Inconel-718

I get more questions about drilling small holes in Inconel 718 than almost any other topic. A recent Practical Machinist thread about drilling 3mm holes 160mm deep in Inconel 718 at HRC 40-45 got over 3,500 views. The user was struggling with drill breakage, centerline deviation, and surface finish. The root cause in that thread was the same one I see most often: coolant pressure at 8 bar (116 psi) when the job needs 100 bar or more. Here is what I have learned about getting this application right. ...

Inconel 718 is a nickel-based superalloy used in aerospace and power generation components. It retains its strength at high temperatures but is extremely difficult to machine. The material work-hardens rapidly and retains heat at the cutting edge. I have drilled hundreds of holes in Inconel 718 across multiple jobs. Every one was a battle against heat, work-hardening, and tool wear. Here is what works for me. Cutting Parameters for Inconel 718 The cutting speed is the single most critical parameter. Above 25 m/min, the edge degrades rapidly from heat. Below 15 m/min, the tool rubs instead of cutting and work-hardens the surface. I start at 20 m/min and adjust based on tool life. ...

I started drilling additively manufactured metal parts expecting them to be harder than wrought. The porous, layered structure looked like it would eat tools. The data surprised me. AM metals — specifically laser powder bed fusion Inconel 718 — machine differently than wrought. Tool wear is lower, cutting forces are lower, and the wear mechanism shifts from adhesive to abrasive. Understanding these differences changes how you set up parameters and select tooling. ...