The source of power for the aircraft is the engine, which is a very important part of the entire engine's power turbine section and is the more difficult part of the entire turbine engine. Among them, the most laborious and difficult one is the processing of the turbine blade root groove. The material of the turbine disk is generally a nickel-based alloy, and the hardening phenomenon during processing is quite obvious, and the machinability is very poor. Moreover, the turbine blade root groove must be matched with the root of the blade, so the precision of the cooperation is very high, and the machining is very difficult. The broaching tool can meet the requirements of high precision and low surface roughness of the turbine blade root groove.
1. Characteristics of broaching tools
The broach is a special tool that is expensive to manufacture and therefore economical for mass production. At present, the broaching of standard round holes and spline holes has been standardized, and good economic effects can also be obtained in small batch production. The cutting speed of the broach is generally low, commonly used 1.02 ~ 7.8m / min, the cutting thickness is very thin, so the razor surface quality is high, the tooth wear is very slow, the life and processing precision is very high. When processing holes, it can reach IT7~9, even up to IT6. The production efficiency of the broach is very high. This is because the broach has a large number of working teeth, and the cutting edge for each tooth to work is long, and can be coarse, semi-finished and finished at the same time in one working stroke. The broaching process has the following advantages: 1 Short processing time and high efficiency. 2 The processing precision is high and the deviation is small. 3 The surface quality is good. 4 The processing method is economical, and the processing personnel skills can be processed without skill.
The broaching tool can meet the requirements of high precision and low surface roughness of the turbine blade root groove. The key to razor machining the turbine blade root groove to ensure high precision and low surface roughness is the design and manufacture of the turbine disk root groove precision broach. For the special material of the turbine disk, difficult to process and high precision of the root groove and low surface roughness value, the broach is reasonably designed, the broach material is selected reasonably, and the advanced heat treatment method is adopted to solve the key technology in the broach manufacturing process. The manufacturing process finally reaches the goal of mass production, and the tool quality and performance have reached the international advanced level.
2. Technology key
(1) overall design of the broach
For the complex shape of the blade root groove, the broach is designed as a thick broach, a semi-finish broach, a fine broach, used in groups, one broaching; the rough broach pulls off most of the cutting allowance, semi-finishing The knife trims the tooth profile and the fine broach is finalized for broaching.
(2) broaching mode selection
The rough broach adopts the progressive broaching method to pull out the original shape of the blade root groove, the semi-finishing broach adopts the lifting processing method to trim the groove type, and the fine broaching knife adopts the same-type broaching method, and the razor-shaped surface needs to be shovel Grinding the back angle.
(3) broach selection
The material used in the general broach is W6Mo5Co4V2 high-speed steel. When it is heat treated, it can reach Rockwell hardness of 63-66HRC. Because the material of the turbine disk is high-temperature resistant nickel-base alloy, the processability is poor, and the turbine wheel is The precision is very high. Although the cemented carbide tool is superior to high-speed steel in terms of hardness, wear resistance and cutting amount, its shortcoming is that it cannot withstand large impact force and its strength is low, only 1/3 of high-speed steel. Difficulty in heat treatment; the manufacture of solid carbide tools is difficult, the workability is poor, and the grinding of the profile must use a diamond wheel. Ordinary high-speed steel can not be used because of its low performance index in terms of strength and hardness. Powder metallurgy high-speed steel, such as CPM-42, T15, etc., is superior to other high-speed steels in terms of toughness, hardness and grindability, and is suitable for processing. Slot broach. In addition, the hardness of M42 (W2Mo9Cr4VCo8) cobalt high-speed steel can reach 67-69HRC after heat treatment. It can also have high red heat hardness and high wear resistance when the temperature is increased to 600-620 °C during processing. High strength and other properties, so the choice of M42 for the turbine turntable blade root broach is also suitable.
(4) broach heat treatment
Powder metallurgy high-speed steel CPM-42, T15, etc. as broach materials, heat treatment has the following characteristics: 1 too long quenching time or too high temperature is prone to "over-burning" phenomenon, broach life will be reduced. 2 After quenching, the brittleness is large, and quenching cracks are easy to occur. 3 combined with the tooth profile of the blade root groove broach, the diameter of the tooth tip is large, and it is easy to produce quenching crack and grinding crack. 4 The temperature control device can ensure that the broach does not produce “overburning†and the hardness meets the requirements. 5 quenching hardness needs to meet the process requirements. 6 Avoid quenching cracks and grinding cracks.
(5) Technical key
After the broaching of the fine broach, the final tooth shape of the turbine turntable is formed, and the precision of the precision broach directly affects the tooth profile accuracy and surface roughness of the turbine turntable. The processing of precision broaches is the most critical, the most complicated and the most difficult to process.
Fine broach processing should solve the following technical key: 1 Ensure that the broach has a vertical tolerance of 0.005mm on all sides. 2 Guaranteed broach tooth profile tolerance 0.005mm. 3 Guaranteed broach M value, K value tolerance ± 0.002 5mm. 4 After the squeegee is shoveled, the cutting teeth do not leave the cutting edge, and the calibration tooth edge belt is even. 5 precision broach tooth shape error 0.005mm.
Therefore, to ensure that the final machined surface meets the demand, the design of the precision broach should pay attention to the following points: 1 The fine broach is formed by the outer plane of the wheel groove, the broach at the bottom of the groove groove, the knives of the groove groove forming, etc. 3 Part of the composition. The tooth lifting amount and the tooth pitch of each part of the broach are different. The lifting amount of the precision broaching tool is small, and it is smaller in the full-tooth cutting. For the whole precision broaching tool, the tooth lifting amount should be designed as the front. Big and small. 2 In order to improve the service life of the precision broach and ensure the correctness of the contour, the broach profile is designed to take the minimum size of the groove contour, so that the broach body is at the maximum size of the wheel groove contour. 3 In the full-tooth type fine cutting, the pulling force suddenly increases, the broach is prone to vibration, and the chipping or broaching is broken. Not only the workpiece is damaged, but also the broach is lost. To avoid this, the design is avoided. In the precision broaching, the number of teeth in the full-tooth type cutting is calculated, and the root and the bottom of the teeth are opened to the chip flutes to ensure effective chip breaking.
(6) sharpening of the broach
The broach will wear gradually when it is used. When the broach wears to a certain condition, it will affect the accuracy of the final machining and the life of the whole set of broach. Therefore, when abnormal conditions occur in the machining, such as sudden drop of surface quality or vibration of the broach When increasing, the broach must be placed on the tool grinder to re-sharp. Generally, the sharp broach is limited to the part of the rough broach. The grinding position is limited to the back bevel. The grinding broach mostly uses CBN. Grinding wheels or diamond grinding wheels, grinding one tooth at a time, and paying attention to correct the tooth pitch to avoid excessive grinding. After the blade is ground, each broach must be tested and demagnetized before it can be used again.
(7) Special equipment and testing equipment for broach processing
The grooving broach is used to process aircraft, trains, ships and other parts. It has complex shapes, high precision requirements, strict technical requirements, and is difficult to process. It requires special processing equipment and testing instruments.
The testing instruments mainly include: one X-ray flaw detector (domestic); one projector in Milan (100 times magnification); two portable hardness testers in Germany; four universal microscopes; high-precision verticality and straight line The inspection has one.
(8) Groove machining and shovel equipment
In order to make the boring boring tool, our company specially purchased two powerful CNC high-precision plane forming grinding machines from Germany aba company and Germany BLONM company, the minimum feed amount is 0.001mm, with independent small shaft and automatic measuring pitch, etc. Function, eight-axis six-linkage, six-axis linkage dressing grinding wheel, automatic dressing grinding wheel, automatic compensation, used to machine the grooving grooving tooth shape and shovel grinding, can also be used to process high-precision forming broach, such as car engine special type The broaching, the squeegee and the like fully satisfy the high precision requirements of the tooth shape of the grooving squeegee and the shovel grinding process.
(9) Machining of the front and rear corners of the grooving broach
Our company also imports two automatic CNC broaching grinding machines from Germany for processing the front and rear corners of the broach, with automatic measuring of the pitch and other functions, ensuring uniform grinding amount and cutting oil cooling function to ensure sharpening. In the process, it is not rubbed or burned, and the surface roughness value can reach Ra=0.1μm.
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Tag: broach, turbine disk, broaching, grooving, shovel
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