Gear Hobbing Research Articles

Influence of the tool profile on the wear behaviour in gear hobbing

Being the dominating green manufacturing technique to create external gears gear hobbing is of major industrial importance. The technology is characterized by a simultaneous superposition of kinematics and tool profile. Even though these tool profiles are standardized, in industries they are regularly being altered to fit the gear designer's demands regarding strength and contact ratio. Cutting gears with these modified and partly extreme tool profiles some geometries show critical wear behaviour. Despite existing experience-based knowledge, no systematic knowledge base is available. Therefore, this paper summarizes geometrical influences of the tool profile on the wear mechanisms. A variety of different tool profiles and gear geometries were tested within the fly cutting analogy test. The effects were also studied by means of FEM-simulation and interpenetration simulation. Finally, the wear phenomena were matched with load parameters.

Research on Applying Nano Cutting Oils in Spur Gear Hobbing Process

Nanolubricant mixing the normal lubricant with nanoparticles, gradually becomes a new trend study for metal cutting enhancement. An addition of the nanoparticles improves lubricating properties and convective heat transfer coefficient (cooling properties) of nanolubricants. In the present work, nanolubricant is formulated by using dispersions of 0.3% Al2O3 nanoparticles in normal industrial oil VG46 for enhancement of gear machining performance of SCM420 steel. Comparative study of flank wear, crater wear and gear profile error in gear hobbing with normal oils in the existing production line as well as nanolubricant is studied. This study clearly reveals that tool wear, and gear profile error are reduced by the use of nanolubricant compared to that of normal oils. The paper results not only contribute the deeper understanding of the novel performance of nanoparticles in conventional cutting fluids, but also show a very promising solution to achieve the engineering economy effectiveness in gear machining.

The Process Parameters Optimization Model of Gear High-speed Dry Hobbing and Its Application System Development

The Process Parameters Optimization Model of Gear High-speed Dry Hobbing and Its Application System Development

Mechanistic approach applied to the gear hobbing process

This paper proposes a new approach to simulate 3D cutting force components generated during the finishing hobbing process of larger spur gear parts. This new approach combines three modelling steps. In the first step, the profile of the undeformed chip created for every hob’s tooth is calculated using the geometrical simulation of the gear hobbing process. In the second step, the calibration of the specific force coefficients (cutting and edge effects) is obtained from a 2D numerical model. In the final step, a mechanistic model is applied to the hobbing process. The results of this investigation are presented in terms of the analysis of the undeformed chip characteristics and the evolution of the hobbing cutting forces.

Study on the influence of gear hobbing and shaft misalignments on the geometric interference of cylindrical worm gear set

Geometric interference can occur in cylindrical worm gear set that makes use of oversized hob to cut the worm gear. In particular, the interference occurs easily in the design with high lead and low pressure angles. The interference results in a corner contact. In this study, we examined the influence of the machine tool setting errors of the worm gear hobbing and the influence of the shaft misalignments of the worm gear set on the interference. To determine the interference, we used the surface separation topology based on differential geometry. In addition, we also examined the hob oversize range required to avoid the interference under the condition of the machine tool setting errors and shaft misalignments. This study found that the interference can be avoided not only when the hob oversize is larger than the upper limit, but also when the hob oversize is smaller than the lower limit. This study also found that the interference can be avoided by applying the intended errors on the machine tool setting and shaft alignment, without manipulating the hob oversize.

Relief grinding of planar double-enveloping worm gear hob using a four-axis CNC grinding machine

Compared with single-enveloping worm gearing, double-enveloping worm gearing can provide the same load capacity with a more compact volume and a higher efficiency. However, that the relief grinding of its hob can not be finished automatically till now limits its applications because all of the cutting edges on the hob have different shapes and spiral angles. In this paper, a pioneering method is proposed to relief grind the planar double-enveloping worm gear hob by adding two additional translational motions of the generating plane in addition to the rotation motions of the hob and the generating plane. A mathematic model is built for the relief grinding of the hob. A series of related data of the four motion parameters when grinding different points of the land edges of the different hob teeth are solved out, and the relief surfaces of different hob teeth can be ground continuously by using the data. The method is verified by using software VERICUT. Furthermore, a worm gear hob is relief ground on a four-axis CNC enveloping worm grinding machine by using this method.

Further Development of a Cutting Force Model for Gear Hobbing

For the process design of a cutting process, the knowledge of the cutting force is of fundamental importance. The cutting force influences the dimensioning of machine components and process parameters [1]. A precise interpretation of those process elements enables for high manufacturing and component accuracy. Due to the complexity of the chip geometries, the cutting force in gear hobbing is calculated by using a penetration calculation. The applied cutting force models have been developed by BOUZAKIS [2] and GUTMANN [3] in the 1980s. These models are based on data from longitudinal turning processes. Advancements in machine tool technology of the past decades have led to more efficient processes. The use of new cutting materials allows for higher speeds and feeds. This led to larger chip thicknesses. The bases of the models by GUTMANN and BOUZAKIS covers today's usual hobbing parameters not extensive enough. The influence of tempered levels on the cutting force is not included in the models. Therefore, the aim is to create a cutting force model and adjust the calculation base after GUTMANN. A radial turning process with interrupted cutting is used as analogy process. The influence of the heat treatment at 42CrMo4 is to be examined for the cutting force. This will be compensated in three different tensile strengths. The investigated process parameters are extended beyond the current state of the art.

Prediction of the hobbing cutting forces from a thermomechanical modeling of orthogonal cutting operation

The common external cylindrical gears are manufactured by gear hobbing process. The particularity of this operation is due to the nature of the interaction between the tool cutting edge and the workpiece material which is more complex than in conventional machining operations such as turning, milling or drilling. This can affect significantly the thermomechanical process of the chip formation. The main goal of this paper is to propose a coupled approach to analyze accurately the cutting edge effect and to predict the evolution of cutting forces during the finishing hobbing process. This model is based on two parts: (i) during the hobbing operation, the evolution of the undeformed chip section generated by each hob's tooth is determined from the CAD geometrical simulations and (ii) the cutting forces are calculated from a mechanistic model. In this mechanistic approach, the specific force coefficients (cutting and edge effects) have been determined from a thermomechanical model, based on the ALE (Arbitrary Eulerian Lagrangian) approach, by considering the material characteristics such as strain rate sensitivity, strain hardening and thermal softening. It can be noted that the ALE approach allows to accurately take into account accurately the cutting edge effect and to analyze the triboligical conditions at the tool-chip interface (i.e. the contact nature: sliding, sticking or sticking-sliding contact). Indeed, this kind of information is of great importance to analyze the effect of cutting condition on the tool wear. The numerical and experimental results are compared for several cutting velocities in orthogonal process. The present approach leads to a three dimensional cutting force model for hobbing process and appears as an interesting alternative to the classical mechanistic approach which requires many experimental tests to determine the cutting force coefficients. Finally, the proposed model has been applied to analyze a finishing hobbing gear with very large sizes (several meters).

Tool’s Edges Fragmentation at Gear Hobs – A Method to Reduce Cutting Vibrations

One of the reasons causing vibration for gear hob toothing is the shock at the tool’s entry, which is generated by the great length of the cutting edge entering the metal at the same time. This paper proposes a fragmentation of the cutting edge so that its length is much smaller. Moreover, the cutting scheme is also changed, so that the entire tooth line of the piece is made with four consecutive teeth of the tool. Therefore, the impact force input generating shock and vibration is significantly reduced.

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

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

Machinability improvement of gear hobbing via process simulation and tool wear predictions

Typical processes of producing transmission gears involve hobbing, milling, or shaping of a forged stock to obtain the desired gear geometries. Among all these machining processes, gear hobbing is an efficient method of manufacturing high-quality gears. In this paper, a three-dimensional (3D) finite element model is presented to simulate the gear hobbing processes. The model is used to simulate the complicated kinematic motion between the hobbing tools and the gear workpieces and to perform a coupled thermo-mechanical analysis on the tools and the workpieces during the chip removal process. Cutting forces, torques, and temperature and stress distributions of the hobbing tools and workpieces are predicted using the proposed model. The tool wear progression in gear hobbing is analyzed in terms of tool geometry by a combined experimental-analytical method. The model considers the complex geometry of hob tooth profiles with multiple teeth engagement and can provide more insights into complicated gear hobbing processes. Based on the simulations with various tool geometries, a new tool geometry is arrived, which reduces spindle torque and shows a significant tool wear reduction. The modeling results are further validated through a direct comparison between the predicted and measured chip shape, torque, and tool wear rate.

Process Concepts for Gear Finish Hobbing

In the process chain for gear manufacturing, gear hobbing is one of the most productive processes for soft machining of gears. To reach a high quality after the soft machining, for example in gear finish hobbing, the requirements on the hobbing process increases significantly. To get a high quality part after soft machining, the process of gear hobbing is mostly divided in a roughing and a finishing cut. In the roughing process, the most amount of the material needs to get machined. The finishing process is used to get a high quality shape of the gear and to get low surface roughness. To get low cutting forces in the finishing step, the material stock after the roughing process has to be minimized. A low amount of stock on the flank offers the possibility to use high cutting speeds.This paper deals with the investigation of the two cut processes in the gear hobbing. Especially, the tool life of different tool concepts are taken into account. The process design offers the opportunity to use the same tool for the roughing and the finishing cut or the choice of different tools. Using different tools, a special tool design for the finishing step would be possible. A comparison between these two concepts is the focus of the investigation.

Calculating the Workpiece Quality Using a Hobbing Simulation

Gear hobbing is one of the most productive manufacturing processes for cylindrical gears. The quality of the gears is a result of the tool quality, the precision of the workpiece, tool clamping and kinematics of the machine. The dry gear hobbing process allows machining of gears with a quality according to the DIN standard of up to IT 5. To evaluate which gear quality is possible to machine with a given clamping and hob it is useful to simulate the process in advance. This is also an opportunity to order the required quality of the hob according to its application.The objective presented in this paper is to simulate non-ideal gear hobbing processes and to calculate the geometry and topography of the workpiece. To achieve this goal, a simulation for continuous gear hobbing was developed. By calculating planar intersections of transverse sections of both gear and tool, the resulting gear geometry is determined. Beside it is possible to calculate different characteristic values for the hobbing process such as chip thickness and cutting volume. By an evaluation of tool and clamping tolerances these deviations can be used to modify the simulation model. Afterwards a non-ideal hobbing simulation can be performed and the resulting gear geometry can be analyzed using a virtual measurement machine. An advantage of this non-ideal simulation is also the possibility of calculating the tool load taking these deviations into account and to use the results for further process designs to reduce the risk of tool failure.The virtual measurement machine analyses the geometry according to VDI/VDE 2612/2607 and DIN 3961. The resulting measurements of the flank and lead lines can be used for a classification of the gear quality. By using this simulation program it is possible to reduce the costs and time effort of setting up a new hobbing process.

ホブ切り歯車の単一ピッチ誤差測定の新たな手法（ガウシアンフィルタを通した歯すじ形状測定結果の適用）

Improving quality of hobbed gears must yield high accuracy of ground gears. This can be achieved by measuring hobbed gears accurately. Pitch deviations are most crucial in grinding processes with a worm type grinder. In the preset study, a new measuring method is proposed for single pitch deviations. In this method, measured helix trace data are conditioned with Gaussian Filter to be divided into short- and long-wavelength components. Single pitch deviations are calculated from the long-wavelength components around the center of facewidth. The calculated deviations showed 62.6 % lower variation in iterative measurements.

A Tooth Flank Crowning Method by Applying a Novel Crossed Angle Function Between the Hob Cutter and Work Gear in the Gear Hobbing Process

In this paper, a novel longitudinal tooth flank crowning method is proposed by setting the crossed angle between the hob cutter and work gear as a linear function of hob’s traverse feed movement in the gear hobbing process. However, this method makes twisted tooth flanks on the hobbed work gear. Therefore, a variable pressure angle hob cutter is applied to obtain an anti-twist tooth flank of hobbed work gear. A computer simulation example is performed to verify the superiority of the proposed novel hobbing method by comparing topographies of the crowned work gear surfaces hobbed by a standard hob cutter and a variable pressure angle hob cutter.

The Model of Spatial Forming with Multi-cutting-edge for Cylindrical Gear Hobbing and Its Application

The Model of Spatial Forming with Multi-cutting-edge for Cylindrical Gear Hobbing and Its Application

ホブ切り歯車の単一ピッチ誤差測定精度の向上

ホブ切り歯車の単一ピッチ誤差測定精度の向上

A continuous optimization decision making of process parameters in high-speed gear hobbing using IBPNN/DE algorithm

High-speed gear hobbing, especially dry hobbing, is an economical and environmentally friendly way to machine massive workpieces. Considering the fact that high-speed gear hobber are more expensive than the conventional machine tool and the same is true of the corresponding cutters, it is requisite that process parameters are decided appropriately so as to obtain the ideal comprehensive machining effect. What is more, the classical decision-making method of process parameters scarcely consider parameters’ adjustment in the hobbing process of a batch of gears. To resolve the problems, this work presents a hybrid improved back propagation neural network/differential evolution (IBPNN/DE) approach to do a continuous optimization decision making of process parameters in high-speed gear hobbing. Gear hobbing effect evaluation model is first structured to assess the machining effect. The optimization population of the process parameters, which is the input of the DE module, is generated by the IBPNN module. Using the DE algorithm, the best of best process parameters are obtained during the course of working. Finally, a test case is presented to give a clear picture of the application of the optimization approach. The results reveal that the proposed IBPNN/DE method has better performance than the general decision-making method under the comprehensive evaluation criterion over a batch of workpieces.

Linkage model and manufacturing process of shaping non-circular gears

Current research of non-circular gear processing mainly focuses on gear hobbing. However, this method has many limitations including being unable to process internal gears or non-circular external gears with a concave pitch curve and is likely to undercut when processing non-circular gears of greater curvature with a smaller number of teeth. Gear shaping, in contrast, is a method that is able to overcome the limitations of gear hobbing. Relevant studies on gear shaping have focused on the theoretical bases rather than the concrete processes and tools. Through the combination of shaping theory and practice, this paper aimed to derive a linkage model for shaping non-circular gears, and to refine the feeding strategy, and develop a cutter retraction and cutter setting method. Finally, with a pair of 3-order sinusoidal-gear-ratio non-circular gears, this paper demonstrated the entire process in a CNC gear-shaping machine, thus proving the accuracy of the mathematical model and providing a valid reference for shaping non-circular gears.

Parametric Design of Gear Hob Cutter

The gears are some of the most used mechanical transmission due to the advantages its provide: constant transmission ratio, high power transmitted, high efficiency, small size, silent operation, precision kinematic, etc. This causes the wheel to be one of the most valuable machine elements both in terms of accuracy and processing technology as well. From the technological point of view due to high precision and productivity, one of the most methods used is processing with gear hob cutter. Although the tool profile does not depend on the number of teeth on the wheel, but only its module, large diversity of gear requires the design of gear hob cutters tailored to existing needs. As it is known the gear hob cutters are complicated and expensive gear cutting tools, both due to the manufacturing process and in terms of design, requiring a significant amount of calculations, high effort from the designer and consequently results in a large cycle of design. For this reason, the literature and in various websites, there are many studies and research information to optimize the design process and increase accuracy of gear hob cutters.