Thursday, May 28, 2009

Direct Editing in History-Based CAD

In a recent post by Deelip Menezes titled “Direct Editing and Direct Modeling” Deelip brings up the fact that within the context of history-based modeling, this term can refer to two different things. He notes that in a typical history-based system like Alibre, a direct edit to geometry will result in a new “Move Face” feature that will be added and ordered into the tree. He then notes that in SolidWorks using the Instant3D functionality, the edit is not recorded into the tree. The two technologies referred to here are very different as I will explain below. Unfortunately they are both often referred to as “Direct Editing”. You can access his article by clicking on the link to his blog under “My Blog List”.

As I mentioned above, in the context of history-based modeling, the term “direct editing” is used to describe two completely different things:

1) Some history-based CAD systems (almost all of them now) have at least one or two functions that will allow a user to directly manipulate geometry – at the geometry level. When this manipulation is done within a history-based model the system must track the edit in the tree otherwise the next time the model is regenerated, the edit will be lost. This type of editing is great for parts in which the history tree has become unmanageable or overly complex and you just need to make a quick change, or when you are working with imported geometry. Direct manipulation of a B-Rep solid is not a trivial thing and many of these history-based systems don’t have the capabilities to solve complex topology problems. As such much of this capability can be very limited. This technology is the heart and soul of history-free direct-modeling CAD. A history-free CAD tool must be very good at solving topology problems, whereas a history-based system relies more on the tree.

2) Some history-based CAD systems provide the capability of dynamically manipulating parameters. Such is the case with SolidWorks and their Instant3D capability. This edit graphically appears to be a direct edit as defined in #1 above. In reality it is very different. There is no new “move” feature added to the tree, only existing parameters that are being dynamically edited. This method simply provides instant feedback of the parameter edit rather than waiting for a model regeneration. It requires that a parameter exist in the model. As such it may not always work, based on how the model was created in the first place, and as with any history-based edit it can impact child features. It also may not work for imported data. This is not new technology. IronCAD has been using it ever since it came into existence many years ago. We will certainly see much more of this technology in history-based CAD. Just to be clear, in history-free direct-modeling, you can also dynamically manipulate parameters, it’s just that the parameters are not history-based.

As I have mentioned before, there are really only two fundamental technologies used in mechanical “solid modeling” CAD today; 1=history-based (CSG+B-Rep hybrid) or 2=history-free (B-Rep). Direct geometry editing and dynamic parameter editing (or whatever we want to call it) can be available in both. It’s just a matter of how the geometry is managed; with history or without. They both have their pros and cons and each can greatly impact the design process.


Wednesday, May 27, 2009

A Fun Project

My wife says I have way too many hobbies. She’s wrong of course. One of the “few” hobbies that I enjoy is building and flying RC airplanes. I am now flying the so called “giant scale” airplanes. My most recent airplane is a 1/3 scale model of an Extra 330 aerobatic airplane. The wing span is 102” and it is powered with a two cylinder 100cc 2 stroke engine.

Prior to the 100cc plane I was flying a 50cc Extra300.

A while back I had the unfortunate experience of disassembling this plane during a fairly hard landing. The landing really wasn’t all that hard, it was just that in the months leading up to this incident I had been making good progress in removing much weight from the airframe in trying to improve its performance. Unfortunately my weight reduction efforts eventually led to some compromises in the integrity of the airframe to the point that… well you know.

I could have purchased a replacement fuselage and had the plane flying again, but I decided to see if I could rebuild it. A friend had the same fuselage that I could use to measure parts, another offered to make the parts for me on his CNC router, so I decided to give it a try.

I spent a few hours measuring parts and sketching them out on paper. I then modeled all of the parts in 3D using CoCreate. As the assembly came together I adjusted the models as needed to get a good fit.

With the 3D models created and fit together, the necessary data was sent to the router to get the parts manufactured.

These parts fit together so well that they actually held together without glue. After spending some time cleaning up the old fuselage, the new assembly was fitted into what was left of the originally fuselage. With some glue and clamps the fuselage was as good as new.

The plane is now in great flying condition and I still enjoy flying it. I think I will just leave the weight alone this time. It is safe to say that had I used my 2D sketches and 2D drawings to manufacture the parts I would have had to correct a few mistakes and even make some of the parts over. With 3D models the parts were perfect, the first time.


Monday, May 18, 2009

Model Based Definition (MBD) – What’s the Hold-Up?

Recently I have been talking with several companies about the possibility of reducing their dependency on fully detailed drawings. In a recent post titled “The Maturity Curve of Product Development” I used the following chart to show the different stages that companies go through as they learn to leverage their electronic CAD data deeper and broader into the product development process.

Model Based Definition (MBD) is a term used to describe the addition of information to the 3D model such that the model can represent the complete definition of parts and assemblies. For most companies, this complete definition is usually developed and managed in the 2D drawing and other related documents. At its fullest extent, model based definition can make it possible to reduce and even eliminate the need for 2D drawings.
Recently, Matt Lombard at asked if any of his readers were using the 3D CAD Standards that are laid out in the ASME Y14.41 standard. This standard basically defines how 3D models are to be documented and annotated to fully represent the complete definition. So far he has not received too many responses, and no response that indicates the use of this standard and MBD.
Much time goes into creating fully detailed drawings. They can be expensive to create and manage. They can be easily misinterpreted. If developed from a 3D model, there is much duplication of effort. With duplication of effort comes a higher potential for error. Drawings can quickly become detached or unrelated to the 3D model. Once printed, they can become even more detached from the 3D model, and the opportunity for error increases. So, what’s the holdup?

Example from ASME Y14.41

Same part annotated in CoCreate Modeling
I have read a few success stories about MBD, but I have yet to witness one. As engineers at Hewlett Packard, we were successful with reduced content drawings, but we never made it to a “drawing-less”, or MBD process. There have been many claims to successful MBD in aerospace, automotive, and high tech electronics. I have visited many of these companies and am still looking for some good examples. I have seen some small examples from some progressive individuals or even small groups that have been able to push forward with MBD to some extent, but nothing that encompasses the complete product lifecycle. Maybe I just haven’t visited the right places.
What does it take to move to a model based definition? The technology exists. Most all modern 3D CAD tools have some capability for MBD. Some are better than others. Several free viewers are also available to read and view these annotated parts and assemblies. I would love to hear from some of the readers.  What are the challenges you would face, or are facing?

Same part viewed in eDrawings

Same part viewed in 3D PDF
As I stated in the post regarding the maturity curve, making the move up the curve will be an evolutionary move – one step at a time. First, you need to understand where, when and why part and assembly definitions exist in printed form. I see a significant use of computers on the shop floor, in manufacturing and assembly. It’s even becoming common to see 3D representations of parts and assemblies on the monitors. But it’s equally common to see a printed 2D drawing lying on the workbench next to the monitor.
As we continue to move to 3D based product design and manufacturing, the development and management of drawings will become a duplication of resources and effort, effort that we may not be able to afford much longer.
Here are some challenges to MBD that people have shared with me.
  • The culture chasm, it’s a giant leap
  • Quality management/inspection
  • Compliance with industry specific regulations
  • Our suppliers, partners
  • Cost & disruption vs. value
  • Inadequate tools/technology
I recently needed to make a part on the lathe in my garage that I first designed in 3D. I didn’t take my laptop with me; I took a printed drawing – hum…


I recently published another article on MBD that can be found here. It perhaps provides a more broad perspective on what MBD can be.