With the extensive application of digital design and manufacturing technology, product development based on CAD model has become the mainstream model in the aviation manufacturing industry, where the CAD model and material blank, which are usually based on parts, are obtained by removing material or deformation CAD model Geometry has been the part entity Although this model has played a huge role in promoting aeronautical manufacturing progress, years of industrial practice have also shown that it is a very time-consuming and technically challenging job, especially for Development of titanium alloy components requiring high performance, complex structure and being widely used in the aviation industry.
In response to this situation, there is a revolutionary digital manufacturing technology - laser rapid prototyping technology. This technology to break the traditional removal of materials or deformation of the manufacturing model, the use of 'discrete + accumulation' of additive manufacturing ideas from CAD model step Completion of component manufacturing has significant advantages such as no need of mold, unlimited complexity of geometry, short processing cycle, low manufacturing cost, high flexibility and excellent overall performance, etc. The technology has rapidly become the vanguard of aviation superpower since the advent of the 90's Development of an advanced manufacturing technology.
As an aviation powerhouse, the United States leads the development of this advanced manufacturing technology and realizes the R & D and engineering application of laser rapid prototyping and manufacturing of titanium alloy structural parts for aircraft. Currently, laser rapid prototyping technology has become a large-scale titanium Alloy structural parts of the core manufacturing technology.
In the F / A-18E, F22 and F35 and other advanced fighters, a large number of titanium alloy, stainless steel and other materials, thin-walled structural parts, complex stiffeners and cavity structures are made using this technology. Beijing University of Aeronautics and Astronautics Professor Wang Huaming Of the research team broke through the laser rapid prototyping of large complex components such as titanium alloy, ultra-high strength steel and other materials, and has successfully carried out engineering applications.
Professor Wang's team won the first prize of National Invention of Technology by 3D Laser Rapid Prototyping Technology and the research team of Professor Huang Weidong from Northwestern Polytechnical University carried out a great deal of research work on the related theories, technologies and applications of laser rapid prototyping.At present, Laser rapid prototyping technology has been able to produce the main bearing of aviation components, the largest part of the projection area has reached 12m2, and material utilization in more than 70%.
Laser rapid prototyping technology principles, key steps and advantages
In principle, laser rapid prototyping breaks down the conventional processing idea of "material removal or deformation" and uses the principle of "additive" to shape the part, which uses laser with energy concentration, easy control and low cost industrial energy The advantages of precise control and control of laser light speed, to achieve the fine accumulation and processing of materials to rapidly create high-density complex metal components.
The main process and the key steps of laser rapid prototyping are as follows: firstly, the CAD model of the part is sliced, the part mesh model is separated into a series of 2D contour data similar to computer grayscale image according to a certain thickness; and then the contour data is generated Can control the movement of the laser CNC driver to drive the laser from bottom to top layer by layer deposition of metal powder deposition, and finally get the organization of dense, high-performance 'near-net shape' parts complete laser rapid prototyping manufacturing process shown in Figure 1 .
Figure 1 Laser rapid ripening process
In order to solve the problem of singularity problem in classical algorithms, aiming at the CAD model slicing problem in laser rapid prototyping, Liu Houcai et al. Proposed a fast algorithm of intersection based on silhouette edges. According to the geometric information of triangular patches in STL model, Thickness, set up grouping matrix, and reduce the number of intersection and traversal of triangular facets by constructing local dynamic topological relations among triangular facets.
The technique is based on the classic algorithm of computer graphics intersection algorithm, and the rapid generation of images at all layers is achieved by optimizing the number of traversal of triangles.In general, algorithms of CAD model slicing and driver generation based on contour data are relatively mature, The laser cladding process involves complicated physical, chemical, mechanical and metallurgical problems, which is a difficult problem that restricts the development and application of laser rapid prototyping technology.
Research and application status quo
Internal organization and defect formation mechanism
Laser rapid prototyping process can be described as:
Continuous delivery to the laser cladding area of the metal powder melting, that is under the action of the laser beam, the substrate or the previous layer of the local remelting cladding layer, and mixed into the alloy melt;
◆ metal melt flow in the pool until the temperature within the pool tend to be consistent and the melt alloy composition tends to be uniform;
◆ As the outline changes, the melt in the moving pool quickly solidifies out of balance.
The above process takes place in a small, short-lived liquid pool, which is a very complex non-equilibrium short-time physical metallurgy process. The interaction between laser, metal powder and molten pool is shown in Fig.2.
Figure 2 laser, powder bath interactive process diagram
Chen Jing and others used high-speed photography to observe the formation and evolution of the liquid pool during laser rapid prototyping in real time. Zhang Fengying et al. Studied the formation mechanism of defects during laser rapid prototyping of titanium alloys. The defects of pores mainly depended on the bulk density , Poor fusion and laser energy density, lap-lap ratio and the single-stage Z-axis travel.Because of the variety of laser rapid prototyping process is extremely complicated, the internal structure of the internal components and the formation mechanism of internal defects and other key issues Difficulties.Beijing University of Aeronautics and Aeronautics and Astronautics Institute of Shenyang's 'production and research' research team made substantial progress in this area, breaking the parts deformation, cracking prevention and internal quality control problems.
Simulation and Simulation of Forming Process
In order to obtain stable and high-quality components, accurately grasp the formation rules of internal structure and internal defects during laser rapid prototyping, more and more attention has been paid to simulation and optimization of forming process parameters and forming process.
Jia Wenpeng et al. Simulated the formation of molten pool and the evolution of free interface shape and the deposition process of cladding by the finite element method of life and death, and simulated the capture of particles by the weld pool and the reflection of powder by the interface temperature and momentum loss of powder particles LAGRANGIAN particle tracking model to achieve the tracking of powder particles.
Based on ANSYS, Ma Liang et al. Established the parametric finite element model of temperature field and stress field of laser forming process by using the secondary development technology. The thermal stress field in the laser forming process was simulated by the mobile heat source and the unit life and death technology. On the basis of calculating the evolution law of temperature field, the causes of thermal stress fields such as plastic compression zone, plastic stretching zone and unloading zone are revealed.
In view of the process characteristics of laser rapid prototyping, Tan Hua et al. Studied a closed-loop control system based on real-time monitoring principle to adjust process parameters to obtain high-performance and high-quality components and discussed the further development of monitoring and closed loop control system .
Application Status of Laser Rapid Prototyping
As a transformative technology, laser rapid prototyping technology is mainly for parts that are in high demand, complex in complexity and hard to be processed or material is removed. Two titanium alloy fittings of F-22 aircraft in the United States are shown in FIG. 3 , Using laser rapid prototyping technology, the overall performance than the traditional processing methods have been greatly improved, and manufacturing costs reduced by 20% -40%, the production cycle has also been shortened by 80%.
Figure 3 F-22 laser rapid prototyping titanium alloy parts
Beijing University of Aeronautics and Aviation Group and China Aviation Industry Group set up a laser company in the Air, laser rapid prototyping technology research results of industrialization.The project for the first time in the world breakthrough in the aircraft titanium large-scale integral main bearing structure of the laser forming process, mechanical properties Control and engineering of complete sets of equipment and technical standards has been successfully carried out in China on many types of aircraft engineering applications.Figure 4 for the first time publicly displayed using laser rapid prototyping technology to produce a large titanium alloy parts.
After years of in-depth research, Professor Huang Weidong from Northwestern Polytechnical University has also made outstanding achievements in laser rapid prototyping technology. The large titanium alloy parts manufactured by the laser rapid prototyping technology shown in FIG. 5 are the main load-bearing components of a type of machine.
Application Analysis of Helicopter Manufacturing
● rapid manufacturing of moving parts
Helicopter rotor lift system The main propulsion dice, tail rotor dice and automatic tilt (collectively referred to as 'moving parts') manufacturing is the core technology of helicopter manufacture.Mobile parts as the main load-bearing parts, complex structure, poor working environment, High fatigue strength, and most of the materials such as TB6 titanium alloy and high-temperature alloys difficult to process materials.If using laser rapid prototyping technology, it has considerable or better overall mechanical properties.
In addition, laser rapid prototyping has the advantages of mold-independent, unlimited geometric complexity, short production cycle and high material utilization, especially suitable for the design changes of moving parts.Therefore, laser rapid prototyping technology to manufacture helicopters Of the moving parts to improve the dynamic mechanical properties of components, reduce manufacturing costs and shorten the development cycle is of great significance.
● Quick repair of moving parts
Helicopter moving parts are important load-bearing components that withstand blade-induced centrifugal forces, bending moments, shimmy moments, etc. Therefore, moving parts are the most easily worn parts of a helicopter. Moving parts are costly, and in the event of defects or Defect, only the overall replacement, may result in hundreds of thousands, even millions of losses.
Rapid prototyping is a point-by-point additive manufacturing, so only the defect parts as a special substrate, the geometric reconstruction of the defect site, the reconstruction of the geometry of the slice layering, and finally the use of laser rapid prototyping technology can quickly repair Parts Because the controllability of laser energy over time and space and power density is much higher than other industrial sources of energy, the adverse effect of the repair heating process on repaired parts can be minimized.
In addition, since the laser rapid prototyping process can synchronously control the composition and structure of the alloy, the inherent properties of the component can be restored by controlling the composition of the repair area and the organization of the repair area and the body of the component, thus saving the huge economic and time Loss, but also improve the utilization of resources, in line with low-cost, sustainable development strategy.
Conclusion and Outlook
Helicopter industry is experiencing rapid changes as an important part of aviation manufacturing industry, and there is no permanent and permanent solution to make the industry bigger and stronger. Only by constantly strengthening research and development can the development trend be followed Powerful forest. Laser rapid prototyping technology brought great technical advantages will lead the development of advanced manufacturing technology. Helicopter moving parts manufacturing technology helicopter manufacturing company is the embodiment of manufacturing capacity, from the cost, efficiency, quality, the use of Laser rapid prototyping technology to move the manufacture and repair of components with great technical and economic benefits, as the future development of moving parts manufacturing technology priority.