CLASS A SURFACING A Class surfacing and its importance: A class surfaces are those
aesthetic/ free form surfaces, which are visible to us (inte (in terio rior/e r/exte xterio rior), r), hav having ing an opt optima imall aes aesthe thetic tic sha shape pe and hig high h surface quality. Math Ma them emat atic ical ally ly cl clas ass s A su surf rfac ace e ar are e th thos ose e su surf rfac aces es wh whic ich h ar are e curvat cur vature ure co conti ntinuo nuous us whi while le pro provid viding ing the sim simple plest st mat mathem hemati atical cal repre rep resen sentat tation ion ne neede eded d for the des desire ired d sha shape/ pe/for form m and doe does s no nott have any undesirable waviness. Curvature continuity: It is the continuity between the surfaces
sharing sharin g the sa same me bou bound ndary ary.. Cur Curvat vature ure co conti ntinui nuity ty mea means ns tha thatt at each point of each surface along the common boundary has the same radius of curvature. Why Class A is needed:
We al alll un unde ders rsta tand nd th that at to toda day y pr prod oduc ucts ts ar are e no nott on only ly de desi sign gned ed considering the functionality but special consideration are given to its form/aesthetics which can bring a desire in ones mind to own that product. Which is only possible with high-class finish and good forms. This is the reason why in design industries Class A surface are given more importance.
Understanding Class A surfaces:
1. The fillets - Generally for Class A, the requirement is curvature cont co ntin inuo uous us an and d Un Unif ifor orm m fl flow ow of fl flow ow li line nes s fr from om fi fill llet et to pa pare rent nt surface value of 0.005 or better (Position 0.001mm and tangency to about 0.016 degrees). 2. The flow of the highlight lines - The lines should form a uniform family fam ily of lin lines. es. Gra Gradua dually lly wid widen ening ing or nar narrow rowing ing but in gen genera erall never pinching in and out. 3. The control points should form a very ordered structure - again varying in Angle from one Row to the next in a gradual manner (this will yield the good Highlights required). 4. For a Class A model the fillet boundary should be edited and moved to form a Gentle line - and then re-matched into the base surface. 5. Matched iso-params in U & V direction are also a good representation representatio n of class A.
6. The degree (order) of the Bezier fillets should generally be about 6 (also for arc Radius direction) sometimes you may have to go higher. 7. Also you have to take care of Draft angle, symmetry, gaps and matching of surfaces Created with parent or reference surfaces. surfaces. 8. Curvature cross-section needles across the part - we make sure the rate of Change of curvature (or the flow of the capping line across the top of the part) is Very gentle and well behaved.
The physical meaning:
Class A refers to those surfaces, which are CURVATURE continuous to each other at their respective boundaries. Curvature continuity mean me ans s th that at at ea each ch "p "poi oint nt"" of ea each ch su surf rfac ace e al alon ong g th the e co comm mmon on boundary has the same radius of curvature. This is different to surfaces having; Tangent continuity - which is directional continuity without radius continuity - like fillets. Point co Point conti ntinui nuity ty - onl only y tou touchi ching ng wit withou houtt dir direct ection ional al (ta (tange ngent) nt) or curvature equivalence. In fa fact ct,, ta tang ngen entt an and d po poin intt co cont ntin inui uity ty is th the e en enti tire re ba basi sis s mo most st indu in dus str trie ies s (ae aerros ospa pace ce,, sh ship ipbu buil ild din ing g, BIW etc ). For th the ese applications, there is generally no need for curvature. By definition:
Class A surface refers to those surfaces which are VISIBLE and abide to the physical meaning, in a product. This classification is primar pri marily ily use used d in the aut automo omotiv tive e and inc increa reasin singly gly in con consum sumer er goods (toothbrushes, PalmPC's, mobile phones, washing machines, toilet lids etc). It is a requirement where aesthetics has a significant contribution. For this reason the exterior of automobiles are deemed Class-A. BIW is NOT Class-A. The exterior of you sexy toothbrush is Class-A, the interior with ribs and inserts etc is NOT Class-A. QUESTION:
What is Body_in_white Body_in_white? ? What is class A surface? Are the int inter erior ior tri trim m (A, (A,B, B,C C pil pillar lar,, das dash h boa board, rd, ce cente nterr con consol sole, e, handles) of a car using class A surface? Anybody using the basic design bundle of UG for class A surfacing? UG\Shape Studio?
How does it compare with Catia? Ans:1
A cl clas ass s A su surf rfac ace e is an anyt ythi hing ng th that at yo you u th the e cu cust stom omer er se sees es.. i. i.e. e. exterior panels and interior surfaces. A Class B surface is something that is not always visible i.e. the underside of a fascia that you would have to bend down to see. A Class C surface is the back side of a part of a surface that is permanently covered by another part. BIW is stuff like the body side etc.. Ans:2
Actually Actual ly 'b 'body ody in wh white ite'' is the term use used d to de descr scribe ibe the wh whole ole vehicle body after it has been welded/bolted together before it is painted or any parts are attached on the fit up line. Ans:3
We also use it to mean after it has been painted - I always assumed that the white bit refers to primer. Next step is to fit the windscreen and an d ba back ckli ligh ght, t, wh when en it be beco come mes s th the e gl glaz azed ed bo body dy in wh whit ite, e, or BIW+G. ANS: 4
BIW - Some surfaces are Class A, i.e. body side, roof, sill appliqué. I heard some time ago from a old designer that the term BIW comes from when cars were built from wood, they were painted white as it gives the frame a uniform color so imperfections were easily visible.
Ans:5
BIW meaning Body In White is so called due to its appearance after the application of the primer to the entirely Body panel assembled vehicle just before going into the painting process. Usually the primer is white or silver grey which gives the so called name. ANS: 6
Catia is mostly used for BIW design (Ford switching to catia, and Toyota). Is this because it could easily create quintic surfaces? With UG with Design bundle only, most of the surfaces created are cubic. ------------------------------------------------------------------ANS: 7
A class surface means - it is not just seen surface and unseen surface In normal no technical words, A class surface means
It is smoo smooth th looking looking reflective reflective surface surface with no disto distortio rtion n of light highli hig hlight ghts, s, wh which ich mov moves es in a sm smoot ooth h un unifo iform rm des design igner er int inten ended ded formations. when you create - car body panel, due to their complex shapes it not possible to create the surface with one single face /patch so you make multiple face/patch ( surface is a group of face/patch added together.) when these things are added, at the boundary of joining you need to have connectivity and continuation of minimum order two. for example In case one, one, at the connectin connecting g boundary boundary of two patches patches you have common boundary but it is sharp corner. this does not qualify as A class surface. In case case two - at the conne connecti cting ng bounda boundary ry of two patche patches s have common boundary and no sharp corner - but you have tangent continuity, this also does not qualify as A class surface. In case case two - at the conne connecti cting ng bounda boundary ry of two patche patches s have comm co mmon on bo boun unda dary ry an and d no sh shar arp p co corn rner er - yo you u ha have ve ta tang ngen entt continuit conti nuity y and curvatu curvature re continui continuity ty this does quali qualify fy as A class class surface. ( sine curve is good example for curvature continuity. but you can not call it a A class surface ) reason reas on is very simple the real require requirement ment of aesthetic aesthetic and good good looking and designer intended shape is not there. ANS: 8
For obtaining Class-A surfaces, CATIA is more commonly used due to its inherent ability to model very high quality surfaces in general. But,, any en But engin ginee eerin ring g so softw ftware are (C (CATI ATIA, A, UG, IDE IDEAS AS,, Pro Pro-E, -E, etc etc)) cannot develop a Class-A surface. This being due to engineering calculations involved in any surface generated by such softwares. For pure Class-A surfaces you would need styling softwares like Alias, Studio, etc. The use of any software would depend on the level of expectations placed on you. If your projects need only the modeling of the trim, generic engg softwares will do, but if you intend to go down right from styling, you would need Studio, etc. ------------------------------------------------------------------ANS: 9
IHO, Catia V4 has added a tool called Blend surf that is able to obtain obt ain vir virtua tuall cur curvat vature ure co conti ntinui nuity. ty. Pre Previo viousl usly, y, eve even n sty stylin ling g wa was s comfor com fortab table le wit with h mo model delss- an and d he hence nce too toolsls- def defini ining ng fil fillet lets s wit with h
conics, and many OEMs still accept this for Class-A surfaces. Catia V5 has GUI interfaces to impose curvature continuity the same way that Alias-Wave front Studio Tools (Auto Studio) does. They are both based on piece-wise polynomial equations, for what its worth. While a conic fillet is not technically curvature continuous, there are many vehicles, including luxury models, that have utilized them for Class-A surfaces and downstream- parts. Considering the tolerances in creating molds and dies and then producing parts from them.... a sheet metal panel is not a math model. ------------------------------------------------------------------ANS: 10
It is tr true ue th that at it is to toug ugh h to ma make ke go good od cu curv rvat atur ure e co cont ntin inuo uous us surface in UG, but not impossible. Reme mem mbe berr one thi hing ng A-c -cla las ss do doe esn sn''t me mea an ju just st cur urv vat atu ure continuity. and smooth reflections on CAD surface. it is lot more than that. Imagine. what happens to your A class surface in case pressed sheet sheet metal body body panel. and molded plastic components. components. The Th ey hav ave e to re rettai ain n th the ere in inte ten nde ded d smoo ooth thne nes ss an and d oth the er characteristics to remain A class. to achieve this this lot of other other things has to be taken care while designing A class surfaces. For example : 1- Line features on body body side external panel and feature feature on hood panel which is very very common, are to be designed designed to avoid skidding while they are pressed. like wise 2 -Fl Flan ange ge wi widt dth h an and d ot othe herr th thin ings gs ar are e to be ta take ken n ca care re wh whil ile e designing desig ning fenders fenders wheel wheel arch area for avoiding avoiding bulging effect effect and skidding effect. 3 - Fuel lid opening area, plunged flange for bulge effect. 4 - Panel stretching needs to be taken care. Lot many other things go in designing A class sheet sheet metal panels for door door , roof etc. 5 - In case case of plastic, plastic, sink marks and other things. ANS: 11
In Europe a 'A' class surface is generally taken to be the visible side of any component / assembly - a 'B' class surface generally relates to the opposite (or inside) face of an 'A' surface - i.e. the surface which defines the thickness of the part, and is where the mounting and reinforcing reinforcing detail detail tends to be located. located. 'B' class class surfaces surfaces can also be referred referred to as 'engineerin 'engineering g surfaces. I have not personally heard of any surface being referred to as a 'C' type. Cati Ca tia, a, wh whil ile e it is ok fo forr su surf rfac acin ing g te tend nds s to be mo more re us used ed fo forr generating engineering engineering surface detail and solid models models - software
packages like ICEMSURF tend to be more used for generating visual quality surfaces. ------------------------------------------------------------------ANS: 12
True A-class surfacing - especially on vehicle exteriors goes further than G2 or "curvature" continuity. G3 is often sought on the more major block surfaces. G3 deals with curvature "acceleration", i.e. the rate of change of curvature across a boundary. G2 means as has been described before that the curvature value is the same across a boundary. G3 means that the surface curvature leading to the boundary is changing shape at the same rate. Its like driving a car round a bend, you start off straight then gently add steering lock to the poin po intt wh wher ere e yo you u ne need ed no mo more re,, th then en yo you u ge gent ntly ly wi wind nd of offf th the e steering until you're straight again. If you look at the curve your car made, this would be G3. A-Class and B-class would refer to surface quality required for the component which is different to A-side and B-side which refers to which is the visible/non visible part of a component. ICEM surf is considered the best tool for speedy A-class surfacing due to the sophisticatio sophistication n of its real-time diagnostics. The consequence:
The co The con nse sequ que enc nce e of th thes ese e su surf rfac aces es ap apar artt fr from om vi visu sual ally ly an and d physically aesthetic shapes is the way they reflect the real world. What would one expect to see across the boundary of pairs of point contin con tinuit uity, y, tan tangen gentt con contin tinuit uity y and cur curvat vature ure co conti ntinui nuity ty sur surfac faces es when reflecting a straight and dry tree stump in the desert???? Point Continuity (also known as G0 continuity) - will produce a reflection on one surface, then at the boundary disappear and reappea app earr at a lo locat cation ion sli slight ghtly ly dif diffe feren rentt on the oth other er sur surfac face. e. The same reflective phenomenon will show when there is a gap between the surfaces (the line markers on a road reflecting across the gap between the doors of a car). Tangent Continuity (also known as G1 continuity) - will produce a reflection on one surface, then at the boundary have a kink and continue. Unlike Point continuity the reflection (repeat REFLECTION) is continuous continuous but has a tange tangent nt discontinuit discontinuity y in it. In analogy, analogy, it is "like" a greater than symbol. Curvature Continuity (also known as G2 continuity, Alias can do G3!) - this will produce the unbroken and smooth reflection across the boundary.
To achieve the same Class 'A' surfaces that automotive manufa man ufactu cturer rers s de deman mand, d, co consu nsumer mer pro produ duct ct man manufa ufactu cturer rers s hav have e availed themselves of the same advanced surface modeling tools. What Wh at is a Cl Clas ass s 'A 'A'' su surf rfac ace? e? Th The e si simp mple le an answ swer er is th that at it is a perfectly smooth surface with no anomalies, in which all adjoining surfac sur faces es hav have e cur curvat vature ure con contin tinuit uity. y. Thi This s me means ans tha thatt whe where re two surfaces meet, the graduation of one into the other is achieved with wi thou outt di disc scer erni nibl ble e ab abru rupt pt tr tran ansi siti tion ons. s. Th The e te tech chni niqu ques es us used ed to crea cr eate te Cl Clas ass s 'A 'A'' su surf rfac aces es ty typi pica call lly y re resi side de in to top p le leve vell su surf rfac ace e modeling software developed for the motor industry, rather than mid-range mechanical CAD packages that have evolved from 3D solid modeling for mechanical assemblies.
