Machine tools | Focus weight materials in our shared industry, and fibreglass composite is also highly abrasive when cut, requiring highquality tools (and frequent checking and replacement) for both. Among the least challenging and most cost-effective materials used in CNC machining today are aluminium alloys, with 6061-T6 being the metal used most widely for machine cutting. Despite its high strength-to-weight ratio, it cuts far more easily than steel and titanium, and it is better at absorbing heat and avoiding thermal deformations than many other metals. Additionally, given the commodity nature of aluminium, it can be acquired from a huge variety of suppliers in tubes, cubes, sheets, bars and other shapes in order to produce anything from a landing strut, to a body fairing, to an engine block. Many aerospace customers are also increasingly seeking machined 7075 aluminium parts because of the material’s greater strength-to-weight ratio. Although it is harder than 6061 and hence goes through tools faster (as well as being costlier), it cuts more easily than stainless steel and titanium. The survey UAV market in particular might benefit from the rising number of CNC companies capable of working with materials such as Invar. These nickelbased alloys exhibit an extremely low thermal expansion coefficient – similar to that of glass – as well as very low magnetism, making them ideal for lensholders in optical systems. However, as with titanium, cutting this material precisely and efficiently takes a certain learning curve, potentially including a plethora of test cuts before a workshop can supply Invar parts with volume, consistency and confidence. Quality control As mentioned, the tool and the machine are typically blind systems that cannot provide reliable feedback to the machinist as to whether the workpiece and the tool are faring well. While one might assume that a laser or similar type of scanner could be integrated within the milling chamber for mid-process measurements of the part, attempts at such configurations have been hampered by constant occlusions from the tool and from the powders, moisture and debris prevalent throughout the chambers. There are a few exceptions and workarounds to this, however. One of the simplest is that some CNC machines will integrate physical probes – be it a workpiece probe, a tool probe, or one of each – consisting, for instance, of a sapphire on the end of a plastic needle (not dissimilar to CMMs) that the operator can manually call upon to accurately measure different features of the workpiece or the tool while the cutting machine is stopped. Alternately, such probes can form part of a CNC programming set-up, designed to take measurements of tools or workpieces while in-process. Theoretically, a high-priority geometric feature on a customer’s part could be manufactured by ‘walking it in’; for instance, a hole could be bored inch by inch, with the tool extending into the block some way, then retracting to allow a probe to take internal measurements. With that precise data gathered, the CNC programmer could account for any insufficiencies thus far in the hole’s width or inconsistencies in its geometry while programming the machine’s next (and possibly corrective) steps. This approach can also be adopted for the tool when cutting stainless steel or an especially stubborn titanium, measuring it at regular intervals to identify early signs of wear. In general, greater automation is becoming key, not only for ensuring consistent quality but also for resolving the immense workforce cost that comes with operating and maintaining CNC machinery. Achieving automation in CNC machining is challenging, however, requiring close pairing with production planning software, automated tool checking and replacement mechanisms, supervising algorithms, robotic arm-type systems for installing blocks and removing workpieces, autonomous carting of raw materials and finished batches, and more – all of which together demand great expense and time. But once all this is done, being able to press a button and know with confidence that a series of parts will be milled and finished as required, even through the night or over multiple shifts and days, without the need for an engineer to continually check that no mistakes have been made, will become invaluable as long-endurance UAVs and other uncrewed systems become 93 Uncrewed Systems Technology | August/September 2025 Using high-end machines and tools is critical for cutting harder materials such as stainless steels, titanium alloys and ceramics (Image courtesy of Kagoshima Seiki Co., Ltd.)
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