Expert advice for drilling holes in aerospace components

Five-axis machines are common for the machining of aerospace components because they enable access to a variety of different angles and minimize the need for operators to handle the part. z1b/iStock/Getty Images Plus

Aerospace components such as landing gear and structural parts to the smallest of brackets vary in size, complexity, and purpose. However, the need for accuracy in aerospace components is as demanding as in the medical and automotive manufacturing industries.

Accuracy is paramount for manufacturers of these parts—everything must be done correctly. In the air, failure can be disastrous.

When it comes to holemaking, operations can be as simple as drilling small holes, extremely complex cross holes, deep holes, or even a multitude of holes. The more holes, the more the conversation shifts from how to get it done to how to overcome challenges and how fast a machine can produce the holes.

The experts weigh in on how to efficiently and effectively drill precision holes in aerospace components.

Most machine shops assume that holemaking, especially drilling, is easy. While it may seem easy at first, drilling poses many considerations and issues to mitigate to ensure precision operations can be achieved.

“Start off doing your own homework,” said Slawomir Swierczek, assistant sales manager at KITAMURA Machinery of USA, Mount Prospect, Ill. “Start looking into magazines or social media, talk to your peers working in the industry, and take advantage of platforms like IMTS and trade shows to do research. Put that information in front of the technical experts. They will give the recommendations.”

Not all machines are designed to handle high-precision drilling operations. Technical experts and machine builders can provide machine recommendations based on the application. Qualifying that a machine can, in fact, produce holes with the accuracy needed is essential. Machine shops should select a machine based on size and accuracy to ensure it can handle holemaking requirements for large aerospace components.

The type of hole, number of holes, and different hole features will make a difference in the way to approach the operation. For example, blind holes and through holes require different coolant types. Also, debris that gets lodged in blind holes and multiple holes in a row needs to be cleared out. It’s something to keep in mind. If the hole requires additional finishing operations, like tapping or boring, that debris in the hole can negatively impact hole quality.

There are many things to keep in mind to ensure that holemaking operations go smoothly. Understanding the project parameters will help shops mitigate any potential issues that are commonly associated with drilling.

Aerospace materials have a wide spectrum of characteristics that pose unique challenges.

A machine must have a work envelope that can accommodate some of the larger aerospace components. Machine selection based on size and accuracy will help lead to better holemaking. Vasyl Stetsyuk/iStock/Getty Images Plus

For example, Ti-6Al-4V, a titanium alloy, is commonly used for aerospace components and offers an exceptionally high strength-to-weight ratio, resistance to fatigue and corrosion, and the ability to maintain strength at high temperatures. It often is used for aerospace components that are both lightweight and tough. For the most part, this titanium alloy tends to be easier to machine than other titanium alloys designed for aerospace.

Ti-6Al-4V often is used for airframes, compressor blades, discs, fasteners, hubs, seals, spacers, structural parts, and complex turbine engine components.

Ti5553, or Ti-5Al-5Mo-5V-3Cr, on the other hand, is a titanium alloy that is 50 per cent stronger than Ti-6Al-4V and must be machined with rigid equipment. The experts agree that machining this material requires a different approach than other titanium alloys. According to Swierczek, reducing the cutting speed is a good start, but this will require operators to rely on the machine’s forces to push the drill. Working at a low speed with this material is essential to avoid creating high temperatures. A machining strategy that focuses on chip thinning and lighter depth of cut will help balance the material’s high strength.

Ti5553 is generally used for landing gear and airframe structures like fuselage and wing components.

“Aerospace materials, like titanium and INCONEL, are very expensive,” said Chad Brunn, applications manager at NIIGATA Machine Techno USA, Elk Grove Village, Ill. “It’s important to understand the load placed on the tool and limiting factors that lead to losing a cutting tip or edge because that can not only wreck the drill but could lead to scrapping very expensive parts.”

Choosing the right machine often depends on the size and shape of the components to be machined. Once a machine is determined to be the right size, machine shops must then look at other features and details. The size of the tooling that will be used has to match the power of the spindle, which is going to drive the drill, then the application specifications will help determine the level of accuracy and rigidity needed.

“Some machines can produce smaller holes very quickly,” said Swierczek. “Others are designed to produce extremely precise holes. What it really comes down to is matching the size of the tooling required to the right spindle.”

The use of 5-axis machines for machining aerospace components has become commonplace, as these machines enable access to a variety of different angles and minimize the need to handle the part. This is especially important for high-precision drilling, where any positional deviation can lead to off-spec holes.

Because of the tight tolerances and accuracies required for aerospace components, implementing a 5-axis machine offers many benefits.

“Positioning and accuracy are some of the biggest challenges for holemaking operations,” said Brunn. “This is especially true with a 5-axis, where you are working with five separate axes. You have to make sure that all are in the correct plane and positioned properly.”

The KITAMURA Mytrunnion series 5-axis machining centres have the capacity and power to cut a vast array of materials used in today’s demanding industries such as aerospace, medical, and moldmaking. KITAMURA

This is where a horizontal machining centre (HMC) makes a lot of sense. According to Brunn, an HMC’s configuration allows for gravity to play a better role, especially when performing holemaking operations. These machines offer good chip evacuation and can often access four to five sides when operating with a pallet.

“With a 5-axis trunnion table HMC, the machine can effectively drill on five sides,” said Brunn.

Other features that can provide benefits to shops when it comes to drilling operations include accelerometer sensors and adaptive control.

A low-frequency machine design can help with holemaking operations. Look for machine kinematics that allows for pallets to be pulled down on the machine with a low amplitude of vibration.

Adding an accelerometer sensor can measure mechanical vibration levels and help operators understand how much vibration enters the equation and adjust accordingly.

Related to pallets, today’s machine tools range in the number of cups and cones used to seat the pallet. The more cups and cones, the more rigid the setup.

Adaptive control, as it relates to drilling, can sense the load that’s being put on the tool. The system has a baseline of what the load should be and monitors as the machine drills. It will either slow it down or stop drilling altogether to limit any damage to the tool or part.

“Adaptive control will adjust to the cutting conditions, which is especially important when working with expensive workpieces,” said Brunn.

In addition to machine selection and performance, process development is essential. With the materials designed for aerospace component manufacturing, choosing the right drill will help a machine shop ensure that it is working with the correct cutting angles, sharpness, and coatings.

“You definitely don’t want to find yourself in a situation where you have to drill 50 holes, but the drill you have will only make about 20 before the edge gets dull, creating a large burr, or worst-case scenario, breaks inside the hole,” said Swierczek. “Now, you have an even bigger issue because you have a drill stuck in a part that can cost thousands of dollars.”

To avoid this, machine shops must do their homework before getting started by consulting with tooling manufacturers about the application to gain an understanding of the limits of the machine and drill.

Brunn added that while proper tool selection is important, so is partnering with a reputable tool supplier. Choosing a generic, off-the-shelf drill might work in some applications, but when it comes to aerospace components, a name-brand, rigid tool is best.

A rigid setup is key to the successful drilling of aerospace components.

“Proper fixturing will make all the difference,” said Swierczek. “If you don’t hold the component correctly or if you don’t have support on the backside of the hole location, especially with the thin-walled parts we see in aerospace, then you will encounter flexing and deflection.”

This leads to holes that will be off-location and no longer feature perfect roundness, appear more oval instead. In applications where accuracy is paramount, rigid and application-specific fixturing can mean the difference between a good or bad hole.

Senior Editor/Digital Editor Lindsay Luminoso can be reached at [email protected].

KITAMURA Machinery, kitamura-machinery.com

NIIGATA Machine Techno USA, niigatausa.com