ce can help help in decidin deciding g 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

Page 24 of 45


5.3 ISO ISO-Pa -Param rametr etric ic Cur Curve ve dis distri tribu butio tion n Distribution of ISO-curves is the primary indication of a good quality patch.

Bad ISO-curve distribution Note: Distri Distribut bution ion of ISO-Pa ISO-Param rametr etric ic curves curves is not 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: Smoo Smooth th vari variat atio ion n distribution

in

ISOISO-Pa Para rame metr tric ic

curv curve e

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

Page 25 of 45

Subject: Class-A Surface Guidelines 5.4 Pat Patch/ ch/Fac Face e over over buildi building ng and trim trimmin ming g of Patch/ Patch/Fac Face e 5.5 Min Minimu imum m Descri Descripti ptive ve profi profile le for for surfac surface e creati creation on While 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 hig high h numb number er of of profi profile le to defin define e the the patch patch may may result result in bad bad qua qualit lity. y.

f)

Patch Patch with with mini minimu mum m numb number er of of constr constrain aints ts posse posses s charac character terist istics ics like like,, good good dist distrib ributi ution on of ISO-parametric curves, Better parameterization.

Refer image for more information Defining profiles

Patch over building

Trimming profiles

Image 5.5-42

Page 26 of 45


5.6 Sy Symm mmet etry ry Cr Crit ite eria 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 Co Continuity

h)

Tange angenc ncy y and and curv curvat atur ure e cont contin inui uity ty

i)

Curvature va variation

j)

No directional va variation

Symmetry Plane

Curvature of good symmetry patch Note: In this this case case Posit Positio ional nal,, Tange Tangency ncy,, and and curvature continuities are fulfilled. Observe the length and shape variation of curvature normal in the marked area.

Image 5.6-43 Symmetry Plane

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

Page 27 of 45


5.7 5. 7

Tran Tr ansi siti tion on Su Surf rfac ace e

Case study for the use of transition surface and its advantages advantages

Front fa fascia with tr transition su surface

Front fa fascia with ithout tr transiti ition su surface Figure 5.7-3

C

M

M T C

Observe

Observe

Two 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”

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

Figure 5.7-4

Page 28 of 45


Irregular

Uniform ISO-curve distribution

Observe

Observe

Uniform distribution of ISO-curves Irregular distribution of ISO-curves in main between main surface and transition surface. surfaces. Thi This s is the the resu result lt of usin using g a tran transi siti tion on surfac surface, e, which which gives gives more more contro controll over over creating corner and joining surfaces. Figure 5.7-5

Observe

Observe

Uniform variation in ISO-curve shapes. Synergy in variation of gaps between ISOcurves distribution.

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

Figure 5.7-6

Page 29 of 45


5.8 5. 8

Surf Su rfac ace e Com Compl plet eten enes ess s

Surface should be complete in all respects. Check for the following imperfections imperfections like incomplete filleting operation, operation, untrimmed patches, undefined corners, etc. Refer images for further reference:

Observe untrimmed bottom patch

Untrimmed patch Figure 5.8-7

Observe marked area

Inco Incomp mple lete te

corn corner er

and and Figure 5.8-8

Page 30 of 45


5.9

Fillets

While creating fillets for joining joining two surfaces/patches, surfaces/patches, avoid using circular / cylindrical 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 improv improve e the aesth aestheti etic c effec effects, ts, it is sugg suggest ested ed to use conic conical al blen blendin ding, g, which which is avail availabl able e in software’s like CATIA and EUCLID-3. Limit the use of mechanical mechanical blending to following areas 1)

Unsee Unseen n areas areas like like corne corners, rs, Flan Flange ge line line blen blendin ding, g, Jogg Joggles les on on flang flanges es etc. etc.

2)

Less Less imp import ortan antt areas areas,, like like where where fillet fillet radiu radius s requi required red R is is < 5.

R

Mechanical Filleting

R

Image 5.9-45 Conical Filleting

Conical Filleting

Image 5.9-46

Page 31 of 45


6)

Clas Cl asss-A A su surf rfac ace e ve veri rifi fica cati tion on 6.1 6. 1

Pat atc ch pro prop per erti ties es ISO-parametric Curve distribution/Patch parameterization

Polynomial representation representation of a surface, defined by a network of lines and points, called control points nts or pol poles. es. These hese points nts are are dis distri tribute buted d over sections. Image 6.1-47

6.2 Con Connec nectiv tivity ity Ana Analys lysis is / G0 G0 - Con Contin tinuit uity y

Global connectivity analysis This method is used for finding out the gaps in surface topology connections. connections. Connectivity analysis result for hood surface is shown in following images.

Image 6.2-48

Page 32 of 45


Green

Global connectivity analysis Wire frame model of the hood surface, shown before submitting for connectivity analysis Note: Observe green lines in surface

Image 6.2-49

Global connectivity analysis Green lines

Result of connectivity analysis

Red lines

Gaps Gaps more more than than 0.05 0.05 are are show shown n in “red red”” colour Gaps Gaps less less than than 0.05 0.05 and and free free edges edges are still shown in “green “green”” colour. Note: 1)

Thre Thresh shol old d valu value e for for conne connect ctiv ivit ity y anal analys ysis is used used in this this case case is 0.05.

2)

Method of result display software dependent. dependent.

is

Image 6.2-50

6.3 6. 3

Tang Ta ngen ency cy An Anal alys ysis is / G1 G1-Co -Cont ntin inui uity ty Global Tangency Analysis This method is used for finding angle between two adjacent patch along a common edge. Note: 1)

Thre Thresh shol old d valu value e for conne connect ctiv ivit ity y anal analys ysis is used in this case is 0.05.

2)

Observ Observe e magen magenta ta colo coloure ured d lines lines in surf surface ace..

3)

Method of dependent.

Image 6.3-51

result

display

is

software

Page 33 of 45

Subject: Class-A Surface Guidelines 6.4 6. 4

Curv Cu rvat atur ure e An Anal alys ysis is Surface/Patch curvature analysis of a curve Layin Laying g on a surfac surface e for unifo uniform rm variat variatio ion n in curvature Note: Curvature analysis of roof is shown.

Image 6.4-52

6.5 6. 5

Refl Re flec ecti tion on An Anal alys ysis is

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

Image 6.5-53

6.6 6. 6

Dyna Dy nami mic c Hi High ghlig light ht An Anal alys ysis is

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's view point. It is a simplified reflection model. As with reflection lines, highlights magnify discontinuities on a supporting surface.Tangent surface.Tangent plane discontinuity between two patches in a surface is shown up as discontinuous discontinuous highlights. Discontinuous 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.

Display of the Dynamic Highlights created on a roof surface

Page 34 of 45

Subject: Class-A Surface Guidelines Image 6.6-54

6.7 6. 7

Abso Ab solu lute te Cu Curv rvat atur ure e Ana Analy lysi sis s

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 6. 8

Mean Me an Cur Curva vatu ture re Ana Analy lysi sis s

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

6.9 Max Maximu imum m and and Mini Minimum mum Cur Curvat vatur ure e Analy Analysis sis 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 These two values are the main curvatures Image 6.9-57

6.10 Guas Guassian sian surfa surface ce Analy Analysis sis It describes the local shape of a surface in one point:

Page 35 of 45

Subject: Class-A Surface Guidelines If it is positive, the point is elliptic, i.e. the surface has locally the shape of an ellipsoid around the point. 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

7)

Curv Cu rvat atur ure e Ana Analy lysi sis s – A cas case e stu study dy

Good roof surface

Defective roof surface

Observe Smoothness of surface

Observe Smoothness of surface

Uniform Dispersion of light in reflection zone

Uniform Dispersion of light in reflection zone

Image 6.10-59

Page 36 of 45


Good roof surface


Observe Smoothness of Dynamic highlights

Observe Smoothness of Dynamic highlights

Uniform variation in dynamic highlight line shapes

Uniform variation in dynamic highlight line shapes

Uniform Gap between dynamic highlight lines

Non-uniform Gap between dynamic highlight lines

Image 6.10-60

Good roof surface


Mean curvature analysis result

Mean curvature analysis result Image 6.10-61

Good roof surface


Observe absence of local depression in Guassian curvature analysis result

Observe presence of local depression in Guassian curvature analysis result

Image 6.10-62

Page 37 of 45


8)

Summ Su mmar ary y of Cl Class ass-A -A Su Surf rface ace St Stan anda dards rds 8.1

Classifica Clas sification tion of compo components nents and Appli Applicable cable Class Class-A -A stand standards ards

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

Figure 8.1-9

Plastic Trims

External Panels

Internal Panel

Painted/Textured Seen

Painted/Textured Unseen

Painted/Textured Seen

PaintedTexturedUn dUnseen

Class A Standard I

Class A Standard II

Class A Standard II

Class A Standard III

Figure 8.1-10

Page 38 of 45


8.2 8. 2

Clas Cl asss-A A St Stan anda dard rd-I -I

Applicable For

Characteristics

Standards

1) External seen seen Sheet Sheet metal metal panels

G0 – Positional Continuity

0.01

G1 – Tangency Continuity

0.05

2) Exterior se seen painted plastic trims

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 8. 3

Clas Cl asss-A A St Stan anda dard rd-I -II I

Applicable For 1) Exterior se seen pla plastic stic textu exture red d trims 2) Interior seen pla plastic stic textu exture red d trims 3) Interior seen pla plastic stic textu exture red d trims 4) Interior seen sheet metal panels

Characteristics

Standards


0.02


0.05


0.02

Patch descriptors

Refer Section 5.2


Refer Section 5.4

Fillets



Refer Section 9

Dynamic highlights

Refer Section 6.6

Table 8-2

Page 39 of 45


8.4 8. 4

Clas Cl asss-A A Sta Stand ndar ardd-II III I

Applicable For 1) External unsee nseen n area reas of Sheet metal panels Example: Areas of Body side panel hidden after door closer, Lamp pockets, Mirror pockets on door frame, Etc. 2) Unseen painted and text extured ured pla plastic stic trims

Characteristics

Standards


0.02


0.1


0.05

Patch descriptors

Refer Section 5.2


Refer Section 5.4

Fillets



Refer Section 9

Dynamic highlights

Refer Section 6.6

Note: 3)

Take Take care care for not not chan changin ging g “stylin “styling g inten intent” t” shape shapes s and and featur features es in all all above above case cases. s.

4)

Seen Seen means means - areas areas which which are are comi coming ng in in line lines s of dire direct ct visu visual al angl angle e of a person person standi standing ng nex nextt to the car, and sitting inside the car.

5)

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

6)

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

7)

Decide Decide the the maximu maximum m allowe allowed d deviat deviation ion for Class-A Class-A surface surface creation creation from Digitised Digitised data for each each model.

8)

Take Take the appr approva ovall from Styl Styling ing dep depart artme ment nt in case case of of deviat deviatio ion n from from digiti digitize zed d data. data.

9)

Observ Observe e for for regula regulator tory y requir requireme ements nts duri during ng the the crea creatio tion n of Class Class-A -A surfa surface ces. s. Example: Minimum external and internal projection regulations.

10)

At the stage stage of desig design n verificati verification, on, change changes s done done on styled styled surface surface with with respect respect to the the Styling Styling-freeze should be documented and agreed upon.

Page 40 of 45


9)

Manu Ma nufac factu turi ring ng Cr Crite iteri ria’ a’s s – Ca Case se st studi udies es

Objective 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 knowledge of the stylist and product engineers. The cases explained here are not to be considered as guidelines. guidelines. While designing the panels for manufacturability, proper attention needs to be given for following aspects of sheet metal components. 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 9. 1

Tips Ti ps for for manu manufa fact ctur urab abil ilit ity y of hood hood

Shaded image of hood panel Image 9.1-63

Page 41 of 45


Figure 9.1-11

Page 42 of 45


9.2 Tip Tips s for for man manufa ufactu cturab rabili ility ty of fen fender der

Shaded Image of Front fender Left Image 9.2-64

Page 43 of 45


d D

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

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

50R – Minimum Radius Radius to be kept

Incase of radical radical under sweepingat rear of wheel arch, Reduce Reduce theflange flange with to minim inimumpossi umpossible ble

Feature line line near wheel arch, high ris risk k of skidding skidding, if the the panel is is stretched stretched to the maximumlimit umlimit

Figure 9.2-12

9.3 Tip Tips s for manu manufac factur turabi abilit lity y of Rear Rear quart quarter er pane panel l Keep the feature line line away fromflange fromflange line line by minim inimum25m um25mm, to avoid avoid skidding skidding effect. effect.

Do not leave the feature line line sharp for avoiding local stretching, stretching, onthe fillet. fillet. Complete themby using using conical fill filleting eting option with maximum possible ratio Flang Flange Line

Minim Minimumangle umangle suggested suggested between the two surfaces creating this kind of feature is 20

ο

Figure 9.3-13

Page 44 of 45


Figure 9.3-14

Page 45 of 45


Figure 9.3-15

CLASS A

Recommend Documents