Domestic development of cutting tools for the hott

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Domestic development of 171/172 CNC cutting tool

1 introduction

Tianjin steel pipe company is the main manufacturer of seamless steel tubes for oil casings and couplings in China. In the late 1980s, the company introduced two CNC special machine tools (171/172 cutting machine tools for short) from PMC company of the United States for cutting and processing seamless steel tubes. The machine tool adopts the processing mode that the spindle drives the cutter head to rotate (i.e. the cutter rotates) and the workpiece is stationary, which can avoid the vibration caused by the non-circular pipe and uneven wall thickness during the processing of the ordinary cutting machine tool using the workpiece rotation processing mode, so as to reduce the cutting caused by vibration and the damage to the machine tool spindle. In addition, because the pipe is in a static state during processing, the clamping, adjustment, tool setting and other processes are reduced, which greatly improves the production efficiency, ensures the continuity of processing, and reduces the production cost

171/172 four cutting knives are uniformly installed on the cutter head of the cutting machine tool (see Figure 1). When the machine tool is working, the spindle drives the cutter head to rotate. Under the control of processing instructions input into the computer, four cutting knives synchronously feed and withdraw, and the cutting process is completed at one time. Since four cutting knives participate in cutting at the same time, that is, each knife only undertakes 1/4 of the total cutting amount, the tool has small machining allowance, light cutting load and long service life

Figure 1 Schematic diagram of cutting tool installation

171/172 cutting tools for cutting machine tools have high requirements for the accuracy and interchangeability of relevant blades, tool bodies and their accessories. Due to the use of fixed size cemented carbide blade, the blade can be replaced quickly during processing; The structural design of the cutter also considers the size adjustability within a certain range, so the cutter bar of one specification can be applied to the processing of pipes (4 "~ 10") of various specifications, realizing the multi-purpose of one cutter. Since the cutting tool has strong specificity, strict dimensional accuracy requirements (parallelism, perpendicularity, flatness errors are within the range of 0.005 ~ 0.010mm), and high requirements for hardness, wear resistance and other performance indicators, since the machine tool was put into operation, the tool has been dependent on imports, which is not only expensive, consumes a lot of foreign exchange, but also has a long supply cycle, which is difficult to meet the needs of on-site production. For this reason, since 1994, we have made domestic development of cutting tools for cutting machine tools and achieved success

2 cutting tool structure and working conditions

2.1 tool structure and size adjustment

the structure of cutting tool is shown in Figure 2. Because the 171/172 cutting machine tool has a large range of processing dimensions (4 "~ 10"), and the ability to deal with trade protectionism has been enhanced, and only three specifications of tools are used. Therefore, a size adjustment mechanism is designed in the tool, and the size adjustment is realized by adjusting screw ta-2938. The adjustment steps are as follows: place the blade on the lower tool holder tb-4121, press the upper pressing plate ta-2872 with the fastening screw 3, and clamp the blade on the lower tool holder

Figure 2 cut off the tool structure diagram

then place the tool in the tool preset room in the tool adjustment gauge te-2665 shown in Figure 3 and fix it. By turning the handle tb-2468, the adjustment screw ta-2938 can be adjusted to the required size, and then tighten the screw 4 (see Figure 2), press the half nut pressing plate ta-3058-a, and fix the adjustment screw ta-2938, that is, the setting of the processing size is completed. Install 4 cutting knives with adjusted size on the cutter head of the cutting machine tool to cut off

Figure 3 tool adjustment gauge

Figure 4 tool design figure

2.2 tool working conditions

working temperature: normal temperature; Cutting speed: 200 ~ 600ft/min(61~183m/min); Spindle speed (adjustable):100 (400) r/min; Coolant: emulsified oil; During machining, the cutter moves radially in the cutter head groove

3 tool material selection

from the analysis of the use of imported blades, the blade material is YT series cemented carbide. According to the design structure of the cutter body (the thickness of the cutter body is 22.6mm, the length is 247.25mm, and there are 6 hollowed grooves on it), if the cutter material is improperly selected, it is very easy to deform during heat treatment, and it is difficult to meet the flatness design requirements of 0.01mm. According to the experience of Harbin No.1 tool factory in processing similar products, the cutting tool material is finally selected as 42GrMo after process test

4 tool design and manufacturing process

4.1 tool design

when designing a tool, first map the tool samples, investigate and analyze the on-site installation and use, and finally determine the design scheme. The cutting tool for 171/172 cutting machine tool is composed of blade, upper and lower pressing plates, adjustable bolts, half nut pressing plates, screws and tool body. The tool design drawing (taking 4 "~ 10" cutting tool as an example) is shown in Figure 4

4.22.4 circuit thousand disturbance control manufacturing process

due to the high precision of cutting tools, complex shape and many grooves, it is easy to produce machining deformation. Therefore, when formulating the machining process, we should take the method of milling and grinding as the main, and check each process to ensure the machining accuracy of the tool. The processing process of cutting tools is: forging → milling and grinding the shape → rough milling multiple grooves → quenching and tempering treatment → drilling, tapping → semi fine milling multiple grooves → fine milling each groove to size → semi fine grinding the shape → surface nitriding treatment → liquid sand blasting → fine grinding to size → finished product inspection → packaging and warehousing

5 tool heat treatment process

according to the particularity of the tool structure and the use requirements, the heat treatment of the tool needs to be carried out first, and the quenching and tempering hardness is 28 ~ 32hrc. After semi finishing, the surface nitriding treatment shall be carried out. The thickness of nitriding layer is 0.4 ~ 0.6mm, and the hardness is 600 ~ 750hv. After heat treatment, ensure that the cutter does not deform and meets the design accuracy requirements

6 conclusion

the organization believes that the installation and use of more than 5 years have proved that the dimensional accuracy, surface hardness, wear resistance, durability and other performance indicators of the domestic cutting tools for 171/172 CNC cutting machine tools have reached the level of similar foreign products, and have completely replaced the imported tools in production. Compared with imported tools, domestic tools have great advantages in terms of supply cycle and purchase price. The successful localization of cutting tools ensures the production needs of Tianjin steel pipe company, shortens the supply cycle of cutting tools, and reduces the processing cost. (end)

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