**Abstract:** Reverse engineering has become a widely used technique in the manufacturing industry. Utilizing reverse methods for mold design and production is a crucial approach to shorten the product development cycle, enhance product quality, and ultimately establish an independent design and manufacturing system. This paper outlines the reverse manufacturing process of the top cover mold for the LZ6460 passenger car and presents an example of generating a curved surface from point cloud data. **Keywords:** reverse engineering; CAD/CAM; mold; top cover **Introduction** In the product development and manufacturing process, geometric modeling technology plays a significant role. However, due to various factors, many products are not described by CAD models. Designers and manufacturers often face physical samples, making it necessary to convert these into CAD models using specific techniques. This allows them to leverage advanced technologies like CAD, CAM, RPM, and PDM for processing or managing the product. Currently, this method of obtaining mathematical models from physical prototypes has evolved into a distinct category within CAD/CAM, known as "Reverse Engineering." By reverse engineering real-world objects, it becomes possible to fully utilize modern manufacturing and management technologies during the design and production stages. Additionally, reverse engineering enables rapid replication of physical samples, making it a key foundation for concurrent engineering. **1. Traditional Design and Manufacturing Methods for Automotive Panel Molds** For self-designed models, covers were traditionally handmade by sculptors, leading to inevitable imperfections. Occasionally, copying parts were used directly for profiling, which transferred all defects from the sample to the mold. As a result, the final product inherited the flaws, leading to poor smoothness, low accuracy, and poor fit. Moreover, traditional mold-making methods involved extensive manual corrections, uneven gaps, repeated repairs, and unstable quality with long lead times. If CNC machines were used, wax testing was required to verify the tool path, further increasing the time and cost. The major drawback of traditional methods is that the resulting mold cavity lacks flexibility for modification or redesign. **2. CAD/CAM-Based Design and Manufacturing Methods** The integration of CAD/CAM technology is essential for modern mold design and manufacturing. It effectively addresses the shortcomings of traditional methods. A CAD model can directly generate NC commands and communicate with machine tools via DNC interfaces, replacing analog data transfer with digital communication. This streamlines the design and manufacturing process. In addition, CAD systems allow for appearance analysis, component assembly, interference checks, and NC machining simulation, enabling design modifications and reducing manual labor. This significantly shortens the new product development cycle and improves product quality. The application of CAD/CAM in the manufacture of the LZ6460 passenger car top cover mold results in a product with a smooth, symmetrical, and accurate appearance, offering convenience for future modifications and long-term use. **3. Reverse Design Method and Process** **3.1 Selection of CAD/CAM Software** Currently, there are several commercial CAD/CAM integrated systems with comprehensive functions. The author chose Delcam/Copycad for reverse design and processing. Key steps include: - Input and processing of digitized points, including data input and transformation. - Triangulation of the digital model based on user-defined tolerance for direct programming. - Using Imageware/Surfacer to generate NURBS surfaces. The system offers two main approaches: either directly generating surfaces from scan points without building curves first, or constructing peripheral curves before generating surfaces using boundary and internal scan points. This includes: - Scanning point analysis and processing, accepting data from different sources such as scanning machines or photogrammetry (ASC files). - Fast and accurate conversion of scanned points into NURBS surface models. - Surface model accuracy and quality analysis. - Real-time interactive modification of curves and surfaces. **3.2 Reverse Design Method** **3.2.1 Data Measurement** With the advancement of laser technology, non-contact measurement methods such as raster scanning, holography, depth image 3D measurement, and laser triangulation have been widely used. These methods overcome systematic errors from contact-based measurements, such as probe bar rigidity and compensation issues in coordinate measuring machines. This has elevated reverse engineering to a new level. Using the scanning function of a high-speed CNC milling machine, the top cover's surface is digitized, and probe compensation must be considered during measurement. Due to measurement errors, the resulting data undergoes processing, including removing dead pixels, handling blind zone data, homogenization, and smoothing. The top cover point cloud is shown in Figure 1. **3.2.2 Geometric Modeling** Geometric modeling is the core of reverse engineering. The modeling process involves data processing to extract key features of the input data. Common techniques include data adjustment, copying, trimming, density modification, smoothing, noise removal, and sharp corner retention. The quality of the model depends not only on how well it fits the physical shape but also on the smoothness of the surface and the continuity of its connections. Curve and surface smoothness should meet certain criteria, such as second-order continuity, absence of extra inflection points, and uniform curvature variation. There are two main modeling approaches: 1) Use Copycad software to generate triangular surfaces directly from the point cloud (STL model), then program NC machining. 2) Use Surfacer to generate a NURBS surface model from the point cloud for mold design and processing. **General Steps for Copycad Processing of LZ6460 Top Cover Scanning File:** 1) Load the ASC file and display the top cover scan. 2) Edit and delete redundant points. 3) Generate two-way scan lines. 4) Offset the model based on the probe radius. 5) Generate a triangular surface, as shown in Figure 2. After this, the triangular surface can be used directly for programming and machining. **General Steps for Generating Surfaces Using Surfacer:** 1) Read the ASC file, showing the point cloud of the door inner panel. 2) Draw the boundary of the surface. 3) Use the Fitw/CloudandCurves command to generate the surface and extend the trim. 4) Analyze and compare the generated surface with the original point cloud to obtain error conditions. 5) Export the surface to .igs or .vda format and edit in professional CAD software. After the surface is generated, mold design and programming can proceed. **4. Other Applications of Reverse Engineering** **4.1 Restoration of Damaged or Worn Parts** When parts are damaged or worn, CAD models can be reconstructed through reverse engineering to restore and repair them. Surface wear and damage may cause measurement errors, requiring the reverse engineering system to possess reasoning and judgment capabilities, such as symmetry, standard size, parallelism, and perpendicularity. Finally, the part is machined. **4.2 Digital Model Inspection** Scanning and measuring processed parts, then reconstructing a CAD model using reverse engineering allows comparison with the original CAD design to detect manufacturing errors and improve inspection accuracy. **5. Conclusion** The application of reverse engineering successfully completed the design and manufacturing of six molds for the LZ6460 passenger car's sunroof top cover and front sunroof reinforcement plate. The profile matching of the parts meets the requirements, and the design and manufacturing cycle was reduced from 6 months to 4 months.

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