Aircraft construction: titanium the tool-challenge under control
Nowhere is the search for new materials more intense than in the field of aircraft construction. The reasons for this are easy to see: on the one hand, depending on where in the aircraft they are used, the materials must withstand particularly high stresses – in the turbines, for instance, extremely heat-resistant grades of steel are used. At the same time, however, it is important to lower the total weight of the aircraft and so minimize fuel consumption. Taken together, this makes titanium an extremely desirable material. The challenges this presents to the tools used for machining titanium are illustrated by a number of applications from the USA.
Even the material itself is high-tech. Wherever metals are exposed to extreme stresses, titanium alloys are now indispensable. They are used in medical technology as much as they are in automobile construction.
But it is in aircraft construction that titanium has really earned its laurels. The wide range of the material's strengths is uniquely advantageous here. Titanium alloys are light in weight, insensitive to shocks and blows, and only undergo low expansion when heated. At the same time, they are resistant to chemical attack because, like aluminum, they quickly develop a protective, passivating surface layer. The positive properties just described, however, also directly contribute to the challenge that titanium alloys present to any machining tools, as Scott Feimster from LMT Onsrud explains: “Titanium is difficult to machine due to its physical properties. Titanium is a poor heat conductor so the heat can build up quickly on the cutting tool. Because titanium is a reactive metal it can alloy and chemically react with material in the cutting tools which cause galling, welding, smearing and rapid destruction of the cutting tool.” For these reasons, many companies are constantly on the search for new tool solutions.
Tools proven in the aircraft industry
It is not uncommon for the search to lead directly to LMT Onsrud. The wide spectrum of cutting tools from the company, whose headquarters are in Libertyville, near Chicago, has been proven over many years in the aircraft industry – and particularly includes the machining of titanium alloys. The two following examples illustrate typical challenges met in aircraft construction:
- Machining geometries with high depth and complexity is a regular task when manufacturing components for aircraft engines, and this is exactly the field of one American supplier company. The production planners there were looking for a more economical tool solution for cutting the titanium alloy 6AL-4V. "The tool that was previously in use was out of its depth. In order to machine the deep, narrow pockets in the component, the cutter necessarily has to be unusually long. Not only did the tool break frequently, but the machining quality on the surface of the titanium alloy was poor," explained Feimster. LMT Onsrud was able to offer the company a "plug and play" solution: by using two different titanium finishers of different lengths (depending on the geometry of the component) from the EMC series, the machining quality was improved. At the same time, the tools had the attraction of a significantly better tool life.
- Similar results were achieved through the application of the 4-flute titanium rougher from LMT Onsrud for machining a control lever at another aircraft construction company. The goal was to increase the number of components made by each tool. "The cutters used until now could only make about 50 components. At that point it was necessary to change the tool. This was just too little for the factory management. The lifetime of a 4-flute titanium rougher from LMT Onsrud, on the other hand, extends over about 75 parts", explains John Hansen of LMT Onsrud.
Other sectors – comparable performance jumps
An example of an application from the power supply sector shows how it is not just in aircraft construction that titanium is a challenge to machining tools. For the production of highly stressed components, such as are found inside pumps for salty or chlorinated water, many producers of course make use of titanium alloys. In one American company, a pump sensor is made of the titanium alloy 6AL-4V. "We were able to achieve spectacular success through the use of the 8-flute titanium finisher from LMT Onsrud“, said Bill Trites from LMT Onsrud, confirming the positive impressions obtained from aircraft construction. "The number of components produced with each tool rose from the three managed by the previous tool to 36 parts, while at the same time it was possible to lift the machining feed rate from 1.2 inches to 8 inches a minute."