Why are CNC machining titanium alloy parts both difficult to machine and expensive?

• Why are CNC machining titanium alloy parts both difficult to machine and expensive?
  • What is a Titanium Alloy?
  • What is CNC machining of titanium alloys?
  • Characteristics of CNC Machining of Titanium Alloys
  • Properties and Parameters of General-Purpose Titanium Alloy Materials
  • Parameters, Performance, and Applications of Common Titanium Alloy Brands
  • Why are Titanium Alloy Parts Difficult to Machining?
  • Challenges of CNC Machining Titanium
  • Techniques for CNC Machining Titanium Alloy Materials
  • Common Surface Treatment Processes for Titanium Alloy CNC Parts
  • The Impact of CNC Machining of Titanium Services on Manufacturing
  • Applications of CNC Machining of Titanium Alloy Parts
  • Partner with Elimold on CNC Machining Projects of Titanium Alloys
  • Summary
  • FAQs

While titanium alloys offer excellent performance and applications, their high price and complex machining requirements limit their widespread use across various industries, except for small-scale applications in aerospace and medical fields requiring high-precision parts and products. Today, I will not only answer your questions but also delve into the complexity, challenges, and best practices of titanium machining. As a precision machining center with extensive experience in titanium alloy processing, Elimold will guide you through understanding why titanium alloys are expensive and difficult to machine.

What is a Titanium Alloy?

Titanium alloys are various alloys made from titanium and other metals. Titanium was developed as an important structural metal in the 1950s. Titanium alloys possess high strength, good corrosion resistance, and high heat resistance, making them a lightweight, strong, durable, and highly corrosion-resistant metal. Furthermore, they exhibit excellent toughness and hardness, a low coefficient of friction, wear resistance, and biocompatibility.

Titanium is typically classified into grades 1, 2, 3, 4, 7, and 11. The first 11 grades are considered pure alloys, while the next 11 grades are alloys. Due to its unparalleled hardness and strength, titanium has consistently been ranked as one of the most sought-after metal types in the world. The main titanium alloys used in CNC machining include Ti-6Al-4V and Ti-6Al-4VEli. The first is known for its exceptional strength, and the second for its biocompatibility.

Due to its low coefficient of friction and excellent wear resistance, titanium is an excellent choice for high-stress applications. Because of its high hardness and poor thermal conductivity, titanium is difficult to machine using traditional techniques, making CNC machining the optimal choice for machining titanium alloy parts.

What is CNC machining of titanium alloys?

Titanium alloys are just one of many materials that can be machined using CNC machining. The machining process is not significantly different from that of ordinary stainless steel or aluminum alloys. The main processes used in CNC machining of titanium alloy materials include turning, milling, boring, drilling, grinding, tapping, sawing, and electrical discharge machining, following the manufacturing process described below. The CNC manufacturing process is as follows:

1. Material Preparation: First, titanium raw material is prepared, the CNC machine tool is fixed, and the worktable is installed.
2. Tool Selection: Suitable cutting tools are selected to meet the machining requirements, primarily carbide or ceramic end mills, drills, and inserts. The geometry of the part to be machined is determined.
3. Tool Setup: Appropriate tools are loaded into the CNC machine tool’s tool holder, and the equivalent machining is correctly aligned before all machining operations.
4. Workpiece Setup: The CNC machine tool has a coordinate system that allows the definition of the direction of the cutting operations. This involves describing the workpiece’s coordinate system and then developing the tool relative to the CNC machine tool path.
5. Roughing: This process uses larger cutting tools moving at higher speeds and feed rates to remove excess material from the titanium blank. The roughing step continues to form the preliminary shape of the part while minimizing machining time.
6. Finishing Operations: The final dimensions and tolerances of custom parts are still the responsibility of the finishing operations, where roughing has already achieved the final dimensions. Here, they must perform contouring, profiling, and drilling operations, which require small cutting tools to achieve smaller depths using higher feed rates and slower leading-edge speeds.
7. Drilling and Tapping: Conversely, certain features, such as mounting holes and threaded inserts, can be drilled, tapped, and threaded in titanium alloy CNC parts to meet assembly requirements in this process.
8. Deburring and Surface Finishing: Deburring is the process of removing any sharp edges generated during the manufacturing process from the parts.

Characteristics of CNC Machining of Titanium Alloys

First, titanium alloys have a low thermal conductivity, only 1/4 that of steel, 1/13 that of aluminum, and 1/25 that of copper. Because titanium alloys dissipate heat slowly in the cutting zone, it is not conducive to thermal balance. During cutting, heat dissipation and cooling are poor, easily leading to high temperatures in the cutting zone. After machining, the part deforms and rebounds, resulting in increased cutting tool torque, rapid edge wear, and reduced durability. Secondly, titanium alloys have low thermal conductivity, causing cutting heat to accumulate in a small area near the tool, making it difficult to dissipate. This increases friction on the tool’s rake surface, making it more prone to chipping, and accelerates tool wear. Finally, titanium alloys have high chemical reactivity, easily reacting with tool materials during high-temperature machining, forming soluble and diffusive substances that can cause tool sticking, burning, and breakage.

Properties and Parameters of General-Purpose Titanium Alloy Materials

Property	Value
Density	4.51 g/cm³
Melting Point	1668°C
Tensile Strength	434 MPa (at room temperature)
Elastic Modulus	116 GPa

Parameters, Performance, and Applications of Common Titanium Alloy Brands

Alloy/Grade	Description	Advantages	Disadvantages	Applications
Grade 1 Commercially pure titanium with low oxygen content.	One of the most commonly used grades of titanium. It is the most ductile and the softest titanium alloy.	Excellent relative formability and machinability, corrosion resistance, and impact toughness.	Lower strength compared to the other titanium grades.	Chemical processing, desalination, medical industry, automotive parts, airframe structure.
Grade 2 Commercially pure titanium with standard oxygen content.	Pure titanium, known as the workhorse of the titanium industry.	High corrosion resistance, good weldability, strength, ductility, and formability. High relative machinability.	Not as strong as other titanium grades, but stronger than grade 1	Aircraft engines, hydrocarbon processing, chlorate manufacturing, medical industry.
Grade 3 Commercially pure titanium with medium oxygen content.	Grade 3 is the least commercially used, but it possesses good mechanical properties.	High strength and corrosion resistance. Good relative machinability.	Less formability than grades 1 and 2.	Medical industry, marine industry, aerospace structures.
Grade 4 Commercially pure titanium with high oxygen content.	Known as the strongest of the four commercially pure grades.	Very high strength and corrosion resistance. Okay relative machinability.	Hard to machine, requires slow speeds, high coolant flow, and high feed rates.	Cryogenic vessels, heat exchangers, CPI equipment, surgical hardware, airframe components.
Grade 5 Titanium alloy – Ti6Al4V	This is the most commonly used alloy of titanium. It contains 6% aluminum and 4% of vanadium.	High corrosion resistance and high formability. Poor relative machinability.	Less strong than the other alloys.	Critical airframe structures, power generation, marine & offshore applications.
Grade 6 Titanium alloy – Ti5Al-2.5Sn	The most commonly used for airframe and jet engine applications.	Good weldability, stability, and strength at elevated temperatures.	Intermediate strength for titanium alloy standards.	Airframe & jet engine applications, liquid gas & propellant containment for rockets and space vehicles.
Grade 7 Titanium alloy, sometimes considered “pure”  – Ti-0.15Pd	Similar to grade 2, but this one contains small quantities of palladium, enhancing corrosion resistance.	Extremely good corrosion resistance, excellent weldability, and formability.	Not as strong as other titanium alloys.	Chemical processing & production equipment components.
Grade 11 Titanium alloy, sometimes considered “pure”  – Ti-0.15Pd	Similar to Grade 7, but with a lower tolerance for other impurities.	Excellent corrosion resistance, optimum ductility, and formability.	Even lower strength relative to grade 7.	Marine applications, chlorate manufacturing, desalination.
Grade 12 Titanium alloy – Ti0.3Mo0.8Ni	This highly durable alloy contains 0.3% of molybdenum and 0.8% of nickel.	Great weldability, excellent strength at high temperatures, excellent corrosion resistance.	It costs more than the other alloys.	Shell and heat exchangers, hydrometallurgical applications, aircraft  & marine components.
Grade 23 Titanium alloy – T6Al4V-ELI	Also known as TAV-EIL in the market, which stands for Extra Low Interstitial. It is similar to Grade 5 but with higher purity.	Great ductility and formability, good fracture toughness. Optimum biocompatibility. Poor relative machinability.	Has a lower strength than the other Titanium Alloys.	Orthopedic pins & screws, orthopedic cables, surgical staples, orthodontic appliances.

Why are Titanium Alloy Parts Difficult to Machining?

Titanium metal parts have relatively high strength among engineering materials. Its compressive strength is comparable to stainless steel, but its weight is only 57% of stainless steel. Other advantages of titanium include a low proportion of titanium, high thermal compressive strength, thermal stability, and good corrosion resistance. The high machining difficulty of titanium parts is primarily due to titanium’s low thermal conductivity, resulting in very high cutting temperatures. Under the same conditions, the cutting temperature for machining ordinary titanium alloys is more than twice that of 45# steel, as the heat generated during machining is difficult to dissipate through the workpiece. Additionally, titanium has a low specific heat capacity, causing rapid temperature increases during machining. Consequently, the temperature of the cutting tools is very high, leading to significant tool wear and reduced lifespan.

Furthermore, titanium’s low elasticity makes the machined surface prone to springback, especially severe in thick-walled parts. This can cause significant friction between the cutting edge and the machined surface, resulting in tool damage and chipping. Titanium also has high chemical reactivity; high temperatures can cause it to react with oxygen, hydrogen, and nitrogen, increasing its strength and decreasing its plasticity. The oxygen-rich layer formed during heating and forging further complicates machining.

Challenges of CNC Machining Titanium

Titanium alloys have a low Young’s modulus. Young’s modulus is essentially the stiffness of a material. In actual CNC machining, this means that titanium is more susceptible to springback and chatter than other materials. This can lead to issues with the surface quality of the finished product and other problems. Titanium is sticky (just like aluminum is sticky and will stick to the tool). The combination of work hardening and stickiness produces long chips that get tangled in everything. These tangles make titanium machining almost impossible to fully automate, and faulty chips stuck to the cutting edge can cause tool breakage, especially when entering or exiting the cut. Titanium generates a lot of heat, but it is not a good conductor of heat. Titanium’s toughness is the main reason for its high heat generation; because it is not a good conductor of heat, the heat is difficult to dissipate. Compared to other materials, we rely more on coolant than chips for heat dissipation to avoid damaging our cutting tools. Titanium is prone to work hardening, which is caused by insufficient heat control during cutting. Titanium alloys have very high cutting pressures, meaning that the tool is strongly affected when entering or exiting the cut, and if this is not controlled, it will lead to excessive tool breakage when entering or exiting the cut.

Techniques for CNC Machining Titanium Alloy Materials

(1) Use inserts with a positive angle geometry to reduce cutting force, cutting heat, and workpiece deformation.

(2) Maintain a constant feed rate to avoid workpiece hardening. The tool should always be in the feed state during the cutting process. The radial depth of cut (a_e) during milling should be 30% of the radius.

(3) Use high-pressure, high-flow-rate cutting fluid to ensure thermal stability during machining and prevent workpiece surface deformation and tool damage due to excessive temperature.

(4) Keep the insert edges sharp. Dull tools cause heat accumulation and wear, easily leading to tool failure.

(5) Machining should be done when the titanium alloy is at its softest possible state, as hardening makes the material more difficult to machine. Heat treatment increases the material’s strength but also increases insert wear.

(6) Use a large tool tip radius or chamfered entry to bring as much of the cutting edge into the cutting area as possible. This reduces cutting force and heat at each point, preventing localized breakage. When milling titanium alloys, among the various cutting parameters, cutting speed has the greatest impact on tool life (vc), followed by radial depth of cut (ae).

(7) During machining, titanium molecules in the workpiece accumulate on the front of the cutting tool and are “welded” to the cutting edge under high pressure and high temperature, forming a built-up edge. When the built-up edge peels off from the cutting edge, it carries away the carbide coating of the cutting tool. Therefore, titanium alloy machining requires special cutting tool materials and geometries.

Common Surface Treatment Processes for Titanium Alloy CNC Parts

Every material has its advantages and disadvantages. To further improve the corrosion resistance, high-temperature oxidation resistance, wear resistance, and fretting wear resistance of titanium alloy parts, surface treatment after CNC machining is an effective way to further expand the application range of titanium alloys. Surface treatment processes for titanium alloys cover almost all current methods for metal surface treatment, including metal electroplating, chemical plating, thermal diffusion, anodizing, thermal spraying, low-pressure ion processes, electronic and laser surface alloying, unbalanced magnetron sputtering coating, ion nitriding, PVD film formation, ion plating, nanotechnology, etc. How to Select and Use the Correct Grade of Titanium

Selecting and using the correct grade of titanium depends primarily on the specific requirements of the application. Titanium is a high-strength metal with low density and excellent corrosion resistance. It is widely used in aerospace, medical, chemical, and marine engineering fields. Before selection, it is best to consult a materials expert or supplier to ensure that the selected material meets all the requirements of the specific application. Material testing may also be necessary to verify its suitability for specific application conditions. If you are unsure which grade of titanium alloy you need, please contact us.

The Impact of CNC Machining of Titanium Services on Manufacturing

CNC machining is a powerful manufacturing technology and a powerful tool that has had a significant impact on the development of manufacturing worldwide over the past few decades. As mentioned earlier, this technology can produce precise titanium parts with minimal variation in shape or size. This makes it an ideal method for producing components for applications such as aerospace, where tight tolerances are critical to product performance. Furthermore, CNC machine tools can produce multiple identical copies of parts with minimal variation in shape or size, making them ideal for production purposes where accuracy and consistency are paramount. Overall, CNC machining is a highly versatile technology that has had a significant impact on the titanium manufacturing industry in recent years.

Applications of CNC Machining of Titanium Alloy Parts

CNC machining of titanium alloy materials has wide applications in many industries. Let’s compare them in more detail.

Aerospace	Engine blades, landing gear, shafts,interior structures, compressor wheels, connectingrods, engine compartments, and many more.
Medical	The biocompatibility of Titanium makes itideal for Bone growth stimulators, spinal fusiondevices, bone plates, orthodontics, and fake bodyparts.
Marine	deck, shackles, snap hooks, pressure vesselssubmarine probes, and more.
Automotive	Frames, fasteners, mufflers, exhaustPipes, engine valves, load-bearing springs, and manymore parts.
Others	oil & gas, construction, architecture, jewelrysports, and EV.

Partner with Elimold on CNC Machining Projects of Titanium Alloys

Elimold’s team of engineers possesses a deep understanding of the complex mechanical properties of titanium alloys. Utilizing cutting-edge machining technologies and anticipating future trends, they ensure your project not only gets finished, but also achieves exquisite precision. The widespread application of titanium in the medical, aerospace, and energy sectors highlights its versatility. Elimold’s commitment to precision, quality, and sustainability perfectly aligns with the evolving needs of these dynamic industries.

Looking ahead, continuous exploration of new materials, innovation in CNC technology, and a steadfast commitment to sustainable practices will further elevate the level of CNC machining of titanium alloys. Elimold will continue to lead this transformation, not only providing CNC machining services but also striving to build strategic partnerships with you to achieve your vision. Contact Elimold today to begin your CNC machining project of titanium alloys.

Summary

The high difficulty and cost of CNC machining titanium alloy parts are primarily due to the inherently high selling price of the material itself, as well as its physical properties. These factors combined result in higher manufacturing costs quoted by manufacturers when customizing titanium alloy CNC parts. It is believed that with the continuous research and exploration of the manufacturing industry and the vast number of scientific and technological workers, our understanding of titanium alloys will gradually deepen, and more technical means will emerge for the machining of titanium alloys, which will reduce the price when manufacturing titanium alloy parts.

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