Contract manufacturing
What’s possible with micro MIM
The miniaturisation of components and functional surfaces requires high geometrical precision during the manufacturing process. Micro metal injection moulding offers new opportunities for the reliable and reproducible production of micro-components for a wide range of applications. Micro metal injection moulding allows components with ultra-small dimensions to be manufactured. A prime example is a replica of the smallest bone in the human body, which is the stirrup in the ear. It features a diameter of 1.4mm and a thickness of 280µm. This is, however, just one example of what micro injection moulding can offer. The smallest component produced at research institution Fraunhofer IFAM is an electronic component with a side length of below 250µm. Micro injection moulding also allows ultra-fine structures to be realised on macroscopic components. For example, microstructured surfaces are being manufactured, which can be used as microfluidic systems for microanalysis or as structured surfaces for influencing surface functionality, for example, cell adhesion on medical implants, wear resistance or heat dissipation. Depending on the material used and the cavity, geometries having a diameter of just a few microns and true-to-shape can be manufactured.
Potential dimensions: ■Structure size ■Thickness
■Aspect ratio ■Density
■Tolerance Source: Fraunhofer IFAM
and costly to produce. As a rule of thumb, it’s good to avoid designing a part with an edge radius smaller than 0.005 to 0.006in.
Above right: MIM versus machining – MIM provides a significant benefit over machining.
Below: MIM uses metal powders mixed with polymers to form its parts.
Like plastics, a good MIM part can still have undercuts and threads. However, these do require more complicated tooling. The tooling will need to have cams or side actions to form undercuts. They slide into place before the mould closes and slide out of the way before the part ejects from the tool. As one might expect, this also increases the cost of the tool; however, in macro terms, the return on investment is better than having each part machined secondarily to make the undercut – especially at higher unit volumes. Threads can be integrated into the tool, but there needs to be ‘flats’ on the sides of the threads to accommodate a flat parting line.
< 10µm
< 300µm up to 16:1 > 99%
< 1% for 2mm structure size MIM versus machining
Assuming that the availability of programming, machines and labour input is there, machining might seem like the most appropriate process methodology for small precision metallic components. In terms of speed to market, including prototyping, CNC machining is a strong contender. When considering a machined approach, things like tools, fixturing and work holding requirements are often significant constraints, especially as the complexity of parts increases. The higher the Rockwell rating – a measure of the hardness of the material – the more difficult machining becomes, as feedstock and processing speeds need to be altered.
The most advantageous aspect MIM brings is the ability to scale the process up into a repeatable, consistent, and high-tolerance production process, especially as the component complexity escalates. In terms of value, MIM provides a significant cost advantage of CNC machining once production requirements get into the thousands.
Why consult with an expert? The overarching issue most design or manufacturing engineers make, when approaching a micro metal component requirement, is overlooking MIM entirely. As outlined earlier, MIM is a relatively new process that is often incorrectly associated as a sub-niche within the context of pressed powdered metals – this is an errant assumption. The technology, from alloy formation all the way through to the vacuum sintering phase, differs entirely from any other metallic shape processing method. Successfully working with the MIM process requires collaboration between the device designer and those with technical expertise at the processing company. The technical competency of the MIM provider will quickly ascertain if any given design will successfully work in the MIM process. ●
32 Medical Device Developments /
www.nsmedicaldevices.com
Advanced Powder Products
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