Abstract
As a very common type of laser additive manufacturing technology, laser material deposition (LMD) is widely used, having exceptional application advantages including surface enhancing, repairing damaged parts with high value-add, and building functionally graded material. At present, the continuous wave laser is a common laser mode used in the LMD process. The investigation of pulse shaping, which can add a degree of control over the thermal history, is limited. In this study, the effects of pulse shaping on the geometrical characteristics, microstructure, and microhardness were investigated through conducting single-track experiments with different laser shapes, including continuous, rectangular, ramp up, ramp down, and hybrid ramp. The results indicated that the clads created by continuous and ramp up laser shape presented the maximum and minimum dimensions of geometrical characteristics, respectively. The rectangular and hybrid ramp laser shape deposited the clads with similar dimensions. The continuous laser shape produced the clad with the coarsest microstructure and lowest hardness because of the lowest cooling rate. The smallest grain size and highest hardness presented in the clad were seen with the rectangular laser shape owing to the biggest cooling rate. The cooling rates in ramp up and ramp down were restrained by the gradual heating and gradual cooling, respectively.
Highlights
Compared to conventional subtractive manufacturing processes such as turning and milling in which products can be fabricated by removing material from a large stock or sheet, additive manufacturing (AM), whereby the material is added layer upon layer to produce a 3D object directly from a computer aided design (CAD) model without attendance of any molds or tools, possesses many superiorities like energy saving, reduction of costs, improvement of material utilization, etc. [1,2,3]
In the laser material deposition process, a high-powered laser beam acts as heating energy to create a molten pool on the surface of substrate, and the metallic powder is delivered from the powder nozzle into the molten pool simultaneously by a flowing inner gas [7]
This work conducted single-track deposition experiment to investigate the effects of pulse shaping on the geometrical characteristics, microstructure, and microhardness of single-track clad based on different shapes of laser
Summary
Compared to conventional subtractive manufacturing processes such as turning and milling in which products can be fabricated by removing material from a large stock or sheet, additive manufacturing (AM), whereby the material is added layer upon layer to produce a 3D object directly from a computer aided design (CAD) model without attendance of any molds or tools, possesses many superiorities like energy saving, reduction of costs, improvement of material utilization, etc. [1,2,3]. Gharbi et al studied the influence of a pulsed laser regime on the surface finish induced by LMD on a widely used titanium alloy (Ti6Al4V) Their finding confirmed that high mean power improved surface finish and using a pulsed mode with large duty cycles was clearly shown to provide smoothening effects [22]. The results indicated that the splash of powder in the fabricating process is alleviated, the quality of deposition improves, and the width decreases owing to the use of pulse shaping [15]. This work conducted single-track deposition experiment to investigate the effects of pulse shaping on the geometrical characteristics (width, height, and depth), microstructure, and microhardness of single-track clad based on different shapes of laser. The effect of thermal history created by different shapes of laser on the cooling rate of molten pool in the laser material deposition process was analyzed
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