Precision Gears Research Articles

Die design and process optimization of plastic gear extrusion

The flow velocity of the melt in the extruder was simulated by using software Polyflow, and the size of the die channel with the best flow uniformity was obtained. The die profile shape is obtained by reverse design. The length of the shaping section is determined by Ansys transient thermal analysis. According to the simulation results, the design and manufacture of extrusion die of plastic gear and vacuum cooling setting were obtained. The influence of the five process parameters on the precision of the plastic gear were studied by the single factor analysis method, such as the die temperature T, the screw speed R, the die spacing S, the vacuum degree M and the hauling speed V. The optimal combination of process parameters was obtained by using the neural network particle swarm optimization algorithm(T = 197.05 °C, R = 9.04rpm, S = 67mm, M = −0.0194MPa). The tooth profile deviation of the extruded plastic gear can reach 9 level of accuracy.

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.

Torsional Fatigue Strength of Newly Developed Case Hardening TRIP-Aided Steel

The torsional fatigue strength of newly developed case hardening steel, i.e., transformation-induced plasticity-aided martensitic steel subjected to vacuum carburizing followed by fine particle peening, was investigated for the fabrication of downsized precision gears with high torque capacity and wear resistance. The surface-hardened layer properties—i.e., high Vickers hardness, high compressive residual stress, and a large amount of retained austenite—considerably increased the torsional fatigue limits of vacuum-carburized and fine particle peened TM and JIS-SNCM420 steels, although the notch-sensitivity to fatigue was increased. The relation between torsional and rotational bending fatigue limits for the smooth specimens was found to be between the maximum principal stress and the minimum shear strain energy criterions. On the other hand, this relation for the notched specimens was represented through the maximum principal stress criterion.

Effects of Vacuum-Carburizing Conditions on Surface-Hardened Layer Properties of Transformation-Induced Plasticity-Aided Martensitic Steel

The effects of carbon potential in vacuum-carburization on the surface-hardened layer properties of the 0.2%C-1.5%Si-1.5%Mn-1.0%Cr-0.05%Nb transformation-induced plasticity-aided martensitic steel were investigated for the fabrication of precision gears. The volume fraction of retained austenite and hardness in the surface hardened layer of the steel increased with increasing carbon potential. Subsequent fine-particle peening enhanced the hardness and the compressive residual stress via severe plastic deformation and strain-induced martensite transformation, especially under a high carbon potential. The severe plastic deformation mainly contributed to increased hardness and compressive residual stress and the contribution of the strain-induced martensitic transformation was relatively small.

Formation mechanism study on tooth surface of two gear finishing processes: combined theoretical and experimental approaches

As the necessary conditions, high precision and good mechanical performance gear is very important for a high speed and precision transmission system. To meet the requirement of the performance, gear finishing processes including gear honing and gear grinding have been mainly adopted. To compare the tooth surface of these two gear finishing processes, this paper gives the formation mechanism of gear tooth surface texture and conducts some comparative experiments on the gear surface texture and residual stress. Based on the spatial engagement principle and the discrete points of work-piece gear tooth spiral involute surface, the tooth surface contact area models of gears from the two processes are built, respectively, and the prediction models of honing paths and grinding paths are generated according to the velocity vector of the sampling points on tooth surface. Then the contrast and verification tests of the prediction models are carried out on internal gearing power honing machine and worm wheel gear grinding machine, respectively. Results indicate that the predicted curve shape honing paths and the longitudinal linear shape grinding paths of tooth surface are both similar to the experiment ones, respectively. Furthermore, some detailed quantitative analyses of tooth surface qualities including surface texture and tooth surface residual stress has been finished. It is found that the surface roughness value of gear grinding work-piece gear tooth surface is lower than that of gear honing process and the distribution of compressive residual stress on gear tooth surface is associated with the principles and parameters of the two processes. This research has theoretical and instructional significance for the improvement of gear honing and grinding processes.

Problems in Gearing Standardization and Some Results in Normative Documentation Development. Part 1. Standardization in the field of gear precision, failure modes and manufacturing

Рассматривается современное состояние и общие тенденции в развитии системы стандартизации в области зубчатых передач. Обсуждаются проблемы гармонизации стандартов ГОСТ, СТБ с международными и национальными стандартами других стран, в частности, стандартов, регламентирующих требования по геометрии исходных контуров, показателям точности, детерминированным и вероятностным методам расчета на прочность, то есть вопросы разработки рекомендаций по созданию проекта новых базовых стандартов, не противоречащих требованиям стандартов ISO и сохраняющих полезные стороны отечественных документов, имеющих многолетний опыт использования. Кроме того, при переходе к международным стандартам необходимо учитывать специфику установленных норм прочности, производства и эксплуатации зубчатых передач в различных отраслях техники. Показаны недостатки стандартов ГОСТ на зубчатые передачи, которые ранее были основой, регулирующей отношения между покупателями и производителями зубообрабатывающего оборудования и инструментов. В настоящее время зарубежное станкостроение создало принципиально новые конструкции оборудования и инструмента для производства и контроля зубчатых передач. Принципиально изменилась технология изготовления зубчатых передач. Отечественные изготовители зубчатых передач продолжают пользоваться устаревшими стандартами и сохраняют принципы старых технологий изготовления зубчатых передач. В связи с необходимостью реагировать на требования по снижению шума и повышения ресурса зубчатых передач начинается закупка отдельных видов зарубежного зубообрабатывающего оборудования. Попытки внедрить современное зубообрабатывающее оборудование для изготовления зубчатых передач по устаревшим стандартам ГОСТ и в устаревшие технологии в конечном итоге не приводит к требуемому улучшению качества изготовления зубчатых передач. Отдельные разделы посвящены конкретному описанию стандартов, касающихся видов повреждений зубчатых колес и технологических процессов их изготовления.

Low-loss gears precision planetary gearboxes: reduction of the load dependent power losses and efficiency estimation through a hybrid analytical-numerical optimization tool

In the field of robotics, extremely accurate gearboxes are mandatory in order to ensure the adequate precision required by the automatic processes. For these applications, planetary gearboxes represent one of the most attractive solutions because they ensure high reduction ratios in a compact solution. However, their compactness and high power density, imply some thermal limitations. In order to overcome this problem, new gear designs have been studied by a hybrid analytical-numerical approach in order to reduce the power dissipation and, consequently, the operating temperatures. The efficiency increase is obtained mainly by a reduction of the module of the gears. This, together with other modifications of the tooth form (pressure angle, profile shift, etc.), allows to reduce the relative sliding between the tooth flanks that causes the power loss maintaining at the same time an adequate load carrying capacity. Low-loss gears have already been studied by other authors on bigger gears. Furthermore, by means of dedicated CFD simulations performed with an especially developed tool based on the open-source code OpenFOAM®, it has been shown that the sliding optimized design has a positive impact also on the churning power losses. The global winning in terms of reduction of the gear meshing power losses can be assessed in about 50%, depending on the reduction ratio. The new design has been validated by means of experimental tests performed in the internal laboratory of the company. The results have fully validated both the numerical approach and the new design.

Effects of fine particle peening on fatigue strength of a TRIP-aided martensitic steel

The effects of fine particle peening on the fatigue properties of a transformation-induced plasticity-aided martensitic steel with a chemical composition of 0.2% C, 1.5% Si, 1.5% Mn, 1.0% Cr, and 0.05% Nb (mass%) were investigated for applications in precision gears. When this steel was subjected to fine particle peening after heat treatment, higher fatigue limits and lower notch sensitivity were achieved compared with those of SNCM420 martensitic steel. The increased fatigue limits are principally associated with higher hardness and compressive residual stress on and just below the surface, as well as low surface roughness. Fine particle peening also increased the threshold stress intensity factor range in stage I, and decreased the crack propagation rate in stage II in this steel. The crack propagation behavior was mainly suppressed by (1) high hardness and high compressive residual stress, and (2) the strain-induced martensite transformation of retained austenite and high internal stress resulting from a difference in flow stress between the soft martensite matrix and the finely dispersed hard MA-like phase that developed during fatigue deformation.

Numerical Control Simulation and Experimental Study on End Milling Ordinary Cycloidal Gear in Five-axis CNC Machine Tool

A machining method of end milling cycloidal gear using ball end mill is proposed based on the analysis of grinding and side milling ordinary cycloid gear. The machining principle of end milling cycloid gear using 5-axis CNC milling machine is analyzed and the geometric model of end milling cycloid gear is established. At the same time the NC simulation of the machining process is conducted. End milling ordinary cycloid gear is conducted using five-axis machining center and it verifies the feasibility and scientific of end milling ordinary cycloidal gear. The machining precision of the cycloid gear is measured using a three coordinate measuring machine, and it verifies the reliability and usefulness of the machining method. It proves that the machining method can achieve grinding precision. Using end milling instead of grinding cycloid gear is achieved in order to improve the machining efficiency.

Optimization of the Isothermal Forging Process of a Spur Bevel Gear

In this paper, the optimization of the parameters of the isothermal forging technology to form spur bevel gear was studied. The goal of the optimization is to decrease the forming load during the process. Then, some factors included the ratio of height to diameter of billet, thickness and position of punching recess, deformation temperature and velocity were taken as the optimization values and the orthogonal experimental method was employed to carried out the optimization. After the optimization, a set of optimum technology parameters were obtained. The result demonstrates that the precise spur bevel gear can be formed with less forming load and without causing under-filling and folding defect by using the isothermal forging and choosing suitable parameter, which provides reference to form the spur bevel gear.

Temperature distributions in form grinding of involute gears

A comprehensive thermal model is developed to analyse the heat transfer mechanism in form grinding of involute gears. The model analyses the thermal effects of a transient non-uniform heat source, moving with a three-dimensional curved shape, on the involute tooth profile. The variation of the contact geometry along the tooth profile is considered and analysed in detail, including the local grinding depth, equivalent wheel diameter and local contact arc length as well as the variation of the three-dimensional heat flux distribution and the heat partitioning to different thermal parts on the curved tooth profile. Based on the model established, the grinding temperature distribution patterns along the involute contact profile under different Peclet numbers, numbers of teeth and gear modules have been investigated. Along the tooth profile, the temperature increases significantly with the rolling angle. Grinding temperatures along the tooth profile of a straight spur gear, made of 20CrMnTi low-carbon steel, are measured using a special test rig designed with thermocouples imbedded into workpiece at different measurement positions. The results demonstrate that the calculated temperature distribution along the tooth profile has a rather good agreement with the measured result. This research provides a new method to predict grinding temperature in form grinding mode of precision gears.

Determination of burn thresholds of precision gears in form grinding based on complex thermal modelling and Barkhausen noise measurements

Thermal damage control in high efficiency form grinding of precision gears is critical for obtaining the required gear surface integrity and ensuring the contact strength in service life. Complex thermal models have been developed to determine the variation of burn thresholds of power under different grinding parameters in form grinding mode of gears. The thermal models analyse in detail the variation of local contact geometry between the grinding wheel and gear surface, and the variation of heat partitioning to different thermal parts including the workpiece, wheel, grinding fluid and grinding chips. The burn thresholds of power in the form grinding of carbonised steel gears have been determined by relating the grinding temperature with the Barkhausen Noise and micro-hardness measurements for the ground surfaces. The models and the determined burn thresholds can be used for presetting the parameters and conditions of grinding process and monitoring the grinding process to avoid the occurrence of thermal damages to the gear surfaces.

Enhancing the Precision of Timing Gear Used in Automobile by Making Use of Azotizing Deformation

Statistic analysis about the effect of heat treatment deformation on tooth profile deviation distribution of the timing gear used in automobile is done with mathematical statistics. Based on the research on the effect of the heat treatment deformation on tooth profile deviation, helical deviation and common normal length etc, the processing measure, tolerance and correcting quantity before and after azotizing treatment can be adjusted to optimize the gear process and to enhance processing precision of the gear.

3D Software Technology, Applicable in Elaboration of the Spatial Face Gear Drives for Incorporation into Robot Systems

The study treats a specific technological approach for the elaboration of small manufacturing series of highly precise hyperboloid gears with small module of the teeth and with not big dimensions of the gear mechanism. It is based on the application of the elaborated by authors mathematical models, algorithms and computer programs for synthesis upon a pitch contact point and upon a mesh region. A special feature of the established approach is the application of 3D software prototyping and 3D printing of the designed transmissions. The presented here models of the transmissions with crossed axes and face mated gears are indented for implementation into the driving of two type robots: bio-robot hand and walking robot with four insect-type legs.

Design and performance of an ultra-flexible two-photon microscope for in vivo research.

We present a cost-effective in vivo two-photon microscope with a highly flexible frontend for in vivo research. Our design ensures fast and reproducible access to the area of interest, including rotation of imaging plane, and maximizes space for auxiliary experimental equipment in the vicinity of the animal. Mechanical flexibility is achieved with large motorized linear stages that move the objective in the X, Y, and Z directions up to 130 mm. 360° rotation of the frontend (rotational freedom for one axis) is achieved with the combination of a motorized high precision bearing and gearing. Additionally, the modular design of the frontend, based on commercially available optomechanical parts, allows straightforward updates to future scanning technologies. The design exceeds the mobility of previous movable microscope designs while maintaining high optical performance.

Effects of Fine Particle Peening on Fatigue Strength of Transformation-Induced Plasticity (TRIP)-Aided Martensitic Steel

The effects of fine particle peening on the torsional strength of a transformation-inducedplasticity (TRIP)-aided martensitic (TM) steel were investigated for applications to precision gears. Fine particle peening increased the fatigue limits and lowered the notch-sensitivities of steel, compared with quenched and subsequently tempered SNCM420 steel. In addition, fine particle peening lowered the fatigue crack propagation rate in TM steel with a high threshold value of the stress intensity range. These results were associated with (1) higher Vickers hardness, (2) higher compressive residual stress, and (3) a larger amount of untransformed retained austenite in the surface layer when compared with SNCM420 steel.

S1120102 微小平歯車の耐久試験に関する基礎研究

In recent years, it became possible to manufacture a highly precise and high-strength metal micro gear. However, the systematic evaluation about load carry characteristics of the micro gear is not reported. Accordingly, we have developed a test equipment which can perform endurance tests of the micro gear easily. And we evaluated performance of the endurance test equipment which we developed. In this study, we considered the lubrication condition as a basic study on endurance test of micro spur gear. As the result, we obtained the following results; (1) In the non-lubrication condition, even if it was quite low torque and was quite low rotational speed, damage was confirmed in a short time. (2) There is a possibility that enough lubrication condition can be maintained by a drop of lubricating oil. (3) When a lubricating oil scattered, fusion or plastic flow was observed. (4) The endurance test equipment which we developed has possibility that appropriate meshing can be achieved.

S1120203 フェースギヤの高精度歯切り

S1120203 フェースギヤの高精度歯切り

311 動力吸収式歯車試験装置を用いた高精度平歯車の振動に関する実験研究(機素潤滑設計II)

311 動力吸収式歯車試験装置を用いた高精度平歯車の振動に関する実験研究(機素潤滑設計II)

Comparative Study of Wire-EDM and Hobbing for Manufacturing High-Quality Miniature Gears

With increasing emphasis on miniaturization, the demand for manufacturing the high-quality fine-pitched miniature gears is growing continuously. Inability of the conventional processes to manufacture high-quality miniature gears compels the need to explore a process which can economically manufacture precise and accurate gears required by the various miniature products used for different scientific, industrial, and domestic applications. This article reports on exploring and subsequently establishing wire electric discharge machining (WEDM) process as a superior, economical, and viable alternative for manufacturing the high-quality miniature gears through a comparative evaluation of process capabilities of WEDM and gear hobbing which is the most commonly used conventional process. The evaluation concentrated on those capabilities of these two processes which affect functional performance and service life of the miniature gears. This included microgeometry parameters (i.e., profile error and pitch error) and surface integrity aspects (i.e., surface topography, surface roughness, microhardness, and microstructure). The miniature gears manufactured by WEDM were found to be of superior quality (of DIN standard 5) and surface integrity than the hobbed gears (of DIN standard 10).