A Guide to Machining Difficult-to-Cut Materials: Stainless Steel, Titanium, Inconel, and More

Key Takeaways

Difficult-to-cut materials are metals and alloys that are challenging to machine due to their properties. They often cause problems such as the following:

• Reduced cutting tool life

• Difficulty achieving smooth surface finishes

• Challenges with dimensional accuracy

• Welding or adhesion caused by cutting heat

Characteristics of Difficult-to-Cut Materials

Hard-to-machine metals

This primarily includes materials with high hardness and poor machinability (e.g., stainless steel, titanium). Additionally, soft materials like the 1000 series of pure aluminum are also considered difficult-to-cut.

Unclear machinability

New materials with little to no machining data, such as Inconel and Hastelloy.

Materials with a high risk of ignition or flammability during processing

Materials that can ignite or pose hazards during processing, such as magnesium.

Examples of Difficult-to-Cut Metals

Stainless Steel

Stainless steel is an alloy of steel with chromium (10.5% or more) and nickel. It offers excellent corrosion resistance, heat resistance, and oxidation resistance, and is widely used in various fields such as aviation and medical applications.

Challenges when machining stainless steel include:

• It has low thermal conductivity, trapping heat during cutting.

• It exhibits work hardening, increasing hardness under machining conditions.

• Its high affinity with tools causes chips to weld to the cutting edge.

These factors shorten tool life and make high-accuracy machining difficult.

Titanium

Titanium is about two-thirds the weight of iron, with high tensile strength, heat resistance, and excellent corrosion resistance. It is also elastic, returning to its original shape after bending.

Challenges when machining titanium include:

• Chatter and tool wear from chips during cutting

• Flammability of those chips under heat

• Low thermal conductivity, leading to tool alloying or chemical reactions

Inconel

Inconel is a nickel-based alloy that also contains chromium, iron, and carbon. It maintains very high strength at high temperatures and has excellent oxidation and creep resistance, maintaining its high strength in corrosive environments. It is used in power plants, jet engines, sports cars, waste incinerators, etc.

Challenges when machining inconel include:

• It keeps its high strength at elevated temperatures

• It has low thermal conductivity, causing heat buildup

• Cutting data is limited, often requiring trial and error for machining conditions

Magnesium

Magnesium is the lightest practical metal, with superior specific stiffness and strength relative to weight compared to iron or aluminum. Comparatively, it is easier to cut and requires less cutting power than aluminum.

The main challenge when machining magnesium is safety:

• Magnesium burns fiercely if ignited

• Contact with water when heated can generate flammable gases

• Fires are hard to extinguish with standard methods

Strict fire prevention measures, ventilation, and chip cleaning are essential when handling magnesium.

CNC Machining of Difficult-to-Cut Materials at Yumoto Electric

Yumoto Electric delivers high-quality components fast, worldwide. We provide precision machining for a wide range of metals using milling, turning, and specialized metal processing. We have experience with over 200 materials including aluminum alloys, stainless steel, molybdenum, and titanium. 

If you’re unsure about material selection or machining methods, we offer complimentary consultations to help optimize your design and production. For any questions, please feel free to contact us.