Inconel Machining: Alloy Types, Applications, & Machining Tips

Inconel machining

Different metals and alloys are compatible for CNC machining; Inconel is one of such machining alloys. It comes in different grades and is suitable for applications that require withstanding high mechanical stress, extreme heat, and corrosive environments.  

Inconel alloys are also known as “Super Alloys”, offering high strength, toughness, and corrosion resistance. However, they are difficult to machine due to their toughness and work-hardening property. 

Therefore, machining Inconel requires an understanding of its properties, machining grades, tooling options, and potential challenges.

What is Inconel Alloy?

Inconel alloy

Inconel is a Nickel(Ni) & chromium(Cr) alloy with additional elements like Iron, molybdenum, and carbon in minor amounts. Moreover, it is an engineered metal that offers high strength at elevated temperatures and resistance to oxidation and corrosion. 

According to the specific Inconel grade, the proportion of Nickel, Chromium, and other constituent metals differs, which also impacts the alloy properties. Nickel content ranges from 45 to 75 %, Chromium 14 to 31 %, molybdenum 0 to 17%, and so on. 

You can use Inconel 625, 718, 600, and X-750 grades as the CNC machining Materials. Their high tensile strength and fatigue life make them useful in various applications, including aerospace, marine, automotive, and chemical processing.

Is Inconel Difficult to Machine? 

Yes, Inconel material is difficult to machine as compared to stainless steel, aluminum, copper, and titanium. The high work-hardening, excessive heat generation, high cutting force, and hardness of Inconel make it difficult to machine. However, it does not mean that you can not machine this alloy into complex parts. 

According to the AISI Index, it has a 12 % machinability rating, which is significantly lower than stainless steel 70 % and titanium alloys’ 15 to 35 %. 

To machine Inconel alloys, you need carbide cutting tools or tools with a hard coating like TiAlN. Additionally, setting the correct cutting force, depth, feed rate, and cutting speed is essential. 

What Makes Inconel Machining Challenging?

As the machinability of Inconel is relatively lower than other metals & alloys, it requires careful considerations, advanced technologies, and expertise for Inconel machining.

Let’s take a look at core challenges and what factors cause them.

Work Hardening

Due to low thermal conductivity, the inconel alloys accumulate the heat and tend to work-harden quickly at a high rate. As work hardens, it makes it challenging to machine. 

High Cutting Forces

The toughness of Inconel demands higher cutting forces, which contribute to the plastic deformation and material can smeat or compact while removing chips. Additionally, higher forces also speed up the tool wear.

Excessive Heat Generation 

Since Inconel maintains stability in high temperatures and does not transfer away, an immense amount of heat is generated and builds up on the tool and workpiece.  As a result, it makes it difficult to machine. You require special tooling and an effective coolant system. 

Work Material Deflection

Another challenge in Inconel machining is the risk of workpiece deflection, which causes dimensional inaccuracies, poor surface finish, and even failure of the project. Therefore, understand the machine dynamics and high cutting forces to securely clamp the material. 

What Are the CNC Machining Inconel Grades?  

Inconel machining alloys

Some Inconel grades are more machinable than others. What makes one grade different from is the proportion of Nickel, Chromium, and other constituents in the alloying composition.  

 Let’s discuss common inconel machining grades: Inconel 625, Inconel 600, and Inconel 718. 

Inconel 600 Alloy 

This alloy grade contains more than 72% of nickel and 14 to 17 % of chromium. The high nickel content makes it highly resistant to oxidation in harsh operating conditions. Subsequently, the austenitic microstructures contribute to thermal stability.

The higher nickel also increases the work-hardening while machining. Therefore, the Inconel 600 machining requires proper lubrication along with specialized tools. 

Furthermore, strength, corrosion resistance, and good weldability make the 600 grade also compatible with stamping and other metal forming processes. Inconel 600 metal stampings require hard die tooling and can be shaped into complex sheet metal parts.

• Advantages: Good fabrication properties and hard austenitic structure. 
• Machining Challenges: High work hardening rate and heat build-up in the machining area.  

Inconel 625 Alloy 

In addition to Nickel(≥58%) and Chromium (23%), molybdenum, niobium, and titanium are added during Inconel 625 casting. As a result, Inconel 625 becomes stronger than 600, offering excellent fatigue and creep resistance. 

Subsequently, machining Inconel 625 is more challenging due to the inclusion of hard niobium in the composition. The tool wear can be rapid, so use an optimized feed rate and cutting speed. 

• Advantages: Superior strength, excellent fatigue resistance in harsh environments, and good weldability. 
• Machining Challenges: Rapid tool wear due to Niobium and molybdenum carbides, and ductility makes it difficult to control chip removal.

Inconel 718 Alloy 

Inco 718 alloy involves a smaller amount of nickel than 600 & 625, about 50-55%, followed by ~20% of chromium, ~ 5.5 % of Nb +Ta. It provides high mechanical strength at elevated temperature, up to 705°C. Subsequently, this alloy grade is also known as aerospace inconel due to its superior strength at high temperatures. 

Comparing Inconel 625 vs 718 machinability, 718 Inconel grade is also more challenging to machine. It causes high work-hardening while machining. Therefore, you need aggressive machining strategies, like a rigid setup, high cutting force, and carbide tooling. 

• Advantages:  It retains strength up to ~705 °C and is suitable for aerospace and heavy-duty uses.
• Machining Challenges: Hardening rate greater than 600 requires rigid setups and aggressive cutting

Inconel CNC Machining Processes

Inconel alloys are compatible with numerous CNC machining processes, including milling, turning, drilling, and EDM. Each of these processes has the capability of performing multiple operations to shape the inconel workpiece. 

Let’s discuss four major Inconel CNC machining processes:

Inconel CNC Milling 

Inconel Milling

CNC milling machines or machining centres are used for Inconel milling, which can perform multiple operations and craft complex 3D shapes.  High feed per tooth with radial tool engagement is recommended for Inconel CNC milling. Consequently, milling performs facing, profiling, slotting, threading, etc. 

You can use solid carbide end mills coated with PVD TiAlN or AlTiN for Inconel workpieces. It helps to retain tool hardness at high cutting temperatures. 

The complexity of parts depends on the axes and overall capabilities of the machine. A 3-Axis CNC Milling makes simple 3D shapes, whereas a 5-axis CNC milling center makes super alloy parts that are complex with intricate internal features. 

Inconel CNC Turning 

Inconel turning

CNC tuning is for cylindrical items, like shafts, rods, shoulders, and profiles on them. It involves removing material from a rotating Inconel bar using a computer-controlled program. Turning can perform multiple machining operations with crosonding tools, such as single-point cutters, drill bits, boring bars, CNC groving tools, and reamers. 

For Inconel turning, use moderate cutting speeds, slower feeds, and small cutting depths. However, you can increase cutting depth while roughening the surface. Meanwhile, use sharp-edge inserts for finishing passes. 

Inconel CNC Drilling 

Drilling Tools for Inconel

Inconel drilling requires long and hard coating bits with an effective coolant flow & chip mechanism. Inconel manufacturers typically use carbide drills that have through-coolant. You can start the drilling with a feed of 60-85 surface feet per meter(SFM), but decrease both feed & speed for deep holes. 

Furthermore, if you need further operations on drilled holes, such as threading, tapping, boring, and reaming, use CNC machines instead of manual ones. 

Inconel EDM Machining 

EDM cut Inconel parts

EDM machining involves a non-contact material removal process, so it can cut, shape, and drill hard Inconel alloys. Instead, EDM relies on precise electrical discharge that melts the material without direct contact of cutting tools and the workpiece. 

You can choose Inconel EDM for creating micro features, small holes, deep cavities, and 2D carving. Unlike Milling & turning, there is no issue of tool wear. 

Best Practices for Inconel Machining 

As Inconel is not an easily machinable material, it requires several considerations in tooling, machining variables, material removal process, and rigid setup. 

We use the following best practices for Inconel machining:

• Monitor Tool Wear Regularly: Tool wear affects the chip formation and reduces the accuracy. Therefore, inspect them regularly and replace them if needed. 
• Solutionized Inconel: Heat the alloy and cool it instantly, which refines the grain structures and reduces tool stress, and improves chip control. 
• Use Ceramic Cutting Tools: One of the best ways to reduce work hardening is to use ceramic tools. They allow for continuous cutting of Inconel material.
• Maintain Consistent Feed: The repetitive tool motion causes higher heat generation and leads to workhardening, so avoid peck drilling and maintain a constant & continuous feed during drilling. 
• Choose the Right Tool Geometry: Use sharp, positive-rake tools with strong edges. They can minimize cutting forces and prevent work hardening.
• Consider Post Processing: Based on the requirement of accuracy, surface finish, and mechanical properties, consider post-processing like CNC grinding machining services, and heat treatments. 
• Use High-pressure Coolant: A continuous coolant flow is essential while machining Inconel to avoid the heat buildup and better chip evacuation, ensure a rigid setup by minimizing tool overhang, and stable work clamping.

Tools for Inconel Machining

As mentioned before, due to rapid work hardening and low machinability of Inconel, you need specialized tooling with hard coating. 

The table below outlines the common tools for inconel machining:

Applications of Inconel CNC Machining

CNC machined Inconel items

CNC-machined Inconel Parts are used across the industries, including aerospace, automotive, Power & Gas, marine, nuclear energy, and chemical processing. 

The table below outlines why inconel machining is beneficial in these industries, with examples:

Read More: 5-Axis CNC Machines

Inconel Machining Costs 

The inconel machining costs are typically higher than the cost of machining aluminum, steel, copper, and other materials with higher machinability. A simple machining project might cost over $1000 and goes way higher for complex and large-sized Inconel parts. 

However, the exact machining cost might vary depending on factors like alloy type, machining process, work hardening rate, equipment used in the process, required tooling, etc. 

Do You Need Inconel Machining Parts? Contact ProleanTech

As we discussed, machining Inconel alloys requires a deep understanding of their properties and strategies to tackle the low machinability. Therefore, you need expertise and advanced CNC machines to craft the Inconel parts precisely.

At ProleanTech, we have more than a decade of experience handling Inconel alloy and other difficult-to-machine materials. Our CNC machining services encompass detailed planning of tooling & machining process to deliver accurate results.  

For further information or an estimation of your project, upload your design and get a quote. 

Conclusion 

Inconel machining is challenging compared to other CNC materials. The main issues are high work hardening, hardness level, tooling, and machining variables. Addressing these issues can deliver you quick cycle times, desired accuracy, and finish, while boosting the tool life. 

You need to use special tools with hard coating, optimal feed & speed, and a continuous cooling system. So, you can seamlessly cut, mill, turn, and drill the Inconel alloys. 

If you are outsourcing the inconel machining parts, assess the capabilities of CNC machining manufacturers before the contract, such as the inconel alloys they can machine, the precision they can offer, the complexity, and the cost implications. 

FAQ’s

Why is Inconel difficult to machine?

The low thermal conductivity of Inconel accumulates the heat during machining. It causes work hardening and makes the material difficult to machine. 

What is the machinability of Inconel?

Inconel has lower machinability than steel and aluminum; it has 12 % AISI machinability. 

What materials cannot be CNC machined?

Materials that are extremely brittle and abrasive can not be CNC machined, such as some ceramics and glass. Additionally, you can not machine very soft materials like foam.

Is Inconel 625 hard to machine?

Yes, Inconel 625 is hard to machine due to its hardness and work hardening. But, they can be machined with hard-coated carbide tools. 

What are the disadvantages of Inconel?

Poor machinability, rapid tool wear, risk of dull tools, poor heat transfer properties, and material cost are the disadvantages of Inconel.