Cutting Force Fluctuation Suppression and Error Homogenization of Noncircular Gear Hobbing Based on the Tool Shifting Method

The current research on noncircular hobbing mainly focuses on the linkage model and motion realization.However,the intermittent cutting characteristics of hobbing would increase uncertainties in the manufacturing process.In this paper,a hobbing machining model with tool-shifting characteristics was proposed to solve the problems of cutting force fluctuation and inconsistency of tooth profile envelope accuracy at different positions of the pitch curve in noncircular gear hobbing.Based on the unit cutting force coefficient method,the undeformed chip volume generated by interrupted cutting was used to characterize the fluctuation trend of the hobbing force.The fluctuation characteristics of the cutting force generated by different hobbing models were compared and analyzed.Using the equivalent gear tooth and hob slotting numbers,an analysis model of the tooth profile envelope error of the noncircular gear was constructed.Subsequently,the tooth profile envelope errors at different positions of the pitch curve were compared and analyzed based on the constructed model.The transmission structure of the electronic gearbox was constructed based on the proposed hobbing model,and the hobbing experiment was conducted based on the selfdeveloped noncircular gear CNC hobbing system.This paper proposes a hobbing method that can effectively suppress the fluctuation of the peak and whole circumference cutting force and reduce the maximum envelope error of the whole circumference gear teeth.

VARIABLE INERTIAL DAMPER AND ITS APPLICATION IN ZERO-DRIVE GEAR HOBBING MACHINE

A variable inertial damper, whose viscous damping coefficient can be adjusted by changing the gap between inertia wheel and motor spindle, is designed in servomechanism of zero-drive hobbing machine and is directly attached on the motor spindle. The mathematical model of servo system with inertial damper is built. By using theoretical analysis and system simulation, it is demonstrated that the variable inertial damper with optimal damping coefficient and moment of inertia should lead to no resonance point in wider frequency range of exciting force. Therefore, its application in zero-drive hobbing machine makes this system not only achieve higher system stiffness to overcome load torque fluctuation, but also gain better stability.

STUDY ON WEAR AND DESTRUCTION OF HOB IN GEAR HOBBING

The wear and destruction appearances of hobs are researched. The reasons ofthe wear and destruction of hob are analyzed. And the influence of the change of the hobbing forceand the hobbing temperature on the wear and destruction of hob in gear hobbing is also analyzed. Ingear hobbing, the main wear mechanisms are adhesion and ploughing when cutting the 20CrMnTi gearusing W18Cr4V high-speed steel hob.

Investigation of Nanofluids as Potential Cutting Fluids in Gear Hobbing Processes of AISI 4118 Steel

The present work focuses on the performance of nanofluids called CN46-NanoAl2O3.80 formulated by using dispersions of nano aluminum oxide （Al2O3） in the ISO VG46 industrial oil on machining performance during gear hobbing of AISI 4118 steel. In machining gears, hobbing is one of the most important processes, especially to produce various gear shapes for adapting to diverse applications. However, the demand for high quality brings attention to product quality, particularly the roughness of the machined gear surface because of its effect on product appearance, function, and reliability. For additional improvement, applying nanofluids may produce superior product quality, as the rolling action of billions of nanoparticle units in the tool chip interface can significantly decrease the friction led to reduce the cutting forces. In addition, the characteristics of heat transfer of nanoparticles can contribute to reduce tool wear. In this experimental study, the performance of nanolubricant compared with the case of using ordinary cutting-fluid systems in the existing production line is investigated. The experimental results reveal that the tool life of the hob is significantly enhanced of 55.2%, gear surface roughness is smaller （27.3%）, and gear accuracy is significantly increased by using the nanofluid. This result, therefore, shows a promising solution to achieve the engineering-economy effectiveness in gear machining.

YKJ3180H Economy NC Gear Hobbing Machine

The YKJ3180H Economy NC GearHobbing Machine is a new variety,developed recently by the ChongqingMachine Tools Works to meet clients’demands. Its most prominent feature is its highproduction efficiency ( able to complete awork cycle automatically), high processingprecision (Grade 7 or higher according to theGB 10095) and its cost competitiveness. This product is used in the machinetool and machinery industries at automobiles,tractors, gears and gear box factories. It canbe used for processing spur gears and helicalgears, automatic radial feed wormwheels,tapered gears and crowning gears; so it isespecially applicable in factories usingcrowning gear couplings, such as metallurgy,mining, lifting transport and the chemicalmachinery.

STUDY ON THE CUTTING TEMPERATURE IN GEAR HOBBING

According to work tool thermocouple principle,the equipment for measuring hobbing temperature is developed.The changing character of cutting temperature in gear hobbing,the relation between cutting conditions and hobbing temperature,and the influence of cutting conditions on hobbing temperature are discussed by means of experiments.All these have provided the reference standards for the equitably selecting cutting conditions and geometrical parameter of hob,prolonging the life of gear hobs,and predicting processes of gear hobbing.

Improved Relief Grinding Method of Gear Hob with Equal Relief Angle

The regrinding error is the main factor affecting the eligible length of hob tooth,how to decrease the regrinding error is a hot issue in the research area of hob grinding.At present,researches focus on changing the trajectory of relief moving,because of no unified relief grinding path planning method,the research result is restricted in the practical application.For solving the problem,the calculation model of the hob relief angle is established with the Archimedes relieving motion to analyze the interaction between the increasing relief angle of the hob and the accelerating tooth profile errors.Based on it,the improved relief grinding method of gear hob is proposed with equal relief angle（ERA）.Furthermore,the relief grinding method with ERA is developed with the following two steps.Firstly,the convergence numerical solution algorithm of the tooth top curve is designed to form the wheel motion path which is compared with that of traditional grinding.The second step is to establish the solution model of ERA grinding wheel.In order to verify the effect of the method,hob grinding simulation system of 3D solid was built under the AutoCAD environment.The regrinding errors is analyzed by intercepting the hob axial profiles of the various regrinding angles with Boolean operations and further converting it to basic rack tooth,then the simulation example of zero rake straight flute hob is used to compare the regrinding errors between ERA grinding and traditional grinding.Finally,the experiments were implemented on the five-axis CNC relief grinder with the relief motion of ERA grinding driven by cam.The results of experiments show that the method can effectively reduce the regrinding errors of hob and grind expediently gear hob of AA rank and over.This research provide an effective model of relief moving path plan reducing regrinding error,and have practicable value in CNC relief grinder.

A New Manufacturing Method for Hourglass Worm Gear Hob Based on a Semi⁃automatic CAD

The top relief surfaces of an hourglass worm gear hob are ground manually in the traditional manufacturing process,which cannot ensure the width of the land surfaces of the hob.Moreover,each geometric feature of the hob has been produced through different manufacturing techniques and machine tools,which results in low efficiency.To solve this problem,we propose a semi-automatic computer aided design(CAD)method for hobs.The point clouds of each feature surface of a hob are calculated by combing mathematical equations of the top relief surfaces built by the proposed method with other existing equations of hob surfaces.According to the point clouds,the method can achieve the automatic modeling for the hob in three-dimensional(3D)software by classifying and extracting the parameter information of the feature-hierarchical knowledge of the hob.Based on the generated 3D model,the entire surfaces of the hob can be manufactured on a four-axis computer numerical control(CNC)milling machine through only twice clamping.Verification of the width of the land surface of the hob manufactured by semi-automatic CAD method on a measuring projector proved the precision of the designed width can be ensured.The edge of the contact area on the worm wheel in a meshing experiment is clear and distinct,which means the worm gear drive is meshed well and the hob manufactured by the proposed method has improved machinability.The method simplifies the processing technique,and improves the design efficiency and production accuracy.

Modeling and experiment of grinding wheel axial profiles based on gear hobs

Hobbing is one of the crucial gear manufacturing processes with high precision and high efficiency.In order to improve the accuracy of hobbing and hob relief grinding,more precise grinding wheels are demanded for relief grinding in the production of gear hobs.In this paper,a new and accurate mathematical method for calculating the axial profile of grinding wheel based on the corresponding gear hob to be ground is proposed.Considering that most researches have been conducted to focus on the optimization of hob geometric feature and only can be applied to a specific type of hand of helix and rake angle of gear hobs.The method in this paper can be served as a general algorithm for generating axial profile of grinding wheels on the basis of the spatial envelope theory,the principle of coordinate system transformation,and studies on normal profile of single-tooth.The accuracy of grinding hobs is based on applying the approach in practical manufacturing.Taking two typical different kinds of pre-grinding gear hobs as examples for calculation and experiment,the results of tooth profile errors strengthen the position that the validity and feasibility of this method,it can be employed for gear hob design and grinding processing.