A Class
surfacing and its importance:
A class surfaces are those aesthetic/ free form
surfaces, which are visible to us (interior/exterior), having an optimal aesthetic
shape and high surface quality.
Mathematically class A surface are those surfaces
which are curvature continuous while providing the simplest mathematical
representation needed for the desired shape/form and does not have any
undesirable waviness.
Curvature continuity: It is the continuity between
the surfaces sharing the same boundary. Curvature continuity means that at each
point of each surface along the common boundary has the same radius of
curvature.
Why Class A
is needed:
We all understand that today products are not only
designed considering the functionality but special consideration are given to
its form/aesthetic 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.
How to make
good class surface?
To achieve a good class surface it requires good
surfacing skills and understanding of the form or flow of the reference object.
In this highlight plot (color plot /zebra plot), curvature plot (needle/value)
of the surface is a very help full tool.
Highlight
plot :
Highlight is the behavior of the form or Shape of a
surface when a light or nature reflects on it. This reflection of light or
nature gives you an understanding about the quality of surface. This reflection
required should be natural, streamline and with uniformity.
Our
Understanding for Class A surfaces:
1. The fillets - Generally for Class A, the
requirement is curvature continuous and Uniform flow of flow lines from fillet
to parent 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 of lines. Gradually widening or narrowing but in
general 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 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. We also take care of Draft angle, symmetry, gaps
and matching of surfaces Created with parent or reference 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.
