How to Choose the Right Cutting Tool Material (CNC & Lathe Guide)

In the world of CNC machining and turning, the cutting tool is the knight's sword. Choosing the right cutting tool material is one of the most crucial decisions for optimizing production efficiency, reducing costs and improving part quality. If you use the wrong tool, you will face frequent problems such as tool chipping, poor surface finish and low productivity.

This guide will take you through the main cutting tool materials and provide a clear framework to help you make the best choice based on the processing task.

Why is the material of cutting tools so important?

The cutting process generates extremely high heat and pressure. The tool material must resist:

· Wear Resistance: Prevents being worn by chips and maintains sharpness.

· Hardness: It must be harder than the material being processed, especially at high temperatures (referred to as "red hardness").

· Toughness (Toughness) : It can withstand impact and intermittent cutting forces, preventing chipping and fracture.

· Hot Hardness: The ability to maintain hardness at high temperatures generated during cutting.

No material can be perfect in all aspects. The process of selection is to find the best balance among these attributes to address specific processing challenges.

Detailed explanation of the main cutting tool materials

The following are the most commonly used types of cutting tool materials today, ranked from the most general to the most specialized.

High-Speed Steel (HSS)

What is it: It is a high-grade alloy tool steel made by adding elements such as tungsten, molybdenum, chromium and vanadium.

· Advantages: Excellent toughness, low cost, capable of manufacturing very complex tool shapes (such as drills, taps, broaches), and easy to regrind.

· Disadvantages: Poor wear resistance and thermal hardness (softening at approximately 600°C), and the cutting speed is much lower than that of cemented carbide.

· Best applications: Low-speed machining, intermittent cutting, tools with complex geometries, non-ferrous metal processing, repair workshops and small-batch production.

2. Carbide

What is it: It is sintered by powder metallurgy process with tungsten carbide (WC) particles and cobalt (Co) binder. Tungsten carbide provides hardness, while cobalt provides toughness. This is the absolute main force in modern CNC machining.

· Advantages: It has excellent wear resistance and thermal hardness (up to 1000°C), and the allowable cutting speed is more than 2-3 times that of HSS. It has extremely strong versatility.

· Disadvantages: More brittle than HSS and more expensive.

· Best application: Semi-finishing to finishing of the vast majority of materials, from steel, stainless steel to cast iron and superalloys. (Note: Cemented carbide itself is a broad category, and its performance can undergo significant changes through coating and composition adjustments.)

3. Coated Carbide

What is it: A very thin (a few micrometers) super-hard material film is deposited on a hard alloy substrate through CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition) processes.

· Common coatings:

· Titanium nitride (TiN) : Universal golden coating, enhancing wear resistance.

· Titanium nitride (TiCN) : More wear-resistant than TiN, blue or gray.

· Titanium aluminum nitride (TiAlN)/chromium aluminum nitride (AlCrN) : High-end coating. At high cutting temperatures, an alumina layer is formed, which has extremely high thermal hardness and oxidation resistance, making it highly suitable for high-speed machining and dry cutting.

· Advantages: The coating significantly enhances surface hardness, thermal barrier performance and lubricity, increasing the tool life by several times.

· Best Application: It almost covers all processing scenarios, and the choice depends on the material being processed. TiAlN is an excellent choice for processing steel and cast iron.

4. Ceramics

What is it: It is mainly divided into two categories: alumina (Al2O3) -based (used for high-speed cast iron processing) and silicon nitride (Si3N4) -based (used for high-speed rough machining of cast iron).

· Advantages: It has higher thermal hardness and wear resistance than cemented carbide, good chemical stability, and extremely high cutting speed.

· Disadvantages: Extremely brittle, poor tolerance to impact and intermittent cutting, and not suitable for viscous materials such as aluminum.

· Best application: High-speed finishing and dry cutting of cast iron and superalloys.

5. Cubic Boron Nitride (CBN)

What is it: An artificial material with a hardness second only to diamond. It is usually sold in the form of small CBN tips welded onto hard alloy inserts.

· Advantages: Extremely high hardness and thermal stability, making it highly suitable for work hardening steel and chilled cast iron.

· Disadvantages: The cost is extremely high and the toughness is average.

· Best application: Finishing of quenched steel with hardness higher than 45HRC (such as die steel, gears). It is the first choice for the "turning instead of grinding" process.

6. Polycrystalline Diamond (PCD

What is it: It is made by sintering artificial diamond particles at high temperature and high pressure, and is usually also welded onto a hard alloy substrate.

· Advantages: The hardest and most wear-resistant cutting material available today.

· Disadvantages: It is extremely expensive, very brittle, and can undergo chemical reactions with iron-based materials (steel, cast iron) (carbon will diffuse at 800°C), so it cannot be used for processing ferrous metals.

· Best application: High-speed and high-precision processing of non-ferrous metals and abrasive (abrasive) materials, such as silicon-aluminum alloys, composite materials, carbon fibers, plastics, copper and high-silicon aluminum alloys.

How to choose: Decision Flowchart and Key Factors

When choosing tool materials for your application, please think in the following order:

1. Workpiece Material to be processed (Workpiece material) - this is the primary factor!

Aluminum, copper, composite materials, etc. : PCD is the best choice for high speed, high quality and long service life. Uncoated cemented carbide is an economical choice.

· Carbon steel, alloy steel, stainless steel: Coated cemented carbide (TiAlN/AlCrN) is a universal choice. For low-speed or complex cutting tools, HSS still has its place. For quenched and hardened steel (>45HRC), CBN is selected.

· Cast iron: Coated hard alloy is very effective. For high-speed processing, ceramics are an ideal choice.

· High-temperature alloys (such as Inconel alloy, titanium alloy) : Special hard alloy grades with special tough coatings (such as AlCrN) are required. Ceramics and CBN may also be applicable.

· Non-metallic (plastic, wood, etc.) : Uncoated hard alloy or HSS is usually sufficient. For reinforced plastics with strong abrasiveness, PCD has the longest lifespan.

2. Processing Operation Type

· Rough machining vs. finish machining: Rough machining requires toughness (select a hard alloy grade with better toughness), while finish machining prioritizes wear resistance and hardness (choose a harder grade or CBN/PCD).

· Continuous cutting vs. Intermittent cutting: Milling is usually intermittent and requires high toughness (hard alloy or HSS). Turning the outer circle is usually continuous and can use harder and more brittle materials (such as ceramics).

3. Machine Tools & Setup

Old machine tools or Settings with insufficient rigidity are prone to vibration and require tools with better toughness (such as tough cemented carbide or HSS).

Modern high-speed and high-rigidity CNC machine tools can fully leverage the performance of ceramics and coated cemented carbides.

4. Cost Considerations

· Initial cost vs. unit cost: Although CBN and PCD blades are very expensive, in mass production, due to their extremely long service life and extremely high processing efficiency, they can significantly reduce the processing cost of each part.

· Small-batch, prototyping: Coated cemented carbide offers the best versatility and value balance. HSS remains cost-effective for extremely complex shapes or very small amounts of work.