M Aerospace RTC
Get to know the DED technology of M Aerospace RTC
What is Additive Manufacturing?
Additive manufacturing, usually known as 3D printing, has been in development since the 1980s. This technology has revolutionized the modern process of design and manufacturing, it allows development of new products and prototypes in a shorter period of time and at a lower cost, this depends on the technology to be implemented.
This technology lets you produce tridimensional physical objects directly from a CAD file by deposition of layer by layer of material, plastic commonly being the most used one.
Direct Energy Deposition (DED) Additive Manufacturing (AM)
Direct Energy Deposition (DED) is one of the most complex 3D printing processes, utilized normally to repair or add material to an already manufactured part. It is a process in which an energy source such as a laser beam or an electron beam is utilized to melt the material. In a similar way to various powder technologies, the material is melted by applying a molten mass upon a plate, upon which the powder is melted forming a deposition and creating the desired shape layer by layer.
According to the ASTM/ISO standard about terminology for AM (ISO/ASTM 52900-15), “DED is an additive fabrication process in which thermal energy is focused to fuse materials as they’re deposited”.
This technology is at the frontier between material extrusion and powder fusion, due to that, it’s possible to make models from nothing utilizing this technology, but it’s mainly used in industrial applications that require to repair huge elements such as turbines and helices that are damaged, to increase the service life of the element in which this technology is applied and as a solution to the breakage and deterioration of these elements.
Nowadays the DED process seems to be the predominant method to direct deposition of metal due to its high performance, low waste and greater construction volume. However, Laser Powder Bed Fusion (LPBF) keeps being used in high precision applications that require layers thinner than 250 millimeters.
This technology is one of the 7 categories of additive manufacturing process, DED being even more utilized in hybrid fabrication.
DED technology was developed by Sandia National Laboratories in the 1990s under the name of LENS (Laser Engineering Net Shape) and then commercialized by Optomec Design Company. Due to the variations on the energy source and end use, DED is also known as Laser Metal Deposition (LMD), 3D Laser Coating and Direct Light Fabrication (DLF).
Depending on how this technology is used it is how the material will be deposited, either through a plate or above a component to be repaired, this is done by a multi axis arm (normally 4 to 5 axis arms are used). The material is deposited by a nozzle and as the deposition is being done, a heat source (generally a laser beam, an electron beam or a plasma arc) melts the material simultaneously, which is deposited layer by layer, this process is repeated until either the desired shape is achieved or the element to be repaired is restored. This process is characterized by having a great accuracy and being able to be used with polymers and ceramics, but its usually done with metals.
At the center of a DED system there is the head of the nozzle, which consists of its energy source and the supply nozzles which provide the powder supply, all of these supply nozzles converge on a deposition point in which the energy source is focused (e.g. laser beam). A multi axis CNC header or an articulated arm.
Normally, the build platform is part of the CNC multi axis system that includes the head of the nozzle.
An easy way to explain its functioning it’s by a series of steps which are executed by the DED system used, in this way, the action with which we want our additive manufacturing system to operate is carried out. These steps are explained below:
1. Using geometric data obtained from the CAD file, both the nozzle head and the build platform move to generate the 3D geometric characteristics.
2. The laser beam melts the surface and creates a small pool of molten metal on the substrate at the start of a long build route.
3. The feeding lines supply the powder through the nozzle in this molten pool.
4. Using geometric data obtained from the CAD file, the head controlled by CNC, the plate (or bed) or both, move along the build route to create the shape of the metallic part.
As it can be seen on the steps above, the functioning of a DED system is similar to printing with any other method.
In laser-based powder-supplied DED, the fused material is deposited by “blowing” the metallic powder through small nozzles or holes in a fusion bath created by laser. Depending on the power and type of laser used, the laser beam is focused to create a known dot size (e.g. 0.5 or 1 mm for a 500 watts laser versus 1.5 or 3 millimeters for 2.5 kilowatts laser). The depth and speed of the resulting molten mass are dictated by the laser scan speed (or the piece movement on the build platform below the laser) and the energy absorption and thermal conductivity of the raw material that’s being deposited.
The size of the fusion pool, the speed of laser movement and feeding speed (speed at which the powder is blown through the nozzles to the laser) dictate the quantity of powder that it’s captured by the fusion pool, and ultimately, the quantity of material fused to the piece: the layer that’s bellow and the adjacent material inside the layer that’s being built. A huge fusion pool, that’s hot, of slow movement will have a higher powder capture rate (70 to 80 percent in the best case) than a smaller fusion pool or with faster movement (capture rate of 20 to 30 percent in the worst case). However, the thermal history and, therefore, its microstructure and mechanical properties of the part will be different in the two cases. This is one of the challenges with DED, namely, adjusting the parameters of your process to guarantee a fast build time.
Once building rates are optimized for DED tend to be a bit faster than those of powder beds (Powder Bed Fusion or PBF). The size of the laser point for DED is at least 10 times bigger in comparison to the one used in PBF. This creates an objective fusion pool bigger for the powder to hit it, being melted and fused. Also, bigger powder particles tend to be used in DED systems (50 to 150 microns of diameter in DED versus 20 to 50 microns to PBF), as they tend to flow better and provide more surface area to accelerate the melting process. Bigger powder particles also allow thicker layers in comparison to PBF, that means less layers to build when using DED.
Types of Direct Energy Deposition
Even though DED technology can be used to make metallic, ceramic and polymeric parts it’s mainly used to make metallic pieces. DED can be classified by the following groups according the energy source used to melt the metal, and are therefore classified as follows:
Laser-based DED systems: they utilize the laser beam as their main energy source.
Electron beam DED systems: they utilize an electron beam to diffuse the raw material powder.
Plasma or Electric arc DED systems: they utilize an electric arc to fuse a wire.
DED technology can be subdivided in the following types according to the raw material that’s being used to create the pieces:
Powder based DED systems: they’re fed powder by a nozzle and it’s melted by a laser or electron beam.
Wire based DED systems: they’re fed by wires through a nozzle and utilize laser beams, electron beams or a plasma arc to create the fused bath.
DED is mainly used in diverse key industries such as aerospace, gas & oil, as well as the naval industry, for example, in hulls and airplanes structures, refractory metals components, repair and reconditioning of tools of ballistic material and marine propulsion, etc.
This technology can be implemented for various applications and fields, the following are examples for different applications and fields:
Repairing high value pieces (fabrication errors, production damages, piece modifications, etc.)
Increasing service life of pieces (for greater spawn of time)
Material coating (wear resistance, corrosion resistance, high and low temperature resistance, etc.)
Surface reinforcement (reinforcement for low carbon steels or high speed steels)
Manufacturing of parts and prototypes (with non complex geometries)
It’s worth noting that the following examples are just a few possible applications and fields to which one can implement this type of technology. Notwithstanding, these examples are usually the main uses that are given to this technology and the various fields in which it is used. As technology evolves, this type of technology tends to improve and be used in a greater number of fields and therefore their applications tend to increase, so the limits to which this technology is implemented varies according to who is utilizing it.
As any other process of subtractive manufacturing, parts made by DED can be heat treated, hot isostatic pressing, machining or any of the usual finishes, which opens new applications. The majority of hybrid manufacturing systems utilize DED and its popularity has increased over time, thanks to the applications and fields in which it is applied.
According to the type of application and necessary equipment for the development of fabrication with DED technology it can be implemented to diversify other services in which this technology can be applied, to mention a few are:
Laser cutting: It’s a thermal cut which utilizes fusion or vaporizing highly concentrated energy to cut metal with the heat of a laser beam, generally with the assistance of a high pressure gas. With this process in which a laser beam can cut various materials, either metallic or non metallic.
Laser beam welding: It’s a welding process by fusion that utilizes energy provided by a laser beam to fuse and recrystallize the material or materials to join, in this way it produces the union of various elements. Normally it utilizes some type of gas like helium and argon, that serves as a protector gas.
Laser hardening: It’s the surface hardening in certain zones of the part, by a laser sweep, adjusting the speed, temperature and power of the laser, in this way it achieves minimum material deformation.
Laser engraving: The surface of the material is fused and evaporated by a laser beam, eliminating the necessary material. The result obtained on the surface is an engraving.
Normally direct energy deposition (DED) is utilized with metal which tends to be in powder or wire form, however, it’s possible to use this technology with polymers and ceramics.
Of the different types of elements that can be used with this technology, there are metals, as mentioned before. Any type of metal that can be welded can be printed with DED additive manufacturing. These metals include, to mention some, titanium and its various alloys, tungsten, niobium, tantalum, stainless steel, nickel and it’s various alloys, aluminum, etc. The type of wire used varies between 1 and 3 mm of diameter and its powder particles; its size it’s similar to the ones used in powder metallurgy processes, which are between 50 and 150 microns.
DED can utilize this wire feeding technology, where heads of a DED printer can employ a greater variety of materials for printers at a lower price. The only disadvantage is that the system resolution it’s necessarily limited by the wire thickness, typically about 1 mm of diameter.
The current market counts with a great quantity of 3D printers manufacturers, both of metals as of many other materials for printing, being in DED technology metal the main material to use. There exists a diverse market depending on the type of technology you wish to utilize, therefore it’s recommended to research the type of technology to be implemented and consequently the type of material to use, in this way you can start the investigation of which provider would be the adequate to get the desired printing technology.
Advantages and disadvantages of additive manufacturing by DED
Despite the different uses, characteristics, applications and fields in which this technology can be utilized, doesn’t exempt it from having some disadvantages, but having disadvantages means that it has advantages in its own favor, in the table below we show some its advantages and disadvantages:
Great quantity of materials: Additive manufacturing by Direct Energy Deposition (DED) is a mature process, so there is advanced R&D regarding which materials can be applied.
Great operation quality: It adds a small heat contribution to the base piece, with almost null deformation and also null corrosion. It contributes to high density and low porosity.
Variable thickness: In comparison to other additive manufacturing processes, the measurements can vary from 0.03 mm to a few centimeters of diameter.
Existent parts: It can be applied in existent parts to achieve coatings or do reparations.
Production ratios: In comparison to other additive manufacturing processes, it achieves a high ratio value of 3-10 mm3/s.
High build rates: The higher deposition rates of DED on a relatively lower resolution means a higher build rate in comparison to other metallic additive manufacturing processes.
Dense and strong parts: DED creates parts with higher density, so that its mechanical properties are as good as the ones from forged or cast materials.
Almost finished shape: The parts can have almost finished shapes and therefore require minimum post-processing.
It can be used to repair: Ideal for applications that require the addition of material to existent parts, therefore, it lends itself to repair applications.
Bigger parts: Parts comparatively of greater size can be built utilizing DED, and can measure up to at least 1 meter of height.
Easy change of material: Since the material is fed during the process by separate powder containers, it’s easy to refill or change the material.
Waste material reduction: DED only deposits the necessary material during the process, which means less waste in comparison to processes like Powder Bed Fusion, SLS & DMLS where the entire building platform has to be filled with metallic powder.
Productive limitations: Additive manufacturing by direct energy deposition suffers by production limitations associated with the maneuverability of its work axes.
Geometric complexity: It suffers a deficiency related to the capacity to produce any geometry.
Fabrication process: It’s necessary to give a surface finish and perfection the dimensions used, after additive manufacturing, also the surface roughness is greater than in other additive manufacturing processes, obtaining a value of 60 to 100 microns.
High capital costs: DED systems are comparatively more expensive than other types of additive manufacturing systems for metals.
Low construction resolution: The parts made by the use of DED technology have a lower resolution and more deficient surface finish in comparison to various of the different types of existent additive manufacturing processes. The surface will look sandy or like done by an investment casting process and will require a secondary post-processing, such as machining or water jet, which will add more time and cost to the fabrication and finishing of the part.
Doesn’t use support structures: Due to the nature of the way the DED technology builds parts, support structures cannot be used during the fabrication process.
Tolerances: DED machines generally can achieve a finer tolerance of 0.25 mm, which makes small features difficult to achieve.
Frequently Asked Questions
How does it work DED technology?
In a similar way to any other additive manufacturing technology, first you need to have the 3D model by means of a CAD design tool and subsequently it starts to do the material deposition by layers until it creates the desired shape according to the design elaborated.
What type of materials can be used in DED technology?
It can be used a huge variety of materials in the DED process, being generally metals the most used, including combinations of metals (alloys), including in these materials are: titanium, aluminum, tungsten, stainless steel, super alloys, ceramics, polymers and other special materials.
What part size can be built with DED technology?
DED can be used to build and repair objects that extend up to 5 meters, among the largest items that can be printed today.
When is DED printing a good option?
DED technology is a good solution to create or repair huge metallic parts. However, because DED machines sacrifice some quality for speed, it isn’t ideal it’s use where precision and smooth surfaces are critical.
How is DED printing used to repair parts?
DED printing can add layers of metal on designated parts that are worn or broken to prolong its life spawn and return them to usability.
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