C. P. Paul

Three-Dimensional Conduction Heat Transfer Model for Laser Cladding Process

Cladding is the process of depositing a superior built-up layer on a substrate by fusion. In the present study a three-dimensional conduction heat transfer model is developed and solved using the finite-volume method in a nonorthogonal grid system for a blown-powder laser cladding process. Comparisons with experimental data for deposition of copper powder on SS316 stainless steel show that the developed model can predict the geometry of the buildup layer above the substrate within an acceptable range of tolerance. The overall absorption of the CO2 laser radiation is in the range of 14–17%.

Enhancement of Deposition Quality in Micro-plasma Transferred Arc Deposition Process

Micro-plasma-transferred arc (µPTA) wire deposition is a cost-effective additive layer manufacturing process used for remanufacturing/repair of high-value components. Prediction of geometry and cross-sectional area of each deposition track and deposition overlap between the successive deposition tracks helps in optimizing the deposition strategies and automated repair and remanufacturing of the components by µPTA process. This paper presents investigations on enhancing the deposition quality in µPTA process by approximating deposition geometry as an elliptical arc with an objective to predict its cross-sectional area and to optimize the deposition overlap between the successive deposition tracks. The model was validated using the experimental apparatus developed for the µPTA wire deposition process. The predictions were compared with the previously developed models of deposition geometry considering it as an arc of parabola, circle, and cosine function. The results proved the superiority of the elliptical function-based model over the previous models for predicting cross-sectional area and overlap of the deposition track for µPTA wire deposition process. The deposition overlap was optimized to predict the center distance between successive deposition tracks to maximize the quality of deposit over a flat surface.

An Experimental Investigation and Analysis of PTAW Process

Experiments are conducted to deposit SS304 L powders on SS316 plates by plasma transfer arc welding process with varying four input process parameters, namely scanning speed, powder feed rate, stand-off distance, and current. The effects of these four input process parameters on deposition geometry, dilution, and bead continuity are investigated in this study. Attempts have been made to explain the experimental results with only two compound parameters, “energy deposition per length” and “powder deposition per length” instead of four independent input process parameters. It is observed that the variation of dilution is very little when the scanning speed increases from 100 to 600 mm/min and other process parameters remain constant. When the powder feed rate increases and other parameters remain constant, initially the dilution decreases rapidly and attains a minimum value which do not change further with increase in powder feed rate. It is also observed that the dilution remains almost constant around 6–9% as the stand-off distance changes from 7 to 11 mm and other process parameters remain constant. The formation of nonuniform bead is found to be due to insufficient energy deposition per length per mass of supplied powder.

Numerical Simulation of Laser Rapid Manufacturing of Multi-Layer Thin Wall Using an Improved Mass Addition Approach

An improved mass addition approach based on enthalpy balance is used for the numerical simulation of the temperature distributions and geometries during laser rapid manufacturing (LRM) of a multi-layered thin-wall. The approach involves the estimation of the local track height at every node along the track width on the substrate/previously deposited layer by simultaneous balancing of the excessive enthalpies above solidus temperature about the laser axis and the material interface at the substrate/previously deposited layer for material addition during the laser rapid manufacturing of a multi-layer thin wall. It takes laser power, laser beam size, scan-speed, powder feed rate, powder stream diameter, and time-delay between the deposition of two subsequent tracks as user-defined input, and computes the temperature distributions and the geometries of the deposited layers across the process domain in a dynamic fashion. In the present study, the laser rapid manufacturing of five layered thin walls of SS 304L on a work piece of the same material was simulated for various combinations of processing parameters and compared with experimental results. The percentage errors in simulated and corresponding experimental cumulative track heights along with track width were calculated and compared with those of other existing models and the results of present approach were found to be the least. The result indicates that the height and width of the layer under deposition depends on the geometry and temperature distribution of previously deposited layer and, consequently, governed the final geometry of thin wall.

Analysis of Discontinuous Bead Formation by PTAW Process

This research investigates the effects of input parameters on discontinuities in bead formation during material deposition by the plasma transferred arc welding (PTAW) process. Experiments based on L27 orthogonal array have been carried out by deposition of stainless steel powder (SS304 L) on stainless steel plate (SS316). Three types of depositions have been observed, namely continuous, partially continuous and discontinuous deposition. A process map has been developed, based upon powder and energy deposition per length, where the above-mentioned three types of depositions are distributed. The discontinuities in the deposition can be overcome by increasing the energy deposition per length or by reducing the powder deposition per length.

Lasers in Materials Processing

Laser is undoubtedly one of the most important inventions of the twentieth century. Today, it is widely deployed for a cornucopia of applications including materials processing. Different lasers such as CO2, Nd:YAG, excimer, copper vapor, diode, fiber lasers, etc., are being used extensively for various materials processing applications like cutting, welding, brazing, surface treatment, peening, and rapid manufacturing by adopting conventional and unconventional routes with unprecedented precision. In view of its potential for providing solution to the emerging problems of the industrial materials processing and manufacturing technologies, a comprehensive program on laser materials processing and allied technologies was initiated at our laboratory. A novel feature-based design and additive manufacturing technologies facilitated the laser rapid manufacturing of complex engineering components with superior performance. This technology is being extended for the fabrication of anatomically shaped prosthetics with internal heterogeneous architectures. Laser peening of spring steels brought significant improvement in its fatigue life. Laser surface treatments resulted in enhanced intergranular corrosion resistance of AISI 316(N) and 304 stainless steel. Parametric dependence of laser welding of dissimilar materials, AISI 316M stainless steel with alloy D9, was established for avoiding cracks under optimum processing conditions. In the domain of laser cutting and piercing, the development of a power ramped pulsed mode with high pulse repetition frequency and low duty cycle scheme could produce highly circular, narrow holes with minimum spattered pierced holes. A review of these experimental and some theoretical studies is presented and discussed in this chapter. These studies have provided deeper insight of fascinating laser-based materials processing application for industrial manufacturing technologies.

Laser-Assisted Manufacturing: Fundamentals, Current Scenario, and Future Applications

This chapter presents the basic principles, applications, and future prospects of various laser-assisted manufacturing techniques used for material removal, joining, and additive manufacturing. The laser hazard and safety aspect is also briefly included.

On the microstructure of a thin wall formed under thermal and stress fields induced in laser solid freeform fabrication process

In laser solid freeform fabrication (LSFF), the final microstructures and consequently the physical properties of the successive deposited layers of additive materials are determined through melting, solidification and solid state transformations caused by a moving laser beam. In this paper, temperature distribution and stress field induced during the multilayer LSFF process and their correlation with the local microstructure formation are studied throughout the fabrication of a four-layer thin wall of SS304L. For this purpose, parallel to the experimental investigation, a coupled 3D time-dependent numerical model is employed to simulate the process. The numerical and experimental results show that stress concentrations formed at the end points of the wall are the locations prone to potential delaminations and crack formations. Different types of microstructures, such as dendritic with and without secondary arm spacings, are observed at various locations within the same layer due to different cooling rates.

Comparative Investigation on the Effects of Laser Annealing and Laser Shock Peening on the As-Manufactured Ni–Ti Shape Memory Alloy Structures Developed by Laser Additive Manufacturing

An indigenously developed laser additive manufacturing (LAM) system was deployed to fabricate complex structures of Ni–Ti shape memory alloys. LAM is opted for samples development as it gives the advantage of fabricating complex structure precisely as per the requirement with good composition control. As-made samples were brought under two different surface processing techniques of laser annealing (LA) and laser shock peening (LSP). In general, LA is carried out to reduce the residual stress to improve the sample’s functional life, and LSP is done to induce compressive stress in the samples to improve the fatigue life and prevent the samples from fracture. Wide research has been done in the past to find the effects of LA and LSP on the samples to characterize the improvement of the samples in their respective accord. Both LA and LSP were carried out using pulsed green Nd:YAG laser. Since Ni–Ti is a shape memory alloy (SMA), there is no much exposure about the shape memory property of the sample before and after LA and LSP. In this chapter, an attempt has been made to investigate the surface morphology, crystallinity and shape memory effect of Ni–Ti fabricated by LAM. Obtained results are homogenous microstructure, good crystalline nature and better shape memory effects through LA or LSP. The surface morphology, phase transformation temperature and microstructure of laser annealed Ni–Ti structures were studied with scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). Laser energy density of 1100 mJ/cm2 at 532 nm wavelength was used for LA. Same laser energy density at 1064 nm wavelength was used for LSP. Novel output regarding the shape memory nature of the materials was obtained.

Microstructural Development Due to Laser Treatment and Its Effect on Machinability of Ti6Al4V Alloy

Application of the laser in machining has been demonstrated to improve the machinability in several metals and alloys. A very high heating and cooling rate during laser treatment tends to modify the microstructure significantly. In some materials, the change in the microstructural features affects the machinability of the materials. In this work, microstructure evolution due to laser treatment and its effect on the machinability of Ti6Al4V was studied using advanced characterization techniques. The microstructure of the surface and subsurface of the cylindrical Ti6Al4V rod was modified using a high-power laser source with varying laser scanning speeds. The laser treatment resulted in three distinctly different microstructures along the radial direction of the rod; these were classified as the lath dominant zone, a mixture of laths with equiaxed grains and equiaxed grains surrounded by bands. Rapid heating and cooling during laser scanning lead to the formation of the martensite phase and local strain development. Further, at the boundaries of laths, compressive twins (57 deg