Selective laser sintering:Welcome to this new section dedicated to discussion and introduction to additive manufacturing technologies.In these weekly articles we will analyze from time to time a more or less known technology.Characterizing it in broad terms to have a clearer idea of all the facets of 3D printing. That, as we will see, are not limited to wire FDM and resin printers.
The first technique we will analyze you can use to process polymers and is sls or selective laser sintering.
The component construction process starts from virgin material in the form of powder.It is placed in hoppers at the side of the construction platform. Or in a side chamber (as you can see in the picture).The treated materials are usually Nylon PA12, PA11, PA6 in normal variants. And, in addition, you can charge them with particles such as glass or glass filled, aluminum, short carbon fiber.
Distributing the powder on the construction platform by a roller (also called rake or racla) that creates with its movement, from one side to the other of the construction platform.This forms a uniform, thick layer of powder.
It causes the creation of the thickness by the movement of the construction platform (build platform – z axis of construction) downwards.The source of energy that brings the material to fusion is a laser. Which through two sets of lenses focus first and then direct over the entire area of the platform (x & y axes) creating layers of 100 micron thickness.
Here is the image that clarifies the ideas
It heats the machine’s construction chamber to a temperature close to the melting temperature of the polymer.This allows to contain shrinkage and deformation of the components produced thanks to the reduced temperature difference.
This feature also allows to reduce power of the energy source (laser).As it must only provide the energy to pass from the temperature of the chamber to that of fusion.At the end of the construction process it is therefore necessary to wait for the gradual cooling of the construction chamber, which you must slow in order to allow a uniform withdrawal and cooling and to prevent deformations resulting from thermal stresses.
This technology has advantages in terms of media.The powder, the machine is heating and compacting, is self-supporting. You therefore do not require any supports of any kind and during the construction you can make a three-dimensional nesting of the components that you want to produce, as you can see in the following image
The components, once you complete the construction process, you must sandblast it. It helps to remove the powder partially sintered on the walls of the component.
At the end you can sieve and reuse the unused powder, but only the “free” one and not close to the piece. The latter part is partially sintered due to its proximity to the fully sintered area of the workpiece.
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