Research on Application of Straight Bevel Gear Milling Technology
In the intersecting shaft transmission, bevel gears are widely used, and the processing of spur bevel gears is still dominated by gear planers. Affected by equipment and heat treatment, the machining accuracy is basically at the GB7 level, and the improvement of machining efficiency also has certain limitations.
In recent years, the PHOENIX II CNC bevel gear milling machine developed by Gleason has the function of processing straight bevel gears and spiral bevel gears. Tooth technology, with the application of carbide blade tools, the machining efficiency and machining accuracy of straight bevel gears have been greatly improved.
1. Development of processing methods for straight bevel gears
Compared with the rapidly developing spiral bevel gear processing technology, the processing technology of straight bevel gears has developed relatively slowly. The commonly used processing methods of spur bevel gears include disc-shaped modulus milling cutter milling, circular broaching, paired planer cutter, double cutter head milling, etc. Among them, the tooth planing process is widely used. The tooth planing process is based on the principle of the tooth hobbing method. Two straight planing knives are used as tools to process the spur bevel gear. Relatively speaking, the processing efficiency is not high, and it is difficult to ensure that the spur bevel gear drum teeth are surface processing requirements. The double-disc generation milling method uses two paired disc milling cutters to simultaneously cut the tooth surfaces on both sides of a certain tooth slot of the tooth blank in one process to complete the processing of straight bevel gears. The PHOENIX Ⅱ CNC gear milling machine adopts a new process method of milling the straight bevel gear with a single disc milling cutter, which can greatly shorten the processing cycle time of the straight bevel gear. Compared with the mechanical machine tool, the efficiency is higher.
Gear planer, double disc gear milling machine, PHOENIXⅡ gear milling machine
Comparing the three processing methods, the tooth planing processing equipment and the double disc milling cutter generate the mechanical transmission chain used in the gear milling machine, which is limited to the processing of straight bevel gears. The advantages of PHOENIXⅡ CNC gear milling machine are even greater.
(1) Equipment cost advantage: The straight bevel gear processing function is added to the spiral bevel gear milling processing equipment, and one machine is used for multiple purposes. Equipment technical transformation cost.
(2) Accuracy advantage: the main cutting edge of the disc milling cutter has a certain negative inclination angle, which can easily realize the processing of the spur tooth surface of the bevel gear. The shape of the contact area can improve the contact accuracy of the straight bevel gear, and effectively avoid the harm caused by the edge contact of the gear. After batch processing verification, it can stably reach the processing accuracy of GB6 level.
(3) Advantages of production efficiency: The efficiency of straight bevel gears is obviously improved compared with that of mechanical machine tools by CNC milling.
2. Straight bevel gear milling tool
Milling tool form:
Gleason PHOENIX II CNC gear milling machine for straight bevel gears using powder metallurgy Coniflex ® solid cutter heads and Coniflex ® Plus cutters with Pentac® carbide inserts.
Structural features of milling cutter:
The main parameters of the tool are:
(1) Tool pressure angle
Related to the dish angle of the tool, the Spindle Angle of the PHOENIXⅡ CNC gear milling machine 275HC is a fixed value of 23°. It is equal to the sum of the tool pressure angle and the dish angle. The dish angle is the concave angle of the main cutting edge of the disc milling cutter, which affects the bulging amount of the tooth surface processed when the disc milling cutter develops the tooth surface. The amount of crowning affects the size of the contact area of the bevel gear. Usually, the calculation software of straight bevel gear is used for theoretical simulation of the contact area, and the size of the pressure angle of the disc milling cutter is preliminarily determined. The size of the pressure angle of the milling cutter is not arbitrarily selected, but is selected according to the pressure angle series.
(2) Corner fillet
It is usually calculated and generated according to the main parameters of the bevel gear. The milling movement makes the root fillet formed by the machined part slightly larger than the tool nose fillet. It can be confirmed that the nominal design value of the tool nose fillet is equal to or slightly larger than that of the tool. The minimum fillet radius specified in the drawing, the first part of the straight bevel gear is processed and debugged using WANGONG display projection detection to prevent problems such as overcutting during processing.
(3) Tool offset distance
The width of the tool shown in Fig. 4 is determined by the width La of the large end and the width Li of the small end of the gear to be machined. The tool offset distance needs to satisfy the condition that it is greater than half of La and less than Li at the same time. The width is designed and generated by the straight bevel gear calculation software according to the parameters of the bevel gear. If the tool misalignment distance is not appropriate, the small end will be overcut or the big end will remain. Too wide a knife offset will cause overcutting of the tooth root arc, and a narrow tooth slot at the small end is more likely to cause overcutting. If the knife offset is too small, it will cause the tooth root to remain, and the large end tooth slot width is more likely to remain. It can be solved by calculation and trial cutting to verify whether the knife error distance is correct.
The calculation of the maximum tool offset distance is as follows
In the formula: Ton is the large-end arc tooth thickness of the matching gear; Bo is the big-end tooth root height; ϕ is the pressure angle; FW is the tooth surface width; Ao is the outer taper distance.
In the formula: WT, max is the maximum tool offset distance; Stock-allownce is the machining allowance.
Gear milling tool material:
The commonly used materials for integral disc milling cutters for straight bevel gears, such as ASP2023, ASP2030, are coated: TiN, TiAlN, etc. The material of a spur bevel gear is 18Cr2Ni4WA, which is a high-strength medium-alloy carburized steel. It can also be nitrided and tempered. The cutting performance of the ASP2030 TiAlN coating tool is slightly better than that of the ASP2023 TiN coating. .
Aeronautical materials have the characteristics of high hardness, high strength and high toughness. They also face the problems of poor processing performance, high processing difficulty, low processing efficiency and high tool cost in production and processing, which puts forward higher requirements for processing tools. The promotion and use of cemented carbide cutting tools not only optimizes the processing plan, solves the problems of work hardening and processing deformation, but also improves the service life of the cutting tools and ensures the consistency of large-scale processing results. In the machining of spur bevel gears, Coniflex® Plus tools equipped with Pentac® carbide inserts are gradually replacing the powder metallurgy Coniflex® solid cutter head, which also pushes the machining of spur bevel gears to high speed.
3. Machining Technology of Straight Bevel Gear Milling
Spur bevel gear milling is developed based on the spur bevel gears designed by professional bevel gear software, and the machining programs and testing programs are generated by the software, which are imported into the gear milling machine and the gear detector respectively. For straight bevel gear milling processing and adjustment, first cut a single tooth, adjust separately to ensure that the single tooth profile, tooth thickness and tooth depth of a pair of straight bevel gear pairs are qualified, and then cut a complete full tooth. Ensure that the gear profile, tooth thickness, tooth depth, pitch deviation fpt, pitch deviation Fpt, runout Fr and other characteristics of the large wheel and the small wheel are qualified respectively, and on this basis, the rolling inspection of the contact area is carried out.
When adjusting the milling of bevel gears, after the first pair of bevel gears are processed and tested on a rolling inspection machine, the actual contact area obtained is often not completely consistent with the simulated ideal contact area. After excluding various factors such as fixtures, press Adjust the contact area according to the actual situation.
Generally, the bad contact area is mainly distributed along the tooth height direction and the distribution along the tooth length direction is not ideal. The unsatisfactory distribution in the tooth height direction is mainly caused by the tooth shape error. It can be adjusted by changing the pressure angle. The pressure angle increases and the contact area moves. Towards the tooth tip, the pressure angle decreases and the contact area moves towards the tooth root. The unsatisfactory distribution of the tooth length direction is mainly caused by the tooth direction error. It is adjusted by changing the helix angle. The helix angle increases, the contact area moves to the small end, and the helix angle decreases, and the contact area moves to the large end. Figure 6 uses the bevel gear calculation software to adjust and correct the position of the contact area.
In the process of straight bevel gear milling, the main cutting edge of the disc milling cutter has a certain inclination angle with the end face of the milling cutter, that is, the drum shape forms an angle. At this time, the cutting edge is equivalent to a conical surface with an inner taper angle. The disc milling cutter can easily process the tooth surface of the straight bevel gear, which is also the unique feature of the disc milling cutter. Compared with processing methods such as tooth planing, it is easier to ensure the processing requirements of spur bevel gear drum teeth, the shape of the contact area is oval, and the contact state is better. However, the disc milling cutter does not move along the tooth length, and the bottom of the tooth slot is slightly concave. The value of this concavity is related to the radius and tooth width of the disc milling cutter. The maximum depth of the concave arc at the bottom of the milling groove is shown in formula (3):
In the formula: ΔH is the maximum depth of the concave arc at the bottom of the tooth groove; Fw is the tooth width of the gear; ϕ is the pressure angle; Du is the diameter of the disc milling cutter.
4. Solutions for closed-loop machining of straight bevel gears
The straight bevel gear processing unit is composed of bevel gear CNC gear milling machine, bevel gear sharpening machine, gear testing center, bevel gear rolling detection machine and other equipment. Combined with the application of bevel gear design, processing and measurement software, a closed-loop bevel gear is formed. The processing process reduces the difficulty of processing and adjusting bevel gears, and improves the production efficiency and processing accuracy of straight bevel gears.
Gleason bevel gear software includes multiple functional modules, such as Cage spiral bevel gear module, Straight Bevel [Mechanical] straight bevel gear software, FEA finite element analysis and other functional modules. The software modules used in the development of spur bevel gears are shown in Figure 7.
Straight Bevel [Mechanical] is used for the design of straight bevel gears, calculates the parameters of the straight bevel gear, determines the parameters of the cutting tool, runs to generate the design parameter card of the straight bevel gear and the tool design parameters, and is used for the generation and Preparing for the design of knives. UNICAL is used for the analysis and adjustment of the contact area of straight bevel gears, the adjustment of tooth thickness and backlash, the determination of tooth root overcut, timing analysis, generation of CMM inspection programs, and machining programs. The Summary Manager is used to convert the machining program generated by the UNICAL software operation into the machine tool program recognized by the machine tool, and to analyze and simulate the overtravel simulation verification of the machine tool caused by the tool length, fixture height, etc., to reduce the risk of first-piece debugging of straight bevel gears. GAGE is used for bevel gear measurement, and generates bevel gear anti-adjustment parameters according to the measurement results. It can also establish a standard gear inspection program for bevel gear inspection to ensure the consistency of straight bevel gear processing and better interchangeability.
PHOENIXⅡ CNC gear milling machine is used for the processing of straight bevel gears, equipped with a sharpener for sharpening of straight bevel gear milling cutters, gear inspection center is used for single inspection of bevel gears, rolling inspection machine is used for contact area A comprehensive inspection of several independent functions constitutes a bevel gear machining unit. Use professional bevel gear software to complete the design of bevel gear parts, the design of tool parameters, and the generation of machining programs and inspection programs. The machining program is input into the gear milling machine. After the gear cutting is completed, the gear inspection center uses the incoming inspection program to complete the measurement of the bevel gear. At the same time as the inspection report is obtained, the reverse adjustment data for the processing adjustment of the bevel gear is generated, and the reverse adjustment data is input into the gear milling machine, namely It can be processed and adjusted to achieve better precision requirements for bevel gears. The whole process forms a closed-loop machining solution from design, machining, measurement, measurement data feedback and then debugging. And the processing and debugging process is more efficient, more automatic and intelligent, reducing operations that rely on human experience, and greatly improving the production efficiency and processing accuracy of spur bevel gears.
5. Validation of straight bevel gear milling for an aviation product
Taking a group of straight bevel gears in the aviation high lift system as an example, the conventional spur gear bevel gear planing processing method was changed to powder metallurgy high-speed steel integral disc milling cutter milling processing method, and then the tool was changed to a cemented carbide cutter Strip tool for machining straight bevel gears. Through the improvement, the processing efficiency and gear precision of this group of spur bevel gears are greatly improved.
Machining method of spur bevel gear
For comparison, the powder metallurgy disc tool was used before the improvement, and the processing data of the cemented carbide tool after the improvement is shown in Table 1 and Table 2.
This group of spur bevel gears has been changed from two-cycle processing of double-rolling to one-processing of double-rolling by improving the processing method of parts. Secondly, with the application of tool technology, the cutting parameters are correspondingly improved, the tool speed is increased from 80-100r/min to 400r/min, the line speed is increased from 55-80m/min to more than 200m/min, and the cutting time is shortened from 60-90min to 400r/min. 15min or so. At the same time, the tooth profile accuracy of the parts is guaranteed to be stable, the tool life is increased, the auxiliary time such as tool sharpening and processing adjustment is reduced, the processing cycle of the straight bevel gear is shortened, the processing efficiency is improved, the processing cost is reduced, and the bevel gear parts of aviation products are satisfied. Develop short-cycle production requirements.
The improvement of machining quality, taking a straight bevel gear as an example, is shown in Figure 10.
Before the improvement, the overall tool processing of powder metallurgy high-speed steel was used. The tooth profile accuracy was affected by tool wear and other reasons, and the tooth profile accuracy was unstable. After grinding 5~10 parts at a time, the tooth profile changes and tooth root contact occurs, which needs to be re-sharpened. knives. The tool is sharpened many times, the debugging time of the parts after each sharpening is long, and the rejection rate is high.
After the improvement, the tooth profile accuracy is improved, the carbide blade tool is used, and the number of parts processed at one time is more than 500, the number of parts processing and adjustment is reduced, the processing and debugging time is shortened, the quality is more stable, and the processing efficiency is higher.
After batch processing verification, the improved straight bevel gear can stably reach the machining accuracy of GB6 level, and at the same time, the modified drum tooth surface can be guaranteed. The contact area is oval with a clear outline, and the contact area is in better condition. The drum-shaped tooth surface can effectively avoid the harm caused by the edge contact of the gear, and reduce the influence of the spur gear pair on the load change in the meshing transmission and the sensitivity of the straight gear pair to the installation error.
6. Concluding remarks
Based on the Gleason CNC bevel gear milling technology, this paper takes the straight bevel gears used in the angular variable speed reducer products of the aviation high lift system as the research object. , measurement and other aspects of application research, through the processing and verification of straight bevel gear parts, continuously accumulating the processing data of spur bevel gears, and forming processing solutions for spur bevel gear systems, which are helpful for improving the production efficiency and processing quality of spur bevel gears. certain reference value.