As with machining, forging, casting, and stamping, 3D printing starts in the same place — design of the end part. Much like traditional manufacturing, additive manufacturing is reliant on computer aided design (CAD) models as the main component of production of the part.
Requirements of a CAD package
While most CAD packages will allow for the creation of models to be used in additive manufacturing, there are a few key features and functions that should be confirmed before moving forward with any particular one.
The first and most important aspect is the ability to generate 3D models. Some software is specifically designed for prints, drawings, or other 2D designs and lacks the ability to generate full models. An appropriate CAD package will allow you to either parametrically or directly model 3D surfaces, which will allow for easy export into the most common 3D printing file, the STL.
The ability to export native CAD designs into an STL file is required for nearly all 3D printers. STL (an abbreviation of “stereolithography”) files are translations/exports of CAD models into triangular surfaces and planes, which are commonly interpreted into G-code, the most widely adopted Computer Aided Manufacturing (CAM) language for automated machine tools. Generating an STL to match your design is vital to the success of a 3D print, which we’ll cover in more detail below.
Outside both requirements of 3D modeling and generation of an STL, there are numerous other “nice-to-haves” that are included in some CAD packages which make preparation for additive manufacturing easier and allow for additional value-add. Examples such as 3DXpert for SolidWorks, Netfabb for Fusion 360, or 3YOURMIND for Siemens NX are add-ons and plugins that remove some of the translation steps, or even allow for direct printing to the printers from the native applications itself.
What’s an STL file?
The STL (Stereolithography) file, sometimes referred to as “Standard Triangle Language” or “Standard Tessellation Language”, was created by 3D Systems in 1987 and has become widely adopted as the standard file for models for 3D printers industry-wide. These files are exports from native CAD files and describe “raw, unstructured triangulated surfaces by the unit normal and vertices (ordered by the right-hand rule) of the triangles using a three-dimensional Cartesian coordinate system” [Wikipedia, “STL (file format)”, 2019]. Briefly stated, STLs are an approximation of CAD models into a set of triangles, converting features such as splines, p-lines, arcs, extrusions, and sweeps, into triangular simples and composites.
Converting an STL
While each CAD software has different configuration options and features for exporting STLs, there are a few things that will be common to each solution and are important to pay attention to:
- Binary / ASCII - While there is a large difference between the encoding of both formats, fundamentally Binary and ASCII are functionally similar, with the caveat that Binary files tend to be far smaller and are handled with less processing power than most slicing software. Unless specifically required, Binary is typically preferred due to the smaller file size.
- Units - The definition of the STL file does not include measurement units. When exporting the model, pay attention to both the units of the native CAD as well as the expected units of the printer/slicing software. Most slicing softwares have a configuration for units, but most common deployments by default are expecting millimeters (mm).
- Resolution - This will be the most varied attribute between CAD packages, but in general the goal is to ensure that the minimum tolerances/deviations are smaller than the finest feature the 3D printer is capable of producing. For example, if the finest resolution the 3D printer can produce is 100 micron, then the STL should have tolerances within 100 micron for diameters, angles, tessellation sections, etc.
There will be other attributes (e.g. color can be included in STLs), but the above points are key to pay attention to in order to generate an STL that’s representative of native CAD.
Common Industry CAD Solutions
Within manufacturing, engineering, and design industries, there are numerous commonly used CAD packages; Some are specific to industry and use-case, but many are common between verticals and applications. Below are just a few of the many commonly used CAD applications typically used by enterprises and manufacturing operations:
SolidWorks, launched in 1995 and acquired by Dassault in 1997, is one of the most prevalent CAD packages across engineering, manufacturing, and design. Touted as one of the easiest to learn parametric CAD packages available, according to the publisher, “over two million engineers and designers at more than 165,000 companies were using SolidWorks as of 2013”. In addition to the core CAD package, SolidWorks offers numerous additional products and modules for simulation, specific industries, and rendering/graphic design.
Dassault Systèmes CATIA
CATIA, originally created in 1977 as Dassault Aviation’s own design platform for defense/aerospace applications, is an enterprise-scale software that is heavily used within aerospace, automotive, and industrial equipment design. With over 40 years of heritage, CATIA is a mature and feature-heavy PLM solution, with integrated support from CAD through CAM.
Autodesk Fusion 360
Fusion 360, initially released in 2013 and published by Autodesk, is a 3D-centric CAD release (in contrast to Autodesk’s classic AutoCAD) which differentiates itself with both a native version for Mac OSX and Windows 7/8/10 as well as free versions available for hobbyists, students, and instructors. Much like Dassault’s offering, Fusion 360 benefits from access to the rest of Autodesk’s plethora of solutions and add-ons.
Creo, formerly known as Wildfire and Pro/E, is one of the first 3D CAD solutions to become available, launched in 1987. Published by PTC, Creo is built on the first rule-based constraint (parametric) 3D modeling system. Today, Creo is part of a suite of 10 applications from PTC which provide assembly modelling, FEA, direct/surface modeling, and tooling design functionality.
Siemens NX, originally Unigraphics NX and acquired by Siemens in 2007, is an enterprise-scale solution that not only allows for both direct and parametric modelling, but also engineering analysis and CAM functionality directly within one solution. In addition to CAD/CAE/CAM/Simulation functionality, NX has numerous industry- and material-specific packages to enable an extended feature-set specific to certain applications.
Onshape, released in 2015, is one of the few CAD offerings that is entirely SaaS (Software-as-a-Service) based, which is a key differentiator in a landscape of primarily on premise and hardware-intensive solutions. Onshape allows for access via browser and Android/iOS, and with real-time collaboration by multiple users on a single design across any supported platform.
In closing, there are a lot of choices for CAD software in the market depending on industry, company size, and required features — but nearly all of them enable the ability to take models and bring them to life via additive manufacturing and 3D printing. From hobbyists and students to enterprise-level mechanical and design engineers, the benefits of additive manufacturing can be had by all to produce real-life parts and assemblies quicker and easier than ever before.