Additive manufacturing is a production process that allows you to create three-dimensional objects by adding material layer by layer until the desired shape is obtained. Unlike traditional subtractive manufacturing methods, such as milling or turning, additive manufacturing builds objects by adding material rather than removing it. We have already explored the differences between additive manufacturing and traditional manufacturing, but in this article we will discuss Additive Manufacturing in more detail.
According to the definition of Additive Manufacturing given by the ISO/ASTM 52900:2021 terminology standard, “it is a process of joining materials to make parts (3.9.1) from 3D model data, usually layer (3.3.7) upon layer, as opposed to subtractive manufacturing and formative manufacturing methodologies”
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3D printing is a type of additive manufacturing. Additive manufacturing is a process of creating three-dimensional objects using 3D printing. These two terms are often used interchangeably, therefore, mentioning additive manufacturing or 3D printing will mean referring to the additive approach to distinguish it from subtractive manufacturing processes, such as machining, in which material is removed from a larger block to get the desired shape.
In recent years, the market is increasingly relegating the concept of additive manufacturing to the 3D printing production process by putting it on the same level as traditional methods, as it enables the production not only of prototypes but also of finished parts, associating 3D printing with hobbyist or domestic solutions, called Desktop.
Additive manufacturing dates back to the 1980s, when Chuck Hull introduced stereolithography (SLA) technology at 3D Systems. SLA used a laser to solidify layers of light-sensitive resin, allowing for the creation of three-dimensional models. Over the years, several other 3D printing technologies have been developed and commercialized: from selective laser melting (SLM), which uses a laser to melt and solidify metal powders, to fused material deposition (FDM/FFF), which extrudes a layer of melted plastic material to build the object layer by layer.
From the 2000s onwards, additive manufacturing evolved and began to be increasingly used for the additive manufacturing of prototypes in various industrial sectors, such as aerospace and automotive, as it allowed to reduce time and costs of development. Advanced materials, such as high-performance thermoplastic polymers and metal alloys, have been introduced, expanding the possibilities of additive manufacturing.
In recent years we have witnessed a real change of pace, with an unstoppable speed in terms of progress with new 3D printing technologies and new perspectives for innovation in an ever wider range of sectors: from biomedical to space, from construction to naval, from energy to industrial, each with 3D printing processes and materials developed ad hoc based on individual needs. In the future, 3D printing technology is expected to further revolutionize the way things are designed and produced, providing new opportunities for customization, sustainability and efficiency in production.
The additive manufacturing process begins with the creation of a three-dimensional digital model of the desired object using computer-aided design (CAD) software. This model is then divided into thin layers, usually a few micrometers thick. The most famous file format for 3D printing is the STL (Standard Tessellation Language or alternatively Standard Triangulation Language), introduced in the 90s for the communication of three-dimensional data between design software and 3D printing machines. Once the digital project has been obtained, we move on to the setting phase of the print parameters through a slicing software. Generally, this is a crucial step that could also affect the success and quality of the 3D printed parts. Choosing the printing settings to make a 3D part is essential before starting any job on the machine.
During the 3D printing process, the build material is deposited or melted according to the specifications of the digital model, hardened or solidified, and then the process is repeated for each layer until the object is complete. Once the object is fully printed, it can undergo further finishing, such as removing supports or sanding, to achieve the desired final shape.
As already explained in this article about the advantages of 3D printing, the advantages of using additive manufacturing compared to traditional methods are, in summary:
• Complex geometries: The additive approach allows for greater design freedom than conventional methods. With 3D printing it is possible to obtain objects with complex geometries, impossible to obtain with subtractive technologies. This advantage opens up new opportunities for custom product design.
• Custom production: Additive manufacturing offers the ability to create customized products according to specific customer needs. Thanks to the flexibility of the process, changes to the design can be made quickly and cost-effectively, allowing for the production of smaller batches or even single pieces.
• Reduction of production costs: while the initial costs of industrial 3D printing equipment can be significant, additive manufacturing can offer long-term economic benefits. For example, it can eliminate the need to create expensive tooling to produce small batches of products. Additionally, reducing material waste and production time can help reduce overall costs.
• Reduced production time: With 3D printing it is possible to obtain a significant reduction in production times as the additive method does not need special tools or molds and allows the production of finished parts by reducing assembly times.
• Reduction of material waste: In additive manufacturing, material is deposited only where it is needed, reducing material waste compared to subtractive processes, such as milling or turning. This leads to more efficient use of resources and can reduce costs associated with purchasing and managing materials.
• Digitization of the warehouse: Additive manufacturing enables a new concept of warehouse by transforming it from physical to digital. In a digital warehouse, digital files of the three-dimensional models of the objects are stored, together with additional information such as the printing specifications, the materials used and other characteristics, useful for 3D printing the parts whenever and wherever needed.
Additive manufacturing is used to produce prototypes, custom parts, tools and much more. It has applications in several industries, including automotive, aerospace, energy, medical, architecture and fashion. The most used additive manufacturing applications are:
• Additive production of functional prototypes: 3D printing allows for the rapid creation of physical prototypes of products, allowing engineers and designers to test and evaluate the design before launching mass production. This reduces the development time and costs associated with producing traditional prototypes.
• Additive manufacturing of custom parts: Additive manufacturing enables the efficient production of customized parts. This technology finds application in areas where the production of parts tailored to specific customer or patient needs is required.
• Additive manufacturing of tools and equipment: the most common. 3D printing is used to produce custom tools, fixtures and devices. For example, it can be used to create specialized tools for machining materials or ad hoc fixtures.
• Additive manufacturing of lightweight and complex components: Additive manufacturing allows to create components with complex geometries that would be difficult or impossible to produce with traditional methods. This technology is used in the automotive, aerospace and mechanical industries to create light, strong and complex parts such as turbines, engine housings and structural components. By combining technology with advanced materials, such as super polymers and composites, we help companies obtain even faster lightweight and optimized parts for the final application.
1.7.1
Introduction to Powder Bed Fusion TechnologiesNowadays the additive manufacturing market offers a wide variety of AM technologies based on both metal and polymeric powders. These technologies evolve quite fast bringing new features and specs that make them more reliable, faster and more accurate. Hence, we can find more industrial applications of additive manufacturing, not only for rapid prototyping and design validation but also for final-use parts and industrial productions.
Powder based additive manufacturing is a technique of layer by layer manufacturing where an energy source is applied to melt or sinter metal, polymer and ceramic based materials.
Technologies reviewed in this book are the following:
PBF-EB/M (Electron Beam Powder Bed Fusion of Metals) (or EBM—Electron Beam Melting)
PBF-LB/M (Laser Beam Powder Bed Fusion of Metals) (or SLM—Selective Laser Melting)
PBF-LP/P (Laser Beam Powder Bed Fusion of Polymers) (or SLS—Selective Laser Sintering)
PBF-IrL/P (Powder Bed Fusion of Polymers with Infrared Light) (or MJF—Multi Jet Fusion).
Powder Bed Fusion Principles
Powder bed technologies use fine particles of different nature (metallic, ceramic or polymeric) as feedstock, we can find that depending on the am technique, they are provided with different power sources which aim is to consolidate the material creating 3D printed parts from fine powder layer by layer.
These AM technologies allows the production of very complex geometries using a heat source to fuse the powder particles layer by layer transforming the feedstock into solid parts.
Normally the PBF technologies work under a protected atmosphere so that the feedstock is processed in the right conditions avoiding oxidation during the process and therefore making possible that the powder can be used again after each build. Altough AM scenario is continuously evolving and different groundbreaking energy sources are being launched, PBF technologies use the following standard energy sources so as to selectively sinter the powders (Table 1.1).
Table 1.1 Type of powerFull size table
Powder Bed technologies provide us with certain design freedom that varies depending on the technology and the materials to be processed, as general benefit of AM in comparison with traditional methods, we can create very complex geometries, inner channels and connections thanks to this design freedom that AM brings. Nevertheless, as in any process, AM technologies present also some kind of limitations that are gathered afterwards.
As a general overview of PBF technologies, they are all provided with powder tanks/deposits where the fine particles are picked up and delivered every layer by a raking system designed specifically for each process. Machines are also provided with a build platform that moves down as well as an energy source that sometimes is a punctual beam and sometimes heating lamps made up of UV bulbs. Although there are some “closed software” machines, we can normally adjust a wide variety of parameters within the process that enable us the development of new materials for AM.
In the PBF process the phenomenon called “melt pool” appears in a very small area where the laser source is describing the melting pattern. However nowadays we find very fast technologies based on heating bulbs as the Multi Jet Fusion Technology from HP where there is not a specific sintering/melting spot but the whole layer sintered at the same time.
Melt pool behaviour and energy deposition will vary depending on the process parameters and of course every material will require specific sets of processing parameters.
1.7.2
Electron Beam Technology (PBF-EB/M)PBF-EB/M uses high-energy electron beam to fuse metal powders. The process takes part under a very high vacuum environment which allows reducing oxygen content during the heating-melting process. The production rates of the PBF-EB/M are much faster than the PBF-LB/M because of the high beam speed and the layer thickness parameter (higher than PBF-LB/M due to bigger particle size distribution in comparison with PBF-LB/M). Process is carried out while the powder and build platform is preheated so that parts manufactured by PBF-EB/M have neither internal stresses nor distortions. Process temperatures can vary depending on the material to be processed.
Since the particle size distribution (PSD) of PBF-EB/M is bigger, the feedstock used in this technology is cheaper than the one used in PBF-LB/M (sieving yields are more optimistic for bigger particles). As drawbacks, since the process is done while preheating, the “cake” obtained once the build ends is made up of parts surrounded by slightly sintered powder which makes difficult the part cleaning, especially when there is presence of small ducts and channels where powder remains trapped, for this reason a powder recovery systems (PRS) is required in the PBF-EB/M process, the aim of this so-called “PRS” is to blast powder from the same nature that the one processed in order to remove the sintered powder attached to the processed parts. Moreover, due to the increased size of particles in comparison with LPBF particles, surface roughness is especially accentuated in PBF-EB/M parts.
PBF-EB/M Components
In the PBF-EB/M production chain we will find the components pointed out in the following lines, all of them must be ATEX (Atmospheres EXplosible) approved:
PBF-EB/M Machine: (3D Printer) core of the process where the parts are produced inside the high vacuum cabinet.
Loading trolley: powder is stored in two hoppers that deliver a small amount of material to cover the build area each layer, the trolley is needed to handle the hoppers that can weigh between 40–80 kg.
Powder Recovery System (PRS): (sandblasting equipment) the same powder used during the fabrication is also applied at high speed in this PRS in order to remove the sintered powder sticking to the parts. This powder is used again in further builds.
Vacuum cleaner: after each build, the PBF-EB/M cabinet is opened and must be cleaned up from powder present all over the chamber. Powder recovered by the vacuum cleaner is sieved and used again in further builds.
PBF-EB/M machines are made up of three basic units: EB-Gun cabinet where the e-beam is generated, build chamber where the parts are built and control unit where the technicians manage the process parameters and mechanical adjustments. Giving a closer look at the PBF-EB/M Chamber, we can see two hoppers (tanks where the powder is stored before any build starts) and a heat shield placed just beneath the build area. The heat shield is a metal-plate structure necessary to keep the upper surface and the powder cake at a certain temperature during the whole build, this part prevents the damage of other componentes placed inside the chamber.
Regarding the build area, a rake is in charge of the powder delivery, it moves from one hopper to the oher picking a specific amount of powder that is deposited in the melting area where the parts are built. An overview of the PBF-EB/M technology is presented in Fig. 1.18.
On the other hand, the EB-Gun is made up of different kind of “lenses” present along the beam EB-Colum, focusing lens is aimed to increase or decrease the diameter of the spot. This parameter gives us the opportunity to modify the energy denisity deposited, whereas the deflection lens is aimed to describe the melting patterns stored in the layered file. These are not really lenses but magnets that distort the electron beam shape before it hits the powder bed.
Regarding the materials that PBF-EB/M is used to process, Arcam has the monopoly of EB technologies, and they are offering specific machines for specific materials as TiAl. But by large Ti based alloys and CoCr are the standard alloys.
It does not mean that the machines are not able to process other materials, as it has been demonstrated by AIDIMME several times, process (not only software but also hardware) can be adjusted so that the machine deals with nonstandard materials as pure Copper, Nickel based superalloys, and nanomodified Ti64 between others.
PBF-EB/M Workflow
Process starts from the very fist step of machine preparation where the technician cleans the build chamber from the previous build; it requires specific tools and liquids specially designed in order not to damage the components. During this fist step, powder that might have been spreaded within the chamber must be removed using an ATEX vacuum cleaner.
Once the machine has been cleaned up, there are certain short-term replaceable parts that must be doublechecked and changed if necessary, as the filament, the heat shield plates or rake plates and the thermo couple and ground wire. Technician must doublecheck the state of those parts as a preventive action in order to avoid possible issues. Provided that the machine is clean and the spare parts changed powder hoppers full of material are introduced into their clamping system, some powder is delivered by the rake so as to perform what in AM we call “bed levelling” in addition a beam calibration and powder measuring sensors calibration are mandatory as well.
Build preparation must be carried out by experienced technicians since a proper procedure will lead to a flawless build.
Once the machine is prepared and the powder loaded, air is pumped outside of the chamber until vacuum gauges reach a certain value. High vacuum is required in order not to damage the raw material and get good results in the consolidated parts.
Parallel to the tasks described below, the job file is prepared. The technician allocates the parts inside the build volume trying to face them in an optimal position, this is so important since many support structures can be replaced by positioning the part in a strategic place. Three different softwares are used to prepare a job file:
Materialise Magics: is used to put the parts inside the build envelopment, support structures can be tailored in Magics for different materials and also for different technologies, during the allocating process the scale factors are applied to each model in order to compensate possible part distortions, these scale factors are controlled each build. Supports and scturtures are generated in Magics.
Build assembler: is used to generate the project file (Arcam Build File). The model generated in the previous “Magics” step is loaded into this software in order to separate the different geometries (wafer, support, melt) so that specific process parameters are usead for each kind of geometry, layer thickness is also set in this step.
PBF-EB/M Control software simulator: prior to running a job, the build must be simulated so as to prevent possible issues as defects in the layering or supports. This step is carried out in order to verify the build file. In the PBF-EB/M simulator the technician is able to doublecheck every single layer of the build.
Once the 3D models are layered and loaded into the EB-Build software, a first step of start plate preheating takes part, this task is aimed to ramp up the temperature of the build platform that will be kept withing the entire build by several preheatings performed on the top surface of every single layer. Part construction phase is dividided into various steps as: powder preheating, contour melting, hatch melting, and wafer (supports and structures). During this phase a huge amount of variables and complex formulas modify the energy deposition depending on the trajectories to be described.
Once the process completes the last layer, a controlled cooling-down phase takes place. When the bottom temperature reaches a certain low temperature, machine can be opened and cake recovered. This cake full of semi-sintered powder is sandblasted and parts appear attached to the build platform by the support structures that are removed afterwards.
Many variables are controlled during the process and can be assessed in order to troubleshout possible issues that sometimes arise. A log file as well as a report is generated after the process in order to evaluate these variables.
Last but not least, when it comes to process parameter development for nonstandard materials, the user is able to modify plenty of variables such as scanning speed, focus offset, line offset, beam current, process temperature, number of contours, layer thickness and many other complex functions that affects the results obtained in the molten material.
1.7.3
Laser Melting (PBF-LB/M) TechnologyLaser based powder bed technologies (PBF-LB/M) are the most common and extended metal additive manufacturing nowadays. These Additive Manufacturing machines offer different specifications such as as low temperature preheating, mutiple lasers, very small area for fine detailed parts and huge build envelopments for bigger parts.
PBF-LB/M uses similar principles as PBF-EB/M since both selectively melt the powder bed that is delivered layer by layer. However, there are some important diferences between these metal AM technologies.
Particle Size Distribution of PBF-LB/M powder is finer ((15–53 µm or 20–63 µm) therefore layer thickness parameter in this technology is slightly thinner than in PBF-EB/M. Foreseeably the parts obtained by laser-based technologies present better surface roughness but on the other hand the production rates are longer and the feedstock prices higher (sieving yields of finer particles are lower). PBF-LB/M technologies work under protected atmosphere, normally Ar or N, but in this case the chamber is at room temperature or low preheating temperatures up to 400 °C, which means that parts suffer from internal stresses and therefore post heat treatments are necessary to be applied as post processes. Nonetheless working at room temperature brings some benefits as non sintered powder nearby the processed parts, this eases the powder removal from the inner channels/geometries. Hence, we can manufacture very complex internal geometries because non melted powder is easy to remove afterwards.
PBF-LB/M Components
Laser based machines are made up of the build unit itself, a protective gas generator or deposit and the powder recovery system that gathers the non melted material and sieves possible contaminating particles.
PBF-LB/M Machine (3D Printer): core of the process where the parts are produced. Latest laser based technologies lauched are equipped with a closed powder control loop in charge of the powder handling and storing.
Powder Recovery System: powder recovered after each build is used again in further builds.
Protective gas deposit/generator: provides the machine with inert gas so as to generate the protective atmosphere during the whole process.
Inside the build chamber, we can find the build tank where the build platform moves downwards and the powder deposits. Layer by layer the squeegee blade picks a cerain amount of powder that is delivered into the build envelopment.
An overview of the PBF-LB/M technology is presented in Fig. 1.19.
Most parts of the PBF-LB/M machines offered in the market are equipped with a fiber laser which works in a wavelength of 1064 nm (red spectrum laser). This is so because the absorption values of the standard materials present good values at this wavelength levels. Nevertheless, latest developments show that lasers of different wavelengths as the green laser (505 nm) can be usefull for specific materials which present low absorption.
Regarding the standard materials that Laser based technologies are used to process, we can find stainless steel 316, aluminium, titanium alloys, maraging stells, copper alloys, 17-4ph, chromium cobalt or inconels between others.
PBF-LB/M Workflow
As pointed out in the PBF-EB/M section, the first step in laser-based technologies is machine preparation and build job assembly, technicians must clean the machine up and make sure that the powder is properly stored in the deposits of the PBF-LB/M machine. Short-term spare parts must be changed as well, in this process the squeegee blade must be double-checked since it could have been damaged while delivering powder during the build.
Bed levelling process must be carried out in order to ensure good weldability in the very first layers and chamber inertization as well.
PBF-LB/M build preparation is quite similar than PBF-EB/M but some considerations must be kept in mind as for instance the fact that we cannot nest parts in the Z axis but only if they are connected by support structures to parts attached to the build platform. Normally support structures required in PBF-LB/M technologies are denser than in PBF-EB/M technologies because of the room temperature conditions (non sintered powder) and the very fast cooling rates that take place during the process.
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Regarding the melting process of laser based technologies, it varies depending on the strategy that each machine manufacturer follows, but normally the approach in laser based process is to perform controlled melting areas with equivalent energy. Concept laser M3 linear machine for instance follows the island pattern in which every layer is basically split into small squares of a certain dimension (5 × 5 mm) that are randomly melted afterwards in order not to accumulate the energy in specific areas of the layered geometries. These approaches are considered in order to reduce the swelling phenomenon.
Parameters that can be modified within the process are; current, laser speed or frecuency if the laser is pulsed, focus diameter (affects the shape of the laser), vector pattern (direction of the scanning vectors), overlap between scan tracks hatch-contour, number of contours between others.
Metal additive manufacturing processes are managed by very complex functions that vary the energy deposition. When it comes to a process parameter development for a new material, many variables can be modified in order to achieve good results in the consolidated material.
1.7.4
Selective Laser Sintering (PBF-LB/P) TechnologySelective laser sintering (PBF-LB/P) is an additive technology that uses a laser source (normally a CO2 laser of 10,600 nm) to transform polymeric-based powder into solid parts based on 3D CAD models.
PBF-LB/P was one of the first additive manufacturing technologies developed in the mid 80-s, since then, the process has been adjusted to a wide variety of materials.
In the PBF-LB/P machines we can normally find two powder tanks where fine powder of a PSD 20–80 µm is stored and the build platform located in the middle. PBF-LB/P works under protected atmosphere (normally Nitrogen) and at a certain process temperature which is specific for each material. This temperature ramps up the temperature of the powder layer up to 12–16 ℃ below the melting point and the laser puts the remaining energy to melt the polymeric powder.
Some of the benefits of Selective Laser Sintering technologies are: (i) big parts can be manufactured, (ii) high strength polymers can be processed as polyamide, (iii) PBF-LB/P does not need support structures, thus design rules are much more flexible just trying to reduce the material as much as possible, and (iv) PBF-LB/P is able to reproduce very small geometries.
Nevertheless, powder not transformed into a part is affected by heat during the process; hence it must be refreshed with virgin powder in order to be reused again in the next build. Most part of the production costs of the PBF-LB/P technology comes from the feedstock; therefore, powder reusability is a key factor in order to cut down the part costs.
As a drawback, depending on the machine temperature stability is an important issue to deal with, because slight variations in the temperature whithin the process will lead to part distortions, curling and other typical issues of additive manufacturing.
PBF-LB/P Components
Among the components required within the PBF-LB/P process it can be found:
PBF-LB/P cabinet where parts are built.
Mixing station where already used powder is mixed and refreshed with virgin powder after each build.
Powder recovery system where powder is sieved and possible comntamination or over sintered powder is removed.
Focusing on the production station and especially on the sintering unit, a low power CO2 laser is located on the top part of the machine. This laser is guided by two galvo mirrors that deflect the laser up to the powder bed. The roller picks a small amount of powder from the tanks and delivers it through the workpiece area creating a thin layer which is heated and melted.
In the PBF-LB/P machines we can also find several heaters allocated in diferent areas, some of them are aimed to preheat the workpiece area whereas others heat the powder tanks so that powder delivered is slightly heated before the deposition and therefore distortions are minimized.
In case of polyamide 12, which is the most common material processed by sintering technologies, process temperature is ramped up to 178–180 ℃, it is rather important to keep a constant temperature along the entire build in order to reduce part distortions.
An overview of the PBF-LB/P technology is presented in Fig. 1.20.
Fig. 1.20(Source AIDIMME facilities)
PBF-LB/P chamber scheme
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PBF-LB/P Workflow
As described before machine and build preparation are crucial to achieve good results; the chamber must be cleaned up from powder of the previous build and bed levelled. Some preventive actions should be carried out in order to improve the results as for example cleaning the exit window of the CO2 laser since some very fine powder remains sticked to the face inside the chamber after each build.
Given the benefit of a support free technology means that parts can be placed anywhere within the build envelopment. Nowadays, it can be found nesting softwares as Materialse Magics which supports the technician in the parts allocation improving the build density as much as possible. The more parts fit in the build envelopment the cheaper the unitary costs will be.
Once the machine has been cleaned up and the powder stored in the tanks, the chamber is inertized and heaters are turned on.
Te build platform starts moving down while the powder is spreaded in a first phase called warm-up. This warmup stage aims to create a 10–12 mm height cake with no parts which pretends to create a heat barrier between the parts and the build platfor avoiding in this way phenomena like curling.
Once the warmup phase reaches 10–12 mm build starts; powder is dispersed by a roller in the shape of a fine layer. During the whole process a couple of heaters keep the temperature of the build platform at a certain point below the melting point of the material to be sintered. Once the layer has been deposited the laser source scans a cross-section of the 3D model (layered model) fusing the particles together in order to create a solid part. This process is repeated for each layer until parts are completed.
Once the build ends there is a cooling down phase where temperature is reduced in a controlled manner. A drastic cool down can lead to part deformation and distortions thus it is very important to naturally cool down the cake before removing the parts manufactured in each build. This phase takes between 12–24 h depending on how high the so-called cake is.
Powder reusability in PBF-LB/P is critical since most part of the production costs come from the feedstock itself, therefore a wrong powder reusability methodology can lead to a very affected powder batch that does not allow us to create high quality parts since phenomenon called “orange peel” appears (Fig. 1.21). For this reason, depending on the area where we recover the powder, we will treat the batch as more affected by heat or less affected by heat (Fig. 1.21).
Fig. 1.21(Source AIDIMME)
Powder recovery from PBF-LB/P cake. Affected areas
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It can be found in bibliography some methods like the Melt Flow Rate Test (MFRT) where we can quantify how affected the powder is. This method measures the time while a certain amount of powder is melted through an extruder at a specific temperature. Depending on this value already used feedstock must be refreshed in a controlled manner improving the reusability yields.
Looking deep into the selective laser sintering process, there are many variables that can be controlled (depending on the manufacturer) so that process can be adjusted to different materials. Some of them are: slicer fill scan spacing (distance between lines), laser power, and number of contours, layer thickness and temperature control variables.
Standard materials processed by PBF-LB/P are: Polyamide 11 & 12 & glass filled, TPU.
1.7.5
HP Multi Jet Fusion (PBF-IrL/P) TechnologyMulti Jet Fusion (PBF-IrL/P or MJF) is the named technology of the manufacturer Hewlett Packard (HP) developed in the last few years. Based on a similar concept like selective laser sintering but a complete new approach this technology allows creating end-use polymeric parts in high production rates and low cost per part.
The groundbreaking concept developed by HP has revolutionized the additive manufacturing scenario because parts conceived by this technology are completely isotropic and due to the high speed and production rates it can substitute injection molding at certain points for low production industrial parts for end-use and not for prototyping.
As benefits respect conventional PBF-LB/P, as pointed out, the build ratios and high strength materials isotropically consolidated by the technology, there is no need of support structures, PBF-IrL/P is able to reproduce very small and accurate details and most important; process stability and temperature stability are completely controlled by the HP software. This closed control loop leads to very good repeatibility and reliability in comparison with standard PBF-LB/P Systems.
As drawback, process parameters are locked thus development of new materials is not a possibility for these machines.
Standard materials offered are: polyamide 11 & 12 and gass filled PA, and TPU.
PBF-IrL/P Components
As an industrial scale 3D printer, the entire production chain is monitorized by the PBF-IrL/P software, on the one hand we can find the build unit where powder is processed and transformed into solid parts, on the other hand the PRS and part recovery station which manages the powder reusability ratios and mixes the powder from the last build in order to ensure good part quality.
Within the PRS we can also find the fast cooling unit that enables a slightly faster cool down phase and is normally used when parts are not so slim.
Part recovery requires minimal time and labor. After the print job is completed, finished parts are recovered from the cake and excess of powder is removed using auxiliary sandblasting equipments.
An overview of the PBF-IrL/P components in pointed out in Fig. 1.22.
Fig. 1.22(Source AIDIMME facilities)
PBF-IrL/P technology components
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PBF-IrL/P Workflow
Giving a closer look to the printing unit, it is equipped with high intensity High Voltage bulbs that heat the chamber, a powder dispenser and binding head.
As in any AM technology, machine preparation is similar; printing module is loaded with powder and machine cleaned up.
Warm up volume is also required in order to generate the heat barrier and after the warmup phase, parts are manufactured layer by layer. At this step the powder dispatcher moves back and forth and deposits a thin powder layer on the build area. Binding/UV head moves above the powder layer injecting two components called “fusing agent” and “detailing agent”. Fusing agent is aimed to reduce the melting point of the powder (black agent) powder that is injected with this material will be transformed into parts. Whereas detailing agent is aimed to increase the melting point, the detailing agent is applied in the border between the part and the non sintered powder in order to improve the surface quality and to stop the heat dissipation, it some way it creates a heat barrier that surrounds the part.
Once the build ends a natural cooling or a fast cooling can be carried out depending on different factors as the shapes included in the cake. Fast cooling is normally used when parts are small-size.
1.7.6
Metal Binder Jetting (MBJT) TechnologyDuring the last few years, the additive manufacturing scenario has been evolving with a recent batch of innovative technologies where Metal Binder Jetting can be found.
MBJT follows the principles of Metal Injection Moulding (MIM) applied to a layer-by-layer technique (Binder jetting process).
Even tough the MBJT is not widespread yet, many important companies related to the additive manufacturing market are about to launch their own MJBT machines. Some of the benefits that this technology are very fast production ratios, very small features compared to the conventional Metal AM technologies like PBF-LB/M and PBF-EB/M, support free parts during the construction process (not during debinding and sintering) and a wide variety of materials (any material that can be sintered).
In addition, metal powders are not melted during the printing process thus many issues related to part distortions (residual stresses) dissapear.
As drawbacks, parts need to be debinded and sintered after the part construction. Debinding can lead to part distortions if not properly done and sintering leads to srinkage thus part size in this kind of process is cruzial.
MBJT Components
As basic components in the production chain of metal binder jetting, we observe that a debinding furnace and a high temperature furnace (sintering) will be required as well as a sandblasting equipment in addition to the 3D printer itself.
Metal binder jetting machines are made up of a powder dispatcher head or raking system that delivers fine powder layers and a binder jetting head with multiple inkjets that deposits very small droplets of binder in order to join the particles and a curing system to polymerize the binder agent.
Parts manufactured up to this step remain in a fragile green state infiltrated with a polymeric matrix and require being post processed in a sintering furnace that creates the full-metal part.
Binder jetting machines can work with a huge range of metal alloys, but they can also handle ceramic and sand-based materials.
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