The aerospace industry is the primary consumer sector for titanium alloys. Although titanium alloy products possess excellent performance, they are generally quite expensive. There are multiple reasons for the high price of titanium alloy parts, among which the high cost of machining is a significant factor. The high cost of titanium CNC machining is caused by its high friction and severe tool wear during cutting. The machining speed for titanium is 50% lower than that for steel, making its manufacturing cost higher.
Types and Properties of Titanium and Its Alloys
Titanium alloys can be classified into α-phase titanium alloys, β-phase titanium alloys, and α+ β-phase titanium alloys. Among the three, α-titanium alloys have the best machinability; α+ β alloys rank second; and β-titanium alloys are the worst. Regarding physical and mechanical properties, α-titanium alloys have moderate strength and toughness, good weldability, strong oxidation resistance, and relatively high creep strength. β-titanium alloys have strong heat treatment reinforcement capabilities, as well as good forgeability and cold forming performance. α+ β titanium alloys possess better strength and toughness than α-titanium alloys, can be strengthened via heat treatment, are weldable, and exhibit good fatigue performance.
| Types | Example Grades |
| α-phase titanium alloy | Commercially pure titanium. Grade 1,2,3,4 |
| β-phase titanium alloy | Ti-6Al-4V, Ti-550, Ti-6-2-4-6 |
| α+ β-phase titanium alloy | Ti-15V-3Cr-35n, Ti-10V-3Fe-3Al |
Titanium resembles steel in appearance, being silver-gray and lustrous. The main properties of titanium alloys are as follows:
High Strength-to-Density Ratio
Commonly used α+ β type titanium alloys have a strength of 1010–1177 MPa and a density of 4.5 g/cm³, whereas alloy steel typically reaches a strength of 1275–1569 MPa with a density of 7.9 g/cm³. The specific strength of titanium alloys is far greater than that of other metal structural materials, allowing for the manufacture of components with high unit strength, good rigidity, and low weight.
High Thermal Strength
Titanium alloys have good thermal stability and high-temperature strength. At 300–500°C, their strength is approximately 10 times higher than that of aluminum alloys, and working temperatures can reach 500°C. The commonly used Ti6Al4V titanium alloy can operate for long periods at 350°C.
Good Corrosion Resistance
When working in humid atmospheres and seawater media, the corrosion resistance of titanium alloys is superior to that of stainless steel. They have strong resistance to pitting, acid corrosion, and stress corrosion; their resistance to alkali, chlorides, organic chlorine substances, nitric acid, and sulfuric acid is excellent, which is 15 times that of ordinary stainless steel.
Poor Thermal Conductivity
The thermal conductivity of titanium is very low, at 15.24 W/(m·K), which is about 1/4 of nickel, 1/5 of iron, and 1/14 of aluminum. The thermal conductivity of various titanium alloys is even lower, generally about 50% of that of pure titanium.
Low Elastic Modulus
For example, the elastic modulus of titanium Ti6Al4V is 110 GPa, which is about 1/2 that of steel, making titanium alloys prone to elastic deformation.
Additionally, titanium alloy materials possess characteristics such as high hardness, high melting point up to 1672°C, non-toxicity, and non-magnetism. Apart from the advantages of high specific strength, heat resistance, and corrosion resistance, titanium alloys are also compatible with carbon fiber reinforced polymer (CFRP) materials. The strength and stiffness of titanium match well with composites, achieving excellent weight reduction effects. Furthermore, because their electrochemical potentials are relatively close, galvanic corrosion is unlikely to occur.
Impact of Physical and Chemical Properties on Machining
The physical and chemical properties of titanium alloys have a significant impact on their machinability. Regarding thermal conductivity, titanium Ti6Al4V has a thermal conductivity of only 16.7 W/(m·K), which is 1/3 lower than that of No. 45 steel (54 W/(m·K)). During the cutting process, it is difficult for the cutting heat to dissipate through conduction within the material. Approximately 85% of the cutting heat concentrates in the tool-chip contact zone, causing excessive local temperature rise. Infrared thermal imaging monitoring of the titanium alloy turning process reveals that at a cutting speed of 50 m/min, the rake face temperature reaches as high as 980°C. In this high-temperature environment, tool hardness drops significantly, aggravating diffusion wear and adhesive wear. Simultaneously, titanium alloys possess very high high-temperature chemical activity. When the cutting temperature exceeds 600°C, the material reacts rapidly with oxygen and nitrogen in the air to form hard, brittle compounds such as TiO and TiN. These compounds not only alter the tool’s surface morphology but may also form micro-cracks on the tool surface, thereby accelerating tool failure.
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Impact of Mechanical Properties on Machining
The mechanical properties of titanium alloy present new challenges for machining. Its strength ranges from 900 to 1200 MPa, with a yield strength greater than 800 MPa; this high resistance to deformation greatly increases the cutting force. In titanium alloy turning experiments, under conditions of a cutting speed of 40 m/min, a feed rate of 0.15 mm/r, and a depth of cut of 0.8 mm, a main cutting force of 850 N was observed—approximately 1.8 times that of turning No. 45 steel under the same conditions. High cutting forces not only require higher machine tool rigidity but also easily cause excessive stress on the tool and tool failure. Titanium alloys have high hardness (30–40 HRC) and low plasticity, making them extremely prone to producing serrated chips during cutting. High-speed photography observations show that during the formation of serrated chips, cutting force fluctuation amplitudes reach 30%–50%, leading to vibration in the cutting system and producing chatter marks. This causes the surface roughness (Ra) to rise from a steady-state 1.2 μm to 2.5 μm.
Titanium CNC Machining Processes
CNC Turning
Process optimization for titanium alloy turning tools should be comprehensively considered from three aspects: geometric parameter design, material selection, and actual application effects. Regarding geometric parameters, the rake angle is generally 6°–8°, which ensures both edge sharpness and edge strength. A clearance angle of 8°–10° is recommended to reduce friction on the flank face effectively. The inclination angle should be negative, between -5° and 0°, which is particularly suitable for interrupted cutting. The nose radius should be controlled between 0.4 and 0.8 mm, which not only improves tool tip strength but also avoids vibration caused by an excessively large radius.
In terms of tool selection, using YG8, YG6X, or other ultra-fine grain carbides (0.5–1 μm) as a substrate, combined with TiAlN or AlCrN composite coatings, can significantly improve the tool’s high-temperature resistance. In structural design, reinforced chip breakers and double-sided edge designs have become mainstream. International renowned brands, such as Sandvik’s CoroTurn® 107 series, Kennametal’s Kyon® 2100 series, Iscar’s HELITURN® HTP series, and Mitsubishi Materials’ VP15TF series, are all specialized products developed for titanium machining to meet different requirements from roughing to finishing.
Actual machining parameters need to be adjusted according to the specific operation characteristics, as shown in Table 1.
Table 1. Typical machining parameter configuration
| Machining Type | Cutting Speed (m/min) | Feed Rate (mm/r) | Depth of Cut (mm) | Recommended Tool |
| Roughing | 40~60 | 0.15~0.25 | 1.5~2.5 | Sandvik |
| Finishing | 80~120 | 0.05~0.1 | 0.2~0.5 | Kennametal |
Practical data indicate that the service life of optimized tools increased from the original 15 minutes to 90 minutes, surface roughness improved by 50%, and per-unit cost decreased by 40%. Systematically selecting tools and optimizing process parameters can not only significantly improve machining efficiency and quality but also effectively reduce manufacturing costs, holding significant application value in aerospace and other high-end manufacturing industries.
CNC Milling
When milling titanium alloys, tool selection and optimizing process parameters are crucial. Geometric parameter design must address the following key issues: First, adopt a large helix angle structure of 30°–45°; this can drastically improve chip evacuation efficiency while reducing cutting force by 15%–20%, effectively lowering cutting vibration. Second, the rake angle should be controlled at 6°–10° using a positive rake design, and the clearance angle at 8°–12° to minimize wear on the flank face. To improve edge strength, it is recommended to use a T-land width of 0.1–0.15 mm and a corner radius of 0.4–0.8 mm.
The following core principles should be followed when selecting tools: For material, use ultra-fine grain carbide with a grain size of 0.5–0.8 μm as the substrate, paired with high-performance TiAlN or AlCrN coatings. In structural design, use an unequal pitch design to reduce machining vibration and increase chip flute volume by 20%–30% to improve chip evacuation efficiency. All tools must meet aerospace-grade precision standards.
Currently, major global tool brands provide professional CNC machining solutions for titanium alloys. Sandvik’s CoroMill® Plura series (e.g., Plura HFS 4F) features a 45° helix angle and TiAlN coating, making it particularly suitable for high-efficiency milling of titanium alloy structural parts. Kennametal’s HARVI™ Ultra 8X (e.g., KU40T) employs a variable helix design with AlCrN coating, making it suitable for machining complex cavities in aerospace applications. Mitsubishi MWS end mills (e.g., VQX4 type) use CBN coating, possessing ultra-high hardness suitable for high-precision impeller machining.
Excellent results have been achieved in practical applications. An airline adopted this scheme to machine TC4 titanium alloy structural parts, resulting in a 200% increase in tool life (from 15 to 45 parts), surface roughness stabilizing at Ra 0.4–0.6 μm, and a 40% increase in machining efficiency. These improvements not only greatly reduced production costs but also significantly improved product quality.
Recommended parameter configurations differ according to different machining types, as shown in Table 2.
Table 2. Typical machining parameter configuration
| Machining Type | Tool Model | Cutting Speed (m/min) | Feed per Tooth (mm/z) | Axial Depth (mm) |
| Roughing | Plura HFS | 40~60 | 0.08~0.12 | 1.5~2.0 |
| Semi-finishing | HARVI KU40T | 60~80 | 0.06~0.08 | 1.0~1.5 |
| Finishing | MWS VQX4 | 80~100 | 0.04~0.06 | 0.2~0.5 |
CNC Drilling
When optimizing the process for titanium alloy drilling tools, special attention should be paid to geometric parameters, material selection, and actual machining effects. Regarding geometric parameters, a point angle of 130°–140° is recommended to effectively reduce axial cutting force; a double point angle design (e.g., a 90° + 140° combination) can effectively improve chip evacuation. Adopting a helix angle of 25°–35° balances chip evacuation performance with rigidity; meanwhile, increasing the flute volume by more than 30% can solve the difficulty of chip evacuation in titanium alloys. The margin should be polished, with the width controlled at 0.1–0.15 mm, and a chamfer design of 15° × 0.05 mm adopted to effectively improve edge strength.
Regarding tool selection, 0.5–0.8 μm ultra-fine grain carbide is used as the substrate, supplemented by high-performance TiAlN or AlCrN coatings. In structural design, to ensure cooling effects, internal coolant holes (diameter ≥ 1.5 mm) must be considered, and a non-uniform margin design should be used to suppress machining vibration. All tools must undergo continuous drilling tests to confirm that hole precision reaches IT7 grade. Currently, the main titanium alloy specialty drills on the market include: Sandvik’s CoroDrill® 880 series (suitable for deep hole machining), Kennametal’s Beyond™ EVO series (specialized for aerospace structural parts), and Walter’s DC170 series (high-precision hole making).
Actual machining parameters need to be adjusted according to the hole diameter, as shown in Table 3.
Table 3. Typical machining parameter configuration
| Hole Range (mm) | Recommended Speed (rpm) | Feed Rate (mm/rev) | Coolant Pressure (bar) |
| Φ3~Φ6 | 800~1200 | 0.03~0.05 | 30~50 |
| Φ6~Φ10 | 600~900 | 0.05~0.08 | 50~70 |
| Φ10~Φ20 | 400~700 | 0.08~0.12 | 70~100 |
Practical application shows that the life of optimized tools increased from the original 50 holes to 140 holes, an increase of 180%, while hole diameter precision was stably controlled within ±0.02 mm, and machining efficiency increased by 35%. Research indicates that systematically selecting tools and optimizing process parameters can not only significantly improve machining efficiency and quality but also effectively extend tool service life, which is of great significance to the production costs of China’s aerospace and other high-end manufacturing industries.
About Getzshape
Getzshape delivers globally compliant, precision titanium machining service. We specialize in Ti6Al4V (TC4) and TA1, TA2 grades for aerospace, medical, and industrial needs. Leveraging advanced CNC machining and strict quality control, we ensure accuracy and on-time delivery for prototypes to large production runs. As your end-to-end titanium parts manufacturing partner, we streamline sourcing, machining, post-processing, and logistics. Count on Getzshape for reliable, cost-effective titanium solutions that exceed expectations.
