P91, T91 material machining tool to improve problems

Introduction
P91, T91 heat-resistant steel materials, durable high strength, good oxidation resistance and corrosion resistance, have been widely applied to 300MW, 600MW boiler products. As the P91, T91 material is martensitic steel is very hard, its machining performance is poor, thus cutting tool provides updated requirements. In this paper, P91, T91 material collection bins in the process of machining tools to analyze problems and propose an improved method.
1 P91, T91 material collection container machining process
Boiler plant in the collection box set box there are three machining processes: Flashlight docking groove processing; cylinder body pores processing; pressure pipe fittings after the end chamfer. Flashlight docking groove in the boring machine for machining, processing and pore chamfering the pipe ends are accomplished by the drilling.
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2 Analysis of the problems and tools to improve
Pore body tube processing
Currently, 300MW, 600MW boiler tube who pore box set mostly in the form of welding groove CE standard form (Figure 1), which forms the hole cutting tools and forming an ordinary twist drill blade, the blade is formed by welding groove requirements designed by the high-speed steel W18Cr4V made. (Figure 2)
In machining, the layer of material being processed will have a severe plastic deformation, which occurred in hardening, through hardening material, its hardness is much improved than the original hardness. Under normal circumstances, the metal material of higher hardness and strength, the larger the cutting force, cutting temperature is higher. P91 material strength and hardness are high, especially in high-temperature, high hardness, thus cutting in the following questions:
(1) high intensity, thus cutting power; (2) the higher hardness, especially high-temperature hardness than other metal materials, processing of plastic deformation and hardness due to further hardening; (3) low thermal conductivity, high temperature and thus cutting ;
Ordinary high-speed steel drill bit is made by the ordinary, its low hardness and heat resistance, processing and P91 materials, processed materials caused by the hardness and strength are high, thus cutting power when cutting speed increases, the cutting temperature will be increased, the bit will change the microstructure, hardness of the martensite transformation for the trust's lower body, low sorbite or hardness of austenite, thus cutting the loss of the ability to produce " burning knife "phenomenon. Especially in the weld, the processing is very difficult to increase the number of drill grinding. Welding process with the formation of the blade groove, the formation of a thin blade, blade hardness and low heat resistance, high hardness and high cutting forces in the role, the blade fragile, loss increase, with the blade than the processing of materials processing P91 higher than normal amount of material about five times, cutting only 40r/min, feed rate 0.2mm / r, low production efficiency.
For the above, we use in the processing time for cutting alloy drill, carbide cutting temperature due up 800 ~ 1000 ℃, high temperature hardness (Table 1), doubling the cutting speed, reducing tool sharpening, improve production efficiency.


Pressure after the pipe joint analysis of the problems chamfer
With the continuous development of production, the quality of the components of the boilers have become increasingly demanding, pressure test a test 300MW, 600MW boiler set box fillet quality an important tool. 300MW boilers with the following difference is, 300MW, 600MW boiler set box fittings using roll form is not sealed, but the use of water in the pipe weld joint top of the form of seal gland. For common materials, water pressure after the removal of water with a gas cutting method gland, then chamfer, as T91 material hardness increased rapidly after gas cutting and difficult process, and therefore can not use gas cutting methods to remove water gland, but with bit gland drilling off the water, and then chamfer.
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As the hardness of the weld after welding a lot higher than the base material, and the uneven distribution of hardness, easy to form a chip breaking cutting, and because of 300MW, 600MW and more for the long pipe fittings and pipe form, drilling jig used for the V-shaped frame, which the entire processing system less rigid. With ordinary twist drill cutting, due to welds, high hardness, easy to "burn knife" and chipping, reducing tool life, and because of poor processing system rigid drill easily broken, the tool of serious damage, consumption of large . Actual production, drilling speed 50r/min, feed rate 0.3mm / r, 10 or so drill bit will wear a drill pipe joint, not only reduces production efficiency, and increased labor intensity. If the use of alloy drill, carbide toughness as poor, with low bending strength, rigidity poor conditions in the cutting, the cutting process of the vibration, easy to crack the blade alloy.


Fittings for the chamfering, the processing system, poor rigidity of the situation, we use the water processing tapered countersink gland weld. Use tapered countersink drill, the cutting edge to increase, as well as its own direction, increasing the cutting stability. In actual production, with counterbore countersink taper drill countersink cutting change weld grinding, cutting speed of up to 200r/min, the feed capacity of 0.5mm, and reduce the "burning knife" phenomenon, improve labor efficiency, while reduce the loss of the tool, reducing costs.