Kamran Shah

Effects of Melt Pool Variables and Process Parameters in Laser Direct Metal Deposition of Aerospace Alloys

Despite considerable advances in of laser direct metal deposition (LDMD) process optimization, there is rather limited work reported on the effects of melt pool variables on the final deposit characteristics. This article considers the effects of process parameters and melt pool characteristics on the deposition of Inconel 718 powder on a Ti-6Al-4 V thin wall. A 1.5 kW diode laser and LDMD system is used to produce a series of deposits. Images of the process are captured using Cu-vapor laser illumination and a high speed camera with long range microscopy optics, and quantitative results are extracted via image analysis. Process parameters such as carrier gas flow rate, powder mass flow rate and laser operating mode (CW and pulsed) and in process variables such as quantified melt pool disturbance, and final part characteristics are correlated and discussed. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and energy dispersive X-ray spectroscopy (EDS) are used to analyze deposited clads in terms of elemental composition and flow characteristics in the deposition melt pool. Melt pool disturbance is found to be a vital parameter in determining the surface roughness of the final part. An inverse relation between the mean surface disturbance of the melt pool and the surface roughness of the part is observed, and carrier gas flow rate and powder mass flow rate both affect the overall melt pool size. The work has implications for the selection of process parameters for commercial laser deposition processes–the speed with which powder is delivered to the melt pool as well as the mass flow rate may need to be taken into account when calculating build rate and for a good surface finish requiring minimum post process finishing a stable melt pool may actually be the worst situation.

Fuzzy Logic Based Edge Detection in Smooth and Noisy Clinical Images

Edge detection has beneficial applications in the fields such as machine vision, pattern recognition and biomedical imaging etc. Edge detection highlights high frequency components in the image. Edge detection is a challenging task. It becomes more arduous when it comes to noisy images. This study focuses on fuzzy logic based edge detection in smooth and noisy clinical images. The proposed method (in noisy images) employs a 3×3 mask guided by fuzzy rule set. Moreover, in case of smooth clinical images, an extra mask of contrast adjustment is integrated with edge detection mask to intensify the smooth images. The developed method was tested on noise-free, smooth and noisy images. The results were compared with other established edge detection techniques like Sobel, Prewitt, Laplacian of Gaussian (LOG), Roberts and Canny. When the developed edge detection technique was applied to a smooth clinical image of size 270×290 pixels having 24 dB ‘salt and pepper’ noise, it detected very few (22) false edge pixels, compared to Sobel (1931), Prewitt (2741), LOG (3102), Roberts (1451) and Canny (1045) false edge pixels. Therefore it is evident that the developed method offers improved solution to the edge detection problem in smooth and noisy clinical images.

Experimental Study of Direct Laser Deposition of Ti-6Al-4V and Inconel 718 by Using Pulsed Parameters

Laser direct metal deposition (LDMD) has developed from a prototyping to a single metal manufacturing tool. Its potential for creating multimaterial and functionally graded structures is now beginning to be explored. This work is a first part of a study in which a single layer of Inconel 718 is deposited on Ti-6Al-4V substrate. Single layer tracks were built at a range of powder mass flow rates using a coaxial nozzle and 1.5 kW diode laser operating in both continuous and pulsed beam modes. This part of the study focused on the experimental findings during the deposition of Inconel 718 powder on Ti-6Al-4V substrate. Scanning electron microscopy (SEM) and X-ray diffraction analysis were performed for characterization and phase identification. Residual stress measurement had been carried out to ascertain the effects of laser pulse parameters on the crack development during the deposition process.

A verified model of laser direct metal deposition using an analytical enthalpy balance method

Analytical modelling of a quasi-stationary laser melt pool without mass addition can be achieved using relatively simple moving surface heat flux solutions. However, including mass addition from a coaxial powder stream alters the laser flux and energy and mass flow pathways and often leads to the problem being modelled using numerical methods. The model described in this paper combines an analytical beam attenuation model to account for beam powder interaction above the melt pool with series of standard solutions for a moving Gaussian heat source to calculate melt pool size and substrate isotherms. A negative enthalpy method is used to compensate for the mass addition to the melt pool. The model is verified using a variety of methods and can predict powder stream mass and temperature distribution at the substrate and final melt pool shape in three dimensions from the major laser direct metal deposition process variables. The model highlights the role of beam-powder interaction in the process.

Observation of the Starting and Low Speed Behavior of Small Horizontal Axis Wind Turbine

This paper describes the starting behavior of small horizontal axis wind turbines at high angles of attack and low Reynolds number. The unfavorable relative wind direction during the starting time leads to low starting torque and more idling time. Wind turbine models of sizes less than 5 meters were simulated at wind speed range of 2 m/s to 5 m/s. Wind turbines were modeled in Pro/E and based on the optimized designs given by MATLAB codes. Wind turbine models were simulated in ADAMS for improving the starting behavior. The models with high starting torques and less idling times were selected. The starting behavior was successfully improved and the optimized wind turbine models were able to produce more starting torque even at wind speeds less than 5 m/s.

Laser Micro Processing of Carbide Tool Insert

For a number of applications there is evidence that the tribological conditions for mating surfaces can be improved by surface texturing. Literature shows that texturing the tool rake face can have a positive influence on tribological properties. This research focuses of the texturing of tool rake surface by laser machining. Compared to other texturing techniques, laser provides the flexibility of machining customized textures on tool surface. This paper deals with the assessment and optimization of the process parameters for generation of textures on cemented carbide inserts under ambient conditions by using a femtosecond laser. The paper is a significant contribution to the efficient and rapid generation of customized surface texture on hard tool inserts.Copyright

The significance of melt pool variables in laser direct deposition of functionally graded aerospace alloys

Laser Direct Metal Deposition (LDMD) has developed for a range of diverse applications, from high precision manufacturing to repair. Although functional grading of surface coatings is well established, research into three-dimensional intermetallic grading as an alternative to welding is ongoing. This paper considers the functional grading of Ti-6Al-4V to Inconel 718 for aerospace applications. A 1.5 kW diode laser and LDMD system is used to produce a series of graded thin wall deposits. Images of the process are captured using Cu-vapour illumination and a high speed camera with long range microscopy optics and quantitative results extracted via image analysis. Process parameters, in process variables such as quantified melt pool disturbance, and final part characteristics are then correlated and discussed. By monitoring in process variables, the work aids in better understanding what happens during LDMD, especially when material transition occurs, and how this leads to final deposit characteristics.

Direct diode laser deposition of functionally graded Ti-6AL-4V and inconel 718 components

Laser direct metal deposition (LDMD) has developed from a prototyping to a single metal manufacturing tool. Its potential for creating multi-material and functionally graded structures is now beginning to be explored. In this work, three dimensional functionally graded structures of Ti-6Al-4V and Inconel 718 are fabricated by laser direct metal deposition (LDMD) on Inconel 718 substrate. The multi-track parts are built at a range of powder mass flow rates using a side nozzle and 1.5 kW Diode laser operating in both continuous and pulsed beam modes. Microstructure characterization and phase identification are performed by optical microscopy and X-ray diffraction. Only two samples are free of macro-scale cracks, one prepared with a continuous laser beam and one prepared with the beam in pulsed mode. XRD results show the presence of the brittle Ti2Ni phase in all samples.