Aerospace Sets A High Bar

I have had the opportunity to work in several industries machining parts and programing machine tools over the course of the past 32 years. Without a doubt, machining parts for aerospace companies is the most demanding. Of course, the compensation reflects the difficulty.

The global aerospace parts manufacturing market reached $913 billion in 2023, according to Grand View Research, a market research and consulting company headquartered in San Francisco. Grand View Research also noted that the market segment is expected to grow at a compound annual growth rate of 4.2% through 2030.

As rewarding as aerospace machining can be, however, breaking into the aerospace market is not easy.

Aerospace work is challenging for one simple reason — safety, which we all appreciate when flying. Component failures on an airplane can cause catastrophic problems. Because of the critical nature of aerospace parts, engineers subject their part designs to countless calculations, physical tests and multiple design reviews to ensure everything is right. There is little allowance for error, and every feature is tightly controlled to ensure the component functions as designed and tested.

For shops not currently in the market, even getting the opportunity to submit a quote can be a challenge. Sourcing teams in large aerospace companies are under extreme pressure to control costs while improving inventory turns and ensuring there are no stocking issues. It is a challenging role, so keep in mind that buyers have limited time to process new vendors through a bureaucratic maze.

They are also hesitant to accept the risks associated with poor quality, late deliveries or working with vendors who lack financial stability. These combined elements can make it almost impossible to get an opportunity to quote, if you can even get the opportunity to talk to someone in sourcing.

Winning the work is only the beginning. Next comes the qualification process that, when complete, demonstrates the vendor is capable of successfully manufacturing the part with no quality issues. While I’m sure most shops have been through some kind of qualification before, aerospace qualifications are on another level.

Qualifications for the aerospace industry are intense. Most machined parts require 100% dimensional inspection. That means every single dimension on the drawing will be measured, usually on a batch of parts, to demonstrate that the machining processes are repeatable and success is not a one-off event. There is no allowance for error, and one incorrect dimension on one part can sink the qualification.

Once a shop has made it to the qualification phase, it becomes apparent that aerospace tolerances are tight. Tight is a relative term, and means different things depending on the industry and type of machining that is performed. When considering the mechanical function, aerospace tolerances are typically tighter than those found on other types of parts. For example, the tolerance on a bearing journal for industrial equipment may have a total range of 0.0005" while the tolerance range on the same size journal for an aerospace component would be just 0.0002". Tapped hole locations on a normal industrial part may be +/- 0.015", but the same type of part in an aerospace application would require a three-datum true-position call out of 0.005". I have seen a true position tolerance of 0.005" for a tapped hole that mated with clearance holes that were 0.020" larger than the screw diameter.

Compounding the difficult tolerancing are the materials that are often used for aerospace components. Anything that goes inside of an engine is going to be made from one of the many materials that fall into the not-fun-to-machine category, like titanium, nickel alloys and other nasty materials that can live in harsh environments. Exotic materials like nickel alloys are used extensively in jet engines because these materials retain their strength and other mechanical properties at elevated temperatures. However, the same material properties that make exotic alloys good for use in a jet engine makes them difficult to machine. The nickel alloys used in jet engines are the most difficult to machine materials used in industry.

Airplanes use immense amounts of aluminum, which is easy to machine. So, aluminum aerospace parts must be easy, right? In some ways, yes. Knocking off aluminum chips is easy. Tools don’t burn up. You can run as fast as you want. No bird nest of stringy chips. However, these parts are subject to the same qualification requirements as others with close tolerances, and present a different type of challenge.

A large number of aluminum aerospace parts are made from wrought alloys in the form of bar or plate. These wrought alloys like to move around when they are machined. Machining a large volume of chips from a piece of plate relieves the internal stress and can make those parts wander all over the place. A large aluminum structural part can be dimensionally perfect until it is unclamped. Then it begins to bend, curl and bow out of tolerance. Of course, shops that make these kinds of parts have ways of mitigating such problems, but they have learned these lessons the hard way over many years.

So, if a shop nails the qualification with tight tolerances on a difficult-to-machine material, then everything should be like machining any other part, right? Not really.

It is normal for aerospace manufacturing processes to be “frozen” or “locked” after a successful qualification. This means the shop does not have the same freedom to change manufacturing processes to address cost, productivity or quality issues that it would if it were making tractor parts.

Aerospace companies, often compelled by agencies like the FAA, do not allow manufacturers to change manufacturing processes without initiating a requalification. The restrictions vary depending on the part and the consequences of failure, but there is always some level of control over machining processes. These controls make process improvements challenging and can be a barrier to reducing manufacturing costs.

All the challenges of aerospace machining make it exceptionally profitable — and once qualified, a shop is almost guaranteed to keep the work. I did mention that aerospace machining can be rewarding.