The Basics of CNC Machining Titanium

With its excellent strength-to-weight ratio and corrosion resistance, titanium is one of the most commonly used and sought-after metals by industrial engineers, architects, and consumer product designers. Titanium was named after the Titans of ancient Greek mythology, and it often lives up to its name.

Titanium has desirable material properties, and it’s also relatively easy to machine. Titanium can be welded (in an inert atmosphere) and can be CNC machined just like stainless steel. It also lends itself to nearly every surface treatment: sandblasting, powder coating, and electrophoresis all produce good results when applied to titanium. Of course, there are metals that are more machineable than titanium, but titanium has good formability and mechanical properties.

That being said, designing and manufacturing titanium parts isn’t always the same as aluminum parts or parts made from lower-cost materials. With titanium billets costing about 10 times more than 6061 aluminum, you want to make sure you get your parts right the first time. This post discusses the basics of CNC machining titanium, including the most appropriate applications, machining considerations, and surface finish options.

1.What is titanium?

Titanium is a lustrous transition metal that was discovered in England in the 18th century. It has a silvery appearance and, despite its low density, is extremely strong. This makes it a valuable commodity in industries where lightweighting is particularly important. In addition to its good strength-to-weight ratio, titanium is highly resistant to corrosion (seawater, chlorine, and acids) and is not toxic even when used in large quantities. This makes it particularly useful in the medical field, where it can be used in implants and other medical devices. In manufacturing, titanium is often alloyed with elements such as iron, aluminum, and vanadium.

2.Why Use Titanium?

Despite its high price, titanium is a very popular material. Reasons to use titanium include:

1. High strength
2. Corrosion resistance
3. Good strength-to-weight ratio
4. Ductility
5. Good machinability
6. Surface treatment options
7. Recyclable

For these reasons, titanium is often used in industries such as aerospace, automotive, and medical. Titanium aerospace CNC machining includes aircraft engine parts, fuselage components, rotors, and compressor blades. In fact, aerospace drives titanium production: two-thirds of the titanium produced in the world is used in aircraft engines and fuselages. In the medical field, titanium alloy parts include surgical implants (such as long-term hip replacements) and instruments. The metal is also used to make items such as wheelchairs and crutches.

3.Why CNC Machine Titanium?

For the most accurate and affordable titanium parts, CNC machining is almost always the best manufacturing technique. To understand why, let’s look at the alternatives.

Manufacturers rarely cast titanium parts. This is because heated titanium reacts violently with oxygen, which is present in trace amounts in many of the refractory materials used for casting. One solution is to use stamped graphite casting—using oxygen-free graphite castings—but this produces parts with very rough surface textures and is unsuitable for most medical, aerospace, and industrial applications. Titanium parts can also be made using lost wax casting, but this requires a vacuum chamber. A newer option is to use additive manufacturing to create titanium parts. A handful of 3D printing technologies, such as selective laser melting (SLM), electron beam melting (EBM), and direct energy deposition (DED), can process titanium 3D printing materials. However, these 3D printing systems are very expensive, and many industries have not yet certified 3D printed titanium for safety-critical end-use parts.

Compared to other methods, CNC machining is a precise, safe, versatile and affordable way to manufacture titanium parts.

4.Things to consider when machining titanium alloys

Titanium is an excellent material for many applications, but it has its own unique characteristics that must be taken care of during CNC machining. Things to consider when machining titanium include:

①Heat buildup

Titanium alloys are harder than common CNC machining and milling materials such as aluminum alloys. This leads to increased tool wear and increased heat buildup at the contact point. For these harder titanium alloys, it may be necessary to reduce the speed of the CNC machine while using a larger chip load. High-pressure coolant can also reduce the burden on the cutting tool and help produce higher-quality titanium alloy parts.

Some commercially pure titanium (grade 1-2) may be less prone to excessive heat generation, but precautions should still be taken.

②Scratching

Compared with titanium alloys, industrial pure titanium has more prominent problems with undercutting and built-up edge. Grade 1-2 titanium alloys may become sticky during machining and eventually stick to the cutting tool. However, this can be alleviated by using high-pressure coolant and ensuring fast chip evacuation. If this problem is not solved, it will also aggravate the problem of heat accumulation and accelerate the dulling of cutting tools.

③ Workpiece clamping

Titanium and its machinable alloys are not as rigid as other common metals, so they need to be held tightly during CNC machining. In addition to a rigid machine setup, it is also beneficial to maintain constant tool movement without interrupting the cut.

5.Surface treatment after titanium alloy machining

CNC machined titanium parts can be improved by various surface treatments to meet functional or aesthetic purposes. Surface treatments include:

1. Smoothing
2. Polishing
3. Sandblasting
4. Brushing
5. Painting
6. Chrome plating
7. Metallization
8. PVD coating
9. Powder coating
10. Electrophoresis