Additive tooling is the process of using a 3D printed part for tooling purposes. For this project, the 3D printed part will be used to manufacture injection molded parts. While additive tooling has many restrictions in comparison to the conventional way of tooling, it allows a manufacturer to build prototypes much faster, design with more complexity, and allows products to be more cost effective. Personal designs can be done quicker and at a lower cost for varied output volumes. Figure 1 shows a 3D printed polymer insert that took much less time to design and manufacture than if it were made out of metal. This insert has the advantage to be replaceable easily than machining and entire steel mold and cavity.
Figure 1. 3D printed polymer insert fixed inside a metal mold
Brief explanation of project
Our project will focus on the creation of a 3D-printed polymer injection mold insert and the experimental analysis of the polymer mold cavity compared to a typical stainless steel cavity. The analysis will include measuring the shrinkage, warpage and cooling cycle of a molded part using our polymer resin cavity and comparing it to the part created with conventional metal cavities. Moreover, we will analyze different polymer resins and select which one would be the best fit for injection molding applications. The experimental process will be done using a BOY XS injection molding machine.
Preliminary designs and manufacturing considerations
The design, pictured in figure 2, has been selected in order to evaluate the polymer cavity performance. Actual preliminary models of the cavity will be done through Solidworks and the initial simulations of the injection molding process will be done through Moldex3D. Our 3D printed insert will be fixed in an aluminum plate. This aluminum plate will be secured in front of the existing stainless steel mold in the injection molding machine and will not have cooling channels drilled in it. Therefore, the cooling channels from the stainless steel mold will be in charge of cooling the parts injected.
Fig 2. Tensile Stress Specimen created from injection molding machine
Proposed first print trial or experiments
One initial idea is to use a high temperature resistant thermoplastic or thermoset as the material for the cavity since this will be exposed to temperatures of 200 °C and we would not want any deformation or melting of the insert. Two trials will be done in our quest to find the optimal material for the insert. First, the insert will be printed using FFF technique with a graphite filled thermoplastic polymer. Then, SLA will be used to print a thermoset insert. An important aspect to take into consideration when using FFF is the part smoothness. Depending on the thermoplastic used, acetone might be used to make the part as smooth as possible and reduce the possibility of having poor quality finish in the injected parts.
Other considerations for the printing of the part include the following:
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- Dimensions of the cavity and runners. The runners are going to be 3d printed in the polymer insert. It is critical that they align with the existing runner system in the other half mold. Hence tolerances are important in designing the insert.
- If the insert is 3D printed using FFF, what type and what amount of infill will be used for the cavity? (Orientation of the layers: square, triangles, hexagonal). Cooling will be our biggest challenge since polymers have bad thermal conductivity.
- How much would the finished part be affected, considering different infill percentage? (shrinkage, warpage)
After the above considerations have been addressed we can model the mold using the material properties of the selected material and geometry of the selected infil. To save on cost and time of manufacturing, preliminary simulations will be done using Moldex3D.
Sources:
[1] http://blog.stratasys.com/2016/06/29/berker-3d-printed-injection-molds/
[2] https://www.3dhubs.com/knowledge-base/3d-printing-low-run-injection-molds
[3] https://www.3dhubs.com/knowledge-base/3d-printed-injection-molds-materials-compared
Team members:
Camila Montoya, Fred Montero, Taylor Valdez, Hector Perez, Jamelah Travis