Does anyone know of a good way to convert a 3D print file, like STL, to STEP - a useable file format for plastic injection molding companies?

I have tried to convert the files through a couple of programs without success. The most requested file is a STP or STEP file. If there’s no easy way to convert it, which I don’t think there is, does anyone know someone good at re-creating CAD files?


a good way to convert a 3D print file like STL to STEP a useable file format for plastic injection molding companies

I don't know much about plastic injection molding companies, but I do manipulate a lot STEP, STL files and I do know that it is possible to achieve "a good way to convert […] STL to STEP file format […]". For the record, the manufacturing process isn't recorded within these files format (at least not yet) so you don't have to specify the final use.

However, this is a delicate process which isn't easy for beginners in CAD engineering.

As said before, the STL files is a tessellation of a surface with triangles, while STEP defines precisely the surface with curves. It's basically the difference between raster graphics and vector graphics: most fully automatic reconversions programs (such as Inkscape in case of images), would create something quite approximate to the real shape. Manual programs would require time and knowledge of the needed tools (Inkscape can do it too, in case of images).

For the record, asking for a STEP file to be a STL file is as easy as transforming a vector graphic to a raster graphic, it's a one-click transformation. What you are asking, the reversed, is complicated.

What will be done if you import a STL file to a standard CAD program, it will consider each triangle as a defined unique surface, and in most cases, the standard CAD program will have a lot of difficulties to handle the STL. It could then export it to a STEP file, but this will make a huge, incredibly heavy file difficult to handle (I've seen STEP files over 300 MB while the STL was less than 10 MB).

The good way to do so, is to go through a reverse engineering program that handles better these troubles. I don't know any being free, and they all require extensive experience, expansive licenses and a bunch of time generally. For instance, I know that Catia, SpaceClaim or 3-Matic are programs that work very well for your issue, but they are both very far from affordable or easy to handle if you aren't a CAD designer.

Another bad way would be to pass through a 100% automatic reconstruction/conversion to STEP, but it would make something not exactly accurate to the original part, and may not be of any use depending of your application.

My best advice for this would be to find someone or some enterprise that can practice the good way from your STL to have the STEP file you want. You should also very much specify for what use your file is, because as a design engineer I wouldn't generate the same STEP file depending of the use of each surface.

I hope this answer isn't too much a disappointment for you, I know it won't solve your problem but it can help you understand why it is such a hard problem.

  • 3
    $\begingroup$ This should be the accepted answer! $\endgroup$ – 0scar Nov 29 '18 at 22:14

I've been able to manipulate an STL file using the hobbyist version (free) of Fusion 360. There's a series of steps involved that may require some research and experimentation, at least it did in my case.

One loads the STL file into Fusion 360 by using Insert, Mesh.

Once loaded, turn off history.

The next step is to convert the mesh file to BREP.

In that form, the surfaces can be edited and the model can be modified if necessary.

I have not exported to STEP, but have confirmed that Fusion 360 supports STEP as a valid export file format.

Both links provide additional information that may be of value to your project.

Consider also to double check your STL file to ensure it is manifold. Meshmixer is useful for such purposes. One model imported into Fusion 360 had entire faces removed due to a manifold error in the original model.


The fact you may be able to produce a STP file is no guarantee the company will be able to injection mold it.

You should ask the intended recipient of the file what are the actual requirements they need for making the injection mold.

STEP and STL are not two different ways to store the same information. They are two different standards with different goals. Both can describe the geometry of a solid shape, but STEP has plenty more of functionality designed to store information about the manufacturing process of the part.

For example, while most CAD software deals with the STEP substandard AP 203 "configuration controlled 3D design" it may be that the company you are trying to work with requires information about the injection molding process itself, that would probably be regulated by the AP 223 part of the standard ("exchange of design and manufacturing product information for cast parts").

If that is the case, I strongly doubt any CAD software will be able to automagically create that information out of thin air.

With an analogy: it is like you were dealing with a TXT file and the publishing company asked for a DOCX one. You may easily save the TXT as a DOCX, but what the publisher is really after is a document with a hierarchy of titles, font information, formatting, etc... and just saving the TXT as DOCX won't automatically generate those.


It depends very much on the molding company, and how much engineering service you can afford to buy from them.

Some will remodel your entire part anyway, to make it suitable for molding. Others will only accept specific formats and parts that are engineered 100 % ready to be molded.

So talk to them first, if they only use your file as a template, it won't matter what format it is in.

To answer the question:

I believe FreeCad can load STL, and export STP but, like Mac said, it may not be the result you need.

STL = Surface Tessellation Language. This stores the geometry as approximated by a mesh of triangles. It is incapable of perfect curves, so there is some information lost when the model was exported to STL.

STP or STEP can represent surfaces correctly, but only if that information is present in the model. Put in a tessellated model and it will still be tessellated.


I found a website, CadMesh, to convert the file for me. So far they are a free platform. I recommend to give it a shot.

Doing some research on internet I also found this good tutorial: Bantam Tools Blog - Convert STL to STEP

But the FreeCAD software seems to have some limitation on handling complex shapes. It may work for you.

Step 1: Download a Conversion Tool


Step 2: Import Your STL File

  • Open FreeCAD.
  • Create a new file (File menu > New).

FreeCAD1 mesh design

(Credit: OpenSCAD Chess by Tim Edwards)

Step 3: Repair the Mesh


FreeCAD2 analyze repair

Step 4: Convert Your Mesh to a Shape

  • From the toolbar dropdown menu, choose Part.
  • Select your mesh in the left pane.
  • Leave the Sewing Tolerance at 0.10 and click OK.


Step 5: Convert the Shape to a Solid


  • Select the newly created shape.

FreeCAD5 convert to solid

FreeCAD6 done

Step 6: Export Your Solid to a STEP File

  • Select your newly created solid file in the left pane.
  • From the File menu, choose Export.
  • Save your file.

FreeCAD7 export

You're done!

  • $\begingroup$ Welcome to the stack. $\endgroup$ – Davo Apr 12 '19 at 19:08
  • 2
    $\begingroup$ Please refrain from link-only answers, they might not work tomorrow or in the future due to link rot. explain what is in the links. $\endgroup$ – Trish Apr 13 '19 at 8:08
  • $\begingroup$ I have updated your answer for you, with the relevant info from the link. Next time please include the information yourself. As has been stated already, links tend to die and when they do, your answer would not be much use. Thanks. $\endgroup$ – Greenonline Apr 13 '19 at 14:17

Converting mesh files to solid formats is a complex task. While converting files from mesh to solid you should look for accuracy, number of patches, nurbs pattern, file size and many other variables that should be taken in consideration based on the use you will give for the solid file. I have compiled some thoughts as a starting point for your research. Make sure your STL/OBJ/PLY (mesh) file has a decent quality. You can use free software to validate your file such as Meshmixer and MeshLab. You will CONSIDERABLY increase your chances by having a watertight model. If the model does not have a closed mesh, you will most likely have a hard time/fail converting it.

There are 4 ways to do it:

1 – Using a free software This is a valid solution for a simple shape models. The best tutorials are posted here on GrabCAD. Here are some tutorials available on internet: https://grabcad.com/tutorials/how-do-i-convert-stl-graphics-to-a-solid-model Convert STL (or OBJ) Mesh to SOLIDWORKS Model (NURBS) How to convert STL to STEP using FreeCAD https://blog.bantamtools.com/convert-stl-to-step

2 - Professional software solution This is probably the best solution for companies with a high conversion volume on CAD/CAM demand. Some of these companies offer a free software version for students. The best solutions I have found: - 3D Systems Geomagic Wrap - Fusion 360 - Power Surfacing (SolidWorks plugin) - TransMagic

3 - Hiring a professional freelancer This is the best option for a one-time project, higher chance to get a decent converted file for an affordable price. Try to look for the feedback/customer review before hiring someone. I have seen professionals charging as cheap as US$25 per model/conversion. You can check on these options (there are many others): https://www.upwork.com https://www.fiverr.com https://www.freelancer.com

4 - Online conversion platform There are solutions with instant delivery/conversion, and others that take some hours to send you the file. I found solutions varying from free online conversion to pricy service. There are prices as low as US$1 per model/conversion. You may need to do some touch up on the files converted from automated platform before you send it to a CNC or other CAD/CAM machine. You can check on these platforms: http://cadmesh.com https://www.convertcadfiles.com/

Have in mind that, the higher is the model complexity (shape) the harder is to convert the model. If trying to convert a 3D scanned model, make sure to have a closed mesh and a high-density mesh definition.

During your Google research, you can also use the term “model surfacing”.

Good luck!


Your Answer

