The aviation industry is one of the most demanding customers of component manufacturers: Therefore, only reliable, certified suppliers work for them, and they are understandably very selective in their choice of production equipment. But what does a traditional company like Krueger Aviation do when it needs an extremely sophisticated machine for plastics finishing at short notice?

The reference list of Krueger Aviation GmbH from Barsbuttel near Hamburg reads like a Who's Who of the aviation industry: The long-established Hanseatic company supplies more than 300 companies in the industry - from Airbus, Lufthansa Technik and Safran to ZIM Flugsitz. The components are also in demand from manufacturers of ships and railways. 40 employees use thermoforming, CNC machining and 3D printing to produce semi-finished products as well as complex finished parts and assemblies from plastic. "We help our customers design components, certify them or even switch from one manufacturing process to another," explains Florian Ehinger, Head of Customer Service. "Increasingly, however, customers are coming in with an aluminum component and asking: could you suggest a plastic that we might be able to use there instead of aluminium?"

Optical quality plays an important role

Among the company's particular specialties are high-quality mirrors made of special plastics, for which the northern Germans are among the world's leading suppliers and for which they have received several awards such as the "Crystal Cabin Award". The Barsbuttel plant also thermoforms polycarbonate (PC), polyamide (PA 66) and polyphenylsulfone (PPSU) covers for lighting and seat fittings, as well as other components for cabins and toilets. But all components have one common denominator: they are so-called visible parts without a load-bearing function. Ehinger: "Visual quality plays an important role in all our components. That's why we put a lot of effort into this."

Just-in-time delivery is another requirement: The aviation industry insists on extremely short delivery times, even for components that are usually produced in small batches and customised. Therefore, Krueger Aviation optimises all processes from development and production to handling. But how does a traditional company, now in its fourth generation and with a company history of over 100 years, proceed when it needs a milling machine that is both highly precise and extremely fast at short notice for the finishing of deep-drawn plastic parts, known as trim milling?

Machine search leads to Unterallgau

The northern Germans first took a close look at machines from well-known companies nearby, but then came across HG Grimme SysTech GmbH from Wiedergeltingen in the Unterallgau district. What speaks in favor of HG Grimme is that, like Krueger Aviation, it is a family-run, medium-sized company. It has also specialised in a high-tech niche of plastics processing. Since as early as the 1980s, it has been producing CNC machining centres for the finishing of thermoformed parts, a rarity in Germany at the time. Since 2010, the Bavarians have also been building CNC gantry machining centres.

However, it is not only the competence in plastics processing and the support at eye level that convince the northern Germans. "HG Grimme's performance potential for our form of plastics finishing is ideal for us," says Ingo Horster, Chief Technical Officer (CTO) at Krueger Aviation. "And then there was also a 5-axis CNC gantry milling machine, which was a perfect fit in terms of compact size and its performance. HG Grimme made only minor adjustments to the demonstration machine. And after a short time we were able to start trimming deep-drawn parts."

The term "minor adjustments" is probably due to Hanseatic understatement, because Krueger Aviation had a special request: As a workpiece fixture, the northern Germans have developed a vacuum clamping table that, together with semi-finished products, even holds complex shaped components at high milling speeds in a process-safe and vibration-free manner. Until now, the vacuum clamping table developed in-house was made of wood or ureol. HG Grimme was now to manufacture a solid all-aluminum version. The desire for an even more robust clamping table is understandable, since the new gantry machines in the X/Y axis at a speed of up to 80 meters per minute

"We can now machine components on one machine in three and five axes," the CTO is impressed to report. "Now we even succeed in milling a wide variety of items synchronously on the left and right sides at the same time. "A removable partition wall made of Makrolon makes it possible to set up on one side of the table while milling on the other. The fact that the beam with the milling head does not move from front to back, but from left to right, has also proven itself here. The operator can therefore work completely undisturbed on the second side of the table during the milling process. Horster praises the now more dynamic and at the same time more stable machining. In addition, the CNC system in gantry design works so precisely in the um range despite the high milling speed that subsequent polishing is often unnecessary.

Dynamic machining with milling head supported on one side

An unusual sight for metalworking experts is the very compact milling head, which can rotate a maximum of 540° and swivel up to 365°. "Because high forces do not occur here as in metalworking, we can work with a milling head mounted on one side," explains Horster. "With it, we also mill the typically filigree workpieces very dynamically, because we can now swivel the head down very far without the risk of the milling head colliding with the table or the fixtures." The risk of collision is now much lower than with the previous machine.

The experience with the first milled components was good. Krueger Aviation initially started with thermoformed semi-finished products made of the plastic ureol and is now also testing components made of other plastics for the aviation industry, which will then be subject to the "first article inspection" by customers. "So far, everything is working excellently," reports Horster. "We're not on the stopwatch when it comes to milling: but it's definitely the case that the throughput time per workpiece has been reduced by half."