Many structural components, such as twisted variable cross-section structures, are used extensively in various industries, including aerospace, biomedical devices, ocean machinery, or other fields, such as marine propellers and combustor chambers of jet engines. Most parts have geometric characteristics, such as large-angle twists, large-angle bends, and spatial gradient-change cross-section structures. Under some working conditions and application requirements, the abovementioned twisted variable cross-section structure parts are difficult to process using conventional subtractive manufacturing techniques, such as the casting and milling processes. Using powder-feeding metal additive manufacturing, such as laser melting deposition (LMD) technology, can effectively avoid this problem and achieve excellent precision and near-net shaping of complex structure parts without a physical model. There have recently been a few reports on the route planning for this type of geometric characteristics structure in the field of laser melting deposition technology, both at home and abroad. Thus, a continuous gradual slicing and discrete method is proposed to obtain the route information and complete the forming.

The typical horizontal slicing can no longer meet the forming needs of the abovementioned structure, given that the structure sections examined in this research exhibit spatial geometric characteristics of large twist angles, large bending angles, and spatial gradient-change cross-section structures. A continuous gradual slicing and discrete method was proposed to layer, slice, and separate the forming parts to realize laser metal deposition forming of this structure. The original three-dimensional model is first constructed and segmented using the aforementioned procedure. The six-axis KUKA robotic arms can then be equipped with position and posture data. Finally, multiple experiments were performed to obtain the best forming process parameters and excellent forming parts. After the forming experiment, the geometric parameters of the formed part are measured based on model analysis, and three points along the deposition angle are selected for cutting and sampling.

The continuous gradual slicing method is proposed to complete the layering of twisted variable cross-section structure parts, and discrete deposition units with different geometric characteristics are obtained [Fig. 7(a)]. The homogeneous transformation matrix is obtained by rotating each deposition discrete unit as a point in the base coordinate and tool base coordinate systems. Thus, its position and posture information is determined (Fig. 9). According to the information above, the deposition units with different spatial orientation information (Fig. 10) are spliced horizontally to gain the actual deposition track. In the forming stage, a powder-feeding head and six-axis robot were used to achieve the twisted variable cross-section structure parts.

A continuous gradual layering method is proposed that is based on the inside-laser powder-feeding technology and the principle of laser metal deposition; the twisted variable cross-section structure is sliced according to its geometric characteristics, and the sliced layer and deposition units are successfully obtained. The layering problem of the twisted variable cross-section structure is solved, and the laser metal deposition accumulation of the twisted variable cross-section structure is also realized. The results of the formed parts are as follows: the formed part has a high surface smoothness and forming accuracy; the bending angle and torsion angle of the formed parts are 46.18° and 44.79°, and the errors with the original design angle are 2.62% and -0.47%, respectively; the diameter of the initial circular section and the side length of the end square section of the formed part are 59.63 mm and 60.72 mm respectively, and the errors with the original design size are -0.62% and 1.20%. There are no obvious defects, such as pores and cracks, on the formed part's surface, and each formed part's structure is dense and uniform. Finally, the continuous gradual layering forming technique effectively improves the forming ability of LMD technology for the twisted variable cross-section structure parts. This provides support for its wider application in the additive manufacturing field.