Gear Hobbing Research Articles

Hobbing of Cylindrical Gears without Machining Fluid

The hobbing of external gears by a worm mill without machining fluid is considered, theoretically and experimentally. The performance of worm cutters made of high-speed powder steel is investigated.

Study on mapping rules and compensation methods of cutting-force-induced errors and process machining precision in gear hobbing

Based on the homogeneous coordinate transformation method and finite element simulation method of a whole hobbing machine, this paper proposes a highly applicable force-induced error model for a high-speed dry hobbing machine. The number of parameters needed in the error estimation can be effectively reduced by using this model, which has great value in industry application. According to the engagement features of the conjugating surface and the principle of two-degrees-of-freedom hobbing, the meshing equation was deduced and the force-induced errors of the system were mapped to the normal errors of gear surface. In this way, the mapping relationship between different kinds of force-induced errors and hobbing precision can be obtained. Then, the theoretical tooth surface and the real tooth surface under the influence of force-induced errors were respectively calculated by using a numerical simulation method. Based on numerical simulation results, the mathematical relationship between the tooth profile root-mean-square error (RMSE) and the compensation variables was obtained, as well as the optimal value of the compensation variables. The following experimental results validate the feasibility and accuracy of this error compensation method. This study has an important guiding role in the improvement of dry gear hobbing precision.

A Method to Generate the Spiral Flutes of an Hourglass Worm Gear Hob

All of the cutting edges on an hourglass worm gear hob have different shapes and spiral angles. If the spiral angles are small, straight flutes are typically adopted. However, for hobs with multiple threads, the absolute values of the negative rake angles on one side of the cutting teeth will greatly affect the cutting performance of the hob if straight flutes are still used. Therefore, spiral flutes are typically adopted to solve this problem. However, no method to determine the spiral flute of an hourglass worm gear hob has been proposed until now. Based on the curved surface generating theory and the hourglass worm forming principle, a method for generating the spiral flute of the planar double enveloping hourglass worm gear hob is proposed in this paper. A mathematical model was built to generate the spiral flute. The rake angles of all cutting teeth of the hob are calculated. The laws of the rake angles of the cutting teeth for four hobs with different threads from one to four threads were analyzed when straight flutes and spiral flutes are adopted. The laws between the value of the negative rake angles of the hob with four threads and the transmission ratio were studied. The most appropriate transmission ratio for generating the spiral flute was obtained. The machining of the spiral flutes was simulated using a virtual manufacturing system, and the results verify the correctness of the method.

Taguchi-fuzzy multi-response optimization in fly cutting process and applying in the actual hobbing process

BackgroundApplying nanofluid made by adding alumina nanoparticles to industrial oil may reduce the cutting force, friction, and cutting temperature and, from that, improve the tool life in the hobbing process. However, it is difficult to set up the experiment for the actual gear hobbing process, because measuring the cutting force and temperature in the hobbing process is very complicated and expensive. Therefore, a fly hobbing test on the horizontal milling machine was performed to simulate the actual hobbing process.MethodsIn this research, the fuzzy theory was combined with the Taguchi method in order to optimize multi-responses of the fly hobbing process as the total cutting force, the force ratio Fz/Fy, the cutting temperature, and the surface roughness.ResultsThe optimal condition—A1B1C3 (the cutting speed 38 mpm\\, the nanoparticle size 20 nm, and concentration 0.5%)—was determined by analyzing the performance index (FRTS) of the fuzzy model. Furthermore, this condition was applied to the actual hobbing process in the FUTU1 Company and compared with the actual conditions of this company and other conditions using the nanolubricant with 0.3% Al2O3, 20 nm. The results show that it can reduce a maximum 39.3% of the flank wear and 59.4% of the crater wear on the hob when using the optimal conditions.ConclusionsThe study indicates that the optimal condition determined by using Taguchi-Fuzzy method can be applied in the FUTU1 company with the high efficiency.

The Deformaton of The Gear Hob’s Generating Surfaces Due to Re-Sharpening

Abstract The side relief faces of the monolithic involute gear hob are machined through relieving. The resulting surfaces are bevel helical surfaces in which the side cutting edges result from the intersection of these with the helical rake face. Theoretically, the gear hob is derived from an involute worm. Resharpening decreases the diameter of the hob, thus the edges became closer to the axis, and as a consequence they will be situated on a smaller worm than the original. The present paper analyses the deviation of the re-sharpened gear hob’s carrying worm from the theoretically perfect involute worm whose characteristic dimensions were adjusted considering the re-sharpened gear hob characteristic diameters. It was proven that the evolution of the errors is significantly different from that described in the literature. Thus, increasing the new gear hob diameters in comparison with the calculated dimensions is unnecessary, because it cannot reduce the error to half with this procedure. The mathematical model was built up accepting that the edges result from the intersection of an involute worm with a helical rake face and the side relief faces result from the rototranslation of the edges on a bevel helix leading curve dressed by the relieving parameter.

Improvements in the micro tooth surface topography of hobbed spur and helical gears

A new model of the gear hobbing process is presented in this paper to determine the micro tooth surface topography in spur and helical gears. The model is based on the generation of tooth surfaces by successive cuts of the finite number of hob teeth, as they come into interaction with the gear tooth. For every relative position of the hob and the gear, an analysis is carried out to find the active cutting edge points which generate the gear tooth surface. Repeating this procedure for all the selected gear tooth surface points, the micro topography of the gear tooth surface is determined. Therefore, the developed method determines the deviations of the manufactured tooth surface from the theoretical tooth surface of spur and helical gears. The method is applied to improve the micro tooth surface topography of spur and helical gears, namely to reduce the deviations of the hobbed tooth surface. Spur and helical gear examples are used to demonstrate the effectiveness of the method.

Prediction of the cutting forces in gear hobbing and the wear behaviour of the individual hob cutting teeth

In this paper, a mathematical model is presented, by which the cutting forces in a gear hobbing process and the wear behaviour of the hob's all cutting teeth are predicted. The load on each individual hob cutting tooth varies heavily in the gear hobbing process. To predict the cutting force, and subsequently the tool wear, a detailed determination of the chip geometry is needed. The undeformed chip geometry is continuously determined by analytical differential description presented in previous research. In the model all cut chips are determined for the full production cycle of a gear blank, where the gear blank boundaries are considered. Considering the full production cycle is needed to get an understanding of the load the tool will experience and the wear behaviour of the hob teeth. [Submitted 17 January 2017; Accepted 24 November 2017]

Prediction of the cutting forces in gear hobbing and the wear behavior of the individual hob cutting teeth

In this paper, a mathematical model is presented, by which the cutting forces in a gear hobbing process and the wear behaviour of the hob's all cutting teeth are predicted. The load on each individual hob cutting tooth varies heavily in the gear hobbing process. To predict the cutting force, and subsequently the tool wear, a detailed determination of the chip geometry is needed. The undeformed chip geometry is continuously determined by analytical differential description presented in previous research. In the model all cut chips are determined for the full production cycle of a gear blank, where the gear blank boundaries are considered. Considering the full production cycle is needed to get an understanding of the load the tool will experience and the wear behaviour of the hob teeth. [Submitted 17 January 2017; Accepted 24 November 2017]

Design and Analysis of Split Fixture for Gear Hobbing Machine

Compared to the conventional gear hobbing fixtures, split fixture can effectively reduce job set-up time during the manufacturing process. This paper investigates the behaviour and analysis of split fixture under varying static loading conditions. Design of the part was established by considering the ability of the split fixture to carry jobs of various diameters. In order to validate the design, Static structural analysis was carried out on two positional configurations of the split fixture. A load of 1 ton was applied on the resting face of the fixture to simulate the effect of holding the job. The analysis included a study of the Stress, Deformations, and Modal analysis at different resonating frequencies to check for failure of design. By applying varying loads similar to practical conditions, it was observed that the design successfully withstood the applied forces without failure and a factor of safety of 142 was achieved in a critical loading case. Investigating the effect of dynamic loads on the Split Fixture and including auxiliary assembly components in design analysis

A Life Cycle Ecological Sensitivity Analysis Method for Eco-Design Decision Making of Machine Tool

Reducing the ecological footprint of the machine tool is one of the great challenges in terms of the global sustainable development goals. Eco-design of the machine tool is now regarded as one of the effective methods to reduce the environmental pollution from the source. This paper proposes an ecological sensitivity analysis method enabling ranking of the alternative eco-design measures in a time efficient way regarding the life-cycle environmental impact to support eco-design decision making of machine tool. Based on the presented frameworks and procedures, the potential ecological improvement measures can be identified and the ecological improvement potentials of these measures with various options could be quantified. Realization of this method is analyzed by a case study of gear hobbing machine. The goal of this paper is expected to give a complementary support for decision-making on eco-design of the machine tool.

Design and Analysis of Split Fixture for Gear Hobbing Machine

Compared to the conventional gear hobbing fixtures, split fixture can effectively reduce job set-up time during the manufacturing process. This paper investigates the behaviour and analysis of split fixture under varying static loading conditions. Design of the part was established by considering the ability of the split fixture to carry jobs of various diameters. In order to validate the design, Static structural analysis was carried out on two positional configurations of the split fixture. A load of 1 ton was applied on the resting face of the fixture to simulate the effect of holding the job. The analysis included a study of the Stress, Deformations, and Modal analysis at different resonating frequencies to check for failure of design. By applying varying loads similar to practical conditions, it was observed that the design successfully withstood the applied forces without failure and a factor of safety of 142 was achieved in a critical loading case. Investigating the effect of dynamic loads on the Split Fixture and including auxiliary assembly components in design analysis.

About the Profile Accuracy of the Involute Gear Hob

Abstract Gear hobs are the most widely and frequently used gear cutting tools. During the time passed between the moment of invention (Schiele, 1876) and the present, gear hobs reached a considerable evolution regarding the geometry, the profile of the edge, the relieving technologies finalizing in the latest constructive and design solutions. This paper deals with the calculus of the edge profile in the case the basic worm of the hob has involute helicoid surfaces. In order to obtain a constant grinding allowance on the relief faces of the gear hob teeth it is necessary to compute the edge of the roughing relieving cutter. The equations are deduced considering that the provenience involute worm is a one teethed helical gear with shifted profile. The presented mathematical model proves that linearizing the relieving cutter profile is not an adequate solution if aspiring to higher precision.

A thermal energy balance optimization model of cutting space enabling environmentally benign dry hobbing

Dry hobbing is a well-known environmentally benign process for gears production by eliminating serious pollution and occupational health hazards in the shop floor. However, due to the absence of the cooling and lubrication of cutting oil, it requires quite accurate monitoring and adjustment of the accumulation of thermal energy within the cutting space to reduce the thermal deformation of machine tool. In this paper, an analytical method is proposed to reveal the mechanism of thermal energy accumulation in dry hobbing. And further, a thermal energy balance optimization model is developed to minimize the average temperature of cutting space by optimizing the heat-carrying efficiency of chips, the temperature of compressed air, and the mass flow rate of air filter. The comprehensive learning particle swarm optimization (CLPSO) based solution method is designed to search the optimal solutions of the proposed model. To verify the performance of the proposed thermal energy balance problem, a case study has been conducted and the experimental results showed that the maximum difference of the average temperature of cutting space reduced by 16.3%, and the M-value of hobbed gears was effectively controlled, which demonstrated the effectiveness of the proposed approach.

Prediction and optimization of hobbing gear geometric deviations

Hobbing is a precision gear manufacturing process with high efficiency and low cost. High precision gears are essential components for high-end equipment to meet the requirement of extreme operation conditions. In order to further improve the precision of gear hobbing process as well as lower the gear manufacturing cost, this paper proposes a model for predicting the hobbing gear geometric deviations and optimizing the hobbing processing technique. The relationship between gear hobbing processing technique and gear geometric deviation is modeled applying the improved Particle Swarm Optimization and Back Propagation algorithm. The performance of the proposed method is compared with the existing optimization and back propagation method and validated by experiments. The accuracy of both algorithms is evaluated by the Root Mean Square Error between the predicted and experimental values. The result shows that the gear geometric deviations predicted by the proposed algorithm yields better performance and are in reasonably good agreement with experimental data. Employing the proposed model, the gear hobbing process parameters can be optimized to minimize gear geometric errors, and thus improve the gear manufacturing precision.

A disk tool cutting method for bevel gear manufacture on a five-axis machine

Two main popular cutting methods for bevel gear mass production, face milling and face hobbing, both require dedicated tools and machines available from only a few machine tool companies, which makes production more costly. This paper thus proposes a cheaper, more flexible alternative for producing small or medium batches of large bevel gears, a disk tool cutting method using a five-axis machine. In this method, the machine coordinates are derived based on tooth surfaces. The target’s topographic points of tooth surface are applied to construct a fitted surface which is then used to further refine the cutter-contact points to improve the precision of the gear produced. At the same time, mathematical models are established for both the tool and the machine. A coordinate transformation matrix is then generated by aligning the coordinate system of the tool’s reference point with each of the work gear cutter-contact points. Because different machines employ identical transformation matrices for producing the same workpiece, the machine’s five-axis coordinates can be derived using inverse kinematics. These coordinates are the resource to generate the NC machining data that allows NC verification software to perform cutting simulations. The simulation results verify the correctness of the mathematical models.

A novel multi-objective optimization approach of machining parameters with small sample problem in gear hobbing

Low carbon gear hobbing is an environmentally friendly way to machine massive workpieces. The appropriate process parameter decision-making is of great significance to improve processing quality, reduce the machining time, production cost, and carbon emission in gear manufacturing. This paper first proposes a support vector machine/ant lion optimizer/gear hobbing (SVM/ALO/GH) integrated approach to do the multi-objective optimization of machining parameters for solving small sample problem of batch production. The first population of process parameters is generated by the multi-class SVM method. Pareto improvement and ALO algorithm are employed to obtain the optimal process parameters. Finally, the case study is presented to give a clear picture of the application of the optimization approach. The results uncover that the proposed SVM/ALO/GH method has better performance than the improved back propagation neural network/differential evolution (IBPNN/DE) algorithm over the small sample problem.

Non-circular gear continuous generating machining interpolation method and experimental research

Current non-circular gear manufacturing process all use discrete machining method, which generates a large number of small line segments, brings in approximate error, and leads to high-order discontinuity of the whole tool path curve. The tooth surface quality will be decreased significantly due to the vibration of machining tool caused by the discontinuity of machine tool motion trajectory especially in high-speed machining. In addition, the processing speed and efficiency will be limited due to the unsmooth kinematics profile. This paper proposes a non-circular gear completely continuous generating machining interpolation method. The non-circular gear machining electronic gearbox is developed to compute the real-time interpolation point data to guarantee the strict generating motion relationship between the workpiece spindle, feed shaft, and cutter spindle during the gear manufacturing process according to the derived linkage model for non-circular gear hobbing and generate continuous smooth machining trajectory. The proposed interpolation method is implemented on the self-developed CNC system based on the embedded CNC system hardware structure platform and verified experimentally on a gear hobbing machine. A pair of two-order oval non-circular gear is machined, and the roll and application experiments on a kind of gear pumps are done to illustrate the machining performance and provide a high efficiency and precision machining method for non-circular gear.

A life cycle approach to characterizing carbon efficiency of cutting tools

Cutting tools are extensively used in subtractive manufacturing systems for achieving the desired products. The advancement of cutting tool technology promotes the development of efficient and green machining. However, as one of the auxiliary consumptive materials, cutting tools have a crucial impact on the sustainability of machining systems. Thus, the development of sustainability urgently requires characterizing the impacts of cutting tools. This paper investigates the environmental impacts of cutting tools from the life cycle aspect based on the material and energy consumption during the material extraction, manufacturing, use, and recycling of cutting tools. Carbon emission is applied to measure the impacts of cutting tools on the sustainability of the machining system. Then a life cycle carbon efficiency approach based on the service life of the cutting tool is presented to characterize the life cycle carbon emission characteristics of cutting tools. A gear hobbing system with five kinds of hobs was introduced as a case study to characterize the life cycle carbon emissions and efficiency of hobs. It indicates that substrate and coating material type, manufacturing process, coating method, and regrinding times all influence the carbon emissions and efficiency of hobs to different extents. A high-speed dry-cutting hob exhibits excellent carbon efficiency in addition to carbon emissions.

Modified worm gear hobbing for symmetric longitudinal crowning in high lead cylindrical worm gear drives

A single enveloping worm gear of cylindrical worm gear drive is cut by an oversized hob. The oversize provides a longitudinal crowning on the worm gear tooth surface. However, when a lead angle of the worm becomes higher, the longitudinal crowning becomes more asymmetric. The asymmetrically crowned worm gear surface makes the gear contact more sensitive to the certain direction of misalignment. To change the longitudinal crowning from asymmetric to symmetric, a method of modified worm gear hobbing is proposed. The modification uses a modified machine tool setting and a modified hob specification. A new hobbing mechanism or hob geometry is not required in this method. Results of the proposed modification are confirmed by using a surface separation topology based on differential geometry, and contact pressure analysis based on finite element method.

Research on cutting vibration characteristics of face-milling involute gear

Abstract Traditional machining methods, such as gear hobbing, gear shaping and gear milling, etc, are commonly used for cutting machining of gear tooth profile, which cannot meet huge machining demand of gears to a certain extent. This article proposes to utilize a face-milling machining method in involute gear machining, which can be used to reduce production cost effectively. Cutting vibration generated during cutting machining has a direct effect on the machining accuracy and machined surface quality of workpiece. Therefore, it is desiderated to perform in-depth research regarding this issue. ADAMS software was used to establish a rigid-flexible coupling virtual prototyping model of face-milling gear milling system and a cutting vibration system model. Cutting vibration analysis was performed for face-milling gear by adopting quick sine frequency sweep method, so that the frequency response characteristics of workpiece in three directions X , Y and Z and space were acquired. The research results will provide reference and theoretical foundation for actual application of face-milling gear machining technology.