Titanium alloys are typical representatives of "lightweight, high-strength, heat-resistant" materials. Its strength is higher than steel's, but its density is only about 60% of its density, and it can be used for a long time in a temperature environment of 300 to 350 ° C.Widely used in the engineering field.
The most representative is the aerospace field: aero-engine fan blades and low-pressure compressors/part of high-pressure compressor blades/impellers/blisks/casings, fuel tanks for aerospace vehicles, and rocket engine casings and other important parts Mostly made of titanium alloy. In the automotive industry, the use of titanium alloys for engine valves/connecting rods and exhaust systems, and other components are of great significance to the weight reduction of the body and the noise reduction of the engine. Thanks to its outstanding biocompatibility, titanium alloys have also become the metal material of choice for human implants and bone repair.
However, due to the characteristics of high strength, low thermal conductivity, and high chemical activity, the machining of titanium alloys is complex, and it faces problems such as low processing efficiency, rapid tool wear, and poor processing quality. Scholars at home and abroad have carried out a series of studies on this and discussed the characteristics of titanium alloy cutting/grinding processing under various typical process conditions and the application effects of various tools. Through these studies, a more comprehensive and in-depth understanding of the cutting/grinding processing characteristics of titanium alloys has been formed. In this paper, the research progress of cutting/grinding titanium alloys will be analyzed in combination with the above aspects.
The main problems of titanium alloy cutting/grinding
(1) The cutting/grinding temperature is high.
Titanium alloys have high strength and good thermal strength, so a lot of heat is generated during the cutting/grinding process. However, the thermal conductivity of titanium alloys (less than 7 W/(m·K)) is much lower than that of steel and aluminum alloys;
during the cutting/grinding process, part of the heat can be removed by cutting/grinding chips, cutting fluid and In addition to the tool/abrasive conduction, only a small amount of the remaining heat can be conducted to the inside of the workpiece in time, resulting in a large amount of cutting/grinding heat accumulating in the contact area.
On the one hand, the tool wear speed is accelerated, and on the other hand, the heat-affected layer on the surface of the workpiece becomes thicker, which reduces the mechanical properties of the part. Processing efficiency sometimes has to be reduced to mitigate the adverse effects of accumulated heat.
(2) The elastic deformation of the workpiece material is large.
The elastic modulus of titanium alloy is low, so the elastic deformation is large during the cutting/grinding process, which restricts the machining accuracy, especially the machining accuracy of thin-walled parts.
In addition, the elastic deformation and recovery of the workpiece material is an important inducement for cutting vibration.
If the elastic deformation of the workpiece material is large, the contact area between the workpiece material and the tool/abrasive particle will increase, resulting in serious wear on the flank of the tool/abrasive particle.
(3) The phenomenon of tool adhesion is serious.
Titanium alloy has good plasticity, and the cutting edge and workpiece material are prone to "cold welding" phenomenon under the action of contact pressure, resulting in adhesion of workpiece material.
In addition, the chemical activity of titanium alloy is high, and the titanium element is easy to chemically react with carbon, nitrogen and other elements in the tool material and oxygen in the air under the action of cutting/grinding temperature, which aggravates the interaction between the tool and the workpiece material.
Tendency to stick. Adhered workpiece material can cause a small amount of tool/abrasive material to come off when peeled off. Severe adhesion phenomenon is one of the main reasons for the rapid tool wear when cutting/grinding titanium alloys.