The application prospect of the hottest global 3D

Analysis on the application prospect of global 3D printing technology in the aviation field

Abstract: 3D printing can support aviation designers to achieve the high economic goal of maximizing the assembly and minimizing the assembly quantity. Through 3D printing technology to manufacture integral parts, it is possible to integrate the maintenance and structural parts, greatly reduce the weight caused by the number of parts and assembly process, and significantly reduce the difficulty of aircraft design and assembly

3d printing technology began to appear in the late 1970s, and is mainly used in "rapid prototyping" in product development stage and "rapid manufacturing" in production stage. 3D printing technology is similar to the surfacing process used in industrial production. The reason why it is called 3D printing is to use CAD and computer 3D model data in the molding process to combine two-dimensional substrates into a three-dimensional structure through different fusion methods. The process methods used in aviation production mainly include laser near net shape forming (lens), laser selective melting (SLM) and electron beam selective melting (EBSM)

the weight reduction effect of 3D printing complex frame structure blank is relatively obvious. For example, the blank weight of F-22 maximum area forged structure frame is 2790 kg, the net weight of blank after processing is only 144 kg, and the material removal ratio reaches 95%! If the disc-shaped complex structural parts are manufactured according to the verified process requirements, the forging process cannot directly make the detailed structure, and the material utilization rate is only about 10% of the blank weight. Casting can complete the rough molding of some details, and the actual utilization rate of blank can reach 20% - 25% of the total weight. 3D printing can directly make the shape close to the finished product. Considering the surface processing technology and material quality requirements, the finished parts can reach 60% - 70% of the total weight of the blank, and the material utilization rate and machining efficiency have been greatly improved

on the contrary, the reuse effect of casting mold is relatively good, and the finished core can be manufactured in batches. Although the cost of forging die is very high and the requirements of process equipment standards are high, forging is also conducive to the formation of batch production blanks. 3D printing adopts the process of additive manufacturing, whether only one or 100 in batch, there is no difference in the production time and cost of a single piece, and the molding process requirements and quality control of parts are more strict

comparison between 3D printing and other blank making methods

at present, the aviation application of 3D printing technology is mainly focused on metal structures, mainly titanium alloy and alloy steel with great difficulty in blank forming and processing, while aluminum with low difficulty in processing is more suitable for forging and casting. 3D printing of aviation parts has been widely used. The 3D formed TC4 joint used abroad for F-22 has reached twice the design fatigue life, the structural strength of the wing root hanger of f/a-18 has reached 225% of the design requirements, and the fatigue life has also reached four times the design requirements. The inlet accessories of C-17 and other models have also begun to apply 3D printing in batches, and some 3D printing parts have been able to replace sheet metal and precision castings in the manufacturing of existing models

China has made great achievements in aviation 3D printing. Many models have applied the load-bearing structure of 3D printing, which has achieved the effect of shortening the manufacturing cycle and simplifying the process. The effect on product weight reduction is also obvious. There is even a claim of weight reduction of 40% in the promotional materials. Many domestic military fans have great hopes for aviation structure weight reduction based on this 40% and similar statements. Although this 40% is theoretically possible, it is subject to very strict conditions and application restrictions

slm finished products have high dimensional accuracy, but the control effect of the structural density of the formed body is not good, and it is difficult to bear the structural effect of high load. Lens is mainly used for 3D printing of load-bearing structures. According to the published shape comparison of 3D printing overall frame blank, the blank weight of 3D printing is only about 15% of that of forging, which is the technical advantage of 3D printing, but the weight reduction ratio of blank does not represent the weight comparison of final finished products. The design of the overall structural framework of the aircraft should take into account the lightness and firmness, as well as the consistency between the process and the mechanical/physical and chemical properties of the finished product. The structural design must strictly meet the requirements of standardization. There is no big difference in the design of similar structures of different aircraft types

the structural design of the finished 3D printing load-bearing frame disclosed in the exhibition is no different from that of the forged frame, and the difference is only reflected in the process of blank forming. The lens and SLM processes for 3D printing are relatively mature. Whether laser or electron beam is used as the energy source, or powder or silk is used as the substrate, the physical and chemical conditions of the material itself will not change due to different processing methods. According to the existing technology, the theoretical density of the material sintered by near net shape is nearly 1% lower than that of the forging. The density of the powder material formed by selective melting is relatively small, and the density difference between the powder material and the forging is also less than 3%. The better the process conditions are, the smaller the material density difference is

no matter what 3D molding method is used, if there is no big difference in the material properties of the same parts, there will be no significant difference in the weight of the finished parts. Therefore, the weight reduction effect achieved by the processing method of 3D printing blank is very limited. Considering that the material performance of 3D printing is not perfect at present, compared with the mature forging structure tolerance insurance design, the net weight of the same design structure is even heavier

according to the published data, the tensile strength and hardness of the finished parts of 3D printed titanium alloy have reached the standard of forgings, but the fatigue life and crack tolerance are greatly affected by the process, and there is still a lack of conditions to comprehensively replace forging in the future. The overall forging framework is widely used in aircraft manufacturing in the United States, and the application of high-risk 3D printing is not active enough, which takes into account the factors of finished product life and difficult quality control. While applying 3D printing load-bearing structure in the manufacturing of new machines, China has also invested a lot of money and technical force in the development of large-scale forging presses, which is also because 3D printing cannot meet the batch production requirements of large-scale manufactured products. 3D printing and forging/casting have their own advantages. As long as the aviation design and production system is still based on traditional industrial technology, forging/casting and rolling will still be the main process forming means, the structural weight reduction effect of 3D printing is difficult to be reflected

weight reduction measures based on manufacturing technology breakthrough

according to the weight reduction standard, the difference between the density of 3D printing and forging is less than 1%. In order to achieve the goal of avoiding defects and improving material properties, the smaller the density difference is, the better. According to the actual production conditions, if the finished product weight of a simple frame is close to 300kg, the blank weight of die forgings is about 2700kg, and the blank weight of 3D printed frame can be reduced to close to 500kg, but the theoretical difference between the finished product weight and forging is less than 1kg, which is only slightly larger than the converted value of dimensional error of overall machining. Therefore, compared with the final indicator of finished product weight, the weight reduction effect of 3D printing is almost negligible

so how did the claim of 40% weight reduction in promotional materials come from? This should be explained from the aircraft structure technology. The more complex the structure of metal products in modern aviation manufacturing, the higher the difficulty of processing. Many combined curved surface structures must also rely on numerical control equipment. The advanced fighter after the third generation adopts wing body integrated aerodynamic design, which greatly improves the structural strength and design performance of the aircraft. This design actually existed in the 1930s, but it was not used in the early stage of jet fighter application. There are a large number of continuous surfaces in the fusion structure frame, and the process of manufacturing these surfaces is very difficult. The requirements of angle control and surface continuity processing technology are high, so it is difficult to rely on ordinary machining equipment for batch manufacturing. After the extensive application of numerical control equipment in the 1970s, three-axis numerical control machine tools became the means of surface machining, and aircraft began to make more use of structural surfaces to improve aerodynamic design

continuous curved surface variable angle structure is bound to produce semi enclosed space. The designer must consider the machinable factors when designing the body structure. The semi closed or closed complex structure is difficult to form and process as a whole, and must be decomposed into multiple independent Machinable parts to meet the requirements of structure shape and process by using assembly. The problem of assembly is that each part must meet the requirements of independent strength, and the thickness of independent bearing force should also be guaranteed for structures such as structural members and purlins. When riveting and bolting combined parts are used, the strength of the hole at the fastening position of the standard part must also be higher than the strength of the part. If an L-shaped profile with a wall thickness of 2mm is to be fixed with bolts, the thickness of each bolt hole position should exceed the average thickness. If rivets are used, multiple rivet holes need to be evenly distributed

the assembly requirements increase the structural weight of the parts, and the combined standard parts also increase the overall weight. For some small complex light metal structures, the weight of the combined standard parts is even higher than the weight of the parts themselves. If the assembly can be formed directly through technological means, the integrated structure will achieve obvious weight reduction effect

if the thickness of the two assembled panels is 2mm, the integral panel after its integration needs less than 3mm, and the weight can be significantly reduced by canceling the rivet construction requirements. In the improved design of F-16 fighter, the United States used precision castings in the structural improvement of the front fuselage, using integral aluminum alloy castings to replace riveted assemblies, reducing the weight of precision castings that replace assemblies with a total weight of more than 11kg to 4.7kg. When using composite materials to replace metal materials, although the weight of the single structure of the composite wall panel is higher than that of aluminum alloy, the composite wall panel bonded with purlins as an integral structure can eliminate the independent purlins and fixed rivets of the assembly, and the total weight is reduced by nearly 30% compared with the composite metal structure

3d printing directly reflects the weight reduction advantage mainly by printing complex closed/semi closed parts, directly replacing the assembly composed of multiple parts. The weight of parts can be greatly reduced, and the number of rivets and bolts for fixing parts can also be reduced. This is the most direct application of 3D printing weight reduction

integrated weight reduction of aircraft structure is the most effective measure. Aviation system has been striving to realize the integration of structural parts for a long time, especially after composite materials are applied to aviation structural parts, the overall structure of curved stiffened wallboard has shown outstanding advantages in reducing weight and reducing the number of parts compared with metal assemblies. The technology level of composite materials has developed rapidly, and now there are all composite aircraft, but composite materials not only have the problems of high cost and difficult process, but also have the use difficulties of high maintenance and repair in the manufacture of large parts, which limits the application range of composite materials in large parts of aircraft structure. Modern composite materials can not replace the metal materials of structural parts, and 3D printing is conducive to the integration of metal and a variety of metal/non-metal composite structures through highly flexible molding methods, so as to form an aviation light weight structure together with composite materials

3d printing can not only play a role in weight reduction in structural manufacturing, but also be conducive to the weight reduction and improvement of finished product installation and system layout. The supporting structure of the airborne finished product mounting bracket or moving device is complex, and it is not a force bearing structure, which is very suitable for 3D printing. If the assembly parts commonly used now are replaced by 3D integral parts, and the selective melting method with high dimensional accuracy is used for integral molding, it will be conducive to improving the structural consistency and the way of loading and unloading renewal