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In the machining process, you can create the details you can create with the tools of your choice. The size of the tool determines the minimum size of the hole and groove of the part. In the additive manufacturing process, similar to the size of the tool of interest, we need to pay attention to the laser spot size. The laser spot heats the metal powder, and each laser spot creates a micro-melting pool. From the melting of the powder to the cooling to a solid structure, the size of the spot and the amount of heat generated by the power determine the size of the micro-melting pool, thereby affecting the parts. Microcrystalline structure.
Consistency, control and traceability of high quality manufacturing requirements. Dynamic beam focusing provides tight focus control from laser melting to different temperatures, allowing the new optical solution of the selective laser melting system to more consistently control laser processing conditions.
In this issue, what is going on with dynamic focus? Think about whether the dynamic zoom system will give the SLM device more power and more laser heads.
Small change, big breakthrough
Basic knowledge of laser melting
The image below shows the laser energy heated powder particles and how the heat spreads to the adjacent powder. In order to melt the powder, sufficient laser energy must be transferred to the material to melt the powder in the central zone to create a fully dense portion, but at the same time the heat is transmitted beyond the circumference of the laser spot, affecting the surrounding powder. Therefore, the minimum manufacturing size is generally larger than the laser spot, and the amount of sintering beyond the laser spot depends on the thermal conductivity of the powder and the energy of the laser.
Image: Laser spot and adjacent heated material
Both the diffused laser energy and the laser scanning speed of the bath are carefully adjusted and controlled to achieve consistent metal alloy characteristics and layer thickness. The focus of the laser beam is the key to affecting the properties of the alloy during the melting process. To achieve a consistent process depends on controlling the laser spot size, it is necessary to make the laser energy density consistent with the energy transferred to the adjacent powder.
This requires a clearly focused beam of light, and any inconsistency in focus can result in insufficient powder melting of the material that is transmitted beyond the melting zone and can result in poor dimensional tolerances and surface finish. If the size of the focused spot is greatly increased, it may result in a finished assembly containing a large amount of incompletely melted powder and uncontrollable material properties.
Focused challenge
The ideal laser beam has a Gaussian intensity distribution such that the most intense position of the energy is the beam at the center of the laser and reduces the energy distribution to its edges. As we move away from this focus, the cross-sectional area of ​​the beam increases, reaching twice the minimum size. The smallest dimension at a distance is called the Rayleigh length (in the figure below):
Image from Wikipedia
In optics, especially laser, we set the saddle waist (the lowest point shown in the figure) to A, the cross-sectional area is a, along the direction of light propagation, when the cross-sectional area is 2a due to scattering, we Let B be here, Rayleigh length or Rayleigh range is the length from A to B (ie ZR shown in the figure). The relevant parameter is the conjugate focal length, b, which is twice the Rayleigh length. Rayleigh length is very important when the light wave propagates in a Gaussian model. At the Rayleigh length, the radius of the spot increases to 1.414 times the radius of the saddle, and the area increases to twice the area of ​​the saddle spot, so that the energy density of the light is greatly reduced.
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