Inconel 718 is a high-performance alloy known for its excellent strength and heat resistance, but it presents challenges when it comes to machinability due to its hardness, toughness, and work hardening characteristics.
Machinability of Inconel 718:
1. Work Hardening
Inconel 718 has a tendency to work-harden quickly, meaning the material becomes harder and more difficult to machine as it is cut. This can make machining more challenging, especially in conventional machining processes.
2. Cutting Speed & Tool Wear
The alloy's high strength and hardness lead to increased tool wear. Therefore, cutting speeds should be slower than typical steel machining operations to minimize tool degradation.
Cobalt-based or ceramic tools are often recommended for longer tool life.
Carbide tools are typically used due to their ability to withstand the high temperatures and mechanical stresses during machining.
3. Heat Generation
Inconel 718 generates significant heat during machining, which can lead to thermal damage to both the material and cutting tools. Using coolants (preferably with high lubricating properties) is essential to reduce temperature and extend tool life.
4. Tool Types for Machining
Cobalt-based tools: These are often preferred for machining Inconel 718 because of their hardness and wear resistance.
Carbide tools: Commonly used in turning, milling, and drilling due to their wear resistance.
Ceramic tools: Sometimes used for rough machining, though they can be brittle.
5. Machining Operations
Turning: Often done with low cutting speeds and high feed rates to minimize heat generation and tool wear.
Milling: Utilizes high cutting speeds with proper cooling techniques to prevent excessive wear.
Drilling: Use of high-quality drills and slow speeds is recommended to avoid rapid tool wear.
Grinding: It is sometimes used for finishing work, although it requires specific grinding wheels and lubricants to avoid damaging the material.
6. Challenges
Work Hardening: The material can harden rapidly under the tool, requiring constant pressure to maintain cutting efficiency.
Tool Deflection: Due to its high strength, Inconel 718 can cause excessive tool deflection, leading to an uneven surface finish.
7. Cooling and Lubrication
Proper cooling and lubrication are critical to manage heat during machining. Use high-pressure coolant systems to maintain cutting efficiency and prevent the tool from overheating.
Tips for Efficient Machining of Inconel 718:
Use sharp tools: Ensure the cutting tools are sharp to minimize the chance of excessive work hardening.
Control cutting speed: Use lower cutting speeds to reduce heat and tool wear.
Use appropriate coolant: Apply cutting fluids or coolants to manage temperature and improve tool life.
Feed rates: Maintain high feed rates to reduce the formation of a built-up edge (BUE) on the tool.
Conclusion
While Inconel 718 presents some machining challenges, with the correct tools, techniques, and coolant use, it can be successfully machined. Always adjust cutting speeds, feeds, and cooling strategies to optimize productivity and reduce wear on tools.
