By Nigel Flowers, Managing Director, Sumitomo (SHI) Demag UK
Every computer, audio device, smart phone and digital camera requires plastic housing, circuit boards and wiring to function. And as electrical, communication and information devices shrink and get lighter, so too does the size of their components. Moulding these parts – many of which are plastic and can house and connect the smallest processing chips – requires tremendous precision and durability.
Downsizing has become an increasingly common term used in all type 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 twenty years and principally relates to the manufacture of injection moulded plastic parts that have a shot weight of less than one gram.
Figure 1: Micro-moulded electrical connectors, gears, and switches can have a shot weight of less than 1g
Once classed a niche market, the limit of what can now be moulded has reduced to parts as light as 0.0003g, with walls as thin as 0.0004in and dimensional tolerances to ±0.0005in. By 2012, the global polymer and thermoplastic micro moulding market – covering medical, automotive, electronics and telecommunications – was valued at $308m and this growth is expected to continue. Researchers have predicted that the value of micro-IM will reach $763.6m by 2019 and $897.3m by 2020.
After packaging and construction, electronics is the third biggest user of plastic components. Growth in demand for micro-IM electronic parts has been driven largely by developments in the digital and wireless device world, most notably sleeker, thinner smart phone designs. The challenge here has been to offset the larger battery sizes that maintain power and accommodate all those extra features consumers seek by making all other electrical components, like inductors, capacitors, duplexers, power amplifiers and more, smaller.
Another growing market for micro-electronic plastic parts is the automotive industry – specifically vehicle electronics. Here, micro-injection moulding is used to manufacture connectors, gears and micro switches, all of which are growing in demand as more and more complexity is added into vehicle electronics. As miniaturisation continues, we are seeing more sensors in cars, while the demand in electronics is driven by on-going innovation and advancements in nanotechnology, specifically sensors and circuits.
In the global fibre optics market, this particular technology is adopted for moulding gears such as micro connectors, ceramic holders and optics housing. Other applications comprise micro engines, micro drive control systems and micro-mechanic rotators.
Figure 2: The global fibre optics market uses micro connectors, ceramic holders, and optics housing
Geared up for change
In many cases, the evolution of moulding machines has been revolutionary, allowing moulders to enter markets that were not possible using historical hardware. For very small shot weights we used to have plunger systems – similar to a syringe. These were used on specialist machines designed to produce components for specific markets. However, some of these specialist machines could cost up to £200,000, making entry into this market unviable for many moulders. In 2001, there were concerns about the higher pressures required for micro-IM (up to 40,000psi, compared with 20,000psi for traditional moulding) as well as handling, inspecting and packaging miniature components. Around that time, it was also recommended that this moulding process should not be carried out on machines larger than 20 tonnes, because it was difficult to control and stabilise such small shot sizes, potentially leading to part damage and a lack of repeatability in the production process.
Fast-forward to the modern day and a new generation of all-electric machines have brought vastly increased levels of precision, made possible thanks to advanced direct drive technology. We are now able to achieve very high levels of repeatability while a specific 14mm screw design improves the dosing, which is critical in micro-IM. Working with shot weights of between 0.1g to 1g means that designers can now consider miniaturisation of components as it’s now more cost-effective.
Using the 14mm screw, traditional 50- and 75-tonne IntElect electric machines from Sumitomo (SHI) Demag can be deployed. The screw design is the smallest screw capable of processing standard plastic resins. Importantly, the 14mm 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 14mm plasticising unit contains around 8cm3 of plastic material at the screw. Traditionally, they would be used to run all sorts of different components with shot weights that were much larger than 1g, but the 14mm screw gives us small shot weights and the fine control that we need.
Figure 3: A micro-injection unit installed on a Sumitomo (SHI) Demag 250kN machine
Automation for greater precision
As well as offering repeatability and a stable production process, Micro-IM also relies on a certain level of automation to ensure that the moulded items stay in optimal condition with regards part quality and hygiene, ensuring electrical components aren’t exposed to dust or particles and production efficiency. Cleanrooms are used if the components are supplied to the pharmaceutical, aerospace, military or biotech industries, but in the electronics sector this situation is less typical, unless the part is being surface treated or used as a decorative layer.
Once you’ve moulded the parts – which could be as small as a match head – you have to make sure you none are lost within the machine or on the floor. Vacuums are often used to extract these parts from the IM machine, to save operators getting into direct contact with them, which could cause contamination. Many machines have a complex automated end of arm tooling systems to ensure they remove the parts without damaging them.
One example that highlights the importance of automation is inserting contact pins into electronic switches. It requires great precision, ensuring precise placement of pins into the moulding tool. Equally, tracking and collecting such diminutive parts during the ejection process is equally essentially, with sensors monitoring the loading and unloading of the mould.
Despite more automation and smaller components, the process of micro-IM isn’t that dissimilar to creating larger parts. Shot-to-shot precision is where the main difference lies. If we allow more material under the check valve on a 10g part it isn’t a big issue, but if the part weight is 0.1g it becomes a major problem. Historically, micro-IMs would have used hydraulic machines, which meant dealing with variations in oil temperature and compressibility. Those drawbacks are removed from the equation with the new generation of all-electric units.
Mastering micro-IM manufacturing
For complete filling of the cavities during moulding, machines use a dynamic injection process. Because it 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 award-winning activeFlowBalance. With activeLock, process consistency is increased, fluctuations are reduced and the risk of rejects minimised. The contra-rotation of the screw closes the 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.
Figure 4: Robots are often used in to insert pins into electrical switches and connectors and remove parts from moulds
There are also other modifications that could be considered when looking to switch to micro-injection moulding, one being better illumination in the mould space. Being able to see more easily what is going on is a simple thing but easily overlooked. Also, people may want a vacuum pump in the mould – when the mould is closed you may want to take the air out and put a vacuum in there to allow the material to flow better. The last thing you want is an air pocket or a void, which in percentage terms of a micro component could be significant. Ionisation is also good – not just to keep the parts clean, but also to keep the static out to ensure parts don’t stick together and are easier to handle.
What does the future hold?
Rapid development of various micro technologies, including micro-optics, nanotechnologies and microfluidics, mainly in Western Europe, is expected to increase demand for microinjection polymer moulding. More specifically, Germany holds a large amount of the European market for microinjection moulding on account of the country’s lead position in automobile manufacturing.
The trend for smaller electronic devices looks set to continue, with data connectivity top of the agenda. Nanotechnology is gaining rapid traction across a range of industries, including computing. In the future it won’t be just the size of components that matter, but the degree of engineering involved.
Likewise, design advances in automotive, driven in part by rapid developments in microfluidics technology, are expected to boost demand significantly in micro-IM. By 2020 the use of plastics in automotive will increase by 75% meaning that the average car will incorporate 350kg of plastic, around 150kg more than in 2014.
As a whole, the European market is expected to grow at a CAGR (compound annual growth rate) of 13.8% between 2013 to 2020. Asia Pacific, which is largely an untapped market holds even greater potential and has been estimated to achieve 14.9% CAGR in the same timeframe.