3D-Printed Prototype Molds Versus Aluminum Tooling

Aluminum prototype mold	3D-printed cavity set
1. Design the mold	1. Design the mold
2. Program and cut in CNC machine	2. Upload design to printer
3. Create the mold components	3. Create the mold components
4. Build the frame	4. (Not necessary)
5. Final fitting	5. Final fitting
6. Polish	6. (Not necessary)

Of course, these steps have been simplified for explanatory purposes. They also make a few assumptions that should be noted. In particular, step four for the 3D-printed cavity set assumes that an initial investment has been made to build a universal frame to support 3D printed cavities in the injection molding machine. Once that is complete, Lammon notes, all future 3D-printed cavities could be designed to fit the existing frame.

Setting those caveats aside, steps two, four and six represent considerable time savings via the additive process. Notably, step two represents a significant reduction in the amount of processing time and manpower necessary to create the part. Programming cutter paths and CNC machining the aluminum block can take several hours, while uploading a CAD file to the 3D printer is nearly instantaneous. The printing cycle certainly takes time, but the need for skilled operator attention is practically nil.

Overall lead time for this final product created with a conventional aluminum prototype mold is typically one week, Lammon says, whereas production of a set of 3D-printed cavities was only two days. However, Lammon notes that while there was a significant amount of time saved during the tooling process, the opposite can be said during the molding process.

The overall cycle time in PPT’s case study was 175 seconds when using the 3D-printed cavities. With the aluminum mold, that time was only 44 seconds. This can be explained largely through the discrepancies between allowable heat and pressure. While the mold temperature was 70 degrees in the 3D-printed cavities, it was 125 degrees for the aluminum mold. The barrel temperatures reached 450 degrees with the 3D printed cavities, versus 520 degrees for the aluminum mold. And finally, the 3D-printed cavities required a 60-psi decrease on injection pressure, which represents a 10 percent reduction on velocity and a 50 percent increase of fill time to that of the aluminum mold.

While PPT’s case study found overall savings in both cost (25 percent) and turnaround time (50 percent) when using the 3D-printed cavities, there are still limitations that need to be overcome. The plastic cavities used in PPT’s study were printed with a proprietary digital ABS material from Stratasys, and finding the right mixture of materials that will increase the life of a 3D-printed mold will take time. Depending on the chosen resin, today each cavity set can produce between 50 and a few hundred shots—a small fraction of what’s achievable with aluminum (not to mention steel). Success rates can be increased by experimenting with gate location and size, but Lammon notes that design details nearest the gate will be more susceptible to wear and/or damage. PPT is experimenting with other steps that can be taken to extend the life of the 3D-printed cavities, such as increasing gate and runner sizes well over what would be necessary in an aluminum mold.