Technical Officer Articles
3D printing of Twin Crankcases
We have modelled the Twin crankcases at 1/3 scale
The crankcase holding down holes are as depicted on a drawing held at the VOCSC.
Just a simple description of 3D printing.
We use Fused Filament Fabrication as a method of 3D printing. In this thermoplastic material is heated and extruded through a nozzle. A spool of filament is loaded into the printer and fed through to the extrusion head. Once the printer nozzle has reached the desired temperature, a motor drives the filament through the heated nozzle melting it. The printer then moves the extrusion head around, laying down melted material at a precise location, where it cools down. Once a layer is complete, the build platform moves down and the process repeats, building up the part layer-by-layer.
The range of plastics include ABS, Nylon, Polyester, etc. One adjusts the printer to cope with these materials.
To make a component, one has to start with a 3D model. There are many 3D CAD programs to do that; the output from these CAD programs commonly use STL files.
Once you have a STL file, you can use that as the input file for so-called slicer programs that generate the g-code that the printers understand. We load the g-code onto a memory card which fits the printer.
We have an Ultimaker printer and they use Cura as the slicing program. There are some limitations using this printer, mainly the build volume (8x8x12""); anything too large will have be made in pieces and joined together afterwards.
Because FFF printing produces an anisotropic part (i.e. varying mechanical properties in different directions) it is important to properly orient the part.
Commonly, we use infill percentage of 20%, but for some parts we use 100% infill, based on the use of the part; 100% for parts we want to use, 20% for checking the form and fit.
It is also important to consider support materials, often made from the same plastic; wherever there are unsupported surfaces in the part, or bridges, or overhangs, then you want support to be printed. Of course this increases the build time, and expense, but does guarantee that you make a useable print.
Why do 3D Printing?
It enables us to evaluate fit and form in the Drawings Project.
It enables us to make patterns for sand or investment casting.
It allows for functional parts to be made (e.g. gearbox lever, propstand support, pinion for the speedo gearbox).