Considerations for choosing the material of end mills

The selection of the material for end mills requires a comprehensive consideration of processing requirements, material properties, and cost-effectiveness. The following are the key decision-making factors and their application logic analysis:

First, the compatibility of the material properties of the workpiece

Hardness of metallic materials

Low-hardness materials (≤HRC30) : such as aluminum alloys, copper alloys, cast iron, etc. Common high-speed steel (such as M2) can meet the requirements, which is low in cost and easy to grind. For example, when processing 6061 aluminum alloy, the M2 high-speed steel end mill can work stably at a cutting speed of 20m/min, and the surface roughness can reach Ra0.8μm.

High-hardness materials (HRC40-65) : Hard alloy (such as WC substrate +Co binder) or CBN coated tools should be used. For example, when processing quenched steel (HRC50), ultrafine-grained cemented carbide (such as PVD-TiAlN coating) can withstand a high temperature of 800℃, and the tool life is more than 10 times longer than that of high-speed steel.

For difficult-to-machine materials such as titanium alloys and high-temperature alloys, hard alloys with high tantalum/niobium content (such as K20 grade) or ceramic-coated tools should be selected. For instance, when processing TC4 titanium alloy, using Si₃N₄ ceramic-coated end mills can achieve a cutting speed of up to 80m/min, and the tool life is 50% longer than that of cemented carbide.

Material viscosity and thermal conductivity

Viscous materials (such as stainless steel, pure nickel) : Low-friction coated tools are required. For instance, AlCrN coating can reduce the coefficient of friction to below 0.3 and minimize the adhesion of chips. For instance, when processing 316L stainless steel, the built-up edge formation rate of AlCrN-coated end mills is reduced by 70%, and the processing efficiency is increased by 40%.

Low thermal conductivity materials (such as titanium alloys and Hastelloy) : High thermal stability coatings are required, such as nano-multilayer TiAlN/TiSiN composite coatings. Their thermal diffusion coefficient is 30% higher than that of ordinary coatings, which can prevent tool softening caused by concentrated cutting heat.

Second, the matching degree of processing technology requirements

Cutting parameter requirements

Low-speed heavy-load (≤30m/min) : High-speed steel end mills are more suitable due to their high toughness. For instance, in the mold roughening process, the M42 high-speed steel end mill (containing 8% cobalt) can withstand a cutting depth of 0.5mm per tooth, and its anti-chipping performance is superior to that of cemented carbide.

High speed and high efficiency (≥50m/min) : Cemented carbide or CBN tools are the mainstream choices. For example, in the processing of aviation aluminum alloys, the material removal rate of PVD-TiAlN-coated carbide end mills reaches 150cm³/min at a cutting speed of 120m/min, which is 10 times higher than that of high-speed steel.

Machining accuracy and surface quality

Precision machining (Ra≤0.4μm) : Ultrafine-grained cemented carbide (such as sub-micron WC grains) or diamond-coated tools are required. For instance, in optical mold processing, when CVD diamond-coated end mills are used, the surface roughness can reach Ra0.1μm, and the tool wear rate is only 1/20 of that of cemented carbide.

Three-dimensional complex curved surfaces: A combination of high-rigidity substrates and low-friction coatings is required. For example, when processing aero-engine blades, solid carbide + PVD-Altin-coated end mills are adopted. During helical interpolation machining, the tool deflection is controlled within 0.01mm, and the profile accuracy meets IT5 grade.

Third, balance the tool life and cost

Single-piece processing cost

Mass production: Hard alloy or CBN tools reduce the cost per piece by extending their lifespan. For example, in the processing of automotive engine blocks, PVD-TiAlN-coated carbide end mills are adopted. A single tool can process 5,000 pieces, and the cost of a single tool is 60% lower than that of high-speed steel.

Small-batch and multi-variety: High-speed steel end mills have a cost advantage due to their ability to be reground multiple times. For instance, in mold repair, a single M2 high-speed steel end mill can still meet the Ra1.6μm requirement after three regrinding operations, and the total usage cost is only one-third of that of cemented carbide.

Tool failure modes and costs

Chipping failure is dominant: a high-toughness matrix is required (such as cobalt-containing high-speed steel or gradient structure cemented carbide). For example, when processing quenched gears, using K10 carbide end mills containing 6% cobalt, the anti-chipping performance is improved by 40% compared with ordinary K10, and the tool life is extended to 2,000 pieces.

Wear failure is dominant: High-hardness coatings (such as CBN or nanostructured coatings) are required. For instance, when processing the blanks of cemented carbide tools, the use of CBN end mills can extend the tool life to 500 meters, which is 20 times longer than that of cemented carbide, and reduce the amortized cost per piece of tool by 85%.

Fourth, adaptability to special environments

High-temperature processing environment

Dry cutting: It requires an oxidation-resistant coating (such as TiAlSiN or CrAlSiN), and its oxidation temperature can reach 1100℃. For instance, when dry machining superalloys, Cralsin-coated end mills maintain hardness at 900 ° C, and their tool life is only 15% less than that of wet machining.

High-speed intermittent cutting: High thermal shock resistance coatings (such as multi-layer gradient coatings) are required. For example, when processing the planetary carrier of a wind power gearbox, the use of TiN/TiCN/Al₂O₃/TiN multi-layer coated end mills has increased the thermal shock resistance by 50% and reduced the tooth breakage rate to less than 0.5%.

Corrosive environment

Acidic/alkaline media: Corrosion-resistant coatings (such as DLC or AlCrN/Si₃N₄ composite coatings) are required. For instance, when processing sulfur-containing stainless steel, the corrosion resistance of AlCrN/Si₃N₄ composite coated end mills is three times higher than that of ordinary AlCrN, and the tool life is extended to 800 pieces.

Cutting fluid contamination: Hydrophobic coatings (such as fluorocarbon-based coatings) are required. For instance, when processing aluminum alloys, using end mills with fluorine-containing hydrophobic coatings can reduce the adhesion of impurities in the cutting fluid and lower the tool wear rate by 30%.