Gear Hobbing Research Articles

Analysis of the tooth root roughness of hobbed gears

For the design of power transmissions, an increase in power density is necessary. This leads to higher requirements for the tooth root design of the respective gears with high load capacity. The permissible tooth root stress of gears is influenced by the roughness at the tooth root. The influence of different process and tool designs on the roughness at the tooth root was determined for hobbing. To predict the roughness at the tooth root, a model was developed with which the roughness at the tooth root can be calculated. The model can be used as a helpful tool for gear design.

Numerical Simulation of Gear Heat Distribution in Meshing Process Based on Thermal-structural Coupling

The thermal balance state of high-speed and heavy-load gear transmission system has an important influence on the performance and failure of gear transmission and the design of gear lubrication system. Excessive surface temperature of gear teeth is the main cause of gluing failure of gear contact surface. To investigate the gear heat distribution in meshing process and discuss the effect of thermal conduction on heat distribution,a finite element model of spur gear is presented in the paper which can represent general involute spur gears. And a simulation approach is use to calculate gear heat distribution in meshing process. By comparing with theoretical calculation, the correctness of the simulation method is verified, and the heat distribution of spur gear under the condition of heat conduction is further analyzed. The difference between the calculation results with heat conduction and without heat conduction is compared. The research has certain reference significance for dry gear hobbing and the same type of thermal-structural coupling analysis.

Calculation of Roughness Parameters during Ultrasonic Hobbing from the Viewpoint of the Theory of Elastic-Plastic Contact

This article analyses the process of occurrence of the surface roughness during the ultrasonic hobbing of the fine pitch gears from the viewpoint of the theory of elastic-plastic contact, and suggests analytical solutions and regression equations to estimate the roughness parameter Ra in both conventional and ultrasonic machining.

Prediction of processing time and energy consumption and optimization of machining parameters in gear hobbing

This paper studied the characteristics of time and energy consumption of gear hobbing in batch production of small modulus gear. A method of integrating design of experiment, response surface method and multi-objective salp swarm algorithm (DOE/RSM/MMSA) is proposed for the complex optimization of machining parameters (namely hob rotation speed, cutting feed and depth of cut) in gear hobbing process. This paper uses three-level factorial design method to design gear hobbing experiments, and carries out mathematical and statistical analysis on the experimental results. It is found that cutting feed is the most significant machining parameter followed by hob rotation speed and depth of cut to reduce processing time and energy consumption. The prediction model of processing time and energy consumption in gear hobbing process is obtained through response surface methodology. The relative error rates of the predicted value and the actual value of the processing time and energy consumption are 0.11% and 0.09% respectively, indicating the validity of the model. Multi-objective salp swarm algorithm is used to optimize the machining parameters to minimizing processing time and energy consumption. Finally, through the comparison with the existing research results, it is concluded that the optimized machining parameters have better processing effect to achieve minimized processing time and energy consumption, which shows the effectiveness and rationality of the method proposed, and provides references for the decision-making of machining parameters in workshop.

A precision generating hobbing method for face gear with assembly spherical hob

In order to improve the processing precision and shorten the hob manufacturing cycle of the face gear, a precision generating hobbing method for face gear with the assembly spherical hob is proposed. Firstly, the evolution of the cylindrical gear to spherical hob basic worm is analyzed, then the spherical hob basic worm is designed, thus the basic worm and spiral angle equation of spherical hob are obtained. Secondly, based on the design method of the existing hob, the development method of the assembly spherical hob is analyzed, the cutter tooth and the cutter substrate of the assembly hob are designed, and the whole assembly is finished. Thirdly, based on the need of face gear hobbing, a numerical control machine for gear hobbing is developed, and the equation of the face gear is obtained. Fourth, for reducing the face gear processing errors induced by equivalent installation errors, the error analysis model is established and the impacts of each error on the gear tooth surface are analyzed. Finally, the assembly spherical hob is manufactured and the gear hobbing test is completed. According to the measurement results, the processing parameters of face gear hobbing are modified, and the deviation of tooth surface is significantly reduced.

Online estimate and compensation of the gear machining error based on electronic gearbox cross-coupling controller

A novel method for online estimate and compensation of the gear machining error based on the flexible electronic gearbox (EGB) is introduced. EGB is a multi-axis controller, which is used to realize the gear generation process. Gear processing quality is directly dependent on the control precision of EGB. The present work focuses on the estimation, analysis, and compensation of the gear machining error during the gear hobbing process. First, an efficient method for the online evaluation of the helical gear tooth profile deviation, pitch error, and helix deviation is presented, from the perspective of the combination of the multi-axis linkage control structure model and the gear processing technology. Second, the online compensation architecture for the five-axis gear hobbing linkage is proposed, which is composed of an asymmetric cross-coupling controller and a master-slave EGB controller. Simulation results show that the proposed online compensation architecture has better control precision, in comparison to the conventional EGB. Finally, experiments are performed on a six-axis gear hobbing machine, where higher accuracies are obtained for the helical gear, processed by the proposed method.

Multi-component energy modeling and optimization for sustainable dry gear hobbing

Sustainable machining becomes a key priority for manufacturing industries due to the ever growing energy costs, associated environmental impacts and carbon emissions. As one of the frequent activities in metal machining, dry gear hobbing contributes to a significant portion of energy consumption. Process parameter optimization is an effective method of decreasing energy from process control perspective. However, hobbing parameter optimization is rarely involved in previous studies. To this end, a multi-component energy model is first developed on a basis of energy characteristics analysis of dry gear hobbing machines. Then, the optimization of hobbing parameters for the minimizing energy consumption and production cost is formulated as mathematical programming problem with a systematic consideration of machining constraints. Finally, the optimization problem is solved by a modified multi-objective imperialist competitive algorithm (MOICA). The results demonstrate that the energy-efficient gear hobbing can be achieved through a collaborative effort of predictive modeling and parameter optimization.

Prediction of Cutting Forces in Gear Hobbing of Cylindrical Gears

Prediction of Cutting Forces in Gear Hobbing of Cylindrical Gears

Development of an application-oriented tool life equation for dry gear finish hobbing

Gear finish hobbing offers high potentials regarding economic and ecological aspects. Pre- and finish machining can be realized using only one machine and a complete dry process chain can be implemented as the hard finishing process by grinding is neglected. During the finishing cut, a small stock on the gear flanks is machined using high cutting velocities. The combination of high cutting velocities and small chip thicknesses leads to machining conditions in the finishing cut, which differ from those of regular gear hobbing and influence the tool wear behavior. As the finishing cut also determines the gear quality, a focus on tool life and achievable geometry is important.This paper deals with tool wear investigations for the finishing cut in dry gear finish hobbing. Different cutting substrates were investigated and evaluated with respect to the process productivity, tool life and wear behavior. For this purpose, empirical studies were conducted using the established fly-cutting analogy trial for gear hobbing. Based on the results of the wear investigations and theoretical considerations, a tool life equation for the application-oriented design of dry gear finish hobbing was derived. Cutting velocities from vc = 250 m/min up to vc = 2250 m/min were investigated under dry cutting conditions. The derived equation for tool life takes the allowable tool wear width VBmax into account, which allows a process design with respect to the required gear quality. As the productivity of gear finish hobbing is decisively determined by the selection of suitable tool and process parameters, material coefficients were implemented in the equation and determined for the investigated cutting substrates. The paper concludes with a verification of the derived tool life equation. The present work contributes to the identification of potentials and limits of gear finish hobbing. The results will serve manufacturing engineers as basis for their decisions for implementing this technology in series production.

Theoretical analysis of the Influence of workpiece spindle vibration displacement on machining accuracy of gear hobbing machine

In order to study the vibration characteristics of the workpiece spindle of a gear hobbing machine, this paper established a mathematical model for the workpiece spindle vibration displacement in the x-axis direction. To verify the reliability of the proposed model, a series of experiments were run on the CNC gear hobbing machine. The relative error between the experimental data and the calculated values was lower than 5 %, which proves that our proposed mathematical model is qualified to be a research tool for the investigation of the variation law of the workpiece spindle. According to the analysis results, the workpiece spindle vibration displacement literally decreases with the increasing order, and the hobbing process with high hob revolution speed and small cutting depth is preferable for gear hobbing accuracy.

Researching of commonalities and differences in cold forging of spur and helical gears

Modern automobiles are equipped with a large number of gear transmissions. In the powertrain, for example, they are used as multi-stage manual transmissions and in the interior for mirror and seat adjustment. Machining manufacturing processes—like gear hobbing and shaping—represent the state of the art in gear manufacturing due to high manufacturing accuracy and flexible machining possibilities. With regard to economic, ecological and technical aspects, cold forging offers a promising production technology. In conventional transverse and forward extrusion processes, the ejection process is a challenge due to high forces and a negative influence on the gearing accuracy. One variant of forward extrusion is the so-called “Samanta” process, whereby an additional ejection step is avoidable by sequential forming of the gears. For the establishment of this process in industry, the increase of the achievable gearing accuracy and the achievable tool life is of major relevance. Thus, a deeper process understanding as well as knowledge about the influences on the process results is beneficial. In this context, the aim of this research work is to produce spur and helical gears by the “Samanta”-process. In addition to the resulting component properties, the characteristics of the process are determined. On this basis, commonalities and differences in cold forging of spur and helical gears are investigated to gain a principle process understanding. These findings are also used to derive possible approaches for improving component and process properties in future research work. The results reveal that cold forging of spur and helical gears by the “Samanta”-process results in characteristic properties and specific challenges within the gear types. Furthermore, a geometric adaptation in the gearing area of the used die promises enormous potential for a positive influence on the process results for both types of gearing.

Study on the effect of force-thermal coupling error on the gear hobbing accuracy and its visualization

A force-thermal coupling error model was proposed to investigate the coupling effect of thermal error and force-induced error on the machining accuracy. Based on the developed model, numerical simulations were conducted to unveil the temperature distributions of both the assembly and the worktable, as well as corresponding displacement errors. Besides, based on the two-degrees-of-freedom hobbing locus motion, an equation to characterize the meshing relation between the hob and the workpiece was deduced with the consideration of the force-thermal coupling errors. By using this equation, an interface, which can visualize the gear hobbing process and map the force-thermal coupling error to the resultant gear profile, was developed in the MATLAB. Further comparison between experimental data and simulation results prove the credibility of our proposed method.

Analysis of the cutting conditions for radial-axial infeed strategies in gear hobbing

This paper focuses on the analysis of the infeed process during gear hobbing. A penetration calculation for the simulation of gear hobbing has been extended in order to analyze the geometric penetration values for variable infeed strategies. With this method, the influence of the infeed angle on the cutting conditions is analyzed and evaluated with regard to the tool load. For the investigated tool-workpiece-combination, a nonlinear regression has been conducted in order to design the process according to the maximum chip thickness. The paper concludes with the presentation of the effect of the infeed angle on characteristic machining values.

High-efficiency gear hobbing technics based on fuzzy adaptive control of spindle torque

In this paper, the problem of relatively low efficiency of the current gear hobbing process is addressed through fuzzy adaptive control of the cutting force. The paper studies the influencing factors of the cutting torque of gear hobbing, and the relationship between the feed rate and the cutting torque is established. Based on the relationship and the fuzzy adaptive control method, a high efficiency gear hobbing method is designed. A methodology using the static spindle torque rather than the dynamic one as the feedback signal of the fuzzy controller is also presented, which can deal with the severe cutting torque fluctuations during gear hobbing. The input and the output scaling factors of the fuzzy controller can also be tuned online to adapt to different types of gears or various cutting conditions. The key issue of determining the reference value of the spindle torque is also resolved through analysis of the spindle torque data in a trial cut. The proposed method is simulated and implemented on a numerical control gear hobbing machine, which cuts spur gears and helical gears. The simulation and experimental results are in a good consistency. The efficiency is improved considerably, which saves as high as 40% and 30% cutting time of the gear hobbing process in the first and second set of experiments, respectively.

Critical study on the thermal-structural characteristics of worktable assembly of a dry hobbing machine

Dry hobbing machine is a kind of specialized machine tool to manufacture high-quality small-module gears. With the development of shipbuilding, automobile, and wind power industries, higher request on the dry gear hobbing accuracy is called. The thermal-induced error, which accounts for 50–70% of machining error, needs to be reduced more efficiently. Hence, in-depth investigation on the thermal-structural characteristics of the dry hobbing machine is indispensable. In this paper, thermal-structural coupling numerical simulations were conducted to investigate the heat transfer process as well as thermal-induced deformation of the worktable of a YDE3120CNC gear hobbing machine in the large-volume gear production. New equations were used here to describe the convection heat transfer happened on the worktable assembly. Verifying test results proved the feasibility of the newly proposed numerical method. Following numerical simulation, results indicated that during the gear hobbing process, the highest surface temperature of the worktable assembly appeared at the top surface of the fixture, and corresponding thermal-induced deformation reached the maximum of 49.9 μm. Besides, in a large-volume production, the worktable assembly would attain thermal equilibrium in 15,000 s. Hence, the assumption widely used in previous studies on gear hobbing machines that the worktable assembly could be treated as an ideal solid without any thermal deformation is wrong. The thermal-induced deformation of the worktable assembly should be considered in the subsequent development of the thermal error compensation system.

Design and correction method of spiral flute rake face of an hourglass worm gear hob

Design and correction method of spiral flute rake face of an hourglass worm gear hob

A Designing and Generating Method for Grinding Relief Surfaces of a Dual-Cone Double-Enveloping Hourglass Worm Gear Hob

Land widths and relief angles of a dual-cone double-enveloping hourglass worm gear hob are important factors that influence the life and the hobbing performance of the hob. Both of them are obtained by generating relief surfaces of the hob. Due to the reason that all teeth of this type of hob have different profiles with each other, all of the relief surfaces are difficult to generate for keeping all cutting teeth with uniformed relief angles and uniformed land widths. For the purpose that land widths and relief angles could be machined precisely, this paper puts forward a designing and generating method for grinding the relief surfaces. The relief surfaces are ground using the same double-cone grinding wheel as grinding the helical surfaces of the worm. Based on the theory of gearing, the mathematical model for grinding relief surfaces is built. Motion parameters when grinding the different points of the land edges on different teeth of the hob are solved. A generating simulation is built by putting those motion parameters into a four-axis hourglass worm-grinding machine. The results of the simulation show that the relief surfaces can be ground continuously and the land widths and the relief angles meet the requirements.

Crowning Analysis of Involute Helical Pairs Shaved by CNC Gear Shaving Machine with Two Synchronous Axes

Gear Shaving is one of the most efficient and economical ways to finish gears after gear hobbing or gear shaping. In tradition, the shaved gear can be crowning by shaving machine with the rocking mechanism. In this paper, we propose a mathematical model of a CNC shaving machine with two synchronous axes. The proposed mathematical model can be used to calculate the crowning tooth surface of the gear in parallel-shaving process.

Hob Strength in Gear Cutting

The strength of gear hobs in cutting worm gears is calculated by the finite-element method, on the basis of SolidWorks/Simulation software.

A method for thermal characteristics modelling of hob assembly on dry hobbing machine

Gear hobbing is the use of machinery to manufacture external gears. With the booming motor industry, there are more requirements for gear hobbing accuracy than ever before. Thermal error – as a major source of error in a dry hobbing machine – must be effectively compensated to achieve accuracy. Thus, studies on the thermal error of hob assembly are important both in theory and practice. This paper discusses the development of a valid numerical modelling method for the hob assembly of a dry hobbing machine. The equations used to determine the values of heat sources and heat transfer coefficients are given. The temperature field and thermal deformation of the hob assembly were obtained by thermal-structural coupling numerical simulations. Numerical results showed that the deformation can maximally reach to 94.5 µm, which is non-ignorable in the thermal deformation analysis of the whole dry gear hobbing machine. Subsequently, by comparing the simulation results and experimental data, the newly proposed method to determine the forced convection heat transfer coefficient proved more fitting for describing the airflow pattern inside the gear hobbing zone. The satisfactory agreement between simulation results and experimental data also suggests that the numerical analysis method proposed in this paper can provide an effective research tool to optimize the design of hob assembly. And the results obtained by the proposed method can be used for thermal error modelling in real error compensation.