Creo

Debating the Most Efficient Way to Go from Concept to Documentation

April 15, 2014 By Barb Schmitz Leave a Comment

The conceptual phase of design is the only one within the product development window that must be inherently fluid, and in a sense, should be done in a leisurely manner. What, you ask? The word “leisure” is probably not used often when it comes to designing products, right? OK, let me explain.

In order to fully evaluate a suitable number of potential design concepts, engineers and designers must have the luxury of time. After all, how can you determine an optimum solution until you’ve discounted an adequate number of bogus ones? Unfortunately, not many of them get that time.

According to a conceptual design study conducted by PTC, 92% of respondents felt that their product development process would benefit tremendously from the ability to evaluate more concept ideas before moving forward into detailed design and documentation. Another 61% said that the concept design process is often cut short to due schedule constraints.

Time, after all, is critical to meeting design production schedules and shipping products on time. It’s the underlying reality of all those involved with product development.

This concept design for Yamaha was created by a Alberto Agnari. It included concept boards, sketches and traditional and digital renderings.

Which route to take: direct or feature-based?

Once a concept design has been approved and moved forward, time is of the essence. During our “The Pros and Cons of 3D Modeling Paradigms” webinar, one of the questions posed to our panel of speakers was in regards to what modeling paradigm is best in terms of time efficiency when moving from the concept stage to the documentation state, keeping in mind that a good percentage of the dimensions can be automatically generated within the history-based model. The answers were surprising and I thought worth sharing.

Dan Staples, vice president, Solid Edge Product Development, Siemens PLM Software

In a history-based system the dimensions are in the sketches and then those are retrieved into the drawing. In a direct modeling system, or at least in Solid Edge, the dimensions take the form of what we call PMI (product manufacturing information) or the 3D dimensions that are on the faces of the model instead of in the sketches. That doesn’t change the ability to retreat those into the drawing. The fact is that they’re on the faces instead of the sketches, same thing in terms of ability to retrieve those that are in the drawing and use them.

Brian Thompson, vice president of Creo Product Management, PTC

Yeah, I think if you have good workflows for creating or showing those dimensions in the 2D context, it could be similar in terms of efficiency to do either. I don’t see one modeling paradigm strongly standing out. There’s good efficient workflows for creating dimensions on models that have no underlying sketches, and there’s good workflows for showing them on models that do. As Dan and I have said, dimensions in the direct modeling environment can, in fact, still drive geometry if the user tells the system that’s what he wants.

You can still even get that behavior. Maybe not to the level you would get with a large feature-based, history-based parametric model, but you could still get that behavior. There may be some circumstances where one is slightly better than the other, but I’d say it’s fairly close in terms of efficiency to create that documentation. Would you agree Dan?

Dan Staples

I would actually say it’s somewhat more efficient. One of the constraints we forget about is that when you build up a history-based model, you build it up sketch by sketch by sketch. That’s not necessarily a natural way to dimension the part. In fact, it’s pretty bad practice in terms of a dimensioning scheme because you tend to have a lot more dimensional stack ups than you would like. Whereas if you’re in a direct modeler, you can put in dimension between two faces on the model that are far from each and there’s 50 features in between, and so you can actually have a much more natural dimensioning scheme that’s more immediately usable in the drawing when you see direct models in my opinion.

Brian Thompson

Yeah, I think we’ll agree there that bad modeling technique and your history-based parametric modeling will make it even harder in the drawing to do that. If you got a good, well-done history tree then maybe it’s not as hard but it’s a good point.

The bottom line

Though it’s not easy to sum up all the good points here, its clear the most time-efficient way to move your designs from concept to documentation is to use best practices when it comes to how you model your products and good dimensioning workflows. In other words, the use of good modeling techniques will always get you from Point A to Point B faster, whether you’re working in a direct modeling or feature-based modeling 3D CAD system.

If you missed the “Pros and Cons of 3D Modeling Paradigms” webinar, you can watch it in its entirety here.

Barb Schmitz

The Role of Associativity in Direct Modeling

April 1, 2014 By Barb Schmitz Leave a Comment

When designers and engineers think about design associativity, they often think about history-based 3D modeling systems. CAD software that deploys a history-based approach to modeling requires engineers to anticipate and define feature constraints, relations and dependencies, which ensures that any design change will update all related downstream geometry. That’s design associativity.

Though they require a lot more work, thought and pre-planning on the part of the user, history-based modeling systems provide users with a methodical, orderly and powerfully automated way to create models. The problems arise, however, when changes have to be made, a rather common occurrence at all stages of development. Even small design changes cause a domino effect so users must carefully consider the impact a change will have to associated parts.

Design associativity is not exclusive to history-based 3D modeling approaches. Image courtesy of PTC.

Is there associativity in direct modeling?

During The Pros and Cons of 3D Modeling Paradigms webinar, one of the questions asked of our panel of experts was what is the role or definition of associativity in direct modeling? Our panelists each brought a unique perspective to that question, which I thought was worthy of sharing.

Dan Staples, vice president of Solid Edge Product Development, Siemens PLM Software

To me the word associativity with parametrics is the notion that changing one thing changes other things that are associative. Things can be related to one another and things can be dimensionally driven and, therefore, association between the dimension and the faces. The key difference is that it doesn’t cause a linear regeneration of the treetop to bottom. That expensive piece is you edit the first feature and you pay for all subsequent thousand features.

That’s not true in a direct modeling system. However, there is the notion of associativity, meaning that things can happen. Dimensions are edited and faces moved, or Face A is associated with Face B and, therefore, it should move also. That’s associativity by my definition, and it’s perfectly valid in a direct modeling system.

Chad Jackson, principal analyst, Lifecycle Insights

There is probably a finer point here, which is there’s design associativity and there’s deliverable associativity. You might want to have design intent because of intent ripple has a change ripple across multiple parts in the same assembly. You might want to have that. Obviously when you change a part, you want the drawing to update and you want a service assembly animation to update. I think in both of those cases, neither are really limited by direct modeling. I think they are separable.

Brian Thompson, vice president, Creo Product Management, PTC

Maybe another way to look at is when you’re building in a history-based parametric modeling system, every selection that you make of some other geometry to create a dimension or to lay it on the line in a sketch or whatever it may be, it does create a dis-associativity that you as an engineer you have to consider: is that an important thing? Is that aspect important to my design intent? If it is, that can be a very powerful thing and they’re inherent in the design process.

Whereas with direct modeling, I would say that kind of thing is very much put in right at the top of mind of the engineer as they’re working through the direct modeling process. They will put that in into the design as they see fit. It’s something that the design engineer consciously decides; I want to create dis-associativity. It just doesn’t happen as a natural part of the design process, whereas in history-based systems, it very much is ingrained. Selections that you make do in fact create associative references unless you specifically say no I don’t want that. It’s usually the opposite assumption in direct modeling.

If you missed “The Pros and Cons of 3D Modeling Paradigms” webinar, you can still see it here.

Barb Schmitz

Preparing Models for Simulation: Which 3D Modeling Paradigm is Best?

March 3, 2014 By Barb Schmitz Leave a Comment

Simulation technology has its origins in the labs of universities and specialists groups within the aeronautics and automotive industries. Today, however, simulation software has moved from research labs into mainstream product design and engineers and designers are increasingly using simulation tools to guide their design choices.

How simulation tools are used today

As designs progress throughout the development cycle, a sequence of decisions and adjustments are made, affirming that the design is on the right path. When used properly, simulation tools can help guide engineers on that path by providing with a way to make better decisions in order to design better products faster and at lower cost.

To make it easier to incorporate simulation into product development, many CAE programs are tightly integrated with CAD software. The integration of CAD and FEA enables engineers to test ideas, adjust designs, explore, and verify to confirm that designs are on the right track, minimizing the risk of flawed designs moving forward when changes are most costly.

Preparing models for simulation

When models are ready to be simulated, engineers and designers often have to simply them in order to be able to perform simulations on them. During our recent “Pros and Cons of 3D Modeling Paradigms” webinar, the question of which 3D modeling technique works best when models are going to be simulated was posed to our speakers. I think their respective responses are worth sharing.

Chad Jackson, principal analyst, Lifecycle Insights.

I think that both those technologies (direct modeling and feature-based modeling) work with simulation but in two very different scenarios. I think with direct modeling, it helps you with simplification and abstraction of model prior to analysis. Now, if you try and do that through feature-based approaches, you can run into model failures and you have got to find the guy that originally designed it to really make progress there.

Direct modeling is a really good fit there if you’re looking at one model and you want to get it ready for simulation. However, there are a lot of organizations today that deal with a lot of variance of products or parts. Feature-based modeling is a great way to automate the generation of those variances and that applies to simulation as well when you look at things like design-of-experiment studies, optimizations and things like that. I think both have a fit but very different uses.

Dan Staples, vice president, Solid Edge Product Development, Siemens PLM.

The only thing I would add is that when you talked about the abstraction, and I think when you get to that it’s typically the analyst who is getting something from the designer and he needs to abstract it for purposes of analysis. The thing about direct modeling, in general, is it’s for someone who’s not a CAD expert and hasn’t been indoctrinated into the history tree and the recipe that most of us got indoctrinated into 10 or 15 years ago.

History-based modeling techniques are intuitive, but only because we had a beat into our heads for many years. Certainly, I think if you were to ask the average guy on the street or the guys who’s an analyst and not exposed to CAD on a daily basis in terms of modeling, it’s just a lot easier to approach the kind of changes you needed to make by using direct modeling.

Brian Thompson, vice president, Creo Product Management, PTC.

It’s not merely a matter of direct modeling style changes for purposes of the abstraction or for purposes of simplification, but it’s also the analyst who does his first round analysis. He gets a result and he realizes well, ‘I’ve got an issue with the stress here or there’ and the analyst then wants to go in and modify the the model, not for simplification or abstraction purposes, but because he’s got stress problem. He could go through the pain of going back and asking the engineer to make that change or he could maybe do some exploratory work with the model himself.

With direct modeling he doesn’t need to worry about the original design intent of the model. He can make direct modeling-based changes to the model in order to explore how to reduce the stress or how to change the natural frequency or whatever type of analysis he’s doing in order to achieve the design goal without having to cycle back through the person who understood the original design intent of the model. Lots of good reasons to use direct modeling there.

If you missed the “Pros and Cons of 3D Modeling Paradigms” webinar, you can watch it in its entirety here.

Barb Schmitz

The Challenges of Model Editing in the Multi-CAD World

February 27, 2014 By Barb Schmitz Leave a Comment

In today’s world, most engineers and designers are now accustomed to dealing with CAD data created in other CAD systems. With design collaboration with suppliers, partners, and customers being a key component of today’s product design, the use of multiple CAD systems has become the norm.

As a result, companies must become proficient at working with CAD data in multiple formats in order to succeed. Not only must they be able to send and receive data in multiple CAD formats, but also they must be able to quickly get to work on that CAD data without having to rebuild models from scratch or waste too much time fixing data to get clean geometry.

On average, companies use 2.7 different CAD systems internally. Here’s another daunting statistic: nearly half (49%) of companies struggle with importing models created in other CAD tools into their 3D CAD system, and another 59% say modifying imported models from other CAD tools is difficult using their CAD software.

Vital design cycle time is wasted when models must be recreated; yet making changes to those models is also problematic as intelligent features and patterns built in by feature-based CAD authoring systems are often lost once imported into another CAD system. So what is a company to do when navigating through multi-CAD environments?

Nearly half of all product development companies continue to struggle with how best deal with CAD data originating in other CAD systems. Image courtesy of Siemens PLM.

During the Q&A portion of a recent webinar, “The Pros and Cons of 3D Modeling Paradigms,” a question was posed to the speakers as to how best to approach making changes to CAD models that were created in a different CAD system. I think the responses are worth sharing as it’s something with which half of all companies continue to struggle.

Brian Thompson, vice president of Creo Product Management at PTC
“It’s pretty obvious that data inoperability between CAD systems has been tried at the feature level, and it’s generally not all that successful, at least not in a robust way. In general, when you take data in from another CAD system, you’re going to get information like assembly structure but for the geometry, you’re going to get just a closed volume, assuming that the data translation for the solid or the geometry came across well. Unless you want to just use your own history-based features to cut geometry out and recreate it from scratch, direct modeling tools are an ideal set of tools to manipulate geometry that’s come in from a CAD system in which you don’t have the features any longer.

It’s a pretty nice approach to be able to move faces, to align faces, to resize analytic geometry, to symmetrically change a model if it looks like it might be symmetric. There’s lots of tools built into most direct modeling environments that will give you great control over geometry regardless of the fact that that geometry had no features when it came over. You can actually use direct modeling tools to really control that geometry in pretty sophisticated ways despite the fact that when you got it, you didn’t get any features at all.”

Dan Staples, vice president of Solid Edge Product Development, Siemens PLM.

“I would just add that I don’t think it is, to be honest, any contest. If you were to be reading data from another system and you could choose to read it into the history-based environment and non-history-based environment, definitely read it into the non-history-based environment. You have much more flexibility and ability to make the changes you want to make.

I would suggest that in fact if you’re a diehard history-based user, but your system supports a non-history sort of mode, that this is where you want to try it. Certainly we’ve seen our users who when they want to get started with, in our case, synchronous technology and they are asking themselves ‘do I want to use it or do I not want to use it?’ Well, by gosh, the first place to use it (direct modeling) is with that imported data, it’s definitely a homerun there.”

Chad Jackson, principal analyst at Lifecycle Insights and a speaker at the webinar, authored a whitepaper that addresses the challenges of working in multi-CAD environments. You can read “Multi-CAD Data, Unified Design” here. To listen to the entire “The Pros and Cons of 3D Modeling Paradigms” webinar, click on this link.

Barb Schmitz

The failed promise of parametric CAD, final chapter: A viable solution

November 18, 2013 By Evan Yares 5 Comments

What is the failed promise of parametric CAD? In short, model reuse.

It’s a lot more difficult than it ought to be, for a variety of reasons. Several months back, I wrote a series of articles discussing those reasons, as well as some of the solutions that have come up over the years. What was missing from the series was a final chapter; a detailed description of what could prove to be a viable solution to problems with model reuse: the resilient modeling strategy.

The resilient modeling strategy (RMS) is the brainchild of Richard “Dick” Gebhard. I wrote about Dick last June, in the article A Resilient Modeling Strategy. He’s a low-key guy with deep experience and serious expertise in the practical use of MCAD software. Over his career in CAD, he’s been a reseller for CADKEY, Pro/E, and most recently, Solid Edge.

RMS is a best practice for creating CAD models that are stable and easily reusable (even by inexperienced users.) It can be learned and easily used by typical CAD users, it preserves design intent in models, and provides a mechanism by which managers or checkers can quickly validate a model’s quality.

When Dick first started thinking about the concepts that make up the resilient modeling strategy, it was natural that it was in the context of showing the advantages of Synchronous Technology (The Siemens PLM brand name for its version of direct modeling.) In our discussions about RMS over the last year or so, I pointed out that, while I thought that RMS did indeed demonstrate the benefits of hybrid history/direct modeling in Solid Edge, for it to be taken seriously, and not be unfairly dismissed as a marketing initiative for Solid Edge, it needed to work with a wide variety of MCAD tools. I think Dick got where I was coming from, because he’s continued to refine and generalize RMS, with feedback from users of a number of MCAD systems.

In its current incarnation, RMS works particularly well with Solid Edge, as might be expected, but also works very well with Creo, NX, CATIA, and IronCAD (all of which are hybrid history/direct systems.) Further, with a few modifications, it can provide compelling value with SolidWorks, Inventor, and Pro/E (all of which are primarily history-oriented systems.)

It’s significant that RMS is also free to use. While Dick is available to provide presentations, seminars, and training, he has not attempted to patent, or keep as trade secrets, the underlying concepts of RMS. (He does claim a trademark on the term “Resilient Modeling Strategy,” which means that organizations offering commercial training on RMS will need to get Dick’s OK to use the term.)

Dick has posted an introductory presentation on RMS at resilientmodeling.com. While the entire presentation is 20 minutes long, the first 3-1/2 minutes cover the problems that people invariably experience when reusing or editing history-based CAD models. Watching that much will likely convince you to watch the rest.

On Wednesday, November 20, at 10:00 AM PST, Dick will be hosting a webinar on RMS. It’s scheduled to last just 30 minutes, with the emphasis on content, not hype. If you’re a serious CAD user or a CAD manager (or, for that matter, you work for an MCAD developer), it’ll be well worth your time to attend.

TL;DR: Resilient Modeling Strategy is a best practice for creating high quality reusable 3D MCAD models. It works with many CAD systems, it’s easy to learn and use, and it’s free. Big payoff for MCAD users.

Presentation at resilientmodeling.com

The failed promise of parametric CAD part 5: A resilient modeling strategy

June 25, 2013 By Evan Yares 3 Comments

The model brittleness problem inherent with parametric feature-based modeling is a really big deal. And it’s something, honestly, that I don’t have a great answer for. I’ve even asked a few power users who I know, and their answers seemed to involve a bit of hand-waving, and a reference to having lots of experience.

While best practices are a potentially good step forward, they need to be straightforward enough that mere mortals (as opposed to power users) can follow them.

Around Christmas last year, I got a call from Richard Gebhard, an engineer’s engineer, who has made his living selling CAD, and training people to use it (including more than his fair share of power users), for longer than he would like me to admit. (I’m pretty sure I’ve been in the CAD industry longer than him, though.) Richard told me he had something he wanted to show me, and if I’d take the time to meet him, he’d buy me lunch.

What Richard showed me was a way of creating and structuring CAD models that made a lot of sense. It not only reduced parent-child dependencies, but it made them more predictable. And, more importantly, it made it a lot easier for a mere mortals to scan through the feature tree, and see if there were any grues (it’s a technical term. Feel free to look it up.)

Over the next several months, we had lunch several times. I made suggestions. He rejected some, accepted some, and thought about others. At the same time, he was bouncing his ideas off several of his best power users (including his son). By a couple of months ago, he had refined his system to the place where it would work impressively well with nearly any parametric feature-based CAD system. So, he went to work finalizing his presentation.

I had mentioned that Delphi, by patenting some of the elements of horizontal modeling, limited the number of people who could benefit from it. (Worse for them, they patented it, then filed bankruptcy. That didn’t help much.) Richard’s goal wasn’t to monetize his process. His goal was to evangelize it. To help CAD users—both power users and mere mortals—to get their jobs done better.

Richard and I had talked, over time, about what he should call this process. At first, I liked the word “robust.” In computer science, it is the ability of a system to cope with errors during execution. In economics, it is the ability of a model to remain valid under different assumptions, parameters and initial conditions. Those are good connotations. But, then I thought of one of my favorite examples of robustness. The first time I visited Russia, I noticed that the apartment buildings were built of thick poured concrete. Very robust. And nearly impossible to remodel.

Richard’s system wasn’t robust. It was resilient. So, he has named it the Resilient Modeling Strategy. RMS.

So far, I’ve written over 2,600 words, to provide some background on the problems of parametric modeling, and some of the solutions that have been offered over the years. But, after all that, I’m not going to tell you anything more about RMS. At least, not yet.

Tomorrow, Wednesday, June 26, Richard will present RMS for the first time ever, at Solid Edge University, in Cincinnati, Ohio. His presentation will start at 9:00AM local time, and will be in room 6 of the convention center. If you’re there, put it on your calendar. If not, you’ll need to wait until Richard gets back to Phoenix, and I publish a follow-up post.

RMS is not anything difficult, or fundamentally new. It’s just an elegant distillation of best practices, designed to work with nearly any parametric CAD system, and simple enough that it doesn’t get in the way. It’ll help you make better CAD models faster.

The failed promise of parametric CAD part 4: Going horizontal

June 25, 2013 By Evan Yares 12 Comments

In the early 90s, Ron Andrews, a senior product designer at Dephi’s Saginaw Steering Systems Division, became fed-up with the difficulties of editing parametric CAD models. So, he and a team of his colleagues, including Pravin Khurana, Kevin Marseilles, and Diane Landers, took on a challenge of trying to find a solution.

They came up with an interesting concept that they called horizontal modeling. Here’s a description of it from their patent abstract:

“Disclosed is a horizontal structure method of CAD/CAM manufacturing where a base feature is provided and one or more form features added to it to form a model. The form features are added in an associative relationship with the base feature, preferable a parent child relationship, but are added in a way as to have substantially no associative relationships with each other. The result is a horizontally-structured Master Process Model where any one form feature can be altered or deleted without affecting the rest of the model. Extracts are then made of the Master Process Model to show the construction of the model feature by feature over time. These extracts are then used to generate manufacturing instructions that are used to machine a real-world part from a blank shaped like the base feature.”

Here’s a picture that makes it clearer:

The simplest explanation I can give for it is this: You create a base feature, and bunch of datum (working) planes. You attach all the child features to those datum planes. Viola: no parent-child problems.

I admit that I’m not going to do justice to horizontal modeling in this conversation. There’s actually quite a bit to it, and it makes a lot of sense when coupled with computer-aided process planning (CAPP.)

Horizontal modeling has a handful of problems. First, it does a pretty good job of killing the possibility of having design intent expressed in the feature tree. Next, it works better with some CAD systems than others. (When horizontal modeling was in the news, SolidWorks had a problem managing the normals on datum planes, so it didn’t work too well.) The deadliest problem is that Delphi got a bunch of patents on the process, then licensed it to some training companies. From what I can see (and I may be wrong), none of these training centers offer horizontal modeling classes any more.

While, technically, you can’t use horizontal modeling without a patent license from Delphi, the concepts at its core are fairly similar to things that CAD users have been doing for years. A few years ago, Josh Mings posted on a couple of online forums that “Horizontal Modeling is just one word for it, you may also know it as Skeleton Modeling, Tier modeling, Sketch Assembly modeling, CAD
Neutral Modeling, or Body Modeling.” (It’s actually two words for it, but I get his point.)

Horizontal modeling is not a silver bullet solution for the problems inherent in parametric feature-based CAD. It’s just a best practice—a strategy for getting around the problems. It seems to be headed in the right direction, but it suffers from the complexity that comes from trying to fix too many problems at once.

Next: A Resilient Modeling Strategy

The failed promise of parametric CAD part 3: The direct solution

June 25, 2013 By Evan Yares 5 Comments

Direct modeling—a syncretic melding of concepts pioneered by CoCreate, Trispectives, Kubotek (and many others)–has shown the most promise to cure the parametric curse.

Direct modeling is today’s hot CAD technology. PTC, Autodesk, Siemens PLM, Dassault (CATIA, but not so much SolidWorks), IronCAD, Kubotek, Bricsys, SpaceClaim (and certainly some other companies I’ve forgotten) all have their own unique implementations of it.

The common thread in direct modeling is to use standard construction techniques when modeling, and feature inferencing (or recognition) when editing. It’s easier said than done. It’s taken about 35 years of industry research to get to the place we are today—where you can click on a face of a model, and the system will recognize that you’re pointing to a feature that has some semantic value. And that’s not even considering the tremendous amount of work that has been required by legions of PhD mathematicians to develop the math that lets you push or pull on a model face, and have the system actually edit the geometry it in a useful manner.

For the CAD software, figuring out which way to edit a selection is almost a mind reading trick: A user clicks and drags on a part of a model. What would they like to happen? In some cases it’s easy: Drag once face of a rectangular block, and the system will just make it longer or shorter. But if the block is full of holes, bosses, and blends, it becomes a lot more complicated. What should the system do if you drag a face so far back that it consumes another feature, and then pull it back to where it was? Should the consumed feature be lost forever, or should the system remember it in some way, so it can be restored?

There are no right answers. It seems that no two direct modeling systems handle the decision of what is a “sensible” edit in the same way.

While direct modeling absolutely solves the model brittleness problem inherent with parametrics, it does it by simply not using parametrics. Even with hybrid parametric/direct CAD systems, the answer to the parametric curse is still to not use parametrics when you don’t need to.

The solution of “use direct modeling when you can, and learn to live with parametric hassles when you can’t” just isn’t very satisfying to me.

Next: Going horizontal

The failed promise of parametric CAD part 2: The problem is editing

June 25, 2013 By Evan Yares 4 Comments

In the previous post, I wrote about the failed promise of parametric CAD: problems such as parent-child dependencies and unwanted feature interactions, coupled with no easy way to either prevent, or check for them.

The difference between modeling and editing in a parametric CAD system is simply the difference between creating things from scratch, and modifying things you’ve already created. The distinction may seem academic, but it is only when editing that parent-child dependencies are a potential problem.

Consider a scenario, of creating a parametric part—one that you’ve worked out in your head pretty well ahead of time—where you start from scratch, modeling sequentially, and spending all your time working on the most recent feature without needing to go back to edit upstream features.

In that context, the model’s parent-child dependencies would exist, but would be benign. They’d never get in your way. That is, until you went back to edit the part.

In most cases, people don’t build models from scratch without periodically going back to adjust earlier features from time to time. In that process, they’ll catch, and be able to deal with, some of the dependencies. But not likely all, or even most, of them.

I’ve heard experienced CAD people use an interesting term for models with hidden and untested parent-child dependencies: Parts from hell. When you’re trying to modify them, you never know when a small change might cause them to completely fall apart. I think a better, more descriptive, term is brittle: Hard, but liable to break or shatter easily.

This also suggests a descriptive term for CAD models which are not liable to break or shatter easily: resilient.

I’ve only ever seen one group of users who could consistently create complex yet resilient parametric parts models from scratch: PTC application engineers from the early to mid-1990s. Of course, they could only do it during customer benchmarks, with parts they’d practiced ahead of time, where they had worked-out and memorized all the steps, and where they had a good idea of the parameter ranges. Even then, if you were to ask them to change a dimension that would cause a topological change, the models might unceremoniously blow up.

Not to paint too bleak a picture, there are certainly CAD power users who have the skills to create resilient CAD models. I’ve met more than a few of them: true professionals, who by combining experience, insight, and education, have earned the respect of their peers. They understand how to structure CAD models to avoid any problems with brittleness.

Nah. I’m just messing with you. Power users struggle with this just like us mere mortals. It’s just that their models don’t usually fall apart until you go outside the scope of parametric changes they had anticipated. Give power user’s carefully crafted CAD model to a user who has a black thumb (I’m sure someone comes to mind), and they’ll find ways to blow it up that the power user never imagined.

Next: The direct solution

The failed promise of parametric CAD part 1: From the beginning

June 25, 2013 By Evan Yares 28 Comments

The modern era of 3D CAD was born in September 1987, when Deere & Company bought the first two seats of Pro/Engineer, from the still new Parametric Technology Corporation. A couple of years later, Deere’s Jack Wiley was quoted in the Anderson Report, saying:

“Pro/ENGINEER is the best example I have seen to date of how solid modelers ought to work. The strength of the product is its mechanical features coupled with dimensional adjustability. The benefit of this combination is a much friendlier user interface plus an intelligent geometric database.”

According to Sam Geisberg, the founder of PTC:

“The goal is to create a system that would be flexible enough to encourage the engineer to easily consider a variety of designs. And the cost of making design changes ought to be as close to zero as possible. In addition, the traditional CAD/CAM software of the time unrealistically restricted low-cost changes to only the very front end of the design-engineering process.”

To say Pro/E was a success would be a terrible understatement. Within a few years PTC was winning major accounts from the old-line competitors. In 1992, on the strength of its product, PTC walked away with a 2,000 seat order from Caterpillar that Unigraphics had thought was in the bag.

The secret to Pro/E’s success was its parametric feature-based solid modeling approach to building 3D models. To companies such as Deere and Caterpillar, it offered a compelling vision. Imagine being able to build a virtual CAD model of an engine, and, by changing a few parameters, being able to alter its displacement, or even its number of cylinders. And even if that wasn’t achievable, it would be a great leap forward to just be able to rapidly create and explore design alternatives for parts and assemblies.

Yet, things were not that easy. In 1990, Steve Wolfe, one of the CAD industry’s most insightful observers, pointed out that Pro/E was incapable of making some seemingly simple parametric changes.

Pro/Engineer placed limits on the range of parameters. (A designer could not increase the dimension of L2 to point that L3 vanished.)

David Weisberg, editor of the Engineering Automation Report (and from whose book, The Engineering Design Revolution, I have liberally cribbed for this article), pointed out the fundamental problem with parametrics:

“The problem with a pure parametric design technique that is based upon regenerating the model from its history tree is that, as geometry is added, it is dependent upon geometry created earlier. This methodology has been described as a parent/child relationship, except that it can be many levels deep. If a parent level element is deleted or changed in certain ways it can have unexpected effects on child-level elements. In extreme cases (and sometimes in cases that were not particularly that extreme), the user was forced to totally recreate the model… Some people described designing with Pro/ENGINEER to be more similar to programming than to conventional engineering design.”

Weisberg barely scratches the surface of the issues that can create problems.

In 1991, Dr. Jami Shah wrote an Assessment of Features Technology, for Computer-Aided Design, a journal targeted to people doing research in the field of CAD. He identified that there were problems with features:

“There are no universally applicable methods for checking the validity of features. It is up to the person defining a feature to specify what is valid or invalid for a given feature. Typical checks that need to be done are: compatibility of parent/dependent features, limits on dimension, and inadvertent interference with other features. In a study for CAM-I, Shah et al. enumerated the following types of feature interactions:

interaction that makes a feature nonfunctional,
non-generic feature(s) obtained from two or more generic ones,
feature parameters rendered obsolete,
nonstandard topology,
feature deleted by subtraction of larger feature,
feature deleted by addition of larger feature.
open feature becomes closed,
inadvertent interactions from modifications.”

The important thing to notice here is that, not only are there multiple failure modes for features, there are also no universal methods for validating features. It’s left up to the user to figure out. And that process, as Weisberg hinted, is much too difficult.

Since the early days of Pro/E, a lot of work has been done, both by PTC and other companies in the CAD industry, to improve the reliability and usability of parametric feature-based CAD software. Yet, the problems that Weisberg and Shah identified still exist, and still get in the way of users being able to get the most from their software.

Next: The problem is editing.

Creo

Debating the Most Efficient Way to Go from Concept to Documentation

The Role of Associativity in Direct Modeling

Preparing Models for Simulation: Which 3D Modeling Paradigm is Best?

The Challenges of Model Editing in the Multi-CAD World

The failed promise of parametric CAD, final chapter: A viable solution

The failed promise of parametric CAD part 5: A resilient modeling strategy

The failed promise of parametric CAD part 4: Going horizontal

The failed promise of parametric CAD part 3: The direct solution

The failed promise of parametric CAD part 2: The problem is editing

The failed promise of parametric CAD part 1: From the beginning

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