TC4 titanium alloy is a metal material with excellent mechanical properties, high temperature resistance, corrosion resistance, and other properties. It is also known as the future metal and is widely used in aerospace, defense technology, biomedicine, and other fields. However, titanium alloys have high hardness, strength, plasticity, and toughness, as well as poor thermal conductivity, resulting in poor machinability and are typical difficult to machine materials. As a result, during the processing of TC4 titanium alloy, there are problems such as high cutting temperature, high cutting force, difficulty in chip breaking, difficulty in improving cutting speed, and rapid tool wear, which lead to microcracks and work hardening layers on the machined surface, resulting in poor surface roughness, high residual stress, and the formation of a large number of burrs, high-temperature burns, and subsurface damage, seriously affecting the surface integrity and service performance of the parts. In this regard, people often use cooling and lubrication methods to improve the cutting area to ensure the high efficiency, high precision, and high-quality processing of titanium alloys.

In recent years, minimal quantity lubrication (MQL) has been commonly used as a new type of lubrication method in mechanical machining. It is achieved by atomizing cutting fluid into the tool interface through compressed gas, providing lubrication for machining.

Although micro lubrication can solve the problem of excessive use of pouring cooling lubricants, there is still a bottleneck of insufficient lubrication due to the small amount of cutting fluid. To solve this problem, researchers have used plasma cleaning coupled with micro lubrication as cooling conditions. Due to the abundance of active particles in plasma and its proven ability to regulate material properties, it can reduce the contact angle of cutting fluid on the workpiece surface, accelerate the spreading of cutting fluid on the workpiece surface, and not damage the material.

Plasma cleaning

The main components in plasma include non ionized gas molecules, charged ions, electrons, and various free radicals. Plasma cleaning technology is to treat the surface of the sample by utilizing the properties of these active components. By using a plasma generator to excite the reaction gas, ionization occurs, and a series of reactions occur with the pollutants on the surface of the sample to be cleaned, thereby removing the pollutants and achieving the cleaning effect

Analysis of Contact Angle of TC4 Titanium Alloy Before and After Plasma Cleaning

The contact angle reflects the wettability of the liquid on the surface of the workpiece and can indicate the spreading state of the liquid on the surface of the workpiece. The smaller the contact angle, the better the spreading effect of cutting fluid at the cutting interface and the better the cutting lubrication effect.

Figure 1 Contact angle of bio oil after plasma cleaning of titanium alloy

Figure 1 shows the changes in contact angle of bio oil on the surface of titanium alloy after plasma cleaning treatment. It can be seen that before plasma cleaning treatment, the contact angle of bio oil on the surface of TC4 titanium alloy is 36.6 °; After 5 seconds of plasma cleaning, the contact angle of bio oil on the surface of TC4 titanium alloy decreased to 26.5 °; After 20 seconds of plasma cleaning, the contact angle decreased to 11.4 °. Plasma cleaning can effectively reduce the liquid contact angle on the surface of TC4 titanium alloy, enhance its surface wettability, and promote the spreading of bio oil at the cutting interface.