CAD файлдарын аудару әдісі

Method of CAD drawing file translation
CAD data exchange is a method of drawing data exchange used to translate between different computer aided design (CAD) authoring systems or between CAD and other downstream CAx systems. Many companies use different CAD systems and exchange CAD data file format with suppliers, customers, and subcontractors. Since the 1980s, a range of different CAD technologies have emerged. They differ in their application aims, user interfaces, performance levels, and in data structures and data file formats. For interoperability purposes a requirement of accuracy in the data exchange process is of paramount importance and robust exchange mechanisms are needed.

Neutral file exchange uses an intermediary neutral format to translate data between CAD systems. This method starts from a pre processor embedded in the original CAD system, which generates the neutral file from the originating CAD format. The target CAD system post processes the neutral file and converts it into the target native format. Some neutral formats are defined by standards organizations such as IGES and STEP while others are proprietary but still widely used and are regarded as quasi industry standards. This format differs from other formats in that it only supports the communication of free form curve and surface data with associated comments, but no other geometric or non geometric entities. Therefore, it is limited to representations by parametric polynomials, but this covers the great majority of free form CAD systems. It includes Bézier, B Spline and Coons tensor product types of surfaces and corresponding curves. The VDA FS specification is released in the German Industrial Standard DIN 66301. PDES (Product Data Exchange Specification) Originated in 1988 under the Product Definition Data Interface (PDDI) study done by McDonnell Aircraft Corporation on behalf of the U. S. Air Force. PDES was designed to completely define a product for all applications over its expected life cycle, including geometry, topology, tolerances, relationships, attributes, and features necessary to completely define a part or assembly of parts. PDES can be viewed as an expansion of IGES where organizational and technological data have been added. In fact, the later PDES contained IGES. The development of PDES under the guidance of the IGES organization and in close collaboration with the International Organization for Standardization (ISO) led to the birth of STEP. Parasolid can represent wireframe, surface, solid, cellular and general non manifold models. It stores topological and geometric information defining the shape of models in transmitting files. These files have a published format so that applications can have access to Parasolid models without necessarily using the Parasolid kernel. Parasolid is capable of accepting data from other modeler formats. Its unique tolerant modeling functionality can accommodate and compensate for less accurate data. IGES (Initial Graphics Exchange Specification) An outdated format originated in late 1979 and initially published by the American National Standards Institute (ANSI) in 1980 preceding the large scale deployment of the CAD technology in the industry. This file format considers the product definition as a file of entities, with each entity being represented in an application independent format. These systems have their own proprietary intermediate format some of which will allow reviewing the data during translation. Some of these translators work stand alone while others require one or both of the CAD packages installed on the translation machine as they use code (APIs) from these systems to read/write the data. Some companies also use these low level toolkits to create import or export plug ins for other CAD applications.

Datakit CrossCad/Ware: SDK to read and write CAD formats.

Datakit CrossManager: Multi formats CAD translator. PolyTrans|CAD: Multi formats CAD translator. Transmagic: Multi formats CAD translator.

Datakit CrossCad/Plg: Import and export plug ins for Rhino, SOLIDWORKS,
PolyTrans|CAD: Import/export plug ins for 3ds Max, Maya, CADMATIC and Visual Components. Power translators: Import plug ins for 3dsMax.

Data quality can be addressed intrinsically and extrinsically. Intrinsic problems are those related to the CAD model’s structure before any translation process begins, while extrinsic problems relate to those issues appearing during translation. The development of STEP is the best solution to solve the extrinsic problems, extending its current capabilities to support 2 D parametric sections, 3 D parametric assemblies, and history based modeling. Product data quality is a key issue to avoid intrinsic data exchange problems and simplify the integration of downstream applications in the design chain. As each CAD system has its own method of describing geometry, both mathematically and structurally, there is always some loss of information when translating data from one CAD data format to another. One example is when the translation occurs between CAD systems using different geometric modeling kernels, in which the translation inconsistencies can lead to anomalies in the data. like loss of the original color of the parts, or incorrect position of bodies. This is no longer the case with modern standards like STEP AP242, which embeds Validation Properties. Validation Properties are key characteristics of the model (Center of Gravity of a solid, wet area of a surface, PMI characteristics or even check points on a shape), stored by the emitting system and checked by the receiving system. This allows to control the quality of the imported data. Quality of exchange using STEP is so important that regular benchmarks are run by independent associations (AFNeT, PDES, inc., ProSTEP iViP) to check exchanges between various CAD and PLM systems. Some CAD systems have functionalities to compare geometry of two models. So, user can compare the model before and after translation from one CAD to another one to estimate quality of the translation, and to fix found defects. But often such functionalities can compare only tessellations of two models. It is really hard algorithmic problem to compare topological elements of two 3D models and restore their associativity to show groups of modified faces, because there are very different representation of geometry data in different CAD systems, but sometimes it is possible. For instance, the component LEDAS Geometry Comparison based on C3D kernel can be integrated in CAD system (like Autodesk Inventor,) to compare 3D models and pinpoint all of the differences between them.

Two CAD/CAM/CAE PLM trends have been driving CAD Data Exchange technology. One is the need for close interaction throughout today’s extended multiCAD enterprises. The other is the increased reliance on digital mockups to permit visualization, design in context, simulation and analysis of large scale assemblies prior to the actual manufacture of the physical product. Ongoing advances in data exchange technology have enabled significant fulfillment of those needs. The ability to visualize medium if not large scale assemblies was one of the early successes of these CAD translation formats. Hardware improvements and the development of lightweight formats supported larger scale assemblies. Current advances now allow an “Active Mockup.” This technology allows design in context with simulations such as dynamic clearance analysis and automatic generation of motion envelopes. Active mockups allow the edit of components from directly within the multi CAD assembly. Multiple level of detail displays support interactive performance even in huge assemblies.

NC programming typically requires that the geometry received from a CAD system, whether in wireframe, surface, solid or combined formats, be free from any irregularities and inconsistencies that may have occurred in the CAD phase of geometry creation. Data exchange from CAD to CAM must therefore include tools for identifying and repairing those inconsistencies. These tools are typically included in the data exchange software of each CAM solution set. In a true PLM environment, CAD to CAM data exchange must provide for more than the transfer of geometry. Product Manufacturing Information, whether generated by the designer for use by manufacturing, or generated by the manufacturing organization for use by design, must be a part of the data exchange system. STEP NC was designed to carry GD&T and other PMI through CAD and CAM into a CNC.