Materials in the aircraft’s body
Davis, Brian
Manufacturing for the aerospace industry traditionally involves making highly reliable, precision parts in low volume. Materials involved are usually difficult to machine high strength, light weight metals such as stainless steel, titanium, and high-nickel steel alloys. Machine tools have to be specially designed for rigidity and large-part handling, while the cutting tools must handle high speed, high temperature cutting requirements.
In the past, we looked at our existing products and chose the best for a particular job. Now we are more interested in targeting the cutter to the material, process and machine tool. There is, therefore, more cooperation between the manufacturer and cutting tool maker to develop new designs before any cutting takes place. For example, we developed our new CoroMill 790 segmented aluminum router specifically for the high speed machining so important to the aerospace industry.
Composites and titanium, which continue to grow in this industry, will need even more job-specific tools. Getting a new tool approved in the aerospace industry takes a lot of time. With all the testing and approvals of new tools and processes, it is not uncommon to have a new tool finally implemented in production a year after its first introduction.
Because aerospace materials themselves are more costly, the need for reliability is higher. There is more pressure to get it right the first time. And, because aerospace parts are made in relatively low volume, scrap is a much larger concern. Machining errors, or selecting an ineffective cutter, entails much greater consequences.
Many aircraft parts have pockets, and the industry still uses a lot of the older vertical milling machines. As a result, chips stay in pockets, and there is a lot of re-cutting that wastes tool life and sends more heat into the part. Usually such parts are cut with HSS. Recently, indexable cutters have been making a strong push toward these difficult applications.
In general, when cutting aluminum, an average speed for roughing or medium machining would be from 150 to 200 ipm (3.8-5 tn/min). For finishing, with a lighter DOC, speeds are around 500 ipm (12.7 m/min).
When cutting aluminum or titanium, you need very fast cutting action. You don’t want to put a lot of heat or stress into the metal. If you are not careful, you can cause microcracks that can initiate failure later, particularly with finishing cuts.
Recently, there has been more use of alpha-beta stage titanium. The use of alpha-beta titanium alloy is growing in military aircraft because of the greater survivability it provides, and in commercial aircraft because of its high strength-to-weight ratio.
To meet this need, we developed a finishing tool in conjunction with a large aircraft manufacturer. Long edge applications are very common within the aerospace frame industry. The Coromant finishing long-edge cutter achieves finishes comparable to that of solid and brazed carbide tools. Component surfaces show no mismatch between the inserts. The long edge cutter maintains the very high tolerances common within this industry.
Materials in the Aircraft’s Body
Brian Davis, Product Specialist- Milling, Sandvik Coromant, Fair Lawn, NJ
Copyright Society of Manufacturing Engineers Mar 2002
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