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Tech Focus: Hot Runners When microns matter

| Author / Editor: Aaron Johnson / Steffen Donath

How does a company transition from manufacturing small parts to the micro-scale? Can these parts be produced cost-effectively? What is important when partnering with another company?

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Micro moulding projects are often highly strategic, highly complex, and also expensive.
Micro moulding projects are often highly strategic, highly complex, and also expensive.
(Source: Accumold)

There is enormous demand from across the industry today for microscopic thermoplastic components with exacting micron tolerances and high-precision geometries. In addition, lead-time pressures are commonplace these days in many industrial sectors, and so the concept of so-called concurrent engineering is standard, with the idea of “over-the-wall” product development being replaced by different departments working in parallel.

As such, when locating a specialist micro-moulder, it is important to find one with the wherewithal to achieve exacting micro-tolerances and expertise at the design, tooling, manufacturing, assembly, validation and measurement stages of the micro-product and component development process. This will ensure that the need for lengthy and costly design reiterations is minimised, thereby making it possible to achieve micron tolerances cost-effectively and in a timely fashion.

Micro-injection moulding

Micro-moulding is an art form honed over many years of expertise and troubleshooting. It is vital that micro-moulders have the business culture, personnel and equipment in place to provide the service needed to ensure a successful project outcome. Micro-moulding for OEMs from a variety of industry sectors calls for the ability to cater for low, medium and high-volume runs in a variety of different materials, all requiring different levels of validation. Micro-moulders must also have expertise in handling, storing and processing often extremely expensive and sensitive materials that in many instances will be used in safety-critical applications.

The transition from injection moulding machines that can effectively produce small parts to, machines that can produce micro-parts and features is very important, and micro-moulders must be able to utilise state-of-the-art equipment designed for exacting micro-applications.

The degree of control and repeatability needed in micro-manufacturing requires the moulding press to be equipped for such precision. Traditional machines tend to struggle to maintain accuracy with smaller part dimensions, often causing additional processing issues. Micro-injection moulding machines — which may be manufacturing parts weighting less than 0.005 g — are not only able to handle much smaller geometries and tolerances, but also have a positive effect on material usage, residence time and consequent material degradation common with larger presses.

Micro-tool fabrication

It is in the area of tooling for micro-moulded parts that time and money are often wasted if the micro-moulder does not have the expertise required. Tooling for micro-moulding projects does not require an extrapolation of the rules governing tooling in traditional injection moulding. Features in micro-moulded parts often exceed the allowable tolerances in traditional injection moulding, and similar issues are confronted in the areas of venting and tooling mismatch. Micro-moulders must be in a position to employ an array of moulding technologies, including the latest CNC machining technologies, and also — as is often required — EDM.

Other tooling issues specific to micro-moulding include requirements for an understanding of polishing for micro-mould cavities, and the heating and cooling implications when dealing with extremely thin steel inserts that may be negatively affected by temperatures involved in many moulding applications. In addition, as many micro-moulding applications use high temperature, high-performance materials, such as bio-resorbables, liquid crystal polymers and PEEK, it is necessary to use and understand the nature of tooling materials such as stainless steel rather than traditional tool steels, which may not be able to withstand the high temperatures necessary and may thus corrode.

Process considerations

Process parameters in micro-moulding are in many ways different to traditional injection moulding. The key is an understanding of the balance between melt temperature, injection pressure and injection velocity and their effects on dimensional accuracy. In addition, attention must be focussed on micro-moulds that in many instances require mould alignment to less than 5 microns, and with gate diameters that are typically anything from 60 to 200 microns. Proper venting and runner design are also important for the process to be as efficient as possible.

Due to the often-critical nature of some micro-moulded parts and products, it is often necessary to manufacture under cleanroom conditions. With extremely exacting quality and traceability systems, complete control of the entire manufacturing process is required, and adherence to the parameters set out in ISO 9001 to ISO 13485 can be hugely important, determining the requirements for a comprehensive quality management system for the design and manufacture of safety-critical components.

Quality control

One thing that makes the selection of a micro-moulding supplier a key concern in the design-to-manufacturing cycle is the increased pressure in the area of quality control. Quality control and high-quality requirements are characteristics of many industrial sectors today. This is a direct reflection of the fact that micro-manufactured components in numerous industrial applications are now performing critical functions, and so failure rates — even in high-volume mass manufacture — must be zero. This not only requires painstaking attention to manufacturing process control, but also demands that focus is maintained on quality control procedures and validation.

Cost-effective and repeatable manufacture

It is unsurprising that industry should take advantage of the possibilities that exist through the judicious use of micro-manufacturing technologies and techniques today. Micro-injection moulding, for example, facilitates the cost-effective and repeatable manufacture of small or micro-products to extremely tight specifications, or larger parts with tiny features. In general, wherever possible, moulded products are replacing machined components. The primary advantage of micro-injection moulding over micro-machining is cost, with micro-injection moulding taking no time at all to mould components in relatively low-cost materials compared to machining.

Micro-moulding also facilitates the manufacture of extremely complex geometries and represents a dimensionally stable production process with no particle contamination, and often a better surface finish.

For OEMs seeking to take advantage of the possibilities that exist today for the manufacture of small to micro-plastic parts, partner selection is vital. Aside from assessing the nature of the equipment that a micro-manufacturing partner has in-house (including processing equipment as well as handling, assembly and inspection equipment), finding a supplier with an intimate knowledge of the process and the specific requirements of different industrial sectors is of paramount importance. Accumold’s expertise with small and micro-sized injection moulding is an ideal fit for an array of industrial sectors that require precision thermoplastic components with dimensional stability.

For all industry sectors, Accumold’s pre-eminence in micro-mould tool design and fabrication is also extremely important, as this is the key stumbling block for OEMs attempting to enter the micro-moulding arena. Accumold has in-house mould-building capabilities, with cross-functional teams of designers and toolmakers working together to fabricate tools that are capable of producing production-ready parts the very first time. This reduces the likelihood of multiple and costly design iterations and tool redesign.

Summary

Micro-moulding projects are often highly strategic, highly complex and also expensive, so it is vital that OEMs carefully select a micro-moulding partner with the expertise and depth of knowledge required to navigate often difficult decisions in material and process selection. Only through careful supplier selection can OEMs ensure that they are working with a micro-moulding partner that has the capabilities and values needed to ensure optimal manufacturing outcomes.

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