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Additive manufacturing (AM) is one of the most important and, of course, the most attractive technologies that has attracted the attention of industries and researchers in the last few decades. The direct laser metal deposition (DLMD) method is one of the AM methods that can be used to produce metal parts with good dimensional accuracy and quality. In this research the effect of laser power on the geometrical dimensions and microhardness of 316L stainless teel single-track layers additively manufactured by the DLMD method onto a 4130 steel substrate was studied. In addition, the microstructure of the 316L stainless steel DLMD layers was investigated. The height and the maximum width of the 316L stainless steel DLMD layer, the width of the interface, penetration depth, and microhardness characteristics of the 316L stainless DLMD single-track layers were considered as output responses. The results showed that by increasing the laser power, the height, maximum width of the 316L stainless steel DLMD layer, width of the interface, and penetration depth of the 316L stainless DLMD single-track layers increased. At the maximum laser power of 260 W the maximum height and maximum width of the 316L stainless steel DLMD layer and width of the interface of the 316L stainless steel DLMD layers were obtained at 830, 970 and 615 µm, respectively. The microhardness of the samples varied from 281 to 314 HV. Examination of the microstructure of the 316L stainless steel DLMD layers showed solidification in columnar and equiaxed dendritic structures in all parts of the single-track layers, with the formation of secondary phases in the interdendritic regions. [ABSTRACT FROM AUTHOR]

The laser engraving process on a 3.2 mm thick polycarbonate sheet using a low power CO2 laser is investigated herein. For this purpose the scanning speed, laser power and laser focal position are considered as laser input parameters. Depth of laser beam penetration, engraving width and heat affected zone (HAZ) are supposed to be the process output parameters and the measurements of these areas were made by optical microscope. It should be noted that the pressure of laser assist gas is the same in all samples. In this process, in some samples, the quality of the laser engraving was very suitable, with a maximum penetration depth of 1.25 mm. It is shown that the penetration depth of laser engraving increases with increasing laser power and decreasing the laser speed due to increasing heat input. In addition to the heat input, laser focal point is effective on the interaction time of the laser beam with the workpiece. It was supposed that with decreasing laser focal point and the laser scanning speed, then the laser beam has more interaction time with the polycarbonate sheet, resulting in more significant amount of evaporation, which increases the penetration depth of the laser beam into the workpiece. [ABSTRACT FROM AUTHOR]

Laser surface treatment conducted using a high power diode laser (HPDL) to improve the corrosion resistance of AISI 17-4 PH stainless steel is conducted and investigated. Based on microstructure and corrosion behavior study, standoff distance (SOD) of 60 to 80 mm, laser power of 1000 to 1400 W and scanning speed of 5 to 8 mm/s were considered as process parameters. The martensite formed in this alloy is of a lath morphology and has a dislocated substructure. Microscopic studies have revealed the formation of a Cu-rich phase in the samples aged at temperatures below 550°C. The martensite phase was seen to terminate at packet boundaries where two groups of laths belonging to two distinct orientation variants met. After HPDL treatment the microhardness and corrosion resistance of the 17-4 PH stainless steel were examined. Whereas the microhardness was altered accordingly with variation of the chosen laser operating parameters, the corrosion resistance showed no great improvement. [ABSTRACT FROM AUTHOR]

Titanium and their alloys have high strength to weight ratio, good corrosion resistance and high melting point temperature lead to their application in engineering. Ti-6Al-4V alloy has been widely used in medical, chemistry and aerospace industries. In this research, laser welding of Ti-6Al-4V sheet with the thickness of 1.7 mm performed using a 400 W pulsed Nd:YAG laser. The effects of laser peak power, pulse duration and laser pulse energy on the weld bead profile, weld microhardness, tensile strength and microstructure were studied. Results showed that by increasing laser peak power, decreasing pulse duration and increasing laser pulse energy, the weld penetration increases. Metallurgical observations revealed that welded zone comprises of acicular α' phase within prior coarse β grains. Microhardness distribution is more uniform in welded zone. The microhardness value in the welded zone is the highest which is attributed to high martensitic phase content in the welded zone. The ultimate tensile strength (UTS) values show the variation from 649 to 998 MPa in the Nd:YAG laser welded samples. [ABSTRACT FROM AUTHOR]

In order to investigate the influence of process parameters on the hole geometric features, experiments were conducted based on response surface methodology (RSM) as one of the most useful design of experiments (DOE) approaches. Frequency of the laser beam (80 to 240 Hz), duty cycle (20.00 to 40.00%) and laser power (100.00 to 200.00 W) were considered as independent variables, while the entrance and exit hole diameters and their circularity as well as the hole taper were raised as process outputs. The experiments were performed on samples of thin AMS 5510 stainless steel 321 sheet with thickness of 0.01 inch by a 500.00 W fibre laser. The results indicated that the entrance hole diameter and hole taper decrease when the laser pulse frequency increases and laser power decreases. Also, laser frequency has a double reaction before duty cycle and laser powers on circularity of entrance hole. Minimum hole taper, minimum entrance diameter, and maximum circularity of entrance hole were considered as optimization criteria. Verification experiments were carried out to analyse the results obtained via software. [ABSTRACT FROM AUTHOR]

Butt welds were carried out on Ti-6Al-4V sheets with thickness 1.7 mm using a 2.2 kW CO2 laser welding. The effect of linear heat input on the joint geometry, microstructure and mechanical properties was investigated. The welding process efficiency and the ratio of root width to top width were used to evaluate the joints. The results showed that fully penetrated joints were achieved at linear heat input of greater than 4.00 J/mm. Metallographic observations showed that fusion zone (FZ) consists of acicular α' phase within prior coarse β grains. Increasing linear heat input causes to change the martensitic phase from an acicular like to plate like morphology. Also, the prior β grain size increases because longer time exists for β grain coarsening. The microhardness values in the FZ decrease with increasing the linear heat input. This phenomenon can be attributed to decrease of martensitic phase formation in the FZ. The ultimate tensile strength of the joints ranges from 624 to 1002 MPa at room temperature. [ABSTRACT FROM AUTHOR]

In the present study a pulsed Nd:YAG laser with a maximum average power of 400 W and a 250 A tungsten inert gas (TIG) electrical arc were used as two combined heat sources in hybrid laser arc welding (HLAW). The effect of distance between heat sources, was investigated and the optimum distance selected. Laser beam welding (LBW) and TIG welding parameters were considered constant. The microstructure, micro-hardness and weld bead profile of stainless steel 1.4418 welded were investigated using HLAW, LBW and TIG in the same setting. The influence of heat input on weld pool geometry was surveyed. The results showed that penetration of HLAW doubles that of TIG and were five times that of LBW. Also the grain size in the heat affected zone (HAZ) in TIG was obviously coarse. In the fusion zone, the coaxial grains exist, which the size was the smallest in LBW and was the largest by TIG. [ABSTRACT FROM AUTHOR]

To investigate the influence of fibre laser percussion drilling process parameters on the hole geometric features of Inconel 718 with thickness of 1.0 mm experiments were conducted based on response surface methodology (RSM). Frequency of the laser beam (200 to 400 Hz), duty cycle (30 to 50%), laser power (375 to 425 W) and focal plane position (0.7 to 1.5 mm) were considered as independent variables, while the entrance and exit hole diameters, as well as the hole taper were raised as process outputs. The obtained results indicate that the entrance hole diameter increases as the laser pulse frequency, laser power, duty cycle and focal plane position increase; furthermore, by increasing duty cycle and focal plane position, the hole taper decreases. Minimum hole taper, maximum exit diameter, and minimum entrance diameter were considered as optimization criteria. Verification experiments were carried out in order to analyse the results via software. [ABSTRACT FROM AUTHOR]

In the present study the Nd:YAG laser-tungsten inert gas (TIG) hybrid butt joint welding parameters of stainless steel 1.4418 have been investigated by coupling a pulsed Nd:YAG laser with a continuous wave (CW) TIG source. The experiments were performed based on the response surface methodology (RSM) as a statistical design of experiments approach to investigate the effect of parameters on the response variations, and achieve the mathematical equations to predict the new results. Welding speed (1 to 5mm/s), TIG current (90 to 130 A) and distance of heat sources (1 to 5 mm) were assumed as the input process variables while the weld surface width, weld seam area, and weld penetration were considered as the process responses. Analysed by statistical techniques, the results indicated that the welding speed is the most important parameter among all parameters with a reverse effect on process outputs. Besides, TIG current has a direct influence on all investigated responses. The paper invokes the desirability approach optimization technique to achieve the best geometrical dimensions of weld profiles and validating the theoretical results using the experimental tests. Once the optimum settings are considered, a tensile test was also conducted. [ABSTRACT FROM AUTHOR]