Objective Variable cross-section thin-walled hollow bending and torsion structural parts have been widely used in aerospace, machinery, shipbuilding and other fields, such as propeller structure, hollow blades in steam turbines, etc. These parts generally have the characteristics of twisting and overhanging, free change of section, etc. Its profile is a variable cross-section for bending and torsion, belonging to a relatively complex free surface, which requires high geometric accuracy in production and application. Traditionally, CNC milling, precision casting, special machining and other processing methods are mainly used, but these processing methods have problems of low material utilization, long production cycle and high processing costs, and in some cases can not meet the actual use requirements. Laser melting deposition (LMD) technology is a new rapid prototyping technology, which has the advantages of complex structure of forming parts, near net forming without mold, and simple process. Based on the technology of laser melting deposition (LMD), the laser melting deposition of thin-walled hollow bending and torsion structure with variable cross-section is studied in this paper.
Methods Variable cross-section thin-walled hollow bending and twisting structural parts are three-dimensionally twisted in space, with the characteristics of twisting, overhanging and free change of cross-section. Based on the technology of laser melting deposition (LMD) with optical powder feeding, this paper proposes the discrete layered method of space trajectory element to complete the forming trajectory planning (Fig.5), and proposes the compensation technology of base point offset of space variable attitude to compensate the position offset of the actual attitude change base point (Fig.10). Finally, the laser melting deposition forming of the bending and twisting structural parts with variable cross-section was realized and the dimensional error was effectively controlled.
Results and Discussions In view of the difficulties of forming trajectory planning of such complex structural parts, the discrete layered method of space trajectory element is proposed to layer the structural parts and generate discrete deposition units, and each discrete deposition unit is deposited according to the designed path. In view of the error caused by the smooth curve movement of the manipulator using line segment element fitting in the actual forming process, the space variable attitude base point offset compensation technology is proposed to compensate the position offset of the actual attitude change base point in the forming process, so as to realize the effective control of the size error (Fig.13).
Conclusions Through the above methods, the forming dimensional error is effectively controlled, the forming accuracy is improved, and finally the laser melting deposition forming of thin-walled hollow bending and torsion structural parts with variable cross-section is realized. The dimensional accuracy of the formed structural parts is relatively high, the shape dimensional error is between −0.44% and 1.83%, the average thickness of the structural parts is between 5.9 and 6.19 mm, the microhardness of the structural parts is between 269 and 282.2 HV, and the surface and interior of the structural parts are dense and uniform, without obvious pores, cracks and other defects.
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