I find that alot of my clients get confused when requesting CAD files for their various prototyping and NPD activities.  This is because they generally don’t know what they actually need, and they don’t know what the different file types actually are.  This article is meant to describe all of the ‘important’ CAD file types that are most relevant to new product development, prototyping, and manufacturing.

3D Solid Model Files

SolidWorks Part ( .sldprt, .sldasm)
At LTS, I do most of my CAD work in SolidWorks, which is one of the most versatile and capable CAD programs.  This .sldprt is the raw source file that SolidWorks creates.  It contains all of the feature history, and is fully editable in SolidWorks.  This is part of the work product that I send to the client on conclusion of a project.  It is generally NOT recommended to send the .sldprt file to a supplier, because it contains all of the important IP of the design.  A supplier generally does not need the source file to manufacture parts.  The .sldasm is a SolidWorks assembly file.

Parasolid ( .x_t)
In my opinion, the parasolid file is the best Solid Model file type to send to a supplier.  Think of it as the “TXT” of CAD files.  It is universally accepted by all CAD software.  It contains all of the geometric data, but is stripped of all feature history.  This means that you can’t open the file and ‘edit’ features, ie. change fillet radii, etc.  It is referred to as a ‘dumb’ solid.  You can however, further modify a parasolid.  For instance, you can take a base parasolid file, read it into your CAD software, and create new features, such as cuts or bosses that merge with the existing body.  If your supplier is going to machine a part with CAD/CAM software based on your CAD model, this is the file to send them.

Stereolithography ( .stl)
The STL file is most commonly used by Rapid Prototype (3D printing) suppliers.  It is technically a ‘faceted surface body’, which basically means this file is composed of a series of points in space that form triangular facets that generate the approximate outside surface of a part.  This is not the same as an actual surface body.  It is also the typical output file of a 3D laser scanner.  Realistically, an STL file is useless for everything except making a Rapid Prototype.  Most CAD software can open and ‘view’ a STL, but very little else can be done with it.  For instance, you can’t even select edges or points to take measurements!…(because there aren’t any edges and points, at least as they relate to 3D geometry).  SolidWorks does have some basic abilities to ‘mesh’ a STL into surface and solid bodies, that can be further manipulated…but this usually generates read errors for all but the simplest geometry.

eDrawings ( .eprt, .easm, .edrw)
eDrawings is a free CAD file viewing program offered by SolidWorks, which I highly recommend to my clients to download and install.  It can be found here.  The program will read many different kinds of CAD files including the eDrawings specific files.  Think of it as the ‘PDF’ of  CAD files.  They are generally smaller file size than the source file, non-editable, but contain all of the 3D geometry.  With the eDrawings viewer, you can rotate the model on your screen, as well as perform many other useful productivity tasks.  I like to send eDrawings files to my clients throughout a project so that they can review the design and provide critical feedback.

Others ( .IGES, .STEP, .dwg, .prt)
There are many other file types, used by various CAD software.  These tend not to be universally accessible by all CAD software, and for that reason I tend not to use them when working with clients and suppliers.  However, if there is a specific need, SolidWorks can create and work with all of the major CAD files, but in my experience this is often unnecessary.

2D Drawing Files

SolidWorks Drawing ( .slddrw)
When an engineering drawing is made in SolidWorks, the source file is a .slddrw, similar to the generated .sldprt/.sldasm.  For the same reasons, I only send these files to the client at the end of a project, and I never send them to a supplier.  The engineering drawing has many names, and is sometimes referred to as a ‘manufacturing drawing’, ‘schematic’, or ‘print’…or even ‘blue print’ (which is very much the wrong term to use these days).  Essentially, it is nothing more than a printable, revision controlled document that contains all of the critical information necessary to make a part, including material, heat treat, dimensions and tolerances, and other part specific technical information.

Adobe Acrobat ( .pdf)
If you own a computer, you probably know what a PDF file is.  At LTS, I convert all engineering drawings to PDF format when sending them to the client for review, or to suppliers.  Further, I insist on making combined ‘Print Packages’ that have all of the product prints in a single document, and the package itself is revision controlled.  This way, there is less confusion for the supplier as to what revision is most current for a given part…they can simply be referred to the current revision print package.

Drawing Interchange Format ( .dxf)
The DXF file was 1st introduced with AutoCAD as a 2D drawing file format.  It is my preferred format for sending 2D geometry data to suppliers that will use it to program certain CNC manufacturing processes, such as laser cutting, plasma cutting, water jet cutting, and stamping.

Drawing ( .dwg)
The DWG file is similar in use to the DXF file, but in my experience it has more compatibility issues with certain CAD software, so I prefer to not create DWG as output formats for sending to suppliers.  It is also quite common that receive DWG files produced by other programs (mainly AutoCAD) for the purpose of re-making the parts in SolidWorks.