Micro and precision moulding: how to guarantee success

Micro moulding is now required throughout all sectors of industry, and manufacturers need to be aware of the unique nature of the micro moulding process to ensure optimal product development. Anthony Pruitt reports 

The objective of all micro moulding projects is the timely, cost-effective, repeatable manufacture of often complex and extremely tight tolerance plastic parts and components. The key is to get it right the first time, and this can only be achieved by attention to detail at every stage of the product development process — from design to automated packaging. 

Success in micro moulding is predicated on working closely with a micro moulding vendor from early in the design stage of product development, and on the fact, the vendor is also vertically integrated.  

Effectively, every part of the product development process when micro moulding has the ability to introduce a loss of tolerance. When the key to product success or failure is less than a few micron variations on a critical feature of a component, having control of each aspect of the product development process is critical.

And the key is not just to control each element of the process, but to have it residing under one roof. There is the obvious advantage of teams working together to create optimal outcomes, but also when working in a world when micron tolerances matter, even shifting apart from one location to another during the product development cycle can introduce tolerance creep. 

There are five stages involved in a micro product development process that should be controlled by a micro moulding vendor, namely design and material assistance, micro tool design and fabrication, micro moulding, metrology and validation, and automated assembly/packaging

Key considerations

As manufacturers begin to conceive a micro moulding project, it is important to bear in mind some key issues from inception. Every project should start with the end in mind. You need to understand the basic design approach, and really bottom out what you can and cannot do, as when micro moulding, even the smallest design change can have a significant impact in terms of time and cost or product development.  

Design for Manufacture (DfM) is a fundamental consideration when micro moulding. Each micro moulding project is unique in terms of geometric complexity, shape, and can be made in a wide range of materials, all of which will ultimately affect the ability to manufacture. 

Key areas of focus when considering DfM are reviewing characteristics for moulding including gating, ejection, and parting split lines, and understanding whether the part is designed for moulding simplicity. As a rule of thumb, if you can avoid complex actions within the tool, it ultimately leads to a more robust, low maintenance design which increases uptime and the chances of on-time delivery. Annual volume requirements are also important to consider as this influences cavitation requirements and will directly affect complexity.

Critical to Quality (CTQ) features and tolerances are just as important to project success as a robust mould design, as they represent the product characteristics as defined by a customer (internal and external). CTQs drive mould design decisions by influencing manufacturing methods and a tool layout that would best achieve these critical requirements.

DfM is vital as it truly establishes a partnership between customers and suppliers during the product development process. Engaging early and eagerly shows how committed suppliers and customers are.

Micro tooling

Expertise in micro tool fabrication is one of the most important factors that can influence the outcome of a micro moulding project. Your chosen micro moulder needs to have the in-house ability to fabricate micro tools. Micro tooling is arguably the key enabling technology for any micro moulding project, and here you need to work with a moulder that has years of experience and has the necessary infrastructure to develop the required tool for your application. Outsourcing the production of micro tools can have a huge impact on the viability of a micro moulding project, as even the smallest slip in tolerances can have a huge impact on the attainment of exacting micron-level requirements in the finished part. As a customer, this is an area to focus on, and you need to see that your chosen micro moulder can demonstrate that in-house they can achieve the necessary micron-level tolerances when cutting steel.

Key attributes to look out for ‘under one roof’ are a well-equipped team that has the resources to design, manufacture, produce and verify tools, and highly skilled toolmakers who can creatively push the envelope of conventional tool making. These skilled toolmakers also lead and teach team members and assist with continuous development and growth of the team. A collaborative approach is vital to success, this collaboration meaning a dedicated team working with the customer and also with internal groups in design, tooling, production, and quality. The team that works with you on your micro moulding project should include a sales engineer, a project engineer, and a quality engineer.

Micro moulding

The drivers for micro moulding success are on a basic level in-house experience and the moulding machines available to undertake production. You need to locate a micro moulder that can demonstrate a long track record of moulding to micro tolerances, as micro moulding has its own set of rules and difficulties that can only be understood and navigated by a supplier that has the right pedigree.

Fundamentally, a micro moulder needs to be in a position to ramp up to high volume manufacturing, some suppliers not having the infrastructure to be able to fulfil mass production at the scale demanded by many customers. 

There are a number of factors beyond infrastructural resources and ‘space’, however,  that can influence the ability of micro moulders to mass manufacture successfully. Once again, a collaboration between the micro moulding supplier and the customer is extremely critical. This leads to a profound understanding of how the part needs to be designed and specced to accommodate high volume manufacturing. The key is to set specifications that reflect what is needed and making sure that they are not over-constraining. For example, specifying 10 microns of flash when the design can accommodate 20 will lead to more tool downtime in order to maintain the tighter specification. 

Successful mass production is also influenced by the design and precise fabrication of a low maintenance tool — which is enabled by part design optimisation — along with stress testing and validating the tooling to prove that the tool is robust and ready for production. Pre-production stress testing is often a critical step that is overlooked in the industry causing serious delays. Also important is developing a robust process recipe that provides consistency, including process DOE to understand what influences the CTQ features.

Absolutely fundamental to mass production success is that the design and fabrication and maintenance of tooling must reside under the same roof as production. 

Metrology and validation

Everyone is aware of the saying, ‘if you can’t measure it, you can’t make it’. If you have the inability to measure a part or component accurately then you have zero chance of proving design intent. With this in mind, your chosen micro moulder must be able to demonstrate a suite of top-end metrology solutions that can validate the design intent of your product. Having this facility in-house is also of vital concern, as even the change of environment from production facility to measuring facility can introduce changes in micro part geometry (maybe due to humidity and other variables) which will render validation protocols useless. In house metrology also needs to be seen in the process as well as in the lab to ensure production efficiency.

A robust metrology approach is often overlooked when embarking on a micro moulding project. When making micro-parts, your chosen micro moulding supplier must have invested in equipment that can measure with micron accuracy optically, mechanically, or even to the nanometer-level with white light interferometers. Along with critical equipment, trained and experienced technicians and engineers are vital to achieving consistent and accurate results.

It is also important to realise that even with the most cutting-edge metrology solutions, some features simply cannot be measured and therefore ‘verified’ as equipment accuracy is not precise enough. In such instances your chosen micro moulding supplier must have the experience and knowledge to undertake a performance evaluation of the part or component, proving in the absence of viable data that a part performs its required end use function.

Assembly

It is important to ensure that your micro moulding partner has the capacity and ability to provide customised automated assembly in-house. When looking at the handling issues inherent with microplastics parts, manual assembly is either impossible or hugely costly and time-consuming. Your chosen micro moulder must be able to demonstrate an understanding of — and experience in — the art and science of micro-assembly, with a focus on minimising the level of handling, as at each stage tolerances can be affected.

Assembly is a topic that needs to be undertaken right at the beginning of the product development cycle when initiating DfM discussions. The part needs to be designed not only for its own manufacturability but also for the manufacturability of the overall assembly. Part design should accommodate optimal assembly processes.

Conclusion

Micro moulding projects are often highly strategic, highly complex, and also expensive, so it is vital that you take a proper and in-depth look at your short-listed supplier before committing one way or the other. Only through careful supplier selection can you ensure that you are working with a micro moulding partner that has the capabilities and values you need to ensure optimal manufacturing outcomes.

Anthony Pruitt is Technology Sales Engineer/DFM Manager, Accumold.