Using additive manufacturing to fabricate tooling for PDMS molding can offer cost and lead times that are a fraction of traditional methods. PDMS molding is well known for its ability to hold tight tolerances, though accuracy and repeatability of micro sized features may still be a challenge. By using BMF PµSL technology, PDMS molds for parts that demand such small features are now more achievable than ever. From printing process to materials offered, the microArch system is a solution that is very compatible for PDMS mold fabrication.
File Preparation
When the CAD design work is complete, save the model as an STL file. Be sure to adjust the resolution to a high/ fine setting. This will generate a .stl with smaller facets, which will improve surface smoothness and could therefore save time during post processing.
When orienting the pattern, consider surface quality, feature detail, build time, and post-processing. For master patterns made via additive manufacturing, surface finish is typically prioritized. Using BMF systems, top facing surfaces will have best surface quality. Not all bottom facing surfaces will require support structures and is geometry dependent. Parts with higher total built height will take longer to build. Be sure to also orient the part so that important features are not compromised from post processing such as sanding and bonding.
Materials
Either addition or condensation cured silicones may be used. However, condensation cured silicones (tin catalyzed) silicones are more compatible with BMF materials.
For master pattern material, BMF HTL resin is preferred due to having the best balance of mechanical and thermal properties that make it a good fit for silicone molding. This material also facilitates the de-molding process well.
Printed Pattern Preparation with PDMS Molds Created on microArch
Remove Supports
Refer to our Post Processing Guide for typical procedures on how to wash and post cure parts from the microArch system.
Bond Sections (if necessary)
To bond a pattern that was made in sections, an off the shelf cyanoacrylate glue will work well. A low viscosity formulation is best for assembling the acrylate based resins typically used in BMF systems. Low bloom formulations are recommended.
Smooth Surfaces
The silicone rubber mold will transfer the finish of the pattern to the molded parts, which is overall very smooth when printing at 10-20 um layer thickness which is ideal for capturing detail and de-molding capabilities. At such small layer thicknesses, silicone tends to not “grip” onto layers lines, which is a common occurrence with standard additive processes that use thicker layers.
Clean Pattern
Remove dust and debris from the pattern before proceeding to make the mold, especially if sanding on any pattern surface was done. A recommended technique to remove the material particles off surfaces after sanding is to use an acid brush soaked in isopropyl alcohol.
