RepRap’s new open source software 3D prints PLA beams as stiff as steel

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RepRap, the developer of open source self-replicating 3D printers, has created a new Python script that allows users to 3D print low-cost PLA beams that are as rigid as their steel counterparts.

The open source FreeCAD program is designed to be as accessible as possible, as it only requires users to specify some very basic settings. This includes the length, width and height of the beam, as well as the thickness of the struts and the diameter and number of screw holes in the mounting blocks at each end of the beam. The script then automatically generates the entire beam as a 3D printable model.

RepRap has already tested its program with Creality’s CR-30 Infinite Z-Belt System, which allows printing of bundles of (theoretically) infinite length. The script is also suitable for standard FFF systems, but without a conveyor belt, the printed bundles will be limited to the length of the build plate.

The company wrote in a blog post: “A lot of people have printed long I-beams on this type of machine, but we thought about writing a Python FreeCAD program to generate parametric beams more suitable for 3D printing, by taking advantage of the fact that complexity is more or less free with this technology and that infinite Z-belt printers can print many overhanging shapes without supporting material.

A high stiffness beam automatically generated by the RepRap design script. Image via RepRap.

How it works?

The software represents beam structures as repeating blocks of tetrahedra, known to be very strong, with most materials lining the outer faces. This gives the structures a second high cross-sectional moment, providing sufficient flexural strength in all directions. The diagonal spacers are also angled to ensure that tape printers with 45 ° printing angles can fabricate the entire bundle without using support material.

The RepRap program also automatically generates mounting blocks at the ends of each beam that allow beams to be bolted to each other or to other objects. The larger holes should allow wiring, tubing, and parts such as drive shafts to drop down the center of the beams, while the smaller holes allow angular increments around larger holes.

Beam printing on the Creality CR-30.  Photo via RepRap.
Beam printing on the Creality CR-30. Photo via RepRap.

As stiff as steel

Putting the Python script to the test, RepRap 3D printed a set of PLA beams and subjected one of them to a flex test using a simple weight and dial gauge setup. The length of the printed bundle was 175mm and it weighed 47.7g. Its stiffness was determined to be 1.02 x 10⁻⁴ mN⁻¹, while its flexural stiffness (Young’s modulus * second surface moment) was calculated to be 17.5 Nm².

RepRap determined that a 5mm square steel beam of the same length (175mm) would also weigh approximately 47g. Although the steel beam was physically smaller than the printed counterpart, the company had historically 3D printed a PLA beam that had the same stiffness as the same weight of steel. In addition, the use of 3D printing allows variable beam dimensions, allows for the integration of services within the beam, and makes complex fixture and hole models easily possible.

RepRap’s open source Python program can be found on Github here.

Two 3D printed PLA beams fastened together.  Photo via RepRap.
Two 3D printed PLA beams fastened together. Photo via RepRap.

Design software for additive manufacturing (DfAM) is essential when it comes to taking full advantage of the design freedom that 3D printing offers. Earlier this year, 3D printer maker Stratasys and engineering software developer nTopology added a new masking attachment module to their FDM Fixture Generator design automation tool. The software is intended to streamline the design process for 3D printed jigs, fixtures, and other tools.

Elsewhere, researchers at ETH Zurich have already developed a DfAM IT framework capable of automating the design of complex multi-stream nozzles. The framework acts as an alternative to the conventional CAD software used by engineers today, but allows non-specialist users to design complex geometries specifically for additive manufacturing tooling purposes, such as FDM nozzles.

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The image shown shows two 3D printed PLA beams fastened together. Photo via RepRap.



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