Discussion on the application of the most efficien

2022-08-08
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Discussion on the application of high-efficiency tools in machining large diameter holes (screw holes)

in large power stations, mines, heavy and general machinery industries, many parts such as machine bases, cylinder blocks, pressure chambers and other parts need to be machined with large diameter holes (screw holes). Some holes are large and deep, and the accuracy is also very high, which greatly prolongs the processing cycle. It often takes 4 ~ 6 hours or even longer to process a large diameter hole with traditional high-speed steel drilling and reaming tools. This backward processing method and tools can easily become the bottleneck of production

in order to adapt to the rapidly developing production situation, it is extremely urgent to develop and apply efficient large-diameter tools. Therefore, tool manufacturers and relevant research institutions at home and abroad have accelerated the innovation and research and development of large-diameter hole machining tools, and have achieved gratifying results in recent years

at present, there are two main types of machine tools for machining large-diameter holes (screw holes): one is large-scale CNC boring and milling machines. Because of their high power, good rigidity and high precision, high-efficiency cemented carbide tools suitable for high-speed cutting can generally be used (especially cemented carbide indexable hole machining tools); The other is ordinary large-scale radial drilling machine. Although this kind of machine tool cannot be compared with large-scale CNC boring and milling machine in terms of power, stiffness and machining accuracy, its biggest advantage is low processing cost. At present, most domestic heavy machinery manufacturers still take this kind of machine tool as the main production force, so it is also of great significance to develop efficient large-diameter hole machining (screw hole) tools suitable for large-scale radial drilling machines

1 large diameter hole machining tools used in CNC boring and milling machines

1.1 drilling tools

cemented carbide/high speed steel large diameter composite drill the typical structure of this kind of tools can be seen in Figure 1. The cutting edge of the tool is composed of cemented carbide indexable blade and high speed steel center drill. The high-speed steel center drill is in the center of the drill bit, with low cutting speed, sharp blade and small transverse edge, so the axial cutting force is small, and the drilling can be stable during cutting; The indexable blades on both sides of the drill are arranged crosswise, and the blades with good hardness and strength and the point type carbide chip breaking groove type (generally, the coated blade should be selected), so that the C-shaped chips with small chip area can be obtained during drilling, so as to facilitate the smooth discharge of drilling chips; Drill pipe and drill bit usually adopt internal cooling structure, so that the drilling edge can be fully cooled during drilling, and the cutting fluid can smoothly discharge the cuttings out of the orifice under the injection of high-pressure pump; A cross safety ring is also arranged between the tool bar and the tool head of the tool, mainly to prevent the tool bar from being damaged during overload cutting

Figure 1 carbide/high speed steel large diameter composite drill

with this high-efficiency large diameter composite drill, the cutting speed VC can reach 80 ~ 120m/min, and the feed rate f can reach 0.1 ~ 0.12mm/r. Its cutting efficiency can be increased by 8 ~ 12 times compared with the use of high speed steel drill and expanding tool. The processing range of this kind of drill is generally 80 ~ 170, and it can even process large holes of more than 300 when the power of the machine tool allows. At present, this kind of drill bit has been widely used in Harbin Turbine Factory, Shanghai Longji Metal Co., Ltd. and other units in China. Therefore, for the sake of reasonable material selection

1.2 cemented carbide indexable nesting drill

the structural form of nesting drill can be seen in Figure 2. This tool has high design and manufacturing accuracy. There are three groups of tool blocks, two tool blocks in each group are symmetrically distributed on the tool body. The third group is eccentrically clamped, and the first and second groups are eccentrically clamped with sliding blocks. The height difference between the two adjacent groups of tool blocks is 0.25~0.30mm. The height of two blades in the same group is equal, which plays a good role in chip separation. When cutting 45# steel, the cutting fluid is engine oil, and the oil pressure P is 0.5 ~ 0.7MPa. At present, the carbide indexable nesting drill has been stably applied in Shanghai Shenkong machinery factory and has achieved obvious processing results

Figure 2 large diameter carbide indexable nesting drill

1.3 tools for internal thread processing

efficient processing of large diameter internal threads. There are two types of tool structures that are widely used

whirlwind milling large diameter internal thread cutting head this milling head is an independent process equipment and belongs to machine tool accessories. It is suitable for milling threads on ordinary horizontal boring and milling machines and other machine tools with thread feed system. 1 ~ 4 indexable thread inserts can be installed on the milling head. The cutter also performs circumferential feed and axial feed (i.e. screw feed) while high-speed rotation milling. The structural diagram of the additional internal thread cyclone cutting head can be seen in Figure 3. This device is usually used for the left and right sides of M30 ~ M120 metric and 1.5 "~ 4.5" inch threaded holes Whirlwind milling of right thread

1. Blade 2 Cyclone cutterbed 3 Cyclone milling shaft 4 Motor with adjusting slide 5 Adjusting screw 6 Machine tool spindle 7 Machine tool housing 8 Taper shank 9 Fixing plate 10 Vertical connecting rod 11 Horizontal connecting rod 12 Special block gauge

Figure 3 additional internal thread whirlwind cutting head

cemented carbide thread comb cutter this is a newly developed efficient tool for internal thread processing in recent years. The blade on its head can be single or multiple pieces. Because the pitch on the blade is fixed, the blade of the same specification can be applied to the processing of large threaded holes with different diameters and the same pitch. The cemented carbide thread comb blade is better to choose the coating type, and the cutting speed can generally be 100 ~ 120 m/min. using this tool to process large threads can obtain high efficiency and high quality processing results. When machining threaded deep holes, vibration marks and hole deflection often occur due to the vibration of the tool bar. At this time, the tool bar with anti vibration performance can be selected to solve it. At present, this kind of cutting tool has been applied in Beijing heavy duty motor factory, the first heavy machinery factory and Shanghai Hudong vehicle shipyard. See Figure 4 for the tool structure diagram

Figure 4 carbide thread comb cutter

2 efficient tool for machining large diameter holes on radial drilling machine

2.1 high speed steel large diameter flat drill

this is the most original tool in hole machining. Although it is widely used in the previous processing of single and small batch parts of small and medium-sized non-standard holes because of its simple manufacture and convenient use, it has low cutting efficiency, short tool life Disadvantages such as poor hole machining quality limit the development of this kind of cutting tools. In recent years, because there are more and more parts that need to process large-diameter holes on large-scale radial drilling machines in China, the voice for the development and innovation of efficient drilling tools for large-scale radial drilling machines is also growing. Whether flat drills can be further improved into efficient hole processing tools has also been put on the agenda. Through the research, improvement and development of relevant units at home and abroad, the large-diameter flat drill has been successfully applied to the processing of large-diameter holes in parts in heavy-duty enterprises at home and abroad. Its innovation mainly includes the following points: the tool structure adopts the blade clamp type, and the tool bar has internal cooling holes. During cutting, the blade can be fully cooled under the action of high-pressure coolant; The blade material is high-performance high-speed steel (such as M42) and the surface is coated; Reduce the transverse edge of the tool and appropriately increase the rake angle of the tool to reduce the axial cutting force; The blades on both sides are added with cross chip separation grooves (matching with the chip breaking groove type of the rake face and the reasonable tool feeding amount), so that the chips become C-shaped chips, which is convenient for discharge and reduces the cutting resistance. See Figure 5 for the structural diagram of a typical large diameter hole flat drill

Figure 5 machine clamp high speed steel large diameter flat drill

Harbin electric machinery factory now applies this kind of large diameter flat drill in the hole processing of many product parts, realizing efficient cutting

2.1 high speed steel large diameter composite drill

the structure of the machine clamp high speed steel large diameter composite drill is internally cooled. The difference from the carbide/high speed steel composite drill is that the carbide indexable blades originally used on both sides of the cutter head are changed into two high-performance high speed steel blades with chip splitting grooves on both sides; The blade is subject to enhanced surface treatment (coating or multi-element co infiltration treatment); In terms of tool geometry, different choices are made according to the processed materials. At present, this type of high-speed steel large-diameter compound drill has been applied in Harbin Turbine Factory. Its processing efficiency is more than 3 times higher than that of the original high-speed steel drill and reaming tool. At the same time, the tool life is also significantly improved, and the time of loading, unloading and sharpening tools can be greatly shortened. See Figure 6 for its structural diagram

Figure 6 high speed steel large diameter composite drill

2.3 large diameter internal thread cutter

the traditional method of machining large diameter internal thread holes with large diameter and large spiral angle taps is to use sets of our materials to complete the construction of taps. However, due to the application of multiple taps for machining, and the deflection of the spindle is often prone to cause vibration, it is easy to cause ripple, "double eyelid", thread through-end non-stop end connection and other phenomena in the processing of screw holes. The large diameter spiral groove tap is formed by tapping with a single tap, and the chips can be discharged continuously and smoothly during tapping, with very little resistance; In addition, this kind of tap has a large spiral angle (35 ° ~ 40 °), which can increase the actual rake angle and chip holding space, reduce the cutting torque, make the cutting more stable, and is conducive to improving the machining efficiency and ensuring the quality. The tool structure diagram can be seen in Figure 7. Generally, the application range of large spiral angle tap is M56 ~ M140

a) for ordinary blind holes b) for deep blind holes

Figure 7 large diameter large spiral angle tap

content chip tap content chip tap is an advanced and highly effective processing tap with unique characteristics in many disciplines and fields. It is not only applicable to the processing of large diameter internal thread holes by CNC boring and milling machines, but also applicable to the processing of threaded internal holes on large radial drilling machines

the main features of the inner chip tap are: the chip holding groove of the ordinary tap is an axial groove, while the chip holding groove of the inner chip tap is a chip storage hole with a large enough chip holding space in the front of the tap; The working part of the chip tap is composed of three threads. The thread on the cutting cone plays the role of rough cutting, the discontinuous thread on the cylinder plays the role of standard, and the complete thread on the cylinder plays the role of guidance; The cutting cone of the chip tap is provided with a cutting edge with a left-hand positive edge inclination. When tapping the thread, the chip is pushed forward, so that when the tap returns, it will not be stuck due to the chip. When machining the blind hole, the chip is stored in the chip hole, and the chip is completely isolated from the surface of the processed thread, so the chip removal is ideal, which improves the surface quality of the thread machining

figure 8. See Figure 8 for the structure diagram of the sleeve type chip tap. The processing range of the sleeve type chip tap is M56 ~ M250. The cutting speed VC is usually 2 ~ 6m/min according to the different materials being processed, and the general processing accuracy can reach 6h. At present, this kind of high-efficiency chip tap has been widely used in domestic steam turbine, generator industry and heavy machinery manufacturing industry. (end)

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