FDM Process Facts

At Envision 3D Printing, we believe in educating our customers, so we created this FDM process facts page to help our customers understand the technology. We believe that if our customers better understand the FDM process and products, they will know what to expect, and we will better meet their expectations. If you have any questions, please feel free to email us at sales@envision3dprinting.com and we will do our best to answer them.

The FDM principle used for rapid prototyping services is fairly simple: extrude thermoplastic filament through an extrusion tip onto a build sheet, layer by layer, tracing the shape of each layer first, and then filling in the geometry. Depending upon part geometry, there might also be support material that needs to be extruded onto the build sheet to support features that would otherwise be extruded into air. After a part is printed, any support material is dissolved in a specially designed wash tank. This dissolvable support structure allows us to print assemblies with moving parts.

While the process sounds relatively simple, both the software needed to process the files and the machine that creates the parts are complex. The latest production series Stratasys equipment is based on many years of development, yielding a highly sophisticated machine that produces the best FDM parts on the market, ensuring Envision 3D Printing’s rapid prototyping services are of the highest quality.

FDM technology

FDM parts can be built solid, sparse fill, or double-dense sparse fill and the wall thickness can be varied. A solid build is just like it sounds: the machine traces the outline of the geometry and then fills the interior before proceeding to the next layer. Sparse fill traces the outline of the geometry with two contours and then completes the interior with unidirectional diagonal lines, alternating direction on each layer to create a crosshatch weave pattern. Double-dense sparse fill traces the outline of the geometry with two contours and then completes the interior with bidirectional diagonal lines on the same layer. With double-dense sparse fill, the part is stronger since there are no gaps between the diagonal lines as with sparse fill. Finally, the wall thickness can be varied by adjusting the width and number of contours. By varying the wall thickness, areas around features that will be post-processed (for example, drilled or tapped) can be reinforced.

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                       Solid

SparseFill2

                  Sparse Fill

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      Double-Dense Sparse Fill

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Double Dense with Thicker Wall

While Stratasys machines produce some of the best quality FDM models, some artifacts can be created as a result of the process. For example, when laying down each layer of material, there is always a start and stop point for the extrusion tip. This start and stop point sometimes creates a visible seam, as seen in the photo to the right. While the software has several options to manipulate seam control, the degree to which you can control it depends on part geometry. For example, on parts with many features, it is easy to “hide” the start-stop points. However on parts with few features to interrupt the path, there is usually a detectable seam. We manipulate the seam control to minimize visible seams. Any raised seam can easily be sanded down with a fine grit sandpaper after the part is complete.

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Another artifact of the print process is stair-stepping. Depending on how the part is oriented on the build sheet, this stair-stepping can be minimized or eliminated. For example, if you make a cylinder in the vertical position, as shown in the first picture on the right, there will be no stair-stepping. If you make the cylinder on its side as shown in the second picture on the right, stair-stepping will be visible. This stair-stepping effect will be more pronounced with a lower (thicker) layer resolution. We will orient your part to minimize or, if possible, eliminate visible stair-stepping. As with the seam, parts can be post-processed to smooth the surfaces as needed.

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