xiehe model

An airplane, space plane or just a flying aircraft has more than 500,000 parts, a large part of which must be very precise and durable, ensuring these parts are of the best quality and cost is an important goal of industrial aerospace machining.

Problems in the production of aviation parts

First, a large number of aerospace components are made from a wide variety of materials. The most critical engine components in aircraft operation are made of extremely difficult-to-machine heat-resistant hardenable alloys. These alloys are poor thermal conductors, so heat from machining can build up in the tool. Nickel alloys are often aged or otherwise heat treated, making them difficult to machine. The precision of aerospace parts is much more stringent and the part geometries are much more complex than in other industries.

In addition to direct processing problems, there are many indirect problems. One of them includes production standards. Like the medical industry, aerospace production is one of the most regulated industries in the world, making it difficult to meet all quality requirements.

Weight is extremely important for airspace aircraft. The lighter the design, the less fuel it consumes, so aerospace engineers often design parts with thin walls, lattices, webs, etc. Traditionally, they are machined from solid cast or stamped metal blocks, with a 95% scrap rate for such parts. However, low material efficiency is not the only problem. A practical problem when machining such parts is deformation due to high cutting forces.

If you increase the feed and depth of cut too much, especially with nickel alloys, you risk breaking the wall from vibration or deforming it from overheating. The result is usually that you cut a tiny chip in creep feed, and the total machining time is impossible.

What can you do to reduce machining time and actually machine competitively thin-walled aerospace parts? The first thing you have to do is reduce vibration. The vibrating tool hits the thin wall and bends or breaks it. Therefore, in order to reduce vibration, it is better to reduce the feed rate but increase the number of cutting edges of the milling cutter (or even use multiple tools on the lathe). The best cutting strategy for milling thin-walled aerospace parts is climb milling.

This strategy uses a feed in the opposite direction to traditional milling strategies. This results in lower cutting forces, better surface finish and, most importantly, much less vibration as the cutter enters the thickest wall thickness material.

Trochoidal machining paths for reducing overheating in aerospace alloys

Part overheating due to poor heat transfer is a typical problem with aerospace parts. One machining strategy to reduce heat buildup is called trochoidal milling. It makes great use of the capabilities of CNC machines to follow complex cutting paths. The cycloidal strategy uses a small milling cutter (smaller than a cut anyway) which follows a path similar to the side projection of a spring on a plane. One curve - the mill cuts, then returns during the second curve, then cuts the metal again. This strategy distributes the contact time between the tool and the part to allow time for the cutting fluid to cool both effectively.

Trochoidal turning is similar to milling, using short cut and pause sequences to allow the coolant to do its job and avoid overheating. This strategy has more empty tool runs than the other strategies, but it counteracts this effect by increasing cutting speed and feed.

Choosing the Right Tool for Fast Machining

When it comes to machine tools, CNC machine tools have played a big role, and they have been widely used in aluminum processing. One of the most important ways to improve machining efficiency is to choose the correct tool. If softer alloys are well analyzed and many manufacturers offer solutions for aluminum and other alloys. However, many aerospace materials are classified, so selection must be made on-site.

The art of selecting effective tools for heat-resistant materials must offset the negative characteristics of the material.

Therefore, the perfect tool must have very little vibration, must be very hard, and must be able to withstand high temperatures for consistent life and efficient feeds. A perfect example of a tool used for this type of purpose is a diamond cutting tool.

Synthetic diamond is harder and more durable than carbide inserts, and can work at higher temperatures. Diamond machining has its particularities, but of course it can be modified to meet the needs of aerospace manufacturers. In addition to diamond tools, ceramic tools have also proven to have excellent performance, as they can work at the highest temperatures.

In order to reduce the vibration of the machined parts, it is important to use milling cutters with more cutting edges and sharper corners. These milling cutters minimize the time and distance the tool travels before the next cutting edge hits the material, reducing vibration and allowing you to increase cutting parameters for greater efficiency.