Additive manufacturing technology has opened up the possibilities of producing parts that have a complex geometry and would be quite difficult to obtain using conventional manufacturing processes. The technology covers a host of processes and technologies that offer a full spectrum of capabilities for the production of parts and products with different substrate materials, from polymers to metals.
Additive manufacturing or more commonly known as 3D printing engages layer-by-layer deposition of substrate materials to build a 3D object based on a CAD (computer-aided design) model. This enabling technology drives and encourages innovation with unparalleled design freedom.
It offers advantages that reduce the lead time and the capability to build objects with intricate geometry and complex features at no extra cost. 3D printing is also emerging as an energy-efficient technology and is more environmentally friendly in terms of process emissions and waste generation.
With recent advancements in additive manufacturing, this technology is now open to a much wider industrial section and as the exponential adoption rate continues on all fronts, more and more systems, materials, applications, services, and ancillaries are emerging to enhance its scope of application.
Therefore, there have been a lot of research activities to investigate the possibility of completely replacing conventional manufacturing and building processes with 3D printing. Almost all of the R&D projects are geared towards studying the printing of different materials such as metals, metal alloys, etc.
The earliest 3D printing technologies first became visible in the late 1980s. At that time, they were called Rapid Prototyping (RP) technologies. This is because the process was originally conceived as a fast and more cost-effective method for creating objects and prototypes to support the manufacturing industry.
It has shown promising results which fueled the interest in further developing the process. g In recent days, the increasing availability and access to high-precision measuring solutions and digital technology have contributed to the speedy development of additive manufacturing techniques.
The main advantages of additive manufacturing are connected to the ability to manufacture complex geometries, lighter structures, and the ability to allow customization. These are not readily available and impose great challenges in traditional manufacturing.
For example, an increase in the volume of material removed or objects with more complex geometry generally require longer manufacturing time and higher costs. This means that end-users will have to pay more for the products while also having to wait for an extended time to receive their products.
Often the majority of removed material in conventional manufacturing ends up as waste. Although the wastes can be recycled, the fractional amounts that are discarded will accumulate over time and will eventually put a strain on the environment. This issue would not be present in additive manufacturing processes. Therefore, the printed parts would be lighter and more carbon-friendly.
Additive manufacturing encapsulates a multitude of sensors, technologies and platforms that make it possible to produce printed objects and prototypes directly from 3D CAD models reliably and with high precision.
Some of the techniques used in Additive Manufacturing are:
Stereolithography (SLA) is a 3D printing technique where a platform is dipped into a vat filled with a liquid photopolymer. The 3D object is constructed using a bottom-up approach. A layer of deposited material is created when a UV laser shines through from below the vat and precisely cures a layer of the liquid photopolymer (polymerization). This fabrication method is also known as Photo-polymerization.
This technique involves the use of a binder and a powder-based material. The powder-based material is applied to the build platform with a roller, and then the print head deposits the binder on top.
The binder adheres the layers together, which is usually in liquid form. After depositing one layer, the process is repeated to create more layers until the product is finished. When using this process, you can use different materials as substrates, such as polymers, ceramics, and metals.
Powder bed Fusion
Powder bed fusion deposition involves heating using a thermal energy source such as an electron beam or laser on a layer of powder applied to the platform. This layering process is repeated until the final product is finished.
Directed Energy Deposition
Directed Energy Deposition (DED) is one of the most complex techniques which involves moving robotic arms. A four- or five-axis arm will move around, depositing melted material around a fixed object. The material is melted by an electron beam or laser and will then solidify.
The success of 3D printing manufacturing highly relies on its capability to print any objects and materials. Therefore, there have been many investigations into assessing the feasibility of printing different types of metals and so far, the results have been promising.
Primarily, the settings and process parameters should be adjusted to ensure that the printed products are free of defects. Currently, the 3D printer can use a wide array of materials that are supplied in filament, powder, granules, pellets, resin, etc.
Specific materials are developed for specific platforms with material properties that precisely suit the application. Below is the list of main classes of materials used in additive manufacturing:
Polymers: Common plastic can be used in the 3D printing application; however, ABC (Acrylonitrile butadiene styrene) and PC (polylactide) are the most widely used. Moreover, the common structural polymers, as well as a number of waxes and epoxy-based resins, are also used depending upon the applications. Researchers often mix different polymer powders to create a new structural and aesthetic material.
Metals: Metals and metal composites for industrial-grade 3D printing are widely used, including aluminium and cobalt derivatives. Other metals that exhibit high tensile strength such as Steel, Titanium, Aluminium, Cobalt Chrome Alloy are also used in different 3D printing applications due to the need to print highly durable and robust products.
In addition, 3D printing applications using Gold and Silver have also been considered with applications across the jewellery sector. These are both very strong materials and are processed in powder form.
Ceramics: Ceramics material shows high promise in the space of 3D printing manufacturing and can be used in applications such as extrusion or material jetting. During the printing process, a ceramic slurry can be used as the substrate material to build a green part that can then be sintered.
To reiterate, 3D additive manufacturing shows positive results in producing strong, lightweight and durable products. This rapidly evolving technology is expanding and people have started implementing it across industry verticals.
The success in additive manufacturing is shown by the quality of the products manufactured through the process. Therefore, researchers need to understand the required process parameters to print the products without defects.
They may need to monitor and control the processing temperature. Moreover, they need to also validate and confirm that the printed products exactly match the supplied 3D CAD model. This can be achieved through using and integrating high precision sensors either in the 3D printer itself or as an external tool to measure and validate the printed geometries.
For example, parameters such as positioning of the print head, melting temperature of substrates and validating the dimension of the printed components are some of the most commonly encountered measurement challenges in additive manufacturing.
Especially for measuring the finest details and profile of the printed products, there is a need to use high precision sensors that are able to detect the finest resolutions in the object and can be easily integrated into the machine. Laser scanners can provide the required profile measurement on the objects.
The users only have to choose the scanners that can offer high resolution scanning to read the details on the printed object. This type of measurement is crucial and should be implemented in almost all R&D activities in additive manufacturing, especially when printing new materials. The results allow the engineers to make the necessary adjustment to the machine and incorporate new techniques to achieve superior product quality with less error tolerance.
Position measurement can also influence the accuracy of the printing process. For example, single-point laser displacement sensors that measure based on the laser triangulation principle can be used for accurate positioning and displacement measurements.
Similarly, temperature control is also an important issue to be addressed as it significantly impacts the quality of the final products. The manufacturers should control the deposition temperature and ensure that an adequate heating rate is achieved. These can be easily done with thermal imagers or single-point infrared pyrometers.
As a result, manufacturers will be available to reduce temperature variations during laser processing which minimizes the chance of defects and improves the efficiency of 3D printing.
Sensor technology will continue to develop and will definitely be integral in advancing additive manufacturing technology. They have become more advanced and miniaturized to allow their integration in high-volume manufacturing such as in the commercial 3D printers. More technologies have been developed that enable precise measurement of the above-mentioned parameters at a cheaper cost and easier to be implemented.
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