- The process of creating a product using additive technologies.
- Requirements for models for 3D printing.
- Fixing non-fatal errors with NetFabb.
- Fixing non-fatal errors with MeshMixer.
In this article, we’ll talk about the main and general parameters, which a model should correspond to for getting high-quality 3D printing products. We’ll discuss the general mistakes arising from the process of creating three-dimensional models from the perspective of the high-quality polygonal net and how to fix them fast. The quality issues in the context of the accuracy of the details manufactured are described in another article: Real item size after 3D printing.
The structure of the additive technological manufacturing process.
In line with the represented algorithm at the first stage of creating an item, a 3D model is being designed using CAD software according to specifications and requirements. Then it’s necessary to export the data of a file of solid modeling software in a format compatible with the software of the additive production controlling machine (for example, STL).
The modeling process can be currently carried out not only in a solid-state format but already in STL. Before the next stage, the possible defects of the model are being identified. The model designed for 3D printing should be water-proof, solid and lack cavity walls, which is ensured by using special software. Then the information is being converted from the STL file into commands, following which a 3D printer makes the item, this is so-called G code.
During this procedure, the required scale of the part, the correct space position should be chosen, also, the model should be accurately positioned on the working surface. The end result of the process, strength, item surface roughness, and material consumption depend on this. Following the setting, the model is divided into material layers placed in the part body in one working cycle of the additive machine.
The process is called slicing. Slicing is done using software, which comes with the machine or using special tools (Simplify, Skein-forge, Slic3r, KISSlicer, MakerWare, etc.). The G code obtained at the previous stage is sent to a 3D printer via flash memory and USB cable. In the course of preparing and setting the additive machine, calibration is done, working organs are pre-heated, the model material and the task of equipment working modes’ parameters depending on it are chosen. This stage can be combined with slicing process procedures with the devices of the professional level. As soon as all preparation operations are done, the printing process starts, i.e. layer-by-layer fusing of materials. Its duration depends on the technology type and the chosen parameters of accuracy and quality of the part being manufactured.
- 3D technology file format list.
- FDM (ABS, PLA plactics, FLEX, HIPS, etc..): .STL .OBJ
- SLS (polyamide): .STL .OBJ
- SLA, DLP (photopolymer): .STL .OBJ
- SLM (metal): .STL+STP(STEP) .OBJ+STP(STEP)
- Multicolored plaster: .OBJ + texture breakdown.WRL + texture breakdown
- Polygonal net.
- The polygonal net should be uniform and closed. A model consisting of a few polygonal nets is not allowed! The crossing of polygonal nets is not allowed! Holes in the net are not allowed!
- A few models in one file are not allowed. Every object should be saved as an individual file.
- The polygon should not exceed 500 000.
- Wall thickness is at least 0,9 mm.
- Inverted normals are not allowed! The external normal should look outwards. This problem arises particularly often when mirroring a model in some three-dimensional modeling software.
- The model sizes should correspond to the sizes of the real object.
In 95% of cases, file errors are not critical and can be easily fixed with specialized software, which can be easily found on the Internet. Even if you’re sure the model is right, it would do no harm to check it for correctness once again.
- NETFABB – as a solution to the majority of file errors.
- MESHMIXER – мощная и удобная альтернатива.
The software shows the external part of the polygon with green color; and its internal normal with red color. Ideally, the whole model should be green. If you see red spots, these polygons are inside-out. If the entire model is highlighted in red, it means the whole polygonal net is inside-out.
Even if the model is green but your file has errors, the software will show a big exclamation mark in the bottom right corner, and couldn’t measure the volume of your model.
To repair the part, you need to click on the red cross on the tool bar in the top part of the screen. The software will bring you to the repair mode, and point at the polygonal net’s gaps with yellow color, if any.
This software features the function of deleting or adding polygons, changing sizes or proportions. (Let you study these functions on your own). I recommend studying the whole tool bar to understand how, where and what polygons we can highlight and what we can change.
To invert normals, you need to select polygons, which look the wrong way and click on the inverting normals button. Then click on Apply Repair.
If your part were initially green or inverting normals didn’t remove the exclamation mark and the volume is not estimated yet, you need to apply the automatic repair. To this end, go to the repair mode clicking on the red plus. Choose Automatic repair, then choose Default Repair and then Exstrude.
So, the software did its best to repair the part automatically. Click on Apply Repair.
As a rule, these actions should repair your part. If after these operations, you see the exclamation mark and there’s no volume estimate, you fell in 5% when the model has mistakes of a critical nature, which were made at the modeling stage.
Autodesk MeshMixer is a free software for working with 3D mesh models. You can download the program here. The program does not have tools for creating 3D models but has a wide range of tools for modifying them and preparing them for 3D printing. The main difference between this software and NETFABB is that MESHMIXER officially supports the latest versions of macOS. For me, this is a decisive factor because I always carry a MacBook with me and a Windows computer is only in the office. In turn, NetFabb has stopped supporting software for macOS.
As with Netfabb, you need to drop the STL model into the MeshMixer window.
At first glance, the model looks good but let’s try to test it for 3D printability (to meet the polygonal mesh requirements). To do this you need to analyze the model for errors. To do this go to the “Analisis” section, then click on the “Inspector” button.
On the screen we see how the program highlighted areas on the model with bright colors that do not meet the requirements, and therefore have errors.
In order to fix (cure) these errors, you must click on the “Auto Repair All” button. The program will try to remove errors in automatic mode. Checking before 3D printing is mandatory. Even if the model looks good to you, it is still worth checking. In the picture below you can see the errors that are inside the polygonal mesh, although outwardly everything is fine with the model.
However, this treatment does not always help. For example, if the model has a huge number of errors that the program is not able to remove automatically, then you will have to correct the model yourself in the program where the model was originally created. In case of a large number of errors, the program will indicate their presence even after you have tried to do automatic treatment. The picture below is an example of a very large number of shortcomings and errors that the program is not able to remove itself.
This happens, as a rule, when the model was prepared for rendering, not 3D printing. That is there are a huge number of surfaces but they are not connected into a single mesh.
A very important point! Treatment in automatic mode is based on the principle of adding or removing polygons. Therefore, after the automatic treatment, completely check the model for the correct shape. What if the program deleted something or added something extra.
At the end of the work, it is imperative to analyze the thickness. All programs described in this article support this feature.
May the video card help you in studying the 3D modeling software. =)