December 2014 Design Tip

3D CAD Programs: Functionality and File Formats for Moulding Design

Look around. Nearly everything that you interact with was likely a creation of three-dimensional computer-aided design (3D CAD) - homes, furniture, automobiles, lighting, smartphones, computers. At its most basic level, a 3D CAD program allows engineers to render their design in a three-dimensional model. Depending on the industrial focus of the CAD program and the modular extensions used to support and enhance its software, product developers and engineers are able to design extremely intricate products that can be built or manufactured. At Proto Labs, every single part submitted for manufacturing arrives as a 3D CAD model in one of several different file formats derived from different CAD programs.


There are a few major design programs that are frequently used in 3D CAD model development for prototype and production parts, and to an extent, most play well with one another when files are exchanged between platforms.

Commonly used programs include:

  • SolidWorks (.sldprt)
  • Autodesk Inventor (.ipt)
  • AutoCAD (3D .dwg)
  • PTC ProE/Creo (.prt)
  • CATIA (.catpart)
  • SpaceClaim (.scdoc)
  • SketchUp (.skp)

Additional neutral file formats that can be imported into and exported from most programs:

  • IGES (.igs)
  • STEP (.stp)
  • ASIS (.sat)
  • Stereolithography (.stl) - Proto Labs accepts STL files for its additive and machining services only, but not injection moulding.

The capabilities of each professional design program vary slightly from one to the next, but most contain versions of basic solid modelling; plastic and mould design; weldments, sheet metal, piping and tubing design; and large assembly design.

Data management with revision controls - which is standard in some programs and an extension in others - helps CAD programs efficiently track model changes throughout the design process (including naming conventions) and monitor the historical and present activity with each design. If an engineer is working on a model, other engineers are prevented from unknowingly accessing the design and potentially overriding the work of the initial engineer. Furthermore, if modifications are made to a complicated assembly that contains additional subassemblies, everything above it in its design tree is affected. The intelligence of the data management system allows it to automatically update any other pertinent areas in the assembly that the change in geometry affects.

The 3D model shows Proto Labs' three-part Torus assembly in SolidWorks.

The 3D model shows Proto Labs' three-part Torus assembly in SolidWorks.

There are also productivity tools within many programs that allow for things like geometric and feature comparisons between versions; analysis of thickness, draft, symmetry and other design validations; and Bill of Materials (BOM) generation, among many other functions.

Neutral File Formats

When transferring a 3D model from its native CAD program to an alternative program, the solid model information may remain intact; however, depending on the format, some of the design elements may be lost in translation. That is why when designers are sharing part files between multiple systems, they'll often export their models in a neutral file format that is not bound to a particular vendor, but rather controlled industry groups. The primary file formats with vendor-neutral data are STEP (Standard for the Exchange of Product model data) and IGES (Initial Graphics Exchange Specification), and, to a greater extent with additive manufacturing, STL (Stereolithography).

If you're submitting a neutral file to be manufactured at Proto Labs, we accept both STEP and IGES files for injection-moulded parts. With that said, Proto Labs accepts nearly all file formats. (Note that STL files are limited to our additive and machining services.)

Smart vs. Dumb Models

When you're moving between two programs - regardless of whether it's uploaded into Proto Labs' system or imported into your own - the loss of design intelligence can create what is called a dumb solid (see Figures 1 and 2). When in this state, the model no longer contains its parametric attributes. If the face on one side of a part is moved, it no longer automatically moves any of the other features that are affected. You may be able to recalculate dimensions to create the change, but dragging a face to a new dimension will not propagate to the other design features it affects, so you're limited in that regard. CAD files that work within the same program typically retain that parametric knowledge.

Figure 1: Smart model

Figure 1: Smart model

Figure 2: Dumb model

Figure 2: Dumb model

Proposed Revisions

No matter what file format is uploaded at Proto Labs, we provide automated design analysis on that model within 24 hours. Recently, we've added a new feature to that analysis that not only pinpoints potential mouldability issues, but when a model requires only minor changes - e.g., draft on thin/thick sections – we'll provide proposed revisions on a second model. Our quoting software will document and illustrate exactly what the new model changes are, and you can either accept it or upload a new model. If a SolidWorks part file was submitted, we'll retain and make changes directly within the smart model before sending it back to you. If any other CAD program was used, you'll have the option to download either a STEP or IGES file.

Proto Labs-accepted 3D CAD file formats are listed online at, and if you have a question about a particular program or format, please contact a Customer Service Engineer at +44 (0) 1952 683047 or

Editor's Note: Starting in January 2015, Protomold Design Tips will become Proto Labs Design Tips. The new format will not only include regular injection moulding tips throughout the year, but will expand to include machining and additive manufacturing advice as well. Tips may focus on one service or how all three can work together from prototype to production.