0 Preface
Engine assembly as a key step in the engine manufacturing process has an important impact on engine performance and operational stability. Moreover, the assembly cost and the assembly workload in the engine manufacturing process account for a large proportion, of which the cost accounts for about 40%, and the workload accounts for more than 50% of the total Machine manufacturing workload. Therefore, how to shorten the assembly cycle and how to ensure the assembly quality in engine manufacturing has become an urgent problem to be solved, and the research of flexible and automated tooling provides an effective solution to the above problems.
1 Domestic development status
Domestic research on engine flexible tooling mainly focuses on engine parts, component assembly and engine main unit body and machine assembly, and has many achievements in theoretical research and prototype test, but the overall research and development lags behind abroad.
1 Based on the 3-UPU parallel robot, the disc assembly flexible tooling is shown in Figure 1. The flexible tooling is mainly for the assembly of engine disc parts. The specific working process is: the flexible tooling is placed on the flexible tooling assembly reference surface by a crane and other spreaders, and the position of the disk is detected by the coordinate measuring instrument and the position sensor, and then the positioning block is used to assemble the disk. Achieve positioning and tighten. By adjusting the positioning block to adjust the expansion and contraction of the upper drive slide and the lower drive slide, the assembly of the disc parts of different types of engines can be satisfied, and the assembly reference plate can be positioned and clamped under the condition of the change of the assembly reference piece. The insufficiency of the overall structural design is that there is a certain problem with the connection between the parallel mechanism and the upper and lower driving slide bars; the stability of the tooling is increased when the number of disks held by the positioning block is increased.
2 Engine disc and shaft assembly tooling Figure 2 is an engine disc and shaft assembly tool. The assembly method of disc and shaft is divided into vertical and horizontal assembly. The tool set is mainly composed of a disc positioning clamping structure and a shaft conveying structure, and is designed to realize horizontal and vertical assembly of the compressor disc and the shaft, but the disc positioning device of the tool is positioned for the disc in which the vanes have been installed. There will be interference in the clamping.
3 engine multi-degree of freedom assembly platform multi-degree of freedom assembly platform due to more freedom, so the attitude of the engine assembly process is more, reducing the manual adjustment of the engine position to reduce the workload of the staff, and accordingly The complexity of the platform structure is increased. This type of tooling is mainly suitable for the assembly of the main unit of the engine and the whole machine, and the degree of automation is relatively high. In China, there has been some research on engine automation and flexible assembly tooling. There are few researches on the automation assembly of engine bolts, and the bolt assembly is still manually tightened, and some testing methods are used to ensure the tightening is qualified. In the automotive field, the automatic tightening machine for bolts is widely used, such as automatic tightening of automobile engine bolts and automatic tightening of automobile tire bolts. The automatic assembly of bolts in these aspects provides a favorable reference for the automated assembly of engine bolts.
2 Analysis of bolt force and tightening control method
The connection between the disk and the disk in the rotor of the engine compressor is generally a bolt connection in a detachable connection mode. For example, a certain type of military engine has a bolt connection between each of the low pressure compressor and the high pressure compressor. 24, the traditional tightening method is the manual tightening of the torque wrench. The manual tightening of the starting position is that the compressor disc has been calibrated before leaving the factory, and the calibration also determines the relative position between the compressor discs of each stage. The tightening of the bolts by the automatic tightening machine can realize the simultaneous tightening of the symmetrical position bolts, and the pre-tightening force is detected by the sensor to judge whether the tightening is qualified, and the bolt tightening efficiency is improved under the premise of ensuring the tightening quality. At present, many domestic military engines and commercial engines are connected by a bolt. Many bolts are still used. Based on the common points of bolt assembly on the rotor, combined with automatic assembly and tooling design, the assembly features and assembly of the rotor for bolting. In the process, an automatic assembly tightening machine capable of assembling different types of compressor disk bolts with similar structure is designed. The automatic tightening machine can realize the automatic assembly of the engine compressor disk bolt connection, and can further improve the bolts of the engine compressor disk. Assembly quality and assembly efficiency. The working environment of the engine rotor is usually harsh, mostly in high temperature, high speed and high load environment. Therefore, the unbalance of the rotor has a great influence on the vibration of the whole machine, especially for the bolt connection on the rotor of the compressor to ensure the preload of the bolt. At the same time, the uniformity of bolt tightening is very important for the rotor working. The traditional assembly method has many drawbacks under multiple requirements, and the automatic tightening method can improve the efficiency and quality of the rotor bolt assembly.
2.1 Analysis of bolt tightening force
The analysis of bolt tightening force is the best choice for preloading, because no matter what method is used for assembly, bolting must meet four requirements: bolted parts should be securely jointed under working load. Under alternating load conditions, the bolts should have a long enough life to avoid short-term fatigue damage; the joints should have good sealing under the action of liquid or gas; the bolted parts should not work loosely.
2.2 Analysis of bolt tightening control method
There are three common control methods for bolt tightening: torque control (T), torque-angle control (TA), and yield point (TG). Among them, the torque control method is the simplest and most common control method among the above three control methods. In the tightening process, the pre-tightening force of the bolt is indirectly controlled by controlling the real-time torque of the bolt. The biggest advantage is that the cost is low and the detection method is simple. The tightening quality can be detected by a torque wrench, so the detection method is simple. The advantage of this tightening method is that a more stable tightening quality can be obtained under the premise that the tightening precision is ensured, and the problem that the tightening quality is seriously affected by the friction coefficient of the surface of the screw member is overcome; the bearing capacity of the bolt can be fully exerted. Disadvantages: Since the two values ​​of torque and corner are used as the measured values, the control system of this method is complicated. The yield point control method is to detect the stress change of the thread material during the bolt tightening process, and the yield point of the thread material is used as the monitoring value. When the yield point method is used as the bolt tightening control method, the operation process is to first tighten a specified torque to the bolt. After reaching the specified value, this point is taken as the initial point, and the detection device is started.
The change in the slope value of the tightening curve is monitored in real time until the slope value of the stress-strain curve of the bolt material drops to a preset value indicating that the tightening is completed.
2.3 Analysis of bolt tightening calculation accuracy
The tightening method and the pre-tightening force control method used in the bolt tightening process all have an influence on the tightening accuracy, so the influence of these factors cannot be ignored in the calculation of the bolt tightening accuracy. Meeting the bolt strength requirement during bolt tightening is a prerequisite for tightening accuracy, and a safety factor is introduced to ensure the bolt's own strength.
3 Application of automatic tightening technology in engine assembly
3.1 Overall structure design and working principle
The structure of the engine bolt automatic tightening machine is divided into two parts, namely the tightening part and the positioning part of the disc part. The main part is the lifting and rotating mechanism of the tightening box, the lateral movement mechanism of the rotor positioning clamping table, and the lifting and holding of the rotor positioning clamping table. The rotating mechanism, the tightening shaft rotation and the lateral movement mechanism are composed of four parts. The rotor positioning clamping table lateral moving mechanism, the tightening box lifting and rotating, the tightening shaft rotation and the lateral movement, the rotor positioning clamping table rotating mechanism are driven by the motor, and the rotor positioning clamping table lifting mechanism and the tightening head position fine adjustment are hydraulically driven. The working process is: placing the compressor disk to be tightened by the crane on the reference surface of the rotor positioning clamping table 3, positioning the block on the rotor positioning clamping table to position the assembly structure, and the rotor positioning clamping table is in the lateral movement mechanism Under the driving, the slide rail 6 is moved to the lower side of the tightening chassis 2, and is lifted to the position to be assembled by the hydraulic lifting platform 5, and the assembly position of the rotor is precisely adjusted under the fine adjustment structure work; the screwing head is moved to the designated assembly position. After adjusting the posture, the bolts are capped and tightened, and the rotation of all the bolts is completed by the rotation of the rotor positioning clamping table, thereby realizing the automatic tightening of the engine bolts.
3.2 Automatic tightening machine working principle
Taking a bolt assembly on a rotor of a type 9 engine compressor as an example, the compressor is divided into three parts including a fan stage, a low pressure compressor, and a high pressure compressor, wherein the first, second and third stage compressors are bolted together, The four, five, and six stages are fixed together, and the seventh, eighth, and ninth stages are fixed together. A total of 24 bolts need to be tightened in each part of the week. The rotor positioning clamping table is composed of a fine adjustment mechanism, a rotating mechanism and a hydraulic lifting mechanism. Taking the compressor disc bolt assembly as an example, the positioning block (can be removed and replaced as needed) has a shape design method, and the actual contour of the compressor disc positioning position can be used as a design standard, and the rotor member is externally
The circular contour features are integrated onto four positioning blocks. Positioning method: The positioning blocks in four directions are moved to the rotor positioning point under the motor drive, and the compressor rotor disk is suction-clamped. Moving along the bottom rail under the screw drive to the position to be assembled under the tightening machine, and then the position of the rotor is further accurately positioned by the fine adjustment mechanism on the rotor positioning clamping table. The vertical adjustment is driven by the hydraulic drive to push the rotor to the height to be tightened. During the tightening process, the rotor positioning clamping table is required to drive the compressor disk to rotate. This movement is realized by the worm gear transmission. The tightening device is composed of a support frame and a screw box. The entire tightening box can be moved in the vertical direction to finely adjust the distance between the vertical direction of the rotor to be assembled and the tightening head. The inner shape of the tightening head is designed according to the shape of the nut and can be disassembled and replaced. Since the distribution radius of the bolts on the rotor may vary, the two tightening heads can be moved laterally by the screw drive. The internal shape of the tightening head is the same as that of the nut. The depth design ensures that the entire tightening box does not need to be lowered as the nut descends during the tightening process, but is automatically lowered by the nut tightening process.
The entire tightening process is completed, and this method is also used when loosening. Selection of the assembly reference and the way out: The engine bolt automatic tightening machine is designed with a decentralized skeletal structure, and the bolt assembly method uses a vertical assembly area. The assembly reference is used for the positioning reference of the rotor member to be assembled, the tightening radius adjustment reference of the tightening shaft, and the rotation reference of the rotor, with the central axis between the two tightening shafts in the tightening box as the assembly reference. The engine rotor enters the assembly from the left side and is assembled from the right side after assembly. Firstly, the compressor rotor disk to be assembled is suspended by the spreader to be positioned above the clamping table, and slowly lowered onto the tooling reference surface, and then the positioning block on the rotor positioning clamping table adjusts the rotor disk to the 0 o'clock position. The electromagnetic adsorption system clamps the positioning block to the assembly to be assembled; while positioning and clamping the compressor rotor disk, adjusting the tightening head to the optimal tightening position, then moving the rotor positioning clamping table to the tightening box, and then adjusting the rotor positioning Hold the clamping table and the tightening box to the appropriate assembly position, check the integrity of the fittings and the tightening machine to prepare for assembly; the tightening machine starts working, the staff inputs the corresponding position data through the computer, and the nut is placed on the corresponding bolt. After the moving parts of the tooling reach the designated position, the motor is locked to keep the position unchanged. During this period, the assembly staff should pay attention to various possible assembly problems and adjust them in time to ensure the assembly quality until the assembly work is completed. Once the station is assembled, move the entire assembly to the next assembly station for the next stage assembly.
3.3 Positioning method
The relative position of the reference part and the fixture is determined on the assembly reference piece, and the reference used is called the positioning reference. The positioning mechanism of the fixture is designed according to the shape, number and precision of the positioning reference of the assembly reference (components, components and parts). When the assembly reference member is placed on the fixture, the positioning reference is in contact with the positioning surface of the positioning member such that the assembly reference member has the correct position relative to the clamp and other components, components or parts, and each assembly process of the engine assembly process has Determined assembly reference.
3.3.1 Plane positioning
Plane-based datum is one of the most commonly used positioning methods for engines. The positioning method in which planes or planes are combined with other curved surfaces is a commonly used method. This positioning method generally uses support plates and support nails as its positioning elements.
3.3.2 External cylindrical surface positioning
Centering and support positioning are two basic forms of positioning when assembling a cylindrical surface other than the reference part. In centering positioning, the center axis of the outer cylindrical surface is usually the positioning reference, and the actual contact with the positioning element is the point, line or surface on the assembly reference. When the cylindrical reference support is assembled outside the reference part, the assembly reference piece and the positioning element are in contact with the busbar on the outer cylindrical surface, and the positioning method is usually a V-shaped block and a support plate.
3.3.3 Inner hole positioning
When the engine uses the casing and the disk parts as the assembly reference parts, the hole is used as the first reference to play the main positioning role, and the end face positioning limits the degree of freedom of movement in the axial direction. The degree of freedom of rotation around the axis is usually not used. limit. The advantage of this positioning method is that the positioning hole and the positioning element are in a mating state, thereby ensuring that the axis of the hole is in the correct position, and thus the positioning method is also called centering positioning.
3.3.4 Combined surface positioning
The above-mentioned planar positioning, outer cylindrical surface positioning and inner hole positioning are all located on a single surface, and in the actual assembly process, the assembly reference member is usually positioned by a combined surface, such as two-hole positioning, two outer cylinders. Surface positioning and a surface and a hole plus an outer cylindrical surface and a plane positioning. When combining positioning, a maximum of three surface combinations can be selected. When three surface combinations are selected as the positioning reference, it is necessary to distinguish the first positioning reference, the second positioning reference and the third positioning reference. The first positioning reference is the selected positioning on the assembly reference piece. The surface with the largest support area and the higher relative positioning accuracy in the reference, the second reference.
4 Conclusion
Assembly is an important part of the product manufacturing process, and the quality of the assembly will directly affect the quality and performance of the product. In the manufacturing field, countries are fiercely competing to accelerate the development of the manufacturing industry. Automated assembly in aircraft manufacturing has changed the assembly mode consisting of manual assembly and rigid tooling. The extensive use of flexible tooling not only improves the assembly of the aircraft. Quality, shortened assembly cycle, and reduced aircraft manufacturing costs. However, the assembly of the engine is still using the assembly mode of "manual assembly + rigid tooling", which results in the assembly quality of the engine is greatly affected by human factors, and the engine manufacturing cycle is lengthened. In order to solve the above problems, engine automation and flexible assembly have gradually become research hotspots.
references:
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