Micro molding is part science and part art form. True micro molding DFM engineers are constantly navigating the complicated labyrinth that connects OEM demands, with available micro molding resins to accomplish the goals of the project.
Choosing the correct micro molding resins or plastics seems simple at the project start. Project leaders simply pick the desired material that fits their project goals and inject liquid plastic into a mold. The assumption a process for larger molds applies to micro molding however doesn’t play out in real life scenarios. Thermoplastics and resins behave in unusual ways when micron or half-micron tolerances are required.
While some projects require micro molding resins that are rigid and strong, others require micro molding resins that can maintain an ultra-thin profile. Some projects require micro molding resins that can withstand heat, while others must follow strict guidelines due to extended contact with the human body. Obviously, there are many cases where the desired material simply can’t be used due to some other design restriction.
PEEK for example, a popular choice in medical micro molding, is 30% glass fiber reinforced and pelletized for injection molding, yet it cannot fill ultra-thin areas. Ultem, also an extremely popular option for micro-optics applications, also can’t fill ultra-thin micro molding projects. Consequently, to achieve OEM’s demanding project goals, balanced with various material limitations at micron sizes, our DFM engineers face a Rubix cube of micro mold materials selection.
Complications With Micro Molding Resins
It’s of vital importance to understand the full set of variables that can affect the performance of a molded part. Most available thermoplastics have various grades or versions produced to achieve unique results. Additives that include, but are not limited to glass, carbon, tungsten and other fibers are routinely added to resins. These additives dynamically change how micro molding resins melt, flow and fill in part geometry.
Micro Molding Resins Study
Because Accumold’s DFM engineers are relentlessly studying how various resins and thermoplastics behave at micro sizes, they are also continually educating our customers to help them be more efficient in their future designs. We compared 11 frequently used materials in a thin-wall study and compiled our data in a white paper available for download below. Here is a quick overview of the 11 micro molding resins we used.
Our engineers compared common resins and monitored performance for thin-wall applications. The goal was to see how far various resins could be pushed and record the comparison data for practical real-world use. Normally, the mold would be altered for each resin, but for our study, the mold was not modified for each resin, including the gate or runner system. This was on purpose to give us the purest data possible.
We used the standard processing windows manufacturers specified for each resin as the only variable. In this way, we gave each resin candidate the very best opportunity to fill the part on its own. The critical dimension observed was to maintain a 0.003” thickness in the part of our own design. Because earlier results showed how resin selection affects the desired output when designing a part, the mold was built with a thick to thin transition to create an optimal opportunity for the parts to fill. Obviously, this is an isolated scenario done for testing purposes only. It’s not always possible when designing OEM parts but was done strictly for testing purposes. These tests are helpful in knowing what resins may give the best possible chance for success. The data is useful when matching the properties and features to an OEM project.
Top Eleven Resins / Thermoplastics
Polysulfone PSU UDEL
Polypropylene PP
Polyethylene HDPE
Polycarbonate PC Lexan
Polybutylene terephthalate PBT
PEEK Polyether ether ketone
Nylon Polyamide PPA
LCP Liquid Crystal Polymer
Delrin Acetal Polyoxymethylene POM
Acrylic Polymethyl methacrylate PMMA
Ultem Polyetherimide PEI
Interesting Notes
As our engineers prepared this study on micro molding resins, we assessed a tool used to qualify cavity resin fill called Moldflow. Moldflow analyzes resin property data from resin manufacturers and simulates the resin flow through your design. It can be helpful to better understand where knit lines or end-of-fill might be or determine if your selected micro molding resins will have the desired outcome.
The provided analysis would either fail to estimate correctly or inform our engineers our part was simply not moldable. Our own anecdotal experience confirmed this but we were hopeful to at least show some data. From previous experience, many of the parts we’ve made for decades are considered impossible to mold according to the common flow analysis.
In addition, we asked our suppliers for their verdict on the moldability of our part, requesting their advice on what material would give our mold the best chance to fill. In all cases, they communicated uncertainty our part was moldable — the majority suggested we make the thin-wall section thicker. It’s essential to acknowledge in the niche field of micro molding, the resin data sheets can lead to inconclusive expectations. This is because the data is often determined using larger sample bars. Shocking to non-micro mold engineers is the fact most recommended gate sizes are greater than many of the micro molded parts we produce in our facility. Some data sheets refer to “easy flow” or “high flow” grades likely not referring to a 0.003” thin section with this description.
These uncertainties and lack of data on micro molding resins is the reason we did the study. Please download the full study for free.
Thin-Wall Micro Molding White Paper
The full thin-wall micro molding white paper is available for download for free:
Download The Whitepaper: Material Selection / Thin-Wall Study
