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3D prints post-processing is one of the most crucial steps to achieve a final print. Explore our blog to gain the essential knowledge in this field.
Additive manufacturing gives great freedom in designing parts with complex shapes like lattice structures and internal cooling channels. However, in most cases, the surface finish of 3d metal printed parts is characterized by high roughness, which for many applications is unsatisfactory where a smooth surface finish is required, and prints need additional post-processing techniques. Print surface quality can strongly influence the fatigue strength of the part – its resistance to stresses that change over time and its corrosion resistance.
Classical post-processing methods like the sanding process or grinding with grit sandpaper work well for relatively plain surfaces. However, their use for additively manufactured parts is limited to exposed surfaces, and they don’t work in hard-to-reach areas. Also, it’s important that abrasive materials can get embedded into the surface of the print, which can alter its characteristic crating defects like cracks or corrosion initiation points. Other post-processing techniques, like turning and milling, have similar limits to the previously mentioned and provide smooth surfaces only on the exposed surfaces. Other post-processing solutions using chemical or electrochemical etching suffer similar problems to those previously mentioned. Reaction solutions will reach perhaps all the spaces of printed parts however, the rate of reaction – and surface etching speed can be very different in different areas leading to uneven surface finish. There is the possibility of localized corrosion and edge rounding effect leading to alteration of the designed print objects. Also, chemical compositions must be adjusted for every print material and sometimes even specific geometries. Their advantage is that they are processing the entire print at the same time, so they provide support
It’s true that 3d printing allows the creation of any complex shape however the design freedom comes with pesky support structures that need to be removed after the printing is done. In metal 3d printing, support structures have two roles. They provide strong mechanical support to your 3d print, not allowing the part to be distorted during the printing process. They also are far better at conducting heat than metallic powder surrounding the part. Usually, print surfaces need to be supported if their angle is smaller than 45 degrees. The support removal process for medical implants is usually done manually without specialized support removal machines. This work can be very tedious and can often account for 50% of the costs of implants. Printing parts on support structures is also a great way to ensure easy print removal from the print bed.
Designing for post processing
To achieve the desired print model, the post processing methods need to be accounted for in the design phase of print model preparation. Generally, designers for additive manufacturing try to avoid generating too many support structures as the support material first needs to be printed, which takes time during the part printing. After that, prints require the support material needs to be removed, which can be an even longer process, and it can have an impact on the surface quality. When designing for additive, the support removal process, the print’s surface quality, and specific areas where the rough print surfaces are not acceptable. There are important aspects like what print removal tool is going to be used to remove the completed prints from the print bed and what amount of print material is going to get removed during chosen post processing technique. Taking into account the planned processing is very important, so the dimension of printed are the same as in the print model.
Multiple post-processing methods can be used to remove the prints from the print bed ranging from manual methods like peeling the models with a spatula, cutting with pliers, and with hand-held automatic tools. Depending on the strength of the printed part printed parts can be cutted using abrasive disc from the print table or for more delicate printout wire electric discharge machines (WEDM) can be used. In both cases, the interactions and possible corrosion with cooling fluids were used most accounted for in the design phases. Cooling fluids from cutting or other subtractive methods can be very hard to remove from the complex lattice structure, for example, in medical implants.
Due to the complexity of 3d printed parts, a new post processing techniques are being developed for the effective processing of prints. Those methods need to be both able to post process hard to reach areas like lattice structure and the same time, provide a flexible post processing solutions with surface treatments that adapted to new geometries for each process. Surface finishing machines should be a part of any advanced additive manufacturing facility.
Dry electropolishing is a surface finishing method that uses an electric current to remove surface impurities and improve surface smoothness. Unlike wet electropolishing, this method does not use a liquid solution to conduct the electrical current, instead relying on a gaseous or solid medium. This process is often used for high-precision parts, such as medical implants or aerospace components, due to its ability to produce a highly uniform and smooth surface. Additionally, dry electropolishing does not produce hazardous waste, making it an eco-friendly alternative to traditional wet electropolishing methods.
Vibratory finishing is a post-processing method used in metal additive manufacturing to improve the surface quality and texture of a 3D printed metal part. This process involves placing the part into a vibratory finishing machine with abrasive media, such as ceramic or steel shots, and applying a vibratory motion. This combination of vibration and abrasive media removes surface defects and smoothens the surface of the part. Vibratory finishing is a versatile and cost-effective post-processing method that can be applied to a wide range of metal additive manufacturing technologies, including selective laser melting (SLM), electron beam melting (EBM), and binder jetting. The specific parameters of the vibratory finishing process, such as the vibratory frequency and the type and size of the abrasive media, can be adjusted to create a smooth surface finish.
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