In the development of rocket engines, the continuous increase in thrust and thrust-to-weight ratio demands components to withstand increasingly severe service environments. Turbine casings, as critical parts of these engines, feature complex structures and require highly precise dimensional inspections of their profiles. Traditional inspection methods for aerospace casting parts often suffer from low coverage of profile dimensions, inefficiency, and high manual labor intensity. Three-dimensional laser scanning (3DLS) has emerged as a rapid and non-contact technique for acquiring three-dimensional spatial information of objects. By utilizing laser scanning, it captures surface parameters and point cloud data with high precision, overcoming the limitations of conventional methods. This technology is widely researched and applied in fields such as reverse engineering, digital cities, cultural heritage preservation, deformation monitoring, and precision industrial measurements.
We developed an automated dimensional measurement system based on 3D laser scanning to address these challenges in inspecting aerospace casting parts. This system integrates advanced modules for measurement, logistics, integrated control, and safety protection, enabling comprehensive and efficient inspection of castings aerospace components. The core of our approach lies in leveraging high-precision blue light scanning to generate detailed point cloud data, which is then processed and compared with theoretical models to assess dimensional accuracy. Through this system, we aim to achieve high coverage rates and precise measurements for complex castings aerospace parts, such as turbine housings, which are essential for ensuring engine performance and reliability.
The design of our three-dimensional online measurement system is centered on the specific structural characteristics and scanning requirements of aerospace casting parts. It comprises four main modules: the measurement module, logistics module, integrated control module, and safety protection module. Each module is meticulously engineered to work in harmony, providing functionalities such as automatic workpiece recognition, handling, calibration, measurement, model comparison, and report generation. This integrated approach ensures that the inspection process for castings aerospace components is not only accurate but also efficient, reducing human intervention and enhancing throughput. Below, we detail the components and functionalities of each module, supported by tables and formulas to elucidate key aspects.
The measurement module serves as the heart of the system, responsible for acquiring and processing three-dimensional data. It includes a measurement robot, scanner, calibration plate, measurement software, analysis software, and a workstation. The measurement robot, with six degrees of freedom, precisely adjusts the scanner’s position relative to the workpiece, ensuring stability and accuracy during scanning. The high-precision blue light scanner projects structured light patterns onto the object surface, and using stereo vision principles, it captures distortions to generate point cloud data. The calibration plate is used regularly to verify and maintain the scanner’s accuracy, as environmental factors can affect performance. The measurement software facilitates data acquisition with features like automatic stitching, while the analysis software processes the point cloud data, comparing it with CAD models to produce deviation reports. The workstation handles the computational load for real-time data processing. For instance, the point cloud data processing involves algorithms for noise reduction and feature extraction, which can be represented mathematically. The accuracy of the scanner can be modeled using the following formula for error estimation: $$ \Delta = \sqrt{ \sum_{i=1}^{n} (x_i – \hat{x}_i)^2 } $$ where $\Delta$ is the total error, $x_i$ are the measured points, and $\hat{x}_i$ are the reference points from the CAD model. This ensures that the system meets the stringent requirements for inspecting aerospace casting parts.
| Component | Function | Specifications |
|---|---|---|
| Measurement Robot | Adjusts scanner position with 6 DOF | Stable with brake lock function |
| Scanner | Captures 3D point cloud data | Blue light, high precision |
| Calibration Plate | Calibrates scanner accuracy | Standard reference surface |
| Measurement Software | Acquires and stitches point clouds | Automatic feature matching |
| Analysis Software | Compares data with CAD models | Generates 3D deviation maps |
| Workstation | Processes data in real-time | High-performance computing |
The logistics module handles the automated transportation and positioning of aerospace casting parts during inspection. It consists of a material handling robot, visual positioning system, rotating platform, material stations, and transport clamping fixtures. The material robot, also with six degrees of freedom, is equipped with custom grippers to handle various workpiece shapes securely. The visual positioning system uses 2D cameras to identify workpieces via QR codes and corrects the robot’s path for precise placement. The rotating platform acts as an additional axis, allowing the workpiece to be rotated for full coverage scanning without frequent robot adjustments, thereby improving efficiency. Material stations include positioning rails and carts with interchangeable pallets to accommodate different aerospace casting parts, ensuring consistent orientation. The transport clamping fixtures feature quick-change mechanisms and safety sensors to prevent accidents. The visual system’s accuracy in positioning can be described by the transformation matrix: $$ \mathbf{T} = \begin{bmatrix} \mathbf{R} & \mathbf{t} \\ \mathbf{0} & 1 \end{bmatrix} $$ where $\mathbf{R}$ is the rotation matrix and $\mathbf{t}$ is the translation vector, aligning the workpiece coordinate system with the robot’s frame. This module is crucial for maintaining the integrity of castings aerospace inspections by minimizing handling errors.
| Component | Role | Key Features |
|---|---|---|
| Material Robot | Handles workpiece transport | 6 DOF, customizable grippers |
| Visual Positioning System | Identifies and positions workpieces | 2D cameras, QR code recognition |
| Rotating Platform | Rotates workpiece for scanning | Acts as 7th axis for robot |
| Material Stations | Holds workpieces for processing | Interchangeable pallets, rails |
| Transport Clamping Fixtures | Secures workpieces during move | Quick-change, safety sensors |
The integrated control module orchestrates the entire inspection process for aerospace casting parts through a centralized control cabinet and touchscreen interface. It employs a programmable logic controller (PLC) to manage inputs and outputs, coordinating the measurement robot, logistics robot, scanner, and other peripherals. The touchscreen allows operators to initiate and monitor inspections with a single touch, enabling batch processing of multiple castings aerospace components. Data logging, alarm handling, and safety interlocks are integral to this module, ensuring reliable operation. The control system can be modeled using state-space equations to represent the dynamic behavior: $$ \dot{\mathbf{x}} = \mathbf{A}\mathbf{x} + \mathbf{B}\mathbf{u} $$ where $\mathbf{x}$ is the state vector (e.g., robot positions), $\mathbf{u}$ is the input vector (e.g., control commands), and $\mathbf{A}$ and $\mathbf{B}$ are matrices defining the system dynamics. This ensures seamless automation and real-time response during the inspection of aerospace casting parts.
Safety is paramount in an automated system handling heavy aerospace casting parts. The safety protection module includes mechanical safety switches, emergency stops, safety relays, and enclosures that meet PLe safety standards. The safety switches lock during operation, preventing access to hazardous areas, and are interlocked with the control system. If an emergency stop is activated, all motion ceases immediately. This module ensures that inspections of castings aerospace components are conducted without risk to personnel or equipment. The safety logic can be expressed using Boolean algebra: $$ S = \text{Lock} \land \neg \text{EmergencyStop} $$ where $S$ is the safety enable signal, ensuring that operations proceed only under safe conditions.
In terms of system layout, we optimized the spatial arrangement to avoid collisions between the material and measurement robots while maximizing throughput. Two material stations with dedicated access doors allow continuous loading and unloading of aerospace casting parts, facilitating a smooth workflow. The overall system efficiency can be quantified using the formula for throughput: $$ \text{Throughput} = \frac{N}{T} $$ where $N$ is the number of inspected castings aerospace parts per unit time $T$. This design supports high-volume inspection campaigns for critical aerospace components.
To validate the system, we conducted tests on a low-pressure shell blank of an oxygen pump, a representative aerospace casting part. The inspection focused on profile coverage and dimensional accuracy. The profile coverage rate is defined as the ratio of detectable surface area to the total surface area: $$ \text{Coverage} = \frac{A_{\text{detected}}}{A_{\text{total}}} \times 100\% $$ where $A_{\text{detected}}$ is the area covered by point cloud data, and $A_{\text{total}}$ is the theoretical surface area after hole filling. For the test workpiece, the total surface area was 1,362,750.49 mm², with a detected area of 1,337,207.71 mm², resulting in a coverage rate of 98.1%. This high coverage demonstrates the system’s capability to capture nearly the entire surface of complex castings aerospace parts.
| Feature | Theoretical Dimension (mm) | Tolerance (mm) | Measured Range (mm) | Conformance |
|---|---|---|---|---|
| Diameter | ϕ209.5 | ϕ209_{-2}^{0} | ϕ209.284 – ϕ209.440 | Yes |
| U-Slot Height | 24.5 | 24.5_{-2}^{0} | 24.312 – 24.492 | Yes |
Dimensional analysis was performed by comparing scanned data with the CAD model. For instance, the diameter at ϕ209.5 mm was measured within the specified tolerance, and the U-slot height also conformed to requirements. The deviation analysis uses the formula: $$ \delta = | P_{\text{measured}} – P_{\text{model}} | $$ where $\delta$ is the deviation, and $P$ represents dimensional parameters. The results confirm that the system achieves precise measurements for aerospace casting parts, essential for quality assurance in aerospace applications.
In conclusion, our three-dimensional online measurement system, based on 3D laser scanning, effectively addresses the limitations of traditional inspection methods for aerospace casting parts. By integrating measurement, logistics, control, and safety modules, we have created a robust solution that achieves high coverage and accuracy for castings aerospace components. The system’s design prioritizes efficiency and safety, with optimized layouts and automated workflows. Testing on actual workpieces, such as the oxygen pump low-pressure shell, validated its performance, with coverage rates exceeding 98% and dimensional conformance. This advancement supports the growing demands for precision in aerospace manufacturing, ensuring that critical parts like turbine casings meet stringent standards. Future work could focus on enhancing scanning speed and adapting the system for a wider range of castings aerospace applications, further solidifying its role in industrial quality control.