10 Commonly Used Metal Materials for CNC Lathe Machining

In the field of precision manufacturing, CNC (Computer Numerical Control) lathes, with their high precision, high efficiency, and high flexibility, have become indispensable core equipment in modern industrial production. However, the quality of CNC lathe machining depends not only on the precision of the machine tool itself and the sophistication of the CNC system, but also, to a large extent, on the characteristics of the material being machined.

Different metal materials exhibit drastically different behaviors during machining—some materials have good machinability, enabling ultra-high-speed machining; others, due to their high strength, low thermal conductivity, or high chemical reactivity, pose machining challenges.

Material Overview Quick Reference Table

01 Carbon Steel

Typical grades: 45# steel, Q235, 1045

Carbon steel is one of the more widely used metallic materials in industrial manufacturing. Its carbon content ranges from 0.02% to 2.11%, and it can be classified into low-carbon steel, medium-carbon steel, and high-carbon steel based on its carbon content.

In CNC lathe machining, 45# steel is widely used for machining shafts, discs, and sleeves due to its good comprehensive mechanical properties. After quenching and tempering, the hardness of 45# steel can reach HRC28-32, meeting the requirements of more mechanical parts.

Recommended machining parameters: Cutting speed 180-250 m/min, feed rate 0.1-0.3 mm/r, depth of cut 1-5 mm.

• Recommended Application Areas: Shaft Parts, Gear Blanks, Bolts, Flanges

02 Alloy Steel

Typical Grades: 40Cr, 42CrMo, 20CrMnTi

Alloy steel improves its mechanical and processing properties by adding alloying elements such as chromium, molybdenum, nickel, and manganese. Compared to carbon steel, alloy steel has higher strength, hardness, and wear resistance.

40Cr is the more commonly used alloy structural steel in China. After quenching and tempering, it has good comprehensive mechanical properties and good hardenability, making it suitable for manufacturing important parts with medium cross-sections. 42CrMo, due to its good high-temperature strength and creep resistance, is often used in key parts in the automotive and aerospace industries.

When cutting alloy steel, it is recommended to use carbide cutting tools at a cutting speed of 100–180 m/min. Ensure adequate cooling to extend tool life.

• Recommended Applications: Drive shafts, crankshafts, connecting rods, high-strength bolts

03 Stainless Steel

Typical Grades: 304, 316L, 303, 430

Stainless steel is widely used in food machinery, medical devices, chemical equipment, and building decoration due to its good corrosion resistance and aesthetically pleasing surface.

Stainless steel has poor machinability, mainly manifested in high cutting forces, low thermal conductivity, and a tendency to work hardening and tool sticking. When machining 304 stainless steel, use carbide inserts with a high cobalt content (such as YG8), a cutting speed of 60–100 m/min, a feed rate of 0.08–0.15 mm/r, and sufficient cutting fluid.

316L has stronger corrosion resistance due to the presence of molybdenum and is often used in marine environments and the chemical industry, but it is more difficult to machine and requires a 15–20% reduction in cutting speed.

• Recommended Application Areas: Valves, Pumps, Medical Devices, Food Equipment Parts

04 Aluminum Alloy

Typical Grades: 6061, 7075, 2024, 6063

Aluminum alloys are the more widely used metallic materials after steel. Their density is only 1/3 that of steel, but their strength can reach the level of ordinary steel, and they have good corrosion resistance and electrical conductivity.

Aluminum alloys have good machinability, allowing for high-speed cutting. When machining 6061 aluminum alloy, cutting speeds can reach 400–1000 m/min, with feed rates of 0.1–0.5 mm/r. It is recommended to use dedicated aluminum alloy cutting tools (large rake angle, high edge sharpness), and to use water-soluble cutting fluid or dry cutting.

7075 aerospace aluminum, due to its ultra-high strength (tensile strength can reach over 500 MPa), is widely used in the aerospace field, but its machining is slightly more difficult than the 6061 series, requiring a slight reduction in cutting speed.

• Recommended Application Areas: Automotive parts, electronic casings, bicycle components

05 Copper Alloy

Typical Grades: H59, H62 brass, QSn6-6-3 tin bronze

Copper alloys include brass, bronze, cupronickel, and many other varieties. Due to their good electrical and thermal conductivity and corrosion resistance, they are widely used in the electrical, instrumentation, and shipbuilding industries.

Leaded brass (such as HPb59-1) has the good machinability among copper alloys and is known as a 'free-machining copper alloy'. Its cutting speed can reach 300–500 m/min, and the surface roughness can easily reach below Ra 0.8 μm. Lead-free brass is gradually replacing lead-containing varieties due to environmental requirements, but its machinability is slightly reduced.

When machining copper alloys, a larger rake angle (15–20°) should be used, along with a sharp cutting edge, to obtain good surface quality. Note that copper alloys are prone to built-up edge formation; it is recommended to increase the cutting speed.

• Recommended Application Areas: Conductive components, valves, bearings, precision instrument parts

06 Titanium Alloy

Typical Grades: TC4 (Ti-6Al-4V), TC11, TA2

Titanium alloys possess advantages such as low density (approximately 4.5 g/cm³), high strength, and good corrosion resistance, making them crucial materials for aerospace, medical implants, and high-end sporting goods. TC4 is the more widely used titanium alloy, combining high strength with good machinability.

Machining titanium alloys is extremely difficult, primarily due to its thermal conductivity being only 1/7 that of iron, low elastic modulus (prone to vibration), and high chemical reactivity (easily adheres to cutting tools). When machining TC4, the cutting speed should be controlled between 30 and 80 m/min, requiring the use of a large amount of high-pressure cutting fluid and the selection of fine-grained carbide cutting tools with PVD coating.

Machining Strategy: Use climb milling to reduce the cutting width and increase the depth of cut, avoiding tool dwell on the machined surface to prevent workpiece overheating.

• Recommended Application Areas: Medical Implants, Deep-Sea Equipment

07 Cast Iron

Typical Grades: HT200 Gray Cast Iron, QT600 Ductile Cast Iron, Malleable Cast Iron

Cast iron is an iron-carbon alloy with a carbon content greater than 2.11%, and is classified into gray cast iron, ductile cast iron, white cast iron, malleable cast iron, and vermicular graphite cast iron, etc. Due to its good castability, vibration damping, and wear resistance, cast iron is widely used in machine tool beds, engine blocks, etc.

When machining gray cast iron, because its graphite exists in flake form, the cutting is fragmented, making it less prone to built-up edge formation, resulting in good machinability. Cutting speeds can reach 100-200 m/min, usually dry cutting or compressed air cooling is used, avoiding the use of cutting fluid (to prevent thermal cracking).

Ductile cast iron, because its graphite is spherical, has significantly increased toughness, making it more difficult to machine than gray cast iron, similar to machining low-alloy steel. It requires appropriately reducing the cutting speed and using tool coating.

• Recommended Applications: Machine tool guideways, engine blocks and cylinder heads, brake discs, pump housings

08 Nickel-based Superalloys

Typical Grades: Inconel 718, Waspaloy, GH4169

Nickel-based superalloys maintain good mechanical properties and oxidation resistance at high temperatures, making them irreplaceable materials for high-temperature components such as turbine blades and combustion chambers in aero-engines. Inconel 718 is currently the more widely used wrought superalloy.

Machining superalloys is one of the more challenging tasks in metal cutting. They exhibit strong work hardening tendency, poor thermal conductivity, and cutting forces 2-3 times that of 45# steel, resulting in severe tool wear. When machining Inconel 718, cutting speeds are only 20-40 m/min, requiring the use of ceramic or CBN tools and high-pressure cooling (50-100 bar).

Latest Trends: Adopting new processes such as high-speed milling instead of turning and ultrasonic-assisted cutting can increase machining efficiency by 30-50% and extend tool life by 2-3 times.

• Recommended Application Areas: Nuclear power equipment, petrochemical equipment

09 Tool & Die Steel

Typical Grades: P20, H13, D2, SKD11 Tool steels are widely used in the manufacture of various molds (injection molds, die-casting molds, forging dies). Hot work tool steels (such as H13) need to operate in high-temperature and high-pressure environments, while cold work tool steels (such as D2) require extremely high wear resistance.

Hard turning/milling refers to the cutting process of materials with a hardness of HRC45 or higher, and is an effective alternative to traditional grinding. When machining HRC58 D2 mold steel, CBN inserts should be used, with a cutting speed of 100–150 m/min, a feed rate of 0.05–0.1 mm/r, a small depth of cut (0.1–0.5 mm), and dry cutting or minimal lubrication.

Advantages of hard turning: Precision machining of inner and outer diameters and end faces can be completed in a single setup, with form and position tolerances controlled within 5 μm, a surface roughness Ra of 0.4 μm, and efficiency 3–5 times higher than grinding.

• Recommended application areas: Injection molds, die-casting molds, stamping dies, tool manufacturing

10 Magnesium Alloy

Typical grades: AZ31, AZ91, ZK60

Magnesium alloys are currently the lightest metallic structural materials used in engineering applications. Their density is only 2/3 that of aluminum alloys and 1/4 that of steel, and they possess good vibration damping and electromagnetic shielding properties. Demand continues to grow in the automotive lightweighting, 3C electronics, and aerospace fields.

Magnesium alloys exhibit good machinability, low cutting force, and cutting speeds reaching 600–1000 m/min, resulting in extremely high machining efficiency. However, the greatest safety hazard associated with magnesium alloys is the flammability of the chips. Contact between magnesium chips and water or air can cause combustion or even explosion. Therefore, a dedicated cutting fluid (mineral oil-based) or dry cutting combined with high-flow-rate gas blowing must be used during machining. The use of water-based cutting fluids is strictly prohibited.

Workshop Safety Measures: Equip workshops with dry sand or dedicated metal fire extinguishers (water and CO₂ fire extinguishers are prohibited). Clean up chips promptly to prevent accumulation.

• Recommended Application Areas: Automotive transmission housings, laptop casings

Industry Trends and Technology Outlook

As the manufacturing industry accelerates its transformation towards intelligent and green manufacturing, the CNC lathe metal processing field is showing the following important development trends:

• 1. Widespread adoption of High-Speed ​​Cutting (HSC) technology: Cutting speeds for light alloy materials, such as aluminum alloys, have exceeded 1000 m/min, significantly improving machining efficiency.
• 2. Breakthroughs in machining difficult-to-machine materials: New processes such as ultrasonic vibration-assisted cutting and cryogenic cooling cutting (liquid nitrogen/CO₂) have achieved significant results in the machining of titanium alloys and high-temperature alloys.
• 3. Increased requirements for green manufacturing: Green machining solutions such as lead-free copper alloys and water-based cutting fluids replacing mineral oil are becoming mainstream choices.
• 4. AI-assisted process optimization: Automatic cutting parameter optimization systems based on big data and artificial intelligence can adjust machining strategies in real time according to batch differences in materials, significantly reducing scrap rates.
• 5. The rise of composite machining centers: Multi-process integrated machining methods such as milling-turning and additive/subtractive machining significantly reduce the number of part clamping operations and improve the machining accuracy of complex parts.