Text | Far mountain bamboo leaves
Edit | Far mountain bamboo leaves
preface
It is well known that in the field of gear manufacturing, traditional machining methods often require expensive special machines and special tools, which makes the production of small and medium-sized production series unprofitable.
Therefore, in order to pursue profitability, people now pay more attention to the use of general computer CNC machine tools and standard cheap tools to process gear technology, and study the purpose of "using CNC machine tools for conventional and improved shape gear processing", which is precisely to solve this problem.
So what are the advantages compared to traditional machining machines?
General purpose computer numerical control machine tools
Traditional methods of machining cylindrical gears, such as the hob method or the circumferential slip cutting method, require expensive special machines and special tools, which makes production unprofitable, especially for small and medium-sized series.
Today, with special attention to the technology of manufacturing gears using universal computer numerical control machines and standard inexpensive tools, based on the mathematical models provided, a software was developed to generate code for controlling the machine tool to perform multiple machining of straight tooth lines and cylindrical gears for improving tooth lines.
Using solid carbide milling cutters, whether cylindrical or ball-jointed, gears made of steel with straight tooth lines and longitudinally improved male tooth lines are machined on a five-axis milling machine.
For this purpose, the software must be used to check the manufactured gears on a coordinate measuring machine, evaluate the consistency of the shape, tooth line and pitch, and evaluate the side surfaces of the tooth profiles after machining according to the planned strategy.
Tested using an optical microscope contact profiler, the proposed method is able to provide a very high quality of machined gears compared to competing methods.
The great advantage of this method is the use of tools that are not geometrically associated with the profile of the machined gear, allowing the production process to be independent of standard tooth profiles and profiles.
It is undeniable that cylindrical gears are still the most commonly used type of gear, which are usually machined using the modular hob method, can also use the Fellowes scraper method, or are finished by grinding according to different methods.
Involute cylindrical gears of straight tooth lines are the most commonly used in the transmission devices of many machinery and equipment, and their most common processing method is to use the forming method.
In addition, in single-piece production, they can also be formed using modular discs or finger clip cutters. In the researchers' research, the use of modular disc cutters for gear machining was presented, and the cutting force distribution during the machining process was analyzed.
The accuracy of machining gears depends largely on the process and tools used, the use of common tools such as modular hobs can ensure accuracy, and the use of higher precision tools will contribute to the wider application of multifunctional universal CNC machine tools.
Despite the fact that these tools are usually special and expensive, and machining is carried out on special machines, there is still a growing trend towards the use of non-contact methods to inspect manufactured gears, which shows the popularity of this method.
It is worth noting that polymeric materials are increasingly used as construction materials for gear elements, which can be modified by annealing to improve processing conditions at small gaps, as a rule, gears are machined with special tools, and the accuracy of the described method is analyzed at the same time.
But it is also not easy to increase the accuracy, the method of using mathematical models in the process of geometric design of special tools, which can be used as a basis for optimizing the parameters of milling tools for machining gears.
You know, as gear processing technology becomes more and more demanding in terms of quality and efficiency, it has become very important that the processed gear does not need to be finished on another machine tool during the manufacturing process.
As a result, the integration of all machining processes, from clamping raw materials to finishing, in one machine is becoming an increasing priority, influenced by the "one-time forming" machining concept.
The development of one-shot molding technology involves the integration of selective laser hardening with a multi-axis machining platform, which allows gears to be machined and hardened in one production center.
However, only hardening is not enough, the processing after hardening is the most important, for this reason, people often use grinding as a way to improve the quality of gears after heat treatment, grinding is necessary in the finishing process.
Errors in the finishing process and their further impact on gear operation were also discussed, after which finishing gears using non-Newtonian liquid polishing techniques became a new way to solve this problem.
The quality of the entire gearbox depends on the position of the mating area of the interacting elements, and the fit analysis is mainly used to determine kinematic errors caused by errors in machining and gear assembly, optimization and overall performance of gears.
At present, the predictability of machining parameters, chip formation characteristics during machining, tool wear and the generation of forces during cutting have become the research topics of close attention of the industry, constantly promoting the modernization of the field of gear processing, and at the same time, with the increasing needs of the global automotive industry, an efficient gear manufacturing method is required.
Of course, gear transmission is not only used in automobiles, but also widely used in various mechanical products, including aircraft, ships and power generation equipment, so the production volume of gearboxes is huge.
Based on this situation, the researchers have carried out more in-depth research in the field of designing and building CNC machine tools, so as to realize the development of special gear processing technology, so that the shape and geometry of gears have the ability to freely process.
Research in the field of multi-task CNC machine tools
The advent of multi-task machines in the field of machine tools offers new possibilities for machining large gears on these machines.
However, on traditional gear machining machines, the possibility of using standard tools presents technical challenges in terms of product quality, and it seems completely reasonable to use appropriate solutions and develop CNC machining technology methods as a way to carry out gear machining.
Among the many ways that have been studied, one of the technologies is power scraping technology, as an effective method for producing internal high-precision gears, researchers analyzed the influence of the geometric parameters of the power scraping method on the quality of the manufactured gears.
In this machining method, by visualizing the resulting machined shape, one can accurately analyze the shape change of the gear during machining and the volume of the workpiece material being removed.
Once the internal gears are machined according to the power scraping technique, they are naturally unmatched in terms of quality and efficiency.
However, such an efficient method can be imagined that the machine dedicated to this method would be very expensive, but it is still possible to prepare process technology software to perform geometric evaluation of the processed gear by simulating the gear manufacturing process.
The unlimited possibilities for generating toolpaths and validating models of machined parts in the subsequent preparation phase of production technology offer great opportunities for the use of machine computer control systems.
The researchers analyzed the surface integrity state of various gear machining and concluded that the turning and milling method is comparable to the finishing process of small modular gears.
Since then, new technologies in this area have gradually begun to be embraced, using universal and simple tools, representing the efficient use of universal machining centers in efficient and precise gear manufacturing.
The continuous development of the field of CNC systems has created opportunities for technicians and programmers, resulting in an increasingly wide range of applications, the advantages of parametric programming of CNC machine tools, and the possibility of using this technology in multi-pass method machining gear strategies have also been infinitely amplified, using parametric programming methods to generate code for combined hob machining gear machining.
This aspect has been greatly developed, another aspect of CNC machine tools is also in the process of gradual development, mainly focused on the performance of three-axis machine tools, the use of the simplest kinematics of the machine tool, but the processing of spur gear, can get the fullest efficiency.
Echoing spur gears, spur gears can transmit rotational movements and loads sufficient to meet their work, therefore, the modification of the tooth line should be determined from the strength conditions of the gear, and the research on gear structure optimization, especially tooth shape optimization, has become the next direction of researchers.
Due to fixation, the traces of the mating tooth change under load, turn into point contact, and should be located only in the area of useful tooth surfaces, spur gears with longitudinal modification of the contour are characterized by insensitivity to assembly errors and are able to transmit large loads.
In the course of the study, the influence of shaft torsion angle on gear mating area and overlapping tooth trajectory position is evaluated, and the results show that in the absence of longitudinally corrected involute gears, the influence of errors in gear assemblies on the mating area of gears is very significant.
It turns out that gears can be machined using a variety of methods in the production process, especially with CNC machines, while the method of machining spur cylindrical gears and modifying the tooth line longitudinally on general-purpose CNC machines has also proven to be possible.
The use of universal tools as cylindrical or spherical end mills can represent an alternative to the industrial methods described in the production process, and it should be noted that the roles assumed are consistent.
And thanks to the application of tools that do not have a geometric relationship with the shape of the machining gear profile, the resulting material can be further developed, which makes it possible to produce cylindrical gears with other teeth and contour lines more standard.
The assumption of the above method is to create an involute line from a tangential line or spherical section formed by the tool operation surface, similar to chiseling.
In fact, in the actual machining process, the tool in the form of an end mill with a straight or spherical profile periodically enters the working position, and then the tool profile is mapped to the workpiece.
The tool then extends beyond the workpiece area, during which a relative rolling motion occurs, including rotation relative to the axis of the machining wheel, parallel to the running line of the tool.
Once the tool enters the working position and draws the contour of the machined teeth, it rotates relative to the final machining trajectory, and since the machining traces are lines that are not parallel to each other, they intersect each other, creating an angular transition between the toothed fragments.
Although the machining process will be repeated continuously, the profile of the workpiece is actually angled and the number of times, so the involute profile of the gear teeth is theoretical, and when the number of tool passes increases to infinity during machining, the angular profile follows the involute profile.
The characteristic of the involute profile is that its normal is tangent to the base circle, that is, the circle can be rotated to the continuous points of the contour, so that the contact point between the involute and the normal of the base circle is always located at the intersection of the base circle with a circle.
It can be seen that end mills with vertical axes, tangent to the profile being machined, are set at a constant distance from the horizontal axis of the gear for continuous points, and are displaced or offset only in the horizontal axis, resulting in a change that limits accuracy.
The accuracy of the machining process
The gap between theory and practice is actually caused by the displacement or offset mentioned above, so the accuracy of the contour is particularly important in the actual processing process.
In the gear machining technology under consideration, for any convex profile, the curved profile in the considered section is replaced by a straight section mapped by the tool.
To know, the end mill with a vertical axis when machining is a cylindrical surface tangent to the profile being machined, in general, the number of passes in the finishing process is more, so the distance between the successive passes is small, that is, a small part of the profile is machined, which can be regarded as a straight segment.
The maximum profile angle can be calculated according to the scheme proposed above, and then the error of the profile angle can be calculated, in order to determine the estimated angle of the tooth profile by the assumed method, the profile must consist of a certain number of straight parts, of course, depending on the number of tool passes.
In order to ensure the accuracy of the profile, it is necessary to use computer software to assist the work, and on the basis of the analysis, it is especially important to develop an application that supports the generation of coordinates for modifying the profile and the toolpath for gear machining.
The versatility of the software lies in the fact that it can be matched to any machine with complete standardized functions.
Depending on the parameters of the machine control system, it is important to limit the maximum radius of profile modification, analytical calculations show that the maximum radius tends to infinity, however, limiting this value in this case seems reasonable.
With the help of software is not enough, another very important stage in the preparation of the machine tool is the correct positioning of the workpiece, while maintaining the appropriate parallelism and perpendicularity of the surface.
Finally, achieving small tolerances in the meshing teeth is one of the most important ways to keep gears quiet and undamaged when manufacturing gears, and as the accuracy of gear processing machine tools increases, inspection and measurement methods must also improve.
For this reason, it is necessary to use more accurate tools to measure the surface structure of the gear, and the detailed analysis of the modified contour of the processed gear using the microscope's three-dimensional optical system can greatly ensure the accuracy of the gear profile, and the microscope is also an excellent equipment for evaluating the surface quality after treatment and measuring roughness parameters.
It is not difficult to see that the measurement of surface roughness parameters perpendicular to the direction of the tooth line is very important for machining strategies that use the multi-pass method.
In fact, the measurement results parallel to the tooth line direction depend largely on the cutting data used, and the productivity of the method can be increased without losing the quality of the treated surface by determining the optimal feed rate.
And this is where the most prominent thing compared to the traditional method, machining with tools that are geometrically unrelated to the profile to be machined, opening up many possibilities for the design of the geometric area where the gear is modified.
The high degree of freedom also makes it the darling of the lathe machining production process, which allows the free modification of the fillet area to improve its strength considerations, and in the process of designing the gear, its parameters can be freely selected, and with the same tools, gears with various modulus, even non-standard gears, can be machined.
epilogue
Industrial software for manufacturing gears on CNC machines currently available on the market is very expensive, especially for machines with complex operating dynamics.
However, relatively simple three-axis CNC machines show good results in machining spur gears, which means that high-quality gear machining can be achieved with simple machines and production costs are reduced.
It is believed that in the future, people will be able to further study and explore the potential of this machining method, which can be used not only for the production of cylindrical gears with modified tooth lines, but also for the production of gears with non-linear or non-arc tooth lines.
This will open up more options for innovations in the field of gear transmission, and gears with different tooth line shapes can be designed according to specific needs.