What is a class A surface 4

[ProEpro]

What is the technical definition of a class A surface?

Does it mean something different for a physical model and a cad model?

What software makes class a surfaces and how is it different from "ordinary" cad software?

TIA

ProEpro

http://www.whitelightdesign.com

 

[Chr1s]

An A class surface in the car industry for example is an exterior panel i.e. your door panels, fascias, hood, wing etc..
It is still a 3D CAD model and many packages can be used i.e CATIA etc..
The difference between a Class A surface and say a surfaced model for a hood inner panel is that the surface is much more defined for Class A. The Design Studio are always involved in buying off a class A surface because it is what the customer sees as opposed to a Hood inner (appearance is not much of a concern).
'A' class surfaces will be subject to things like Reflex which is where they will simulate light shining on the surface to make sure there are no imperfections in the surface. They may tweak the surface by tenths of millimeters to get the reflex correct. They will make sure all adjacent surfaces are tangent to each other toget rid of hard lines. They will normally use conics instead of fillet rads to get rid of hard lines at radii. For plastic A surface parts you would be required to show where the parting lines would be as well to make sure they are not going to be objectionable.
Many people can surface a model, good A Class surfacers are much rarer as it is much more skilled.

 

[Chr1s]

To add to my last comment, although a bumper fascia would be an A class surface, it could have A, B and C surfaces called out on it for surface definition once in manufacture. These would be used to describe surface quality for paint etc.. i.e on an A surface no paint sags may be present where on a C surface you may be allowed 1 up to 10mm long. A B surface may be the fog lamp pocket etc... B or C surfaces would normally be out of the normal sight line which may be defined as something like 15 feet back and 6 ft up or whatever the standard is for who you are working for. The surface definitions for this will normally be defined by the concencus of Engineering, the Plant, Quality and the Supplier.

 

[ivymike]

Now I'm ashamed - Chr1s can speak whole volumes on the subject, and all I was going to say was "the ones you have to make extra pretty, or the boss will get mad."

 

[ProEpro]

thanks Chr1s
I was going to give you a star but it won't let me because you are a visitor.
ProEpro

http://www.whitelightdesign.com

 

[trc]

What applications are there to create a class A surface from laser scan data? Does Imageware Surfacer do it? How about RapidForm or Geomagic?

 

[butelja]

I DO NOT work in the automotive area. I have run across a definition in the past for Class A surface that states the elevation, slope, and radius of curvature must be all be continous functions (no step changes) over the entire surface, when evaluated in orthoganal directions.

 

A class A surface is a surface that conforms to a set of tolerances for continuity to surrounding surfaces and smoothness within the surface. The values of those tolerances differ between different manufacturers.

It is virtually impossible to transition directly from scanned data to class A surfaces. Generally the scanned surfaces serve as a reference for comparision to interactivly modeled surfaces.

Geomagic is the SPAM of surface modeling, the first bite is good if you are really hungry, but you'll choke on the rest.

Unigraphics and CATIA are the in;y class A tools worth investing your time to learn.

 

[ProEpro]

Which Unigraphics package are you refering too? The only Class A modeler that I know of UG having is Imageware which they got when they bought SDRC.

Do you know of any references (SAE papers ect.) with those tolerances in them?

ProEpro

http://www.whitelightdesign.com

 

[kenvlach]

You may be talking about a different surface rating system altogether, but for molded plastic parts, see
The Society of the Plastics Industry website at

http://www.socplas.org/

Click Search; the most requested item is the Mold Finish Guide. "Molded, ABS plastic plaque, 8-1/2 x 11", showing typical surface finishes to aid in communication with customers. Includes A-1, A-2, A-3, B-1, B-2, B-3, C-1, C-2, C-3, D-1, D-2, D-3 finishes."

I suppose that CAD programs are used to design the metal mold surface, and hence, the resulting plastic part finish.

 

[ProEpro]

kenvlach

The two meanings of class A surface are entirely different. The one that is the point of this discussion is a vague term meaning for the best possible cad model of the surfaces of a product. Usually a car.

I am familiar with the SPI classification of polishes from D to A. The texture or polish is always called out as a note on the drawing. It is never modeled into the cad data. They also have a cosmetic quality standard that has a class A for the tightest standard.

You are right that there will often be overlap between these areas. Many parts designed with class A surfacing techniques get an A-1 polish and are considered a class A for defects. However, you could texture a surface modeled as Class A or specify a high standard for defects to a simple square.

TRC

Imageware is the only one of the software packages aimed at reverse engineering that is Class A. I believe that Catia has a reverse engineering package that can be used with their class A modeler but I haven't done it. ICEM Surf, Ailias and the other class A modelers maybe able to handle point cloud data but again I do not know first hand.

All the others like Geomagic, Rapidform, Paraform are limited to tangancy or limited curvature continuity.



ProEpro

http://www.whitelightdesign.com

 

[suren7669]

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

In normal no technical words, A_class surface means

It is smooth looking reflective surface with no distortion of light
highlites, which moves in a smooth uniform designer intended
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, 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 curveture continuity this does qualify as A_class surface.

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

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

As for as different S/W showing the cuveture continuity in the surfaces. it works like this

If you create a normal to the tangent line on a point which is lying on a common boundary of both patch or face, the variation in the curvature value between the two normal,should not be more than the threshold value which is set as preference value by the S/W
( Normal is nothing but the curveture value of the face /curve at
that point )

as for as S/W are concerned

Yes ICEM and Imageware can help you create surface
with cuvature continuity, but It is you, who are going to make
A_class .

Dassaults Systems has one S/W which was previously owned
by MATRA and Cisigraph called "Styler " ( old name was STRIM) , which is supposed to be one of the oldest and very good S/W's for reconstructing the surface from digitised data.

Good Luck

Suren