Tools & Strategies for Machining ISO-S Materials in Aerospace

By Scott Causey, International Aerospace Specialist 

Jabro JHP770 and 780

Manufacture of precision components in the aerospace industry requires innovative engineering and technology, especially when machining with newer, high-performance workpiece materials. Today’s ISO-S alloys, namely nickel-, cobalt- and iron-based heat resistant superalloys (HRSA), and titaniums have many beneficial properties that make them great choices for a wide range of crucial applications. At the same time, some of their characteristics make these materials challenging to machine.

ISO-S alloys provide higher resistance to heat and wear, extreme toughness, and unwavering quality and reliability. On the flip side, they have low thermal conductivity, which reduces tool life and causes part distortion. They have tendencies to strain and precipitation harden when machined, which increases cutting forces and further degrades tool life, and the sticky behavior of these alloys creates uncontrolled built-up edge (BUE) and notch wear. Using advanced tools and application strategies can help you maximize the benefits and address the difficulties of machining these alloys. 

• Match the cutter to your desired profile. Application of ISO-S materials is common in aerospace turbine blade production. Seco offers a fir tree cutter with spiral fluting to machine the specialized profile of the blades, which has extremely tight tolerances. The Jabro® fir tree provides a smooth, easy cutting action with an advanced cutter geometry that prolongs tool life and offers unmatched accuracy.

• Limit cutting speeds when cutting titanium alloys. Structural aerospace parts, such as landing gear components, are massive and strong. When manufactured from standard materials, they are also very heavy. Today, manufacturers are using newer, lighter and stronger titanium alloys to produce lighter landing gears, but these new materials are more difficult to machine. One newer alloy is titanium 5553, which includes 5 percent aluminium, 5 percent molybdenum, 5 percent vanadium, and 3 percent chromium content. Its benefit is high tensile strength: 1160 MPa compared to 910 MPa for Ti6Al4V, but this higher tensile strength requires limiting cutting speeds to levels 50 percent of the speeds applied with Ti6Al4V.

• Apply parameters for most-difficult-to-machine material when cutting stacked alloys. Some aerospace applications involve machining components composed of stacks of differing materials. An example is an engine mount featuring a titanium 6Al4V/austentic stainless steel stack. Both materials share some properties including relatively high strength and adhesive properties that cause the cut material to stick to the endmill, and the challenge is to machine the “sandwich” or “hybrid” with adequate chip control and no vibration or burrs.

Seco’s carbide Jabro JHP 770 tool designed for machining titanium is a good solution. This tool incorporates differential flute spacing, radial relief, a specially formed chip space, and a through-coolant channel that minimizes workpiece adhesion and clears chips.

In machining the stacked materials, the key is to apply the parameters for the more difficult-to-machine material. In this example, keep in mind the titanium’s low thermal conductivity. We recommend using a moderate cutting speed of 50 m/min, with a feed of 0.036mm/rev feed, and a 3 mm depth of cut, descending in circular interpolation. 

• High-Speed Steel (HHS) cutters are a productive and cost-effective choice. Many large aerospace components, such as landing gear parts, are machined from solid billets of titanium or stainless steel. For these parts, high-performance HSS tools up to 50 mm in diameter are capable of removing large volumes of material. The HSS tools are very effective on low-rpm, high-torque machines for effective roughing and even finishing of titaniums and stainless steel. The ability to use large diameters and widths of cut enables the tools to provide competitive metal removal rates even when run at lower speeds than those achievable with carbide tools. 

An example of an advanced HSS tool is the Jabro JCO710 HSS-Co cutter with 8 percent cobalt content and a hardness of 67 HRC. The tool features polished flutes to reduce friction and edge build-up, and a variable face profile geometry to cut light and reduce the risk of chatter that causes unacceptable surface roughness values. We have seen these cutters provide more than 800 minutes of tool life when applied at a manufacturer producing large titanium parts. 

The goals of aerospace parts production are top quality, reliable consistency and productivity. As metal producers develop new alloys to meet increasingly demanding high-performance applications, we are engineering new cutting tools and strategies to enable aerospace manufacturers to overcome the challenges of machining these materials. Please contact me to learn more.

About the Author 

As Seco’s International Aerospace Specialist, Scott is responsible for supporting the company’s aerospace segment customers, which includes optimizing current processes and defining new technologies. In his spare time, he enjoys spending time with his family and working with horses.