Modeling, surface & solid 4

[CFDruss]

Hi all, was wondering, as a newbie to UG, what do you feel is better to concentrate on learning solid modeling, or sheet modeling. Also, in what cases is it better to model using solid modeling and when better to use sheet (surfacing) modelling??

 

[cowski]

I advise you to get to know all the tools available to you so you have more 'ammunition' against any particular problem that comes your way. You will quickly find that there is almost always more than one way to do something (and usually more like 1/2 dozen ways at least). There are pros and cons to each method and you will have to experiment to find what works best for you.

I deal with mostly injection molded parts. My end result is always a solid model but I have to do some surface modeling to get there. We will use the freeform tools to model the complex surfaces that we need and use that to trim the solid model.

 

[CFDruss]

got ya, so surfacing tool tend to be good for creating complex surfaces, but you still use the constructed surface to shape a solid

 

[Xwheelguy]

Along with what cowski says....

Basically, there is no one absolute answer to your question. Some parts are easier to create from simple shapes & use boolean (unite, subtract & intersect) operations along with draft, blends & chamfers. Other parts are easier to do completely as surfaces then trim & sew all the surfaces into solids. Finally, you can use a bit of a hybrid approach that uses both boolean/feature operations and surfacing to end up with a solid at the end.

I typically try to stick with solids as much as possible due to edge tolerancing affecting downstream applications like FEA. However there are times when you are forced to use freeform/surfacing to get your solid. I feel only experience will lend a hand when it comes to deciding which is the best approach for the parts that you model.

Just to give you a bit more clarification on cowski's modeling method, it sounds like he has a solid model but uses freeform surfaces that intersect the solid to trim away chunks & incorporate an area of that freeform surface into the solid. This is an excellent example of hybrid modeling.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

 

[CFDruss]

ok, I see, so say with the following examples (which some i wont be attempting to draw obviously casue there are far from my capabilities) from your experience, what aproach would you take, sold, surface or hybrid.

1: A cam shatft and piston
2: I full engine block
3: a car body
4: A wheel
5: a rotor/turbine
6: a model of a mobile phone

Just so i get the jist as a start of what works best with what type of model

thanks

 

[ewh]

First a disclaimer: I have no experience in automotive, so some of the following is an educated guess.

1) hybrid - mostly primitives with some surfacing
2) solids - few free-form surfaces needed
3) free-form - some primitives for holes and such
4) hybrid - Tim can elaborate
5) hybrid - mostly free-form with some primitives (revolved bodies)
6) hybrid - mostly free-form

 

[Xwheelguy]

That's just the problem....I don't know what the parts require as far as modeling necessities....are the blends tangent or is there a need for curvature(G2) or higher continuity for any of the parts? I would have to see the parts & have some design or styling input to come to a closer solution.

But....just guessing:

1. Hybrid (Freeform with sweeps, extrudes, revolves & blends/chamfers)

2. This will depend on the complexity of the block, but I'd try it as Boolean first. If there's any sort of funneling or transitional surfaces, you'll have to use Hybrid Modeling & use surfaces that extend all the way through the solid to trim off the freeform looking areas.

3. Freeform (because there's probably going to be curvature (G2) or higher continuity). Car body surfaces are usually referred to as Class A (having no imperfections & smooth transitions from one surface to the next surface).

4. I design wheels for a living & I normally use hybrid modeling. However there are some very complex wheel designs that require a lot of surfacing prior to sewing into a solid.

5. Hybrid. The blades will be the freeformed part more than likely.

6. Hybrid. The phone's exterior will probably be Class A surfaces with some nice curvature continuity in the blends. However you could get away with Edge Blends. I look at most cell phones & I think I'd start off with a block & trim it away with surfaces.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

 

[CFDruss]

Hi, sorry to be a pain, but can you tell me what is meant by the following.

Class A surfaces

The need for curvature - G2 or higher?? Whats the difference between having a tangent blend and G2

Whats primitives.

is free-form basically general solid shapes (squares, triangles, etc)

 

[Xwheelguy]

There is no industry standard for Class A surfaces. Think of a hood on a car as being a solid model. The outside of the hood will more than likely be nice smooth surfaces, but the underside of the hood will not have such care taken when making the surfaces. The hood is an example of Class A surfaces, or visually 'perfect' surfaces. No abnormal bumps, creases or abrupt edges. I won't go into detail because there are many different views as to what Class A really means.

Tangency (C1 or G1) is simply tangency, or the surface edges sharing a common edge where the angle between the surfaces is 0° or 180°. Curvature is a more complex continuity. It's the same as tangency but considers the curvature of the surfaces as they run together. It's generally a smoother transition than tangency & the shape is sometimes more conic or elliptical, but not always.

I have always thought of primitives as blocks, cylinders, cones, spheres & torii (plural of torus which is a donut shape). They are the simplest geometric solids. I may be missing a few in there as well.

Freeform is exactly like it sounds. It has no general shape; it's free flowing & has less control than say a stepped block. Freeform surfaces can be smoother looking. Your F1 car body is an example of a freeform shape, as the body has several different cross sectional shapes.

UG's Modeling documentation has some good explanations for some of these terms. It's usually easier to SEE an explanation of continuity versus trying to understand it from a written definition.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

 

[Xwheelguy]

I would suggest you not worry about understanding continuity at the moment. Just have a FIRM understanding of what tangency means when working with curves & surfaces. You can learn about curvature continuity at a later time, as it's a more difficult type of modeling. Again, use the UG documentation for these questions....it's an invaluable resource & offers visual aids. I cannot stress this enough. So many of the answers are right there!

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

 

[ewh]

Tim,

You deserve a star for your patience and clear explanations!

 

[CFDruss]

Yes, your patiece has been great, and i am indebted to you, I know people like me can be annoying most of the time, but we are just trying to learn. many many many thank.

So what is used for free-sorm, is free form built by surfacing??

and with the tangency, what are the c1 and g1 mean, if its to long to explain then dont worry, just point me in the right direction in the manual, cause I cant seem to find much!!

 

[cowski]

Tim,
I agree with ewh, have a star from me too.


CFDruss,
For a quick look at free form options go to the menu: Insert -> Freeform Feature.
These are the options for building free form features. All the tools listed are able to return a sheet, and some (such as swept) will return a sheet or a solid depending on the input curves and options you choose (and modeling preferences). For more info the help files can be a great ... uh ... help.

 

[Rosales31]

Hey Tim - is ENKEI hiring Desing Egns.?

 

[MSPBenson]

You only need to apply tangency or curvature constraints to the edges of a surface where it joins to another surface.

Another good way to think of tangency (G1) and curvature (G2) is as follows.
Tangency leaves a slightly visible highlight line when you view the surfaces that are joining. This is because UG is very mathmatical in it's approach to tangencies (probably something to do with the industry it was originally designed to cater for). Styling packages like Alias are a little more wooly and tend to "blend" the tangency in a bit more.
Curvature interfaces will not leave a visible highlight when viewing/rotating the model.

My top tip for anyone wanting to start learning free form would be to learn how to use "bridge curves" and "through curve mesh" features. I use these more than any other features when creating free form surfaces.

 

[Berserk]

curve creation. Doing splines and sections and sketches.
Making sure endpoints are matching and if needed, tangent.


Being strong in curve creation would help you a lot on Free Form surfacing. I learned free form surfacing while doing molds.

I love solid modelling, but I still rely on my free form for a lot of things, especially Class "A" surfacing.

I could create anything that is made in solid modelling using free form. But I wont be able to recreate some free form models just by using solids.

Thats why I usually do hybrid modelling.

Roark

 

[Xwheelguy]

Thanks to eric & cowski for their support...a star in return for your input as well.

I would suggest if one is interested in a job with my company that you apply or contact human resources.

Taking MSPBenson's comments a bit further:

When creating freeform features, it is of the utmost importance that you pay as much attention to your curves as possible. Normally that means working with splines. Using a 3 to 5 degree spline with as few segments as possible will result in higher quality surfaces (better reflections & transitions).

In UG, Bridge Curve is almost a necessity, however the new Studio Spline in UGNX is VERY powerful & allows for easy continuity assignment & precise control over degree & segmentation. However, it only allows for up to C2/G2 continuity & is NOT present in v18.

Getting back to the original question of freeform, continuity, tangency & curvature....

Freeform modeling is normally constructing single surfaces using curves or other edges to define a surface's boundaries or cross sections. Under normal conditions, the designer will create many freeform surfaces that overlap or extend through one another & then trim them to a smaller size using adjoining surfaces or their edges as trimming boundaries. Once all of the surfaces are trimmed, they are usually sewn together into a multi-surface body. This body can be a solid (if it encloses a volume within a user-defined gap tolerance) or a sewn body of sheets (like a quilt). Continuity can often be assigned to each surface in relation to its adjacent surfaces. Whether it is assigned or not is up to the design intent or if a styling group requires it for visual/aesthetic appeal.

I had to do some digging overnight to get a definition that seemed appropriate concerning continuity. Finally found a good one from a textbook I used for a drafting class I took. It defines continuity as a term used to describe the transition between 2 elements, often curves and/or surfaces.

With that said, let's look at the 4 known types of continuity when dealing with curves & surfaces. I will try to explain them in order from simplest to most complex & encourage for anyone to add their comments or corrections. I should also suggest that the reader try to picture this in terms of 2D curves FIRST, then imagine it applied to surfaces.

The simplest and arguably the most used is positional continuity (C0/G0). Positional continuity simply means the curves/surfaces share a common endpoint/edge. Positional continuity often results in visible creases or corners. A simple example is the surfaces of a cube...the corners are positionally continuous. I personally do not believe that C0/G0 continuity necessarily need to be assigned as most modelers will force curves/surfaces to meet at common points/edges as long as they are within a reasonable tolerance. We'll discuss tolerance in another post....basically it controls accuracy of curves & how close surfaces are to their creation curves as well as controlling gaps between surfaces & model edges.

Moving on to the next type of continuity there is tangent continuity (C1/G1), or tangency. Tangency means the curves/surfaces share a common endpoint/edge AND their transition is 0° or 180°. Applying an Edge Blend to the corner of a cube is an example of tangent continuity.

The next type of continuity is curvature continuity (C2/G2). Curvature means that the curves/surfaces share a common endpoint/edge, the endpoints/edges are tangent AND they share the same radius of cuvature. This type of continuity will produce a smoother looking transition between 2 surfaces than tangency will.

The last type of continuity that is being practically used in UG is for the most part un-named, but for lack of better terms, let's call it acceleration continuity (C3/G3). At this point in time, I personally am not well versed in it's complete definition. From what I understand, acceleration means that the curves/surfaces share common endpoints/edges, they are tangent continuous, they are curvature continuous AND they share the same rate of curvature, or acceleration. At present, it is the smoothest transition possible between curves & surfaces. However, not all CAD softwares offer this type of continuity. UG does support C3/G3 continuity in Bridge Curves for v18, but I think that is it. However, Shape Studio does offer a Styled Blend that supports C3/G3 continuity.

Keep in mind, the higher the quality of curves you produce, the higher in quality your surfaces will be. Over-defining a curve is not always better.

Anyway, I know this is pretty 'deep' stuff & I don't expect a novice user to understand it completely. For a beginner, I'd suggest just understanding the first 2 types of continuity while trying to gather information on the last 2 over time.

I would suggest that for anyone who wants a better understanding of continuity that you take a course led by an instructor & practice using splines a lot.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

 

[Xwheelguy]

Hello Roark...nice to see you here.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

 

[Xwheelguy]

just point me in the right direction in the manual, cause I cant seem to find much!!

Use the search capability when you first invoke UG Documentation & enter the terms you're not familiar with...it should come back with several hits & from there you'll have to sort through them yourself.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com