Inconel 718 CNC Machining Service

Inconel 718 has poor machinability, typically rated at around 12-16% on standard machinability indexes (where free-machining steels like AISI 1212 are rated at 100%). This makes it one of the more challenging nickel-based superalloys to machine, often classified as “difficult to moderate” in the heat-resistant superalloy (HRSA) category.

Key Reasons for Poor Machinability

• Rapid work hardening — The material quickly hardens under cutting stress, increasing forces and tool wear.
• Low thermal conductivity — Heat builds up at the tool tip, leading to high cutting temperatures and accelerated tool degradation.
• High strength and abrasive precipitates — Gamma double-prime (γ″) particles act like abrasives, causing rapid tool wear.
• Tendency for built-up edge (BUE) and welding — Material adheres to the tool, worsening surface finish and wear.

Practical Machining Guidelines

To achieve acceptable results, use specialized approaches:

• Tooling → Coated carbide, ceramic, or CBN inserts; positive rake geometries and sharp edges are essential.
• Cutting speeds → Low, typically 20-45 m/min (65-150 SFM) for turning/milling with carbide; higher (up to 250 SFM) possible with optimized grades but rare.
• Feeds and depths → Moderate to heavy feeds with lighter depths of cut; climb milling preferred to reduce work hardening.
• Coolant → High-pressure through-tool coolant or advanced methods (e.g., cryogenic, MQL) to manage heat.
• Material condition → Machine in the solution-annealed state (softer, ~30-35 HRC) before final age hardening for easier cutting.

With proper techniques, high-quality parts with tight tolerances (±0.0005″) and good surface finishes are achievable, but tool life is shorter and cycle times longer compared to easier materials. It’s widely machined in aerospace despite the challenges, thanks to its outstanding performance properties.

Yes, Inconel 718 can be ground, and it is routinely ground in industry—particularly for finishing aerospace components like turbine blades, disks, and other high-precision parts where tight tolerances and superior surface integrity are required.

However, like its general machinability, Inconel 718 has poor grindability due to its high strength, rapid work hardening, low thermal conductivity, and abrasive precipitates. This leads to challenges such as:

• High grinding forces and temperatures
• Wheel wear
• Risk of surface burns
• Tensile residual stresses
• Subsurface damage

Key Challenges in Grinding Inconel 718

• Heat buildup — Low thermal conductivity causes most grinding heat to stay at the surface, risking burns, cracks, or microstructural changes.
• Wheel loading and wear — Material adhesion and abrasive particles (e.g., gamma double-prime phases) accelerate wheel degradation.
• Surface integrity issues — Conventional grinding can produce poor surface quality, tensile stresses, or microcracks if not optimized.

Practical Grinding Guidelines

Successful grinding is achievable with specialized approaches:

• Grinding wheels — Superabrasives like CBN (cubic boron nitride) are preferred for efficiency and longevity; alumina (WA) wheels often outperform SiC; diamond also works well in some cases.
• Methods — Creep-feed grinding (deep, slow passes) is common for high material removal rates; surface grinding, belt grinding, or robotic systems are used for complex shapes.
• Cooling/lubrication — Aggressive coolant delivery (high-pressure, flood, or MQL/minimum quantity lubrication) is essential; advanced options like internal cooling or eco-friendly fluids improve results.
• Parameters — Lower wheel speeds, moderate depths of cut, and optimized feeds; grinding in the solution-annealed condition (softer) before aging is recommended for easier processing.
• Achievable results — Surface finishes of Ra 0.2–1.6 μm, tight dimensional accuracy, and compressive residual stresses are possible with proper techniques.

Overall, while grinding Inconel 718 is more difficult and costly than easier materials, it is a standard and effective finishing process when done with expertise and the right setup.

Yes, Inconel 718 can be laser cut, and it is a common non-contact process for this superalloy, particularly for sheet metal, thin strips, and complex geometries in aerospace and high-performance applications. Fiber lasers are especially effective due to better absorption by reflective nickel alloys, while CO2 lasers have also been widely studied and used.

Key Challenges in Laser Cutting Inconel 718

• High reflectivity and thermal properties — The alloy’s composition causes initial beam reflection (risking laser damage) and low thermal conductivity, leading to heat buildup.
• Cut quality issues — Potential for kerf taper, recast layers, dross adhesion, surface roughness, and heat-affected zones (HAZ) that may cause microstructural changes or cracking in age-hardened material.
• Oxidation and edge quality — Oxygen assist gas can cause oxidation; thicker materials are harder to cut cleanly.

Practical Laser Cutting Guidelines

Successful results are achieved with optimized setups:

• Laser types → Fiber or disk lasers preferred for efficiency and handling reflectivity; CO2 works but may require higher power.
• Assist gas → High-pressure nitrogen (or argon) for clean, oxide-free edges and minimal dross; avoids reactions and post-processing.
• Parameters → Adjusted laser power (e.g., 2.4–4.5 kW), cutting speed, focus position, and gas pressure to minimize taper, roughness, and recast; higher speeds reduce kerf width.
• Material condition → Often cut in solution-annealed state for better results; post-cut heat treatment may be needed.
• Achievable outcomes → Precise cuts with good surface finish (e.g., low roughness), narrow kerfs, and burr-free edges on sheets up to several mm thick, ideal for slots, contours, and profiles.

Overall, while more challenging than milder steels, laser cutting Inconel 718 is a proven, efficient method when parameters are properly tuned, offering advantages over traditional machining like reduced tool wear and ability to handle complex shapes.