SLS (Selective Laser Sintering) has been developing rapidly since its initial invention for non-metal materials by Texas University. Nowadays, Direct Metal Laser Fabrication (DMLF), as a variant of SLS technique, has been investigated intensively which is aimed at rapid manufacturing of end-use metal products with full functions. For describing the stability and properties of DMLF process, Top Surface Quality (TSQ) was put forward in this paper, which could be a unique and crucially important feature compared with traditional manufacturing methods. Through the systematic and detailed analysis of DMLF process using related theories of additive manufacturing technologies, it was revealed that TSQ was the key factor for controlling the stability of DMLF process and thus tailoring final properties of metallic parts. TSQ was defined as the surface morphology in macro and micro scopes in laser scanning area of unit layers during DMLF, and could be characterized by three key elements: flatness, compactness and cleanliness. Only good TSQ could ensure the stability of DMLF process and excellent performance of metal parts in theory. The flatness was the significant factor to assure the shaping during DMLF while the compactness and cleanliness are the decisive factors to assure the final properties of metal part for DMLF. As an example, the typical top surface defects and their contributing factors in DMLF for Cu-based metal powder mixtures were investigated thoroughly according to the proposed definition and requirements. Moreover, the specific controlling methods of TSQ were provided and discussed. Eventually, DMLF of three-dimensional Cu-based metal sample with complicate structure was successfully performed by taking some effective measures for adjusting TSQ parameters.

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