1、 Grinding characteristics of titanium alloy
(1) High grinding temperature. The deformation coefficient of titanium alloy is small, and extrusion chips are often formed, resulting in serious friction. The stress is concentrated near the cutting edge, producing a lot of heat; The coefficient of thermal conductivity and thermal conductivity of titanium alloy is small, which is only 1/5 of that of carbon steel, making it difficult to emit grinding heat and easy to cause excessive temperature in the grinding area. Under the same conditions, the grinding temperature is about 1.5-2 times that of 45 steel, up to 1000 degrees.
(2) Titanium alloy has high chemical activity at high temperature. Due to the high grinding temperature, the grinding debris is easy to react with oxygen, nitrogen and other elements in the air to form a hard and brittle layer, which accelerates the wear of the grinding wheel.
(3) Because titanium alloy has high chemical activity. Coupled with the local high temperature and high pressure in the grinding area, the adhesion between the abrasive particles and the metal surface occurs due to the affinity, which accelerates the wear of the grinding wheel, affects the quality of the machined surface, and it is difficult to ensure the dimensional accuracy.
(4) Large grinding force. Generally, the grinding force per unit width is about 2-3 times that of ordinary carbon steel, and its radial force is greater than the tangential force.
(5) Easy to burn and crack. Due to the high grinding temperature, large thermal stress is generated on the grinding surface, which not only causes grinding burns, but also grinding microcracks. These microcracks are hairline shaped, and their direction is roughly perpendicular to the grinding direction, and the grinding surface presents yellowish brown spots. Due to the influence of grinding heat, residual tensile stress is produced on the workpiece surface, which reduces the fatigue strength of parts and affects the service life of parts.
(6) Low production efficiency. During grinding, the grinding ratio is very low because the grinding wheel is easy to passivate, adhere and block. Under the condition of ensuring the quality of the workpiece, only the productivity can be reduced.
2、 Selection of grinding wheel
When cubic boron nitride wheel is used to grind titanium alloy, the grinding temperature and residual stress on the machined surface are very low, which can effectively inhibit the generation of cracks, and obtain higher workpiece surface quality and grinding efficiency.
Wheel bond: resin bond should be used for green silicon carbide wheel. Because the grinding force and grinding temperature of ceramic bonded wheel are higher than those of resin bonded wheel.
Generally, when the hardness of the grinding wheel is at the J-L level, the productivity is higher. When a soft grinding wheel is selected, its grinding force and grinding temperature are lower, but the grinding wheel consumption increases significantly.
In addition to cooling and flushing, the grinding fluid is required to inhibit the adhesion and chemical action of titanium and abrasive particles when grinding titanium alloys. Water soluble grinding fluid containing a variety of extreme pressure additives should be selected. For example, the grinding fluid containing chlorine extreme pressure additive has strong lubricating permeability and can inhibit the occurrence of grinding cracks and adhesion. When using, mainly increase the flow and pressure of grinding fluid; The capacity of the water tank should be large enough to keep the grinding fluid at a low temperature. In addition, when grinding titanium alloy, the temperature is high and the chips are flammable. When using oil grinding fluid, pay attention to safety and fire prevention.
