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.

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.

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.

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.

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.

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.

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.

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.

Mathematical Model and Machining Method for Spiral Flute Rake Faces of Hourglass Worm Gear Hob

To improve the cutting performance of an hourglass worm gear hob and the accuracy of the resulting worm gear,the rake angles of the teeth on the pitch circle should be reduced.A method of forming the spiral flutes by using a variable transmission ratio was developed.This method ensures that the rake angles on the indexing torus of each tooth are approximately 0°.Based on the gear meshing theory and the hourglass worm forming method,the discretization mathematical model of the rake face of a planar double enveloping worm gear hob was established by using cylindrical generating surface,and the feed parameters for machining the rake face for a variable transmission ratio were obtained.The spiral flute was simulated and the hob was machined on a four axis CNC milling machine.A contourgraph was used to measure the rake angle.The measurement results showed that the proposed method can reduce the absolute value of the rake angle on both sides of the cutting teeth,which can be used for machining the spiral flute rake face of an hourglass worm gear hob.

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.

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.

Research and Development on NC System of Gear-hobbing Machine based on Zero-programming Technology

By the analysis of roller gear processing technology, combining with gear meshing mechanism and motion relationship, models for rolling gear machining parameter and zero-programming are established. In this paper, the automatic generation technology of NC program for CNC gear machining process has been studied and the zero-programming system architecture of open CNC gear-hobbing machine has been presented. In the design and development of the system, human computer interaction, programming algorithm and the design of each function module have bean done. Application test shows that the expected design requirements have been achieved.

Design and Machining of Combination Gear Cutter Hob

This paper takes the escapement plate of a mechanical pendulum clock as an example,analyses the design of combination form cutter hob for special profile gears, selection of parameters and calculation for tooth profile coordinates and discusses the grinding of cutter hob tooth profile on optical contour grinder.

非圆齿轮滚齿切削力波动特性及抑制研究

滚齿是非圆齿轮加工实现的重要方法,用于节曲线外凸直或斜齿非圆齿轮的高效高精制造,节曲线非圆特性导致滚切力呈现较大幅度波动,影响制造过程稳定性及加工精度,是非圆齿轮滚齿领域需要研究的重要课题。文章基于单位切削力计算原理及圆柱齿轮滚切力的研究成果,采用单次断续切削产生的未变形切屑体积表征滚切力波动态势,构建非圆齿轮滚切未变形切屑模型的获取方法。选取大偏心率卵形齿轮为研究对象,分析滚刀恒速不窜刀联动加工模型所产生的滚切力波动特性,得出该联动加工模型所对应峰值切削力的波动规律。提出一种滚刀恒速并附加窜刀的联动加工模型,该模型具有恒定弧长增量加工特性,对抑制整周滚切力波动具有重要意义,并开展不同滚切深度所对应滚切力波动规律研究,研究结果为非圆齿轮滚切方案的优化制定提供一定的理论依据。

车轴滚齿加工工艺参数GA-BP模型NSGA-Ⅱ优化

研究了高速条件下的滚齿工艺参数设置与优化方面的工作,采用新的非支配遗传算法NSGA-Ⅱ设计了相应的优化数学模型,优化达到最低能耗以及最长的刀具使用期限,再以遗传反向传播算法(GABP)神经网络为目标设置预测模型并建立适应度函数,完成迭代优化后获得匹配滚齿工艺的Pareto最优条件。研究结果表明:这里预测模型经过5次循环计算后,均方差为10-5,得到0.000425的最优值,推断上述网络满足良好的稳定性。刀具寿命误差相对后者降低16%,降低了36%的能量损耗,发现GABP算法具备更优收敛能力。Pareto解集获得了比相近加工样本集更优的性能,因此采用多目标优化模型可以确保加工能耗和刀具使用寿命同时达到最佳状态。该研究对提高的滚齿加工工艺参数以及提高机加工效率具有很好的实际应用价值。

THEORY OF HELICOID OF SPHERICAL HOB

The mechanism of spherical hob's cutting internal gear is explained and the new coneeptof generating gear of spherical hob is presented. The reason why there is theoretical error and thenew method of decreasing the error are also analysed. Some new equations about the mainparameters, the equations of helicoids, the equations of cutting edges and the flank angles of spheri-cal hob are given.

斜齿轮的有效长度和收尾长度的计算

文章基于理论分析并应用Lagrange乘数法以及求解一个一元四次方程,推导得到了与圆柱型齿条配合的斜齿轮所需要的有效长度的解析表达式,并通过SolidWorks软件验证了其正确性。再通过求解一元四次方程,推导得到了斜齿轮的滚齿收尾部分最远端到垂直于工件轴线且包含退刀时滚刀轴线和工件轴线的最短距离线所在平面的距离,即滚齿收尾长度的解析表达式,并通过SolidWorks软件验证了其正确性。这两个表达式为与斜齿轮相关的机械产品的设计提供了重要依据。

非圆齿轮滚切最简数学模型及其图形仿真

推导非圆齿轮滚切加工的最简数学模型并作图形仿真验证。以切削点处工件和刀具的切向速度相等 (即滚刀节曲线和非圆齿轮节曲线保持相互纯滚动 )为基本依据 ,推导出坐标轴联动控制的一组方程式。对该组方程式进一步简化便获得滚切加工的最简数学模型 ,它是一个 3坐标联动的结构。根据最简数学模型 ,利用计算机图形仿真的方法 ,动态地演示出齿形的形成过程及结果。利用图形仿真的结果 ,可以初步分析判断所加工齿轮齿形的各种特征 ,从而为设计和制造的顺利进行提供了有力的支持。

大型数控滚齿机立柱动力学仿真分析

为避免大型数控滚齿机滚削力引起立柱振动而影响加工精度,对大型滚齿机立柱刚度特性及谐响应进行了仿真分析。在滚齿机立柱结构特征、滚刀主轴传动原理及动力学理论基础上,建立了滚齿机立柱与滚刀箱有限元仿真模型,仿真求解得到了立柱模态及谐响应参数。通过立柱动态响应的振动频率与变形量分析,得到了滚齿机加工时立柱设计结构应避开的共振频率范围,揭示了立柱振动变形量的变化规律,提出了立柱结构设计与安装方法的改进建议,为大型数控滚齿机部件的设计优化提供了理论依据与参考。

基于电子齿轮原理的滚齿加工CNC系统的联动结构

介绍一种构成齿轮滚切加工 CNC系统多轴联动控制的模型。它以电子齿轮原理为基础 ,运用脉冲频率的函数变换和加减合成方法 ,获得滚齿加工时机床各个坐标运动的指令。以同步锁相电路结合伺服电机位置控制方法实现电子齿轮功能 ,并且齿数比可以实时刷新 ,具备了函数分频能力。经机床运行试验验证 。