A brief history and the promising future of micro-injection moulding

by Nigel Flowers, June 2018

June 6, 2018

2:24 PM

Nigel Flowers, managing director of Sumitomo (SHI) Demag UK

Downsizing has become an increasingly common term used in all kinds of scenarios and industries in recent years. Yet, in the moulding world, the quest to go small is nothing new. Micro-injection moulding (micro-IM) has been around for over two decades and principally relates to the manufacture of injection moulded plastic parts that have a shot weight of less than one gram.

At the turn of the 21st century, the opportunities being presented by micro-IM were slowly being realised. Once classed a niche market for moulders in the automotive, electronics, medical and telecommunications sectors, the limit of what could be moulded was being brought down to parts as light as 0.0003 g, with walls as thin as 0.0004 in. and dimensional tolerances to ±0.0005 in. By 2012, the global polymer and thermoplastic micro moulding market was valued at US$308 mn and this growth is expected to continue. Researchers have predicted that the value of micro-IM will reach US$763.6 mn by 2019 and US$897.3 mn by 2020¹.

Growth in demand for micro injection moulded parts has been driven largely by the medical and healthcare sector, which, in 2012, accounted for one third of the total market. Typical items being moulded using the technology include catheter components, blade holders, dental prosthetics, hearing aids and implants.

Another growing recipient of micro injection moulded parts is the automotive industry—specifically in terms of vehicle electronics. Here, it is used to manufacture connectors, gears and micro switches, all of which are growing in demand as more and more complexity is sought.

In the global fibre optics market, micro-IM has been adopted for parts such as connectors, ceramic holders and optics housing. Other applications are micro engines, micro drive control systems and micromechanics rotators.

Geared up for change

The evolution of moulding machines has allowed moulders to enter markets not previously possible using historical hardware. Back in the day, plastics equipment manufacturer Sumitomo (SHI) Demag offered plunger systems, similar to a syringe, for very small shot weights. These plunger systems were employed on specialist machines designed to produce components for specific markets. However, some of the machines cost up to £200,000, making entry into the micro-IM market unviable for many moulders.

In 2001, there were concerns about the higher pressures required for micro-IM (up to 40,000 psi, compared with 20,000 psi for traditional moulding) as well as handling, inspecting and packaging of miniature components. Around the same time, it was recommended that micro-IM not be carried out on machines larger than 20 tonnes, because it was difficult to control and stabilise such small shot sizes, which could potentially lead to part damage and a lack of repeatability in the production process.

Fast forward to today and Sumitomo (SHI) Demag offers a new generation of all-electric moulding machines, which afford vastly increased levels of precision, made possible thanks to advanced direct drive technology.

These machines achieve very high levels of repeatability, and a specific 14 mm screw design improves their dosing, which is critical in micro-IM. Being able to work with shot weights of between 0.1 to 1 g means that designers can consider miniaturisation of components because it is more cost-effective.

Using the 14 mm screw, 50- and 75-tonne IntElect machines can be deployed. Importantly, the screw enables users to limit the amount of material used by adapting nozzle body length and diameter to minimise residual time of material in the barrel. The 14 mm plasticising unit contains around 8 cm³ of plastic material at the screw. Ordinarily, the machines would be used to run all sorts of components with shot weights much larger than 1 g, but the 14 mm screw allows for small shot weights and the fine control required for micro-IM.

Automation for the people

As well as offering repeatability and a stable production process, micro-IM also relies on a certain level of automation to deliver production efficiency and ensure that the moulded items remain in optimal condition in terms of part quality and hygiene (in the case of medical components). Typically, if the item is for the medical industry, it needs to be run in a clean room from a hygiene point of view. In the electronics sector, this situation is less typical, unless the part is being surface treated or used as a decorative layer.

After producing micro moulded parts, it is necessary to ensure that they do not get lost in the machine or on the floor. Vacuums are often used to extract the parts from the injection moulding (IM) machine to save operators coming into direct contact with them and risking contamination. Additionally, many machines have a complex, automated end-of-arm tooling system to remove the parts without damaging them.

An application that highlights the importance of automation is ballpoint pen tips. There are typically 32 cavities in the mould and each pen tip weighs 0.0037 g, presenting a huge challenge in trying to track and collect them after production. The ability for the tips to be cleared from the machine quickly and easily means it is one less process to worry about and overall efficiency can be improved.

Despite more automation and smaller components, the micro-IM process is not that dissimilar to creating larger parts. Shot-to-shot precision is where the main difference lies. If more material is allowed under the check valve on a 10 g part, it is not a big issue, but if the part weight is 0.1 g, it becomes a major problem. Historically, micro-injection moulders would have used hydraulic machines, which meant dealing with variations in oil temperature and compressibility. Those drawbacks are removed from the equation with the all-electric machines.

Mastering micro-IM manufacturing

For complete filling of the cavities during moulding, the machines use a dynamic injection process. As they must run steadily and with complete precision to prevent overfilling, Sumitomo (SHI) Demag direct drives are often supported by an activeLock non-return valve and the company’s activeFlowBalance technology. With activeLock, process consistency is increased, fluctuations reduced and the risk of rejects minimised. The contra-rotation of the screw closes the activeLock non-return valve and ensures a consistent closing behaviour, which is critical for micro-IM shot-to-shot consistency. The activeFlowBalance technology meanwhile uses the expansion of the compressed plasticised material at the point of changeover from injection to holding pressure to top up the filling levels in the partially filled cavities, which happens as a result of their lower counter pressure.

As well as activeLock and activeFlowBalance, there are other modifications that could be considered when looking to switch to micro-IM. One of these is better illumination in the mould, as being able to see what is taking place in the mould more easily is a simple thing but can be overlooked. Another is a vacuum pump in the mould, as moulders may wish to take the air out of the mould whilst it is closed and a vacuum pump allows the material to flow better. The last thing a moulder wants is an air pocket or a void, which in percentage terms of a micro component could be significant. Ionisation is also useful, not just to keep the parts clean but keep out the static and ensure they do not stick together for easier handling.

What does the future hold?

Rapid development of various micro technologies—including micro-optics and microfluidics—mainly in Western Europe, is expected to increase demand for polymer micro-IM in Europe. More specifically, Germany holds a large proportion of the European market for micro-IM on account of increasing medical expenditure and its leading position in automobile manufacturing.

The trend for implantable devices in the medical industry is a significant advance for the sector. Although the overall production process is not altogether different, the type of material used could be. Almost every material one comes across in medical applications can be used in micro-IM; the material selected would obviously depend on what the part will be used for and how. Take, for example, plastic coated in gold and the role it can play in cancer diagnostics and treatment. Research has shown that gold nanoparticles, in some instances, help to target tumours and destroy cancer cells, so they are used in aspects of chemotherapy. The number of minimally invasive surgeries is also on the rise and expected to drive greater adoption of micro-IM over the coming years.

Likewise, design advances in automotive, driven in part by rapid developments in microfluidics technology, are expected to boost demand in micro-IM significantly. According to analyst IHS Chemical (Englewood CO), the use of plastics in automotive will increase by 75 percent by 2020, meaning that the average car will incorporate 350 kg of plastic, around 150 kg more than in 2014².

As a whole, the European market is expected to grow at a compound annual growth rate (CAGR) of 13.8 percent between 2013 and 2020. Asia Pacific, which is largely an untapped market holds even greater potential and has been estimated to achieve a CAGR of 14.9 percent in the same timeframe.

Sumitomo (SHI) Demag UK

https://uk.sumitomo-shi-demag.eu

References

¹Polymer microinjection molding market to reach $897.3 million by 2020. (2015). Grand View Research. Available at: https://www.grandviewresearch.com/press-release/global-polymer-microinjection-molding-market

²Plastics use in vehicles to grow 75% by 2020, says industry watcher. (2015). Plastics Today. Available at: https://www.plasticstoday.com/automotive-and-mobility/plastics-use-vehicles-grow-75-2020-says-industry-watcher/63791493722019

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