With the rapid development of additive manufacturing technology, the usage of composite impellers by 3D printing has more and more expanded in aerospace, energy equipment, and high-tech industries. Though 3D printing technology exhibits tremendous superiority in fabricating complex structures, due to limitations on material properties, forming accuracy, surface quality, etc., a series of post-processing technologies are usually required after printing in order to meet working requirements.
Introduction
Composites, due to their high specific strength, corrosion resistance, and freedom of design, have increasingly become a trendsetters’ choice for 3D printing technology advancement. Especially in the case of impeller manufacturing, utilizing new print mediums like carbon fiber-reinforced polymers (CFRP), glass fiber composites, and ceramic matrix composites can significantly reduce the weight of impellers and enhance fluid performance. As a manufacturing technology, 3D printing can have precise control of structural shapes, whereas due to the 特殊性 (particularities) of composites in the additive manufacturing process such as poor interlayer bonding, high surface roughness, and large material residual stress, these factors heavily influence the service stability of impellers. Therefore, these post-processing technologies must be utilized effectively for compensation and optimization to improve the performance of composite impellers.
Classification and Functions of Post-Processing Technologies
Post-processing technologies play a significant role in improving the performance of composite 3D printed impellers, which mainly include heat treatment, surface treatment, mechanical processing, structure reinforcement, and non-destructive testing. Using these technologies, the printing-induced defects can be effectively removed, and mechanical properties, surface quality, and dimensions of composites can be improved.
Heat Treatment: Stress Relief and Matrix Structure Improvement
Heat treatment is a common post-processing method for thermoplastic composite or resin-based impellers. The process relaxes thermal residual stress developed during printing and stabilizes material size, relevant to strengthen impeller mechanical properties. Especially with ceramic or metal matrix composites, heat treatment also enhances the mechanical and density characteristics of materials through the use of sintering, annealing, etc.
For example, resin composites are typically heat stored at 120–180°C for 2–5 hours, metal matrix composites need annealing at 450–650°C, and sintering temperature of ceramic matrix material typically needs to be raised above 1,000°C. Through heat treatment, internal stress is easily relieved and material mechanical properties can be optimized to better meet actual conditions of use.
Surface Treatment: Improving Finish and Fatigue Life
Due to staircase effect and layered texture normally on the surface of composite impellers in additive manufacturing, the common surface quality is normally rough, which has an impact on aerodynamic performance and fatigue life of impellers. Surface treatment techniques such as sandblasting, polishing, chemical treatment, and plasma treatment can significantly improve surface finish of impellers, reduce surface defects, and enhance fatigue life.
For example, the sandblasting process can remove floating powder and surface contamination, improving surface roughness of the fluid channels, while polishing treatment can improve the mirror smoothness of the impeller surface effectively, suitable for the surface of high-speed rotation blades. Besides, plasma treatment can also improve the bonding force of the composite interface, enabling subsequent coating adhesion and improving further material durability.
Precision Machining: Ensuring Key Dimensional Accuracy
For precision fitting and assembly parts such as impeller shaft holes and the leading edge and root blades, dimensional adjustment remains to be done through CNC precision machining. Diamond-coated end mills and PCD tools must be used when cutting composites in order to avoid interlayer separation and structural damage. Furthermore, with cutting technology of low speed, high rotation speed, and minute cutting depth, a effective improvement on machining accuracy and assurance of assembly accuracy and performance of parts can be achieved.
Structural Strengthening Treatment
To improve the durability of composite impellers, structural reinforcement treatment can further strengthen their mechanical properties. For example, impregnation treatment is applied to enhance bonding force between layers of materials through resin impregnation technology, and hot-press forming may also be employed to improve the density of the overall structure. In addition, depositing metal or carbon fiber-reinforced inserts into stress areas of impellers can also be a good measure to improve the strength and rigidity of impellers for stronger adaptability in high-load and high-strength working environments.
Non-Destructive Testing and Quality Verification
Non-destructive testing provides a crucial link in order to assure post-processing influences and product quality. Standardized test methods are ultrasonic examination, X-ray scanning, and infrared thermography. Ultrasonic examination may be used to evaluate interlayer voids and inclusions in composite impellers; X-ray scanning can indicate fiber breaks and porosity distribution; infrared thermography can quickly spot delamination and local overheats on the impeller surface and inner cavity. With extensive use of non-destructive testing technologies, impeller quality and application safety can be ensured in practice.
Technical Difficulties and Coping Strategies
Large Differences in Thermal Stability of Composites
In heat treatment of 3D printed composites, matrix and reinforcement fiber material thermal expansion coefficients and thermal decomposition temperatures are very distinct, leading to easy delamination or degradation of performance at heat treatment. Accordingly, heating rate and heat retention time during heat treatment must be strictly controlled, and a graded heating schedule is utilized to avoid thermal shock.
Surface Treatment Prone to Cause Structural Damage
Mechanical deburring methods traditionally employed are easy to discontinue the fiber continuity of composites, thereby leading to material performance degradation. Therefore, non-contact or light-impact surface treatment technologies such as chemical etching or laser polishing should be accorded preference in order not to damage composite structure.
Significant Fiber Direction Effect During Machining
The fiber orientation direction in composites significantly affects both machining performance and surface quality. During mechanical machining, the tool path must be tailored in accordance with the direction of the fibers, and a specific CAM module is used to dynamically optimize the tool path to improve machining precision and efficiency.
Engineering Applications and Future Development
At present, 3D printed composite impellers have been widely utilized in low-speed fans, model aircraft propellers, energy-saving ventilating appliances, aerospace non-propulsive systems, and so on. As high-performance composites and the most advanced printing equipment keep on improving, so do their application prospects in high-speed rotating machinery like turbochargers and UAV turbofan engines.
Post-processing technology of composite impellers printed by 3D printing will be developed further in the future. Automated integrated post-processing lines will have a closed-loop process of “printing-machining-testing”, and smart post-processing simulation model can predict material behavior in advance to optimize post-processing parameters. In addition, surface coating technology and functional integration technology will provide more multiple functions for impellers, and thus impellers will be widely used in high-end equipment.
Conclusion
Post-processing of 3D printed composite impellers is a key link to their final performance. Through systematic heat treatment, surface treatment, processing, and quality inspection technology, accuracy, strength, and reliability of impellers can be significantly improved. As post-processing technology and material science relentlessly innovate, 3D printed composite impellers will see wider application in high-performance engineering devices, promoting the growth of aerospace, energy equipment, and industrial manufacturing sectors.
