Titanium and titanium alloys are widely used in aerospace and other fields due to their excellent comprehensive properties such as low density, high specific strength, corrosion resistance, high temperature resistance, non-magnetic properties and good welding performance. However, some of the physical and mechanical properties of titanium alloys have brought many difficulties to the cutting process. Titanium alloy has small deformation coefficient, high tool tip stress, high cutting temperature, high chemical activity, prominent bond wear and diffusion wear, high elastic recovery and high chemical affinity during cutting. Therefore, it is easy to produce stick in the cutting process. Knife, peeling, bite, etc., the tool temperature rises rapidly, causing the tool to wear or even completely destroy.
Because titanium alloy has the advantages of high specific strength, good corrosion resistance and high temperature resistance, titanium alloy has been rapidly developed in the aerospace field since the 1950s. Titanium alloy is one of the main structural materials of modern aircraft and engines, which can reduce the weight of the aircraft and improve the structural efficiency. The proportion of titanium in aircraft materials is 7% for passenger aircraft Boeing 777, 10.3% for transport aircraft C-74, and 8% for fighter aircraft F-4. However, due to the high price of titanium alloy and poor wear resistance, it limits its use.
In recent decades, great progress has been made in titanium alloys and other researches for aerospace applications at home and abroad, and many alloys have also been widely used. This paper discusses the titanium alloy milling technology in aerospace products for the reference of peers.
1. Introduction to titanium alloy
Titanium is an isomer of isotopes with a melting point of 1 720 ° C. It is a close-packed hexagonal lattice structure below 882 ° C and is called α titanium. It is a body-centered cubic character structure above 882 ° C and is called β titanium. Using the different characteristics of the above two structures of titanium, adding appropriate alloying elements, gradually changing the phase transition temperature and phase content to obtain titanium alloys of different microstructures. At room temperature, titanium alloys have three kinds of matrix structures, and titanium alloys are classified into the following three categories:
(1) α-titanium alloy It is a single-phase alloy composed of α phase solid solution. It is α phase at normal temperature or at a higher practical application temperature. It is structurally stable and has higher wear resistance than pure titanium. Strong oxidizing power. At 500 to 600 ° C, the strength and creep resistance are maintained, but the heat treatment is not strengthened, and the room temperature strength is not high.
(2) β-titanium alloy It is a single-phase alloy composed of β-phase solid solution. It has high strength without heat treatment. After quenching and aging, the alloy is further strengthened. The room temperature strength can reach 1 372~1 666MPa; Poor, should not be used at high temperatures.
(3) α + β titanium alloy It is a dual phase alloy, has good comprehensive properties, good structural stability, good toughness, plasticity and high temperature deformation properties, can be well subjected to hot pressure processing, can be quenched and aged Strengthen the alloy. The strength after heat treatment is about 50% to 100% higher than that of the annealed state; the high temperature strength is high, and it can work for a long time at a temperature of 400 to 500 ° C, and its thermal stability is inferior to that of the α titanium alloy.
The most commonly used of the three titanium alloys are α-titanium alloy and α +β-titanium alloy; α-titanium alloy has the best machinability, α + β titanium alloy is the second, and β-titanium alloy is the worst. The alpha titanium alloy is coded TA, the beta titanium alloy is coded as TB, and the alpha + beta titanium alloy is coded as TC.
There are five general body styles of ball Valves: single body, three-piece body, split body, top entry, and welded. The difference is based on how the pieces of the valve-especially the casing that contains the ball itself-are manufactured and assembled. The valve operation is the same in each case.
In addition, there are different styles related to the bore of the ball mechanism itself.
Ball valves in sizes up to 2 inch generally come in single piece, two or three piece designs. One piece ball valves are almost always reduced bore, are relatively inexpensive and generally are throw-away. Two piece ball valves are generally slightly reduced (or standard) bore, they can be either throw-away or repairable. The 3 piece design allows for the center part of the valve containing the ball, stem & seats to be easily removed from the pipeline. This facilitates efficient cleaning of deposited sediments, replacement of seats and gland packings, polishing out of small scratches on the ball, all this without removing the pipes from the valve body. The design concept of a three piece valve is for it to be repairable.
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