CAD modeling technology and software system in reverse engineering

To meet the evolving demands of the market and adapt to the continuous advancement of manufacturing technologies, there is a growing need for reliable CAD data. This enables the effective utilization of advanced forming systems (RF), computer-aided manufacturing (CAM) systems, product data management (PDM), and other cutting-edge technologies. These tools help in managing, revising, and optimizing designs. As a result, a comprehensive solution is required: sample-data-product. This led to the emergence of reverse engineering, also known as reverse engineering (RE). Reverse engineering offers a new and highly efficient approach for reconstructing models in the manufacturing industry, enabling the direct conversion from physical objects to digital geometric models.

There are two main requirements driving the reverse engineering of physical objects. First, physical products represent the most common and extensive form of design outputs in the consumer market, making them ideal and accessible research subjects. Second, during the development and manufacturing process, even though computer-aided design (CAD) has been widely used, many products lack initial CAD models due to various reasons. This means that designers and manufacturers often have to work with physical samples instead.

In reverse engineering, the reconstruction of 3D CAD models involves using scattered point data from the surface of a product to create an approximate model through interpolation or fitting. This step is the most critical and complex part of the entire reverse engineering process, serving as the foundation for subsequent tasks like product manufacturing, rapid prototyping, engineering analysis, and redesign. With ongoing research into reverse engineering and CAD reconstruction theories, commercial applications have gained increasing attention, leading to the development of numerous reverse engineering CAD modeling software systems.

1. CAD Modeling Technology and Software System

3D CAD modeling of a product refers to the process of generating a corresponding CAD model from an existing physical object or part. It includes steps such as grid generation, feature extraction, surface slicing, and surface creation from discrete measurement points. The most critical aspect of the reverse engineering process is providing mathematical support for future engineering analysis, innovative design, and manufacturing applications. This field involves multiple disciplines, including computer science, image processing, graphics, computational geometry, measurement, and numerical control processing. It remains a key area of research both domestically and internationally, especially within CAD/CAM systems.

In real-world products, it's rare to find a single surface. Instead, products are typically composed of multiple surfaces combined in different ways. Therefore, the general steps for CAD model reconstruction include segmenting point cloud data based on geometric features, fitting each surface individually, and then connecting them through transitions, intersections, clipping, and rounding. This results in a complete reconstructed CAD model.

Surface modeling methods in free-form modeling are generally divided into two categories: one is based on triangular Bezier surfaces, and the other is based on NURBS (Non-Uniform Rational B-Spline) curves and surfaces. Each method has its own advantages and limitations.

Triangular Bezier surface fitting is flexible and adapts well to boundaries, making it suitable for complex shapes and irregular surfaces, such as human faces. However, the resulting curved surface may not conform to standard product descriptions and can be difficult to exchange with typical CAD/CAM systems. This requires conversion to NURBS surfaces, which can lead to data loss and errors. Additionally, this method lacks flexibility in modifying surfaces, limiting its practical use.

NURBS-based modeling, on the other hand, unifies analytical geometry with free-form curves and surfaces. It is now the dominant method in CAD/CAM software. NURBS surfaces can be used for interpolation, stretching, rotation, lofting, sweeping, blending, and four-boundary construction. However, they require tensor product data and are less effective for large-scale scattered data, limiting their use in certain cases.

As research in reverse engineering and CAD reconstruction deepens, the commercial application of these technologies has become more prominent, leading to the rise of numerous commercial reverse engineering CAD modeling systems. Today, there are dozens of software packages offering reverse modeling capabilities, broadly categorized into dedicated reverse software (such as Imageware, Geomagic, Polyworks, CopyCAD, ICEMSurf, and RE-Soft) and forward CAD/CAM software with reverse modules (like PTC’s Pro/Scan-tools or UG’s Point Cloud function).

Reverse engineering software typically uses NURBS or triangular domain surface modeling, offering strong point cloud processing capabilities but limited feature recognition and relying heavily on operator experience. While the surface fitting functions are good, they still fall short compared to advanced forward CAD/CAM software. Forward CAD/CAM software primarily uses B-spline or NURBS methods for surface modeling, with robust surface modeling capabilities. However, their point cloud processing functions are not as rich or powerful as those found in dedicated reverse engineering software.

Currently, CAD reconstruction in reverse engineering remains a highly specialized task. Choosing the right reverse modeling system depends on factors like the skill level of the team and the nature of the product. Modular software systems still hold significant practical value. Research comparing commercial reverse software focuses on basic operations, data processing, curve and surface fitting, editing, quality evaluation, and engineering analysis. Whether using dedicated reverse software or forward CAD/CAM software with reverse modules, current systems still lack universal efficiency in handling diverse reverse engineering needs. As a result, using specialized reverse modeling software integrated with forward CAD systems has become a popular approach.

2. Application Examples

In Imageware, the process of constructing a car surface model begins by using the point cloud data processing function to generate feature lines and segment the point cloud. Then, the facet function is used to build the final surface model based on the feature lines and segmented data.

3. Conclusion

CAD modeling in reverse engineering spans multiple research fields. Its theoretical and practical significance lies in enhancing the understanding of three-dimensional object recognition and improving engineering practices. Because of this, it has attracted substantial attention and investment from researchers worldwide. However, current studies are mostly focused on specific objects, data types, and modeling techniques, with limited cross-field communication. Challenges remain in handling complex topologies and unstructured data, and no universally applicable method exists yet.

Reverse engineering, particularly 3D model reconstruction, is still a highly professional task. In addition to understanding product features and manufacturing processes, operators must also be proficient in CAD software and reverse modeling tools, as well as familiar with upstream measurement equipment and the measurement process. This ensures a clear understanding of data structure and the requirements for the reconstructed model. Therefore, the quality of the model is still heavily influenced by the operator’s experience and skill level. Future developments should focus on increasing software intelligence and reducing dependency on manual input.

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