Laser engineered net shaping

Laser powder forming, also known by the proprietary name (laser engineered net shaping) is an additive manufacturing technology developed for fabricating metal parts directly from a computer-aided design (CAD) solid model by using a metal powder injected into a molten pool created by a focused, high-powered laser beam. This technique is also equivalent to several trademarked techniques that have the monikers direct metal deposition (DMD), and laser consolidation (LC). Compared to processes that use powder beds, such as selective laser melting (SLM) objects created with this technology can be substantially larger, even up to several feet long.

The Laser Engineered Net Shaping or LENS is a technology rapid prototyping developed by Sandia National Laboratories that allows manufacturing components of metal directly from a model CAD depositing metal wires or metal powder in a slurry generated by the action of a beam laser of high power on the upper surface of a metal substrate previously deposited on a platform.

The laser beam usually travels through the center of the head and is oriented to a small point using one or more lenses. The XY surface moves bit (raster graphics) to produce each layer of the object individually. The head moves vertically up each time a single layer is made. The metal powder is excreted and distributed around the periphery of the head by means of gravity or carrier gas under pressure. Inert gas is used to protect the solvent pool from atmospheric oxygen, for better control of the layers, since the surface is more moist.

We can use several different materials, such as stainless steel, inkonel, copper, aluminum, etc. Especially interesting are reactive materials, such as titanium. The composition of materials can be constantly and dynamically changing, leading to objects whose properties are mutually exclusive with the use of conventional manufacturing methods.

The advantage of the process is that with it we can produce completely solid metal parts with good metallurgical properties and in the foreseeable future. Manufactured items have almost complete final design, however, it is necessary at the end of machining process. They have a good granulation structure and similar or even better properties than intrinsic materials. Selective laser sintering is currently the only commercial process for rapid prototyping, which can directly produce metal parts. Selective laser welding has fewer material constraints than selective laser sintering and does not require secondary firing operations like some processes.

A high power laser is used to melt metal powder supplied coaxially to the focus of the laser beam through a deposition head. The laser beam typically travels through the center of the head and is focused to a small spot by one or more lenses. The X-Y table is moved in raster fashion to fabricate each layer of the object. The head is moved up vertically after each layer is completed.

Metal powders are delivered and distributed around the circumference of the head either by gravity, or by using a pressurized carrier gas. An inert shroud gas is often used to shield the melt pool from atmospheric oxygen for better control of properties, and to promote layer to layer adhesion by providing better surface wetting.

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Stages of the process
A metal substrate is deposited on a platform
A high power laser beam, appropriately focused through a lens system, hits the substrate and melts the surface, producing a molten slurry
Through a deposition head with raster graphics placed coaxially to the laser beam, metal wires or metal powder are deposited in the pulp to increase the volume
A table moved in the XY plane draws the contours of the section for each layer
Once the layer has been solidified, the table moves vertically upwards and the cycle starts again

Inert gas is used to protect the pulp from the oxygen in the atmosphere and to promote adhesion between the layer and the layer, which also allows a check of the characteristics of the material in solidification.

Other techniques
This process is similar to other 3D fabrication technologies in its approach in that it forms a solid component by the layer additive method. The LENS process can go from metal and metal oxide powder to metal parts, in many cases without any secondary operations. LENS is similar to selective laser sintering, but the metal powder is applied only where material is being added to the part at that moment. It can produce parts in a wide range of alloys, including titanium, stainless steel, aluminum, and other specialty materials; as well as composite and functionally graded materials. Primary applications for LENS technology include repair and overhaul, rapid prototyping, rapid manufacturing, and limited-run manufacturing for aerospace, defense, and medical markets. Microscopy studies show the LENS parts to be fully dense with no compositional degradation. Mechanical testing reveals outstanding as-fabricated mechanical properties.

The process can also make “near” net shape parts when it is not possible to make an item to exact specifications. In these cases post production process like light machining, surface finishing, or heat treatment may be applied to achieve end compliance.It is used as finishing operations.

Through LENS it is possible to obtain a wide range of full-density metal components in copper, aluminum, stainless steel, titanium such as parts for airplanes, medical prostheses and tools for injection molding. Also interesting is the possibility to dynamically modify the composition of the material, producing, in the end, pieces with characteristics that would be mutually exclusive using traditional manufacturing methods.

The products obtained by LENS are “near net shape”, ie almost finished products, which still require post-treatment.

Source from Wikipedia