In the field of aerospace manufacturing, titanium alloys are extensively utilized due to their exceptional properties, making them ideal for producing complex engine components and various intricate parts that enhance the performance and efficiency of aircraft and spacecraft. Lost wax investment casting serves as a primary forming process for titanium alloys, involving multiple stages such as mold fabrication, wax pattern creation, shell building, and subsequent drying, firing, and pouring. The wax pattern, which forms the cavity mold for the final casting, is a critical initial step in the lost wax investment casting process. The dimensional accuracy of the wax pattern directly influences the precision, surface quality, and yield rate of the cast components. Therefore, achieving high-dimensional accuracy in wax patterns is paramount for producing superior castings.
The wax pattern assembly process consists of two main parts: wax part preparation and tree assembly. During wax part fabrication, numerous process parameters—including wax material quality, injection temperature, injection pressure, and holding time—significantly impact the quality of the wax parts. The tree assembly工序 involves welding individual wax parts onto a tree-like structure, known as the runner or浇道, and the quality of this assembly directly affects the coating process and, consequently, the final casting quality. Enhancing the stability and consistency of wax pattern assembly is thus crucial for improving overall process efficiency and product reliability in lost wax investment casting.
Traditionally, wax pattern tree assembly relies heavily on manual operations, where operators use electric soldering irons to heat the contact points of wax parts and the runner, then fix them in place. This manual approach is highly subjective, leading to inconsistent welding results across different wax parts on the same runner, which can adversely affect casting quality. Moreover, human operators cannot maintain continuous work, resulting in reduced productivity and increased defect rates. To address these challenges, we have developed an automatic wax pattern welding system that replaces manual labor with a six-axis robotic arm, ensuring uniformity in each wax part’s welding, reducing rejection rates, and boosting production efficiency in lost wax investment casting processes.
The automatic wax pattern assembly system comprises several integrated components: a wax pattern feeding mechanism, conveying mechanism, rotating mechanism, gripping mechanism, welding mechanism, residual wax removal mechanism for the welding tool, robotic arms, and a control system. The conveying and rotating mechanisms employ servo drives to ensure precise positioning of wax parts and the runner, while the welding mechanism utilizes PID-controlled heating elements to maintain stable temperature regulation for the welding tool. Two robotic arms handle the wax parts and welding tools, ensuring连贯性, stability, repeatability, and流畅性 in operations. The control system processes transmission signals and logic commands to automate the entire process, facilitating seamless integration and operation in lost wax investment casting applications.
The wax pattern feeding mechanism consists of a fixed支架 and a托盘, where the托盘 holds the wax parts to be welded, and the固定支架 secures the托盘 in place using positioning pins. This setup ensures accurate positioning when the robotic arm retrieves the wax parts. The conveying and rotating mechanisms are driven by servo motors and lead screws, moving the feeding装置 to the robotic arm’s pickup location. The rotating mechanism, comprising a servo motor and a rotary table, allows the runner to be rotated, enabling wax parts to be welded at various angles. This enhances flexibility in the lost wax investment casting assembly process.
The gripping mechanism includes the robotic arm, a quick-change device, and clamping fixtures. The quick-change sub-heads connect the clamping fixtures to the robotic arm, allowing for easy adaptation to different wax parts and fixtures. By coordinating with the conveying mechanism, the robotic arm follows a predefined trajectory and uses compressed air to control the clamping fixture’s opening and closing, ensuring stable transportation of wax parts. The welding mechanism involves the robotic arm holding a welding tool and a preheating plate. The welding tool heats and melts the contact points of the wax parts and runner, while the preheating plate contains adhesive wax to reinforce the weld. After heating and preheating, the wax part is securely welded to the runner. The residual wax removal mechanism uses compressed air to blow off any leftover wax droplets from the welding tool surface, maintaining cleanliness and efficiency in the lost wax investment casting system.
To quantify the performance of the welding mechanism, the temperature control can be modeled using a PID controller formula. The output of the PID controller, which regulates the heating element, is given by:
$$ u(t) = K_p e(t) + K_i \int_0^t e(\tau) d\tau + K_d \frac{de(t)}{dt} $$
where \( u(t) \) is the control signal, \( e(t) \) is the error between the desired and actual temperature, and \( K_p \), \( K_i \), and \( K_d \) are the proportional, integral, and derivative gains, respectively. This ensures precise temperature stability during the wax welding process in lost wax investment casting.
The control system is built around a high-performance controller with efficient data processing, stable operation, and robust communication capabilities. It includes one main unit, three input modules, and two output modules, and integrates safety features such as safety light curtains, emergency stop buttons, safety relays, and audible-visual alarms. The controller acts as the master station, while the robotic arms and servo motors serve as slave stations. Communication is established via PROFINET, with the controller and robotic arms configured on the same network segment to enable real-time data exchange and signal processing. This setup ensures that the entire system operates smoothly and responds accurately to sensor inputs and output commands in lost wax investment casting applications.
In terms of system software, the controller’s programming involves configuring the PROFINET interface for the robotic arms, assigning IP addresses and subnet masks, and creating a PROFINET communication link to facilitate seamless interaction. The input and output modules handle signal exchanges, allowing the system to monitor progress and nodes continuously. This integration enhances the automation level, supporting one-button operation and reducing human intervention in lost wax investment casting processes.
The performance of the automatic wax pattern assembly system was evaluated through practical application. Within six weeks of implementation, the system successfully assembled 10,080 wax parts for a specific product, doubling the work efficiency compared to manual methods. This demonstrates the system’s potential to significantly improve productivity and consistency in lost wax investment casting. The following table summarizes the key components and their functions in the system:
| Component | Function | Key Features |
|---|---|---|
| Feeding Mechanism | Holds and positions wax parts for retrieval | Fixed支架 with托盘 and positioning pins |
| Conveying Mechanism | Moves wax parts to robotic arm location | Servo motor and lead screw drive |
| Rotating Mechanism | Rotates runner for multi-angle welding | Servo motor with rotary table |
| Gripping Mechanism | Handles wax parts using robotic arm | Quick-change device and clamping fixtures |
| Welding Mechanism | Heats and welds wax parts to runner | PID-controlled heating tool and preheating plate |
| Residual Wax Removal | Cleans welding tool after use | Compressed air blowing system |
| Control System | Coordinates all components and processes | PROFINET communication with safety features |
Another critical aspect is the optimization of process parameters for wax part fabrication in lost wax investment casting. The relationship between injection parameters and wax quality can be expressed using empirical formulas. For instance, the optimal injection pressure \( P \) can be derived based on wax material viscosity \( \mu \) and flow rate \( Q \):
$$ P = k \cdot \mu \cdot Q $$
where \( k \) is a material-specific constant. This helps in fine-tuning the wax injection process to achieve high-quality wax parts, which are essential for successful tree assembly in lost wax investment casting.
The integration of robotic arms and automation technologies not only enhances consistency but also reduces operational costs. In traditional manual lost wax investment casting, the variability in human performance often leads to inconsistencies in weld quality, whereas the automated system ensures each wax part is welded with identical precision. The use of servo drives in conveying and rotating mechanisms provides high positional accuracy, with error margins minimized to within micrometers. This is crucial for maintaining the dimensional integrity of wax patterns in lost wax investment casting.
Furthermore, the control system’s ability to handle real-time data allows for adaptive adjustments during operation. For example, if a sensor detects a misalignment in the wax part position, the controller can recalibrate the robotic arm’s trajectory instantly. This dynamic response capability is vital for handling the small-batch, high-variety production typical in aerospace applications of lost wax investment casting. The following formula represents the positional accuracy \( A \) achieved by the servo-driven mechanisms:
$$ A = \frac{1}{N} \sum_{i=1}^{N} |x_i – x_{target}| $$
where \( N \) is the number of positioning attempts, \( x_i \) is the actual position, and \( x_{target} \) is the desired position. In our system, \( A \) is maintained below 0.1 mm, ensuring high precision in lost wax investment casting assembly.
In conclusion, the automatic wax pattern assembly system represents a significant advancement in lost wax investment casting technology. By automating the tree assembly process, it addresses the limitations of manual methods, such as inconsistency and low efficiency. The system’s modular design allows for compatibility with various products, making it suitable for the small-batch, multi-variety production common in aerospace manufacturing. Although widespread adoption for diverse products in lost wax investment casting requires further development, the trend toward automation is inevitable. Future enhancements may include more advanced sensors, machine learning algorithms for predictive maintenance, and expanded robotic applications in lost wax investment casting production lines. This innovation not only improves welding efficiency and product quality but also paves the way for more sustainable and cost-effective manufacturing practices in the lost wax investment casting industry.