*Article* **Experiment of Process Strategy of Selective Laser Melting Forming Metal Nonhorizontal Overhanging Structure**

#### **Wentian Shi \*, Peng Wang, Yude Liu and Guoliang Han**

School of Materials Science and Mechanical Engineering, Beijing Technology and Business University, Beijing 100048, China; wangpeng\_12321@126.com (P.W.); liuyd@th.btbu.edu.cn (Y.L.); hanguoliang163@163.com (G.H.)

**\*** Correspondence: shiwt@th.btbu.edu.cn; Tel.: +86-138-1022-3727

Received: 9 March 2019; Accepted: 25 March 2019; Published: 27 March 2019

**Abstract:** To improve the precision of the nonhorizontal suspension structure and the forming quality of the overhanging surface by selective laser melting, the influence of laser power on the upper surface and the overhanging surface forming quality of 316L stainless steel at different forming angles was studied in the experiment. The influence of different scanning strategies, upper surface remelting optimization, and overhang boundary scanning optimization on the formation of overhanging structures was compared and analyzed. The forming effect of chromium–nickel alloy is better than 316L stainless steel below the limit forming angle in the overhanging structure. The better forming effect of chromium–nickel alloy can be obtained by narrowing the hatch space with the boundary optimization process. The experiment results show that the forming of the overhanging structure below the limit forming angle should adopt the chessboard scanning strategy. The smaller laser power remelting is beneficial to both the forming of the overhanging surface and the quality of upper surface forming. The minimum value of surface roughness using the 110 W power laser twice during surface remelting and boundary scanning 75◦ overhanging surface can reach 11.9 μm and 31.1 μm, respectively. The forming accuracy error range above the limit forming angle is controlled within 0.4 mm, and the forming quality is better. A boundary count scanning strategy was applied to this study to obtain lower overhanging surface roughness values. This research proposes a process optimization and improvement method for the nonhorizontal suspension structure formed by selective laser melting, which provides the process support for practical application.

**Keywords:** selective laser melting; nonhorizontal suspension structure; boundary remelting; surface roughness; forming accuracy
