Manual:Preparing models for 3D printing/es

Uno de los principales usos de FreeCAD es producir objetos del mundo real. Estos pueden ser diseñados en FreeCAD, y luego hacerse realidad de diferentes maneras, como comunicándolos a otras personas que luego los construirán, o, cada vez más frecuentemente, enviándolos directamente a una impresora 3D o a una fresadora CNC. Este capítulo le mostrará cómo preparar sus modelos para enviarlos a estas máquinas.

Si has sido precavido al modelar, la mayor parte de las dificultades que puedes encontrar al imprimir tu modelo en 3D ya han sido evitadas. Esto implica básicamente:

Cuando se imprime en 3D, siempre hay que asegurarse de que esta pérdida de calidad se mantiene por debajo de los requisitos mínimos.
 * Asegúrate de que tus objetos 3D son sólidos. Los objetos del mundo real son sólidos, el modelo 3D debe ser sólido también. Hemos visto en capítulos anteriores que FreeCAD te ayuda mucho en ese aspecto, y que el Ambiente de trabajo DiseñoPiezas te notificará si haces una operación que impide que tu modelo sea sólido. El Ambiente de Trabajo Pieza también contiene un [[Image:Part_CheckGeometry.svg|16px]] Comprobar geometría que es muy útil para comprobar posibles defectos.
 * Asegurarse de las dimensiones de sus objetos. Un milímetro será un milímetro en la vida real. Cada dimensión es importante.
 * Controlar la degradación. Ningún sistema de impresión 3D o de fresado CNC puede tomar archivos FreeCAD directamente. La mayoría de ellos sólo entienden un lenguaje de máquina llamado G-Code. El G-code tiene docenas de dialectos diferentes, cada máquina o proveedor suele tener el suyo propio. La conversión de tus modelos en G-Code puede ser fácil y automática, pero también puedes hacerlo manualmente, con un control total sobre la salida. En cualquier caso, es inevitable que se produzca alguna pérdida de calidad de tu modelo durante el proceso.

Abajo, supondremos que se cumplen los dos primeros criterios y que, a estas alturas, usted es capaz de producir objetos sólidos con dimensiones correctas. Ahora veremos cómo abordar el tercer punto.

Exportación a slicers
Esta es la técnica más utilizada para impresión 3D. El objeto 3D se exporta a otro programa (el slicer) que generará el G-code del objeto, cortándolo en finas capas (de ahí el nombre), que reproducirán los movimientos que hará la impresora 3D. Como muchas de esas impresoras son de fabricación casera, suele haber pequeñas diferencias entre unas y otras. Estos programas suelen ofrecer posibilidades de configuración avanzadas que permiten adaptar la salida exactamente a las características de su impresora 3D.

La impresión 3D real, sin embargo, es un tema demasiado amplio para este manual. Pero veremos cómo exportar y utilizar estos cortadores para comprobar que la salida es correcta.

Convertir objetos en mallas
Ninguno de los slicers, en este momento, tomará directamente la geometría sólida como la que producimos en FreeCAD. Así que tendremos que convertir cualquier objeto que queramos imprimir en 3D en una Malla poligonal primero, que el slicer pueda abrir. Afortunadamente, así como convertir una malla en un sólido es una operación complicada, lo contrario, convertir un sólido en una malla, es muy sencillo. Lo único que debemos tener cuidado, es que es aquí donde se producirá la degradación que mencionamos anteriormente. Debemos comprobar que la degradación se mantiene dentro de unos límites aceptables.

Todo el manejo de la malla, en FreeCAD, se hace mediante otro banco de trabajo específico, el Ambiente de trabajo Malla. Este ambiente de trabajo contiene, además de las herramientas más importantes que convierten entre objetos Pieza y Malla, varias utilidades destinadas a analizar y reparar mallas. Aunque el trabajo con mallas no es el objetivo de FreeCAD, cuando se trabaja con el modelado 3D, a menudo se necesita tratar con objetos de malla, ya que su uso está muy extendido entre otras aplicaciones. Este ambiente de trabajo te permite manejarlos completamente en FreeCAD.


 * Convirtamos uno de los objetos que hemos modelado en los capítulos anteriores, como la pieza de lego (que puedes descargar desde el final del capítulo anterior).
 * Abre el archivo de FreeCAD que contiene la pieza de lego.
 * Cambia al Ambiente de trabajo Malla
 * Selecciona el ladrillo lego
 * Selecciona el menú Mallas -> Crear malla desde forma
 * Se abrirá un panel de tareas con varias opciones. Algunos algoritmos de malla adicionales (Mefisto o Netgen) pueden no estar disponibles, dependiendo de cómo se haya compilado tu versión de FreeCAD. El algoritmo de malla estándar siempre estará presente. Ofrece menos posibilidades que los otros dos, pero es totalmente suficiente para objetos pequeños que se ajustan al tamaño máximo de impresión de una impresora 3D.




 * Select the Standard mesher, and leave the deviation value to the default value of 0.10. Press Ok.
 * A mesh object will be created, exactly on top of our solid object. Either hide the solid, or move one of the objects aside, so you can compare both.
 * Change the View -> Display Mode property of the new mesh object to Flat Lines, in order to see how the triangulation occurred.
 * If you are not happy, and think that the result is too coarse, you can repeat the operation, lowering the deviation value. In the example below, the left mesh used the default value of 0.10, while the right one uses 0.01:



In most cases, though, the default values will give a satisfying result.


 * We can now export our mesh to a mesh format, such as STL, which is currently the most widely used format in 3D printing, by using menu File -> Export and choosing the STL file format.

If you don't own a 3D printer, it is usually very easy to find commercial services that will print and send you the printed objects by mail. Among the famous ones are Shapeways and Sculpteo, but you will usually find many others in your own city. In all major cities, you will nowadays find Fab labs, which are workshops equipped with a range of 3D manufacturing machines, almost always including at least one 3D printer. Fab labs are usually community spaces, that will let you use their machines, for a fee or for free depending on the Fab lab, but also teach you how to use them, and promote other activities around 3D manufacturing.

Using Slic3r
Slic3r is an application that converts STL objects into G-code that can be sent directly to 3D printers. Like FreeCAD, it is free, open source and runs on Windows, Mac OS and Linux. Correctly configuring things for 3D printing is a complicated process, where you must have a good knowledge of your 3D printer, so it is not very useful to generate G-code before actually going to print (your G-code file might not work well on another printer), but it is useful for us anyway, to check that our STL file will be printable without problems.

This is our exported STL file opened in Slic3r. By using the preview tab, and moving the right slider, we can visualize the path that the 3D printer head will follow to construct our object.



Using the Cura addon
Cura is another free and open source slicer application for Windows, Mac and Linux, maintained by the 3D printer maker Ultimaker. Some FreeCAD users have created a Cura Workbench that uses cura internally. The Cura Workbench is available from the FreeCAD addons repository. To use the Cura Workbench, you also need to install Cura itself, which is not included in the workbench.

Once you have installed both Cura and the Cura Workbench, you will be able to use it to produce the G-code file directly from Part objects, without the need to convert them to meshes, and without the need to open an external application. Producing another G-code file from our Lego brick, using the Cura Workbench this time, is done as follows:


 * Load the file containing our Lego brick (it can be downloaded at the end of the previous chapter)
 * Switch to the Cura Workbench
 * Setup the printer space by choosing menu 3D printing -> Create a 3D printer definition. Since we aren't going to print for real, we can leave the settings as they are. The geometry of the printing bed and available space will be shown in the 3D view.
 * Move the Lego brick to a suitable location, such as the center of the printing bed. Remember that PartDesign objects cannot be moved directly, so you need either to move its very first sketch (the first rectangle), or to move (and print) a copy, which can be made with the Part -> Create Simple Copy tool. The copy can be moved, for example with [[Image:Draft_Move.svg|16px]] Draft -> Move.
 * Select the object to be printed, and select menu 3D printing -> Slice with Cura Engine.
 * In the task panel that will open, make sure the path to the Cura executable is correctly set. Since we are not going to really print, we can leave all other options as they are. Press Ok. Two files will be generated in the same directory as your FreeCAD file, an STL file and a G-code file.




 * The generated G-code can also be re-imported into FreeCAD (using the slic3r preprocessor) for checking.

Generating G-code
FreeCAD also offers more advanced ways to generate G-code directly. This is often much more complicated than using automatic tools as we saw above, but has the advantage to let you fully control the output. This is usually not needed when using 3D printers, but becomes very important when dealing with CNC milling, as the machines are much more complex.

G-code path generation in FreeCAD is done with the Path Workbench. It features tools that generate full machine paths and others that generate only parts of a G-code project, that can then be assembled to form a whole milling operation.

Generating CNC milling paths is another subject that is much too vast to fit in this manual, so we are going to show how to build a simple Path project, without caring much about most of the details of real CNC machining.


 * Load the file containing our lego piece, and switch to the Path Workbench.
 * Since the final piece doesn't contain anymore a rectangular top face, hide the final lego piece, and show the first cubic pad that we did, which has a rectangular top face.
 * Select the top face and press the [[Image:Path_Profile.svg|16px]] Profile button.
 * Set its Offset property to 1mm.




 * Then, let's duplicate this first loop a couple of times, so the tool will carve out the whole block. Select the Profile path, and press the [[Image:Path_Array.svg|16px]] Array button.
 * Set the Copies property of the array to 8, and its Offset to -2mm in the Z direction, and move the placement of the array by 2mm in the Z direction, so the cutting will start a bit above the pad, and include the height of the dots too.




 * Now we have defined a path that, when followed by the milling machine, will carve a rectangular volume out of a block of material. We now need to carve out the space between the dots, in order to reveal them. Hide the Pad, and show the final piece again, so we can select the face that lies between the dots.
 * Select the top face, and press the [[Image:Path_Pocket_Shape.svg|16px]] Pocket Shape button. Set the Offset property to 1mm, and the retraction height to 20mm. That is the height to where the cutter will travel when switching from one loop to another. Otherwise, the cutter might cut right through one of our dots:




 * Once again, make an array. Select the Pocket object, and press the [[Image:Path_Array.svg|16px]] Array button. Set the Copies number to 1 and the offset to -2mm in the Z direction. Move the placement of the array by 2mm in the Z direction. Our two operations are now done:




 * Now all that is left to do is to join these two operations into one. This can be done with a Path Compound or a Path Job. Since we will need nothing more and will be ready to export already, we will use the job. Press the [[Image:Path_Job.svg|16px]] Job button.
 * Set the Use Placements property of the project is to True, because we changed the placement of the arrays, and we want that to be taken into account in the project.
 * In the tree view, drag and drop the two arrays into the project. You can reorder the arrays inside the project if needed, by double-clicking it.
 * The project can now be exported to G-code, by selecting it, choosing menu File -> Export, selecting the G-code format, and in the pop-up dialog that will open, selecting a post-processing script according to your machine.

There are many applications available to simulate the real cutting, one of them that is also multi-platform and open source, like FreeCAD, is Camotics.

Descargas'


 * The STL file generated in this exercise: https://github.com/yorikvanhavre/FreeCAD-manual/blob/master/files/lego.stl
 * The file generated during this exercise: https://github.com/yorikvanhavre/FreeCAD-manual/blob/master/files/path.FCStd
 * The G-code file generated in this exercise: https://github.com/yorikvanhavre/FreeCAD-manual/blob/master/files/lego.gcode

Leer más


 * Ambiente de trabajo Malla
 * El formato de archivo STL
 * Slic3r
 * Cura
 * Ambiente de trabajo Cura
 * Ambiente de trabajo Trayectoria
 * Camotics