Our CEO, Roger Hargens on expert micro molder’s stringent Micro Molder Requirements:
Even seemingly minuscule aspects of manufacturing micro plastic parts and precision components can have a disproportionate effect on the ultimate accuracy of not only the part but the project. Because tolerances for most projects are measured in microns, there are particular micro molder requirements and best practices to mitigate the risks associated with each step of the design-to-manufacturing cycle.
Micro molded parts are typically less than a gram in weight and can be as light as less than 0.001 grams with tolerances as low as two microns. For manufacturers unfamiliar with such levels of accuracy, and more attuned to the injection molding process on a macro scale, the thought of mass manufacturing parts with such dimensions and tolerances may seem all but impossible, but micro molders do this daily, and often require zero failure rates for parts and components used in safety-critical applications.
It takes a coordinated team of masters in mold design, materials, tooling, molding, validation, and assembly to successfully manufacture customer parts at volume—their attention to detail and attention to process is everything. Especially when you consider the high cost of one error on the entire product development process.
The key is to ensure that areas, where most accuracy variation can occur, are managed with absolute focus. This is why micro molder requirements include an obsessive focus on tooling. Tooling in both design and fabrication is central to success.
Micro Molder Requirements
A great micro tool will produce millions of end-use parts or components repeatably and with the micron features required. One of the biggest contributors to poor tolerance execution is a poorly fabricated micro tool. A bad tool easily eats up all your budget slack and time in one hit.
Tooling and fabrication
As you may suspect, elite micro molders utilize various cutting edge technologies and machines to enhance tool build accuracy, like EDM and other accuracy-focused milling machines, but precision doesn’t start with the machine. Optimizing the tool begins before fabrication, and success is achieved when project leaders ensure tool design, DfMM (Design for Micro Molding) and fabrication engineers work together to ensure successful outcomes.
Experience is the driving force behind success in micro tooling and achieving tight tolerances, the best product development process resides fully in house. This means in-house tool design, molding, metrology, and assembly all reside together. Vertical integration and ultimate control of the micro molding process is of paramount importance.
Once in possession of an accurate and durable micro tool, the focus moves towards the actual molding process. Great micro molders have already considered the best material for the specific application because resins and mold materials behave outside specifications in micro sizes. Even with the right materials and right mold however, an inexperienced molder can become stuck.
If molding on the macro-level is a science, molding on the micro-level is an art and a science. Success can only be achieved when a micro molder has the experience and aptitude to think unconventionally and be creative in any given micro molding scenario. Standard practice in micro molding is anything but standard.
Even with a completed mold, the injection micro molding process isn’t completed by pressing a series of pre-programmed buttons. What a molder can do at a macro scale, doesn’t always translate to a micro-scale. When being constantly pushed to manufacture tinier and tinier parts with more and more exacting features, the “art” comes from tinkering, constantly pushing tech to go beyond its original purpose, and supplementing the process with custom in-house designed tech. All this is combined with a good process development strategies when it comes to anticipating the potential variables within exeprt micro molder requirements.
Variables include residence time, injection pressure, mold temperature, room conditions, and far more. Experienced micro molders dial in such variables for the specific material and geometric complexity of any given application, capping tolerance slippage.
Ultimately the end result is high-pressure, molten plastic injected into a tiny cavity, often containing extremely fragile core pins that can deflect or break. The tooling must be able to stand up to this at scale.
Micro molding metrology and validation
After completion of the molded part comes the “necessary evil” as many see it. Metrology has a key role to play in any micro molding product development process. In this step, it’s of the utmost importance to use measuring technologies that are able to validate end-use products with feature sizes that are always extremely tiny. Without this step, it’s impossible to show that a product conforms to design intent and know it will fulfill its purpose.
As with any measuring tool, there will always be an inherent variation in the measurement system used. Therefore, in a micro molding scenario, it’s essential to establish confidence in the accuracy and reliability of the chosen measurement system(s). While other sources of measurement variation exist, the two key sources are equipment variation (repeatability) and appraiser variation (reproducibility). Reducing repeatability and reproducibility (R&R) variation to the lowest amount possible gives us confidence in detecting variation in the product being manufactured.
Evaluation of the measurement system in terms of Gage R&R are an important element of any continuous improvement activity, especially with micro molding applications. Any variation in the repeatability and reproducibility of the measurement can crucially eat into the low margins for error in terms of tolerance attainment.
The evaluation builds trust in the instruments, operators, and processes. An understanding of measurement system variation helps provide a full understanding of the manufacturing process so that it is easier to predict its future performance and ultimately deliver a more consistent product to the customer.
The micro molder requirements outlined above demand control at every stage in product development. This article has focussed on the three key areas where tolerances need to be managed tightly, but it’s important to note there are numerous additional factors that require attention. Factors such as material variations that lead to differential results when molded, and environmental issues such as humidity and temperature alter the dimensional characteristics of end-use parts. All considerations, however, lead to the same conclusion. Success requires that a micro molder is vastly experienced and vertically integrated.
An earlier version of this article appeared in European Plastic Product Manufacturer Magazine on 5/6/2020.