Study On The Internal Gear Form Griding Process And Equipment Technology

The planetary gearing composed of sun gear, planet gear and internal gear is widely used in mechanical transmissions of crane industry, construction industry, mineral industry, automobile industry, energy industry and other industries. Equipped with hardened gears, the loading capacity and service life of transmission devices can be increased exponentially, and their size and weight can be decreased largely. At present in our country, in order to enhance manufacturing precision and loading capacity of planetary trains, the key is to realize the grinding of internal gears with hardened flanks. As it is difficult for generating method to machine the internal gears, and the CNC gear form grinding machines made in developed countries are very expensive, these make the domestic gear manufacturing factories find other ways to treat the internal gear with hard flanks. For example, after gear shaping or broaching, the internal gear is hardened by nitriding. Nitriding has the special requirements for the gear material and low processing efficiency. Because there is no any further finish machining after nitriding, it is impossible for the gears to have higher profile accuracy and loading capacity. Although there have been the commercial CNC gear form grinding machines in some developed countries, and a few of domestic companies have started to develop this kind of grinding machines, there is still very few report on the research of internal gear form grinding process and equipment technology.In order to change the situation that the gear form grinding machines rely on import from abroad, and promote the development of domestic gear manufacturing industry, it is urgent task to research and develop gear form grinding machine and technology owned the Autonomous Intellectual Property of P.R. China. For this reason, internal gear form grinding process and equipment technology are studied systematically in this dissertation. The primary research contents and accomplishments of this dissertation are as follows:(1) Based on modularization design principle, modular design of internal gear form grinding machine is completed. On the basis of function analysis, the layout of the internal gear form grinding machine is designed, and different modules of the machine are divided. Taking Pro/E software as developing platform and Pro/Toolkit as secondary development tool, a total parametric 3D modeling bank for each module of gear form grinding machine is established. A CAD system to support modular design of gear form grinding machine is developed. And then, the components and subassemblies of gear form grinding machine are designed in detail and selected rationally.(2) Analysis and research on the key components and subassemblies of gear form grinding machine are carried out.3D parametric model of the column of gear grinding machine is established by means of Pro/E. Both static analysis and dynamic analysis are performed by means of ANSYS software. The influences of different rib structures on the dynamic characteristic of column are investigated. The major parameters influencing on column’s performance are found by analyzing the sensitivity of structure parameters, and a new design plan for column is proposed. With the aid in finite element analysis (FEA), the original structure of grinding wheel frame is improved. The finite element model of wheel spindle is set up, and modal analysis on the spindle is done. The critical revolution of the spindle is also calculated.(3) Dressing of involute grinding wheel is investigated and wheel dressing device is developed. According to involute generating principle, the motions required in dressing involute wheel are studied based on "generation method" and "interpolation method" respectively. Mathematical models of two wheel dressing methods are established, and two wheel dressing devices are drawn correspondingly. By comparing the feasibility and economics of the two methods, NC wheel dressing device based on "interpolation method" is finally designed and manufactured.(4) The interpolation software for dressing involute grinding wheel is developed. The tooth profile accuracy of gear form grinding depends mainly on the profile accuracy of form wheel to be dressed. How to dress involute grinding wheel by means of NC technology is the key to the internal gear grinding. The wheel dressing technology suitable for involute profile with arbitrary tooth, module and base circle radius is studied. On the basis of analyzing involute interpolation, taking the normal tolerance 8 as the interpolation accuracy index, the density of interpolation points can be changed constantly with the change of developable angle incrementΔθso that the numbers of interpolation points can meet the requirements not only for interpolation accuracy, but for interpolation efficiency. Taking VC++as developing platform, the wheel dressing software system is developed, which can be applied for dressing involute grinding wheel used for grinding the gears with any parameter and accuracy. The software system consists of four modules:gear parameters input and calculation dialog block, interpolation accuracy calculation and control, dressing route simulation, NC machining code output. By means of this software system, NC machining code can be generated automatically according to the parameters of gear to be machined, and input into the CNC unit through RS232 interface.(5) Internal gear form grinding process is analyzed and researched. Gear form grinding is one of the finishing processes of gears with hard flank. It can remove the excess metals from tooth flank by means of form grinding wheel, and correct completely various errors existed in pre-grinding gear so as to have gear acquire higher machining accuracy and surface quality. The selection and formulation of gear form grinding process have an influence not only on the grinding efficiency, but on the tooth profile accuracy and surface roughness. Based on the autonomous developed CNC internal gear grinding machine, the issues on the selection and dressing of grinding wheel, the selection of grinding fluids, grinding allowance, and grinding variables involved in gear form grinding process are mainly discussed.(6) The factors influencing on gear grinding quality are analyzed, and the measures to improve gear grinding quality are put forward. Gear grinding quality includes many contents. Here means primarily profile accuracy, tooth spacing accuracy, tooth flank roughness, flank grinding burn, and so on. On the basis of analyzing gear shaping accuracy, some major factors influencing on profile accuracy and tooth spacing accuracy in internal gear form grinding are analyzed emphatically in light of gear form grinding principle, and the corresponding measures are proposed. The factors influencing on tooth flank roughness, flank burn are also discussed from gear grinding process, wheel dressing and gear material, the countermeasures to solve these problems are pointed out.(7) Installation and adjustment of CNC gear form grinding machine are completed. Installation accuracy of machine tool has direct influence on the machining accuracy. As to the CNC gear form grinding machine mentioned above, modular design makes the assembly of total machine very convenient. The emphasis is to install and set the NC slide and NC rotary table well. The installation accuracy of NC slide has direct influence on the linear motion accuracy. Therefore, it would have larger influence on the tooth alignment accuracy and accumulative pitch error. As the requirements for the parallelism of ball screw and nut to guide-way, and the distance from the centerline of nut seat to the slide bottom are very strict, it is difficult to ensure these requirements only relying on machining, proper assembly methods must be selected. NC rotary table is used for the indexing of gear. Its indexing accuracy has direct influence on the accumulative pitch error. In practical installation, both eliminating transmission error and reducing moving resistance are considered at the same time.(8) Involute wheel dressing test and internal gear form grinding test are completed. The wheel dressing test includes the generating wheel dressing program and wheel dressing. Firstly, basic parameters of gear to be machined are input into wheel dressing software system. Then, the involute forming process is simulated by means of involute dressing route simulation module. Lastly, the rough and finish dressing of grinding wheel are carried out by means of wheel dressing program generated in the software system. Before grinding the gear, the wheel dressing device, workpiece, center of rotary table, and grinding wheel frame etc. should be set to proper position. Then by inputting machining program manually through the operation panel, the unloading trial run must be done in order to ensure the grinding track correct. Lastly, gear grinding can be carried out. It is found by inspecting the ground gear that the precision with grade 6 can be met whether in tooth error, or tooth alignment error and pitch error.To sum up, internal gear form grinding process and equipment technology are researched in detail in this dissertation. Not only a kind of CNC internal gear form grinding machine and a wheel dressing device are researched and developed creatively, but the mathematical model for internal gear form grinding and machining plan are put forward creatively. A software system for internal gear form grinding is developed. Gear grinding tests show that the gear form grinding machine is simple in design, economical and practical, and has higher machining accuracy and flexibility. In reality, the grinding machine can be used to grind cylindrical spur and helical gears whether they are external or internal gears. The completion of this project would be helpful for changing the situation that gear form grinding machines rely on importation, thus promoting the development of domestic gear machine manufacturing industry.