In the automobile manufacturing process, it is common to implement two types of numbering systems on the vehicle body: the production serial number (also known as a flow number) and the vehicle identification code (VIN). The production serial number is an internal tracking system used by manufacturers to manage and organize production data. It is not regulated by any external standards and is typically unique to each company. On the other hand, the VIN is a mandatory national standard that must be applied to every vehicle. This standard includes specific technical requirements regarding the position, font size, and depth of the markings on the vehicle body.
To apply these numbers, various marking devices are commonly used, such as servo scribing, floating-point needle, rolling embossing, and stamping embossing systems. Among these, rolling and stamping embossing methods rely on pre-made dies or stamps. These techniques are less flexible and have limited adaptability in modern automotive production due to their rigid nature and inability to easily change the marked content. As a result, they are rarely used in current industry practices.
In contrast, floating-point needle and servo scribing systems offer greater flexibility. While both are controlled by numerical systems, the floating-point needle uses high-frequency vibration under pneumatic pressure, which can lead to uneven font thickness and impact damage on the backside of the workpiece. The pneumatic servo scribing method, however, allows for adjustable pressure, resulting in more uniform lettering and fewer burrs. This makes it particularly suitable for marking on different thicknesses of materials, which is why it has become widely adopted in the automotive industry.
This article focuses on the application of servo scribing marking devices specifically for VIN codes, providing insights and practical experience for reference within the industry.
**Principle of Servo Scribing**
The principle behind servo scribing is similar to the planing action of a planer. A typical servo scribing marking machine consists of an industrial computer, controller, marking head, and fixtures. During the engraving process, the marking head is clamped onto the workpiece, and the VIN information is input into the system either manually or automatically. Once the marking command is initiated, the marking needle is pressed against the surface using compressed air. At the same time, the servo motor controls the movement of the marking head along the X and Y axes, following the trajectory of the VIN code. This motion mimics the planing process, allowing precise and consistent engraving. After completion, the marking needle lifts and retracts from the workpiece, and the marking head returns to its original position, ready for the next cycle.
**VIN Code Marking Process**
There are two main approaches to marking VIN codes: before painting (in the welding shop) and after painting (in the assembly shop). Traditionally, VINs were engraved after painting, but this often resulted in paint damage and required additional anti-rust treatments. Moreover, clamping mechanisms could cause scratches on the workpiece. To address these issues, many manufacturers now prefer to engrave directly on sheet metal parts before painting. This approach ensures better rust resistance and avoids damaging the paint layer, though it requires deeper engraving.
**Analysis of Factors Affecting Quality Defects**
Several factors can influence the quality of VIN code marking, including equipment performance, fixture design, environmental conditions, product structure, and operational procedures. Issues such as font deformation, inconsistent shading, and excessive burrs can occur, leading to rework and reduced efficiency.
To improve consistency and reliability, manufacturers have implemented various solutions. These include upgrading the marking head transmission mechanism, improving the needle cavity structure, selecting appropriate scribe needles based on material properties, and optimizing fixture design to ensure accurate positioning and secure clamping.
**Impact of Device Ontology**
The choice of marking device depends on whether the VIN is engraved before or after painting. For post-painting applications, the focus is on protecting the paint surface, requiring lower scribing force and less clamping pressure. However, when engraving on bare sheet metal, deeper marking and stronger clamping are necessary. This has led to the development of more robust marking heads with improved transmission systems, such as dual-rail screw mechanisms, to enhance stability and reduce vibration.
**Fixture Design Considerations**
Fixtures play a critical role in ensuring accurate and stable marking. They must allow for easy operation, provide reliable clamping without damaging the workpiece, and maintain sufficient strength and rigidity. Poor fixture design can lead to misalignment, distortion, and uneven marking quality.
**Environmental and Operational Influences**
External electromagnetic interference and unstable air pressure can significantly affect the performance of servo systems. Proper power supply isolation, noise filtering, and pressure regulation are essential to maintain consistent marking quality. Additionally, the structural design of the sheet metal part—such as flatness, positioning holes, and overall shape—must be carefully considered to ensure optimal marking results.
**Process Optimization**
Traditionally, VIN marking was done during the final assembly stage, which posed challenges due to space constraints and difficulty in clamping. Modern practices have shifted toward single-piece marking, where tools are designed to accommodate a wide range of shapes and sizes, improving efficiency and reducing defects. This approach also allows for easier rework and higher first-pass yield.
**Conclusion**
As the automotive industry continues to evolve, the demand for high-quality, consistent VIN marking is increasing. By analyzing and addressing the key factors that influence marking quality, manufacturers can enhance their production processes and meet stricter quality standards. This article aims to share practical insights and experiences to support continuous improvement in automotive manufacturing planning and execution.
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