Modelling Auto Parts

For the entire discussion on this topic, please click through to the source link above. The snippet below only touches the highlights of the discussion about modelling auto parts.

What is Body_in_white?
What is class A surface?
Are the interior trim (A,B,C pillar, dash board, center console, 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?


A class A surface is anything that you the customer sees. i,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 ofa part of a surface that is permanently covered by another part.

BIW is stuff like the body side etc…

Actually ‘body in white’ is the term used to describe the whole vehicle body after it has been welded/bolted together before it is painted or any parts are attached on the fit up line.

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 backlight, when it becomes the glazed body in white, or BIW+G.

A support to GregLocock & gdodd, 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.

Thank you for clearing up what BIW and the different Class surfaces.

I understand that 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.

Would this affect the Class A surfacing? Our company is
planning on doing interior trim design for GM. Would we need UG/Shape Studio? Or cubic surfaces would be enough.

A_class surface means - it is not just seen surface and unseen

In normal no technical words, A_class surface means it is smooth looking reflective surface with no distortion of light highlights, which moves in a smooth uniform designer intended

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, at the connecting boundary of two patches you have common boundary but it is sharp corner. this does not qualify as A_class surface.

In case two - at the connecting boundary of two patches have common boundary and no sharp corner - but you have tangent continuity, this also does not qualify as A_class surface.

In case two - at the connecting boundary of two patches have common boundary and no sharp corner - you have tangent continuity and curvature continuity this does qualify as A_class surface.

( ps: sine curve is good example for curvature continuity. but you can not call it a A_class surface )

The reason is very simple. The real requirement of aesthetic and good looking and designer intended shape is not there.

@greglocock This discussion is from 2003. Are there any relevant updates in the last 16 years? Or, is the information still true and valuable? Thank you and others for responding.