At the COExperience conference, Philip Vaughan’s session “Semantics: Annotating a 3D Model Is Still Drafting” was a hit. The presentation discussed the similarities and differences between conventional 2D style and the 3D Model-Based Definition (MBD) style with respect to the actual “drafting” effort. Whether you attended the conference or are interested in the topic, discover his answers to commonly asked questions in this article.
Q: Do 2D Drafting rules drive the 3D MBD annotation requirements?
A: Yes.
The ASME Y14 family of Engineering Drawing Standards applies to both the traditional 2D drafting style but also the current 3D MBD style. In fact, most of the standards have been updated to include both methodologies. The Model-Based annotation style is of course limited by the CAD software abilities and functionality, but the base rules are the same. There are some differences in how the dimensional annotations are expressed in the respective drawings, and that is the “style.”
Q: Is there a quick reference for the differences in 2D and 3D dimensioning styles within the ASME Y14 standards?
A: No, there is not.
In the Y14.5 and other Y14 standards, there are examples of how the dimensions are placed and how they appear. Depending on the specific CAD system and the units used (METRIC or U.S. customary INCH) the differences can be slight. The Y14.41 standard does have several preferred methods explained with corresponding examples. The CAD support team within the respective company should develop the preferences according to the Y14 standards and their specific company requirements. There should also be a document for the consumers of the data so they can understand and discern the differences.
Q: Is the use of semantic annotations a requirement for using 3D MBD?
A1: No.
Semantic annotations occur with the application of utilizing the 3D tolerancing and annotation (3D T&A) application within the 3DX environment, as well as the functional tolerancing and annotation (FT&A) workbench in earlier versions of CATIA. The 2D drafting workbench/application does not have the capability of making semantic annotations. That stated, the semantic and non-semantic annotation methods are both capable in the respective 3D T&A and the FT&A annotation tool sets.
A2: Yes.
The need for semantic annotations is a different topic, where the trend is to make the most possible use out of the model as possible. If the 3D model contains all the engineering elements to define the item, why not extract those elements directly to a machine-code-readable capable manufacturing tools or quality verification tools? That is what semantics is meant to be used for, as well as planning, procurement, assembly, and service. Basically, everything along the digital thread of the Model-based enterprise (MBE).
Q: Can you explain simplified drawing?
A: Elements of the simplified drawings began during the 2D-drawing era. Certain notes and dimensional applications were written into rules so that the drafter did not have to add those details on the drawing. According to the ASME Y14.100 and Y14.41standards, a simplified drawing can be either 2D or 3D. The goal of the simplified drawing is to make the drawing cleaner and not as overburdened with detail. The simplified drawing requires all the tolerances applied with enough views to define the item. The simplified drawing does not have to include all the BASIC dimensions and can exclude views of the item that do not add any clarity to the definition. A simplified drawing can be either in 2D or 3D form, but there is a 3D model which remains as the engineering authoritative data. The 3D model is BASIC unless there is a dimension shown on the drawing (2D or 3D) with a +/- or limit tolerance. Since the model is BASIC, the drawing does not have to show those dimensions and the BASIC dimensional data is obtained (interrogated) from the model.
An example: The detailed 2D drawing of the item is fully detailed with all the views and every dimension shown. The quality assurance groups have claimed there are too many dimensions and want to know what is critical. Engineering will respond with “everything should be validated.” But the BASIC dimensions are not actually part of the inspection report, they are checked to verify the location of a tolerance zone but are not actually recorded. So, engineering removes all the BASIC dimensions leaving a drawing with all the requirements shown. That is a simplified drawing. One step further, convert the +/- or limit tolerances to a profile tolerance and then leave the dimension off the drawing, because it is now BASIC. To make this legal, add a note to the drawing stating that BASIC dimensions are to be obtained from the 3D CAD model
Q: How is 3D MBD consumed when there is not a tangible paper drawing?
A: The 3D MBD relies on the 3D CAD model to contain all the dimensional ranges and controls. There are a couple methods in which the data can be consumed and then “paper” versions can be created:
- The 3D model can be exported using the STEP export and then imported into the consumer used CAD system. The annotations within the model will be maintained if the STEP 242 Edition 2 is used for both the export and the import of the data. Since the various CAD systems structure the data within the model differently, the STEP protocols ensure that the data is structured in a manner that can be retrieved with minimal data loss. The STEP file is a derivative of the native CAD file, but it can be verified as a source file. The data can then be exported to print via different methods.
- The 3D model can be output to a 3D PDF. The 3D PDF is a viewable file on the computer that allows rotating and zooming as well as other tools. The 3D PDF can also be formatting for printing which will show each capture on an individual printed sheet.
Q: Are the out of the box settings in CATIA ready for use?
A: No.
The default Presentation Standards consists of files for several standards: ANSI/ASME, ISO and JIS. The ANSI/ASME is a good start, but it is not fully compliant with the ASME Y14 standards. There are several inconsistent options and selections, so the Presentation Standard should be set up in accordance with the company standards and methods. Use the appropriate standard for guidance.
Q: How do you convince engineering departments that it is okay not to create 2D drawings?
A: Training and patience.
The specialized training is essential to get the engineers on board. But it also requires manufacturing, supply chain and quality to be trained. Consumers of the data in digital form is the largest obstacle, and engineers will often point to those. And in many cases the engineers are not wrong. Going to the 3D MBD methodology is a mindset change and all aspects must be prepared for it. One suggestion before launching a whole program on MBD: Pick a small project to work out the MBD details and processes.
The transition will have pains, so be patient as you work through them. There are many obstacles that will need to be worked out, but the main thing to remember is that the item definition is really the same, either a 2D drawing result or a 3D dataset result. The ASME Y14.41 and Y14.47 standards provide the rules and guidance to establish the complete MBD.
Q: What happened to drafters?
A: The drafter (a.k.a., draftsman or draftsperson) position, as a highly skilled member of the engineering team, has slowly been replaced with the smarter CAD packages. For a lot of companies, the drafter roles have been consumed by actual engineers. For some companies, the drafter position still exists but is labeled “designer.” The drafter as a profession is still around, but anybody who makes detailed drawings, 2D or 3D, is still a drafter.
Q: The non-compliances of the software with respect to the ASME standards sounds like a problem, can those items and the workarounds be shared with the COE community?
A: The CATIA 3DX compliance check with the ASME Y14.5 and other Y14.41 standards was done by Bell Textron Inc (Bell) to support Bell engineering efforts. That list is owned by Bell, but there will be service requests and enhancement requests issued to Dassault Systèmes for improvement. Hopefully, the solutions to those requests will end up benefiting all companies using the CATIA software. The workarounds could be shared through COE if there are certain agreements in place, otherwise the workarounds are also considered Bell content.
Q: Our company has talked about going to 3D MBD. What are the main risks and obstacles?
A: The main risk is the data consumption. The 3D MBD is a mindset change when it comes to the item definition.
The 3D mindset change can be an obstacle for a lot of the consumers of the data. But remember that you are still providing the same information as a detailed 2D drawing but in another format. The various CAD programs have been around for 40 years. When the drafting tables were replaced with the CAD stations, there was the same concern. But then the 2D CAD method progressed to 3D wireframe to 3D solid and has dramatically increased in sophistication over the years. MBD is not exactly new either. The Y14.41 standard, which drives the 3D MBD, was released in 2003, after several years of development. Some companies have been using 3D MBD for over 20 years and will never go back to the 2D Drawing methodology.
Another thing to consider is the knowledge base and the respective policies within the company. Having a dedicated “owner” of the policies and procedures to ensure compliance to the ASME Y14 standards is essential to establish and maintain the MBD implementation.
Note: For 3D MBD to be successful, invoke the ASME Y14.41standard in your company. The Y14.41 standard contains the MBD rules and the classification codes. The other Y14 standards provide specific guidance for successful 3D MBD and drawings in general and should be implemented as well.
Note: If your company is fully new to MBD, there are several agencies that provide training and guidance for MBD implementation.
A drafter at heart, Phillip Vaughan has spent 40 plus years in the design and engineering world, including architecture and architectural systems, oilfield drilling and service equipment, offshore oil drilling systems, heavy construction vehicles, military trucks and vertical flight. He has worked in the capacity of drafter, designer, engineer, project lead, checker, checking supervisor, design manager and SME. He holds as associate degree in engineering design from Odessa College and dual degree in architecture and civil engineering from Texas Tech University. He is an ASME-certified geometric dimensioning & tolerancing professional - Sr (GDTP-Sr) since 2011 and is a voting member of seven ASME Y14 Committees, including Y14.41 - Digital Product Definition Data Practices. At Bell Flight, he is a staff engineer and associate technical fellow for the ASME Y14 standards, specifically GD&T and MBD, providing training, mentoring, guidance and policy management. He started drafting on the board in high school, moved to 2D CAD (AutoCAD and CivilSoft), then 3D Wireframe (CADKEY and ANVIL5000) and Solid modeling (Solid Works, Unigraphics, Pro/Engineer-Wildfire-CREO, Inventor and CATIA V6-3DX). When not working, he spends time camping and fishing.