Performing action...
Performing action...
Robert Farrell
August 2002
Defining product data "Interoperability" is not difficult. Most would agree that true interoperability exists when product data can be created once, shared freely throughout product development applications, and be accessible whenever needed. While defining interoperability is relatively easy, achieving it has become an absolute nightmare. Interoperability takes on a whole new sense of urgency depending on one's position in the product development cycle. Upstream (those who create CAD models) and downstream (those who receive CAD models) software users often do not see eye to eye in terms of just how severe and wide the product data interoperability gap has become. Fortunately today technology has emerged allowing users to achieve true interoperability regardless of their role and position in the product development cycle.
The Interoperability Gap
International TechneGroup Incorporated (ITI) met with representatives throughout industry to get a feel for the magnitude of today's product data interoperability problem. It was found that up to 70% of the man-hours spent during Finite Element Analysis and Simulation were wasted with the non-value-added task of reworking or recreating CAD models before analysis could begin. In addition, other downstream applications such as Rapid Prototyping, Numerical Control tool path generation, and Product Data Exchange functions were likewise spending 20-50% of their time reworking CAD files.
These findings are further backed up by studies from the automotive industry that identifies "Interoperability Issues" as the number one obstacle facing industry today. Independent studies by such industry consortiums and analysts such as NIST, Daratech, and D.H. Brown further back up these findings. In fact NIST has concluded that the automotive industry alone wastes over a billion dollars each year due to product data interoperability problems.
It is easy to see how time and money wasted reworking problem CAD files contributes to the rising costs and increased design cycle times of products today. But what are the causes of interoperability problems and what steps can be taken to improve the process?
Upstream: Model Quality is the Key
In many cases interoperability success is determined before the model is even released from design. A quality, geometrically valid CAD model is more likely to flow smoothly downstream. Regardless of cost or the vendor who developed it every CAD system in use today is susceptible to producing files that cannot be manufactured, analyzed or readily exchanged. At the same time, even the most experienced designer can occasionally create models containing hidden errors or anomalies. Often these problems do not surface until well downstream of design presenting more than just minor inconveniences for those who receive them. CAD model problems can bring product development processes to a grinding halt as the user receiving the model must find the problem (Is with problem with the model or a result of the data exchange process?) and corrections are made. When you consider that the downstream processes (analysis, rapid prototyping, CNC, etc.) generally occurring concurrently and independently using different versions of the same original file, you can see the compounded magnitude of the problem.
Types of Model Quality Problems
Model quality problems can be generally categorized into three areas: Structure,
Accuracy, and Realism.
Structure
Structural problems include loop orientation inconsistencies, missing geometry and self-intersecting geometry among others. Structural errors violate the solid modeling application's own rules for what constitutes a correct model. Structural errors can also cause modeling programs to crash without warning. Often this can occur some time after the actual error has been made. Structural errors can cause programs for finite element mesh generation, numerically controlled toolpath generation, and intersystem translation software to behave unpredictably.
Accuracy
Accuracy requirements place limits on gaps between geometric entities such as vertices, edges, and faces that are adjacent. They can also limit the minimum sizes of trimmed entities such as edges, faces, and regions. Non-trivial gaps occur because intersections of curves between non-planar surfaces are approximated in most solid modelers. Approximations are used when the precise intersection between two geometric entities (faces, curves of intersection, vertices where intersection curves meet) is too complex to compute exactly. Solid modelers use different tolerances to compute the maximum deviation allowed between topological entities. If the deviations between entities are too large, toolpath and finite element mesh generation programs can fail. They can uncover gaps in geometry that are too small to be seen in shaded or hidden line images of a model. The translation between programs can also fail if the maximum allowable tolerances between surfaces and edges in the exporting program are larger than those of the importing program.
All CAD modeling systems must balance the accuracy (precision) of models with the amount of geometric information required to define them. Extremely precise models require complex and large data structures to define them. In general, the smaller the gaps, the smaller edges and faces may become in complex models.
Realism
Realism errors can render a part non-manufacturable due to physical limitations. Realism errors include transition cracks and sliver faces. Transition cracks in solid models, like physical cracks in engineering materials, are nearly invisible gaps between features of a model. Like physical cracks, they may not extend completely through the object. Slivers are small, elongated faces that are generated by the system to patch between larger surfaces in a model.
Additional restrictions on the realism of model features are added by many concurrent engineering applications such as FEM, NC toolpath generation, and rapid prototyping. For example, these tools are very sensitive to unrealistic features such as sliver faces, minute edges, and very acute angles between edges at a vertex.
Downstream: Fighting the "Bad CAD" War
Downstream CAD model users involved in manufacturing, injection molding, CNC programming, analysis, rapid prototyping, and so on, are on the front lines of today's "Bad CAD War". These organizations are often caught directly between delivery deadlines and the inability to successfully access customer/supplier CAD files. As a result, an inordinate amount of time is spent fixing or totally recreating CAD files. To accommodate key customers, many manufacturers are forced to take drastic and costly measures. Since their CAD package of choice may not readily accept files from many of their customer's systems, they invest in additional CAD packages to accommodate native CAD data transfers. These CAD packages are used to translate the incoming customer data into an acceptable IGES file that can be imported into their primary CAD package. This is a very expensive solution. Obviously the best scenario is to find a way to make files work allowing manufacturers to pick and choose the software system that meets their requirements --- not those of their largest customer.
Some common causes of data exchange problems stem from:
Overcoming Interoperability Problems
No matter where you are in the product development process you can significantly impact data interoperability. Designers and other upstream software users can have a tremendous impact on improving CAD model usage through Model Quality Testing. By implementing CAD model quality testing, upstream designers can build interoperability and quality into the model as it is being designed. This ensures more effective use of the model downstream.
CADIQ� is an Interoperability testing software tool allowing designers to isolate and then correct design quality problems. Organizations throughout automotive, aerospace, consumer products industries, and more are utilizing CAD/IQ to design interoperability into products.
Until now the downstream user has been pretty much at the mercy of the quality of the file he has received. Receiving models from those implementing model quality testing will go a long way in improving successful use of the models downstream. Still there are times when a particular IGES file may not be imported into the in-house system (this may lie in part with data exchange errors). In these cases the user can turn to geometry repair or healing software such as CADfix�.
CADfix is a software tool designed for the downstream user of the model. The software analyzes the data and highlights problem areas. These problems may be corrected automatically in many instances or fixed manually. Just as important the software allows users to import one type of file, IGES for example, repair the model and output a Parasolid, ACIS, ANSYS, STL, STEP, or other type of file. This feature is extremely valuable for downstream organizations working with a variety of customers / suppliers and software packages.
CADfix offers these users the ability to "heal" and repair these models to the extent that they can use them in their own internal systems -- whether its getting rid of duplicate points/edges or "tightening" up a series of surfaces so that they can be stitched into a solid.
Conclusion
From early design stages through production, interoperability problems can surface throughout the product development process. Fortunately there are steps the average user can take to overcome product data interoperability problems. Methods to improve data interoperability include:
For more information call 513-576-3900 or visit www.iti-global.com.