How it works

SLS is a layer manufacturing technique where the used material is a powder. This powder can in principle be every material that can be sintered, several plastics like nylon and abs, elastomers and casting sand but also some metal alloys.
Mareco uses PA12 powder to produce rapid prototypes and rapid manufactured parts. This page gives a brief explanation of the SLS system Mareco works with.

As Selective Laser Sintering is a layer manufacturing technique the sintered part is built layer by layer. The file needed to create the layers is the so called stl file (stl = structual triangle language). This triangle file will be divided in cross sections of zero thickness, where the distance between the succeeding slices equals the layer thickness. Every slice will be send to the laser sinter machine where it functions as source for the navigation of the mirror system. The laser will follow the inside- and outside curve defined by the slice- file, the area between the curves is the hatch area. A horizontal moving slide divides the plastic powder on a in vertical direction movable working platform. Every downwards step of the table is one layer.
See pictures below.

The powder in and around the products have to stay on the platform. The first function of this loose powder around the parts is a support for the overhanging part sections. The second very important function is the working of the powder as an isolator to prevent the parts to cool down to quick. The sinter room of the machine is filled with circulating nitrogen to prevent oxidation.
The spot diameter of our lasers vary from 0.4 [mm] to 0.6 [mm] (different machines). However, when hitting the powder, a certain area around this spot will be influenced and will be more or less sintered. Due to this effect it is necessary to bring in the value of this area in the set-up parameters which means that this set up diameter will follow the curve, defined by the slice file. The following picture shows a situation where the wall thickness of the product is smaller than the radiating area which causes the effect that the really sintered wall will be larger.
When for instance the designed wall thickness is 0.6 [mm] the sintered wall thickness will be (2x0.8)-(0.6)= 1.0 [mm]. So the minimum wall thickness equals the radiating area. With PA12 this value is 0.60 [mm].

If the wall thickness is greater than, or equals, the radiating area, the designed wall thickness will be the same as the sintered one. See the following picture.

We have the possibility to create automatically a hollow core. This is very useful when a very thick wall or a completely massive product has been designed.
See the following picture.

After the process has finished the products have to cool down, together with the sintered isolation-wall they are put away for 12 to 24 hours, depending on the volume sintered.
After that the products will be taken out of the powder:

                  and here is the result:

Related links:

Fabbers (Digital Fabricator)
Wikipedia

Copyright®  Mareco Prototyping B.V.
Venlo, The Netherlands