What is titanium alloy?

The types of titanium alloys are roughly divided into three categories: alpha titanium alloys, beta titanium alloys, and alpha + beta titanium alloys.

Currently, the most widely used titanium alloy specification is TC4 (Ti-6AI-4V), which is a titanium alloy with an α+β phase structure. Ti-6Al-4V titanium alloy, as an important component of titanium alloy TC4 materials, has won wide applications due to its excellent comprehensive mechanical and mechanical properties. Its high strength and moderate density give it significant advantages in various engineering applications.

What are the properties of titanium alloy?

①. The strength and density of titanium alloy are much higher than that of alloy steel, and it has excellent strength and lightweight properties.

②. Titanium alloy has low thermal conductivity, giving it good thermal insulation properties.

③. Titanium alloy has a low elastic modulus and is prone to deformation during processing.

Titanium alloy has good corrosion resistance, but titanium has poor corrosion resistance to oxidizing oxygen and chromium salt media.

Applications of titanium alloys:

TC4 titanium alloy has a series of advantages such as excellent corrosion resistance, small density, high specific strength, good toughness and weldability, and has been successfully used in aerospace, petrochemical, shipbuilding, automobile, medicine and other sectors. . The most representative one is the aerospace field. In the automotive industry, parts such as engine valves/connecting rods and exhaust systems made of titanium alloys are of great significance to weight reduction of the car body and engine noise reduction. Thanks to its outstanding biocompatibility, titanium alloys have also become the metal material of choice for human implants and bone repair.

Main problems in titanium alloy cutting/grinding processing:

✳ High cutting/grinding temperature

✳ The workpiece material has large elastic deformation

✳ Tool adhesion is serious

✳ The workpiece is prone to burns, deformation and cracks

So, how to choose tools for grinding, grinding and polishing titanium alloy?

1. Cutting titanium alloy

Rapid tool wear caused by high cutting temperatures is the main problem in the titanium alloy cutting process. The thermal conductivity of PCD diamond tools is several times that of cemented carbide. When processing titanium alloy, more cutting heat can be conducted out of the cutting area through the tool; the durability of PCD diamond tools for cutting titanium alloys can reach dozens of times that of carbide tools. Polycrystalline cubic boron nitride (PCBN) tools come second; TiC-based carbide tools and ceramic tools are considered unsuitable for titanium alloy cutting due to low durability and other reasons.

In terms of tool angle, a smaller rake angle is generally selected for cutting titanium alloy to increase the contact length between the chip and the rake face; at the same time, a larger relief angle is selected to reduce the friction between the flank face and the machined surface.

2. Grinding titanium alloy

① General grinding

✳When grinding with a white corundum grinding wheel, the grinding wheel adheres seriously and the grinding temperature is high.

✳When grinding with silicon carbide grinding wheels, the temperature should be lower than that of white corundum grinding wheels. Among them, the effect of cerium silicon carbide grinding wheel is better than that of green silicon carbide.

✳A grinding wheel with mixed abrasives using green silicon carbide or cerium silicon carbide as the main abrasive, and chromium corundum (PA), single crystal corundum (SA), zirconium corundum (ZA) or microcrystalline corundum (MA) as the auxiliary abrasive.

✳The affinity between SiC abrasives and titanium alloys is low, so its grinding effect is better than that of corundum abrasives.

②Superhard abrasive grinding wheel

Ceramic bond diamond grinding wheel have strong capacity, good thermal and chemical stability, are waterproof, heat-resistant, corrosion-resistant, have low wear, maintain grinding performance for a long time, are porous, not easy to block, and have high productivity. It is highly brittle and cannot withstand large impact loads. , add grinding oil (GF-2 or GF-3), the grinding ratio will be 100 times that of ordinary silicon carbide.

Metal bond grinding wheels are also very effective in grinding titanium alloys, with high efficiency, good shape retention and long service life.

The surface quality and roughness of titanium alloy grinded by resin bond grinding wheel are good. When the grinding depth is increased, the contrast with the roughness of ordinary grinding is more obvious.

The electroplated bonded grinding wheel grinds titanium alloy with high efficiency and high material removal rate. It is used for rough cutting and the effect is remarkable.

The study and comparison found that under the current level of grinding tool technology, the grinding wheel wear rate is faster when ordinary grinding wheels grind titanium alloys. For example, the grinding ratio of using SiC grinding wheels to process titanium alloy under ordinary grinding conditions is only about 1. When a superhard grinding wheel is used, the grinding efficiency is increased by dozens or even hundreds of times. In addition, compared with ordinary abrasives, the thermal conductivity of superhard abrasives is significantly enhanced, so a higher material removal rate can be achieved. On the other hand, when using superhard grinding wheels to grind titanium alloys, frequent dressing of the grinding wheels can be avoided, further improving the grinding efficiency. Its machined surface quality is good, with relatively few macro cracks and surface damage.

3. Polished titanium alloy

Due to the instability of its chemical composition, TC4 titanium alloy will react chemically with oxygen and nitrogen under thermal deformation, and even with some oxygen-containing gases. The reaction will produce oxide scale attached to the surface of the workpiece, and the resin CBN abrasive belts are particularly suitable for polishing hard and tough difficult-to-machine materials such as iron-based alloys, titanium alloys, stainless steel, high-temperature alloys, (nickel-based and cobalt-based alloys) and complex-shaped workpieces.

When grinding titanium alloy with CBN abrasive belt, the grinding force is small, the grinding temperature is low, the grinding ratio is very high, and the grinding surface layer is basically in a state of compressive stress, making it an ideal grinding tool for grinding titanium alloy.

Compared with ordinary coated abrasives, CBN abrasive belts not only have the characteristics of high grinding efficiency, high durability, low grinding temperature, good surface quality, and high cost performance, but also have less dust, low noise, and smooth operation during use. Advantages of a good environment. Using CBN abrasive belts to grind pure titanium plates and titanium alloy plates can reduce the surface roughness to about Ra= 0.03 Pm, and ultimately achieve a mirror effect.

---EDITOR: Doris Hu, Jim Jiao

---POST: Doris Hu