At present, most parts of aero-engine use titanium alloy materials, according to the assembly requirements, precision machining surface size accuracy and surface roughness need grinding processing to ensure the quality of parts surface.Due to the physical and mechanical properties of titanium alloy materials, surface burns and surface integrity are easy to occur during grinding. At present, it is urgent to solve the problem of titanium alloy materials grinding, so it is very necessary to choose the right grinding wheel.
1. Property analysis of titanium alloy materials
Titanium alloy can be divided into three categories, alpha titanium alloy, beta titanium alloy and alpha + beta titanium alloy.It has small specific gravity, high specific strength, high temperature resistance, corrosion resistance, super memory, no magnetism, low modulus of elasticity, biocompatibility number, which makes it applied in a wide range of fields.Titanium has a melting point of 1668 ° c and a boiling point of 3400 ° c, higher than that of ferronickel. Therefore, light heat resistance becomes its excellent foundation and can work for a long time at 500 ° c.The new titanium alloy long - term working temperature is even higher, at 300-350℃ its strength is 10 times higher than aluminum alloy.Commonly used alpha beta titanium alloy strength up to 1.2GPa, specific gravity 0.44MPa, specific strength 23-27, are higher than alloy steel.The tensile strength of titanium alloy can exceed 1.5GPa, and a great force must be applied to its processing.
The thermal conductivity of titanium alloy TC11 was worse than that of titanium alloy.The elastic modulus of titanium is about 1/2 of that of steel.
Titanium alloy contains oxygen, hydrogen, nitrogen, carbon, sometimes including silicon, iron and other impurity elements, these elements have a strong reaction, in a gap type exist in the lattice, can make the titanium alloy strength increased, plastic decline, even fracture toughness, low temperature toughness, fatigue strength, corrosion resistance, cold forming and weldability bad.Titanium alloy has high chemical property in high temperature. Under a certain grinding temperature, titanium forms oxidation and nitride protective film, which makes the surface layer hardened and brittle, reduces elasticity, and increases the degree of work hardening. It is easy to stick to the surface during grinding, blocking the grinding wheel, causing grinding overheating and surface integrity reduction.
2. Selection of grinding wheel for titanium alloy grinding
2.1 titanium alloy grinding requires small grinding wheel adhesion, small wear, not easy to block, low grinding temperature
This mainly includes abrasive particle size binder structure shape size.Common grinding wheel is composed of abrasive binder and blowhole.The function of abrasive is to grind the processed material to form a surface that meets the requirements.The function of the binder is to bond the abrasive together to form a certain shape and hardness, so that the abrasive particles can maintain a stable movement track in the grinding process and self-detach.Air hole is in grinding process play chip discharge, cooling and lubrication.Common abrasives include corundum series (alumina), and silicon carbide series.Silicon carbide grinding wheel should be selected for grinding titanium alloy.
2.2 selection of binders
There are two kinds of binder: resin and ceramic:
1) ceramic binder particles have strong capability, good thermal and chemical stability, waterproof, heat resistant, corrosion resistant, small wear, long time maintenance grinding performance, porous, not easy to block, high productivity.Brittleness, can not withstand large impact load.
2) resin bond grinding wheel has high strength, elasticity, good impact resistance, poor thermal stability, poor corrosion resistance, and will soften and lose strength at high temperature.
Ceramic bond grinding wheel should be selected for grinding titanium alloy.
2.3 selection of granularity
Titanium alloys are usually ground with particle sizes of 36#-80#.
2.4 organization hardness of grinding wheel
The grinding of titanium alloy should usually choose a large hole grinding wheel with soft hardness or moderate hardness and loose structure.