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Thinking small: Accumold discusses risk mitigation in micro molding

2020-05-18

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Can you explain how important vertical integration is when looking at risk mitigation in micro molding?

There are many phases in a product development process for micro plastic parts and components, and it takes a coordinated team of experts in design, materials, tooling, molding, validation, and assembly to successfully manufacture customer parts at volume. When working in a micro manufacturing environment when tolerances are measured in microns, it is critical that all involved in the product development process maintain an obsessive focus on mitigating the risk of non-adherence to these tight tolerances, and it is hugely advantageous that all team members are under one roof.

Having each “department” in one place eliminates issues associated with outsourcing any part of the product development process, as achieving micron tolerances requires control, and you can only really control what you undertake yourself. In addition, it allows, for example, the tooling manager or production manager to be engaged early in the product development cycle, helping to avoid having to go back to the drawing board with designs, having to review and change manufacturing processes, and having to recut already extremely expensive and time-consuming to make micro tools.

 

Is it true to say that of all the elements of the product development process, micro tool fabrication is perhaps the most critical for micro molding?

The simple answer here is yes, and yes again! Without a good micro tool, you will not be able to make millions of end-use products repeatably and with the micron features required. Also, a poorly fabricated micro tool could eat up all your tolerance slack for the design to manufacture process in one hit. So, it is important that at the tooling end, the technology for fabrication is used that means you are well within the overall tolerance levels, so that there is some margin as the product development process progresses.

Micro molders need to have at their fingertips an array of technologies that enhance the accuracy of a micro tool, often needing to employ wire EDM and extremely accurate milling machines. But optimizing the tool begins before fabrication, and success is achieved by an experienced micro molder ensuring that tool design and fabrication engineers work together to ensure successful outcomes where the watch words are “ultra-precision” and “right first time.”

 

After tooling there obviously comes the micro molding process. I suppose it is fair to say that this is not just normal molding but smaller?

Yes, you could say that. Many people say that molding on the macro level is a science, and molding on the micro level is an “art” and a science. This is absolutely true, and again plays to the fact that success can only be achieved when a micro molder has the experience and aptitude to think out of the box and be creative in any given micro molding scenario. When micro molding, and when being constantly pushed to manufacture tinier and tinier parts with more and more exacting features, the “art” comes from knowing where and when you can push the limits of micro molding. This is where years of experience is critical, rather than just relying on numbers on a data sheet or flow analysis.

These variables are numerous, but include such things as residence time, injection pressure, mold temperature, etc. An experienced micro molder will manually dial in such variables to optimize the molding process for the specific material and geometric complexity of any given application, and by so doing will be able to keep a lid on tolerance slippage.

Quite obviously, once again, this part of the process also exemplifies the key role of micro tooling in the tolerance attainment equation. Whatever adjustments and fine tuning a micro molder will make to optimize outcomes from the micro molding process per se, ultimately the end result is that high pressure molten plastic will be injected into a tiny cavity, often containing extremely fragile core pins that can obviously deflect or break. The tooling must be able to stand up to this, or all the expertise from the micro molder will be lost.

 

We are used to the phrase, ‘if you cannot measure it you cannot make it’. How important is validation and metrology in risk mitigation?

Metrology has a key role to play in any micro molding product development process, and it is vital to use measuring technologies that are able to validate end-use products with feature sizes that are always extremely tiny. Without being able to do so, it is impossible to show that a product conforms to design intent and is therefore fit for purpose. So, saying, micro molders need to be equipped with state-of-the-art metrology tools and adhere to strict measurement protocols.

With any measuring tool, there will always be an inherent variation in the measurement system used. In a micro molding scenario, it is hugely important 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 should be an important element of any continuous improvement activity, especially with micro molding applications where any variation in the repeatability and reproducibility of the measurement could crucially eat into the low margins for error in terms of tolerance attainment.

 

You have touched upon the key areas where control of tolerances is fundamental. What else do you need to keep an eye on?

There are numerous other factors that require attention such as material variations that can lead to differential results when molded, and environmental issues such as humidity and temperature that can 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.

 

From:MPN