The power source of the aircraft is the engine, and the turbine disk is a very important part of the entire engine power turbine section, and is a more difficult part to process in the entire turbine engine. Among them, the largest amount of work and the most difficult one is the processing of turbine root grooves. The material of the turbine disk is generally a nickel-base alloy, and the hardening phenomenon during processing is quite obvious, and the cutting processability is very poor. Moreover, the root groove of the turbine blade must be matched with the root of the blade, so the precision of the matching is very high, and the machining is very difficult. The broaching tool processing method can meet the high precision and lower surface roughness requirements of the turbine disk root groove.
1. Features of broaching tool
The broach is a special tool, which is very expensive to manufacture, so it is economical to use it in mass production. At present, broaching of standard circular holes and spline holes has been standardized, and good economic results can also be obtained in small batch production. Broach cutting speed is generally low, commonly used 1.02 ~ 7.8m/min, cutting thickness is very thin, so the broaching surface quality is high, the blade wear is very slow, long life and machining accuracy. When machining holes, IT7-9 can be achieved, and even IT6 can be achieved. The productivity of the broach is very high. This is because the broach has a large number of teeth and the cutting edge for each tooth is long, and it can simultaneously perform rough, semi-finish and finish machining in one working stroke. Broaching has the following advantages: 1 Short processing time and high efficiency. 2 high degree of precision machining, small deviations. 3 The surface quality is good. 4 The processing method is economical, and the skill of the processing personnel does not need to be skilled to process.
The broaching tool processing method can meet the high precision and lower surface roughness requirements of the turbine disk root groove. The key to guaranteeing high precision and low surface roughness is the design and manufacture of turret blades for turbine disk root grooves. For the special, difficult-to-machine materials of the turbine disk, high precision of the blade root groove, and low surface roughness values, the broach is reasonably designed, the broach material is reasonably selected, and the advanced heat treatment method is adopted to solve the key technologies in the broach manufacturing process. The manufacturing process finally reaches the goal of mass production, and the quality and performance of the tool have reached the international advanced level.
2. Technical key
(1) Overall design of broach
For the complex shape of the blade root slot, the broach is designed as a rough broach, a semi-finishing broach, a fine broach, used in groups, and broached once; the rough broach pulls away most of the cutting allowance, semi-finishing pulling Knife trimming profile profile, finishing broaching final broaching.
(2) Broaching method selection
The rough broach adopts incremental broaching method to pull out the roots of the blade. The semi-finishing broach adopts the elevation processing method to trim the groove type. The fine broach adopts the same profile broaching method, and the broach-shaped surface needs to be shovelled. Grind the corner.
(3) Broach material selection
The material used for the broach is generally known as W6Mo5Co4V2 high speed steel. After heat treatment, it can reach Rockwell hardness of 63~66HRC. Because the material of the turbine wheel is high temperature resistant nickel-base alloy, the processability is poor, and the turbine wheel is The precision requirements are very high. Although cemented carbide tools are superior to high-speed steels in terms of hardness, wear resistance and cutting amount, they have the disadvantage that they cannot withstand large impact forces, and their strength is low, only 1/3 of that of high-speed steels. Heat treatment is difficult; solid carbide tools are difficult to manufacture, have poor machinability, and the grinding of the profile must use a diamond wheel. Conventional high-speed steel cannot be used because of its low performance index in terms of strength, hardness, etc. However, powder metallurgy high-speed steels such as CPM-42, T15, etc. are superior to other high-speed steels for toughness, hardness, and wearability, and are suitable for processing. Slot pull knife. In addition, M42 (W2Mo9Cr4VCo8) cobalt high-speed steel heat treatment hardness of up to 67 ~ 69HRC, in the processing when the temperature is increased to 600 ~ 620 °C can also have a high red hot hard, and has a very high wear resistance, very Due to its high strength and other properties, the material selection of the turret for the turbine wheel root slot is also suitable.
(4) Heat treatment
Powder metallurgy high-speed steel CPM-42, T15, etc. as broaching materials, heat treatment has the following characteristics: 1 too long quenching or high temperature is easy to produce "over-burning" phenomenon, broach life will be reduced. 2 Brittleness after quenching is large, and it is easy to produce quench cracks. 3 Combined with blade tooth profile characteristics of broach, large diameter at the tip, easy to produce quenching cracks and grinding cracks. 4 The use of temperature control device can ensure that the knife does not produce "over-burning" and the hardness meets the requirements. 5 quenching hardness to meet the process requirements. 6 to avoid quench cracks and grinding cracks.
(5) Technical key
After finishing the broach, the final tooth profile of the turbine wheel is formed, and the precision of the precision broach directly affects the tooth profile accuracy and surface roughness of the turbine wheel. The processing of fine broaches is the most critical, the most complex process, and the most difficult to process.
Fine broach processing to solve the following technical key: 1 ensure that the perpendicularity of the broach on all sides 0.005mm. 2 Ensure that the broach tooth tolerance is 0.005mm. 3 Guarantee the broach M value, K value tolerance ± 0.002 5mm. 4 After the fine broaching, the cutting teeth leave no edge zone, and the calibration tooth zone is even. 5 fine broach tooth shape error 0.005mm.
Therefore, to ensure that the final machining surface meets the requirements, the following points should be noted in the design of the broaching tool: (1) The broaching tool is composed of a round groove, a round plane forming broach, a groove groove bottom forming broach, and a wheel groove contour forming broach, etc. Partly composed. The amount of tooth lift and pitch of the broaches of each part are different. The amount of pull teeth of the fine pull knife should be small, and it must be smaller during full tooth cutting. For the whole broach, the tooth lift design should be before Large and small. 2 In order to improve the service life of the precision broach and ensure the correctness of its contour, the broach profile is designed to take the minimum dimension of the wheel groove contour so that the broaching entity is at the maximum size of the wheel groove contour. 3 In the full-tooth type finish cutting, the pulling force suddenly increases, the broach easily generates vibration, and the broken tooth or broach is fractured. This not only damages the workpiece but also causes the loss of the broach. To prevent this from happening, the design When finishing the broach, calculate the number of teeth during full-tooth cutting, and open the swarf at the root and bottom of these teeth to ensure efficient chip breaking.
(6) The sharpening of the broach
The broach wears gradually. When the broach wears to a certain extent, it will affect the accuracy of the final processing and the life of the entire set of broaches. Therefore, abnormal conditions occur during processing, such as a sudden drop in surface quality or broach vibration. To increase, the broach must be re-sharpened on the tool grinding machine. Generally, the sharpening broach is limited to the rough broach teeth. The grinding position is also limited to the side of the back rake. The grinding broach mostly uses CBN. Grinding wheel or diamond grinding wheel, grinding a tooth at a time, and should pay attention to correct the pitch, to avoid excessive grinding, grinding after the knife edge, each broach must be flaw detection, degaussing, can be used again.
(7) Broach processing equipment and testing instruments
The broaching broaching tool is used to process parts and components such as airplanes, trains, ships, etc. It is complex in shape, high in accuracy, strict in technical requirements, and difficult to process. It requires specialized processing equipment and testing instruments.
The testing instruments mainly include: X-ray flaw detector (domestic); Italian Milan projector (magnification 100 times) one; Germany's portable hardness tester two; Universal tool microscope four; high precision perpendicularity and straight line Degree inspection with a and so on.
(8) Machining of broaching broach and its grinding equipment
In order to do the boring and broaching well, our company specially purchased two powerful CNC high-precision plane forming grinding machines from German aba company and German BLONM company, the minimum feeding amount is 0.001mm, with independent small shaft and automatic measurement of pitch, etc. Function, eight-axis six linkage, six-axis linkage dressing grinding wheel, automatic dressing grinding wheel, automatic compensation, used for processing tooth profile of broaching broach and shovel grinding processing, can also be used for processing high-precision shaping broach, such as automobile engine type The broach, toothed plate, etc., fully meet the high precision requirements of tongue and groove broach tooth profile and shovel grinding processing.
(9) Machining of front and back corners
Our company also imports two fully automatic CNC broach edge grinders from Germany. It is used to process rake angles and rake angles. It has the function of automatic measurement of pitch and so on. It ensures uniform grinding, and it has cutting oil cooling function to ensure sharpening. During the process, it is not buffed or burned, and the surface roughness can reach Ra = 0.1 μm.
