According to foreign media reports, thanks to a new study in Australia, the quality of 3D printed metal parts may soon be improved. Scientists there have determined that ultrasound can increase the strength of these materials by changing their microstructure. The RMIT University team led by PhD student Carmelo Todaro recently tried an existing 3D printing technology called "Directed Energy Deposition (DED)".

In recent years, with the rapid development of 3D printing technology, it is rapidly changing our traditional production methods and lifestyle. As a typical representative of emerging manufacturing technology, the early metal 3D printing technology used in the aerospace field has shifted more to the industrial, automotive, medical, mold, education, and jewelry markets. How much do you know about metal 3D printing technology? Today, Lei Jia Additive Editor will explain the current mainstream metal 3D printing technology for everyone.

It is understood that RMIT researchers used two different common alloys to print samples: Ti-6Al-4V is a titanium alloy commonly used in aircraft components and biomechanical implants; Inconel 625 is a nickel-based high temperature Alloys are commonly used in marine and petroleum industries.

No matter what kind of alloy is used, the deposition surface is actually an acoustic wave detector, that is, a tool that generates ultrasonic vibration. When the metal is solidified, vibration will act on the microcrystals to form a tighter structure. It was found that the tensile strength and yield stress of these materials increased by 12% compared to the same sample without ultrasonic.

Todrao said: "If you look at the microstructure of 3D printed alloys, you will find that they are usually composed of large, elongated crystals. Because of their lower mechanical properties and more prone to cracks during the printing process, this makes them more difficult to be exposed to. Accepted for engineering applications. However, the microstructure of the alloy obtained by using ultrasonic waves in the printing process is obviously different: the alloy crystals are very small and completely isometric, which means that they are in all directions of the printed metal parts. The above is formed evenly."

In addition, by turning the ultrasonic generator on and off during the printing process, it is also possible to create a single project with different microstructures in different areas. This is a quality called "functional grading", which is very useful when considering factors such as low weight or reduced material usage.

Researchers believe that once the ultrasound-enhanced 3D printing technology is further developed, it may also be used to increase the strength of other metals, such as stainless steel, aluminum alloys, and cobalt alloys.

Many types of hydraulic components have been 3D printed in metal. For example, Aidro uses stainless steel printed hydraulic valve blocks to control single-acting cylinders. The company can save space and optimize its internal passages. Compared with traditional components, it has a higher flow rate and lower pressure loss. Since no auxiliary drilling is required, the possibility of external leakage is also eliminated.

In addition, a stackable hydraulic valve was produced using 3D printing design and improvement (Figure 2). The direct-operated pressure reducing valve is made of steel and galvanized to prevent corrosion. When Aidro's customers have a small amount of valve demand, CNC machining is uncontrollable for delivery time and cost. On the contrary, the valve was redesigned and produced using 3D stainless steel, which reduced the weight by 60%. The structural wall is as strong as the original, and the new design results are comparable under the 250bar pressure test.

Methods of metal 3D printing technology:

There are currently five mainstream metal 3D printing technologies: laser selective sintering (SLS), nanoparticle jet metal forming (NPJ), laser selective melting (SLM), laser near net shaping (LENS) and electron beam selective melting (EBSM) technology .

Selective Laser Sintering (SLS)

The entire process device of SLS consists of a powder cylinder and a forming cylinder. The piston of the powder cylinder rises, and the powder spreader spreads the powder evenly on the forming cylinder. The computer controls the two-dimensional scanning trajectory of the laser beam according to the slicing model of the prototype. There are options Ground sinters the solid powder material to form a layer of the part. After one layer is completed, the working piston is lowered by one layer thickness, the powder spreading system is spread with new powder, and the laser beam is controlled to scan and sinter the new layer. This cycle repeats, layer by layer, until the three-dimensional part is formed.

Nano Particle Jet Metal Forming (NPJ)

As we all know, ordinary metal 3D printing technology uses laser melting or laser sintering of metal powder particles, while nanoparticle jet metal forming (NPJ) technology uses a liquid form instead of powder. These metals are wrapped in a tube in the form of liquid and inserted into a 3D printer. When the metal is 3D printed, it is sprayed and molded with "hot metal" containing metal nanoparticles. The benefit is that the metal is printed with molten iron, the whole model will be more rounded, and ordinary inkjet printing heads can be used as tools. When the printing is completed, the build chamber will be heated to evaporate the excess liquid, leaving only the metal part.

Selective Laser Melting (SLM)

The basic principle of laser selective melting technology is to use Pro/e, UG, CATIA and other three-dimensional modeling software to design the three-dimensional solid model of the part on the computer, and then slice and layer the three-dimensional model through the slicing software to obtain the contour of each section Data, the filling scan path is generated from the contour data, and the equipment will control the laser beam to select areas to melt the metal powder materials of each layer according to these filling scan lines, and gradually stack them into three-dimensional metal parts. Before the laser beam scans, the powder spreading device first pushes the metal powder onto the base plate of the forming cylinder. The laser beam then fills the scanning line of the current layer to select the area to melt the powder on the base plate to process the current layer, and then the forming cylinder is lowered by one The distance between the layer thickness, the powder cylinder rises a certain thickness, the powder spreading device then spreads the metal powder on the processed current layer, the equipment transfers the data of the next layer contour for processing, and the processing is performed layer by layer until the entire The parts are processed.

Laser Near Net Shaping (LENS)

Laser Near Net Shaping (LENS) technology uses the principle of simultaneous operation of laser and powder delivery. The computer slices the 3D CAD model of the part in layers to obtain the 2D plane contour data of the part, which is transformed into the motion trajectory of the CNC worktable. At the same time, the metal powder is fed into the laser focusing area at a certain powder supply speed, and it is quickly melted and solidified. Through the layer by layer of points, lines, and surfaces, a near-net shape part entity is finally obtained. The formed part does not require or only a small amount of processing is required. be usable. LENS can realize the moldless manufacturing of metal parts, saving a lot of cost.

Link to this article： Ultrasound can increase the strength of 3D printed metal by 12%

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