Research On Mechanical Behavior Of Laser Rapid Forming Metal Part

Laser Rapid Forming (LRF) is a new and advanced Solid Freedom Fabrication technology which has been developed rapidly in the recent ten years. This technology integrates virtues of Rapid Prototyping and Laser Cladding technology, and can attain directly high performance and dense metal part without mould, with wider application foreground. This paper studies mechanical behavior of Laser Rapid Forming metal part by experiment, including cracking behavior, residual stress distribution and mechanical property.The forming mechanism and influencing factors of crack in laser rapid forming cladding layers are investigated through micro measurement and analysis methods. For nickel-base self-fused alloys, the cracking of cladding layers belongs to the cold crack domain, Which is the result of collective effect of low ductility of such alloys and residual stress induced in cladding layers. For 316L stainless steel alloy, the cracking of cladding layers belongs to the hot crack domain, Which is mainly caused by the separation of liquid films in the grain boundary under the effect of tensile stress in cladding layers. Two kinds of crackings show that the tensile stress induced for asymmetric temperature distribution during laser rapid forming processing is the external reason which results in cracks.The planar residual stresses of Laser Rapid Forming sheet samples are measured by the hole-drilling method. The results show that the residual stress y parallel to laser scanning direction is the major residual stress of samples, which is positive. Comparably, the residual stress z perpendicular to laser scanning direction is smaller.For Ni20 alloy, In the limited cladding height, y is negative near substrate and begins to turn to tensile stress as cladding layers increase, the tensile stress numerical value increases gradually, which implies that residual stress accumulates as laser energy inputs continuously. Z is positive in cladding layers, numerical value is small. The tensile stress decreases as cladding layers increase, has a trend to turn to compressive stress.For 316L stainless steel alloy, In the whole cladding height, y and z are positive. Because residual stress accumulates gradually, y is larger tensile stress near substrate, above one height, y decreases and goes steady as cladding layers increase more,holding low tensile stress state. In the whole cladding height, z numerical value is small, the tensile stress decreases as cladding layers increase, has a trend to turn to compressive stress.Based on the analysis of crack and residual stress, mechanical property of Laser Rapid Forming sample is studied. By measuring the room temperature mechanical property of LRF Ni20 and 316L sample which endure residual tensile stress, the results show the room temperature yield strength and ultimate strength have approach or exceed the traditional forging level for the same alloy.