Titanium CNC Machining: Tips, Challenges, and Grades Guide

Titanium CNC machining is one of the most common machining methods. That’s because titanium is an excellent CNC machining material. It is resistant to high temperatures and chemical corrosion. In addition, it is lightweight and has a variety of other properties that make it unique and popular with manufacturers.

CNC machined titanium parts are also very durable, but can be challenging to machine due to the high tensile strength of titanium alloys.

In this article, we will provide a lot of information about titanium CNC machining, how to choose the right cutting tools to machine titanium alloys, and useful tips to ensure successful machining.

1.Why choose titanium for CNC machining parts?

The main advantages of titanium CNC machining as a manufacturing material include its excellent biocompatibility, high corrosion resistance, and the highest strength-to-weight ratio of all metals. This metal also has excellent ductility and good machinability.

Other reasons to choose titanium for CNC machining parts include:

1. Durability: Titanium has high durability and is ideal for manufacturing CNC machined parts that work in harsh or extreme working conditions.
2. Non-magnetic: This metal is not magnetic. It also has excellent oxidation resistance, so it can resist corrosion.
3. Non-toxic: Titanium is corrosion-resistant, highly biocompatible, and non-toxic, making it ideal for use in the medical industry.

These properties of titanium allow it to be used in a variety of industries, including aerospace, medical, and automotive industries.

2.Is titanium difficult to machine?

Titanium is indeed a relatively difficult material to machine. The primary reason is its poor thermal conductivity. During machining, cutting heat is easily concentrated at the contact point between the tool and the workpiece, causing a rapid temperature rise. This not only accelerates tool wear but also makes tool sticking and galling more likely. Furthermore, titanium alloys are relatively elastic, causing slight deflection under tool pressure, which can easily cause chatter and complicate machining.

Compared to aluminum, titanium is significantly more challenging. While aluminum has excellent machinability, titanium requires more rigorous tool selection and cooling methods. Machining titanium strategies are also more complex and costly than those for ordinary steels. As for Inconel, both are difficult to machine, but the challenges differ: titanium primarily challenges heat management and chip evacuation, while Inconel faces challenges due to its hardness and wear resistance. Overall, titanium alloys are valuable due to their strength-to-weight ratio and corrosion resistance, but machining them requires more effort and cost. Below is a detailed analysis of the challenges of titanium CNC machining.

3.Challenges to Consider When CNC Machining Titanium

Although CNC titanium is a high-quality material with a wide range of uses, manufacturers often encounter challenges when machining it.

These challenges include:

1) High Chemical Reactivity and Wear

When machining titanium alloys, certain gases react with titanium alloys, causing problems such as surface oxidation and embrittlement, which weaken the strength of the parts and reduce their corrosion resistance.

In addition, this metal has a low elastic modulus and high strength, so it becomes sticky when machining. Titanium metal is sticky and may adhere to CNC cutting tools, causing tool failure and damage. In addition to tool damage, wear can also damage the surface finish of titanium metal.

2) Heat Buildup and Cutting Forces

Keeping the temperature low when machining titanium alloys is one of the most difficult challenges. The reason is that titanium alloys have low thermal conductivity, which causes heat to build up in the metal workpiece where the tool moves quickly. If not dealt with, this will wear faster and can negatively affect the quality of the cut surface, especially when machining harder titanium alloys.

For these harder titanium alloys, using higher chip loads and lower rotational speeds on your CNC machine is essential. High-pressure coolant can also help your cutting tools work more efficiently and produce higher-quality titanium parts.

In addition, titanium alloys require large cutting forces, making them difficult to cut. These cutting forces often lead to tool wear, part failure, and high vibration, which can affect product quality and surface finish.

3) Residual and Hardening Stress

Due to the crystal structure of titanium alloys, they are not very flexible, which can cause problems during machining. The crystal structure of titanium alloys can increase cutting forces during machining, reduce machining difficulty, and increase the possibility of residual tension. These tensions can cause the workpiece to distort, crack, or have a shortened service life.

4.Practical Tips for Titanium CNC Machining

Due to the difficulty of titanium machining, many machine shops are reluctant to use this cutting-edge material. Yet, many manufacturers choose to use titanium to produce high-quality parts because of its superior qualities. Fortunately, skilled CNC machinists and toolmakers have developed useful tips for machining titanium.

1) Secure the Part

Anything you can do to reduce vibration will make titanium machining easier, as titanium is prone to tool chatter. To prevent workpiece deflection, secure the part.

In addition, use a top-of-the-line CNC machine with an extremely rigid tool arrangement. To minimize tool deflection, you may even consider a shorter cutting tool.

2) Choose the Right Cutting Tool

Due to the growing demand for titanium, toolmakers are developing new strategies to improve titanium machinability. Cutting tools with titanium carbonitride (TiCN) or heat-resistant titanium aluminum nitride (TiAlN) coatings can extend tool life.

Overall, machinists should select high-quality titanium-specific tools and regularly inspect and replace worn equipment. Also, consider using smaller diameter tools with more cutting edges to ensure that workpiece removal rates remain stable while limiting heat buildup.

3) Consider Cutting Parameters

Temperature control must be carefully controlled when machining titanium alloys. Applying a steady stream of high-pressure coolant to the cutting area is one of the most direct ways to keep the workpiece and tool cool. If the chips are blown away from the cutting area, they will not stick to the machining tool.

In addition, feed rate, spindle speed and chip load must be considered when machining titanium alloys. This requires limiting the pressure on the tool and equipment and avoiding staying in one place too long. Another cutting strategy, such as increasing the axial depth of cut while reducing radial engagement, may also be worth investigating to improve cutting efficiency and reduce machining temperatures.

4) Use high-pressure cooling systems to prevent overheating

Titanium CNC machining requires a very small portion of the tool radius to be in contact, very sharp, and very small feeds per tooth. However, this can cause heat that is difficult to remove from the work area. If left unchecked, it will eventually damage our cutting tools, and the thermal effects can make it challenging to maintain tolerances. Therefore, use the best possible coolant settings when cutting titanium alloys.

High-pressure cooling systems are an effective aid. The spindle may also be essential, depending on the application. Increasing the coolant concentration may also be beneficial when machining titanium alloys.

5.What are some design tips for machining titanium alloy parts?

When machining titanium alloy, due to its inherent properties, extra attention must be paid during the design phase to ensure smooth and hassle-free machining. Specifically, you can:

Avoid thin walls:

Titanium alloy has poor thermal conductivity, and thin walls can easily vibrate or deflect during machining, resulting in inaccurate dimensions. Therefore, avoid designing walls that are too thin, and add support if necessary.

Ensure smooth chip evacuation:

Cutting titanium alloy produces long, thin, and sticky chips. If not properly evacuated, they can easily accumulate on the tool or even weld to it. Design the part to create a chip channel, and use high-pressure cooling to assist with chip evacuation if necessary.

Add chamfers or radiuses:

Adding chamfers or radiuses to part edges can reduce stress concentration, lower the risk of cracks, and create a smoother surface, increasing tool durability.

Design a stable fixture:

Titanium alloy is prone to deformation, and insecure clamping can easily lead to errors. Design the fixture to securely hold the workpiece to prevent shaking during machining.

Consider tool accessibility:

When designing a part, ensure the tool can reach every machining area. Avoid excessive tool overhang, which can lead to unstable cutting.

Allow machining allowance:

Titanium alloys are susceptible to deformation due to heat. Therefore, allowing some machining allowance during design will help maintain dimensional accuracy during subsequent finishing.

Simply put, minimize thin walls, increase chamfers, ensure smooth chip evacuation, maintain stable clamping, and maintain appropriate tool parameters. Allowing some allowance will ensure a smoother machining process for titanium alloy parts.

6.Different Stages of Titanium CNC Machining

Titanium CNC machining is a delicate and technically demanding process, generally divided into seven key stages, each with its own core focus and corresponding technical means:

1) Pre-processing Stage

Before machining, stress relief treatment of titanium alloys is crucial. This reduces stresses within the material caused by forging or heat treatment, minimizing machining distortion and improving machinability and stability. Some high-precision parts may also undergo annealing or heat treatment to achieve a more uniform hardness, laying a good foundation for subsequent machining.

2) Material Selection and Workpiece Clamping Stage

Selecting the appropriate titanium alloy grade and ensuring the workpiece is securely fixed to the machine tool are essential for machining stability. Fixture design can utilize multi-point support, vacuum suction, or custom fixtures to prevent workpiece movement or deflection during cutting, thereby improving machining accuracy.

3) Tool Selection and Coating Stage

Tool selection focuses on high-temperature resistance, wear resistance, and compatibility with the characteristics of titanium alloys. Common carbide tools with TiAlN or TiCN coatings can significantly extend tool life. Tool geometry is also important, such as appropriate rake and helix angles, which help optimize chip evacuation and reduce cutting forces in subsequent cuts.

4) Roughing Stage

The primary goal of roughing is to quickly remove large amounts of material while controlling cutting heat and tool load. Trochoidal milling or plunge milling are common techniques that maintain low radial engagement and reduce tool force peaks. A stable toolpath and adequate coolant flow are also crucial to minimize heat concentrations and prevent premature tool wear.

5) Semi-finishing Stage

The semi-finishing stage focuses on dimensional tolerances and surface quality while preparing for finishing. Common techniques include contour milling, machining with small tool diameters, and optimizing toolpaths to ensure smooth chip evacuation, minimize heat buildup, and maintain surface integrity. Speed ​​and depth of cut require careful control to reduce cutting loads.

6) Finishing Stage

Finishing is a critical stage for achieving high precision and smooth surfaces. Common techniques include climb milling, contour milling, and micro milling, all using low depths of cut and moderate cutting speeds. High-pressure coolant or gas cooling effectively controls tool temperature, preventing tool wear while ensuring the required part surface quality.

7) Post-machining Stages

After machining, deburring, polishing, surface treatment, and inspection are required. For aerospace or medical parts, non-destructive testing may also be performed to ensure that the parts meet strict standards for dimensions, surface finish, and safety.

Through the strategic arrangement of these seven stages, titanium CNC machining effectively addresses the challenges of heat concentration, tool wear, and chip handling, while ensuring part accuracy and surface quality. Each stage has a clear focus, making the machining process both systematic and efficient.

7.Different Titanium Alloy Grades for CNC Machining

There are various grades of titanium and titanium alloys, each with its ideal uses, advantages, and disadvantages. Let’s look at these grades in detail.

1) Grade 1 (Pure Titanium, Low Oxygen Content)

Of the most commonly used types of titanium alloys, this titanium alloy is the softest and most ductile. Grade 1 titanium alloys have excellent machinability, impact toughness, corrosion resistance, and formability.

On the downside, it has lower strength compared to other grades of titanium alloys. This grade of titanium alloy is suitable for medical, automotive, and aerospace industries.

2) Grade 2 (Pure Titanium, Standard Oxygen Content)

This is also known as workhorse titanium. It has high corrosion resistance, strength, formability, weldability, ductility, and low strength. Grade 2 titanium can be used in the medical and aerospace industries for the production of aircraft engines.

3) Grade 3 (Pure Titanium, Moderate Oxygen Content)

While this titanium is less commercially popular than Grades 1 and 2, it has good mechanical properties. It has high corrosion resistance as well as machinability and strength. It is used in the medical, marine, and aerospace industries.

4) Grade 4 (Pure Titanium, High Oxygen Content)

This grade of titanium has high strength and corrosion resistance. However, it is not easily machined and usually requires large amounts of coolant and feed rates. Grade 4 titanium can be used in cryogenic vessels, CPI equipment, airframe components, heat exchangers, etc.

Grades 1-4 above are all pure titanium, and the next section describes different grades of titanium alloys.

5) Grade 5 (Ti6Al4V)

Grade 5 titanium alloy contains 4% vanadium and 6% aluminum. It is not as strong as the other alloys, but has high corrosion resistance and formability. It is ideal for power generation, offshore and marine applications, and critical airframe structures.

6) Grade 6 (Ti 5 Al-2.5Sn)

This titanium alloy has good stability, strength, and weldability, especially at high temperatures, and can be used in the production of airframes and jet engines.

7) Grade 7 (Ti-0.15Pd)

This grade of titanium alloy is similar to Grade 2, the only difference being the addition of palladium to improve its corrosion resistance. Grade 7 titanium alloy has excellent formability and weldability. It is well suited for the production of chemical processing equipment.

8) Grade 11 (Ti-0.15Pd)

Grade 11 titanium is very similar to Grade 7. However, it is more ductile and less tolerant of other impurities. It is weaker than Grade 7 and can be used in the marine and chlorate manufacturing industries.

9) Grade 12 (Ti0.3Mo0.8Ni)

Grade 12 titanium alloy is expensive, has 0.8% nickel and 0.3% molybdenum, and has excellent weldability, high temperature strength, and corrosion resistance. It can be used for housings and heat exchangers, marine and aircraft parts, etc.

10) Grade 23 (T6Al4V-ELI)

Grade 23 titanium alloy, also known as ultra-low interstitial titanium alloy or TAV-EIL, has similar properties to grade 5 titanium alloy, but is purer. Grade 23 titanium alloy has good fracture toughness and biocompatibility, but relatively poor machinability. Grade 23 titanium alloy can be used to produce orthopedic pins, screws, surgical nails and orthodontic appliances.

8.How to choose the right titanium CNC machining tool?

It is usually a bad idea to use any cutting tool when machining titanium alloy with CNC. Here is how to choose the right cutting tool for milling titanium alloy or using other CNC machining techniques.

1) Consider the number of cutting edges of the cutting tool

You must increase the number of cutting edges of the end mill to shorten the product processing cycle. For titanium alloys, the more teeth there are, the less chatter. For example, a 10-flute end mill, while suitable for chip loads in most materials, is very suitable for titanium alloys. This is mainly due to the need to reduce radial engagement.

2) Avoid interrupted cuts and keep the cutting edge sharp

Due to its low Young’s modulus, titanium is both strong and resilient. This means that in order to efficiently and frictionlessly remove chips from the surface, we need a sharp tool.

Avoid interrupted cuts whenever possible, as they can hammer chips into a sharp tool, which can cause premature tool failure.

3) Consider cutting tool coatings

Coatings can greatly improve a tool’s ability to withstand the heat generated by titanium. TiAlN (titanium aluminum nitride) is a suitable coating to consider. It has lubricity and resists built-up edge, galling, and chip welding, and is particularly suited to the temperatures during machining.

4) Try high-feed milling cutters when CNC machining titanium

High-feed milling cutters are suitable for maintaining low engagement when machining titanium alloys in both the axial and radial directions. These tools are built to perform this task effectively.

9.Surface treatment of titanium CNC machined parts

A range of surface treatment techniques, including titanium polishing, can enhance the functionality and aesthetics of CNC machined titanium products.

These surface treatments include:

1. Polishing
2. Anodizing
3. Chrome Plating
4. Powder Coating
5. PVD Coating
6. Brushing

10.Applications of Titanium CNC Machining Parts

Titanium machined parts are durable, corrosion resistant, and aesthetically pleasing. These properties make them suitable for a variety of industries.

1) Marine/Navy Industry

Titanium has a higher corrosion resistance than most natural metals. This corrosion resistance makes it an ideal material for the production of propeller shafts, underwater robots, rigging equipment, ball valves, marine heat exchangers, fire protection system pipes, pumps, exhaust pipe bushings, and shipboard cooling systems.

2) Aerospace

Titanium is a highly sought-after material in the aerospace industry due to its many excellent properties. These properties include a high strength-to-weight ratio, excellent corrosion resistance, and the ability to survive extreme heat environments.

Titanium parts in the aerospace industry include seat components, turbine components, shafts, valves, housing and filter components, and oxygen generation system components.

3) Automotive

In the automotive field, the titanium vs. aluminum debate has been raging, with aluminum having the upper hand due to its availability and cost-effectiveness. Despite this, titanium is still used in the production of automotive parts.

The main uses of titanium and its alloys in the automotive sector are in the production of valves for internal combustion engines, valve springs, retainers, automotive fender brackets, suspension nuts, engine piston pins, suspension springs, brake caliper pistons, engine rocker arms and connecting rods.

4) Medical and Dental

Titanium has a variety of applications in the medical industry due to its high corrosion resistance, low electrical conductivity and physiological pH.

Titanium parts used in the medical industry include tapered, straight or self-tapping bone screws, dental implant screws, skull screws for cranial fixation systems, spinal fixation rods, connectors and plates, orthopedic pins, etc.

11.Conclusion

Titanium and its alloys require careful processing to achieve optimal part production. It is a very different metal from similar metals such as steel and aluminum. It requires the use of the right tools, expertise and patience.

Choose Xavier as your titanium alloy parts machining partner

Xavier is a professional CNC machining company specializing in a wide range of titanium alloy parts. We provide high-precision, high-quality titanium CNC machining services at competitive prices for a wide range of industries. Leveraging advanced five-axis machining equipment and precision machine tools, our team of engineers can quickly respond to customer needs and efficiently handle a wide range of orders, from prototypes to small batches and large-scale production.

FAQ:

Is titanium alloy more difficult to machine than aluminum?

Yes, titanium alloy machining is significantly more challenging than aluminum. This is because titanium has low thermal conductivity, which means heat easily accumulates at the cutting edge during machining, causing accelerated tool wear. Therefore, machining titanium alloys typically requires specialized tools with high-temperature coatings, reduced spindle speeds, and high-pressure coolant to control temperature. Aluminum, on the other hand, dissipates heat better, allowing for high-speed machining with conventional tools, resulting in higher efficiency.

Is titanium alloy more difficult to machine than Inconel?

Both are difficult to machine, but the challenges differ. Titanium alloys easily accumulate heat and require controlled cooling; Inconel is very hard, especially at high temperatures, causing severe tool wear, requiring exceptionally wear-resistant and high-temperature-resistant tools. In short, each material requires a suitable machining strategy based on its specific alloy composition and application.

Is titanium alloy more difficult to machine than steel?

Both titanium alloys and steel have their own machining challenges. Titanium alloys tend to accumulate heat in the cutting zone, causing rapid tool wear during machining. While steel has better thermal conductivity than titanium, cutting certain high-hardness steels also causes significant tool wear, and the high cutting forces can easily cause deformation.

What is the feed rate when milling titanium alloys?

Generally, the cutting speed for titanium alloy inserts ranges from 40–150 m/min, with a feed per tooth of 0.03–0.15 mm. Specific parameters need to be adjusted based on the machine tool, tool, and workpiece size.

How can titanium alloys be stress-relieved?

Heat treatment can be used to relieve stress while maintaining titanium’s ductility and strength. A common method is to heat the forging to 595–705°C (1100–1300°F) for 1–2 hours, followed by natural air cooling.