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06-03-2016

High Strength and Minimal Roughness

Effect of Process Parameters during 3-D Printing

During "Fused Filament Fabrication" (FFF), the strength of the parts depends on how well the individual strands fuse with one another. A research project has now systematically investigated the effect of nozzle temperature, volumetric flow and film thickness.

Layered structure of the test bars: The outer contour is printed first in each layer, followed by filling with strands at an angle of 45° (© HsKA)

Most inexpensive desktop 3-D printers employ the "Fused Filament Fabrication" (FFF) principle during which a plastic strand (filament) is extruded through a heated nozzle. This is how the print head builds up the plastic part in layers. A research group has now fabricated test specimens from PLA using different process parameters. The work used and "Ultimaker 2" open-source printer. During the experiments, the three parameters that have a major affect on the temperature of the extruded mass were varied - these are the nozzle temperature, the volumetric flow and the layer thickness.

The investigations showed that the tensile strength increased with increasing nozzle temperature. Moreover, the relative effect of layer thickness and volumetric flow on strength decreased. The effects of a change in volumetric flow were somewhat less pronounced. A high volumetric flow reduces the strength, but at the same time the volumetric flow is decisive for the printing speed. At an increased volumetric flow, a good strength value can be achieved only by increasing the temperature; the effect of layer thickness decreases.

Increased layer thickness improves strength - especially at a low volumetric flow. It also affects the print time, since fewer layers need to be printed when the layer is thicker. With increasing layer thickness, the roughness increases; thus, the surface quality decreases. There is thus a basic conflict between the quality features of "tensile strength" (high layer thickness) and "surface quality" (low layer thickness). This conflict can be alleviated by increasing the printing temperature, because this has a very beneficial effect on the tensile strength while hardly affecting the roughness at all.

The highest tensile strength of 62.9 MPa was achieved by a sample printed at maximum printing temperature, lowest volumetric flow and highest layer thickness. The lowest tensile strength of all specimens was 39.3 MPa. The lowest mean roughness was 20 μm, the highest 113 μm. (hs)

contact

Hochschule Karlsruhe – Technik und Wirtschaft (HsKA)
Moltkestraße 30
D-76133 Karlsruhe
Tel. +49 0 721 925-0
Fax +49 0 721 925-2000
www.hs-karlsruhe.de

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