MICRO MOULDING | ARTICLE
ADVANCES IN
Micro Moulding words | Enric Sirera, Ultrasion SL
Sometimes, it is fair to say that new technological developments are truly ground-breaking.
Everyone in industry is used to announcements from companies about the next big thing, the next development that will revolutionise the way manufacturers manufacture. Sometimes there is some meat on the bone, but more often than not, such apparent advances are not that innovative, and do not turn the current modus operandi on its head.
It may just be, however, that in the area of micro moulding, a newly commercialised technology is about to challenge the accepted norm, and may well represent a step change in the way that companies approach their micro moulding projects.
Traditional Micro Injection Moulding
Micro moulding — more often than not referred to as micro injection moulding — has been a key technology assisting OEMs as they strive for smaller and smaller parts. The drive towards miniaturisation means that micro system technologies are becoming more and more important, and micro injection moulding fits the bill for many manufacturers as it has mass production capabilities and relatively low production costs.
In addition, it is a technology that has evolved from a well established macro technology, and therefore the learning curve for use on a micro level is not seemingly that dramatic. (Companies with an intimate knowledge of micro injection moulding as opposed to macro injection moulding will, however, testify to the fact that the process does need to be completely relearned on the micro level.)
Injection moulding, whether undertaken on a macro or micro level, is a technology that takes plastic in the form of granules, which are transferred from a hopper into a plasticising unit where they are melted. The material is then forced under high pressure inside a mould cavity where it is subjected to holding pressure for
<< Figure 1: The Sonorus 1G ultrasonic micro moulding machine from Ultrasion SL. >>
a period to compensate for material shrinkage, and then freezes into the shape of the mould, before being ejected, and the process starting again.
Initially, micro moulding machines were modified, traditional, large-scale injection moulding machines, but today there are a number of machines that have been developed that address the vagaries of micro moulding specifically. Despite their sophistication, however, these micro moulding machines do have limitations, and these limitations in many instances prohibit the wide-scale fabrication of micro components. Key among these limitations is that the nature of the end-shape processes imposes limits on the allowed geometrical designs to ensure demouldability. Also, quality issues can be a problem for high aspect ratio features.
Perhaps of most importance, however, is the low dosage precision in micro injection moulding machines, which results in a significant amount of material being rejected during injection. In some instances in traditional micro injection moulding, over 90% of the polymer is wasted, which is of critical importance when using expensive polymers for advanced applications.
Continued on page 10 9| commercial micro manufacturing international Vol 7 No.1
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