Heat resistant superalloys (HRSA) in aerospace engine components face extreme performance demands. What makes them incredibly durable in the high pressures and temperatures of an engine also makes them notoriously difficult to machine. It is essential that workshops know how to successfully equip themselves for HRSA engine components, which can cost tens of thousands of dollars each, in order to avoid making very costly mistakes.

Ensuring process security is the key to a store’s success. To achieve repeatability and high quality when machining HRSA aerospace engine components, it is essential that workshops follow some of the best practices. While these relate to machining HRSA in general, each HRSA type, engine component, and feature has its own considerations, tools, and techniques.

Work with material properties

HRSAs are difficult to machine because they are heat resistant, and machining them by shear generates heat. When workshops machine a part of steel, the chips that break off from it absorb the heat from the machining process. In HRSA, the chips resist rather than absorb heat, returning it to the tools or the workpiece. The heat generated can transform the carbide in the cutting tool into a plasticized or sintered state, and the inserts can fracture; damage a tool or, worse yet, an engine component.

To protect tools and parts, it is important that the HRSA machining process produces as little heat as possible. One way is to use tools that cut and shear HRSA rather than pushing the material. Another solution is not to remove too much material too quickly, for example by burying the cutting insert deeply into the material and plowing. Instead, a series of lighter, faster cuts are more efficient and produce less heat. Most computer-aided manufacturing (CAM) packages offer this trochoidal, or dynamic, technique that makes it easier to apply magazines.

General HRSA cutting best practices apply to different material bases. For aerospace engines, the HRSA can be classified into two basic elements with completely different cutting conditions, based on nickel and titanium. In most cases, when turning, use uncoated tools to machine titanium as it is chemically reactive, especially at high temperatures. Since most coatings contain titanium as well as oxygen, nitrogen and carbon, there is a possibility that the titanium in the coating and the part will react. If this is the case, the titanium in the part can either remove the coating from the insert by adhesive wear or weld the material to the insert.

On the contrary, nickel-based materials generally require a tool coating. They are more difficult to machine, so the area footage per minute (sfm) should be around 40-50% slower than titanium.

Understanding how HRSA titanium and nickel bases react to other materials can reveal additional machining benefits. While this is increasingly becoming an industry standard, some workshops may not be aware that it is possible (and beneficial) to use tools made from materials other than traditional carbide to optimize manufacturing processes. roughing and finishing and increase productivity. For example, workshops can use ceramics to roughen nickel at higher speeds. (However, never machine titanium with ceramic. It can start a fire that is extremely difficult to put out). For finishing, shops can use polycrystalline diamond (PCD) for titanium and cubic boron nitride (CBN) for nickel-based materials to be machined at high speeds.

HRSAs create more forces to machine than aluminum or steel, so to save a considerable amount on installation, time and set-up it is essential to have the right machine for different operations.

While it might not be possible for stores to buy new machines all at once, consider upgrading the machines that will have the greatest impact. Older machines, such as a vertical lathe, can be used to roughen the exterior and in some cases the interior to remove coarse scale on a forging or casting, so it makes more sense to invest in more. new machines optimized for feature-based finishing. job.

Consider the needs of each feature

The intricate components of an aerospace engine have to be flawless and luckily there are standard aero engine tools and inserts available from tooling companies such as Sandvik Coromant that precisely machine every groove, pocket and slot.

A popular machined engine component, the turbine disc, has different types of undercuts. Optimized angular inserts can precisely machine every complex feature. Most of the discs have small, sharp peaks called seal fins. Standard seal fin inserts have a built-in clearance to carefully machine these precise features. Using a seal fin insert, one can perform a technique in which the insert rises, sweeps, and then descends in the opposite direction to avoid creating a burr or pushing the pick.

If machining components with slots and pockets is not difficult enough, blisks come up with a few other factors to consider. Blade geometry and depth, material, and machine all affect programming and tools. A plunge milling This strategy can make the machining of narrow and deep grooves faster and more cost effective. Some unique solid carbide cutters have geometries specifically designed to plunge material into deep and narrow slots. A solid carbide end mill with a deeper seat can machine these geometries all the way to the bottom.

The coil, combustion housings, and shaft are common engine components. When stores get tools to machine these components, they should look for certain portfolio features that improve process safety. Optimized grades can increase reliability, resist wear, improve machining accuracy, and extend tool and insert life. The choice of tool grades is particularly important to improve process safety; no one wants to scrap a component because the insert failed in the middle of the finish. The optimized geometries are crisp and can withstand high edge pressures, and the cushioned tools improve stability, process safety and component quality.

Expand knowledge

Each optimized tool has its own machining technique, so it is essential that workshops partner with a specialist who can teach them. Some tool vendors, such as Sandvik Coromant, have dedicated engineering teams to support workshops and their aerospace projects, visit workshops and share the best ways to approach materials, features and components, as well as machine recommendations, select tools, complete CAM programming, and assist with fastening.

Some suppliers also offer in-house machining, ideal for small workshops with few machines and great ambition for growth. They can send a new HRSA material they are unfamiliar with to a supplier’s machining lab who can test and recommend the best tools, techniques and cutting data for it. Sandvik Coromant, for example, has its training center and machining application and development Center in Mebane, North Carolina, near Raleigh-Durham, specifically for customer testing and training.

When looking for a specialist, choose one that has a full portfolio of aerospace products. This ensures quick access to tools and techniques specific to their needs and operations, from roughing to finishing, or from a complete component to a specific function.

Ensuring process security

As aerospace machining research and development (R&D) efforts advance and more optimized tools become available, new best practices and techniques will emerge, making more projects possible for workshops of all abilities and sizes. sizes.

Machining aerospace engine components is not a one-size-fits-all approach. Every detail can be carefully examined, from the base material to the component, including function, process and individual tool. Every opportunity contains decisions that can improve process safety and improve the productivity of a shop and the quality of engine components it can offer.

Sandvik Coromant

About the Author: Bill Durow is the Director of the Global Project Office for Aerospace, Space and Defense at Sandvik Coromant. He can be reached at [email protected]