Programming and Processing of Drawing Dies for Outer Covers

In the context of mold manufacturing, the selection of appropriate processing methods and the development of efficient numerical control (NC) programming play a critical role in enhancing product quality, reducing production time, and lowering overall costs. These factors are especially important when it comes to automotive exterior cover molds, which directly influence the aesthetic quality of the final vehicle. Ensuring precision and consistency through optimized programming and machining techniques remains a key challenge in the continuous improvement of mold design and production. Automotive exterior cover molds consist of various components such as side walls, doors, fenders, hoods, roofs, trunks, and more. Among these, the overall side wall mold is particularly complex due to its intricate geometry and high demands on accuracy. This paper focuses on the overall side wall drawing die as a case study, exploring the best practices for selecting programming methods and machining strategies. **Overall Programming Strategy** For rough machining of large drawing dies, the primary goal is to remove the maximum amount of material in the shortest possible time, provided that cutting conditions allow. The choice of NC programming parametersâ€”such as tool path strategy, spindle speed, feed rate, step-over, and depth of cutâ€”plays a crucial role in balancing efficiency and cost. Proper planning of roughing operations, based on past experience with smaller, complex molds, can significantly improve both productivity and tool life. During semi-finishing, the focus shifts to maintaining surface integrity without leaving visible tool marks. While this phase allows for greater flexibility in partitioning, itâ€™s essential to ensure that residual material is minimized to avoid complications during the finishing stage. Different tool path algorithms may lead to varying levels of leftover material, requiring careful planning of supplementary programs if necessary. Finishing operations have a direct impact on the final surface quality of the mold and, consequently, the quality of the produced parts. It is advisable to invest more time in the early stages of programming to ensure surface accuracy and avoid costly post-processing by fitters. This proactive approach not only improves quality but also reduces rework and delays. **Analysis of Die Structure and Machining Process** Figure 1 shows the physical structure of an integral side wall punch. Before any machining begins, it's essential to verify digital and physical coordinate systems, material thickness, directional orientation, and surrounding part information. Errors in these areas can lead to significant losses and must be carefully avoided. Data transfer between different software platforms like CATIA and DELCAM can sometimes result in inaccuracies such as gaps, overlaps, or unwanted scraps. While these issues may not affect general molds significantly, they can have a major impact on the surface quality of outer cover drawing dies. Therefore, thorough inspection and targeted corrections are necessary before proceeding with the NC program. **Roughing Procedure Preparation** Given the large surface area of the overall side wall drawing die, using a rigid CNC machine with large-diameter tools is more economical and efficient. In China, due to limitations in casting blank quality and uncertainty in unbalanced blanks, it's still common practice to use D50mm or D40mm ball-end tools for rough machining in different areas. This method remains cost-effective in real-world production settings. **Contour Roughing Program** The contour roughing process involves removing material along the edge of the workpiece. However, improper tool paths can lead to excessive wear or even tool breakage. To prevent this, test runs should be performed before full-scale roughing. The contour must be processed first, followed by finish machining, to ensure safe and effective operation. **Local Processing and Contour Roughing** Steep surfaces around the punch are typically handled using contour roughing, but some flat areas require localized processing. If local processing is skipped, the cutting load can increase abruptly, leading to potential errors in parallelism or three-dimensional offset programming. These steps are essential for ensuring consistent tool performance and minimizing machining risks. **Three-Dimensional Offset Roughing** This method is used for steep areas where layer-by-layer machining is not feasible. Although it reduces the number of tool lifts, it may result in uneven machining heights. Careful verification of tool paths is necessary to avoid unexpected collisions or tool damage. **Parallel Roughing** After completing the steep areas, the top flat surface can be processed using a parallel roughing strategy. The flat area is divided into multiple layers, allowing for efficient material removal and better control over tool engagement. **Semi-Finishing Program Preparation** Clearing the root before semi-finishing is essential to avoid interference. The length of the tool determines the extent of the clear root program, and collision checks must be performed. Multiple passes with different tool sizes are often required to achieve the desired surface finish. **Finishing Program Compilation** The finishing process involves fine-tuning the surface using smaller tools like D16 and D10 ball-end cutters. Adjustments for tool wear and sharpness are crucial to prevent overcutting. The finishing tool path must be carefully planned to maintain accuracy and avoid damage to the mold surface. **Partitioned Machining** To maximize efficiency and reduce tool wear, it's beneficial to divide the machining process into different zones. Each area can be processed using the most suitable method, whether it's three-dimensional offset, spiral roughing, or standard milling. This approach ensures optimal performance across all sections of the mold. **Conclusion** The automotive exterior cover mold plays a vital role in determining the final appearance of the vehicle. By applying scientific machining methods and optimizing NC programming, manufacturers can enhance mold quality, reduce production cycles, and lower overall costs. Attention to detail in roughing, semi-finishing, and finishing stages, along with proper partitioning and tool selection, is essential for achieving high-quality results efficiently.

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Suzhou Johnson Automation Technology Co., Ltd. , https://www.cn-johnson.com