SLM technology of deep dissection metal 3d printing technology (selected laser melting)

-Reprinted from 3D Tribe
The metal powder we usually see is like this.

After experiencing irresistible reasons, it changed into the following figure.

It is said that the culprit is the laser, metal powder after all what process?

Today, I took you along the SLM(Selective Laser Melting) selective melting technology to deeply dissect.

First look at the "crime scene" SLM280 metal 3D printer

SLM280 molding bin internal elements

Let us understand this formation process:

Each final part is formed by melting layer by layer, each melting layer, the platform is lowered, and the new powder is spread over this layer to repeat the above process. The real forming principle is that the laser hits the powder layer with a certain energy density, so that the powder in the scanned area reaches a molten state. The energy density received by the powder is related to many factors of the laser, such as scanning speed, scanning spacing and scanning power. The energy of the laser forms a heat-affected zone on the surface of the metal powder to form a molten pool, which affects the welding effect of the surrounding powder forming.

The laser will scan to the melting area to be formed according to certain rules and directions. According to the reasonable naturalization scanning path of different materials, the scanning area will be divided into strips, checkerboards, etc., which can effectively release the internal stress of the parts. Planning each layer of scanning vectors can reduce internal defects to obtain parts with higher density and better mechanical properties.

So in the process of selective melting, which aspects can we use to improve the performance of the final product? We can focus on several important aspects, the following is an enlarged view of the same material under different surface spacing, we can see that with the expansion of the surface spacing to a certain range, there will be very obvious internal defects:

Although the large distance between the scanning surfaces can significantly improve the forming speed, the range of the molten pool is limited. If the distance is too large, the overlap rate of the cladding width will be too small, and if it is serious, the effect shown in Figure 3 will be produced.
Let's analyze the other two factors, laser power and scanning speed are also the core parameters that determine the energy density, which directly affect the porosity of the molded parts, and the porosity directly affects the mechanical properties of the finished product.

As an example of the aluminum alloy in the above figure, we can find that the porosity of the part decreases with the increase of the laser power and the decrease of the scanning speed. This trend is because the higher energy density makes the powder better melting, so is the higher the energy density, the better? Of course not so simple, first of all, the energy is too high will also make the internal gas of the parts can not be ruled out to produce voids. The following figure:

Under many conditions, the laser parameters produce results that are not linear, and the process becomes relatively complex at high energy densities, for example:

The above figure shows the influence of laser power, scanning speed and scanning spacing on the density in the study of copper alloy. It can be seen that with the expansion of scanning spacing, the energy density decreases, but the density does not change much. This phenomenon is influenced by peritectic and eutectic.
Let's look at the impact of different spot diameters on the printing effect:

The light spot cannot be too large. Under the same energy density, with the change of the light spot diameter, the energy will be concentrated on the upper surface. The powder below each layer cannot be effectively melted under the influence of the laser molten pool, which directly affects the quality of the parts. The tensile strength of the part in the vertical direction is reduced, and cracks are more likely to occur.

To sum up, many factors need to be considered in order to obtain the ideal printing effect. Only by constantly exploring more suitable processes can the disadvantages be better overcome. SLM technology is applied to various fields. For more technical details, please call Tribe 400-690-7753! More technical sharing please look forward! (Tribes of Three MR.Gao)

References
Analysisof defect generation in Ti–6Al–4V parts made using powder bedfusion additive manufacturingprocesses -2014
Selectivelaser melting of AlSi10Mg alloy Process optimisation and mechanical propertiesdevelopment -2015
ManufacturingFeasibility and Forming Properties of Cu-4Sn in Selective Laser Melting -2017