Updated: Apr 9
Utilizing 3D printed tooling can be a quick and inexpensive method to produce prototype or low volume runs (when compared to aluminum or steel tooling costs and lead times) of plastic parts. With this step-by-step guide we aim to highlight the critical areas of the process to help you have more success with your 3D printed tooling (molds) and MicroMolder.
Design your tool using your favorite CAD program. In our example we designed a tool that will produce two small measuring spoons. The tool design consists of a core side and a cavity side.
This design and other example tool design CAD files can be found for download here.
Core side of the tool
Cavity side of the tool
Helpful Hint #1:
When designing your 3D printed tool it is important to use a generous amount of draft angle. 3D printed tools typically come off the printer with a coarse surface finish similar to a light matte bead blasted finish. This texture can cause the finished plastic part to bite into the 3D printed tool. The light mechanical adhesion of the plastic part to the 3D printed tool can make it difficult to extract the finished part if the draft is too little. Draft angles of 3 degrees or greater will make it much easier to extract the finished part from the tool.
We recommend at least 3 degrees of positive on shallow areas and 5+ draft at minimum on deeper features.
Helpful Hint #2:
Due to the brittle nature of most 3D printed resins it is important to add radius on all corner features of the tool core and cavity. Doing so will help improve part ejection from the mold and and help to extend the life of the printed tool. Sharp corners and thin rib or boss sections of a tool tend to fail first during molding.
We recommend a minimum of .020" or greater on all corners.
Use a stereolithography based 3D printer to produce your tool. FDM printers and thermoplastic type filaments can not be used for 3D printed tooling. A tool produced with thermoplastic filaments will bond to the thermoplastic being injected into the cavity. The end result of this combo will prevent the part from being removed from the mold.
For the print highlighted in the image we used our Form2 SLA printer from Formlabs. For the resin we used Formlabs High Temp resin. We also recommend the Formlabs Ridged 10X. Other printer resins can be used but we have found that the high temperature resilient resins generally last longer and can produce more parts before needing to be replaced.
With the printed tool still in the "green" stage (before post curing) we remove all build support nibs from the tool halves as well as sand the bottom of each tool on a sanding board to create a flat mating surface for the tool to M.U.D. box (multi use die box). If the tool is not flat to the M.U.D. box there will be a high probability that the printed tool will fail/crack during high compression in the injection molding machine.
Using a sheet of 100 grit sand paper that is glued to a flat board we lap sand the bottom of the printed tool.
The finished result should yield and even flat surface with no high or low spots.
During post curing stage of the 3D printed tool we go one step further to create a flat and parallel interface by curing each tool half inside its respective M.U.D. box half. Because the printed part is still in it's green state it will have some forgiveness when applying pressure and can yield slightly without cracking. By fastening the print to the M.U.D. box with light pressure we are able to insure a flat and parallel interface once the print is fully cured.
Tools fully cured and bolted to their respective M.U.D box frame
Step 5: (optional)
Applying a release agent such as Stoner or other silicone based release agents will help improve the mold life and aid in easy removal of finished parts. Apply a few heavy coats before the first shot of plastic and rub it in with a cloth or rag. We re-apply a thin coat every third or fourth injection shot.
Once you have completed these steps your ready to mold some parts on your machine.
Helpful Hint #3
We highly recommend starting with a non-hygroscopic plastic such as polyethylene or polypropylene. These plastics are very forgiving, have good flow characteristics, lower melting temperatures and produce lower levels of fumes when processing at melt temperatures.
Install your tools into the machine.
Run the injection cycle and make adjustments to the barrel temps, injection time, clamp pressure and cooling time as needed. If your using MicroMolder these settings can be stored on the machine for future use.
Completed injection cycle with parts ready for removal.
From left to right: We made adjustments to injection time, clamp pressure and barrel temperature settings to dial in the right configuration needed to produce the part with this tool.
Helpful Hint #4
When working with 3D printed tooling it is very important to keep the mold closed together in the machine after the injection of plastic for a longer duration than that of a similar design in aluminum or steel tooling. Because 3D printed resins (especially high temperature rated resins) act as a thermal insulator it can take 1 - 3 minutes for the injected plastic to fully solidify enough for ejection of the part from the tool. Every plastic is different and will require experimentation to find the correct cooling time.
Remove the finished parts from the tool.
Flashing at the parting line can be hard to eliminate on 3D printed tooling due to the uneven surfaces or less than perfectly flat mold mating surface of the printed tool halves.
Trim the parts from the gates and remove any unwanted flashing.
Finished prototype parts produced in Polypropylene
An important note regarding parts produced using 3D printed tooling:
3D printed tooling is a great option for prototype and non-cosmetic parts. However, due to the layer line print structure of 3D printed molds any part produced with these molds will exhibit the same surface finish as the mold. These visible layer lines might be less than ideal for high end cosmetic parts.
Hand sanding and/or polishing can help to reduce the layer lines from the tool and can also aid in part ejection from the tool but we recommend performing these post processing steps only after you have determined the mold design to be functional. It would be a shame to polish a tool to perfection only to have the tool fail to perform due to improper core/cavity design geometry, too little draft or incorrect gate size and vent location.
In the example we used for this guide it has been determined that the tool design performs correctly and fills both cavities. It would now be safe to perform post processing steps such as sanding and polishing to produce a more cosmetic part.
Visible layer lines in the injection molded part.
For questions regarding our process or anything else related to MicroMolder don't hesitate to contact us at email@example.com
For more tooling examples and inspiration checkout the Made With MicroMolder page on the site.