3D printing technology applied in the field of large castings and forgings
At present, the application and research of 3D printing technology mainly focuses on the processing and repair of precision parts such as aerospace, electronics and medical, but there are few applications in the field of large-scale castings and forgings mainly based on iron-based metals. Large casting and forging products, such as thermal power spindles, nuclear power heads, turbine blades, etc., are tens of tons of weights, and the current metal 3D printing technology averages 1kg/h processing speed and material cost per kilogram of thousands of yuan. The use of large-scale casting and forging integral 3D printing technology to complete the manufacture of large castings and forgings can not be achieved. However, this is not to say that 3D printing technology cannot be widely used in the field of large castings and forgings. As long as it is applied properly, 3D printing technology can be an indispensable important production process in the manufacture of large castings and forgings, like casting, forging and welding, and it can be used in the process of technological innovation, cost reduction and efficiency improvement in the large casting and forging industry. Important role. Based on the research results of current metal and non-metal 3D printing technology in other fields, this paper analyzes the application direction of future 3D printing technology in the field of large-scale castings and forgings mainly based on iron-based metals, thus serving the large casting and forging industry. Development provides a reference. 1. Metallic material 3D printing technology The performance of metal materials such as large-scale parts such as titanium alloy large-scale integral main bearing structural parts can reach or approach the level of forgings. The 3D printing technology repairs the turbofan engine blade technology to achieve the requirements of the parts in the 3D printing and the joint area of ​​the part base. Compared to conventional soldering, metal 3D printing repair has the following features: (1) The heat affected zone is small and does not affect the stress distribution of the matrix structure; (2) no heating and subsequent heat treatment; (3) The 3D printing organization is densely combined with the base metallurgy, and the performance is close to the original structure of the part; (4) The tissue performance of the 3D printing area reaches the forging level; (5) Automatic control with less machining allowance. 1.1 Partial 3D printing forming of large forgings Taking the AP1000 nuclear power main pipeline as an example, the design requires ultra-low carbon-controlled nitrogen stainless steel forging. The main difficulty in forging production is the formation of two nozzles, and the forging material utilization rate is below 15%. Inspired by the 3D printing technology to repair the turbofan engine blades, the formation of the main nuclear power pipeline can be simplified into forging or extrusion of stainless steel pipe + 3D printing nozzle forming, which can greatly reduce the production difficulty and cost of the nuclear power main pipeline. Large forgings such as nuclear power main pipes and multi-nozzle heads with local hard-to-form features can be formed by forging body + 3D printing. This method will greatly reduce the difficulty and cost of forgings in the overall quality of forgings. And cycle. In addition, the idea of ​​partial 3D printing of large forgings can be extended to 3D printing and tailoring of large parts. If the 3D printing area and the metal material properties of the 3D printing area and the substrate bonding area can meet the forging requirements, this indicates that the 3D printing tailor welded forgings can be used instead of the overall large forgings in the future. 1.2 Large forging defect repair Quality problems such as excessive defects on the surface and interior of large forgings and insufficient machining allowances due to lack of material may lead to the overall scrapping of forgings, resulting in huge economic losses and energy waste. Because the properties of the welded structure are lower than the forging structure, the forgings generally do not allow repair welding, and the emergence of metal 3D printing technology can change this situation. At present, some material properties of metal 3D printing can reach the level of forgings. If the combination of 3D printing tissue and forging substrate can meet the requirements of forgings, 3D printing technology can be used to partially repair the defective area of ​​large forgings, thereby improving the qualification rate of forgings. In the future, with the improvement of 3D printing technology, similar to large castings, such as repair welding, large forgings also allow 3D printing repair, which will be a revolutionary breakthrough for the production process of large forgings. 1.3 Large parts online repair Large parts such as generator rotors, turbine blades, and marine crankshafts may have local cracks, wear and deformation failures during use. Traditional repair welding methods require machining, preheating, welding, machining, and heat treatment. repair. The repair work needs to be carried out on large professional equipment, but the performance of the repair area is lower than the original organization of the parts, which increases the maintenance cost and maintenance period, and the maintenance effect is not satisfactory. The portable mobile metal 3D printing device, which combines robot and 3D printing technology, can change the status quo, achieve on-site repair of large parts, and even online repair. The specific steps of robot metal 3D printing technology to repair large parts are: (1) Determining the repair plan and pre-processing the repaired area; (2) Three-dimensional imaging technology is used to model the repaired area in three dimensions; (3) converting the three-dimensional model of the repaired area into a robot moving path; (4) Determine 3D printing parameters, robot positioning, and repair; (5) Surface treatment and detection of the repair area. 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