MICRO MACHINING | ARTICLE
Tales Cryogenics found that flexures made using the photochemical etching process met these demanding requirements and retained their properties even aſter many years of continuous operation.
As Tales Cryogenics assessed the nature of the flexure required, it looked at a number of manufacturing processes and suppliers before choosing Precision Micro and photochemical etching. Beyond Precision Micro’s reputation as one of the world’s leading photochemical etching suppliers, the fact that the company was purchased by global engineering group Meggit plc in 2012 (the strapline of which is “Smart Engineering for Extreme Environments”) reinforced the symbiosis with Tales Cryogenics.
Te purity of the metal used in the flexure, however, was ultimately the key to supplier selection, as it was vital that potential fracture sites in the grain were eliminated, and this was only achievable with the consistency required through the use of chemical etching and Precision Micro’s expertise.
As a manufacturing process, photochemical etching has one key atribute when it comes to part integrity, and that is that during the production process, it does not affect or degrade material properties.
Te specific flexure used in the cryogenic cooler has been made since the 1990s, and initially, production of the flexures via machining and wiring were assessed, but these processes leſt small burrs on the parts and recast layers that would compromise performance. Te photochemical etching process, as previously mentioned, is characterised by the fact that it induces no tension in the material being worked and leaves no burrs.
While cost is an ever present concern when assessing alternative manufacturing technologies, in niche and highly critical part manufacture like the flexures for the satellite application, its importance is matched by the location and use of a process that guarantees accuracy, repeatability and conformance with extremely exacting tolerances and maintenance of material integrity.
Such considerations were of special concern for Tales Cryogenics as the flexure component that was produced by Precision Micro was essential to the reliability and system life-time of the company’s LSF and LPT coolers, which Tales sells to a variety of customers who use them to cool high-sensitivity sensor systems. Examples of these applications include gamma ray detectors, detectors for thermal night vision and infrared spectroscopy detectors for use in satellites for observation of the earth. For all customers, long product life and high reliability are essential, as replacing the coolers in such instances is at best costly, and when a satellite is in space, at worst impossible.
As these linear coolers contain pistons moving back an forth at around 50 Hz, mounting them on a flexure spring with a radial stiffness and a low axial stiffness is essential for contact-free operation, which ensures that litle or no wear occurs during use.
14 | commercial micro manufacturing international Vol 7 No.6
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