Literature Review on Laser Deposition TechnologyResearch Paper

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Laser Deposition Technology (LDT)

Laser Deposition Technology refers to the procedure whereby a metal powder is introduced in the focused beam of a high-power laser in strongly monitored atmospheric conditions. The surface of the target material is melted by the focused laser beam and a tiny molten pool of base material is produced by the target material. Powder supplied on the same point is absorbed by the molten pool, hence producing a deposit, which might vary from 0.005 to 0.040 inches in thickness, and 0.040 to 0.160 inches in wideness. The resultant deposit might then be utilized to construct or mend metal parts meant for various uses [2].

LDT is simply a "blanket name," which covers several "like" procedures (such as direct metal deposition (DMD), laser metal deposition, and laser additive manufacturing (LAM) among others), which utilize a focused laser beam as the source of heat for the deposition of the powdered metals [2].

b. Applications of Laser Deposition Technology

LMD technology strives to tackle the subsequent industry requirements: decrease of production waste products, decrease of equipment costs, fixing of parts which are expensive to substitute or hard to effectively mend, decrease of the lead times of parts, deposition of new materials, and customization of parts on the fly.

There exist three major areas whereby LDT could be utilized in industry and production [2]:

Laser Repair Technology (LRT)

It deals with the repair of damaged parts. While operating any kind of mechanical device having moving components, fixing and reconstruction of the damaged metal parts is part of daily life. Fixing of the damaged parts usually saves the money that could have been utilized to buy novel ones.LRT makes it possible and cheap to fix components that were initially un-fixable [2].

Laser Cladding Technology (LCT)

This is concerned with the cladding of materials. It is a procedure that mends surfaces on parts through first machining down the damaged surface and later reconstructing it through the deposition of cladding materials in fine coats, so as to repair the damaged surface. Good candidates for the LCT procedure are seal, coupler, and bearing surfaces in shafts, which are usually thought of as non-repairable [2].

Laser Freeform Manufacturing Technology (LFMT)

It deals with conducting near-net-shape freeform structures directly from CAD files. This procedure begins with a CAD drawing of a component. A tool path file is then constructed from this electronic drawing. The part is later constructed by the laser deposition system, coat by coat. LMFT is capable of constructing intricate shapes, prototyping as well as constructing various parts in shorter time spans, compared to other methods [2].

The economic advantage of this particular technology is in its capability to increase value to the part through the deposition of layer(s) of material, so as to considerably raise the functioning life of costly parts, which require working reliably for long durations of time in costly procedures. The properties of the coat permit functioning in raised temperatures, or better, rust and wear resistance. For instance, this was applied when TWI and Rolls Royce collaborated and originally the Birmingham University created a LMD mending process for "Single Crystal" (SX) turbine seal parts. This process had been so profitable that Rolls Royce strategized to install a LMD manufacturing plant to refurbish their Trent 500 parts. This move allowed them to recover considerable amounts in the Trent turbines productions. In addition, LMD offers room for "near-net-shape" production that considerably decreases waste products as well as the tooling expenses [3].

c. The Components of Laser Deposition Machine

The hardware components are the; feeder conduit, focusing optics, powder feeder, powder splitter, separate chiller for optics and nozzle, interfaces to laser systems, and powder nozzle(s) [4]. There also exist software packages, which drive the hardware parts. The software is called the laser control software and the system control software, respectively [7].

d. The Control Parameters that can Influence the Quality of the Finalized Products

Laser Parameters- these include numerous factors like the flounce, laser energy, the stoichiometry, and the deposition flux. Usually, the nucleation density rises with the increase of the deposition flux [5].

Surface Temperature- it possesses a great influence on the nucleation density. Usually, the nucleation density rises with the increase in temperature [5].

Substrate Surface- Nucleation as well as growth could be influenced by the surface preparation, the substrate's roughness, and the substrate's miscut [5].

Background Pressure- Quite regular within oxide deposition, an oxygen backdrop is required to guarantee stoichiometric transfer to the film from the target. In case, for instance, the oxygen background is quite little, the film shall grow off stoichiometry that will influence the quality of the film as well as the nucleation density [5].

Significant to note is that the control factors influence the mode of growth of the substrate that is being deposited, which eventually turns out to be one of the following [5]:

Step-flow Growth- Every substrate has a miscut related to the crystal. These particular miscuts produce atomic steps on the surface. Here, atoms fall on the surface and diffuse to a step edge prior to meeting a nucleated surface island. The developing surface is seen as steps moving across the surface. This mode of growth is gotten through deposition on a high miscut substrate or at high temperatures [5].

Layer-by-layer Growth- Here, islands nucleate on the surface till a critical island density is obtained. The island continues to grow with the addition of extra materials till the islands start to collide with one another. This is referred to as coalescence. After coalescence is achieved, the surface has a huge density of pits. The addition of extra material on the surface causes the atoms to disperse into pits to close the layer. This procedure is repeated for all subsequent layers [5]

3D Growth- This particular mode is comparable to the layer-by-layer growth only that, after the formation of an island, an extra island shall nucleate on top of the first one. Hence, the growth does not continue in layer by layer manner, and the surface roughens with the addition of more material [5].

e. Challenges in Current Laser Deposition Technology

"Pulsed laser deposition" (PLD) is a new technique for the production of multi-component fine films. PLD films are utilized in different regions like electro-optics, biomaterials, micro-electronics, as well as tribology. This method's success can be attributed to its simplicity, together with the ease with which stoichiometric multi-component films could be deposited. There exist numerous difficulties, however, that should be overcome prior to the wide ranging industrial implementation of the method [1]. Apart from the problem huge area deposition, another regularly experienced issue is the particulate absorption in the ablated films. Gaining great degrees of deposition is also another challenge. There also exists a significant challenge that is associated with obtaining consistent deposition in intricate shapes, entailing numerous steps [1].Comprehension of the basic procedures taking place in the laser generated plasmas is another challenge [4].

In spite of its great potential, laser deposition technology has long stayed a procedure restricted to the laboratory. Its major challenge lies in satisfactory control of the procedure- to attain a uniform layer with the stipulated properties, the laser powder, makeup of the powder and its distribution, ought to be correctly synchronized and controlled. On the other hand, producers like TRUMPF now provide comprehensive technology packages for laser material deposition uses, which promise suitable control of these features. For TRUMPF systems, the powder introduced is usually a mobile unit having separately programmable powder containers. The feeder mixes the gas/powder mixture originating from the containers into a correctly adjusted powder mass flow [4]. The composition of the flow is constantly monitored by sensors, making sure that there exist no variations in the metallurgical makeup of the layer [4].

2. Control System of Laser Deposition System

(Diagram adapted from Song, 2014)

Laser deposition entails intricate interactions amidst laser beams, processing gas surroundings, substrates, and powders. Sustaining a steady and consistent melting pool in the procedure utilizing a closed loop control system is vital to gain the preferred dimensional precision, mechanical properties, as well as surface quality [7].

There exists a manual as well as a software control system within the laser deposition machine. The laser control software is particularly meant for interfacing with the laser and shall just be utilized shortly by the standard system's user. The system control software shall be utilized to interface with every part of the system [7].

The manual control system entails the following:

Substrate Rotation Motor

This motor is utilized to rotate the substrate in deposition so as to gain the target material's consistent supply on the substrate. The setting is greatly reliant on the degree of fire of your laser, together with the quantity of material, which is deposited in every laser shot. There exist three choices for the manual control: shift to particular angle, manual control, and rotate at a constant speed [7].

System Shutters

They permit the user to close or open the system shutter to safeguard the substrate in the pre-ablation… [END OF PREVIEW]

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